explanation blue bibcodes open ADS page with paths to full text
Author name code: gibson
ADS astronomy entries on 2022-09-14
author:"Gibson, Sarah E."
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Title: Synthetic Lyman-α emissions for the coronagraph aboard the
ASO-S mission. I. An eruptive prominence-cavity system
Authors: Zhao, J.; Zhang, P.; Gibson, S. E.; Fan, Y.; Feng, L.; Yu,
F.; Li, H.; Gan, W. Q.
2022A&A...665A..39Z Altcode:
Context. Strong ultraviolet (UV) emission from the sun will be observed
by the Lyman-α Solar Telescope (LST) on board the Advanced Space-based
Solar Observatory (ASO-S), scheduled for launch in 2022. It will
provide continuous observations from the solar disk to the corona
below a 2.5 solar radius with high resolution. To configure the
appropriate observing modes and also to better understand its upcoming
observations, a series of simulations and syntheses of different
structures and processes need to be done in advance. <BR /> Aims:
As prominence eruptions are the main drivers of space weather, the
need to monitor such phenomena has been set as a priority among the
objectives of ASO-S mission. In this work, we synthesize the evolution
of a modeled prominence-cavity system before and during its eruption
in the field of view (FOV) of LST. <BR /> Methods: We adopted the
input magnetohydrodynamic (MHD) model of a prominence-cavity system,
which is readily comparable to the Atmospheric Imaging Assembly (AIA)
observations. The Lyman-α emission of the prominence and its eruptive
counterparts are synthesized through the PRODOP code, which considers
non-local thermodynamic equilibrium (NLTE) radiative transfer processes,
while the other coronal part such as the cavity and surrounding
streamer, are synthesized with the FORWARD package, which deals with
optically thin structures. <BR /> Results: We present a discussion
of the evolution of the eruptive prominence-cavity system, analyzing
the synthetic emissions both on the disk near the limb and above the
limb as viewed by the coronagraph, as well as the three-dimensional
(3D) data of the MHD simulation. <BR /> Conclusions: The evolution of
the prominence-cavity system exhibits the condensation of cavity mass
onto the prominence and the evaporation of prominence plasma into the
central cavity. The synthetic emission in Lyman-α shows a similar
pattern as in the AIA extreme ultraviolet (EUV) wavelengths before
eruption, namely, the appearance of a "horn" substructure as a precursor
to the eruption. The emission of prominence with an optically thick
assumption is one to two orders of magnitude lower than the optically
thin one. Here, the dimming effect in Lyman-α is analyzed, for the
first time, for the eruptive prominence-cavity system. Accompanying the
prominence plasma motion during the eruption, the apparent dimming shows
a preferred location evolving from the top and bottom of the bright
core to the whole body above the bottom part, while the collisional
component progressively dominates the total emission of the flux rope
bright core at these locations. By analyzing the signal-to-noise ratio
(S/N) with a consideration of LST's optical design, we conclude that
the substructures in the cavity and the bright core of the CME can be
observed with sufficient S/N at different stages in the FOV of LST.
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Title: Solving 3D magnetohydrostatics with RBF-FD: Applications to
the solar corona
Authors: Mathews, Nathaniel H.; Flyer, Natasha; Gibson, Sarah E.
2022JCoPh.46211214M Altcode: 2021arXiv211204561M
We present a novel magnetohydrostatic numerical model that solves
directly for the force-balanced magnetic field in the solar corona. This
model is constructed with Radial Basis Function Finite Differences
(RBF-FD), specifically 3D polyharmonic splines plus polynomials, as
the core discretization. This set of PDEs is particularly difficult
to solve since in the limit of the forcing going to zero it becomes
ill-posed with a multitude of solutions. For the forcing equal to
zero there are no numerically tractable solutions. For finite forcing,
the ability to converge onto a physically viable solution is delicate
as will be demonstrated. The static force-balance equations are of a
hyperbolic nature, in that information of the magnetic field travels
along characteristic surfaces, yet they require an elliptic type solver
approach for a sparse overdetermined ill-conditioned system. As an
example, we reconstruct a highly nonlinear analytic model designed to
represent long-lived magnetic structures observed in the solar corona.
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Title: Magnetoseismology for the solar corona: from 10 Gauss to
coronal magnetograms
Authors: Yang, Zihao; Gibson, Sarah; He, Jiansen; Del Zanna, Giulio;
Tomczyk, Steven; Morton, Richard; McIntosh, Scott; Wang, Linghua;
Karak, Bidya Binay; Samanta, Tanmoy; Tian, Hui; Chen, Yajie; Bethge,
Christian; Bai, Xianyong
2022cosp...44.2490Y Altcode:
Magnetoseismology, a technique of magnetic field diagnostics based
on observations of magnetohydrodynamic (MHD) waves, has been widely
used to estimate the field strengths of oscillating structures in
the solar corona. However, previously magnetoseismology was mostly
applied to occasionally occurring oscillation events, providing
an estimate of only the average field strength or one-dimensional
distribution of field strength along an oscillating structure. This
restriction could be eliminated if we apply magnetoseismology to the
pervasive propagating transverse MHD waves discovered with the Coronal
Multi-channel Polarimeter (CoMP). Using several CoMP observations of
the Fe XIII 1074.7 nm and 1079.8 nm spectral lines, we obtained maps of
the plasma density and wave phase speed in the corona, which allow us
to map both the strength and direction of the coronal magnetic field
in the plane of sky. We also examined distributions of the electron
density and magnetic field strength, and compared their variations
with height in the quiet Sun and active regions. Such measurements
could provide critical information to advance our understanding of the
Sun's magnetism and the magnetic coupling of the whole solar atmosphere.
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Title: The Solaris Solar Polar MIDEX-Class Mission Concept: Revealing
the Mysteries of the Sun's Poles
Authors: Hassler, Donald M.; Harra, Louise K.; Gibson, Sarah; Thompson,
Barbara; Gusain, Sanjay; Berghmans, David; Linker, Jon; Basu, Sarbani;
Featherstone, Nicholas; Hoeksema, J. Todd; Viall, Nicholeen; Newmark,
Jeffrey; Munoz-Jaramillo, Andres; Upton, Lisa A.
2022cosp...44.1528H Altcode:
Solaris is an exciting, innovative & bold mission of discovery to
reveal the mysteries of the Sun's poles. Solaris was selected for Phase
A development as part of NASA's MIDEX program. Solaris builds upon
the legacy of Ulysses, which flew over the solar poles, but Solaris
provides an entirely new feature remote sensing, or IMAGING. Solaris
will be the first mission to image the poles of the Sun from ~75
degrees latitude and provide new insight into the workings of the
solar dynamo and the solar cycle, which are at the foundation of our
understanding of space weather and space climate. Solaris will also
provide enabling observations for improved space weather research,
modeling and prediction with time series of polar magnetograms and
views of the ecliptic from above, providing a unique view of the
corona, coronal dynamics, and CME eruption. To reach the Sun's poles,
Solaris will first travel to Jupiter, and use Jupiter's gravity to
slingshot out of the ecliptic plane, and fly over the Sun's poles
at ~75 degrees latitude. Just as our understanding of Jupiter &
Saturn were revolutionized by polar observations from Juno and Cassini,
our understanding of the Sun will be revolutionized by Solaris.
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Title: 4π Heliospheric Observing System - 4π-HeliOS: Exploring
the Heliosphere from the Solar Interior to the Solar Wind
Authors: Raouafi, Nour E.; Gibson, Sarah; Ho, George; Laming,
J. Martin; Georgoulis, Manolis K.; Szabo, Adam; Vourlidas, Angelos;
Mason, Glenn M.; Hoeksema, J. Todd; Velli, Marco; Berger, Thomas;
Hassler, Donald M.; Kinnison, James; Viall, Nicholeen; Case, Anthony;
Newmark, Jeffrey; Lepri, Susan; Krishna Jagarlamudi, Vamsee; Raouafi,
Nour; Bourouaine, Sofiane; Vievering, Juliana T.; Englander, Jacob A.;
Shannon, Jackson L.; Perez, Rafael M.; Chattopadhyay, Debarati; Mason,
James P.; Leary, Meagan L.; Santo, Andy; Casti, Marta; Upton, Lisa A.
2022cosp...44.1530R Altcode:
The 4$\pi$ Heliospheric Observing System (4$\pi$-HeliOS) is an
innovative mission concept study for the next Solar and Space
Physics Decadal Survey to fill long-standing knowledge gaps in
Heliophysics. A constellation of spacecraft will provide both remote
sensing and in situ observations of the Sun and heliosphere from a
full 4$\pi$-steradian field of view. The concept implements a holistic
observational philosophy that extends from the Sun's interior, to the
photosphere, through the corona, and into the solar wind simultaneously
with multiple spacecraft at multiple vantage points optimized for
continual global coverage over much of a solar cycle. The mission
constellation includes two spacecraft in the ecliptic and two flying as
high as $\sim$70$^\circ$ solar latitude. 4$\pi$-HeliOS will provide
new insights into the fundamental processes that shape the whole
heliosphere. The overarching goals of the 4$\pi$-HeliOS concept are
to understand the global structure and dynamics of the Sun's interior,
the generation of solar magnetic fields, the origin of the solar cycle,
the causes of solar activity, and the structure and dynamics of the
corona as it creates the heliosphere. The mission design study is
underway at the Johns Hopkins Applied Physics Laboratory Concurrent
Engineering Laboratory (ACE Lab), a premier mission design center,
fostering rapid and collaborative mission design evolutions.
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Title: Extracting characteristics of interplanetary CMEs from database
of synthetic white-light images based on ensemble MHD simulations
Authors: Provornikova, Elena; Gibson, Sarah; Wiltberger, Michael;
Dalmasse, Kévin; Merkin, Viacheslav; Malanushenko, Anna; Vourlidas,
Angelos; Arge, Charles
2022cosp...44.2433P Altcode:
In this work, we investigate to what extent properties of CMEs
determined from synthetic white light images represent properties of
simulated interplanetary CMEs. The propagation of an interplanetary CME
with an internal flux rope is modeled with the GAMERA global model of
the inner heliosphere (0.1- 1 AU) coupled with the Gibson-Low (G&L)
model of a self-similarly expanding CME with an internal magnetic
field. The solar wind background in the inner heliosphere is driven
by the Wang-Sheeley-Arge (WSA)-ADAPT corona solution. An ensemble of
CME simulations is created by setting different input parameters of a
CME flux rope in the G&L model (e.g., magnetic field topology and
magnetic field strength, angular width, speed, orientation, latitude,
and longitude). A set of values for each of the defining G&L
parameters are taken from statistical distributions obtained from
an analysis of white light CME imagery near the Sun. To set the CME
magnetic structure we choose four topologies allowed by the G&L
model: spheromak, tethered spheromak, flux rope, and magnetic arcade. We
run an ensemble of a few hundred MHD simulations of interplanetary CMEs
with internal flux rope. The ensemble is used to produce a database of
synthetic CME images in white-light total brightness. We use the CACTUS
package to autonomously detect CMEs in synthetic white light images and
determine CME angular width and variations of CME velocity, mass, and
trajectory during the interplanetary CME propagation. We then compare
results from CACTUS with the ground truth data extracted directly from
MHD simulation output. We analyze cases showing a disagreement between
the true and inferred properties in more detail.
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Title: Exploring Structures and Flows with NASA's under-construction
PUNCH mission
Authors: DeForest, Craig; Gibson, Sarah; Thompson, Barbara;
Malanushenko, Anna; Desai, Mihir; Elliott, Heather; Viall, Nicholeen;
Cranmer, Steven; de Koning, Curt
2022cosp...44.1077D Altcode:
The Polarimeter to UNify the Corona and Heliosphere is a NASA Small
Explorer to image the corona and heliosphere as parts of a single
system. PUNCH comprises four ~50kg smallsats, each carrying one imaging
instrument, that work together to form a single "virtual coronagraph"
with a 90° field of view, centered on the Sun. Scheduled for joint
launch with NASA's SPHEREx mission, PUNCH starts its two-year prime
science phase in 2025. PUNCH will generate full polarized image
sequences of Thomson-scattered light from free electrons in the corona
and young solar wind, once every four minutes continuously. This
enables tracking the young solar wind and turbulent structures within
it as they disconnect from the Sun itself, as well as large transients
such as CMEs, CIRs, and other shocks within the young solar wind. A
student-contributed X-ray spectrometer (STEAM) will address questions
of coronal heating and flare physics. We present motivating science,
expected advances, mission status, and how to get involved with PUNCH
science now.
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Title: Expected results for the cradle of the Solar Wind with the
Polarimeter to UNify the Corona and Heliosphere (PUNCH)
Authors: DeForest, Craig; Gibson, Sarah; De Koning, Curt A.; Thompson,
Barbara; Malanushenko, Anna; Desai, Mihir; Elliott, Heather; Viall,
Nicholeen; Cranmer, Steven
2022cosp...44.1324D Altcode:
The Polarimeter to UNify the Corona and Heliosphere is a NASA Small
Explorer to image the corona and heliosphere as parts of a single
system. Imaging the corona and heliosphere together from a constellation
of four synchronized smallsats, PUNCH will — starting in 2025 —
provide a unique window on global structure and cross-scale processes
in the outer corona and young solar wind. PUNCH science is informed
by, and complements, the results of PSP and Solar Orbiter; and will
synergize with PROBA3/ASPIICS. We present early prototype results from
STEREO/SECCHI and current preparation work to enable PUNCH science
when data arrive, discuss anticipated results from the deeper-field,
higher time resolution imaging that PUNCH will provide, and describe
how to get involved with PUNCH science now.
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Title: Remote Sensing of Turbulence and Solar Wind Structure with
the PUNCH mission
Authors: DeForest, Craig; Gibson, Sarah; Matthaeus, William; Viall,
Nicholeen
2022cosp...44.1212D Altcode:
The Polarimeter to UNify the Corona and Heliosphere is a mission to
observe the corona and the inner heliosphere as a unified system. PUNCH
will produce continuous images of the solar wind and corona between
1.5° and 45° from the Sun, over a two year prime science mission
scheduled to start in early 2025. PUNCH uses visible sunlight scattered
by free electrons in the corona, to track density structures in the
corona and solar wind. We will describe PUNCH's unique 3D imaging
capability, mission structure, and anticipated results measuring the
development of large-scale turbulence, and the large- and meso-scale
structure of the solar wind itself.
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Title: Tracking Movement of Long-lived Equatorial Coronal Holes from
Analysis of Long-term McIntosh Archive Data
Authors: Harris, Jacob; Dikpati, Mausumi; Hewins, Ian M.; Gibson,
Sarah E.; McIntosh, Scott W.; Chatterjee, Subhamoy; Kuchar, Thomas A.
2022ApJ...931...54H Altcode:
Features at the Sun's surface and atmosphere are constantly changing
due to its magnetic field. The McIntosh Archive provides a long-term
(45 yr) record of these features, digitized from hand-drawn synoptic
maps by Patrick McIntosh. Utilizing this data, we create stack plots
for coronal holes, i.e., Hovmöller-type plots of latitude bands,
for all longitudes, stacked in time, allowing tracking of coronal
hole movement. Using a newly developed two-step method of centroid
calculation, which includes a Fourier descriptor to represent a coronal
hole's boundary and calculate the centroid by the use of Green's
theorem, we calculate the centroids of 31 unique, long-lived equatorial
coronal holes for successive Carrington rotations during the entire
solar cycle 23, and estimate their slopes (time versus longitude)
as the coronal holes evolve. We compute coronal hole centroid drift
speeds from these slopes, and find an eastward (prograde) pattern
that is actually retrograde with respect to the local differential
rotation. By discussing the plausible physical mechanisms which could
cause these long-lived equatorial coronal holes to drift retrograde, we
identify either classical or magnetically modified westward-propagating
solar Rossby waves, with a speed of a few tens to a few hundreds of
meters per second, to be the best candidate for governing the drift of
deep-rooted, long-lived equatorial coronal holes. To explore plausible
physics of why long-lived equatorial coronal holes appear few in number
during solar minimum/early rising phase more statistics are required,
which will be studied in future.
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Title: Studying neutrinos at the LHC: FASER and its impact to the
cosmic-ray physics
Authors: Ariga, A.; Abreu, H.; Afik, Y.; Antel, C.; Ariga, T.;
Bernlochner, F.; Boeckh, T.; Boyd, J.; Brenner, L.; Cadoux, F.;
Casper, D.; Cavanagh, C.; Cerutti, F.; Chen, X.; Coccaro, A.;
D'Onofrio, M.; Dozen, C.; Favre, Y.; Fellers, D.; Ferrere, D.;
Gibson, S.; Gonzalez-Sevilla, S.; Gwilliam, C.; Hsu, S. C.; Hu, Z.;
Iacobucci, G.; Inada, T.; Jakobsen, S.; Kajomovitz, E.; Kling, F.;
Kose, U.; Kuehn, S.; Lefebvre, H.; Levinson, L.; Li, K.; Liu, J.;
Magliocca, C.; McFayden, J.; Meehan, S.; Mladenov, D.; Nakamura, M.;
Nakano, T.; Nessi, M.; Neuhaus, F.; Nevay, L.; Otono, H.; Pandini, C.;
Pang, H.; Paolozzi, L.; Petersen, B.; Pietropaolo, F.; Prim, M. T.;
Queitsch-Maitland, M.; Resnati, F.; Rokujo, H.; Salfeld-Nebgen,
J.; Sato, O.; Scampoli, P.; Schmieden, K.; Schott, M.; Sfyrla, A.;
Shively, S. R.; Spencer, J.; Takubo, Y.; Theiner, O.; Torrence, E.;
Trojanowski, S.; Tufanli, S.; Vormwald, B.; Wang, D.; Zhan, G.
2022icrc.confE1025A Altcode: 2022PoS...395E1025A
No abstract at ADS
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Title: Realizing Comprehensive 3D Observations to Probe Magnetic
Energy Storage and Release in the Corona
Authors: Caspi, A.; Seaton, D. B.; Casini, R.; Downs, C.; Gibson, S.;
Gilbert, H.; Glesener, L.; Guidoni, S.; Hughes, J. M.; McKenzie, D.;
Reeves, K.; Saint-Hilaire, P.; Shih, A. Y.; West, M.
2022heli.conf.4058C Altcode:
Understanding impulsive energy release in the solar corona requires
knowledge of the 3D coronal magnetic field and 3D signatures of
energy release through systematic multi-viewpoint observations, in
many wavelengths, including coronal magnetometry.
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Title: Scattering Polarization Diagnostic of the UV Corona
Authors: Casini, R.; Gibson, S.; Newmark, J.; Fineschi, S.; Gilbert, H.
2022heli.conf.4053C Altcode:
A largely unexplored diagnostic of the coronal magnetic field vector
is offered by the linear polarization signature of the Hanle effect
of far ultraviolet (FUV) resonance lines.
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Title: Magnetic Field Measurements in the Large Scale Solar Corona
Authors: Tomczyk, S.; Gibson, S. E.; Cosmo Team
2022heli.conf.4031T Altcode:
Daily measurements of the magnetic structure of the global solar
corona are needed to advance our understanding of critical physical
processes. The COSMO 1.5-m Large Coronagraph will enable coronal
magnetic field observations.
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Title: Coronal Cavities in CoMP Observations
Authors: Rumińska, Agnieszka; Ba̧k-Stȩślicka, Urszula; Gibson,
Sarah E.; Fan, Yuhong
2022ApJ...926..146R Altcode:
Quiescent coronal cavities can provide insight into solar magnetic
fields. They are observed in the coronal emission lines in both
polarized and unpolarized light. In the total linear polarization
fraction (L/I), they often possess a "lagomorphic," or "rabbit-shaped,"
structure that reflects the underlying magnetic field configuration. We
studied quiescent coronal cavities observed between 2012 and 2018 by
the Coronal Multichannel Polarimeter (CoMP). The majority of cavities
in our study had a characteristic lagomorphic structure in linear
polarization. We additionally compared cavity widths as observed in
intensity with sizes of their linear polarization signatures for 70
cavities and found that both features are strongly correlated. Our
results indicate that chances for observing a lagomorphic structure
increase greatly with cavity lifetime, suggesting that the visibility
depends on the spatial orientation of the cavity. Forward-modeled
observations in linear polarization of flux ropes confirmed this
assumption. We conclude that observations of the solar coronal cavities
in linear polarization are consistent with the theoretical model of
flux rope formation and structure.
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Title: New Approaches to Integrated Mission, Data, and Modeling
Frameworks
Authors: Seaton, D. B.; Caspi, A.; Casini, R.; Downs, C.; Gibson, S.;
Gilbert, H.; Glesener, L.; Guidoni, S.; Hughes, J. M.; McKenzie, D.;
Reeves, K.; Saint-Hilaire, P.; Shih, A.; West, M.
2022heli.conf.4057S Altcode:
A new generation of heliophysics missions will require integration of
data from multiple missions with analysis tools and physics-based
models. We discuss strategies to develop a framework for
systems-integrated data and analysis environments.
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Title: Magnetoseismology for the solar corona: from 10 Gauss to
coronal magnetograms
Authors: Yang, Zihao; Bethge, Christian; Tian, Hui; Tomczyk, Steven;
Morton, Richard; Del Zanna, Giulio; McIntosh, Scott; Karak, Bidya
Binay; Gibson, Sarah; Samanta, Tanmoy; He, Jiansen; Chen, Yajie; Bai,
Xianyong; Wang, Linghua
2021AGUFMSH12C..07Y Altcode:
Magnetoseismology, a technique of magnetic field diagnostics based
on observations of magnetohydrodynamic (MHD) waves, has been widely
used to estimate the field strengths of oscillating structures in
the solar corona. However, previously magnetoseismology was mostly
applied to occasionally occurring oscillation events, providing
an estimate of only the average field strength or one-dimensional
distribution of field strength along an oscillating structure. This
restriction could be eliminated if we apply magnetoseismology to the
pervasive propagating transverse MHD waves discovered with the Coronal
Multi-channel Polarimeter (CoMP). Using several CoMP observations of
the Fe XIII 1074.7 nm and 1079.8 nm spectral lines, we obtained maps of
the plasma density and wave phase speed in the corona, which allow us
to map both the strength and direction of the coronal magnetic field
in the plane of sky. We also examined distributions of the electron
density and magnetic field strength, and compared their variations
with height in the quiet Sun and active regions. Such measurements
could provide critical information to advance our understanding of the
Sun's magnetism and the magnetic coupling of the whole solar atmosphere.
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Title: The COMPLETE mission concept for the Heliophysics Decadal
Survey
Authors: Seaton, Daniel; Caspi, Amir; Casini, Roberto; Downs, Cooper;
Gibson, Sarah; Gilbert, Holly; Glesener, Lindsay; Guidoni, Silvina;
Hughes, Marcus; Reeves, Katharine; Shih, Albert; Tomczyk, Steven;
West, Matthew
2021AGUFMSH52A..08S Altcode:
We present the COMPLETE mission concept, currently under study for
the upcoming Heliophysics Decadal Survey. COMPLETE would provide the
first comprehensive measurements of the 3D low-coronal magnetic field
and simultaneous 3D energy release diagnostics from large eruptions
(flares and CMEs) down to small-scale processes (coronal heating and
solar wind outflows). COMPLETE's measurements will finally allow closure
on the long-standing question of exactly how energy is stored, released,
and transported in impulsive events at all scales. COMPLETE comprises
an instrument suite with hard and soft X-ray spectral imagers, gamma-ray
and energetic neutral atom spectral imagers, high-resolution wide-field
EUV filtergram imagers, photospheric Doppler vector magnetographs,
and Hanle-effect UV (Ly-a) coronal magnetographs. Distributed across
three spacecraft at the L1, L4, and L5 Earth-Sun Lagrange points, the
suite on each spacecraft is optimized for the measurements from that
vantage point and for the mission as a whole. Data from all instruments
will be processed to enable systems-level analysis from the entire
observatory. COMPLETE instrument suite is deliberately complementary
across its individual spacecraft, with overlapping fields of view and
optimized capabilities to provide a zone of ideal coverage near the
west limb as viewed from Earth. Within this region COMPLETE provides
comprehensive observations of 3D structures, photospheric and coronal
magnetic fields, and signatures of impulsive energy release within
integrated data products. The COMPLETE mission concept, and the science
and data analysis techniques it espouses, represent a strategic shift
from the nearly ubiquitous current practices of siloed study in isolated
subdisciplines to a comprehensive, unified systems approach to solar,
coronal, and heliophysics.
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Title: Establishing flux rope chirality using white light polarization
data from the PUNCH mission
Authors: Gibson, Sarah; Morgan, Huw; Provornikova, Elena; Malanushenko,
Anna; DeForest, Craig; de Koning, Curt; Fan, Yuhong; Merkin,
Viacheslav; Webb, David
2021AGUFMSH32A..03G Altcode:
Interplanetary Coronal Mass Ejections (ICMEs) are generally expected
to incorporate coherently-twisted magnetic fields, i.e., magnetic
flux ropes. We expect and have observed to some extent evolution
and interactions between flux ropes and the background corona and
solar wind, including rotation, deflection, and potentially continued
topological changes. The upcoming PUNCH mission will provide a full
field of view from pole to pole and fill existing gaps between
coronagraphs and heliospheric imagers, and will obtain polarized
brightness measurements which may be used along with brightness
measurements as a powerful tool for imaging and localizing CME
substructure evolution in transit. Further analysis of these
substructures may then lead to information about the chirality, or
handedness of magnetic twist of the flux rope. In order to demonstrate
these capabilities, we present synthetic polarization from forward
modeled simulations of flux rope CMEs. We compare the 3D position
of substructure that can be extracted from these data to the ground
truth simulation knowledge of the position of mass along the line
of sight. We further consider the implications for chirality and the
robustness of the method to topological variation of the flux rope at
the heart of the ICME.
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Title: Polarimeter to UNify the Corona and Heliosphere: Mission
status, activity, and science planning
Authors: DeForest, Craig; Gibson, Sarah; Killough, Ronnie; Case,
Traci; Beasley, Matthew; Laurent, Glenn; Colaninno, Robin
2021AGUFMSH35C2090D Altcode:
The Polarimeter to UNify the Corona and Heliosphere (PUNCH) is an
in-development mission, now in a combined Phase C/D in the NASA mission
lifecycle, to image the outer solar corona and inner heliosphere as
a unified system. The flight assets comprise four spacecraft to be
launched to 6am/6pm Sun-synchronous Low-Earth Orbit; one spacecraft
carries a Narrow Field Imager (NFI) coronagraph, and three carry
copies of a Wide Field Imager (WFI) heliospheric imager. These prime
instruments are specifically designed to work together as a seamless
"virtual instrument" with a 90° FOV, centered on the Sun. PUNCH
will produce polarized (pB) and unpolarized (B) images of the young
solar wind as it forms and departs the Sun, allowing 3D analysis of
solar wind and CME structure and trajectory. Aa student-contributed
instrument, STEAM, comprises two solid-state X-ray spectrometers
to study coronal heating and flare physics. PUNCH has an open data
policy and all data products will be made available to everyone at
the same time as the mission team. PUNCH is working to a launch
readiness date of 3-Oct-2023. The PUNCH science team comprises
PI Craig DeForest, PS Sarah Gibson, and project Co-Investigators
and Associate Investigators. Organized into six working groups,
we are actively preparing for the 2-year prime mission starting
90 days after launch. Science team meetings are open to all,
and are announced in the usual venues and the PUNCH web page
(https://punch.space.swri.edu). Current preparations include forward
modeling, derivation of predicted image characteristics from existing
data, and development of a suite of analysis tools in the vigorous
open-source Python/NumPy/SunPy millieu. The mission is complemented by
the groundbreaking PUNCH Outreach Program (POP) centered around a theme
of ancient and modern sunwatching, and concentrated in the American
Southwest. POP is specifically designed to support national, as well as
regional, educational and outreach efforts and to stimulate interest
in science by engaging under-represented populations in the focus
region and around the nation. We will present the current technical
status of PUNCH, the primary science objectives and observing plan,
current preparation activity and working group structure, and pathways
to coordinate and/or get involved with the mission.
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Title: Spatio-temporal Drifts of Long-lived Equatorial Coronal Holes:
Do they follow the Local Differential Rotation or Rossby Waves?
Authors: Harris, Jacob; Hewins, Ian; Dikpati, Mausumi; Gibson, Sarah;
McIntosh, Scott; Chatterjee, Subhamoy; Kuchar, Thomas
2021AGUFMSH54A..09H Altcode:
By developing a novel centroid-calculation technique, we analyze
long-term McIntosh Archive data to compute the centroids of long-lived
coronal holes (CH) in the latitude bands of +10 to -10. The technique
involves a two-step algorithm for computing the CH-centroids: (i)
Fast Fourier Transform to determine the surface area that represents
a coronal hole in a specified latitude-band; (ii) Green's theorem
to convert the surface integral to a line-integral along the hole
boundary. After building a Hovmoller-type (longitude-time) diagram
for these CH-centroids, we estimate their latitude-longitude drift
patterns with time. We find that their spatio-temporal drift is
not determined: by the local differential rotation; instead a large
retrograde longitudinal speed of 100-150 m/s overpowers the local
differential rotation speed, causing the resultant drift-speed of these
CH-centroids in longitude with time. We reason that Rossby waves are
the most plausible candidates to cause the retrograde drift patterns
of these deep-rooted, long-lived equatorial coronal holes.
---------------------------------------------------------
Title: Evidence for hot plasma and current sheet formation during
a coronal cavity eruption
Authors: Gibson, Sarah; Bak-Steslicka, Urszula; Fan, Yuhong; Steslicki,
Marek
2021AGUFMSH15D2055G Altcode:
Solar coronal cavities are dark structures with a rarefied
densitycompared with surrounding streamers. They are often observed
as acomponent of the classic three-part structure of a coronal
massejections (CME). Quiescent cavities are observed mostly in the
polarcrown regions and may be long-lived. Some of the quiescent cavities
mayfinally erupt as a CME. We present multi-wavelength observations
of a previously quiescent cavityduring its eruption. We used SDO/AIA
observations to determineDifferential Emission Measure (DEM) maps of
this structure and studiedits kinematics. Our analysis revealed hotter
plasma in the form of ringat the beginning of the eruption and hotter
plasma filling the cavityduring eruption. Our results are consistent
with the model of Fan 2019.We also present evidence of a current sheet
during eruption.
---------------------------------------------------------
Title: Coronal Holes and High Speed Streams within the Heliosphere
SC24 25 Solar Minimum
Authors: Hewins, Ian; Gibson, Sarah; Emery, Barbara
2021AGUFMSH25C2110H Altcode:
In support of the Whole Heliosphere and Planetary Interactions (WHPI)
solar minimum initiative and to highlight the solar and heliospheric
features at this time, we have produced solar synoptic maps of coronal
hole boundaries for the extended minimum period of solar cycle 24 25
(September 2018 February 2020 or CRs 2209 2227) and two of the Parker
Solar Probe times of interest CR2239 (Dec. 2020 Jan. 2021) and CR2242
(Mar. Apr. 2021). These maps are made from two positions around the sun
using SDO (Solar Dynamics Observatory) and Stereo A (Solar Terrestrial
Relations Observatory) EUV data. The first set of maps is made using
SDO AIA 193 and 304 data showing Earths perspective. The second set
of maps is made using STEREO A EUVI 195 data. The maps were made in
the style established by Patrick S. McIntosh that was used to create
the McIntosh Archive of synoptic maps, enabling studies of solar
features and their relation to structures in the solar wind and space
environment of Earth and other planets. For the SDO-based maps with
Earths perspective we have traced the solar wind back to its source
footpoints at or near coronal holes on the maps using the Solar Soft
PFSS (Potential Field Source Surface) of M. DeRosa. We compare these
results to the CCMC model runs for these Carrington rotations and OMNI
solar wind data showing velocity, amplitude on the AP scale, Bz and
DST. Hairy Sun PFSS models showing open and closed field lines are
also included. For the Stereo-A maps we also trace solar wind back
to its footpoints at or near coronal holes. We show solar wind data
gathered by Stereo-A. For the rotations Mars is aligned with Stereo-A,
we look at Maven solar wind data. In both of these cases, we correlate
fluctuations of solar wind data with specific coronal holes in the
maps. All of this data will be organized into a mosaic of coronal hole
and solar wind data. Together, these data provide a comprehensive study
of the organization of coronal holes and high speed solar wind streams
for each Carrington Rotation during the solar minimum period as well as
some Parker Solar Probe post minimum Carrington Rotations of interest.
---------------------------------------------------------
Title: Understanding Solar Eruptions, Solar Wind Formation, and how
the Sun Connects to the Heliosphere through a Polar Perspective
Authors: Viall, Nicholeen; Gibson, Sarah; Hassler, Don; Newmark,
Jeffrey; Seaton, Daniel; Downs, Cooper
2021AGUFMSH34D..01V Altcode:
A major limitation to our understanding of how the Sun connects to the
heliosphere is due to our ecliptic bias: all remote observations of the
Sun and corona have been made from the ecliptic. The ecliptic viewpoint
by itself can never capture the global corona and its connection
to the heliosphere. The ecliptic view has large uncertainties in
measurements of the polar magnetic fields and has limited ability
to measure longitudinal coronal structure. A polar perspective can
provide new ways to test theories of a host of solar and heliospheric
physics problems, from the quiescent processes involved in solar
wind formation, up through transient solar eruptions and coronal
mass ejections (CMEs). Because the structure and strength of the
polar photospheric magnetic fields shape the corona and provide key
input to coronal and heliospheric models, measuring and tracking
the evolution of the polar magnetic fields provides the bones of the
corona-heliosphere connection as well as information on the storage
and release of explosive energy. Images of the corona in EUV and white
light provide the coronal counterpart to the photospheric magnetic
field measurements for connecting the Sun to the heliosphere. They
capture global coronal connectivity and interactions, longitudinal
expansion and structure, and the effects of co-rotation. Since CMEs
tend to deflect toward the equator, a polar view captures essentially
all Earth-and planet-directed CMEs from a view perpendicular to their
direction of propagation. Overall, the discovery space for a polar
imager is enormous. We describe progress on these topics that can
be expected with Solar Orbiter, which will get to 30 degrees orbital
inclination in the extended mission. We also discuss the unique science
that can be done by continuous imaging of the polar magnetic fields
and corona from above 70 degrees for at least a solar rotation, such
as proposed by the Solaris mission.
---------------------------------------------------------
Title: Understanding the coronal origins of global heliospheric
phenomena through 3D measurements with COMPLETE
Authors: Caspi, Amir; Seaton, Daniel; Casini, Roberto; Downs, Cooper;
Gibson, Sarah; Gilbert, Holly; Glesener, Lindsay; Guidoni, Silvina;
Hughes, Marcus; Reeves, Katharine; Shih, Albert; Tomczyk, Steven;
West, Matthew
2021AGUFMSH25F2151C Altcode:
Impulsive solar eruptions (flares, coronal mass ejections) and more
gradual energetic processes (coronal heating in active regions, solar
wind outflows) are powered and governed by the Sun's complex coronal
magnetic field. The evolution of these events in the low and middle
corona has direct impact on global scales throughout the corona and
heliosphere, including as drivers of space weather that affect human
and technological assets, but a coherent understanding of globally
connected behavior necessarily requires understanding its origins at
the Sun. Despite many decades of research, it is still poorly understood
exactly how magnetic energy is stored and impulsively released to power
plasma heating, particle acceleration, and bulk flows. Breakthroughs
have been hindered by two critical limitations: lack of knowledge of
the 3D coronal magnetic field and its evolution, and a similar lack
of insight into how localized energy release manifests and propagates
within 3D coronal structures. Transformative progress to close these
gaps requires systematic observations from multiple viewpoints, in a
variety of wavelengths, and including coronal magnetometry. Recent and
ongoing technological advancements allow us to realize these goals
within a decadal timescale. To that end, we present the COMPLETE
mission concept, currently under study for the upcoming Heliophysics
Decadal Survey. COMPLETEs highly co-optimized and complementary
instrument suite include spectroscopic imagers for X-rays, gamma-rays,
and energetic neutral atoms; high-resolution wide-field EUV filtergram
imagers; photospheric Doppler vector mangetographs; and Hanle-effect UV
(Lyman-alpha) coronal magnetographs. Distributed across three spacecraft
at the L1, L4, and L5 Earth-Sun Lagrange points, COMPLETE would provide
the first comprehensive measurements of the 3D low- and middle-coronal
magnetic field and simultaneous 3D energy-release diagnostics from
large eruptions down to small-scale processes. COMPLETE represents
a strategic shift towards a comprehensive, unified systems approach
to solar, coronal, and heliospheric physics, to enable us to finally
close decades-old questions of how the Suns magnetic field and impulsive
energy release are interrelated, from local to global scales.
---------------------------------------------------------
Title: Preferred Longitudes and Other Characteristics of Polar
Coronal Hole Extensions over Five Solar Cycles
Authors: Emery, Barbara; Hewins, Ian; Gibson, Sarah; Kuchar, Thomas;
Webb, David; McFadden, Robert
2021AGUFMSH55D1879E Altcode:
The McIntosh archive covers coronal holes (CHs) from Skylab in 1973
in Solar Cycle (SC) 20 to Carrington Rotation (CR) 2186 in the solar
minimum of 2009 between SC23-24. We also have CH boundaries in solar
synoptic maps from September 2018 to February 2020 (CR2209-2227) as part
of the Whole Heliosphere and Planetary Interactions (WHPI) project in
the solar minimum between SC24-25. Polar CHs are found in most parts
of the solar cycle, except for solar maximum, often with low latitude
extensions. We examine the characteristics of polar CH extensions as
a function of hemisphere to document their number, their latitudinal
extent, and determine any preferred longitudes. Other studies have found
preferred longitudes of clusters of long-lived CHs, and especially of
active regions, where active regions are often anti-correlated with
the equatorial extensions of polar CHs. We anticipate changes in the
characteristics of polar CH extensions over four or five solar cycles,
and we examine also their relationship to other low-latitude long-lived
CHs, and to active regions.
---------------------------------------------------------
Title: Early Results from Whole Heliosphere Planetary Interactions
(WHPI) Campaigns
Authors: Thompson, Barbara; Allen, Robert; de Toma, Giuliana; Gibson,
Sarah; Qian, Liying
2021AGUFMSH11A..03T Altcode:
The Whole Heliosphere and Planetary Interactions (WHPI) is an
international initiative focused around the solar minimum period that
aims to understand the interconnected sun-heliospheric-planetary system,
by facilitating and encouraging interdisciplinary activities. Particular
WHPI science foci include the global connected structure of the
heliosphere and planetary space environments/atmospheres, the
origins and impacts of high-speed solar wind streams, CMEs from
sun-to-heliopause, and comparative solar minima. This is achieved
through a series of coordinated observing campaigns, including Parker
Solar Probe perihelia, and virtual interactions including a dedicated
workshop where observers and modelers get together to discuss, compare,
and combine research results. We present a summary of the outcomes and
activities of the WHPI science workshop held September 13-17, 2021,
and an update on the repository of data (observations and models,
Sun to solar wind to planets) that have been gathered.
---------------------------------------------------------
Title: The COronal Magnetism Observatory (COMO)
Authors: Casini, Roberto; Newmark, Jeffrey; Fineschi, Silvano;
Burkepile, Joan; Gibson, Sarah; Gilbert, Holly; Raouafi, Nour
2021AGUFMSH15G2092C Altcode:
Structuring of solar coronal plasma by the magnetic field is the
key to understanding the fundamental physical processes of energy
dissipation in the corona. The coronal magnetic field is crucial to
understanding coronal dynamics and space weather. We present the
COronal Magnetism Observatory (COMO), a new polarimetric imaging
solar coronagraph for the FUV (H Ly-alpha), to be deployed to the
International Space Station. COMO will provide the first global maps
of the magnetic field and solar wind properties from 1.1 to 3 Rsun.The
instrument will measure the linearly polarized scattered light from
the low through the middle corona with a spatial sampling of 2.8
arcsec/pixel. The science mission relies on a variety of different
polarization diagnostic methods (unsaturated Hanle effect, Doppler
dimming) to infer information on the magnetic state of the active
low corona, and the solar wind velocity/acceleration in the middle
corona. The instrument design is an adaptation of the internally
occulted coronagraph for the Sounding-rocket Coronagraphic Experiment
(SCORE), successfully flown in 2009 as part of the NASA HERSCHEL
experiment, and the dual-beam polarimeter adopts a newly developed,
highly stable, Al-MgF2 multilayer coating for the polarization analyzer.
---------------------------------------------------------
Title: A 3D Mesh-Free Solver for Magnetohydrostatic Simulations in
the Corona
Authors: Mathews, Nathaniel; Flyer, Natasha; Gibson, Sarah
2021AGUFMSH15G2084M Altcode:
An understanding of coronal magnetism is vital to heliophysics,
but typical methods to model such fields are not robust to the true
complexities present in the Sun. We present a first-of-its-kind forced
magnetohydrostatic numerical solver for the purpose of reconstructing
coronal magnetic fields. This solver is constructed with Radial Basis
Function finite differences as the core discretization, in a novel
application of that method. This discretization allows the solver to
use scattered datasets. We perform accurate reconstruction of a highly
nonlinear analytic flux rope model, and investigate an application of
the solver to the coronal magnetic field inverse problem.
---------------------------------------------------------
Title: The Solaris Solar Polar MIDEX Mission Concept: Revealing the
Mysteries of the Sun's Poles
Authors: Hassler, Don; Gibson, Sarah; Newmark, Jeffrey
2021AGUFMSH34D..07H Altcode:
Solaris is an exciting, innovative & bold mission of discovery to
reveal the mysteries of the Suns poles. Solaris was selected for Phase
A development as part of NASA's MIDEX program. Solaris builds upon
the legacy of Ulysses, which flew over the solar poles, but Solaris
provides an entirely new featureremote sensing, or IMAGING. Solaris
will be the first mission to image the poles of the Sun from ~75
degrees latitude and provide new insight into the workings of the
solar dynamo and the solar cycle, which are at the foundation of our
understanding of space weather and space climate. Solaris will also
provide enabling observations for improved space weather research,
modeling and prediction with time series of polar magnetograms and
views of the ecliptic from above, providing a unique view of the
corona, coronal dynamics, and CME eruption. To reach the Suns poles,
Solaris will first travel to Jupiter, and use Jupiters gravity to
slingshot out of the ecliptic plane, and fly over the Suns poles
at ~75 degrees latitude. Just as our understanding of Jupiter &
Saturn were revolutionized by polar observations from Juno and Cassini,
our understanding of the Sun will be revolutionized by Solaris.
---------------------------------------------------------
Title: Large ensemble simulations of CMEs in the inner heliosphere:
toward constraining distributions of CME parameters near the Sun
Authors: Provornikova, Elena; Merkin, Viacheslav; Malanushenko, Anna;
Gibson, Sarah; Vourlidas, Angelos; Arge, Charles; Dalmasse, Kevin
2021AGUFMSH32A..01P Altcode:
In this work, we take a comprehensive approach which combines
physics-based simulations, observations and statistical methods
toward understanding the evolution of coronal mass ejections in
the inner heliosphere and linking characteristics of CMEs near the
Sun and their plasma and magnetic field properties as they would be
observed at 1 AU. We simulate the propagation of ICMEs using a global
model of the inner heliosphere driven at the coronal boundary by
the Wang-Sheeley-Arge (WSA)-ADAPT model. ICMEs are initiated at 21.5
solar radii using an MHD analytical Gibson-Low (G&L) model of a
self-similarly expanding magnetic bubble with defining parameters (e.g.,
latitude and longitude, magnetic field topology and strength, angular
width, speed, orientation). The ICME propagation is simulated using
the inner heliosphere version of the Grid Agnostic MHD for Extended
Research Applications (GAMERA) MHD model, which is a reinvention of the
high-heritage Lyon-Fedder-Mobarry (LFM) code. A set of values for each
of the defining G&L parameters was constrained by the statistical
representation of CME images near the Sun. Intending to span the solar
cycle, we model ICME propagation in different solar wind backgrounds
corresponding to rising, declining, and minimum solar cycle phases. A
grid of CME parameters and three solar wind backgrounds constitute
a parameter space for 50,000 ICME simulations. We describe types and
a structure of the output data from simulations and an algorithm of
automatic performance of many thousands of runs. We discuss methods to
incorporate CME data from both solar observations and in-situ at 1 AU
in a statistical study to construct posterior predictive distributions
of CME model input parameters.
---------------------------------------------------------
Title: Latitude Variations in Primary and Secondary Polar Crown
Polarity Inversion Lines and Polar Coronal Hole Boundaries over Five
Solar Cycles
Authors: Emery, B. A.; Webb, D. F.; Gibson, S. E.; Hewins, I. M.;
McFadden, R. H.; Kuchar, T. A.
2021SoPh..296..119E Altcode:
We undertake a five solar-cycle (SC 19 - 23) ≈55-year (December
1954 to August 2009) study of the high latitude polarity inversion
lines (PILs) using the recently digitized McIntosh Archive (McA) of
solar synoptic (Carrington) maps. We looked at the evolution of the
median solar latitudes of primary and secondary PILs, and of the polar
coronal hole (CH) boundary for all 732 Carrington Rotations (CRs). We
found hemispheric differences in the "Rush to the Poles" (RttP)
where the polar CH gaps are often longer in the southern hemisphere
(SH), and the secondary PIL reaches its polemost latitude at the end
of its RttP later and more poleward than in the northern hemisphere
(NH). The latitude oscillations found after this poleward peak are
also stronger and often longer in the SH than in the NH, and exhibit
a 22-year variation. The location variations in the CH boundaries and
PILs appear to be at least partly associated with similar variations
in the magnetic field. We also found equatorward expansions of the
polar CHs by ≈50% and equatorward shifts in the PILs that were part
of a disturbance that propagated ≈15°/CR from the SH to the NH in
the descending phase of SC 23.
---------------------------------------------------------
Title: STRIA: A new module within FORWARD towards modelling PUNCH
datasets
Authors: Gilly, C. R.; Cranmer, S.; Gibson, S.
2021AAS...23832802G Altcode:
A new module is being written within the FORWARD toolkit in SSW which
will help us to interpret future observations from the PUNCH mission
(a new heliosphere imager being launched in 2023). This presentation
will consist of preliminary results from this project. The next
step past this striated model (STRIA) will involve placing radially
outflowing blobs of plasma into the model and discerning expected
detection challenges/limits.
---------------------------------------------------------
Title: Identifying Non-potential Energy Hot Spots In A Global
Coronal Simulation
Authors: Corchado Albelo, M. F.; Gibson, S. E.; Linker, J.; Mackay,
D. H.; Dalmasse, K.; Malanushenko, A.
2021AAS...23832803C Altcode:
Observing the global coronal magnetic field remains a difficult task;
limiting our understanding of the evolution of global phenomena in these
external layers of the solar atmosphere. Therefore, we rely on models to
get the solar exterior global field. While models can extrapolate the
magnetic field from surface flux and vector magnetogram observations,
e.g. by assuming a current-free corona, other techniques are used
to simulate the current-carrying field via magnetohydrodynamic (MHD)
evolution or surface flux transport of large scale field, and inserting
current-carrying small scale field structures like twisted flux ropes
into the corona. These current-carrying fields are of interest for
studying solar energetic eruptions like coronal mass ejections and
flares because they provide the energy reservoir needed to drive these
events. Previous studies suggest that ground-based infrared polarimetric
measurements of Fe XIII (1074.7 nm) line correlate with the energy
of the current-carrying field. In this study we generated synthetic
polarimetric observations from a fully-resolved magnetohydrodynamics
model of the August 21, 2017 eclipse. The synthetic observations
were used as input to a diagnostic we developed to identify regions
where the modeling team inserted twisted flux ropes. The diagnostic
evaluated linearly and circularly polarized synthetic observations
of the corona as a means to identify the current-carrying magnetic
energy density. We found that the diagnostic does identify the
distribution of flux ropes in the corona. Thus, our findings motivate
the implementation of polarimetric measurements to identify "hot spots"
in which we can insert flux ropes and a degree of the twist/shear in
the current-carrying field.
---------------------------------------------------------
Title: Polarimeter to UNify the Corona and Heliosphere: Science
Summary and Mission Status
Authors: Deforest, C.; Gibson, S.; Killough, R.; Beasley, M.; Laurent,
G.; Colaninno, R.; The Punch Team
2021AAS...23831304D Altcode:
The Polarimeter to UNify the Corona and Heliosphere (PUNCH) is a
constellation mission being built within NASA's Small Explorer
program. During its two year nominal mission, PUNCH will use a
constellation of four spacecraft as a single visible-light "virtual
coronagraph" with a 90° outer field of view and a 1.25° inner field
of view, to continuously produce global, photometric, 3D images of the
outer reaches of the solar corona and the solar wind itself. PUNCH uses
polarization properties of Thomson scattering to extract 3D information
along its single line of sight from near Earth. <P />The PUNCH science
objectives are to understand both (1) how coronal structures become
the ambient solar wind, and (2) the dynamic evolution of transient
structures within the solar wind. Subtopics include mapping the
evolving flow of the solar wind, identifying microstructures and
turbulence in the young solar wind, locating the Alfvén surface
and other natural boundaries of the corona-heliosphere system,
tracking CMEs and their evolution in 3D, measuring the formation
of solar wind co-rotating interaction regions, and determining the
large-scale dynamics of interplanetary shocks. These are addressed
through deep-field 3D imaging, using the polarization properties
of Thomson-scattered light. <P />PUNCH is finishing up its Phase B
(preliminary design), with KDP-C expected in 2021 July and a Launch
Readiness Date in late 2023. <P />This poster summarizes the science
objectives, novel approach, and current status of the mission.
---------------------------------------------------------
Title: The Solaris Solar Polar MIDEX Mission Concept: Revealing the
Mysteries of the Sun's Poles
Authors: Hassler, D. M.; Newmark, J.; Gibson, S.
2021AAS...23831316H Altcode:
Solaris is an exciting, innovative & bold mission of discovery to
reveal the mysteries of the Sun's poles. Solaris was selected for Phase
A development as part of NASA's MIDEX program. Solaris builds upon
the legacy of Ulysses, which flew over the solar poles, but Solaris
provides an entirely new feature⋯remote sensing, or IMAGING. <P
/>Solaris will be the first mission to image the poles of the Sun
from ~75 degrees latitude and provide new insight into the workings
of the solar dynamo and the solar cycle, which are at the foundation
of our understanding of space weather and space climate. Solaris will
also provide enabling observations for improved space weather research,
modeling and prediction with time series of polar magnetograms and views
of the ecliptic from above, providing a unique view of the corona,
coronal dynamics, and CME eruption. <P />To reach the Sun's poles,
Solaris will first travel to Jupiter, and use Jupiter's gravity to
slingshot out of the ecliptic plane, and fly over the Sun's poles
at ~75 degrees latitude. Just as our understanding of Jupiter &
Saturn were revolutionized by polar observations from Juno and Cassini,
our understanding of the Sun will be revolutionized by Solaris.
---------------------------------------------------------
Title: Simulating the Solar Minimum Corona in UV Wavelengths with
Forward Modeling II. Doppler Dimming and Microscopic Anisotropy Effect
Authors: Zhao, Jie; Gibson, Sarah E.; Fineschi, Silvano; Susino,
Roberto; Casini, Roberto; Cranmer, Steven R.; Ofman, Leon; Li, Hui
2021ApJ...912..141Z Altcode:
In ultraviolet (UV) spectropolarimetric observations of the solar
corona, the existence of a magnetic field, solar wind velocity, and
temperature anisotropies modify the linear polarization associated with
resonant scattering. Unlike previous empirical models or global models,
which present blended results of the above physical effects, in this
work, we forward-model expected signals in the H I Lyα line (121.6 nm)
by adopting an analytic model that can be adjusted to test the roles
of different effects separately. We find that the impact of all three
effects is most evident in the rotation of the linear polarization
direction. In particular, (1) for magnetic fields between ∼10 and
∼100 G, the Hanle effect modifies the linear polarization at low
coronal heights, rotating the linear polarization direction clockwise
(counterclockwise) when the angle between the magnetic field and the
local vertical is greater (less) than the van Vleck angle, which is
consistent with the result of Zhao et al.; (2) solar wind velocity,
which increases with height, has a significant effect through the
Doppler dimming effect at higher coronal heights, rotating the linear
polarization direction in an opposite fashion to the Hanle effect;
and (3) kinetic temperature anisotropies are most significant at
lower heights in open nonradial magnetic field regions, producing
tilt opposite to isotropic Doppler dimming. The fact that the three
effects operate differently in distinct spatial regimes opens up the
possibility for using linear polarization measurements in UV lines to
diagnose these important physical characteristics of the solar corona.
---------------------------------------------------------
Title: Magnetofrictional Modeling of an Erupting Pseudostreamer
Authors: Karna, Nishu; Savcheva, Antonia; Gibson, Sarah; Tassev,
Svetlin; Reeves, Katharine K.; DeLuca, Edward E.; Dalmasse, Kévin
2021ApJ...913...47K Altcode:
In this study, we present the magnetic configuration of an erupting
pseudostreamer observed on 2015 April 19, on the southwest limb of the
Sun, with a prominence cavity embedded inside. The eruption resulted in
a partial halo coronal mass ejection. The prominence eruption begins
with a slow rise and then evolves to a fast-rise phase. We analyze
this erupting pseudostreamer using the flux-rope insertion method
and magnetofrictional relaxation to establish a sequence of plausible
out-of-equilibrium magnetic configurations. This approach allows the
direct incorporation of observations of structures seen in the corona
(filament and cavity) to appropriately model the pseudostreamer
based on SDO/HMI line-of-sight photospheric magnetograms. We also
perform a topological analysis in order to determine the location
of quasiseparatrix layers (QSLs) in the models, producing Q-maps to
examine how the QSL locations progress in the higher iterations. We
found that the axial flux in our best-fit unstable model was a factor
of 20 times higher than we found in our marginally stable case. We
computed the average magnetic field strength of the prominence and
found that the unstable model exhibits twice the average field strength
of the stable model. The eruption height from our modeling matches
very well with the prominence eruption height measured from the AIA
observation. The Q-maps derived from the model reproduce structures
observed in LASCO/C2. Thus, the modeling and topological analysis
results are fully consistent with the observed morphological features,
implying that we have captured the large magnetic structure of the
erupting filament in our magnetofrictional simulation.
---------------------------------------------------------
Title: Inward-propagating Plasma Parcels in the Solar Corona: Models
with Aerodynamic Drag, Ablation, and Snowplow Accretion
Authors: Cranmer, Steven R.; DeForest, Craig E.; Gibson, Sarah E.
2021ApJ...913....4C Altcode: 2021arXiv210312039C
Although the solar wind flows primarily outward from the Sun to
interplanetary space, there are times when small-scale plasma inflows
are observed. Inward-propagating density fluctuations in polar coronal
holes were detected by the COR2 coronagraph on board the STEREO-A
spacecraft at heliocentric distances of 7-12 solar radii, and these
fluctuations appear to undergo substantial deceleration as they move
closer to the Sun. Models of linear magnetohydrodynamic waves have
not been able to explain these deceleration patterns, so they have
been interpreted more recently as jets from coronal sites of magnetic
reconnection. In this paper, we develop a range of dynamical models
of discrete plasma parcels with the goal of better understanding the
observed deceleration trend. We found that parcels with a constant
mass do not behave like the observed flows, and neither do parcels
undergoing ablative mass loss. However, parcels that accrete mass in
a snowplow-like fashion can become decelerated as observed. We also
extrapolated OMNI in situ data down to the so-called Alfvén surface
and found that the initial launch point for the observed parcels may
often be above this critical radius. In other words, in order for the
parcels to flow back down to the Sun, their initial speeds are probably
somewhat nonlinear (i.e., supra-Alfvénic), and thus the parcels may be
associated with structures such as shocks, jets, or shear instabilities.
---------------------------------------------------------
Title: Mapping the global magnetic field in the solar corona through
magnetoseismology
Authors: Yang, Zihao; Bethge, Christian; Tian, Hui; Tomczyk, Steven;
Morton, Richard; Del Zanna, Giulio; McIntosh, Scott; Karak, Bidya
Binay; Gibson, Sarah; Samanta, Tanmoy; He, Jiansen; Chen, Yajie;
Wang, Linghua; Bai, Xianyong
2021EGUGA..23..642Y Altcode:
Magnetoseismology, a technique of magnetic field diagnostics based
on observations of magnetohydrodynamic (MHD) waves, has been widely
used to estimate the field strengths of oscillating structures in
the solar corona. However, previously magnetoseismology was mostly
applied to occasionally occurring oscillation events, providing
an estimate of only the average field strength or one-dimensional
distribution of field strength along an oscillating structure. This
restriction could be eliminated if we apply magnetoseismology to the
pervasive propagating transverse MHD waves discovered with the Coronal
Multi-channel Polarimeter (CoMP). Using several CoMP observations of
the Fe XIII 1074.7 nm and 1079.8 nm spectral lines, we obtained maps of
the plasma density and wave phase speed in the corona, which allow us
to map both the strength and direction of the coronal magnetic field
in the plane of sky. We also examined distributions of the electron
density and magnetic field strength, and compared their variations
with height in the quiet Sun and active regions. Such measurements
could provide critical information to advance our understanding of the
Sun's magnetism and the magnetic coupling of the whole solar atmosphere.
---------------------------------------------------------
Title: Critical Science Plan for the Daniel K. Inouye Solar Telescope
(DKIST)
Authors: Rast, Mark P.; Bello González, Nazaret; Bellot Rubio,
Luis; Cao, Wenda; Cauzzi, Gianna; Deluca, Edward; de Pontieu, Bart;
Fletcher, Lyndsay; Gibson, Sarah E.; Judge, Philip G.; Katsukawa,
Yukio; Kazachenko, Maria D.; Khomenko, Elena; Landi, Enrico; Martínez
Pillet, Valentín; Petrie, Gordon J. D.; Qiu, Jiong; Rachmeler,
Laurel A.; Rempel, Matthias; Schmidt, Wolfgang; Scullion, Eamon; Sun,
Xudong; Welsch, Brian T.; Andretta, Vincenzo; Antolin, Patrick; Ayres,
Thomas R.; Balasubramaniam, K. S.; Ballai, Istvan; Berger, Thomas E.;
Bradshaw, Stephen J.; Campbell, Ryan J.; Carlsson, Mats; Casini,
Roberto; Centeno, Rebecca; Cranmer, Steven R.; Criscuoli, Serena;
Deforest, Craig; Deng, Yuanyong; Erdélyi, Robertus; Fedun, Viktor;
Fischer, Catherine E.; González Manrique, Sergio J.; Hahn, Michael;
Harra, Louise; Henriques, Vasco M. J.; Hurlburt, Neal E.; Jaeggli,
Sarah; Jafarzadeh, Shahin; Jain, Rekha; Jefferies, Stuart M.; Keys,
Peter H.; Kowalski, Adam F.; Kuckein, Christoph; Kuhn, Jeffrey R.;
Kuridze, David; Liu, Jiajia; Liu, Wei; Longcope, Dana; Mathioudakis,
Mihalis; McAteer, R. T. James; McIntosh, Scott W.; McKenzie, David
E.; Miralles, Mari Paz; Morton, Richard J.; Muglach, Karin; Nelson,
Chris J.; Panesar, Navdeep K.; Parenti, Susanna; Parnell, Clare E.;
Poduval, Bala; Reardon, Kevin P.; Reep, Jeffrey W.; Schad, Thomas A.;
Schmit, Donald; Sharma, Rahul; Socas-Navarro, Hector; Srivastava,
Abhishek K.; Sterling, Alphonse C.; Suematsu, Yoshinori; Tarr, Lucas
A.; Tiwari, Sanjiv; Tritschler, Alexandra; Verth, Gary; Vourlidas,
Angelos; Wang, Haimin; Wang, Yi-Ming; NSO and DKIST Project; DKIST
Instrument Scientists; DKIST Science Working Group; DKIST Critical
Science Plan Community
2021SoPh..296...70R Altcode: 2020arXiv200808203R
The National Science Foundation's Daniel K. Inouye Solar Telescope
(DKIST) will revolutionize our ability to measure, understand,
and model the basic physical processes that control the structure
and dynamics of the Sun and its atmosphere. The first-light DKIST
images, released publicly on 29 January 2020, only hint at the
extraordinary capabilities that will accompany full commissioning of
the five facility instruments. With this Critical Science Plan (CSP)
we attempt to anticipate some of what those capabilities will enable,
providing a snapshot of some of the scientific pursuits that the DKIST
hopes to engage as start-of-operations nears. The work builds on the
combined contributions of the DKIST Science Working Group (SWG) and
CSP Community members, who generously shared their experiences, plans,
knowledge, and dreams. Discussion is primarily focused on those issues
to which DKIST will uniquely contribute.
---------------------------------------------------------
Title: Gibson & Low Flux Rope Model: More Than a Spheromak!
Authors: Malanushenko, Anna; Gibson, Sarah; Provornikova, Elena;
Dalmasse, Kévin; Merkin, Viacheslav; Vourlidas, Angelos; Nychka,
Doug; Flyer, Natasha; Arge, Charles
2021cosp...43E1736M Altcode:
Modeling solar coronal mass ejections (CMEs) is very important for
both understanding coronal physics and for improving the accuracy of
space weather forecasts. While it is generally accepted that CMEs
are primarily magnetic structures, the exact properties of these
structures could differ in different models and events. A structure
often considered is a spheromak, a toroidal twisted flux rope, which
is ejected as a CME bubble. Another commonly considered structure is a
twisted magnetic flux rope, which is anchored to the solar surface while
its upper portion is ejected into interplanetary space. In this talk
we will show how a well-known analytical magnetohydrodynamic CME model
(Gibson \& Low, 1998), generally considered a spheromak-like model,
can be extended to represent both standard spheromak and twisted flux
tube configurations, as well as other topologically distinct magnetic
structures. We will begin with the general parameters of the flux rope
in this model (such as size and stretching parameters), and explore
topologically different congurations possible with their variation. We
then present several dimensionless parameters which can be varied to
achieve these different configurations and consider how they relate
to directly observable quantities. This work is particularly timely,
as the Gibson \& Low model is been increasingly used as input to
numerical models of the solar corona and the heliosphere. The ability
to generate topologically different magnetic congurations within this
analytic solution is of great value to such simulations, as well as
for the studies of the flux ropes forming in the solar corona.
---------------------------------------------------------
Title: Extended, Kilogauss Bald Patches in the Super-Flaring Solar
Active Region 12673
Authors: Sun, Xudong; Gibson, Sarah; Welsch, Brian; Titov, Viacheslav
2021cosp...43E1730S Altcode:
Bald patch (BP) is a magnetic topological feature where U-shaped
field lines turn tangent to the photosphere. When accompanied by
shear, BPs suggest the existence of pre-eruption magnetic flux ropes
(MFRs). Previous studies often found them in young solar active regions
(ARs) with patchy flux emergence, or decaying ARs with weaker magnetic
field. Here we report on a coherent, strong-field example observed
in the super-flaring AR 12673. The central BP, located in a narrow
delta_x000E_-spot penumbral lane, extended over 10 Mm with field
strength above 2 kG. It formed over a period 10 hr, which featured fast
Doppler downflow, gradual azimuth rotation, field strength reduction,
and field gradient enhancement. It then rapidly disintegrated during
a GOES X9 flare. Coronal field extrapolation reveals a low-lying,
kilogauss MFR with over two turns of twist wrapped inside three
intersecting BP separatrices (BPSs). The early-phase flare ribbons
coincide with BPS foot prints. We discuss the BP formation mechanism
such as flux cancellation, its stability condition, and its role in
the eruption.
---------------------------------------------------------
Title: WHPI: A New Initiative on Solar Minimum
Authors: De Toma, Giuliana; Gibson, Sarah; Qian, Liying; Thompson,
Barbara
2021cosp...43E.916D Altcode:
The Whole Heliosphere and Planetary Interactions (WHPI) is an
international initiative focused around the solar minimum period
that aims to understand the interconnected Sun-heliospheric-planetary
system. The simpler magnetic configuration and infrequency of solar
eruptions makes solar minimum an ideal time to determine how the Sun's
radiative output, magnetic field and outflowing solar wind plasma
interact with the background heliosphere, the Earth and the other
planets. WHPI follows two similar initiatives during the previous solar
minima in 1996 and 2008-2009. The success of these efforts relies on a
broad participation of scientists worldwide and across disciplines. In
2019-2020 WHPI coordinated 3 different observing campaigns, each a
solar rotation long: The first was on Mar 12 - Apr 8, 2019 and targeted
two large, recurrent coronal holes and the associated high-speed solar
wind streams, the second one on Jun 29 - Jul 26 2019 was centered on
the total solar eclipse, and the third one on Jan 15 - Feb 11 2020
corresponded to the 4th Parker Solar Probe (PSP) encounter when the
Earth and many space observatories were near-radially aligned with
PSP. We describe the WHPI effort as an example of interdisciplinary
collaboration and report on the preliminary science results obtained
during the WHPI campaigns.
---------------------------------------------------------
Title: Magnetofrictional Modeling of an erupting Pseudostreamer
Authors: Karna, Nishu; Gibson, Sarah; DeLuca, Edward; Dalmasse,
Kévin; Savcheva, Antonia; Tassev, Svetlin
2021cosp...43E1768K Altcode:
In this study, we present a magnetic configuration of an erupting
pseudostreamer observed on April 19, 2015 on the Southwest limb,
embedding a prominence cavity. The eruption resulted in a relatively
wide CME with a round front and prominence core intersected by a sharp
plume as seen in SOHO/LASCO C2, a partial halo was observed. The
prominence eruption begins with a slow rise and then evolves to a
fast rise phase. We first construct a non-linear force free field
(NLFFF) model of this erupting pseudostreamer using the flux rope
insertion method. The NLFFF model produces the 3D coronal magnetic field
constrained by observed coronal structures and the SDO/HMI photospheric
magnetogram taken 3 days earlier. We then increase axial and poloidal
flux in the model to make it unstable. The field configurations
representing the eruption are not in force-free equilibrium. We
magnetofrictionally evolve the model until the flux rope expands to
three solar radii and compare the modeled CME propagation with the
SOHO/LASCO C2 observations. We perform a topological analysis of the
models in order to determine the location of quasi-separatrix layers
(QSLs) and how the QSL locations are transferred as the simulation
progresses. The model reproduced the LASCO C2 observation structure in
the QSL map. The modeling and topological analysis results are fully
consistent with the observed morphological features implying that we
have captured the large magnetic structure of the erupting filament.
---------------------------------------------------------
Title: SunCET: The Sun Coronal Ejection Tracker Concept
Authors: Mason, James Paul; Chamberlin, Phillip C.; Seaton, Daniel;
Burkepile, Joan; Colaninno, Robin; Dissauer, Karin; Eparvier, Francis
G.; Fan, Yuhong; Gibson, Sarah; Jones, Andrew R.; Kay, Christina; Kirk,
Michael; Kohnert, Richard; Pesnell, W. Dean; Thompson, Barbara J.;
Veronig, Astrid M.; West, Matthew J.; Windt, David; Woods, Thomas N.
2021JSWSC..11...20M Altcode: 2021arXiv210109215M
The Sun Coronal Ejection Tracker (SunCET) is an extreme ultraviolet
imager and spectrograph instrument concept for tracking coronal mass
ejections through the region where they experience the majority
of their acceleration: the difficult-to-observe middle corona. It
contains a wide field of view (0-4 R<SUB>⊙</SUB>) imager and a 1 Å
spectral-resolution-irradiance spectrograph spanning 170-340 Å. It
leverages new detector technology to read out different areas of the
detector with different integration times, resulting in what we call
"simultaneous high dynamic range", as opposed to the traditional high
dynamic range camera technique of subsequent full-frame images that
are then combined in post-processing. This allows us to image the
bright solar disk with short integration time, the middle corona
with a long integration time, and the spectra with their own,
independent integration time. Thus, SunCET does not require the use
of an opaque or filtered occulter. SunCET is also compact - ~15 × 15
× 10 cm in volume - making it an ideal instrument for a CubeSat or a
small, complementary addition to a larger mission. Indeed, SunCET is
presently in a NASA-funded, competitive Phase A as a CubeSat and has
also been proposed to NASA as an instrument onboard a 184 kg Mission
of Opportunity.
---------------------------------------------------------
Title: Designing a New Coronal Magnetic Field Energy Diagnostic
Authors: Corchado-Albelo, Marcel F.; Dalmasse, Kévin; Gibson, Sarah;
Fan, Yuhong; Malanushenko, Anna
2021ApJ...907...23C Altcode:
In the solar corona, the free energy, i.e., the excess in magnetic
energy over a ground-state potential field, forms the reservoir of
energy that can be released during solar flares and coronal mass
ejections. Such free energy provides a measure of the magnetic field
nonpotentiality. Recent theoretical and observational studies indicate
that the presence of nonpotential magnetic fields is imprinted into
the structures of infrared, off-limb, coronal polarization. In this
paper, we investigate the possibility of exploiting such observations
for mapping and studying the accumulation and release of coronal free
magnetic energy, with the goal of developing a new tool for identifying
"hot spots" of coronal free energy such as those associated with
twisted and/or sheared coronal magnetic fields. We applied forward
modeling of infrared coronal polarimetry to three-dimensional models
of nonpotential and potential magnetic fields. From these we defined a
quantitative diagnostic of nonpotentiality that in the future could be
calculated from a comparison of infrared, off-limb, coronal polarization
observations from, e.g., the Coronal Multi-channel Polarimeter or the
Daniel K. Inouye Solar Telescope, and the corresponding polarization
signal forward-modeled from a potential field extrapolated from
photospheric magnetograms. We considered the relative diagnostic
potential of linear and circular polarization, and the sensitivities
of these diagnostics to coronal density distributions and assumed
boundary conditions of the potential field. Our work confirms the
capacity of polarization measurements for diagnosing nonpotentiality
and free energy in the solar corona.
---------------------------------------------------------
Title: What does a magnetic flux rope look like?
Authors: Gibson, Sarah
2021cosp...43E1744G Altcode:
Solar magnetic flux ropes are often represented by the archetypal
"slinky" toy. Although this may be a fair representation of the flux
rope's magnetic field lines, the observational manifestation of the
flux rope at different wavelengths may look entirely different. Forward
modeling explicitly takes into account three crucial factors leading to
the appearance of the flux rope: the physical state of the flux rope's
plasma and magnetic field, the physical process that translates the
physical state into an observable quantity (e.g., Thomson scattering,
collisional excitation, Faraday rotation, etc., etc.), and finally the
observer's position relative to the flux rope. We will use forward
modeling to investigate the observable properties of flux ropes at
multiple wavelengths and in a range of spatial contexts, including
active regions and quiescent prominences, and CMEs in the corona and
solar wind.
---------------------------------------------------------
Title: The Magnetic Skeleton of the Solar Corona Over Several Solar
Rotations: Features, Analysis, and Community Availability
Authors: Malanushenko, A. V.; Gibson, S. E.; Kucera, T. A.; McKenzie,
D. E.
2020AGUFMSH041..02M Altcode:
The magnetic field in the solar corona is thought to be the main
driver for solar eruptive events, such as flares and coronal mass
ejections. The coronal magnetic field is therefore important to study,
but it is difficult to measure directly. Usually, it is studied through
extrapolations based on photospheric magnetograms. As the corona is
thought to be mostly in a state of equilibrium, equations of low-beta
equilibria are often used in order to study the structure of the
field, or to estimate the magnetic energy. One of the complications
that arise from this approach is that the solar photosphere itself is
not a low-beta equilibrium. <P />Images of the solar corona in extreme
ultraviolet (EUV) do not directly measure the magnetic field; however,
they do reveal structures from which information about magnetic field
can be inferred. For example, coronal loops are thought to trace
out magnetic field lines, coronal cavities are bounded by magnetic
surfaces, coronal holes are areas of magnetic flux that is open to
the heliosphere, and plasma flows are also thought to follow lines
of magnetic field. In other wavelengths, coronal spectropolarimetry
(SP) can provide us with proxies for magnetic field strength and
reveal plasma flows along the line of sight, off the limb. The EUV
images and SP data are frequently used to validate magnetic field
models. Additionally, new models are emerging which can use these data
directly as additional constraints. <P />We aggregate available relevant
features seen in EUV and SP data for several solar rotations. We
apply existing techniques to infer 3D constraints on the magnetic
field from these data. The result is an interactive 3D model based on
these constraints for a full rotation, or a "magnetic skeleton". It
is modular, so individual constraints can be easily added, or only
selected constraints can be used. The features could be exported in
either graphical or numerical form. The possible uses of our approach
include validation of magnetic models that are based on extrapolations
alone. Some models allow for using additional coronal constraints
directly. These 'skeletons' can also be used in non-magnetic-modeling
applications, as a simple, interactive reference for features seen in
a given rotation. We make the models available to the community and
show how to obtain and use them.
---------------------------------------------------------
Title: Tracking CME substructure evolution through the solar wind
Authors: Gibson, S. E.; DeForest, C.; de Koning, C. A.; Fan, Y.;
Malanushenko, A. V.; Merkin, V. G.; Provornikova, E.; Thompson, B. J.;
Webb, D. F.
2020AGUFMSH0280005G Altcode:
Future coronagraphs and heliospheric imagers, in particular those
to be launched on the PUNCH mission, will have the capability to
track the evolution of CME substructures as the CME moves through and
interacts with the solar wind. We present analysis using polarization
data obtained from forward modeling simulations of CMEs in the corona
and inner heliosphere. We use these data to track the evolution
of substructures in three dimensions, and consider the diagnostic
potential of internal substructure vs structure at the front of the
CME. In particular, we develop methods for extracting information
about chirality of CME magnetic flux ropes from polarization data.
---------------------------------------------------------
Title: The Polar Field Reversal Process over Five Solar Cycles Using
the McIntosh Archive
Authors: Webb, D. F.; Emery, B. A.; Gibson, S. E.; Hewins, I. M.;
McFadden, R.; Kuchar, T. A.
2020AGUFMSH0020021W Altcode:
We study the polar magnetic field reversal process over five solar
cycles (SCs 19-23, Dec. 1954 - Aug. 2009) using the recently digitized
McIntosh Archive (McA) of solar synoptic maps. This data set allows
the tracking of features such as filaments, polarity inversion lines
(PILs), coronal hole boundaries and sunspots over many consecutive
Carrington rotations. Here we follow the evolution of the polar magnetic
regions of the Sun and how the rush-to-the-poles and other patterns
occur during the period when the polar fields reverse around each SC
maximum. This process was first studied in detail for SCs 20 and 21 by
Webb et al. (1984). The goal then as now is to use the rush-to-the-poles
and CH boundary mapping to better constrain solar interior and dynamo
models. We use the McA data sets to determine the timing and lags
among these events around the maximum of each SC in each hemisphere:
the sunspot number peak, the polarity reversal, the disappearance of
the polar crown filaments and PIL, the first appearance of mid-latitude
CHs of new-cycle polarity, and the earliest complete coverage of each
pole by a coronal hole. With the newly processed McA, we can now extend
this type of study over five consecutive SCs through SC 23.
---------------------------------------------------------
Title: Oscillations in Secondary to Primary Polar Crown Polarity
Inversion Lines around Solar Maximum over Five Solar Cycles
Authors: Emery, B. A.; Webb, D. F.; Gibson, S. E.; Hewins, I. M.;
McFadden, R.; Kuchar, T. A.
2020AGUFMSH006..06E Altcode:
We undertake a five solar-cycle (SC19-23, Dec. 1954 - Aug. 2009)
study of oscillations in the high-latitude polarity inversion lines
(PILs) using the recently digitized McIntosh Archive of solar synoptic
maps. We look at the evolution of the primary PIL, which is the
nearly continuous polar crown filament (PCF) line bounding the polar
coronal hole (CH). The secondary PIL consists of neutral line segments
equatorward of the primary PIL, and it becomes a nearly continuous
PCF line at the end of the rush to the poles before solar maximum when
the polar polarity reverses with the primary PIL disappearing, and the
secondary PIL becomes the primary PIL with the new polarity. This new
primary PIL achieves a maximum poleward latitude of ~+/-57 degrees,
and then relaxes equatorward in oscillations of 2-5 degrees of latitude
with periods between ~10-35 Carrington Rotations (CRs). In 2005, we
saw equatorward drops in the PIL and CH boundaries that started in
the southern hemisphere pole and ended in the north pole, with ~35CR
wave periods before and ~20CR after the break. The oscillations and
breaks are new aspects of the general evolutionary patterns of surface
features that need to be accounted for by interior dynamo models.
---------------------------------------------------------
Title: Contemporary Analysis Methods for Coronagraph and Heliospheric
Imager Data
Authors: Thompson, B. J.; Attie, R.; Chhiber, R.; Cranmer, S. R.;
DeForest, C.; Gallardo-Lacourt, B.; Gibson, S. E.; Jones, S. I.;
Moraes Filho, V.; Reginald, N. L.; Uritsky, V. M.; Viall, N. M.
2020AGUFMSH031..05T Altcode:
Coronagraphs, polarimeters, and heliospheric imagers are providing
new insight into how structures in the solar wind form and develop as
they flow from the inner corona into the heliosphere. With this comes
a whole new frontier of physical observables in 3D, including kinetic
(velocity and acceleration), thermodynamic (density, temperature, and
shock boundary), and magnetic field properties. These measurements
inform and challenge models of global solar wind flow, turbulence,
and CME propagation. We will discuss recent advances in quantifying
physical properties of the corona and solar wind using coronagraph
and heliospheric imager data, and make predictions of what new models
and instrumentation (including the in-development PUNCH mission)
will bring us in the future.
---------------------------------------------------------
Title: The Solaris Solar Polar Mission: Exploring one of the last
Unexplored Regions of the Solar System
Authors: Hassler, D.; Newmark, J. S.; Gibson, S. E.; Duncan, N. A.;
Gosain, S.; Harvey, J. W.; Wuelser, J. P.; Woods, T. N.
2020AGUFMSH0110003H Altcode:
The solar poles are one of the last unexplored regions of the solar
system. Although Ulysses flew over the poles in the 1990s, it did
not have remote sensing instruments onboard to probe the Sun's polar
magnetic field or surface/sub-surface flows. I will discuss Solaris,
a proposed Solar Polar MIDEX mission to fly over the solar poles at 75
degrees inclination to address key outstanding, breakthrough problems
in solar physics, & fill holes in our scientific understanding
that will not be addressed by current or planned future missions. Such
a small, focused, "paradigm-breaking" mission is achievable now with
existing launchers and technology, & is enabled by miniaturized
instrument technology such as the Compact Doppler Magnetograph (CDM),
developed for Solaris to provide magnetic field & Doppler velocity
measurements in a small (15kg) package. Solaris will also provide
enabling observations for space weather research & stimulate future
research through new unanticipated discoveries.
---------------------------------------------------------
Title: WHPI Synoptic Coronal Hole Maps and Solar Wind Studies
Authors: Hewins, I. M.; Gibson, S. E.
2020AGUFMSH0180003H Altcode:
Ian Hewins(1), Sarah Gibson (1), Barbara Emery-Geiger (1) <P />1 =
HAO/NCAR
---------------------------------------------------------
Title: Coronagraphy from the Ground: Current and Future Observations
Authors: Burkepile, J.; Tomczyk, S.; Zmarzly, P.; de Wijn, A.; Gibson,
S. E.; de Toma, G.; Galloy, M. D.
2020AGUFMSH031..03B Altcode:
Ground-based coronagraphs provided the first observations of the
ethereal corona outside of a total solar eclipse in 1931. Invented by
Bernard Lyot, coronagraphs enabled long time-series images and movies
of the emission line corona. Advances in technology have led to more
sophisticated coronagraphs capable of observing polarized light from
spectral lines and the coronal continuum. These observations, coupled
with advances in our understanding of resonance scattering-induced
polarization, have greatly facilitated our knowledge of coronal physics
and explosive events such as Coronal Mass Ejections (CMEs). While
space-based coronagraphs provide spectacular observations of the
extended corona, ground-based coronagraphs continue to contribute
important, unique and complementary inner coronal observations at
a fraction of the cost of a space-based mission. We discuss current
ground-based solar coronagraphs, observations and data products and
highlight future instruments and network capabilities and benefits.
---------------------------------------------------------
Title: Snapshots of Solar Minimum: Data and Model Results From the
Past Two Solar Minima
Authors: Thompson, B. J.; Gibson, S. E.
2020AGUFMSH0180002T Altcode:
We present an overview of the data and models collected for the
Whole Sun Month (WSM; 1996) Whole Heliosphere Interval (WHI;
2008), two international campaigns to study the three-dimensional
solar-heliospheric-planetary connected system near solar minimum. The
data and models from WSM, which occurred during the solar minimum
between Cycles 22 and 23, provided new insight into how solar magnetic
structure forms the corona and inner heliosphere. WSM inspired the
Whole Heliosphere Interval campaign during the next solar minimum, and
the scientific goals expanded to study how solar minimum structures
affect processes in geospace. The data from WHI extended from below
the solar photosphere, through interplanetary space, and down to
Earth's mesosphere. Nearly 200 people participated in aspects of WHI
studies, analyzing and interpreting data from nearly 100 instruments and
models in order to elucidate the physics of fundamental heliophysical
processes. WSM and WHI studies traced the solar activity and structure
into the heliosphere and geospace, and provided new insight into
the nature of the interconnected heliophysical system near solar
minimum. This presentation gives insight into the motivation for the
Whole Heliosphere and Planetary Interactions campaigns.
---------------------------------------------------------
Title: SunCET: A CubeSat Mission Dedicated to the Middle Corona
Authors: Mason, J. P.; Seaton, D. B.; Chamberlin, P. C.; Burkepile,
J.; Colaninno, R. C.; Dissauer, K.; Eparvier, F. G.; Fan, Y.; Gibson,
S. E.; Jones, A. R.; Kay, C.; Kirk, M. S.; Kohnert, R.; Thompson,
B. J.; Veronig, A.; West, M. J.; Woods, T. N.
2020AGUFMSH0300006M Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Tracking Movement of Coronal Holes from Long Term McA Data
Authors: Harris, J.; Dikpati, M.; Gibson, S. E.; Hewins, I. M.
2020AGUFMSH0020010H Altcode:
Features on the surface of the Sun and other layers of the solar
atmosphere are constantly changing, due to its magnetic field. In 1964,
Patrick Mcintosh, a scientist at NOAA's Space Environment Center,
began creating hand-drawn synoptic maps of the sun's magnetic features
and produced nearly 45 years' (about four solar cycles) worth of
these maps. To prevent these maps from being lost,all of these maps
have been digitized in the Mcintosh Archives (McA). This summer,
we processed many years' worth of this data to create stack plots,
which are essentially plots of latitude bands stacked in time. This
allows us to track the movement of solar features, particularly coronal
holes. We calculated the centroids of the coronal holes in successive
Carrington rotations, and estimated the slopes of these patterns as the
coronal holes evolve. To calculate the centroids, we developed a new
method and utilized it with numerical tools in Mathematica. This method
utilizes the Fourier Transform to find an approximation of the outlines
of coronal holes with a series of sinusoids in parametric form. These
parametric equations are then plugged into line integrals to calculate
the centroids. Our method of centroid calculations is accurate in most
cases and is comparable to other accurate methods. Using the slopes of
coronal hole patterns we estimated the velocities and found that the
velocity is more prograde when the coronal holes are at low latitudes,
and more retrograde at high latitudes, which is an expected result
of differential rotation. The velocity was zero at a lower latitude
than expected based on where the Carrington rotation rate is defined
at the photosphere. This implies that the movement of coronal holes
is being influenced by deeply rooted magnetic field lines below
the surface. By superimposing differential rotation on coronal hole
migration velocities and estimating the difference between the two,
we can investigate what other factors influence coronal hole movement,
such as Rossby waves. Learning more about these waves will tell us
more about other forms of solar weather and could help us predict
CMEs. This information could not only advance solar physics but also
help keep our planet safe .
---------------------------------------------------------
Title: Ensemble modeling of interplanetary CMEs with data-constrained
internal magnetic flux rope
Authors: Provornikova, E.; Merkin, V. G.; Malanushenko, A. V.; Gibson,
S. E.; Vourlidas, A.; Arge, C. N.
2020AGUFMSH0030016P Altcode:
Understanding the evolution of the CME magnetic structure as it
propagates through the interplanetary space is a key aspect in the
development of forecasting of magnetic properties of a CME arriving
at Earth and thus its impact on space weather. To analyze processes
of interplanetary CME (ICME)/solar-wind interactions and the role of
CME flux rope specification and solar wind background structure, we
take a statistical approach and perform thousands of data-driven MHD
simulations of ICME propagation in the inner heliosphere. Data-driven
modeling of ICMEs in the inner heliosphere (starting beyond the critical
surface in the corona) presents an attractive and computationally
feasible approach, since it bypasses the complex problem of CME
initiation and eruption in the corona. We simulate the propagation
of ICMEs in the inner heliosphere using a global model driven at the
coronal boundary by the Wang-Sheeley-Arge (WSA)-ADAPT model. ICMEs
are initiated at 21.5 solar radii using an MHD analytical Gibson-Low
(G&L) model of a self-similarly expanding magnetic flux rope
with defining parameters (e.g., location, magnetic topology, width,
magnetic field strength, speed, orientation). The ICME propagation
is simulated using the inner heliosphere version of the Grid Agnostic
MHD for Extended Research Applications (GAMERA) MHD model, which is a
reinvention of the high-heritage Lyon-Fedder-Mobarry (LFM) code. A set
of values for each of the defining G&L parameters was constrained
by statistical representation of solar CME observations. With the
aim to span the solar cycle, we model ICME propagation in different
solar wind backgrounds corresponding to rising, maximum, declining and
minimum solar cycle phases. A grid of G&L parameters and four solar
wind backgrounds constitute a parameter space for thousands of MHD
ICME runs. For each of the simulations we extract synthetic in-situ
observations of ICME as it passes Earth and synthetic white-light
images of an ICME as it propagates in the interplanetary space. We
present an analysis of produced distributions of ICME parameters and
characteristics.
---------------------------------------------------------
Title: The Polarimeter to UNify the Corona and Heliosphere (PUNCH)
Small Explorer Mission: Status and Next Steps
Authors: DeForest, C. E.; Killough, R.; Gibson, S. E.; Beasley, M.;
Henry, A.; Laurent, G. T.; Colaninno, R. C.
2020AGUFMSH0280002D Altcode:
The Polarimeter to UNify the Corona and Heliosphere (PUNCH) is a NASA
Small Explorer mission, to understand the solar corona and young
solar wind as a complete system. Science objectives are to measure
and understand how the ambient solar wind arises from the corona,
and to understand how transient events (such as CMEs) propagate and
evolve in the inner heliosphere. PUNCH uses direct, global, spatially
continuous, three dimensional imaging in polarized visible light,
to observe the outer corona and inner heliosphere as elements of a
single, connected system. PUNCH comprises four matched and synchronized
small-satellite observatories, operating as a "virtual instrument"
to image Thomson-scattered light from low-Earth orbit. PUNCH is the
first coronal and solar wind imaging mission designed specifically to
produce 3D images from a single vantage point using the polarization
properties of Thomson scattering. In addition, it will produce routine,
several-times-per-day maps of solar wind flow throughout the top of the
corona and bottom of the inner heliosphere, based on motion analysis
of the image stream. PUNCH has an open data policy and is seeking
scientific engagement throughout the heliophysics community. <P />PUNCH
is wrapping up its Phase B (preliminary design), and is working toward
a 2023 launch for a two-year nominal mission. We present a very brief
overview of the mission, describe current status and next steps, and
indicate how to engage with the PUNCH science team and upcoming mission.
---------------------------------------------------------
Title: Untangling the global coronal magnetic field with
multiwavelength observations
Authors: Gibson, S. E.; Malanushenko, A.; de Toma, G.; Tomczyk, S.;
Reeves, K.; Tian, H.; Yang, Z.; Chen, B.; Fleishman, G.; Gary, D.;
Nita, G.; Pillet, V. M.; White, S.; Bąk-Stęślicka, U.; Dalmasse,
K.; Kucera, T.; Rachmeler, L. A.; Raouafi, N. E.; Zhao, J.
2020arXiv201209992G Altcode:
Magnetism defines the complex and dynamic solar corona. Coronal
mass ejections (CMEs) are thought to be caused by stresses, twists,
and tangles in coronal magnetic fields that build up energy and
ultimately erupt, hurling plasma into interplanetary space. Even the
ever-present solar wind possesses a three-dimensional morphology shaped
by the global coronal magnetic field, forming geoeffective corotating
interaction regions. CME evolution and the structure of the solar
wind depend intimately on the coronal magnetic field, so comprehensive
observations of the global magnetothermal atmosphere are crucial both
for scientific progress and space weather predictions. Although some
advances have been made in measuring coronal magnetic fields locally,
synoptic measurements of the global coronal magnetic field are not yet
available. We conclude that a key goal for 2050 should be comprehensive,
ongoing 3D synoptic maps of the global coronal magnetic field. This will
require the construction of new telescopes, ground and space-based,
to obtain complementary, multiwavelength observations sensitive
to the coronal magnetic field. It will also require development of
inversion frameworks capable of incorporating multi-wavelength data,
and forward analysis tools and simulation testbeds to prioritize and
establish observational requirements on the proposed telescopes.
---------------------------------------------------------
Title: The Evolution of Coronal Holes over Three Solar Cycles Using
the McIntosh Archive
Authors: Hewins, Ian M.; Gibson, Sarah E.; Webb, David F.; McFadden,
Robert H.; Kuchar, Thomas A.; Emery, Barbara A.; McIntosh, Scott W.
2020SoPh..295..161H Altcode:
Using the McIntosh Archive of solar features, we analyze the evolution
of coronal holes over more than three solar cycles. We demonstrate
that coronal-hole positions and lifetimes change significantly on time
scales from months to years, and that the pattern of these changes
is clearly linked to the solar-activity cycle. We demonstrate that
the lifetimes of low-latitude coronal holes are usually less than one
rotation but may extend to almost three years. When plotted over time,
the positions of low-latitude coronal holes that remain visible for
over one rotation track the sunspot butterfly diagram in terms of
their positions on the Sun over a solar cycle. Finally, we confirm
that coronal holes do not in general rigidly rotate.
---------------------------------------------------------
Title: Temperature of a long-lived solar coronal cavity
Authors: Bąk-Stęślicka, Urszula; Gibson, Sarah E.; Stęślicki,
Marek
2020past.conf..169B Altcode:
We have analysed a long-lived coronal cavity observed from 17 March
2012 to 21 March 2012. For this cavity we applied a differential
emission measure method to obtain both a temperature distribution and
the average temperature over all five observational days. We find that
the cavity is filled with material hotter than its surroundings. The
temperature remains stable during all five days.
---------------------------------------------------------
Title: Major Scientific Challenges and Opportunities in Understanding
Magnetic Reconnection and Related Explosive Phenomena in Solar and
Heliospheric Plasmas
Authors: Ji, H.; Karpen, J.; Alt, A.; Antiochos, S.; Baalrud, S.;
Bale, S.; Bellan, P. M.; Begelman, M.; Beresnyak, A.; Bhattacharjee,
A.; Blackman, E. G.; Brennan, D.; Brown, M.; Buechner, J.; Burch, J.;
Cassak, P.; Chen, B.; Chen, L. -J.; Chen, Y.; Chien, A.; Comisso,
L.; Craig, D.; Dahlin, J.; Daughton, W.; DeLuca, E.; Dong, C. F.;
Dorfman, S.; Drake, J.; Ebrahimi, F.; Egedal, J.; Ergun, R.; Eyink,
G.; Fan, Y.; Fiksel, G.; Forest, C.; Fox, W.; Froula, D.; Fujimoto,
K.; Gao, L.; Genestreti, K.; Gibson, S.; Goldstein, M.; Guo, F.; Hare,
J.; Hesse, M.; Hoshino, M.; Hu, Q.; Huang, Y. -M.; Jara-Almonte, J.;
Karimabadi, H.; Klimchuk, J.; Kunz, M.; Kusano, K.; Lazarian, A.; Le,
A.; Lebedev, S.; Li, H.; Li, X.; Lin, Y.; Linton, M.; Liu, Y. -H.;
Liu, W.; Longcope, D.; Loureiro, N.; Lu, Q. -M.; Ma, Z-W.; Matthaeus,
W. H.; Meyerhofer, D.; Mozer, F.; Munsat, T.; Murphy, N. A.; Nilson,
P.; Ono, Y.; Opher, M.; Park, H.; Parker, S.; Petropoulou, M.; Phan,
T.; Prager, S.; Rempel, M.; Ren, C.; Ren, Y.; Rosner, R.; Roytershteyn,
V.; Sarff, J.; Savcheva, A.; Schaffner, D.; Schoeffier, K.; Scime, E.;
Shay, M.; Sironi, L.; Sitnov, M.; Stanier, A.; Swisdak, M.; TenBarge,
J.; Tharp, T.; Uzdensky, D.; Vaivads, A.; Velli, M.; Vishniac, E.;
Wang, H.; Werner, G.; Xiao, C.; Yamada, M.; Yokoyama, T.; Yoo, J.;
Zenitani, S.; Zweibel, E.
2020arXiv200908779J Altcode:
Magnetic reconnection underlies many explosive phenomena in the
heliosphere and in laboratory plasmas. The new research capabilities in
theory/simulations, observations, and laboratory experiments provide the
opportunity to solve the grand scientific challenges summarized in this
whitepaper. Success will require enhanced and sustained investments
from relevant funding agencies, increased interagency/international
partnerships, and close collaborations of the solar, heliospheric,
and laboratory plasma communities. These investments will deliver
transformative progress in understanding magnetic reconnection and
related explosive phenomena including space weather events.
---------------------------------------------------------
Title: Convolutional Neural Networks for Predicting the strength
of the Near-Earth Magnetic Field Caused by Interplanetary Coronal
Mass Ejections
Authors: Malanushenko, Anna; Flyer, Natasha; Gibson, Sarah
2020FrASS...7...62M Altcode:
In this paper, we explore the potential of neural networks for
making space weather predictions based on near-Sun observations. Our
second goal is to determine the extent to which coronal polarimetric
observations of erupting structures near the Sun encode sufficient
information to predict the impact these structures will have on
Earth. We focus on predicting the maximal southward component of the
magnetic field ("-Bz") inside an interplanetary coronal mass ejection
(ICME) as it impacts the Earth. We use Gibson&Low (G&L)
self-similarly expanding flux rope model (Gibson&Low 1998), which
allows to consider CMEs with varying location, orientation, size,
and morphology. We vary 5 parameters of the model to alter these CME
properties, and generate a large database of synthetic CMEs (over
36k synthetic events). For each model CME, we synthesize near-Sun
observations, as seen from an observer in quadrature (assuming the
CME is directed Earthwards), of either three components of the vector
magnetic field ("Experiment 1"), or of synthetic Stokes images,
("Experiment 2"). We then allow the flux rope to expand and record
max(-Bz) as the ICME passes 1AU. We further conduct two separate machine
learning experiments and develop two different regression-based deep
convolutional neural networks (CNNs) to predict max(-Bz) based on
these two kinds of the near-Sun input data. Experiment 1 is a proof
of concept, to see if a 3-channel CNN (hereafter CNN1), similar
to those used in RGB image recognition, can reproduce the results
of the self-similar (i.e. scale-invariant) expansion of the G&L
model. Experiment 2 is less trivial, as Stokes vector is not linearly
related to B, and the line-of-sight integration in the optically
thin corona presents additional difficulties for interpreting the
signal. This second CNN (hereafter CNN2), although resembling CNN1
in Experiment 1, will have a different number of layers and set of
hyperparameters due to a much more complicated mapping between the input
and output data. We find that, given vector B, CNN1 can predict max(-Bz)
with 97% accuracy, and for the Stokes vector as input, CNN2 can predict
max(-Bz) with 95%, both measured in the relative root square error.
---------------------------------------------------------
Title: The Science Case for the $4{\pi}$ Perspective: A Polar/Global
View for Studying the Evolution & Propagation of the Solar Wind
and Solar Transients
Authors: Vourlidas, A.; Gibson, S.; Hassler, D.; Hoeksema, T.; Linton,
M.; Lugaz, N.; Newmark, J.
2020arXiv200904880V Altcode:
To make progress on the open questions on CME/CIR propagation, their
interactions and the role and nature of the ambient solar wind, we need
spatially resolved coverage of the inner heliosphere -- both in-situ and
(critically) imaging -- at temporal scales matching the evolutionary
timescales of these phenomena (tens of minutes to hours), and from
multiple vantage points. The polar vantage is uniquely beneficial
because of the wide coverage and unique perspective it provides. The
ultimate goal is to achieve full $4\pi$ coverage of the solar surface
and atmosphere by 2050.
---------------------------------------------------------
Title: Global maps of the magnetic field in the solar corona
Authors: Yang, Zihao; Bethge, Christian; Tian, Hui; Tomczyk, Steven;
Morton, Richard; Del Zanna, Giulio; McIntosh, Scott W.; Karak, Bidya
Binay; Gibson, Sarah; Samanta, Tanmoy; He, Jiansen; Chen, Yajie;
Wang, Linghua
2020Sci...369..694Y Altcode: 2020arXiv200803136Y
Understanding many physical processes in the solar atmosphere requires
determination of the magnetic field in each atmospheric layer. However,
direct measurements of the magnetic field in the Sun’s corona are
difficult to obtain. Using observations with the Coronal Multi-channel
Polarimeter, we have determined the spatial distribution of the
plasma density in the corona and the phase speed of the prevailing
transverse magnetohydrodynamic waves within the plasma. We combined
these measurements to map the plane-of-sky component of the global
coronal magnetic field. The derived field strengths in the corona,
from 1.05 to 1.35 solar radii, are mostly 1 to 4 gauss. Our results
demonstrate the capability of imaging spectroscopy in coronal magnetic
field diagnostics.
---------------------------------------------------------
Title: Reconstructing the Coronal Magnetic Field: The Role of
Cross-Field Currents in Solution Uniqueness
Authors: Mathews, N.; Flyre, N.; Gibson, S.
2020SPD....5121004M Altcode:
We present a new 3D magnetohydrostatic (MHS) direct elliptic solver
for extrapolating the coronal magnetic field from photospheric
boundary conditions in a manner consistent with an assumed plasma
distribution. We use it to study the uniqueness of the reconstructed
magnetic field as a function of how significant the plasma forcing is
on the force balance of the magnetic field. To this end, we consider an
analytic MHS model as ground truth. The model uses two free parameters
to decompose the current into two parts: a magnetic-field aligned
component and a cross-field component. We perform a comprehensive
study of the 2D parameter space to understand under what conditions
the ground truth can be reproduced uniquely. We find that current
oriented perpendicular to the magnetic field has a smaller solution
space than the same amount of current oriented parallel to the magnetic
field, and so MHS regimes with larger proportions of plasma-related
forcing may be a promising avenue towards finding unique magnetic
field reconstructions.
---------------------------------------------------------
Title: Reconstructing the Coronal Magnetic Field: The Role of
Cross-field Currents in Solution Uniqueness
Authors: Mathews, Nathaniel H.; Flyer, Natasha; Gibson, Sarah E.
2020ApJ...898...70M Altcode:
We present a new 3D magnetohydrostatic (MHS) direct elliptic solver
for extrapolating the coronal magnetic field from photospheric
boundary conditions in a manner consistent with an assumed plasma
distribution. We use it to study the uniqueness of the reconstructed
magnetic field as a function of how significant the plasma forcing is
on the force balance of the magnetic field. To this end, we consider an
analytic MHS model as ground truth. The model uses two free parameters
to decompose the current into two parts: a magnetic-field-aligned
component and a cross-field component. We perform a comprehensive
study of the 2D parameter space to understand under what conditions the
ground truth can be reproduced uniquely. We find that current oriented
perpendicular to the magnetic field has a smaller solution space than
the same amount of current oriented parallel to the magnetic field, and
so MHS regimes with larger proportions of plasma-related forcing may be
a promising avenue toward finding unique magnetic field reconstructions.
---------------------------------------------------------
Title: The Solaris Solar Polar Mission
Authors: Hassler, Donald M.; Newmark, Jeff; Gibson, Sarah; Harra,
Louise; Appourchaux, Thierry; Auchere, Frederic; Berghmans, David;
Colaninno, Robin; Fineschi, Silvano; Gizon, Laurent; Gosain, Sanjay;
Hoeksema, Todd; Kintziger, Christian; Linker, John; Rochus, Pierre;
Schou, Jesper; Viall, Nicholeen; West, Matt; Woods, Tom; Wuelser,
Jean-Pierre
2020EGUGA..2217703H Altcode:
The solar poles are one of the last unexplored regions of the solar
system. Although Ulysses flew over the poles in the 1990s, it did
not have remote sensing instruments onboard to probe the Sun's polar
magnetic field or surface/sub-surface flows.We will discuss Solaris,
a proposed Solar Polar MIDEX mission to revolutionize our understanding
of the Sun by addressing fundamental questions that can only be answered
from a polar vantage point. Solaris uses a Jupiter gravity assist to
escape the ecliptic plane and fly over both poles of the Sun to >75
deg. inclination, obtaining the first high-latitude, multi-month-long,
continuous remote-sensing solar observations. Solaris will address key
outstanding, breakthrough problems in solar physics and fill holes in
our scientific understanding that will not be addressed by current
missions.With focused science and a simple, elegant mission design,
Solaris will also provide enabling observations for space weather
research (e.g. polar view of CMEs), and stimulate future research
through new unanticipated discoveries.
---------------------------------------------------------
Title: Solar physics in the 2020s: DKIST, parker solar probe, and
solar orbiter as a multi-messenger constellation
Authors: Martinez Pillet, V.; Tritschler, A.; Harra, L.; Andretta, V.;
Vourlidas, A.; Raouafi, N.; Alterman, B. L.; Bellot Rubio, L.; Cauzzi,
G.; Cranmer, S. R.; Gibson, S.; Habbal, S.; Ko, Y. K.; Lepri, S. T.;
Linker, J.; Malaspina, D. M.; Matthews, S.; Parenti, S.; Petrie, G.;
Spadaro, D.; Ugarte-Urra, I.; Warren, H.; Winslow, R.
2020arXiv200408632M Altcode:
The National Science Foundation (NSF) Daniel K. Inouye Solar Telescope
(DKIST) is about to start operations at the summit of Haleakala
(Hawaii). DKIST will join the early science phases of the NASA
and ESA Parker Solar Probe and Solar Orbiter encounter missions. By
combining in-situ measurements of the near-sun plasma environment and
detail remote observations of multiple layers of the Sun, the three
observatories form an unprecedented multi-messenger constellation to
study the magnetic connectivity inside the solar system. This white
paper outlines the synergistic science that this multi-messenger
suite enables.
---------------------------------------------------------
Title: Major Scientific Challenges and Opportunities in Understanding
Magnetic Reconnection and Related Explosive Phenomena throughout
the Universe
Authors: Ji, H.; Alt, A.; Antiochos, S.; Baalrud, S.; Bale, S.;
Bellan, P. M.; Begelman, M.; Beresnyak, A.; Blackman, E. G.; Brennan,
D.; Brown, M.; Buechner, J.; Burch, J.; Cassak, P.; Chen, L. -J.;
Chen, Y.; Chien, A.; Craig, D.; Dahlin, J.; Daughton, W.; DeLuca, E.;
Dong, C. F.; Dorfman, S.; Drake, J.; Ebrahimi, F.; Egedal, J.; Ergun,
R.; Eyink, G.; Fan, Y.; Fiksel, G.; Forest, C.; Fox, W.; Froula, D.;
Fujimoto, K.; Gao, L.; Genestreti, K.; Gibson, S.; Goldstein, M.; Guo,
F.; Hesse, M.; Hoshino, M.; Hu, Q.; Huang, Y. -M.; Jara-Almonte, J.;
Karimabadi, H.; Klimchuk, J.; Kunz, M.; Kusano, K.; Lazarian, A.;
Le, A.; Li, H.; Li, X.; Lin, Y.; Linton, M.; Liu, Y. -H.; Liu, W.;
Longcope, D.; Loureiro, N.; Lu, Q. -M.; Ma, Z-W.; Matthaeus, W. H.;
Meyerhofer, D.; Mozer, F.; Munsat, T.; Murphy, N. A.; Nilson, P.;
Ono, Y.; Opher, M.; Park, H.; Parker, S.; Petropoulou, M.; Phan, T.;
Prager, S.; Rempel, M.; Ren, C.; Ren, Y.; Rosner, R.; Roytershteyn,
V.; Sarff, J.; Savcheva, A.; Schaffner, D.; Schoeffier, K.; Scime, E.;
Shay, M.; Sitnov, M.; Stanier, A.; TenBarge, J.; Tharp, T.; Uzdensky,
D.; Vaivads, A.; Velli, M.; Vishniac, E.; Wang, H.; Werner, G.; Xiao,
C.; Yamada, M.; Yokoyama, T.; Yoo, J.; Zenitani, S.; Zweibel, E.
2020arXiv200400079J Altcode:
This white paper summarizes major scientific challenges and
opportunities in understanding magnetic reconnection and related
explosive phenomena as a fundamental plasma process.
---------------------------------------------------------
Title: Evolution of the geoeffective April 5, 2010 CME in the inner
heliosphere: A global MHD model with a data-constrained magnetic
flux rope specification.
Authors: Provornikova, E.; Merkin, V. G.; Gibson, S. E.; Malanushenko,
A. V.; Arge, C. N.; Vourlidas, A.
2019AGUFMSH42A..03P Altcode:
Modeling the evolution of internal magnetic structure of interplanetary
coronal mass ejections (ICMEs) is important both for space weather
prediction and for basic understanding of magnetized space plasma
interactions. Data-driven modeling of ICMEs in the inner heliosphere
(starting beyond the critical surface in the corona) presents
an attractive and computationally feasible approach, since it
bypasses the complex problem of CME initiation and eruption in the
corona. Using this approach, we simulate the propagation of ICMEs
through the inner heliosphere using a global model driven at the
coronal boundary by the Wang-Sheeley-Arge (WSA)-ADAPT model. ICMEs
are initiated at 20 solar radii (Rs) using a magnetohydrodynamic
(MHD) analytical Gibson-Low (GL) model of a self-similarly expanding
magnetic flux rope with parameters (e.g., location, geometry, speed,
orientation) constrained by white-light coronograph observations. The
ICME propagation is simulated using the Grid Agnostic MHD for Extended
Research Applications (GAMERA) MHD model, which is a recent reinvention
of the high-heritage Lyon-Fedder-Mobarry (LFM) code. We apply this
approach to the study of a geoeffective ICME which arrived at Earth
on April 5, 2010. This ICME appeared bright in SOHO/LASCO and STEREO
coronagraphs allowing derivation of its parameters near the Sun thus
constraining its properties in our model. However, the orientation of
the flux rope was not determined uniquely from the observations. It was
also not clear which part of the ICME hit Earth and caused the severe
geomagnetic storm. By comparing synthetic white-light images derived
from our MHD modeling with images from SOHO/LASCO and STEREO/HI1 and
HI2, we shed light on the ICME initial orientation and it evolution due
to the interaction with the background solar wind. We further compare
the modeling results with ACE observations at 1 AU and discuss which
part of the CME was probed by the spacecraft.
---------------------------------------------------------
Title: Gibson & Low Flux Rope Model: More Than a Spheromak!
Authors: Malanushenko, A. V.; Gibson, S. E.; Provornikova, E.;
Merkin, V. G.; Vourlidas, A.; Arge, C. N.; Dalmasse, K.; Nychka,
D. W.; Flyer, N.
2019AGUFMSH11C3397M Altcode:
Modeling solar coronal mass ejections (CMEs) is very important for
both understanding coronal physics and for improving the accuracy of
space weather forecasts. While it is generally accepted that CMEs
are primarily magnetic structures, the exact properties of these
structures could differ in different models and events. A structure
often considered is a spheromak, a toroidal twisted flux rope, which
is ejected as a CME bubble. Another commonly considered structure is a
twisted magnetic flux rope, which is anchored to the solar surface while
its upper portion is ejected into interplanetary space. In this talk
we will show how a well-known analytical magnetohydrodynamic CME model
(Gibson&Low, 1998), generally considered a spheromak-like model,
can be extended to represent both standard spheromak and twisted flux
tube configurations, as well as other topologically distinct magnetic
structures. We will begin with the general parameters of the flux rope
in this model (such as size and stretching parameters), and explore
topologically different configurations possible with their variation. We
then present several dimensionless parameters which can be varied to
achieve these different configurations and consider how they relate
to directly observable quantities. This work is particularly timely,
as the Gibson&Low model is been increasingly used as input to
numerical models of the solar corona and the heliosphere. The ability
to generate topologically different magnetic configurations within
this analytic solution is of great value to such simulations, as well
as for the studies of the flux ropes forming in the solar corona.
---------------------------------------------------------
Title: Thermal properties of coronal cavities
Authors: Steslicki, M.; Bak-Steslicka, U.; Gibson, S. E.
2019AGUFMSH11C3408S Altcode:
We have analyzed few dozen of cavities observed between 2012 and 2018
by AIA/SDO, from solar activity maximum to minimum. For each cavity
we applied a Differential Emission Measure method to obtain both
a temperature distribution and a value of average temperature. We
find that cavities are filled with material hotter than surrounding
streamer with temperatures in the range of 1.6-2.2 MK. Differences
between temperatures of cavities and surrounding streamers are in the
range of 0.1 - 0.3 MK. We found that temperatures of both cavities
and streamers vary as a function of different phases of solar activity.
---------------------------------------------------------
Title: Advances in coronal spectropolarimetry
Authors: Gibson, S. E.
2019AGUFMSH33A..03G Altcode:
Our understanding of energetic processes at the Sun is held back by
our current lack of basic scientific understanding of CME magnetic
origins and evolution, and of the coronal magnetism that structures
and drives the solar wind. This motivates the development of
spectropolarimetric instrumentation capable of probing the solar
magnetothermal atmosphere at multiple heights, with sensitivity
to magnetism of varying strength. I will describe recent progress,
future upgrades, and long-term outlook for instrumentation capable of
coronal magnetometry from infrared through visible through ultraviolet
wavelengths. In particular, I will discuss how new capabilities arising
from these instruments will shed a new light on the storage and release
of magnetic energy, CME structure and dynamics, and the role of waves
in solar atmospheric heating and solar wind acceleration.
---------------------------------------------------------
Title: PUNCH: a new view on the middle corona
Authors: Gibson, S. E.; DeForest, C.
2019AGUFMSH13A..06G Altcode:
The Polarimeter to UNify the Corona and Heliosphere (PUNCH)
has recently been selected by NASA as a Small Explorer mission,
to be launched as early as 2022. PUNCH uses a constellation of
three wide-field heliospheric imagers and a central near-field
coronagraphic imager to span the interface between the corona and the
inner heliosphere. Polarized and unpolarized images will be obtained
with greater than ten times the sensitivity of current instruments in
the region covering 6-15 solar radii, i.e., the upper portion of the
"middle corona". This will provide unprecedented views of the global
structure of fast/slow wind flow boundaries, CME substructure and
chirality, and the Alfven zone. This last is of particular interest to
this session, because the riotous torrent that is the young solar wind
implies the boundary between magnetically-dominated and wind-dominated
plasma is likely to be fractal and space-filling. Thus, it is a zone
that likely riddles the middle corona.
---------------------------------------------------------
Title: Coronal Solar Magnetism Observatory Science Objectives
Authors: Gibson, S. E.; Tomczyk, S.; Burkepile, J.; Casini, R.;
DeLuca, E.; de Toma, G.; de Wijn, A.; Fan, Y.; Golub, L.; Judge,
P. G.; Landi, E.; McIntosh, S. W.; Reeves, K.; Seaton, D. B.; Zhang, J.
2019AGUFMSH11C3395G Altcode:
Space-weather forecast capability is held back by our current
lack of basic scientific understanding of CME magnetic evolution,
and the coronal magnetism that structures and drives the solar
wind. Comprehensive observations of the global magnetothermal
environment of the solar atmosphere are needed for progress. When fully
implemented, the COSMO suite of synoptic ground-based telescopes will
provide the community with comprehensive and simultaneous measurements
of magnetism, temperature, density and plasma flows and waves from the
photosphere through the chromosphere and out into the corona. We will
discuss how these observations will uniquely address a set of science
objectives that are central to the field of solar and space physics:
in particular, to understand the storage and release of magnetic energy,
to understand CME dynamics and consequences for shocks, to determine the
role of waves in solar atmospheric heating and solar wind acceleration,
to understand how the coronal magnetic field relates to the solar
dynamo, and to constrain and improve space-weather forecast models.
---------------------------------------------------------
Title: Convolutional Neural Networks for Predicting The Impact of
Interplanetary Coronal Mass Ejections on The Near-Earth Magnetic Field
Authors: Flyer, N.; Malanushenko, A. V.; Gibson, S. E.
2019AGUFMSH34B..07F Altcode:
We present a convolutional neural network (CNN) for predicting the
maximal amplitude of southward component of the near-Earth magnetic
field near from a passing interplanetary coronal mass ejection
(iCME). The input to the CNN is the Gibson & Low (GLOW) flux rope
model (1998) that describes the coronal properties of a CME, where its
morphology and position are controlled by 6 parameters. Our ultimate
goal is to assess the ability of using a CNN architecture (2D or 3D)
as an emulator of the physical processes operating on the CME between
the Sun and Earth. The GLOW model is used as a first, simple test of
a self-similarly expanding flux rope. It is the input to numerical
simulations of CMEs propagating in the solar wind, in particular APL's
Gamera code which uses GLOW as an input. The CNN problem is set up in
two phases: 1) given input data near Sun, sets of three 2D images in
the meridional plane, of the components magnetic field B: Bx, By, Bz,
predict the maximal southward amplitude of the measured Bz at the Earth;
2) given line-of-sight integrated images of the Stokes parameters, U/I,
V/I, Q/I, corresponding to the physical configuration in part 1, predict
the maximal southward amplitude of the measured Bz at the Earth. Results
will be presented for these two different CNN configurations.
---------------------------------------------------------
Title: Solaris: A Case for a Solar Polar Mission
Authors: Hassler, D.; Newmark, J. S.; Gibson, S. E.
2019AGUFMSH13B..02H Altcode:
Solar and Heliospheric physics has experienced a golden age of
discovery over the past 20+ years, and the launches of Parker Solar
Probe and Solar Orbiter promise to add exciting new observations and
insights into our understanding of the Sun-Heliosphere system. So what
is next? Although these missions have, and promise to continue to,
revolutionize our understanding of the Sun, the one region that is
still unexplored is the solar pole…the solar pole is one of the
final frontiers of solar physics. <P />Solaris is a solar polar
mission concept to address some of the fundamental questions that
can only be answered from a polar vantage point. Solaris will obtain
continuous, high latitude (>55 deg.) observations of the solar poles
for multiple solar rotations, providing the continuity necessary to
detect sub-surface flows and follow the evolution of solar transient
activity. The Solaris mission will be able to obtain sustained
coverage of the solar interior and atmosphere from high latitudes,
providing a unique and comprehensive investigation of the global Sun
and heliosphere. <P />This talk will discuss some of these questions
and scientific drivers for a solar polar mission, such as Solaris, and
the requirements these scientific objectives place on the observational
and orbital requirements of the mission.
---------------------------------------------------------
Title: Spectral Properties and Heavy Ion Abundances of Energetic
Particles in SEP and CIR events observed during the first two Parker
Solar Probe Orbits
Authors: Desai, M. I.; Giacalone, J.; Mitchell, D. G.; Szalay, J. R.;
Allen, R. C.; Hill, M. E.; McComas, D. J.; Christian, E. R.; Schwadron,
N.; McNutt, R. L., Jr.; Wiedenbeck, M. E.; Joyce, C.; Cohen, C.;
Cummings, A. C.; Davis, A.; Krimigis, S. M.; Leske, R. A.; Matthaeus,
W. H.; Mewaldt, R. A.; Roelof, E. C.; Labrador, A. W.; Stone, E. C.;
Gibson, S. E.; DeForest, C.
2019AGUFMSH22A..06D Altcode:
NASA's Parker Solar Probe (PSP), successfully launched on August 12
2018, has completed its first two orbits around our Sun. With perihelia
~35 Rs for both encounters, PSP has made the closest-ever observations
of the solar wind plasma, electromagnetic fields, and energetic particle
environment in the inner heliosphere. The Energetic Particle Instruments
(EPI) of the Integrated Science Investigation of the Sun (ISOIS) suite
observed a number of solar energetic particle (SEP) events associated
with flaring regions on the Sun, coronal mass ejections-driven
shocks, and local compression regions, as well as particle events
associated with corotating or stream interaction regions. This talk
surveys the spectral properties and abundances of ~0.1-2 MeV/nucleon
suprathermal H-Fe nuclei during these events and compares them with
prior observations of their counterparts observed at 1 AU. We discuss
these new PSP results in the context of our current understanding of the
origin and acceleration of suprathermal ions, the acceleration of SEPs,
and on the nature of particle transport inside Earth orbit. Finally,
we discuss the implications of these results for existing theoretical
models of the origin of suprathermal tails, and of the acceleration
and transport of SEPs and CIR-associated energetic particle events.
---------------------------------------------------------
Title: The PUNCH Bowl: Data System and Data Products for NASA's
PUNCH Mission
Authors: Thompson, B. J.; DeForest, C.; Gibson, S. E.
2019AGUFMSA11C3231T Altcode:
The Polarimeter to UNify the Corona and Heliosphere (PUNCH) mission
requires a flexible data system because the anticipated user base will
be using the data to tackle a wide range of science problems. Some will
be using PUNCH data in the classic "imager" context, while others will
be accessing the data to study solar wind dynamics. <P />The PUNCH Bowl
provide PUNCH data, metadata, analysis tools, and higher-level PUNCH
data products, which are derived from heliospheric images to provide
additional information about structure and motion. Additionally, the
PUNCH Bowl is your access point for PUNCH Recipes: all of the tools,
code and routines that optimize the use of PUNCH data and streamline
your access. By running the "recipes" users can easily trace and
reproduce the steps used by others with minimal effort. The PUNCH Bowl
is maintained and supported by the PUNCH science team, but welcomes
contributions from users to ensure that everyone is able to easily
access all available tools and methods.
---------------------------------------------------------
Title: Primary and Secondary Solar Polar Crown PILs over Five
Solar Cycles
Authors: Emery, B. A.; Webb, D. F.; Gibson, S. E.; Hewins, I. M.;
McFadden, R.; Kuchar, T. A.
2019AGUFMSH13B..08E Altcode:
Solar filaments are located on polarity inversion lines (PILs) on
the sun. Polar crown filaments are found at high helio-latitudes,
but usually encircle the Sun for a brief period prior to the polarity
reversal around solar maximum. Usually, there are polar crown gaps in
both hemispheres, where coronal holes extend from the polar regions
to lower latitudes. We undertake a five solar-cycle (SC19-23) study
of the high latitude polar crown PILs that encircle the sun each
solar cycle using the McIntosh Archive. The McIntosh Archive consists
of a set of hand-drawn solar synoptic (Carrington) maps created by
Patrick McIntosh from 1964 to 2009 (SC20-23) using H-alpha images and
magnetograms for PILs, and He-I 10830A images for coronal holes since
1974. Most of these maps have now been digitized, with some gaps in
SC20 and SC21. We also digitized the Carrington maps created from
Kodaikanal Solar Observatory data in India by Makarov and Sivaraman
(1986) to extend the study back through SC19. We focus on the large
unipolar magnetic cells which are prominent on the sun after sunspot
minimum, and then the 'rush-to-the-poles' in the ascending part of the
solar cycle before the polarity reverses in the polar regions. PILs
form at the boundaries of the opposite-polarity cells. The primary
polar crown PIL is at the highest latitudes, but a secondary polar
crown PIL becomes visible during the 'rush-to-the-poles' (McIntosh,
2003). The secondary PIL lies about 10 degrees or more equatorward of
the primary PIL, which disappears at high latitudes while the secondary
PIL becomes the primary PIL around 55 degrees north and south. We look
at the evolution of the maximum latitude of these primary and secondary
PILs as well as their median locations. We calculate the slope of the
'rush-to-the-poles', and we see what the hemispherical differences
are and between solar cycles. Our results on the two polar crown PILs
inform us about the solar dynamo activity in the interior of the sun
and help constrain dynamo models.
---------------------------------------------------------
Title: WHPI Hα "McIntosh" Carrington Maps
Authors: Hewins, I. M.; Gibson, S. E.; Webb, D. F.; Kuchar, T. A.;
McFadden, R.; Emery, B. A.
2019AGUFMSH41D3346H Altcode:
In support of the Whole Heliosphere and Planetary Interactions (WHPI)
effort and to highlight solar structure near solar minimum we will
create synoptic maps of solar magnetic features. In particular, we
will utilize Hα, EUV and photospheric magnetic field to represent
filaments, filament channels, and the large scale distribution of the
dominant magnetic polarity. These maps, done in the manner established
by Patrick McIntosh, enable studies how such solar features relate
to structures in the solar wind and in the space environment of the
earth and other planets. Patrick McIntosh contributed three maps to the
initial Whole Sun Months (WSM; 1996), and Robert McFadden, McIntosh's
primary cartographer for Solar Cycle 23, similarly contributed three
maps to the Whole heliospheric Interval (WHI; 2008). Hewins, trained
by McIntosh and McFadden, will focus on CR2215 which represents the
WHPI campaign: "Recurrent Coronal Holes/High Speed Solar Wind Streams",
and CR2219 which is the WHPI campaign: "Total Solar Eclipse Campaign".
---------------------------------------------------------
Title: Polarimeter to UNify the Corona and Heliosphere (PUNCH):
Imaging the Corona and Solar Wind as a Single System
Authors: DeForest, C. E.; Gibson, S. E.; Beasley, M.; Colaninno,
R. C.; Killough, R.; Kosmann, W.; Laurent, G. T.; McMullin, D. R.
2019AGUFMSH43B..06D Altcode:
The Polarimeter to UNify the Corona and Heliosphere (PUNCH) is a Small
Explorer mission from NASA, to understand the solar corona and young
solar wind as a complete system. It comprises four matched cameras all
operating as a "virtual instrument" to image Thomson-scattered light,
from the vantage of four separate spacecraft in Sun-synchronous
LEO. PUNCH is the first coronal and solar wind imager designed
specifically to produce three dimensional images from a single vantage
point. In addition, it will produce routine, several-times-per-day maps
of solar wind flow throughout the outer corona and inner heliosphere,
based on motion analysis of the image stream. Estimated launch date is
early 2023 for a two-year nominal mission. We present a brief overview
of the mission with emphasis on novel techniques used and exploited by
the PUNCH mission, and novel analyses enabled for the science community
by PUNCH.
---------------------------------------------------------
Title: Thermal Properties of Coronal Cavities
Authors: Ba̧k-Stȩślicka, Urszula; Gibson, Sarah E.;
Stȩślicki, Marek
2019SoPh..294..164B Altcode:
We have analyzed 33 cavities observed between 2012 and 2018, from solar
activity maximum to minimum. For each cavity we applied a differential
emission measure method to obtain both a temperature distribution and
a value of the average temperature. We find that cavities are filled
with material hotter than the surrounding streamer, with temperatures
in the range of 1.67 - 2.15 MK. Differences between temperatures of
cavities and surrounding streamers are in the range of 0.11 - 0.32 MK
with an average value of 0.21 MK. We found that temperatures of both,
cavities and streamers, vary as a function of different phases of solar
activity. During solar maximum the structures are slightly hotter
than those observed during solar minimum (1.85 - 2.15 MK vs. 1.67 -
1.88 MK for cavities and streamers, respectively).
---------------------------------------------------------
Title: Forward Modeling of a Pseudostreamer
Authors: Karna, Nishu; Savcheva, Antonia; Dalmasse, Kévin; Gibson,
Sarah; Tassev, Svetlin; de Toma, Giuliana; DeLuca, Edward E.
2019ApJ...883...74K Altcode:
In this paper, we present an analysis of a pseudostreamer embedding
a filament cavity, observed on 2015 April 18 on the solar southwest
limb. We use the flux-rope insertion method to construct nonlinear
force-free field (NLFFF) models constrained by observed Solar Dynamics
Observatory (SDO)/AIA coronal structures and the SDO/Helioseismic
Magnetic Imager photospheric magnetogram. The resulting magnetic field
models are forward-modeled to produce synthetic data directly comparable
to Mauna Loa Solar Observatory/Coronal Multichannel Polarimeter (CoMP)
observations of the intensity and linear polarization of the Fe XIII
1074.7 nm infrared coronal emission line using FORWARD. In addition,
we determine the location of quasi-separatrix layers in the magnetic
models, producing a Q-map from which the signatures of magnetic null
points and separatrices can be identified. An apparent magnetic null
observed in linear polarization by CoMP is reproduced by the model
and appears in the region of the 2D-projected magnetic null in the
Q-map. Further, we find that the height of the CoMP null is better
reproduced by our NLFFF model than by the synthetic data we produce
with potential-field source-surface models, implying the presence of
a flux rope in the northern lobe of the pseudostreamer.
---------------------------------------------------------
Title: Simulating the Solar Corona in the Forbidden and Permitted
Lines with Forward Modeling. I. Saturated and Unsaturated Hanle
Regimes
Authors: Zhao, Jie; Gibson, Sarah E.; Fineschi, Silvano; Susino,
Roberto; Casini, Roberto; Li, Hui; Gan, Weiqun
2019ApJ...883...55Z Altcode:
The magnetic field in the corona is important for understanding solar
activity. Linear polarization measurements in forbidden lines in the
visible/IR provide information about coronal magnetic direction and
topology. However, these measurements do not provide a constraint on
coronal magnetic field strength. The unsaturated, or critical regime
of the magnetic Hanle effect is potentially observable in permitted
lines for example in the UV, and would provide an important new
constraint on the coronal magnetic field. In this paper we present
the first side-by-side comparison of forbidden versus permitted linear
polarization signatures, examining the transition from the unsaturated
to the saturated regime. In addition, we use an analytic 3D flux rope
model to demonstrate the Hanle effect for the line-of-sight versus
plane-of-sky (POS) components of the magnetic field. As expected, the
linear polarization in the unsaturated regime will vary monotonically
with increasing magnetic field strength for regions where the magnetic
field is along the observer’s line of sight. The POS component of
the field produces a linear polarization signature that varies with
both the field strength and direction in the unsaturated regime. Once
the magnetic field is strong enough that the effect is saturated, the
resulting linear polarization signal is essentially the same for the
forbidden and permitted lines. We consider how such observations might
be used together in the future to diagnose the coronal magnetic field.
---------------------------------------------------------
Title: Investigating Coronal Magnetism with COSMO: Science on
the Critical Path To Understanding The “Weather” of Stars and
Stellarspheres
Authors: McIntosh, Scott; Tomczyk, Steven; Gibson, Sarah E.; Burkepile,
Joan; de Wijn, Alfred; Fan, Yuhong; deToma, Giuliana; Casini, Roberto;
Landi, Enrico; Zhang, Jie; DeLuca, Edward E.; Reeves, Katharine K.;
Golub, Leon; Raymond, John; Seaton, Daniel B.; Lin, Haosheng
2019BAAS...51g.165M Altcode: 2019astro2020U.165M
The Coronal Solar Magnetism Observatory (COSMO) is a unique ground-based
facility designed to address the shortfall in our capability to measure
magnetic fields in the solar corona.
---------------------------------------------------------
Title: Spectropolarimetric diagnostics of coronal magnetic field
from UV and visible/IR during solar minimum
Authors: Zhao, Jie; Gibson, Sarah; Fineschi, Silvano; Susino, Roberto
2019AAS...23430212Z Altcode:
The invisible magnetic field in the corona plays an important role
for solar activity, hence measuring the coronal magnetic field
is highly desired. The linear polarization measurements in the
saturated Hanle regime of visible/IR are already obtained by the CoMP
telescope providing information about coronal magnetic direction
and topology. Other observations such as linear polarization in
UV unsaturated Hanle measurements provide important complementary
information about the strength of 3D coronal field. Until such
observations are available, we turn to the FORWARD model (Gibson et
al. 2016) to explore how these polarization data might be used together
to interpret the coronal magnetic field. As a physical state to input
into FORWARD, the analytic magnetic model in this work is adopted
from Gibson et al.(1996), which is an axisymmetric model and gives
a potential field with an exception at the boundary of the helmet
streamer where current sheets are added between the open and closed
fields. The plasma model is adopted from Sittler&Guhathakurta
(1999) and Vásquez et al. (2003), which is consistent with
multi-observations. Given this model input of a 3D distribution of
magnetic field and plasma for solar minimum, we obtain simulated
polarization results in UV and visible/IR wavelengths. This allows us
to consider how such observations might be used together in future to
diagnose the coronal magnetic field.
---------------------------------------------------------
Title: Data-optimized Coronal Field Model. I. Proof of Concept
Authors: Dalmasse, K.; Savcheva, A.; Gibson, S. E.; Fan, Y.; Nychka,
D. W.; Flyer, N.; Mathews, N.; DeLuca, E. E.
2019ApJ...877..111D Altcode: 2019arXiv190406308D
Deriving the strength and direction of the three-dimensional
(3D) magnetic field in the solar atmosphere is fundamental for
understanding its dynamics. Volume information on the magnetic field
mostly relies on coupling 3D reconstruction methods with photospheric
and/or chromospheric surface vector magnetic fields. Infrared
coronal polarimetry could provide additional information to better
constrain magnetic field reconstructions. However, combining such
data with reconstruction methods is challenging, e.g., because of the
optical thinness of the solar corona and the lack and limitations of
stereoscopic polarimetry. To address these issues, we introduce the
data-optimized coronal field model (DOCFM) framework, a model-data
fitting approach that combines a parameterized 3D generative model,
e.g., a magnetic field extrapolation or a magnetohydrodynamic model,
with forward modeling of coronal data. We test it with a parameterized
flux-rope insertion method and infrared coronal polarimetry where
synthetic observations are created from a known “ground-truth”
physical state. We show that this framework allows us to accurately
retrieve the ground-truth 3D magnetic field of a set of force-free
field solutions from the flux-rope insertion method. In observational
studies, the DOCFM will provide a means to force the solutions
derived with different reconstruction methods to satisfy additional
common coronal constraints. The DOCFM framework therefore opens new
perspectives for the exploitation of coronal polarimetry in magnetic
field reconstructions and for developing new techniques to more
reliably infer the 3D magnetic fields that trigger solar flares and
coronal mass ejections.
---------------------------------------------------------
Title: MHD modeling of evolving ICME magnetic structure in the
inner heliosphere
Authors: Provornikova, Elena; Merkin, Vyacheslav; Malanushenko, Anna;
Gibson, Sarah; Arge, Nick; Vourlidas, Angelos
2019shin.confE.230P Altcode:
As CME propagates through the inner heliosphere, evolution of its
structure is influenced by the interaction with the solar wind
streams. I will present our recent simulations with GAMERA code
of propagating flux rope-CME from 0.1 to 1 AU in the background
solar wind. We evaluate self-similarly an erupting CME at 0.1 AU
based on the Gibson-Low model and insert it into our global inner
heliosphere model driven by the Wang-Sheeley-Arge (WSA) model of the
corona, while WSA, in turn, is driven by ADAPT global photospheric
magnetic field maps. To simulate the ICME propagation in the inner
heliosphere, we use the GAMERA (Grid Agnostic MHD for Extended Research
Applications) magnetohydrodynamic (MHD) code which is a reinvention of
the high-heritage Lyon-Fedder-Mobarry (LFM) code. We present modeling
results and focus on the evolution of the large-scale structure of
the CME from the outer solar corona to Earth. In particular I will
present a simulation of the April 3, 2010 CME event.
---------------------------------------------------------
Title: Historical astronomical data: urgent need for preservation,
digitization enabling scientific exploration
Authors: Pevtsov, Alexei; Griffin, Elizabeth; Grindlay, Jonathan;
Kafka, Stella; Bartlett, Jennifer; Usoskin, Ilya; Mursula, Kalevi;
Gibson, Sarah; Pillet, Valentín; Burkepile, Joan; Webb, David; Clette,
Frédéric; Hesser, James; Stetson, Peter; Muñoz-Jaramillo, Andres;
Hill, Frank; Bogart, Rick; Osborn, Wayne; Longcope, Dana
2019BAAS...51c.190P Altcode: 2019arXiv190304839P; 2019astro2020T.190P
This white paper emphasizes critical importance of preservation,
digitization and scientific exploration of historical astronomical
data. It outlines the rationale, provides examples of new science
with such data, and reviews the potential losses to science if nothing
it done.
---------------------------------------------------------
Title: Coronal Mass Ejections from Sun to Earth: Recent Advances in
Modeling and Statistical Approaches
Authors: Malanushenko, Anna; Gibson, S.; Dalmasse, K.; Merkin, V.;
Provornikova, E.; Vourlidas, A.; Arge, C.; Nychka, D.; Wiltberger,
M.; Flyer, N.
2019shin.confE.206M Altcode:
Solar coronal mass ejections (CMEs) are violent eruptive phenomena
which originate on the Sun; their heliospheric extensions, called
interplanetary CMEs, are known for their potential to impact the
whole heliosphere and, in particular, the Earth. While not all CMEs
are launched in such a way as to hit the Earth, those that do can
have big impacts on Earth's magnetosphere. The magnitude of such
impact depends upon many factors such as the CME launch location and
velocity, its positioning within the background solar wind, its mass,
and its magnetic properties such as the orientation of its front with
respect to the Earth's magnetic field. <P />Case studies of how iCMEs
propagate through the heliosphere are complicated by many factors,
including often incomplete input for models. We present and discuss
a different approach. Rather than focusing on modeling a particular
event, we intend to carry out a large statistical study in the event
parameter space. Further, Bayesian statistics will be used along with
large statistical databases of near-Sun and near-Earth observables,
to infer statistical distributions of relevant CME input parameters,
which are capable of yielding given distributions of observables,
for a given stage of the the solar cycle. <P />We use a analytical
flux rope model (Gibson&Low model) and a background solar wind
boundary (Wang-Sheeley-Arge model) as inputs for a new MHD heliospheric
simulation code (Gamera). We give an overview and update of the project
and show first modeling results.
---------------------------------------------------------
Title: COSMO Science
Authors: Gibson, Sarah; Tomczyk, Steven; Burkepile, Joan; Casini,
Roberto; Deluca, Ed; de Toma, Giuliana; deWijn, Alfred; Fan, Yuhong;
Golub, Leon; Judge, Philip; Landi, Enrico; Lin, Haosheng; McIntosh,
Scott; Reeves, Kathy; Seaton, Dan; Zhang, Jie
2019shin.confE..32G Altcode:
Space-weather forecast capability is held back by our current
lack of basic scientific understanding of CME magnetic evolution,
and the coronal magnetism that structures and drives the solar
wind. Comprehensive observations of the global magnetothermal
environment of the solar atmosphere are needed for progress. When fully
implemented, the COSMO suite of synoptic ground-based telescopes will
provide the community with comprehensive and simultaneous measurements
of magnetism, temperature, density and plasma flows and waves from the
photosphere through the chromosphere and out into the corona. We will
discuss how these observations will uniquely address a set of science
objectives that are central to the field of solar and space physics:
in particular, to understand the storage and release of magnetic energy,
to understand CME dynamics and consequences for shocks, to determine the
role of waves in solar atmospheric heating and solar wind acceleration,
to understand how the coronal magnetic field relates to the solar
dynamo, and to constrain and improve space-weather forecast models.
---------------------------------------------------------
Title: MHD simulation of prominence-cavity system and forward modeling
of COSMO/LC line-of-sight magnetic field measurement
Authors: Fan, Yuhong; Liu, Tie; Gibson, Sarah
2019shin.confE..70F Altcode:
We present magnetohydrodynamic simulation of the evolution from
quasi-equilibrium to onset of eruption of a twisted, prominence-forming
coronal magnetic flux rope underlying a corona streamer. The flux rope
is built up by an imposed flux emergence at the lower boundary. During
the quasi-static phase of the evolution, we find the formation of
a prominence-cavity system with qualitative features resembling
observations, as shown by the synthetic SDO/AIA EUV images with the
flux rope observed above the limb viewed nearly along its axis. The
cavity contains substructures including “U”-shaped or horn-liked
features extending from the prominence enclosing a central “cavity”
on top of the prominence. The prominence condensations form in the dips
of the highly twisted field lines due to runaway radiative cooling
and the cavity is formed by the density depleted portions of the
prominence-carrying field lines extending up from the dips. The flux
rope eventually erupts as its central part rises quasi-statically
to a critical height, producing a CME with associated prominence
eruption. Using the MHD model of the prominence-cavity system, we carry
out forward synthesis of the circular polarization signal of the Fe
XIII emission line at 1074.7 nm as would be measured by the proposed
COronal Solar Magnetism Observatory (COSMO) Large Coronagraph (LC)
and infer the line-of-sight (LOS) magnetic field, with the simulated
flux rope observed above the limb viewed linearly along its length. We
find that the COSMO/LC can detect a significant LOS magnetic field
from the flux rope with the measurement most sensitive to the region
surrounding the prominence, i.e. the prominence horn region in the
cavity. The measurement can detect an out-moving LOS field during the
slow rise phase up to the onset of eruption.
---------------------------------------------------------
Title: Coronal Hole Lifetimes Studied with the McIntosh Archive
Authors: Hewins, Ian; McFadden, Robert; Emery, Barbara; Gibson, Sarah;
Webb, David; Kuchar, Thomas
2019shin.confE.188H Altcode:
Through long term observation we can see that coronal holes positions
and lifespans change dramatically over a solar cycle, but tend to
repeat those patterns from solar cycle to solar cycle. By looking at
the positions and lifespans of different coronal holes we can see that
they are interconnected with the extended solar cycle (22yrs) and the
activity cycle (11yrs). The positions of low latitude coronal holes
that remain for over one rotation demonstrate a dramatic similarity
to both sunspots and plage in terms of their positions on the sun over
a solar cycle, forming the classic butterfly pattern.
---------------------------------------------------------
Title: Linear Polarization Observations of Coronal Pseudostreamers
Authors: de Toma, Giuliana; Gibson, Sarah; Dalmasse, Kevin
2019shin.confE..27D Altcode:
Pseudostreamers are common coronal structures that appear at the
solar limb as streamers bordering regions of the same magnetic
polarity. They are locations prone to sympathetic eruptions and
sources of an hybrid kind of solar wind with properties intermediate
between slow and moderately fast wind. The pseudostreamer magnetic
topological skeleton, and in particular the magnetic X-point at their
cusp, imprints a very clear signature in linear polarization that
distinguish pseudostreamers from the larger helmet streamers or two
nearby streamers. We use polarimetric data taken with the Coronal
Multichannel Polarimeter (CoMP) at the Mauna Loa Solar Observatory
from 2013 to 2017 to analyze pseudostreamers and compare them with
PFSS models. The solarsoft software package FORWARD is used to derive
from the models a synthetic linear polarization image that can be
directly compared with the observations and to compute the magnetic
field expansion factor from both observations and models. We find
differences between observations and PFSS extrapolations. In particular,
the height of the magnetic X-point is always higher in the observations,
indicating that PFSS models systematically underestimate the height
of the cusp null point and confirming the previous result of Gibson et
al. in 2017 based on a single pseudostreamer on April 18 2015. Gibson
et al. also noted that the expansion factor for the case they studied
was significantly larger in CoMP observations than expected from a
potential field extrapolation with possible implications for solar
wind speed. Our statistical analysis shows this is not always the
case. We find no clear trend in how the expansion factor derived from
observations compares to models and, at least at the heights covered by
the CoMP field-of-view (up to 1.35 solar radii), the observed expansion
factor cannot be used as meaningful diagnostic for solar wind speed.
---------------------------------------------------------
Title: Major Scientific Challenges and Opportunities in Understanding
Magnetic Reconnection and Related Explosive Phenomena throughout
the Universe
Authors: Ji, Hantao; Alt, A.; Antiochos, S.; Baalrud, S.; Bale, S.;
Bellan, P. M.; Begelman, M.; Beresnyak, A.; Blackman, E. G.; Brennan,
D.; Brown, M.; Buechner, J.; Burch, J.; Cassak, P.; Chen, L. -J.;
Chen, Y.; Chien, A.; Craig, D.; Dahlin, J.; Daughton, W.; DeLuca, E.;
Dong, C. F.; Dorfman, S.; Drake, J.; Ebrahimi, F.; Egedal, J.; Ergun,
R.; Eyink, G.; Fan, Y.; Fiksel, G.; Forest, C.; Fox, W.; Froula, D.;
Fujimoto, K.; Gao, L.; Genestreti, K.; Gibson, S.; Goldstein, M.;
Guo, F.; Hesse, M.; Hoshino, M.; Hu, Q.; Huang, Y. -M.; Jara-Almonte,
J.; Karimabadi, H.; Klimchuk, J.; Kunz, M.; Kusano, K.; Lazarian,
A.; Le, A.; Li, H.; Li, X.; Lin, Y.; Linton, M.; Liu, Y. -H.; Liu,
W.; Longcope, D.; Louriero, N.; Lu, Q. -M.; Ma, Z. -W.; Matthaeus,
W. H.; Meyerhofer, D.; Mozer, F.; Munsat, T.; Murphy, N. A.; Nilson,
P.; Ono, Y.; Opher, M.; Park, H.; Parker, S.; Petropoulou, M.; Phan,
T.; Prager, S.; Rempel, M.; Ren, C.; Ren, Y.; Rosner, R.; Roytershteyn,
V.; Sarff, J.; Savcheva, A.; Schaffner, D.; Schoeffier, K.; Scime, E.;
Shay, M.; Sitnov, M.; Stanier, A.; TenBarge, J.; Tharp, T.; Uzdensky,
D.; Vaivads, A.; Velli, M.; Vishniac, E.; Wang, H.; Werner, G.; Xiao,
C.; Yamada, M.; Yokoyama, T.; Yoo, J.; Zenitani, S.; Zweibel, E.
2019BAAS...51c...5J Altcode: 2019astro2020T...5J
This is a group white paper of 100 authors (each with explicit
permission via email) from 51 institutions on the topic of magnetic
reconnection which is relevant to 6 thematic areas. Grand challenges
and research opportunities are described in observations, numerical
modeling and laboratory experiments in the upcoming decade.
---------------------------------------------------------
Title: Measuring coronal magnetic fields associated with CMEs:
UV spectropolarimetric study
Authors: Zhao, Jie; Fan, Yuhong; Gibson, Sarah
2019shin.confE.144Z Altcode:
Transformative progress into understanding the forces that drive CME
eruption and evolution would arise from spectropolarimetric measurements
of the magnetic fields in the CME and surrounding corona. Linear
polarization measurements in the visible/IR already obtained by the
Mauna Loa Solar Observatory CoMP telescope have established the power
of coronal spectropolarimetry for diagnosing pre-eruption magnetic
field direction and topology. Forward modeling has demonstrated
the potential of future large visible/IR telescopes including DKIST
and COSMO for quantifying the coronal magnetic field strength. In
particular, recent work has shown that COSMO has sufficient aperture
to track the core magnetic strength of the CME during eruption. We
have now extended this analysis to the UV unsaturated Hanle regime, and
will demonstrate how such novel measurements could provide critical new
measurements to constrain the fundamental magnetic nature of the CME.
---------------------------------------------------------
Title: The Whole Heliosphere and Planetary Interactions (WHPI)
Initiative
Authors: Kolinski, Don; Gibson, Sarah; Thompson, Barbara; Bagenal,
Fran; de Toma, Giuliana; McGranaghan, Ryan; DiBraccio, Gina
2019shin.confE.108K Altcode:
The Whole Heliosphere and Planetary Interactions (WHPI) is a scientific
initiative with hundreds of participants worldwide to coordinate
observations and modeling of the solar-heliospheric-planetary system
during solar minimum and to promote and facilitate inter-disciplinary
activities. We do this by organizing observing campaigns and dedicated
science workshops to bring scientists from different scientific fields
together. The aim of WHPI is to better understand how the Sun’s output
affects the heliosphere and planets. The simpler magnetic configuration
of the Sun and the infrequency of CMEs make solar minimum an ideal
time to make such connection. Science objectives of WHPI include:
characterizing the 3D magnetic structure of the Sun and heliosphere
during the current minimum, following the propagation and evolution of
the Sun’s magnetic field through the solar wind and its interaction
with the magnetospheres of the Earth and other planets, quantifying
the effects of the solar radiative output the Earth and other planets,
and investigating the effect of a deep and prolonged solar minimum on
the entire heliosphere. With this poster, we invite the SHINE community
to join the WHPI initiative.
---------------------------------------------------------
Title: The Turing Way: A Handbook for Reproducible Data Science
Authors: Way Community, The Turing; Arnold, Becky; Bowler, Louise;
Gibson, Sarah; Herterich, Patricia; Higman, Rosie; Krystalli, Anna;
Morley, Alexander; O'Reilly, Martin; Whitaker, Kirstie
2019zndo...3233986W Altcode:
Reproducible research is necessary to ensure that scientific work
can be trusted. Funders and publishers are beginning to require that
publications include access to the underlying data and the analysis
code. The goal is to ensure that all results can be independently
verified and built upon in future work. This is sometimes easier said
than done. Sharing these research outputs means understanding data
management, library sciences, software development, and continuous
integration techniques: skills that are not widely taught or
expected of academic researchers and data scientists. The Turing
Way is a handbook to support students, their supervisors, funders
and journal editors in ensuring that reproducible data science is
"too easy not to do". It will include training material on version
control, analysis testing, and open and transparent communication
with future users, and build on Turing Institute case studies and
workshops. This project is openly developed and any and all questions,
comments and recommendations are welcome at our github repository:
https://github.com/alan-turing-institute/the-turing-way. Release
log v0.0.4: Continuous integration chapter merged to master. v0.0.3:
Reproducible environments chapter merged to master. v0.0.2: Version
control chapter merged to master. v0.0.1: Reproducibility chapter
merged to master.
---------------------------------------------------------
Title: Origins of the Ambient Solar Wind: Implications for Space
Weather
Authors: Cranmer, Steven R.; Gibson, Sarah E.; Riley, Pete
2019sfsw.book...41C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Beyond Flatland: A Star of Many Dimensions
Authors: Gibson, Sarah
2018csc..confE..75G Altcode:
The more we have learned about the Sun, the more we can appreciate
its essential complexity. Telescopes confirmed that it was not
an unblemished sphere. Multi-wavelength observations revealed
its structured atmosphere, and ever-higher resolution exposed its
spectacular dynamics. Helioseismology penetrated its depths, and
STEREO views gave us our first three-dimensional perspective. With
Solar Orbiter we will finally leave our ecliptic bias behind and see
the Sun from high latitudes. What will we see? And what could we see
if future missions dwell at near-polar vantages, providing a synoptic
view from above or below? The science enabled by such viewpoints is
broad and deep, with potential both to finally fill known gaps in our
understanding, and to reveal hitherto undiscovered aspects of the Sun
and heliosphere.
---------------------------------------------------------
Title: Solar prominences: theory and models. Fleshing out the
magnetic skeleton
Authors: Gibson, Sarah E.
2018LRSP...15....7G Altcode:
Magnetic fields suspend the relatively cool material of solar
prominences in an otherwise hot corona. A comprehensive understanding
of solar prominences ultimately requires complex and dynamic
models, constrained and validated by observations spanning the solar
atmosphere. We obtain the core of this understanding from observations
that give us information about the structure of the "magnetic skeleton"
that supports and surrounds the prominence. Energetically-sophisticated
magnetohydrodynamic simulations then add flesh and blood to the
skeleton, demonstrating how a thermally varying plasma may pulse
through to form the prominence, and how the plasma and magnetic fields
dynamically interact.
---------------------------------------------------------
Title: The Eruption of a Prominence-carrying Coronal Flux Rope:
Forward Synthesis of the Magnetic Field Strength Measurement by the
COronal Solar Magnetism Observatory Large Coronagraph
Authors: Fan, Yuhong; Gibson, Sarah; Tomczyk, Steve
2018ApJ...866...57F Altcode: 2018arXiv180806142F
From a magnetohydrodynamic (MHD) simulation of the eruption of a
prominence hosting coronal flux rope, we carry out forward synthesis
of the circular polarization signal (Stokes V signal) of the Fe XIII
emission line at 1074.7 nm produced by the MHD model as measured by the
proposed COronal Solar Magnetism Observatory (COSMO) Large Coronagraph
(LC) and infer the line-of-sight magnetic field, B <SUB>LOS,</SUB>
above the limb. With an aperture of 150 cm, an integration time
of 12 minutes, and a resolution of 12 arcsec, the LC can measure a
significant B <SUB>LOS</SUB> with a sufficient signal-to-noise level,
from the simulated flux rope viewed nearly along its axis with a peak
axial field strength of about 10 G. The measured B <SUB>LOS</SUB> is
found to relate well with the axial field strength of the flux rope for
the height range of the prominence and can discern the increase with
height of the magnetic field strength in that height range that is a
definitive signature of the concave upturning dipped field supporting
the prominence. The measurement can also detect an outward-moving B
<SUB>LOS</SUB> due to the slow rise of the flux rope as it develops
the kink instability, during the phase when its rise speed is still
below about 41 km s<SUP>-1</SUP> and up to a height of about 1.3 solar
radii. These results suggest that the COSMO LC has great potential to
provide quantitative information about the magnetic field structure
of coronal mass ejection precursors (e.g., the prominence cavities)
and their early evolution for the onset of eruption.
---------------------------------------------------------
Title: Solar Physics from Unconventional Viewpoints
Authors: Gibson, Sarah E.; Vourlidas, Angelos; Hassler, Donald M.;
Rachmeler, Laurel A.; Thompson, Michael J.; Newmark, Jeffrey; Velli,
Marco; Title, Alan; McIntosh, Scott W.
2018FrASS...5...32G Altcode: 2018arXiv180509452G
We explore new opportunities for solar physics that could be realized
by future missions providing sustained observations from vantage
points away from the Sun-Earth line. These include observations from
the far side of the Sun, at high latitudes including over the solar
poles, or from near-quadrature angles relative to the Earth (e.g.,
the Sun-Earth L4 and L5 Lagrangian points). Such observations fill
known holes in our scientific understanding of the three-dimensional,
time-evolving Sun and heliosphere, and have the potential to open new
frontiers through discoveries enabled by novel viewpoints.
---------------------------------------------------------
Title: The Coronal Solar Magnetism Observatory
Authors: Thompson, Michael J.; Tomczyk, Steven; Gibson, Sarah E.;
McIntosh, Scott W.; Landi, Enrico
2018IAUS..335..359T Altcode:
The Coronal Solar Magnetism Observatory (CoSMO) is a proposed new
facility led by the High Altitude Observatory and a consortium of
partners to measure magnetic field and plasma properties in a large
(one degree) field of view extending down to the inner parts of the
solar corona. CoSMO is intended as a research facility that will
advance the understanding and prediction of space weather. The
instrumentation elements of CoSMO are: a white-light coronagraph
(KCor), already operational at the Mauna Loa Solar Observatory
(MLSO); the Chromosphere and Prominence Magnetometer (ChroMag), due
for deployment to MLSO next year; and the CoSMO Large Coronagraph (LC)
which has completed Preliminary Design Review.
---------------------------------------------------------
Title: The eruption of a prominence carrying coronal flux rope:
forward synthesis of the magnetic field strength measurement by the
COronal Solar Magnetism Observatory Large Coronagraph
Authors: Fan, Yuhong; Gibson, Sarah; Tomczyk, Steven
2018cosp...42E1038F Altcode:
From a magnetohydrodynamic (MHD) simulation of the eruption of
prominence hosting coronal flux rope, we carry out forward synthesis
of the circular polarization signal V/I produced by the MHD model as
measured by the proposed COronal Solar Magnetism Observatory (COSMO)
Large Coronagraph (LC) and infer the line-of-sight magnetic field
BLOS above the limb. With an aperture of 150 cm, integration time of
300 sec, and an observation pixel of 12 arcsec, the LC can measure
a significant BLOS with sufficient signal to noise level, from the
simulated flux rope with a peak azimuthal field strength of about
10 G. The measured BLOS is found to relate well with the axial field
strength of the flux rope within the height range of the prominence,
and can discern the increase with height of the magnetic field strength
along the prominence that is a definitive signature of the concave
upturning dipped field supporting the prominence. The measurement
can also detect above the noise the outward rise of the BLOS due to
the slow rise of the flux rope as it develops the kink instability,
during the phase when its rise speed is still below 15 km/s and up to a
height of about 1.25 solar radius. These results suggest that the COSMO
LC has great potential in providing quantitative information about
the magnetic field structure of CME precursors (such as prominences)
and their early evolution for the onset of eruption.
---------------------------------------------------------
Title: "Building a Magnetic Skeleton of the Solar Corona: Towards
Better 3-D Constraints on the Coronal Magnetic Field
Authors: Malanushenko, Anna; Gibson, Sarah; Kucera, Therese; McKenzie,
David
2018cosp...42E2139M Altcode:
The energy stored in the solar magnetic field is what is powering many
violent explosive events in the solar atmosphere, or the corona. Some
of these events result in the coronal mass ejections (CME's) released
into the interplanetary space. The magnetic field in the solar corona
is therefore very important to know, yet it is very difficult to
measure. Most of the time it is modeled with the magnetic maps at
the solar surface used as boundary conditions. The magnetic maps on
the surface are therefore also important to know, yet the full vector
of the field on the surface is also difficult to measure. Once such
measurements are made, constructing a model capable of predicting
eruptive potential of a given region is on its own a complicated
task. One of the problems arising is that that the equations for
low-beta equilibria, which are often used to describe the coronal
field, do not, strictly speaking, work for the solar surface. In
short, we need better inputs to model the solar corona. The use of
non-magnetic and non-surface constraints on the magnetic field becomes
increasingly popular. For example, the paths of filaments can be used
to guide flux rope trajectories; the loops of active regions, seen
in extreme ultraviolet (EUV) can be used to obtain 3-D trajectories
of magnetic field lines and estimate electric currents flowing along
them. We are currently exploring ways to use other sources of data,
such as flows in prominences and coronal spectropolarimetric data, in a
similar fashion. I will talk about this work, and about our project of
aggregating many different sources of non-magnetic 3-D constraints on
the magnetic field. The resulting 'skeleton' can be used to constraint
global field models, or to validate models obtained in traditional
ways. We intend to develop a pipeline and assemble several skeletons
for several instances in time of the Sun, which we will then release
to community.
---------------------------------------------------------
Title: Tracing the Origins of the Solar Wind by Tracking Flows and
Disturbances in Coronagraph Data
Authors: Thompson, Barbara J.; Attie, Raphael; DeForest, Craig E.;
Gibson, Sarah E.; Hess Webber, Shea A.; Ireland, Jack; Kirk, Michael
S. F.; Kwon, Ryun Young; McGranaghan, Ryan; Viall, Nicholeen M.
2018shin.confE..47T Altcode:
The challenge of identifying transient motions in solar imagery has
been addressed in a number of ways. A variety of methods have been
developed to detect and characterize the motion and extent of coronal
mass ejections, for example. We discuss the adaptation of CME and
solar transient detection methods to trace smaller-scale perturbations
consistent with solar wind motions in the inner heliosphere (out to 10
RSun). We evaluate several methods, and compare the speed and structure
results to model predictions. In particular, we discuss how high-cadence
heliospheric imagery can be used to track small scale solar density
variations throughout the solar wind, serving as a proxy for in situ
velocity detection, but with global and continuous coverage.
---------------------------------------------------------
Title: Magnetic field measurements in the solar corona: facing the
challenge with ground and space based observations
Authors: Bemporad, Alessandro; Fineschi, Silvano; Mancuso, Salvatore;
Gibson, Sarah; Susino, Roberto; Massone, . Giuseppe; Capobianco,
Gerardo; Frassati, Federica
2018cosp...42E.265B Altcode:
Actual limitations in understanding physical processes occurring
in the solar atmosphere are related with our poor capabilities in
measuring magnetic fields in its layers. The knowledge of magnetic
fields in the solar corona is crucial to understand the origin of solar
flares and Coronal Mass Ejections, waves, coronal heating and solar
wind acceleration. For these reasons many different techniques have
been proposed to provide these measurements by analysing the emission
related with many different physical phenomena (e.g.: radio observations
of gyrosynchrotron and free-free emission, infrared observations of
Zeeman effect, visible and infrared obervations of the Hanle effect,
UV-EUV observations of CME-driven shock waves, etc..). In order
to provide a continuous monitoring of coronal fields, new ground-
and space-based instrumentations are currently under development, as
well as new techniques to infer the real fields from the line-of-sight
integrated coronal emission. At the same time, the forward modelling of
the expected emission starting from different possible coronal field
configurations is being developed, allowing the definition of the
required properties for future instrumentation and the verification
of the data analysis results.
---------------------------------------------------------
Title: Pseudostreamer topology revealed by CoMP observations
Authors: De Toma, Giuliana; Gibson, Sarah; Dalmasse, Kévin; Miralles,
Mari Paz
2018cosp...42E.787D Altcode:
Pseudostreamers represent sources of the solar wind whose properties
are a subject of active investigation. Their magnetic structure, and
particularly the expansion of magnetic flux tubes associated with them,
is a matter of current debate. Pseudostreamers are associated with
magnetic nulls, which are known to be locations prone to magnetic
reconnection that potentially facilitate eruptions. A recent study
demonstrated the novel constraints on pseudostreamer topology provided
by coronal spectropolarimetry, in particular linear polarization
measured by the Coronal Muiltichannel Polarimeter (CoMP) telescope at
the Mauna Loa Solar Observatory. That study for the first time provided
a method for determining magnetic expansion in the corona independent
from any extrapolation or global MHD model representation of the
coronal field. It found that this expansion factor was larger and the
magnetic null was higher for a pseudostreamer observed by CoMP than
expected from a potential field calculation. In this work we extend
our analysis to additional observations of pseudostreamers made by
CoMP, for which we identify the magnetic nulls and quantify expansion
factor. Our goal is to understand if there are systematic differences
between these observations and predictions of a potential field model.
---------------------------------------------------------
Title: Global Solar Magnetic Field Evolution Over 4 Solar Cycles:
Use of the McIntosh Archive
Authors: Webb, David F.; Gibson, Sarah E.; Hewins, Ian M.; McFadden,
Robert H.; Emery, Barbara A.; Malanushenko, Anna; Kuchar, Thomas A.
2018FrASS...5...23W Altcode:
The McIntosh Archive consists of a set of hand-drawn solar Carrington
maps created by Patrick McIntosh from 1964 to 2009. McIntosh used
mainly Hα, He-I 10830Å and photospheric magnetic measurements from
both ground-based and NASA satellite observations. With these he traced
polarity inversion lines (PILs), filaments, sunspots and plage and,
later, coronal holes over a 45-year period. This yielded a unique
record of synoptic maps of features associated with the large-scale
solar magnetic field over four complete solar cycles. We first discuss
how these and similar maps have been used in the past to investigate
long-term solar variability. Then we describe our work in preserving
and digitizing this archive, developing a digital, searchable format,
and creating a website and an archival repository at NOAA's National
Centers for Environmental Information (NCEI). Next we show examples of
how the data base can be utilized for scientific applications. Finally,
we present some preliminary results on the solar-cycle evolution of
the solar magnetic field, including the polar field reversal process,
the evolution of active longitudes, and the role of differential
solar rotation.
---------------------------------------------------------
Title: Linear Line-Polarimetry: probing the magnetic field mechanisms
of energy deposition in corona.
Authors: Fineschi, Silvano; Gibson, Sarah; Susino, Roberto; Zhao, Jie
2018cosp...42E1073F Altcode:
Optically-thin, UV spectral lines in corona are linearly polarized by
resonance scattering of chromospheric line-emissions off coronal ions.In
the presence of coronal magnetic fields, the resontantly-scattered
line-polarization is modified by the Hanle effect. Spectro-polarimetric
UV observations from space of these line-emissions, interpreted in
terms of the Hanle effects, are a powerful tool for the diagnostics of
magnetic fields in the solar chromosphere/corona.Through the anisotropic
Doppler-dimmng effect, the linear polarization of optically thin
spectral lines is sensitive to anisotropic ion-velocity distributions
that can be induced by the ion-cyclotron resonance between plasmas and
MHD waves in corona. This effect is believed to influence some heavy
ions in the solar corona. Thus, coronal polarimetry of resonantly
scattered UV spectral lines can also serve as a powerful tool for
probing the magnetic field mechanism(s) of energy deposition in
corona.This presentation reports the parameter study carried out
by forward modeling of the linear polarization of the coronal UV
spectral lines HI Lyman-α, 121.6 nm, and OVI, 103.2 nm. The study was
based on the FORWARD numerical code developed by the High Altitude
Observatory. The study used FORWARD to reproduce synthetic linear
line-polarization maps for different MHD models of the corona.The
results from the parameters study indicate that the Hanle effect
diagnostics is most effective within a few tens of solar radii from
the solar limb in closed-field, active regions where the strength
the coronal magnetic field is within the Hanle effect sensitivity for
the HI Lyman-α and OVI lines (i.e., 2-60 gauss). On the other hand,
the effect of anisotropic velocity field distributions of scattering
ions on the line-polarization emitted by resonance scattering is most
effective in open-filed regions of non-radial solar wind, such as the
interface coronal holes-streamers.
---------------------------------------------------------
Title: A Space Coronal Magnetometry Mission
Authors: Lin, Haosheng; Gibson, Sarah; Savage, Sabrina; Tomczyk,
Steven; Downs, Cooper; Rachmeler, Laurel; Kramar, Maxim; Habbal, Shadia
2018cosp...42E2020L Altcode:
Direct measurement of the polarized spectra of forbidden coronal
emission lines (CELs) is the most powerful tool for the study of
the solar coronal magnetic fields. Due to its low optical density,
simultaneous multi-sight-lines observations of the corona from space
are needed for tomographic inversion to disentangle the 3D structure of
the solar corona. This presentation will describe the mission concept
and instrument design of a future space coronal magnetometry mission,
consists of many clusters of small spacecraft in near-sun heliocentric
orbits to observe the sun to enable tomographic determination of
the 3D magnetic and thermodynamic structures of the corona. The
spacecraft will be equipped with a wide field, super achromatic lens
coronagraph equipped with two 100-slit, 4-channel spectropolarimeters
optimized for measurement of the polarized CEL spectra from space. This
instrument is tentatively named 'mxCSM'- the massively-multiplexed
Coronal SpectroMagnetometer. A prototype mxCSM is currently under
construction with funding from a 2017 National Science Foundation
Major Research Instrument program grant. This space coronal space
magnetometry mission will advance our knowledge of the corona and the
physics of energetic coronal eruptions, and ultimately enable accurate
space weather forecast.
---------------------------------------------------------
Title: Simulating the solar minimum corona in UV and visible/IR
wavelengths with forward modeling
Authors: Zhao, Jie; Fineschi, Silvano; Gibson, Sarah; Susino, Roberto
2018cosp...42E3853Z Altcode:
The magnetic field in the corona is important for understanding
solar activity, but is difficult to measure due to the tenuous
plasma. Therefore many alternative methods have been adopted to get
the 3D magnetic field in the corona, such as extrapolation methods
relying on the photospheric magnetograms. Such extrapolations make
problematic assumptions about the force-free nature of the photosphere,
and are highly sensitive to uncertainties in the photosphere magnetic
measurements. Measuring the coronal magnetic field directly is thus
to be desired, and linear polarization measurements in the visible/IR
are already obtained by the CoMP telescope providing information about
coronal magnetic direction and topology. However other observations
such as circlar polarization in the visible/IR and UV unsaturated Hanle
measurements are needed to better observe the 3D coronal field. Until
such observations are available, we turn to the FORWARD model (Gibson et
al. 2016) which simulates all of these polarization data. As a physical
state to input into FORWARD, the analytic magnetic model in this work
is adopted from Gibson et al.(1996), which gives a potential field
with an exception at the boundary of the helmet streamer where current
sheets are added between the open and closed fields. This analytic
model has the benifit of matching white light and also photospheric
magnetic flux observations at solar minimum. Given this model input
of a 3D distribution of magnetic field and plasma, we obtain simulated
polarization results in UV and visible/IR wavelengths. This allows us
to consider how such observations might be used together in future to
diagnose the coronal magnetic field.
---------------------------------------------------------
Title: Solar Observations Away from the Sun-Earth Line
Authors: Gibson, Sarah E.; McIntosh, Scott William; Rachmeler,
Laurel; Thompson, Michael J.; Title, Alan M.; Velli, Marco C. M.;
Vourlidas, Angelos
2018tess.conf40340G Altcode:
Observations from satellite missions have transformed the field of solar
physics. High-resolution observations with near-continuous temporal
coverage have greatly extended our capability for studying long-term
and transient phenomena, and the opening of new regions of the solar
spectrum has made detailed investigation of the solar atmosphere
possible. <P />However, to date most solar space-based missions
have been restricted to an observational vantage in the vicinity of
the Sun-Earth line, either in orbit around the Earth or from the L1
Lagrangian point. As a result, observations from these satellites
represent the same geometrical view of the Sun that is accessible
from the Earth. <P />Understanding the deep interior structure of the
Sun and the full development of solar activity would really benefit
from fully three-dimensional monitoring of the solar atmosphere and
heliosphere. On the one hand, simultaneous spacecraft observations
from multiple vantage points would allow studies of the deep interior
structure of the sun via stereoscopic helioseismology; on the other,
distributed observations would allow the understanding of the complete
evolution of activity complexes and enhance space weather predictions
dramatically. <P />Presently, observations of the Sun away from Earth
are obtained by the STEREO pair of satellites, which have provided
an unprecedented global view by orbiting around to the far side of
the Sun, and the Ulysses mission, which achieved a high-inclination
(80˚) near-polar orbit (but which, however, did not include any solar
imaging instruments). The forthcoming Solar Orbiter mission, which
will orbit the sun and reach a maximum inclination of 34˚ out of the
ecliptic should provide the first detailed mapping of the sun's polar
fields. In addition, Solar Probe Plus will explore the outer corona
and inner Heliosphere with very rapid solar encounters at a minimum
perihelion 9.86 solar radii from the center of the Sun. <P />We explore
some of the new opportunities for solar physics that can be realized
by future missions that provide sustained observations from vantage
points away from the Sun-Earth line (and in some cases the ecliptic
plane): observations from the far side of the Sun, over its poles,
or from the L5 Lagrangian point.
---------------------------------------------------------
Title: Tracking Flows and Disturbances in Coronagraph Data
Authors: Thompson, Barbara J.; Attie, Raphael; DeForest, Craig E.;
Gibson, Sarah E.; Hess Webber, Shea A.; Inglis, Anfew R.; Ireland,
Jack; Kirk, Michael S.; Kwon, RyunYoung; Viall, Nicholeen M.
2018tess.conf30922T Altcode:
The challenge of identifying transient motions in solar imagery has
been addressed in a number of ways. A variety of methods have been
developed to detect and characterize the motion and extent of coronal
mass ejections, for example. We discuss the adaptation of CME and
solar transient detection methods to trace smaller-scale perturbations
consistent with solar wind motions in the inner heliosphere (over 10
RSun). We evaluate several methods, and compare the speed and structure
results to model predictions. In particular, we discuss how high-cadence
heliospheric imagery can be used to track small scale solar density
variations throughout the solar wind, serving as a proxy for in situ
velocity detection, but with global and continuous coverage.
---------------------------------------------------------
Title: Non Linear Force Free Field modeling of an erupting
pseudostreamer
Authors: Karna, Nishu; Savcheva, Antonia Stefanova; Gibson, Sarah E.;
Tassev, Svetlin
2018tess.conf10412K Altcode:
Coronal mass ejections (CMEs) are the most violent eruptions in our
Solar System. CMEs are responsible for large solar energetic particle
events and severe geomagnetic storms. In this study, we present a
magnetic configuration of an erupting pseudostreamer observed on April
19, 2015 on the Southern West limb embedding a prominence cavity. The
eruption resulted in a relatively wide CME with a round front and
prominence core. In SOHO/LASCO C2 partial halo was observed. The
prominence eruption begins with a slow rise and then evolves to a
fast rise phase. We first constructed a non-linear force free field
(NLFFF) model of this erupting pseudostreamer using the flux rope
insertion method. The NLFFF model produces the 3D coronal magnetic
field constrained by observed coronal structures and photospheric
magnetogram. SDO/HMI magnetogram was used as an input for the model. The
field configurations representing the eruption are not in force-free
equilibrium. We magnetofrictionally relax the model until the flux
rope expands to three solar radii and compare CME propagation with the
SOHO/LASCO C2 observations. From the simulation results, we determine
the process for the eruption by identifying where reconnection takes
place and how much flux is reconnected. We determine the pre-eruption
twist and decay index and how the twist is transferred as the simulation
progresses. In addition, we perform a topology analysis of the models in
order to determine the location of quasi-separatrix layers (QSLs). QSLs
are used as a proxy to determine where strong electric current sheets
develop in the corona and also provide important information about
the connectivity in this complicated magnetic field configuration.
---------------------------------------------------------
Title: Studies of Global Solar Magnetic Field Patterns Using a Newly
Digitized Archive
Authors: Gibson, Sarah E.
2018tess.conf10308G Altcode:
The McIntosh Archive consists of a set of hand-drawn solar Carrington
maps created by Patrick McIntosh from 1964 to 2009. McIntosh used mainly
H-alpha, He 10830Å and photospheric magnetic measurements from both
ground-based and NASA satellite observations. With these he traced
polarity inversion lines (PILs), filaments, sunspots and plage and,
later, coronal holes, yielding a unique 45-year record of features
associated with the large-scale organization of the solar magnetic
field. We discuss our efforts to preserve and digitize this archive. The
original hand-drawn maps have been scanned, a method for processing
these scans into digital, searchable format has been developed, and
a website and an archival repository at NOAA's National Centers for
Environmental Information (NCEI) has been created. Presently ~ 70%
of the final processed archive is complete, from SC 20 through to the
start of SC 24, but with long gaps in SCs 20, 21 and 22. Here we present
preliminary results using the archived maps from SC 21-23. We show the
global evolution of closed magnetic structures (e.g., sunspots, plage,
and filaments) relative to open structures (e.g., coronal holes),
and examine how both relate to the shifting patterns of large-scale
positive and negative polarity regions.
---------------------------------------------------------
Title: Analyzing CME Substructure and Chirality from Synthetic
Polarization Observations
Authors: Gibson, Sarah E.; DeForest, Criag; de Koning, Curt A.;
Fan, Yuhong
2018tess.conf30923G Altcode:
Recent work (Deforest et al., 2017) has demonstrated the power of
white-light polarization for pinpointing the 3D location of CME
substructure and characterizing its chirality using coronagraph
observations. In this paper, we further explore the capability of
this technique by creating synthetic white-light observations from a
simulation of an erupting CME containing realistic substructure. We
extract information about the CME chirality from the synthetic
polarization, and compare to the "ground truth" of the simulation. We
analyze how CME orientation relative to the viewer affects our results,
and consider the implications of this type of analysis for studying
how CME substructure evolves in the young solar wind.
---------------------------------------------------------
Title: Studies of Global Solar Magnetic Field Patterns Using a Newly
Digitized Archive
Authors: Hewins, I.; Webb, D. F.; Gibson, S. E.; McFadden, R.; Emery,
B. A.; Malanushenko, A. V.
2017AGUFMSH54A..01H Altcode:
The McIntosh Archive consists of a set of hand-drawn solar Carrington
maps created by Patrick McIntosh from 1964 to 2009. McIntosh used
mainly Ha, He 10830Å and photospheric magnetic measurements from both
ground-based and NASA satellite observations. With these he traced
polarity inversion lines (PILs), filaments, sunspots and plage and,
later, coronal holes, yielding a unique 45-year record of features
associated with the large-scale organization of the solar magnetic
field. We discuss our efforts to preserve and digitize this archive;
the original hand-drawn maps have been scanned, a method for processing
these scans into digital, searchable format has been developed,
and a website and an archival repository at NOAA's National Centers
for Environmental Information (NCEI) has been created. The archive
is complete for SC 23 and partially complete for SCs 21 and 22. In
this paper we show examples of how the data base can be utilized for
scientific applications. We compare the evolution of the areas and
boundaries of CHs with other recent results, and we use the maps to
track the global, SC-evolution of filaments, large-scale positive and
negative polarity regions, PILs and sunspots.
---------------------------------------------------------
Title: Numerical MHD Coronal Simulations: Energy Statistics and
FORWARD Analysis.
Authors: Nimmo, K.; Rempel, M.; Chen, F.; Gibson, S. E.; Fan, Y.
2017AGUFMSH43A2800N Altcode:
We analyse a recent realistic radiative MHD simulation of the solar
corona that was computed with the extended version of the MURaM
code. The simulation covers the uppermost 8Mm of the solar convection
zone and reaches 115Mm into the solar corona. The simulation covers 48
hours of solar time and simulates the evolution of a complex active
region. The energy release in the corona is highly intermittent and
we identify a total of 118 individual events including flares and a
coronal mass ejection, which we analyse in further detail. From the
simulation we compute an X-ray flux mimicking observations by the GOES
(Geostationary Operational Environmental Satellite) satellite in the
wavelength range 1-8 Å. The power law index for the GOES X-ray flux
for flares of class C and above in this simulation is found to be
1.33452. We analyze the correlation between synthetic coronal emission
during flares and the magnetic energy release in the corona. The latter
is a quantity that cannot be directly determined in observations.The
FORWARD code is a tool used for the purpose of coronal magnetometry. It
can be used to compute synthetic observables from coronal models. We
focus on the interpretation of the High Altitude Observatory's CoMP
observations. The CoMP (COronal Multi-channel Polarimeter) instrument
measures the intensity and the linear and circular polarisation of
FeXIII at 1074.7nm.We discuss some important limitations of coronal
emission line polarimetry when simulating an extremely active solar
region, with emphasis on the influence of high velocities, temperatures
and densities on the FORWARD output.
---------------------------------------------------------
Title: Type III Solar Radio Burst Source Region Splitting due to a
Quasi-separatrix Layer
Authors: McCauley, Patrick I.; Cairns, Iver H.; Morgan, John; Gibson,
Sarah E.; Harding, James C.; Lonsdale, Colin; Oberoi, Divya
2017ApJ...851..151M Altcode: 2017arXiv171104930M
We present low-frequency (80-240 MHz) radio imaging of type III
solar radio bursts observed by the Murchison Widefield Array on
2015 September 21. The source region for each burst splits from
one dominant component at higher frequencies into two increasingly
separated components at lower frequencies. For channels below ∼132
MHz, the two components repetitively diverge at high speeds (0.1c-0.4c)
along directions tangent to the limb, with each episode lasting just
∼2 s. We argue that both effects result from the strong magnetic
field connectivity gradient that the burst-driving electron beams
move into. Persistence mapping of extreme-ultraviolet jets observed by
the Solar Dynamics Observatory reveals quasi-separatrix layers (QSLs)
associated with coronal null points, including separatrix dome, spine,
and curtain structures. Electrons are accelerated at the flare site
toward an open QSL, where the beams follow diverging field lines to
produce the source splitting, with larger separations at larger heights
(lower frequencies). The splitting motion within individual frequency
bands is interpreted as a projected time-of-flight effect, whereby
electrons traveling along the outer field lines take slightly longer
to excite emission at adjacent positions. Given this interpretation, we
estimate an average beam speed of 0.2c. We also qualitatively describe
the quiescent corona, noting in particular that a disk-center coronal
hole transitions from being dark at higher frequencies to bright at
lower frequencies, turning over around 120 MHz. These observations
are compared to synthetic images based on the MHD algorithm outside
a sphere (MAS) model, which we use to flux-calibrate the burst data.
---------------------------------------------------------
Title: Origins of the Ambient Solar Wind: Implications for Space
Weather
Authors: Cranmer, Steven R.; Gibson, Sarah E.; Riley, Pete
2017SSRv..212.1345C Altcode: 2017arXiv170807169C; 2017SSRv..tmp..167C
The Sun's outer atmosphere is heated to temperatures of millions
of degrees, and solar plasma flows out into interplanetary space at
supersonic speeds. This paper reviews our current understanding of
these interrelated problems: coronal heating and the acceleration of
the ambient solar wind. We also discuss where the community stands in
its ability to forecast how variations in the solar wind (i.e., fast and
slow wind streams) impact the Earth. Although the last few decades have
seen significant progress in observations and modeling, we still do not
have a complete understanding of the relevant physical processes, nor
do we have a quantitatively precise census of which coronal structures
contribute to specific types of solar wind. Fast streams are known
to be connected to the central regions of large coronal holes. Slow
streams, however, appear to come from a wide range of sources, including
streamers, pseudostreamers, coronal loops, active regions, and coronal
hole boundaries. Complicating our understanding even more is the
fact that processes such as turbulence, stream-stream interactions,
and Coulomb collisions can make it difficult to unambiguously map a
parcel measured at 1 AU back down to its coronal source. We also review
recent progress—in theoretical modeling, observational data analysis,
and forecasting techniques that sit at the interface between data and
theory—that gives us hope that the above problems are indeed solvable.
---------------------------------------------------------
Title: Beyond sunspots: Studies using the McIntosh Archive of global
solar magnetic field patterns
Authors: Gibson, Sarah E.; Webb, David; Hewins, Ian M.; McFadden,
Robert H.; Emery, Barbara A.; Denig, William; McIntosh, Patrick S.
2017IAUS..328...93G Altcode: 2018arXiv180808215G
In 1964 (Solar Cycle 20; SC 20), Patrick McIntosh began creating
hand-drawn synoptic maps of solar magnetic features, based on Hα
images. These synoptic maps were unique in that they traced magnetic
polarity inversion lines, and connected widely separated filaments,
fibril patterns, and plage corridors to reveal the large-scale
organization of the solar magnetic field. Coronal hole boundaries were
later added to the maps, which were produced, more or less continuously,
into 2009 (i.e., the start of SC 24). The result was a record of ~45
years (~570 Carrington rotations), or nearly four complete solar cycles
of synoptic maps. We are currently scanning, digitizing and archiving
these maps, with the final, searchable versions publicly available at
NOAA's National Centers for Environmental Information. In this paper
we present preliminary scientific studies using the archived maps from
SC 23. We show the global evolution of closed magnetic structures
(e.g., sunspots, plage, and filaments) in relation to open magnetic
structures (e.g., coronal holes), and examine how both relate to the
shifting patterns of large-scale positive and negative polarity regions.
---------------------------------------------------------
Title: Non Linear Force Free Field Modeling for a Pseudostreamer
Authors: Karna, Nishu; Savcheva, Antonia; Gibson, Sarah; Tassev,
Svetlin V.
2017SPD....48.0701K Altcode:
In this study we present a magnetic configuration of a pseudostreamer
observed on April 18, 2015 on southern west limb embedding a filament
cavity. We constructed Non Linear Force Free Field (NLFFF) model
using the flux rope insertion method. The NLFFF model produces the
three-dimensional coronal magnetic field constrained by observed coronal
structures and photospheric magnetogram. SDO/HMI magnetogram was used
as an input for the model. The high spatial and temporal resolution
of the SDO/AIA allows us to select best-fit models that match the
observations. The MLSO/CoMP observations provide full-Sun observations
of the magnetic field in the corona. The primary observables of CoMP
are the four Stokes parameters (I, Q, U, V). In addition, we perform a
topology analysis of the models in order to determine the location of
quasi-separatrix layers (QSLs). QSLs are used as a proxy to determine
where the strong electric current sheets can develop in the corona and
also provide important information about the connectivity in complicated
magnetic field configuration. We present the major properties of the 3D
QSL and FLEDGE maps and the evolution of 3D coronal structures during
the magnetofrictional process. We produce FORWARD-modeled observables
from our NLFFF models and compare to a toy MHD FORWARD model and the
observations.
---------------------------------------------------------
Title: Non Linear Force Free Field Modeling for a Pseudostreamer
Authors: Karna, Nishu; Savcheva, Antonia; Gibson, Sarah
2017shin.confE..52K Altcode:
In this study we present a magnetic configuration of a pseudostreamer
observed on April 18, 2015 on southern west limb embedding a filament
cavity. We constructed Non Linear Force Free Field (NLFFF) model
using the flux rope insertion method. The NLFFF model produces the
three-dimensional coronal magnetic field constrained by observed coronal
structures and photospheric magnetogram. SDO/HMI magnetogram was used
as an input for the model. The high spatial and temporal resolution
of the SDO/AIA allows us to select best-fit models that match the
observations. The MLSO/CoMP observations provide full-Sun observations
of the magnetic field in the corona. The primary observables of CoMP
are the four Stokes parameters (I, Q, U, V). In addition, we perform a
topology analysis of the models in order to determine the location of
quasi-separatrix layers (QSLs). QSLs are used as a proxy to determine
where the strong electric current sheets can develop in the corona and
also provide important information about the connectivity in complicated
magnetic field configuration. We present the major properties of the 3D
QSL and FLEDGE maps and the evolution of 3D coronal structures during
the magnetofrictional process.
---------------------------------------------------------
Title: Editorial: Coronal Magnetometry
Authors: Gibson, Sarah E.; Rachmeler, Laurel A.; White, Stephen M.
2017FrASS...4....3G Altcode: 2017FrASS...4E...3G
No abstract at ADS
---------------------------------------------------------
Title: Magnetic Nulls and Super-radial Expansion in the Solar Corona
Authors: Gibson, Sarah E.; Dalmasse, Kevin; Rachmeler, Laurel A.;
De Rosa, Marc L.; Tomczyk, Steven; de Toma, Giuliana; Burkepile,
Joan; Galloy, Michael
2017ApJ...840L..13G Altcode: 2017arXiv170407470G
Magnetic fields in the Sun’s outer atmosphere—the corona—control
both solar-wind acceleration and the dynamics of solar eruptions. We
present the first clear observational evidence of coronal magnetic
nulls in off-limb linearly polarized observations of pseudostreamers,
taken by the Coronal Multichannel Polarimeter (CoMP) telescope. These
nulls represent regions where magnetic reconnection is likely to act
as a catalyst for solar activity. CoMP linear-polarization observations
also provide an independent, coronal proxy for magnetic expansion into
the solar wind, a quantity often used to parameterize and predict the
solar wind speed at Earth. We introduce a new method for explicitly
calculating expansion factors from CoMP coronal linear-polarization
observations, which does not require photospheric extrapolations. We
conclude that linearly polarized light is a powerful new diagnostic
of critical coronal magnetic topologies and the expanding magnetic
flux tubes that channel the solar wind.
---------------------------------------------------------
Title: Dynamics and diagnostics of the solar corona: unchained
magnetism
Authors: Gibson, Sarah
2017psio.confE..53G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The McIntosh Archive: A solar feature database spanning four
solar cycles
Authors: Gibson, S. E.; Malanushenko, A. V.; Hewins, I.; McFadden,
R.; Emery, B.; Webb, D. F.; Denig, W. F.
2016AGUFMSH11A2220G Altcode:
The McIntosh Archive consists of a set of hand-drawn solar Carrington
maps created by Patrick McIntosh from 1964 to 2009. McIntosh used
mainly H-alpha, He-1 10830 and photospheric magnetic measurements
from both ground-based and NASA satellite observations. With these he
traced coronal holes, polarity inversion lines, filaments, sunspots
and plage, yielding a unique 45-year record of the features associated
with the large-scale solar magnetic field. We will present the results
of recent efforts to preserve and digitize this archive. Most of the
original hand-drawn maps have been scanned, a method for processing
these scans into digital, searchable format has been developed and
streamlined, and an archival repository at NOAA's National Centers for
Environmental Information (NCEI) has been created. We will demonstrate
how Solar Cycle 23 data may now be accessed and how it may be utilized
for scientific applications. In addition, we will discuss how this
database of human-recognized features, which overlaps with the onset
of high-resolution, continuous modern solar data, may act as a training
set for computer feature recognition algorithms.
---------------------------------------------------------
Title: Tapping the Core - a study of Alfvénic energy flow in an
erupting flux-rope configuration
Authors: Fletcher, L.; Dalmasse, K.; Gibson, S. E.; Fan, Y.
2016AGUFMSH31B2564F Altcode:
We analyze the evolution of reconnecting magnetic field in a 3-D
numerical simulation of a partially-ejected solar flux rope, with a
focus on understanding how the flux rope dynamics is linked to the
flow of energy through the field and the solar atmosphere as Alfvénic
Poynting flux. The magnetic flux rope splits in two during its eruption,
with reconnection taking place between the erupting rope and surrounding
fields, and internally in the strong field of the rope. We track the
Poynting flux entering and leaving the simulation current sheets,
and by mapping this down to the solar surface we identify locations of
weak and strong energy deposition in the lower atmosphere. Our tracking
method enables us to link the lower atmosphere signatures to different
stages of the coronal reconnection. We find a predominantly two-ribbon
morphology in the locations of Poynting flux deposition in the lower
atmosphere, in which the transition from reconnection involving weaker
field external to the flux rope, to reconnection involving the flux rope
core field, is accompanied by rapid ribbon spreading. In the core-field
reconnection phase, ribbons move into strong field regions on the
solar surface, and locations of highly concentrated downward-directed
Poynting flux are found, which may be linked to the most energetic flare
`footpoints' seen in optical and hard X-ray emission.
---------------------------------------------------------
Title: New Capabilities for Adaptive Mesh Simulation Use within
FORWARD
Authors: Mathews, N.; Flyer, N.; Gibson, S. E.; Kucera, T. A.;
Manchester, W.
2016AGUFMSM32A..05M Altcode:
The multiscale nature of the solar corona can pose challenges to
numerical simulations. Adaptive meshes are often used to resolve
fine-scale structures, such as the chromospheric-coronal interface
found in prominences and the transition region as a whole. FORWARD is
a SolarSoft IDL package designed as a community resource for creating
a broad range of synthetic coronal observables from numerical models
and comparing them to data. However, to date its interface with
numerical simulations has been limited to regular grids. We will
present a new adaptive-grid interface to FORWARD that will enable
efficient synthesis of solar observations. This is accomplished
through the use of hierarchical IDL structures designed to enable
finding nearest-neighbor points quickly for non-uniform grids. This
facilitates line-of-sight integrations that can adapt to the unequally
spaced mesh. We will demonstrate this capability for the Alfven-Wave
driven SOlar wind Model (AWSOM), part of the Space Weather Modeling
Framework (SWMF). In addition, we will use it in the context of a
prominence-cavity model, highlighting new capabilities in FORWARD that
allow treatment of continuum absorbtion as well as EUV line emission
via dual populations (chromosphere-corona).
---------------------------------------------------------
Title: Probing the Physical Connection between Solar Prominences
and Coronal Rain
Authors: Liu, W.; Antolin, P.; Sun, X.; Vial, J. C.; Guo, L.; Gibson,
S. E.; Berger, T. E.; Okamoto, J.; De Pontieu, B.
2016AGUFMSH43C2587L Altcode:
Solar prominences and coronal rain are intimately related phenomena,
both involving cool material at chromospheric temperatures within the
hot corona and both playing important roles as part of the return flow
of the chromosphere-corona mass cycle. At the same time, they exhibit
distinct morphologies and dynamics not yet well understood. Quiescent
prominences consist of numerous long-lasting, filamentary downflow
threads, while coronal rain is more transient and falls comparably
faster along well-defined curved paths. We report here a novel, hybrid
prominence-coronal rain complex in an arcade-fan geometry observed
by SDO/AIA and IRIS, which provides new insights to the underlying
physics of such contrasting behaviors. We found that the supra-arcade
fan region hosts a prominence sheet consisting of meandering threads
with broad line widths. As the prominence material descends to the
arcade, it turns into coronal rain sliding down coronal loops with
line widths 2-3 times narrower. This contrast suggests that distinct
local plasma and magnetic conditions determine the fate of the cool
material, a scenario supported by our magnetic field extrapolations
from SDO/HMI. Specifically, the supra-arcade fan (similar to those
in solar flares) is likely situated in a current sheet, where the
magnetic field is weak and the plasma-beta could be close to unity, thus
favoring turbulent flows like those prominence threads. In contrast,
the underlying arcade has a stronger magnetic field and most likely a
low-beta environment, such that the material is guided along magnetic
field lines to appear as coronal rain. We will discuss the physical
implications of these observations beyond the phenomena of prominences
and coronal rain.
---------------------------------------------------------
Title: Joint SDO and IRIS Observations of a Novel, Hybrid
Prominence-Coronal Rain Complex
Authors: Liu, Wei; Antolin, Patrick; Sun, Xudong; Gao, Lijia; Vial,
Jean-Claude; Gibson, Sarah; Okamoto, Takenori; Berger, Thomas;
Uitenbroek, Han; De Pontieu, Bart
2016usc..confE..99L Altcode:
Solar prominences and coronal rain are intimately related phenomena,
both involving cool material at chromospheric temperatures within the
hot corona and both playing important roles as part of the return flow
of the chromosphere-corona mass cycle. At the same time, they exhibit
distinct morphologies and dynamics not yet well understood. Quiescent
prominences consist of numerous long-lasting, filamentary downflow
threads, while coronal rain is more transient and falls comparably
faster along well-defined curved paths. We report here a novel, hybrid
prominence-coronal rain complex in an arcade-fan geometry observed
by SDO/AIA and IRIS, which provides new insights to the underlying
physics of such contrasting behaviors. We found that the supra-arcade
fan region hosts a prominence sheet consisting of meandering threads
with broad line widths. As the prominence material descends to the
arcade, it turns into coronal rain sliding down coronal loops with
line widths 2-3 times narrower. This contrast suggests that distinct
local plasma and magnetic conditions determine the fate of the cool
material, a scenario supported by our magnetic field extrapolations
from SDO/HMI. Specifically, the supra-arcade fan (similar to those
in solar flares; e.g., McKenzie 2013) is likely situated in a current
sheet, where the magnetic field is weak and the plasma-beta could be
close to unity, thus favoring turbulent flows like those prominence
threads. In contrast, the underlying arcade has a stronger magnetic
field and most likely a low-beta environment, such that the material
is guided along magnetic field lines to appear as coronal rain. We
will discuss the physical implications of these observations beyond
prominence and coronal rain.
---------------------------------------------------------
Title: Studies Using a Newly Digitized Archive of Global Solar
Magnetic Field Patterns
Authors: Webb, David; Gibson, Sarah; Hewins, Ian; McFadden, Robert;
Emery, Barbara; Denig, William
2016usc..confE..40W Altcode:
In 1964 (Solar Cycle 20) Patrick McIntosh began creating
hand-drawn synoptic maps of solar activity, based on Hα imaging
measurements. These synoptic maps were unique in that they traced
the polarity inversion lines (PILs), connecting widely separated
filaments, fibril patterns and plage corridors to reveal the
large-scale organization of the solar magnetic field. Coronal
hole (CH) boundaries were later added to the maps which were
produced, more or less continuously, into 2009 (start of SC
24), yielding more than 40 years ( 540 Carrington rotations)
or nearly four complete solar cycles of synoptic maps. Under an
NSF grant, these maps are being scanned, digitized and archived
and the final, searchable versions are now publicly available
at NOAA's National Centers for Environmental Information (NCEI) at:
http://www.ngdc.noaa.gov/stp/space-weather/solar-data/solar-imagery/composites/synoptic-maps/mc-intosh/).
We will outline the project and the current status of the archive,
and present some preliminary results demonstrating scientific
applications. For example, computer codes permit efficient searches
of the map arrays. The maps for SC 23 have been completed and we will
show examples of the global evolution of features including filaments,
large-scale positive and negative polarity regions, CHs of each
polarity, CH boundaries, PILs, major sunspots, and plage areas.
---------------------------------------------------------
Title: Scientific objectives and capabilities of the Coronal Solar
Magnetism Observatory
Authors: Tomczyk, S.; Landi, E.; Burkepile, J. T.; Casini, R.; DeLuca,
E. E.; Fan, Y.; Gibson, S. E.; Lin, H.; McIntosh, S. W.; Solomon,
S. C.; Toma, G.; Wijn, A. G.; Zhang, J.
2016JGRA..121.7470T Altcode:
Magnetic influences increase in importance in the solar atmosphere
from the photosphere out into the corona, yet our ability to routinely
measure magnetic fields in the outer solar atmosphere is lacking. We
describe the scientific objectives and capabilities of the COronal Solar
Magnetism Observatory (COSMO), a proposed synoptic facility designed
to measure magnetic fields and plasma properties in the large-scale
solar atmosphere. COSMO comprises a suite of three instruments chosen
to enable the study of the solar atmosphere as a coupled system: (1)
a coronagraph with a 1.5 m aperture to measure the magnetic field,
temperature, density, and dynamics of the corona; (2) an instrument
for diagnostics of chromospheric and prominence magnetic fields and
plasma properties; and (3) a white light K-coronagraph to measure
the density structure and dynamics of the corona and coronal mass
ejections. COSMO will provide a unique combination of magnetic field,
density, temperature, and velocity observations in the corona and
chromosphere that have the potential to transform our understanding
of fundamental physical processes in the solar atmosphere and their
role in the origins of solar variability and space weather.
---------------------------------------------------------
Title: Future space missions and ground observatory for measurements
of coronal magnetic fields
Authors: Fineschi, Silvano; Gibson, Sarah; Bemporad, Alessandro;
Zhukov, Andrei; Damé, Luc; Susino, Roberto; Larruquert, Juan
2016cosp...41E.602F Altcode:
This presentation gives an overview of the near-future perspectives for
probing coronal magnetism from space missions (i.e., SCORE and ASPIICS)
and ground-based observatory (ESCAPE). Spectro-polarimetric imaging of
coronal emission-lines in the visible-light wavelength-band provides an
important diagnostics tool of the coronal magnetism. The interpretation
in terms of Hanle and Zeeman effect of the line-polarization
in forbidden emission-lines yields information on the direction
and strength of the coronal magnetic field. As study case, this
presentation will describe the Torino Coronal Magnetograph (CorMag)
for the spectro-polarimetric observation of the FeXIV, 530.3 nm,
forbidden emission-line. CorMag - consisting of a Liquid Crystal (LC)
Lyot filter and a LC linear polarimeter. The CorMag filter is part
of the ESCAPE experiment to be based at the French-Italian Concordia
base in Antarctica. The linear polarization by resonance scattering
of coronal permitted line-emission in the ultraviolet (UV)can be
modified by magnetic fields through the Hanle effect. Space-based
UV spectro-polarimeters would provide an additional tool for the
disgnostics of coronal magnetism. As a case study of space-borne UV
spectro-polarimeters, this presentation will describe the future upgrade
of the Sounding-rocket Coronagraphic Experiment (SCORE) to include new
generation, high-efficiency UV polarizer with the capability of imaging
polarimetry of the HI Lyman-α, 121.6 nm. SCORE is a multi-wavelength
imager for the emission-lines, HeII 30.4 nm and HI 121.6 nm, and
visible-light broad-band emission of the polarized K-corona. SCORE
has flown successfully in 2009. The second lauch is scheduled in
2016. Proba-3 is the other future solar mission that would provide
the opportunity of diagnosing the coronal magnetic field. Proba-3 is
the first precision formation-flying mission to launched in 2019). A
pair of satellites will fly together maintaining a fixed configuration
as a 'large rigid structure' in space. The paired satellites will
together form a 150-m long solar coronagraph (ASPIICS) to study the
Sun's faint corona closer to the solar limb than has ever before been
achieved. High-resolution imaging in polarized visible-light of shock
waves generated by Coronal Mass Ejections would provide a diagnostics
of the magnetic field in the pre-shock ambient corona.
---------------------------------------------------------
Title: Constraining coronal magnetic field models using coronal
polarimetry
Authors: Dalmasse, Kévin; Nychka, D. W.; Gibson, S. E.; Flyer, N.;
Fan, Y.
2016shin.confE..42D Altcode:
Knowing the 3D coronal magnetic field prior to the trigger of a
coronal mass ejection (CME) is one of the key features for predicting
their geomagnetic effect. Since the magnetic field is essentially
measured at the photosphere, one must rely on models to obtain the
3D magnetic field in the corona. Various coronal observables can then
be used to constrain the parameters, and hence the magnetic field, of
these models. One type of observable that is receiving an increasing
attention is coronal polarization of infrared lines such as the Fe
XIII 10747 A and 10798 A lines observed by the Coronal Multichannel
Polarimeter (CoMP), which are sensitive to the coronal magnetic
field. By combining forward modeling with a novel optimization method
applied to a synthetic test bed of a coronal magnetic flux rope, we
show that the polarimetric signal of coronal infrared lines contains
enough information to constrain the parameters, and hence the magnetic
structure, of coronal magnetic field models. We discuss future plans
for application of our method to solar observations.
---------------------------------------------------------
Title: ROAM: a Radial-basis-function Optimization Approximation
Method for diagnosing the three-dimensional coronal magnetic field
Authors: Dalmasse, Kevin; Nychka, Douglas; Gibson, Sarah; Fan, Yuhong;
Flyer, Natasha
2016FrASS...3...24D Altcode: 2016arXiv160703460D
The Coronal Multichannel Polarimeter (CoMP) routinely performs coronal
polarimetric measurements using the Fe XIII 10747 Å and 10798 Å lines,
which are sensitive to the coronal magnetic field. However, inverting
such polarimetric measurements into magnetic field data is a difficult
task because the corona is optically thin at these wavelengths and
the observed signal is therefore the integrated emission of all the
plasma along the line of sight. To overcome this difficulty, we take
on a new approach that combines a parameterized 3D magnetic field model
with forward modeling of the polarization signal. For that purpose, we
develop a new, fast and efficient, optimization method for model-data
fitting: the Radial-basis-functions Optimization Approximation Method
(ROAM). Model-data fitting is achieved by optimizing a user-specified
log-likelihood function that quantifies the differences between
the observed polarization signal and its synthetic/predicted
analogue. Speed and efficiency are obtained by combining sparse
evaluation of the magnetic model with radial-basis-function (RBF)
decomposition of the log-likelihood function. The RBF decomposition
provides an analytical expression for the log-likelihood function that
is used to inexpensively estimate the set of parameter values optimizing
it. We test and validate ROAM on a synthetic test bed of a coronal
magnetic flux rope and show that it performs well with a significantly
sparse sample of the parameter space. We conclude that our optimization
method is well-suited for fast and efficient model-data fitting and
can be exploited for converting coronal polarimetric measurements,
such as the ones provided by CoMP, into coronal magnetic field data.
---------------------------------------------------------
Title: Diagnostics of Coronal Magnetic Fields Through the Hanle
Effect in UV and IR Lines
Authors: Raouafi, Nour E.; Riley, Pete; Gibson, Sarah; Fineschi,
Silvano; Solanki, Sami K.
2016FrASS...3...20R Altcode: 2016arXiv160608493R
The plasma thermodynamics in the solar upper atmosphere, particularly in
the corona, are dominated by the magnetic field, which controls the flow
and dissipation of energy. The relative lack of knowledge of the coronal
vector magnetic field is a major handicap for progress in coronal
physics. This makes the development of measurement methods of coronal
magnetic fields a high priority in solar physics. The Hanle effect in
the UV and IR spectral lines is a largely unexplored diagnostic. We
use magnetohydrodynamic (MHD) simulations to study the magnitude of the
signal to be expected for typical coronal magnetic fields for selected
spectral lines in the UV and IR wavelength ranges, namely the HI Ly-α
and the He I 10830 Å lines. We show that the selected lines are useful
for reliable diagnosis of coronal magnetic fields. The results show
that the combination of polarization measurements of spectral lines
with different sensitivities to the Hanle effect may be most appropriate
for deducing coronal magnetic properties from future observations.
---------------------------------------------------------
Title: VizieR Online Data Catalog: JCMT Plane Survey: l=30° field
(Moore+, 2015)
Authors: Moore, T. J. T.; Plume, R.; Thompson, M. A.; Parsons,
H.; Urquhart, J. S.; Eden, D. J.; Dempsey, J. T.; Morgan, L. K.;
Thomas, H. S.; Buckle, J.; Brunt, C. M.; Butner, H.; Carretero, D.;
Chrysostomou, A.; Devilliers, H. M.; Fich, M.; Hoare, M. G.; Manser,
G.; Mottram, J. C.; Natario, C.; Olguin, F.; Peretto, N.; Polychroni,
D.; Redman, R. O.; Rigby, A. J.; Salji, C.; Summers, L. J.; Berry, D.;
Currie, M. J.; Jenness, T.; Pestalozzi, M.; Traficante, A.; Bastien,
P.; Difrancesco, J.; Davis, C. J.; Evans, A.; Friberg, P.; Fuller,
G. A.; Gibb, A. G.; Gibson, S.; Hill, T.; Johnstone, D.; Joncas, G.;
Longmore, S. N.; Lumsden, S. L.; Martin, P. G.; Nguyen Luong, Q.;
Pineda, J. E.; Purcell, C.; Richer, J. S.; Schieven, G. H.; Shipman,
R.; Spaans, M.; Taylor, A. R.; Viti, S.; Weferling, B.; White, G. J.;
Zhu, M.
2016yCat..74534264M Altcode:
JPS uses the wide-field submm-band bolometer camera SCUBA-2 (the
Submm Common-User Bolometer Array 2) in the 850um band at a spatial
resolution of 14.5-arcsec. <P />The 850um survey data presented in this
paper cover the l=30° field of the JPS and were observed between 2012
June and 2013 October. The 11 tiles making up the field were observed
on average three times each. A strategy of minimum elevation limits
for given atmospheric opacity bands within the allocated range was
adopted, in order to minimize variations in the resulting noise in
each repeated tile. <P />(1 data file).
---------------------------------------------------------
Title: Tracking a large pseudostreamer to pinpoint the southern
polar magnetic field reversal
Authors: Rachmeler, Laurel; Guennou, Chloé; Seaton, Daniel B.;
Gibson, Sarah; Auchère, Frédéric
2016SPD....4740104R Altcode:
The reversal of the solar polar magnetic field is notoriously hard
to pin down due to the extreme viewing angle of the pole. In Cycle
24, the southern polar field reversal can be pinpointed with high
accuracy due to a large-scale pseudostreamer that formed over the
pole and persisted for approximately a year. We tracked the size
and shape of this structure with multiple observations and analysis
techniques including PROBA2/SWAP EUV images, AIA EUV images, CoMP data,
and 3D tomographic reconstructions. We find that the heliospheric field
reversed polarity in February 2014, whereas in the photosphere the last
vestiges of the previous polar field polarity remained until March 2015.
---------------------------------------------------------
Title: CoMP linear polarization as a probe of coronal magnetic
topology
Authors: Gibson, Sarah; Bak-Steslicka, Urszula; de Toma, Giuliana;
Rachmeler, Laurel A.; Zhang, Mei
2016SPD....4740103G Altcode:
New data from HAO’s Coronal Multichannel Polarimeter (CoMP) have
allowed us for the first time to obtain daily polarimetric observations
of the solar atmosphere, providing unique constraints on coronal
magnetic models. However, due to the relatively-small size of the
telescope, polarization observations are currently limited to linear
polarization measurements, which depend upon the plane-of-sky magnetic
field direction but not its magnitude. Despite this limitation, and
despite the fact that the linearly polarized light measured is optically
thin and so integrated over the line of sight, CoMP linear polarization
has proved useful as a probe of a range of magnetic topologies. In
particular, we will use forward modeling in comparison to CoMP data to
show how linear polarization diagnoses magnetic flux ropes, null points,
pseudostreamers, non-radial expansion factor, and solar cycle evolution.
---------------------------------------------------------
Title: Towards a Data-Optimized Coronal Magnetic Field Model (DOC-FM):
statistical method for diagnosing the coronal magnetic field
Authors: Dalmasse, Kevin; Nychka, Doug; Gibson, Sarah; Fan, Yuhong;
Flyer, Natasha
2016SPD....47.1004D Altcode:
Knowing the 3D coronal magnetic field prior to the trigger of a CME is
one of the key features for predicting their geomagnetic effect. Since
the magnetic field is essentially measured at the photosphere, one
must rely on reconstruction models to obtain the 3D magnetic field in
the corona. Hence, obtaining an accurate model of the real 3D coronal
magnetic field is one of the cornerstones for precise Space Weather
Forecasting. In this work, we propose a new method for data-constrained
reconstruction of the 3D coronal magnetic field. Model-data fitting is
achieved by optimizing a user-specified log-likelihood, quantifying
the difference between a dataset (including e.g. polarization,
extreme-ultraviolet emission, X-ray emission) and its synthetic
analogue. The synthetic data is produced by forward calculations
applied to a 3D magnetic model that depends upon a finite set of
parameters. After introducing the method, we present its validation
on a synthetic test bed consisting of a coronal magnetic flux rope
assumed to depend on three parameters, i.e. latitude, longitude, and
tilt angle. A specific value of each parameter is used to generate
a ground truth and the corresponding synthetic data. We show that
our method performs well and the best-fit parameters provide a good
approximation of the ground-truth parameters. We discuss future plans
for validation and application of our method to solar observations.
---------------------------------------------------------
Title: Simulating Idealized Flux Ropes with the Flux Rope Insertion
Method: A Parameter Space Exploration of Currents and Topology
Authors: Savcheva, Antonia; Tassev, Svetlin; DeLuca, Edward E.;
Gibson, Sarah; Fan, Yuhong
2016SPD....47.0330S Altcode:
Knowledge of the 3D magnetic filed structure at the time of major
solar eruptions is vital to the understanding of the space weather
effects of these eruptions. Multiple data-constrained techniques that
reconstruct the 3D coronal field based on photospheric magnetograms have
been used to achieve this goal. In particular, we have used the flux
rope insertion method to obtain the coronal magnetic field of multiple
regions containing flux ropes or sheared arcades based on line-of-sight
magnetograms and X-ray and EUV observations of coronal loops. For the
purpose of developing statistical measures of the goodness of fit of
these models to the observations, here we present our modeling of flux
ropes based on synthetic magnetograms obtained from aFan & Gibson
emerging flux rope simulation. The goal is to study the effect of of
different input flux rope parameters on the geometry of currents,
field line connectivity, and topology, in a controled setting. For
this purpose we create a large grid of models with the flux rope
insertion method with different combinations of axial and poloidal
flux, which give us different morphology of the flux rope. We create
synthetic images of these flux ropes in AIA passbands with the FORWARD
forward-fitting code. The present parametric study will later be used
to get a better handle on the initial condition for magnetofrictional
and MHD simulations of observed regions containing flux ropes, such
as sigmoids and polar-crown filaments.
---------------------------------------------------------
Title: Preserving a Unique Archive for Long-Term Solar Variability
Studies
Authors: Webb, David F.; Hewins, Ian; McFadden, Robert; Emery, Barbara;
Gibson, Sarah; Denig, William
2016SPD....47.0206W Altcode:
In 1964 (solar cycle 20) Patrick McIntosh began creating hand-drawn
synoptic maps of solar activity, based on Hydrogen alpha (Hα)
imaging measurements. These synoptic maps were unique because
they traced the polarity inversion lines (PILs), connecting widely
separated filaments, fibril patterns and plage corridors to reveal
the large-scale organization of the solar magnetic field. He and his
assistants later included coronal hole (CH) boundaries to the maps,
usually from ground-based He-I 10830 images. They continued making
these maps until 2010 (the start of solar cycle 24), yielding more
than 40 years (~ 540 Carrington rotations) or nearly four complete
solar cycles (SCs) of synoptic maps. The McIntosh collection of maps
forms a unique and consistent set of global solar magnetic field data,
and are unique tools for studying the structure and evolution of the
large-scale solar fields and polarity boundaries, because: 1) they have
excellent spatial resolution for defining polarity boundaries, 2) the
organization of the fields into long-lived, coherent features is clear,
and 3) the data are relatively homogeneous over four solar cycles. After
digitization and archiving, these maps -- along with computer codes
permitting efficient searches of the map arrays -- will be made publicly
available at NOAA’s National Centers for Environmental Information
(NCEI) in their final, searchable form. This poster is a progress
report of the project so far and some suggested scientific applications.
---------------------------------------------------------
Title: Stability Study of Coronal Cavities and Prominences
Authors: de Toma, Giuliana; Gibson, Sarah
2016SPD....47.0339D Altcode:
Cavity/prominence systems are large-scale coronal structures that can
live for many weeks and even months and often end their life in the form
of large coronal eruptions. To determine the role of the surrounding
ambient coronal field in stabilizing thesesystems against eruption, we
examined the extent to which the decline with height of the external
coronal magnetic field influences their evolution and likelihood to
erupt. We selected coronal cavities observed with SDO/AIA during the
rising phase of cycle 24 and divided them in two groups, eruptive and
non-eruptive. The height of the cavity, both at the cavity center and
top, was directly measured from the SDO/AIA images. The ambient coronal
field was derived from a PFSS extrapolation of SDO/HMI magnetograms. We
find that the decay index of the potential field above the coronal
cavity varies significantly in value for both eruptive and non-eruptive
cases but stable cavity systems have, on average, a lower decay index
and less complex topology than the eruptive ones.
---------------------------------------------------------
Title: Division E Commission 49: Interplanetary Plasma and Heliosphere
Authors: Mann, Ingrid; Manoharan, P. K.; Gopalswamy, Natchimuthuk;
Briand, Carine; Chashei, Igor V.; Gibson, Sarah E.; Lario, David;
Hanaoka, Yoichiro; Malandraki, Olga; Kontar, Eduard; Richardson,
John D.
2016IAUTA..29..300M Altcode:
After a little more than forty years of work related to the
interplanetary plasma and the heliosphere the IAU's Commission 49 was
formally discontinued in 2015. The commission started its work when
the first spacecraft were launched to measure the solar wind in-situ
away from Earth orbit, both inward and outward from 1 AU. It now
hands over its activities to a new commission during an era of space
research when Voyager 1 measures in-situ the parameters of the local
interstellar medium at the edge of the heliosphere. The commission will
be succeeded by C.E3 with a similar area of responsibility but with more
focused specific tasks that the community intends to address during the
coming several years. This report includes a short description of the
motivation for this commission and of the historical context. It then
describes work from 2012 to 2015 during the present solar cycle 24 that
has been the weakest in the space era so far. It gave rise to a large
number of studies on solar energetic particles and cosmic rays. Other
studies addressed e.g. the variation of the solar wind structure
and energetic particle fluxes on long time scales, the detection of
dust in the solar wind and the Voyager measurements at the edge of the
heliosphere. The research is based on measurements from spacecraft that
are at present operational and motivated by the upcoming Solar Probe
+ and Solar Orbiter missions to explore the vicinity of the Sun. We
also report here the progress on new and planned radio instruments
and their importance for heliospheric studies. Contributors to this
report are Carine Briand, Yoichiro Hanaoka, Eduard Kontar, David Lario,
Ingrid Mann, John D. Richardson.
---------------------------------------------------------
Title: Division E Commission 10: Solar Activity
Authors: Schrijver, Carolus J.; Fletcher, Lyndsay; van Driel-Gesztelyi,
Lidia; Asai, Ayumi; Cally, Paul S.; Charbonneau, Paul; Gibson, Sarah
E.; Gomez, Daniel; Hasan, Siraj S.; Veronig, Astrid M.; Yan, Yihua
2016IAUTA..29..245S Altcode: 2015arXiv151003348S
After more than half a century of community support related to the
science of “solar activity”, IAU's Commission 10 was formally
discontinued in 2015, to be succeeded by C.E2 with the same area
of responsibility. On this occasion, we look back at the growth of
the scientific disciplines involved around the world over almost a
full century. Solar activity and fields of research looking into the
related physics of the heliosphere continue to be vibrant and growing,
with currently over 2,000 refereed publications appearing per year from
over 4,000 unique authors, publishing in dozens of distinct journals
and meeting in dozens of workshops and conferences each year. The
size of the rapidly growing community and of the observational and
computational data volumes, along with the multitude of connections
into other branches of astrophysics, pose significant challenges;
aspects of these challenges are beginning to be addressed through,
among others, the development of new systems of literature reviews,
machine-searchable archives for data and publications, and virtual
observatories. As customary in these reports, we highlight some
of the research topics that have seen particular interest over the
most recent triennium, specifically active-region magnetic fields,
coronal thermal structure, coronal seismology, flares and eruptions,
and the variability of solar activity on long time scales. We close
with a collection of developments, discoveries, and surprises that
illustrate the range and dynamics of the discipline.
---------------------------------------------------------
Title: Line-of-sight velocity as a tracer of coronal cavity magnetic
structure
Authors: Bak-Steslicka, Urszula; Gibson, Sarah; Chmielewska, Ewa
2016FrASS...3....7B Altcode:
We present a statistical analysis of 66 days of observations of
quiescent (non-erupting) coronal cavities and associated velocity
and thermal structures. We find that nested rings of LOS-oriented
velocity are common in occurrence and spatially well correlated with
cavities observed in emission. We find that the majority of cavities
possess multiple rings, and a range in velocity on the order of several
km/sec. We find that the tops of prominences lie systematically below
the cavity center and location of largest Doppler velocity. Finally, we
use DEM analysis to consider the temperature structure of two cavities
in relation to cavity, prominence, and flows. These observations
yield new constraints on the magnetic structure of cavities, and on
the conditions leading up to solar eruptions.
---------------------------------------------------------
Title: FORWARD: A toolset for multiwavelength coronal magnetometry
Authors: Gibson, Sarah; Kucera, Therese; White, Stephen; Dove,
James; Fan, Yuhong; Forland, Blake; Rachmeler, Laurel; Downs, Cooper;
Reeves, Katharine
2016FrASS...3....8G Altcode:
Determining the 3D coronal magnetic field is a critical, but extremely
difficult problem to solve. Since different types of multiwavelength
coronal data probe different aspects of the coronal magnetic field,
ideally these data should be used together to validate and constrain
specifications of that field. Such a task requires the ability to create
observable quantities at a range of wavelengths from a distribution
of magnetic field and associated plasma -- i.e., to perform forward
calculations. In this paper we describe the capabilities of the FORWARD
SolarSoft IDL package, a uniquely comprehensive toolset for coronal
magnetometry. FORWARD is a community resource that may be used both
to synthesize a broad range of coronal observables, and to access and
compare synthetic observables to existing data. It enables forward
fitting of specific observations, and helps to build intuition into
how the physical properties of coronal magnetic structures translate to
observable properties. FORWARD can also be used to generate synthetic
test beds from MHD simulations in order to facilitate the development
of coronal magnetometric inversion methods, and to prepare for the
analysis of future large solar telescope data.
---------------------------------------------------------
Title: Waves and Magnetism in the Solar Atmosphere (WAMIS)
Authors: Ko, Yuan-Kuen; Moses, John; Laming, John; Strachan, Leonard;
Tun Beltran, Samuel; Tomczyk, Steven; Gibson, Sarah; Auchere, Frederic;
Casini, Roberto; Fineschi, Silvano; Knoelker, Michael; Korendyke,
Clarence; McIntosh, Scott; Romoli, Marco; Rybak, Jan; Socker, Dennis;
Vourlidas, Angelos; Wu, Qian
2016FrASS...3....1K Altcode:
Comprehensive measurements of magnetic fields in the solar corona have
a long history as an important scientific goal. Besides being crucial
to understanding coronal structures and the Sun’s generation of space
weather, direct measurements of their strength and direction are also
crucial steps in understanding observed wave motions. In this regard,
the remote sensing instrumentation used to make coronal magnetic field
measurements is well suited to measuring the Doppler signature of waves
in the solar structures. In this paper, we describe the design and
scientific values of the Waves and Magnetism in the Solar Atmosphere
(WAMIS) investigation. WAMIS, taking advantage of greatly improved
infrared filters and detectors, forward models, advanced diagnostic
tools and inversion codes, is a long-duration high-altitude balloon
payload designed to obtain a breakthrough in the measurement of
coronal magnetic fields and in advancing the understanding of the
interaction of these fields with space plasmas. It consists of a 20 cm
aperture coronagraph with a visible-IR spectro-polarimeter focal plane
assembly. The balloon altitude would provide minimum sky background and
atmospheric scattering at the wavelengths in which these observations
are made. It would also enable continuous measurements of the strength
and direction of coronal magnetic fields without interruptions from
the day-night cycle and weather. These measurements will be made
over a large field-of-view allowing one to distinguish the magnetic
signatures of different coronal structures, and at the spatial and
temporal resolutions required to address outstanding problems in
coronal physics. Additionally, WAMIS could obtain near simultaneous
observations of the electron scattered K-corona for context and to
obtain the electron density. These comprehensive observations are not
provided by any current single ground-based or space observatory. The
fundamental advancements achieved by the near-space observations of
WAMIS on coronal field would point the way for future ground based
and orbital instrumentation.
---------------------------------------------------------
Title: Probing Solar Eruption by Tracking Magnetic Cavities and
Filaments
Authors: Sterling, A. C.; Johnson, J. R.; Moore, R. L.; Gibson, S. E.
2015AGUFMSH53B2489S Altcode:
A solar eruption is a tremendous explosion on the Sun that happens when
energy stored in twisted (or distorted) magnetic fields is suddenly
released. When this field is viewed along the axis of the twist in
projection at the limb, e.g. in EUV or white-light coronal images,
the outer portions of the pre-eruption magnetic structure sometimes
appears as a region of weaker emission, called a "coronal cavity,"
surrounded by a brighter envelope. Often a chromospheric filament
resides near the base of the cavity and parallel to the cavity's central
axis. Typically, both the cavity and filament move outward from the Sun
at the start of an eruption of the magnetic field in which the cavity
and filament reside. Studying properties the cavities and filaments
just prior to and during eruption can help constrain models that
attempt to explain why and how the eruptions occur. In this study,
we examined six different at-limb solar eruptions using images from
the Extreme Ultraviolet Imaging Telescope (EIT) aboard the Solar and
Heliospheric Observatory (SOHO). For four of these eruptions we observed
both cavities and filaments, while for the remaining two eruptions,
one had only a cavity and the other only a filament visible in EIT
images. All six eruptions were in comparatively-quiet solar regions,
with one in the neighborhood of the polar crown. We measured the height
and velocities of the cavities and filaments just prior to and during
the start of their fast-eruption onsets. Our results support that the
filament and cavity are integral parts of a single large-scale erupting
magnetic-field system. We examined whether the eruption-onset heights
were correlated with the expected magnetic field strengths of the
eruption-source regions, but no clear correlation was found. We discuss
possible reasons for this lack of correlation, and we also discuss
future research directions. The research performed was supported
by the National Science Foundation under Grant No. AGS-1460767;
J.J. participated in the Research Experience for Undergraduates (REU)
program, at NASA/MSFC. Additional support was from a grant from the
NASA LWS program.
---------------------------------------------------------
Title: Three-Dimensional Reconstruction of the Electron Density in
the Solar Corona
Authors: Burnett, L. W.; Nychka, D. W.; Gibson, S. E.; Dalmasse, K.
2015AGUFMSH53B2495B Altcode:
The need to understand the Sun's magnetic field motivates much
of present-day solar physics research. Our ultimate goal is to
quantitatively validate models of the global coronal magnetic field by
comparing forward models of synthetic data to real observations. As a
necessary first step, we seek to build a three-dimensional (3D) model
of the electron density in the solar corona, based on white-light
coronagraph data. Given that these observations are two-dimensional
snapshots, we employ a new application of statistical tomography to
piece together the full 3D picture. In an initial step, we demonstrate
that our method is capable of reconstructing geometrically-simple
density formations. We next turn to more realistic coronal density
structures as represented by the global magnetohydrodynamic models made
available by Predictive Science Inc., and integrated to create synthetic
data using the FORWARD SolarSoft codes. Finally, we consider the
application of our method to Mauna Loa Solar Observatory K-Coronagraph
observations, and discuss the strengths and limitations of our method.
---------------------------------------------------------
Title: Towards a Data-Optimized Coronal Magnetic Field Model (DOC-FM):
Synthetic Test Beds and Multiwavelength Forward Modeling
Authors: Gibson, S. E.; Dalmasse, K.; Fan, Y.; Fineschi, S.; MacKay,
D.; Rempel, M.; White, S. M.
2015AGUFMSH54B..04G Altcode:
Understanding the physical state of the solar corona is key to
deciphering the origins of space weather as well as to realistically
representing the environment to be navigated by missions such as
Solar Orbiter and Solar Probe Plus. However, inverting solar coronal
observations to reconstruct this physical state -- and in particular
the three-dimensional coronal magnetic field - is complicated by
limited lines of sight and by projection effects. On the other hand,
the sensitivity of multiwavelength observations to different physical
mechanisms implies a potential for simultaneous probing of different
parts of the coronal plasma. In order to study this complementarity, and
to ultimately establish an optimal set of observations for constraining
the three-dimensional coronal magnetic field, we are developing a suite
of representative simulations to act as diagnostic test beds. We will
present three such test beds: a coronal active region, a quiescent
prominence, and a global corona. Each fully define the physical state
of density, temperature, and vector magnetic field in three dimensions
throughout the simulation domain. From these test beds, and using the
FORWARD SolarSoft IDL codes, we will create a broad range of synthetic
data. Radio observables will include intensity and circular polarization
(including gyroresonance effects) and Faraday rotation for a range of
frequencies. Infrared and visible forbidden line diagnostics of Zeeman
and saturated Hanle effects will yield full Stokes vector (I, Q, U,
V) synthetic data, and UV permitted line Hanle diagnostics will yield
intensity and linear polarization. In addition, we will synthesize
UV and SXR imager data, UV/EUV spectrometric data, and white light
brightness and polarized brightness. All of these synthetic data,
along with the "ground truth" physical state of the simulations from
which they are derived, will be made available to the community for
the purpose of testing coronal inversion techniques.
---------------------------------------------------------
Title: Towards a Data-Optimized Coronal Magnetic Field Model (DOC-FM):
Simulating Flux Ropes with the Flux Rope Insertion Method
Authors: Dalmasse, K.; DeLuca, E. E.; Savcheva, A. S.; Gibson, S. E.;
Fan, Y.
2015AGUFMSH51B2444D Altcode:
Knowledge of the 3D magnetic filed structure at the time of major solar
eruptions is vital or understanding of the space weather effects of
these eruptions. Multiple data-constrained techniques that reconstruct
the 3D coronal field based on photospheric magnetograms have been
used to achieve this goal. In particular, we have used the flux rope
insertion method to obtain the coronal magnetic field of multiple
regions containing flux ropes or sheared arcades based on line-of-sight
magnetograms and X-ray and EUV observations of coronal loops. For the
purpose of developing statistical measures of the goodness of fit of
these models to the observations, here we present our modeling of flux
ropes based on synthetic magnetograms obtained from Fan & Gibson
emerging flux rope simulation. The goal is to reproduce the flux rope
structure from a given time step of the MHD simulations based only
on the photospheric magnetogram and synthetic forward modeled coronal
emission obtained from the same step of the MHD simulation. For this
purpose we create a large grid of models with the flux rope insertion
method with different combinations of axial and poloidal flux, which
give us different morphology of the flux rope. Then we compare the
synthetic coronal emission with the shape of the current distribution
and field lines from the models to come up with a best fit. This fit
is then tested using the statistical methods developed by our team.
---------------------------------------------------------
Title: a Roadmap to Advance Understanding of the Science of Space
Weather
Authors: Schrijver, K.; Kauristie, K.; Aylward, A.; De Nardin, C. M.;
Gibson, S. E.; Glover, A.; Gopalswamy, N.; Grande, M.; Hapgood, M. A.;
Heynderickx, D.; Jakowski, N.; Kalegaev, V. V.; Lapenta, G.; Linker,
J.; Liu, S.; Mandrini, C. H.; Mann, I. R.; Nagatsuma, T.; Nandy, D.;
Obara, T.; O'Brien, T. P., III; Onsager, T. G.; Opgenoorth, H. J.;
Terkildsen, M. B.; Valladares, C. E.; Vilmer, N.
2015AGUFMSH12A..01S Altcode:
There is a growing appreciation that the environmental conditions that
we call space weather impact the technological infrastructure that
powers the coupled economies around the world. With that comes the need
to better shield society against space weather by improving forecasts,
environmental specifications, and infrastructure design. A COSPAR/ILWS
team recently completed a roadmap that identifies the scientific focus
areas and research infrastructure that are needed to significantly
advance our understanding of space weather of all intensities and of
its implications and costs for society. This presentation provides a
summary of the highest-priority recommendations from that roadmap.
---------------------------------------------------------
Title: Towards a Data-Optimized Coronal Magnetic Field Model (DOC-FM):
Statistical Method for Diagnosing the Coronal Magnetic Field
Authors: Dalmasse, K.; Nychka, D. W.; Gibson, S. E.; Fan, Y.
2015AGUFMSH21B2395D Altcode:
Solar coronal mass ejections (CMEs) and solar flares are the
main drivers of space weather. Their potential impact on Earth is
determined by the morphology and orientation of the magnetic structure
associated with these events and its evolution as it propagates into the
interplanetary magnetic field. Knowing the 3D coronal magnetic field
prior to the trigger of a CME is therefore one of the key features
for predicting their geomagnetic effect. Since the magnetic field is
essentially measured at the photosphere, one must rely on reconstruction
models to obtain the 3D magnetic field in the corona. Hence, obtaining
an accurate model of the real 3D coronal magnetic field is one of
the cornerstones for precise Space Weather Forecasting. In this work,
we propose a new method for data-constrained reconstruction of the 3D
coronal magnetic field. Model-data fitting is achieved by optimizing
a user-specified metric, M, quantifying the difference between a
dataset (including e.g. polarization, extreme-ultraviolet emission,
X-ray emission) and its synthetic analogue. The synthetic data is
produced by forward calculations applied to a 3D magnetic model that
depends upon a finite set of parameters. After introducing the method,
we present its validation on a synthetic test bed consisting of a
coronal magnetic flux rope assumed to depend on four parameters,
i.e. height in the corona, latitude, longitude, and tilt angle. A
specific value of each parameter is used to generate a ground truth
and the corresponding synthetic data. We show that, when M does not
possess any degenerate minimum, our method performs well and the
best-fit parameters provide a good approximation of the ground-truth
parameters. We then show how using additional observations can help
in removing any existing degeneracy. Finally, we discuss future plans
for validation and application of our method to solar observations.
---------------------------------------------------------
Title: The JCMT Plane Survey: early results from the ℓ = 30° field
Authors: Moore, T. J. T.; Plume, R.; Thompson, M. A.; Parsons,
H.; Urquhart, J. S.; Eden, D. J.; Dempsey, J. T.; Morgan, L. K.;
Thomas, H. S.; Buckle, J.; Brunt, C. M.; Butner, H.; Carretero, D.;
Chrysostomou, A.; deVilliers, H. M.; Fich, M.; Hoare, M. G.; Manser,
G.; Mottram, J. C.; Natario, C.; Olguin, F.; Peretto, N.; Polychroni,
D.; Redman, R. O.; Rigby, A. J.; Salji, C.; Summers, L. J.; Berry, D.;
Currie, M. J.; Jenness, T.; Pestalozzi, M.; Traficante, A.; Bastien,
P.; diFrancesco, J.; Davis, C. J.; Evans, A.; Friberg, P.; Fuller,
G. A.; Gibb, A. G.; Gibson, S.; Hill, T.; Johnstone, D.; Joncas, G.;
Longmore, S. N.; Lumsden, S. L.; Martin, P. G.; Nguyen Lu'o'ng, Q.;
Pineda, J. E.; Purcell, C.; Richer, J. S.; Schieven, G. H.; Shipman,
R.; Spaans, M.; Taylor, A. R.; Viti, S.; Weferling, B.; White, G. J.;
Zhu, M.
2015MNRAS.453.4264M Altcode: 2015arXiv150900318M
We present early results from the JCMT (James Clerk Maxwell Telescope)
Plane Survey (JPS), which has surveyed the northern inner Galactic
plane between longitudes ℓ = 7° and ℓ = 63° in the 850-μm
continuum with SCUBA-2 (Submm Common-User Bolometer Array 2),
as part of the JCMT Legacy Survey programme. Data from the ℓ =
30° survey region, which contains the massive-star-forming regions
W43 and G29.96, are analysed after approximately 40 per cent of the
observations had been completed. The pixel-to-pixel noise is found to
be 19 mJy beam<SUP>-1</SUP> after a smooth over the beam area, and the
projected equivalent noise levels in the final survey are expected to
be around 10 mJy beam<SUP>-1</SUP>. An initial extraction of compact
sources was performed using the FELLWALKER method, resulting in the
detection of 1029 sources above a 5σ surface-brightness threshold. The
completeness limits in these data are estimated to be around 0.2 Jy
beam<SUP>-1</SUP> (peak flux density) and 0.8 Jy (integrated flux
density) and are therefore probably already dominated by source
confusion in this relatively crowded section of the survey. The flux
densities of extracted compact sources are consistent with those
of matching detections in the shallower APEX (Atacama Pathfinder
Experiment) Telescope Large Area Survey of the Galaxy (ATLASGAL)
survey. We analyse the virial and evolutionary state of the detected
clumps in the W43 star-forming complex and find that they appear
younger than the Galactic-plane average.
---------------------------------------------------------
Title: Waves and Magnetism in the Solar Atmosphere (WAMIS)
Authors: Strachan, L.; Ko, Y. -K.; Moses, J. D.; Laming, J. M.;
Auchere, F.; Casini, R.; Fineschi, S.; Gibson, S.; Knoelker, M.;
Korendyke, C.; Mcintosh, S.; Romoli, M.; Rybak, J.; Socker, D.;
Tomczyk, S.; Vourlidas, A.; Wu, Q.
2015IAUS..305..121S Altcode:
Magnetic fields in the solar atmosphere provide the energy for most
varieties of solar activity, including high-energy electromagnetic
radiation, solar energetic particles, flares, and coronal mass
ejections, as well as powering the solar wind. Despite the fundamental
role of magnetic fields in solar and heliospheric physics, there
exist only very limited measurements of the field above the base of
the corona. What is needed are direct measurements of not only the
strength and orientation of the magnetic field but also the signatures
of wave motions in order to better understand coronal structure, solar
activity, and the role of MHD waves in heating and accelerating the
solar wind. Fortunately, the remote sensing instrumentation used to make
magnetic field measurements is also well suited to measure the Doppler
signature of waves in the solar structures. We present here a mission
concept for the Waves And Magnetism In the Solar Atmosphere (WAMIS)
experiment which is proposed for a NASA long-duration balloon flight.
---------------------------------------------------------
Title: Data-model comparison using FORWARD and CoMP
Authors: Gibson, Sarah
2015IAUS..305..245G Altcode: 2015arXiv151104416G
The FORWARD SolarSoft IDL package is a community resource for model-data
comparison, with a particular emphasis on analyzing coronal magnetic
fields. FORWARD allows the synthesis of coronal polarimetric signals
at visible, infrared, and radio frequencies, and will soon be augmented
for ultraviolet polarimetry. In this paper we focus on observations of
the infrared (IR) forbidden lines of Fe XIII, and describe how FORWARD
may be used to directly access these data from the Mauna Loa Solar
Observatory Coronal Multi-channel Polarimeter (MLSO/CoMP), to put them
in the context of other space- and ground-based observations, and to
compare them to synthetic observables generated from magnetohydrodynamic
(MHD) models.
---------------------------------------------------------
Title: Magnetism Matters: Coronal Magnetometry Using Multi-Wavelength
Polarimetry
Authors: Gibson, Sarah E.
2015IAUGA..2230393G Altcode:
The solar coronal magnetic field is key both to solving fundamental
problems in solar physics such as coronal heating and solar wind
acceleration, and to predicting the internal magnetic structure
and thus space-weather impact of coronal mass ejections. I will
describe the current state of the art in coronal magnetometry, and
present results from the Coronal Multichannel Polarimeter (CoMP)
at Mauna Loa Solar Observatory (MLSO), which since 2011 has taken
polarimetric observations of the solar corona in the near-infrared
on a near-daily basis. I will discuss work in progress that utilizes
forward modeling to synthesize polarimetric data at multiple heights
and vantage points, and at wavelengths from radio to infrared to
visible to ultraviolet. The goal is to use such synthetic testbeds to
determine the ideal set of observations for constraining the coronal
magnetic field, and to establish a Data-Optimized Coronal Field Model
(DOC-FM) that efficiently incorporates these data into global magnetic
models. This work will provide essential tools and motivation for the
planning and implementation of future coronal polarimetric projects
and missions spanning a broad range of wavelengths.
---------------------------------------------------------
Title: Understanding space weather to shield society: A global road
map for 2015-2025 commissioned by COSPAR and ILWS
Authors: Schrijver, Carolus J.; Kauristie, Kirsti; Aylward, Alan D.;
Denardini, Clezio M.; Gibson, Sarah E.; Glover, Alexi; Gopalswamy,
Nat; Grande, Manuel; Hapgood, Mike; Heynderickx, Daniel; Jakowski,
Norbert; Kalegaev, Vladimir V.; Lapenta, Giovanni; Linker, Jon A.;
Liu, Siqing; Mandrini, Cristina H.; Mann, Ian R.; Nagatsuma, Tsutomu;
Nandy, Dibyendu; Obara, Takahiro; Paul O'Brien, T.; Onsager, Terrance;
Opgenoorth, Hermann J.; Terkildsen, Michael; Valladares, Cesar E.;
Vilmer, Nicole
2015AdSpR..55.2745S Altcode: 2015arXiv150306135S
There is a growing appreciation that the environmental conditions
that we call space weather impact the technological infrastructure
that powers the coupled economies around the world. With that comes
the need to better shield society against space weather by improving
forecasts, environmental specifications, and infrastructure design. We
recognize that much progress has been made and continues to be made
with a powerful suite of research observatories on the ground and
in space, forming the basis of a Sun-Earth system observatory. But
the domain of space weather is vast - extending from deep within the
Sun to far outside the planetary orbits - and the physics complex
- including couplings between various types of physical processes
that link scales and domains from the microscopic to large parts
of the solar system. Consequently, advanced understanding of space
weather requires a coordinated international approach to effectively
provide awareness of the processes within the Sun-Earth system through
observation-driven models. This roadmap prioritizes the scientific focus
areas and research infrastructure that are needed to significantly
advance our understanding of space weather of all intensities and
of its implications for society. Advancement of the existing system
observatory through the addition of small to moderate state-of-the-art
capabilities designed to fill observational gaps will enable significant
advances. Such a strategy requires urgent action: key instrumentation
needs to be sustained, and action needs to be taken before core
capabilities are lost in the aging ensemble. We recommend advances
through priority focus (1) on observation-based modeling throughout the
Sun-Earth system, (2) on forecasts more than 12 h ahead of the magnetic
structure of incoming coronal mass ejections, (3) on understanding
the geospace response to variable solar-wind stresses that lead to
intense geomagnetically-induced currents and ionospheric and radiation
storms, and (4) on developing a comprehensive specification of space
climate, including the characterization of extreme space storms to guide
resilient and robust engineering of technological infrastructures. The
roadmap clusters its implementation recommendations by formulating
three action pathways, and outlines needed instrumentation and research
programs and infrastructure for each of these. An executive summary
provides an overview of all recommendations.
---------------------------------------------------------
Title: Coronal Cavities: Observations and Implications for the
Magnetic Environment of Prominences
Authors: Gibson, Sarah
2015ASSL..415..323G Altcode: 2017arXiv170202214G
Dark and elliptical, coronal cavities yield important clues to the
magnetic structures that cradle prominences, and to the forces that
ultimately lead to their eruption. We review observational analyses
of cavity morphology, thermal properties (density and temperature),
line-of-sight and plane-of-sky flows, substructure including hot cores
and central voids, linear polarization signatures, and observational
precursors and predictors of eruption. We discuss a magnetohydrodynamic
interpretation of these observations which argues that the cavity is a
magnetic flux rope, and pose a set of open questions for further study.
---------------------------------------------------------
Title: Coronal Magnetism and Forward Solarsoft Idl Package
Authors: Gibson, S. E.
2014AGUFMSH13A4065G Altcode:
The FORWARD suite of Solar Soft IDL codes is a community resource
for model-data comparison, with a particular emphasis on analyzing
coronal magnetic fields. FORWARD may be used both to synthesize a broad
range of coronal observables, and to access and compare to existing
data. FORWARD works with numerical model datacubes, interfaces with
the web-served Predictive Science Inc MAS simulation datacubes and
the Solar Soft IDL Potential Field Source Surface (PFSS) package, and
also includes several analytic models (more can be added). It connects
to the Virtual Solar Observatory and other web-served observations to
download data in a format directly comparable to model predictions. It
utilizes the CHIANTI database in modeling UV/EUV lines, and links to the
CLE polarimetry synthesis code for forbidden coronal lines. FORWARD
enables "forward-fitting" of specific observations, and helps to
build intuition into how the physical properties of coronal magnetic
structures translate to observable properties.
---------------------------------------------------------
Title: 3D Location of Small Solar Wind Tracers
Authors: Lopez-Portela, C.; Blanco-Cano, X.; Panasenco, O.; Gibson,
S. E.
2014AGUFMSH21B4126L Altcode:
The so-called "blobs" as defined in Sheeley et al., 1997, are
small-scale structures embedded in the continuously expanding
white-light solar corona and are considered to be tracers of the
slow solar wind. As blobs are very faint structures, we considered
long periods (around 2 to 5 days) where there were no coronal mass
ejections (CME). The scarce presence of CMEs during the extended past
solar minimum has permitted the identification of continuous blobs
detachments, allowing us to estimate their un-projected trajectories
between 2 and 15 solar radii (Mierla et al., 2008). In agreement with
the idea that blobs are liberated from the cusps of helmet steamers
(Wang et al., 1998), we constrained the observing region of interest
in the coronagraphs field of view to ±30° from the Sun's equator. We
studied cases where blobs were detected by the coronagraphs C2/LASCO
and COR2/SECCHI, and inferred their source locations using two
packages that implement the 3D potential field source surface (PFSS)
model: (1) PFSS developed by De Rosa (2010) and (2) PFSS (De Rosa)
in FORWARD (people.hao.ucar.edu/sgibson/FORWARD/). The locations of
the origin of blobs that we find, support previous results that track
down the origin of the slow solar wind to regions near the helmet
streamers and pseudostreamers (Wang et al., 2012, Riley&Luhmann,
2012). Additionally, we found that in some cases blobs are coming
from the boundaries of growing or decaying equatorial coronal holes,
where the interchange reconnection issupposed to be faster.
---------------------------------------------------------
Title: Waves and Magnetism in the Solar Atmosphere (WAMIS)
Authors: Ko, Y. K.; Auchere, F.; Casini, R.; Fineschi, S.; Gibson,
S. E.; Knoelker, M.; Korendyke, C.; Laming, J. M.; Mcintosh, S. W.;
Moses, J. D.; Romoli, M.; Rybak, J.; Socker, D. G.; Strachan, L.;
Tomczyk, S.; Vourlidas, A.; Wu, Q.
2014AGUFMSH53B4221K Altcode:
Magnetic fields in the solar atmosphere provide the energy for most
varieties of solar activity, including high-energy electromagnetic
radiation, solar energetic particles, flares, and coronal mass
ejections, as well as powering the solar wind. Despite the fundamental
role of magnetic fields in solar and heliospheric physics, there
exists only very limited measurements of the field above the base of
the corona. What is needed are direct measurements of not only the
strength and orientation of the magnetic field but also the signatures
of wave motions in order to better understand coronal structure,
solar activity and the role of MHD waves in heating and accelerating
the solar wind. Fortunately, the remote sensing instrumentation used
to make magnetic field measurements is also well suited for measuring
the Doppler signature of waves in the solar structures. With this
in mind, we are proposing the WAMIS (Waves and Magnetism in the
Solar Atmosphere) investigation. WAMIS will take advantage of greatly
improved infrared (IR) detectors, forward models, advanced diagnostic
tools and inversion codes to obtain a breakthrough in the measurement
of coronal magnetic fields and in the understanding of the interaction
of these fields with space plasmas. This will be achieved with a high
altitude balloon borne payload consisting of a coronagraph with an IR
spectro-polarimeter focal plane assembly. The balloon platform provides
minimum atmospheric absorption and scattering at the IR wavelengths in
which these observations are made. Additionally, a NASA long duration
balloon flight mission from the Antarctic can achieve continuous
observations over most of a solar rotation, covering all of the key
time scales for the evolution of coronal magnetic fields. With these
improvements in key technologies along with experience gained from
current ground-based instrumentation, WAMIS will provide a low-cost
mission with a high technology readiness leve.
---------------------------------------------------------
Title: Statistical study of the origin and 3D acceleration profile
of small solar wind tracers (blobs)
Authors: Lopez-Portela, Cynthia; Blanco-Cano, Xóchtil; Gibson, Sarah;
Panansenco, Olga
2014shin.confE..44L Altcode:
Blobs are small density enhancements observed in the solar corona
(Sheeley et al. 1997). The study of blob propagation is important
because they are considered to be tracers of the slow component of the
solar wind. To explore the physical mechanisms behind the propagation
of the slow solar wind, we have studied the kinematics of blobs
embedded in the continuously expanding solar corona along the years
2007 to 2008, i.e., during the extended past solar minimum. The
scarce presence of CMEs events during the selected periods of
observation, has permitted the identification of around 100 blob-like
structures on the LASCO and SECCHI coronagraphs on board SOHO and
STEREO missions, respectively. This allowed us to estimate their
un-projected trajectories between 2 and 15 solar radii, using the
Height-Time technique (Mierla et al., 2008). In agreement with the
idea that blobs are liberated from the cusps of helmet steamers (Wang
et al., 1998) and considering their latitudinal distribution during
the selected periods of observation, we constrained the observing
region of interest in the coronagraphs field of view to ≤30°
from the Sun's equator. We inferred their location in the close
solar corona by the tridimensional Potential Field Source Surface
(PFSS) developed by De Rosa (2003) and implemented in the FORWARD
package (people.hao.ucar.edu/sgibson/FORWARD/). Our results support
previous findings that track down the origin of the slow solar wind to
neighboring regions of helmet streamers and pseudostreamers (Wiegelmann
et al., 1998, Wang et al., 2012).
---------------------------------------------------------
Title: FORWARD: Forward modeling of coronal observables
Authors: Gibson, Sarah E.; Kucera, Therese A.; Casini, Roberto; Dove,
James; Forland, Blake; Judge, Philip; Rachmeler, Laurel
2014ascl.soft05007G Altcode: 2014ascl.soft05007F
FORWARD forward models various coronal observables and can access
and compare existing data. Given a coronal model, it can produce
many different synthetic observables (including Stokes polarimetry),
as well as plots of model plasma properties (density, magnetic field,
etc.). It uses the CHIANTI database (ascl:9911.004) and CLE polarimetry
synthesis code, works with numerical model datacubes, interfaces with
the PFSS module of SolarSoft (ascl:1208.013), includes several analytic
models, and connects to the Virtual Solar Observatory for downloading
data in a format directly comparable to model predictions.
---------------------------------------------------------
Title: LOS velocity as a tracer of coronal cavity magnetic structure
Authors: Bak-Steslicka, Urszula; Gibson, Sarah; Fan, Yuhong
2014cosp...40E.184B Altcode:
The Coronal Multi-Channel Polarimeter (CoMP) makes daily observations
of the lower corona in linear polarization, but also measures Doppler
shifts, which allows us to obtain the line-of-sight velocity of
coronal plasma. CoMP observations of polarization of coronal emission
allows, for the first time, an analysis of the coronal magnetic field
direction in quiescent prominence cavities. We present an analysis
of Doppler velocity measurements of the numerous quiescent prominence
cavities. Such observations are common in cavities and characteristic
concentric circles of different values of flow may appear. CoMP data
analysis of quiescent cavities is important for understanding pre-CME
configuration.
---------------------------------------------------------
Title: The Formation of a Cavity in a 3D Flux Rope
Authors: Schmit, Donald; Gibson, Sarah
2014IAUS..300..147S Altcode: 2013arXiv1311.2384S
There are currently no three dimensional numerical models which
describe the magnetic and energetic formation of prominences
self-consistently. Consequently, there has not been significant progress
made in understanding the connection between the dense prominence
plasma and the coronal cavity. We have taken an ad-hoc approach to
understanding the energetic implications of the magnetic models of
prominence structure. We extract one dimensional magnetic field lines
from a 3D MHD model of a flux rope and solve for hydrostatic balance
along these field lines incorporating field-aligned thermal conduction,
uniform heating, and radiative losses. The 1D hydrostatic solutions for
density and temperature are then mapped back into three dimensional
space, which allows us to consider the projection of multiple
structures. We find that the 3D flux rope is composed of several
distinct field line types. A majority of the flux rope interior field
lines are twisted but not dipped. These field lines are density-reduced
relative to unsheared arcade field lines. We suggest the cavity may
form along these short interior field lines which are surrounded by a
sheath of dipped field lines. This geometric arrangement would create a
cavity on top of a prominence, but the two structures would not share
field lines or plasma.
---------------------------------------------------------
Title: FORWARD: A toolset for analyzing coronal magnetic fields
Authors: Gibson, Sarah
2014cosp...40E.986G Altcode:
The FORWARD suite of Solar Soft IDL codes is a community resource for
model-data comparison, with a particular emphasis on analyzing coronal
magnetic fields. FORWARD may be used both to synthesize a broad range of
coronal observables, and to access and compare to existing data. FORWARD
works with numerical model datacubes, interfaces with the Solar Soft
IDL Potential Field Source Surface (PFSS) package, and also includes
several analytic models (more can be added). It utilizes the Chianti
database, and connects to the Virtual Solar Observatory to download
data in a format directly comparable to model predictions. FORWARD
enables "forward-fitting" of specific observations, and helps to
build intuition into how the physical properties of coronal magnetic
structures translate to observable properties.
---------------------------------------------------------
Title: The solar physics FORWARD codes: Now with widgets!
Authors: Forland, Blake; Gibson, Sarah; Dove, James; Kucera, Therese
2014IAUS..300..414F Altcode:
We have developed a suite of forward-modeling IDL codes (FORWARD)
to convert analytic models or simulation data cubes into coronal
observables, allowing a direct comparison with observations. Observables
such as extreme ultraviolet, soft X-ray, white light, and polarization
images from the Coronal Multichannel Polarimeter (CoMP) can be
reproduced. The observer's viewpoint is also incorporated in the FORWARD
analysis and the codes can output the results in a variety of forms in
order to easily create movies, Carrington maps, or simply observable
information at a particular point in the plane of the sky. We present
a newly developed front end to the FORWARD codes which utilizes IDL
widgets to facilitate ease of use by the solar physics community. Our
ultimate goal is to provide as useful a tool as possible for a broad
range of scientific applications.
---------------------------------------------------------
Title: The spatial relation between EUV cavities and linear
polarization signatures
Authors: Bak-Stȩślicka, Urszula; Gibson, Sarah E.; Fan, Yuhong;
Bethge, Christian; Forland, Blake; Rachmeler, Laurel A.
2014IAUS..300..395B Altcode:
Solar coronal cavities are regions of rarefied density and elliptical
cross-section. The Coronal Multi-channel Polarimeter (CoMP) obtains
daily full-Sun coronal observations in linear polarization, allowing
a systematic analysis of the coronal magnetic field in polar-crown
prominence cavities. These cavities commonly possess a characteristic
“lagomorphic” signature in linear polarization that may be explained
by a magnetic flux-rope model. We analyze the spatial relation between
the EUV cavity and the CoMP linear polarization signature.
---------------------------------------------------------
Title: Magnetism and the Invisible Man: The mysteries of coronal
cavities
Authors: Gibson, Sarah
2014IAUS..300..139G Altcode: 2017arXiv171109254G
Magnetism defines the complex and dynamic solar corona. Twists and
tangles in coronal magnetic fields build up energy and ultimately erupt,
hurling plasma into interplanetary space. These coronal mass ejections
(CMEs) are transient riders on the ever-outflowing solar wind, which
itself possesses a three-dimensional morphology shaped by the global
coronal magnetic field. Coronal magnetism is thus at the heart of any
understanding of the origins of space weather at the Earth. However, we
have historically been limited by the difficulty of directly measuring
the magnetic fields of the corona, and have turned to observations
of coronal plasma to trace out magnetic structure. This approach is
complicated by the fact that plasma temperatures and densities vary
among coronal magnetic structures, so that looking at any one wavelength
of light only shows part of the picture. In fact, in some regimes it
is the lack of plasma that is a significant indicator of the magnetic
field. Such a case is the coronal cavity: a dark, elliptical region
in which strong and twisted magnetism dwells. I will elucidate these
enigmatic features by presenting observations of coronal cavities in
multiple wavelengths and from a variety of observing vantages, including
unprecedented coronal magnetic field measurements now being obtained
by the Coronal Multichannel Polarimeter (CoMP). These observations
demonstrate the presence of twisted magnetic fields within cavities,
and also provide clues to how and why cavities ultimately erupt as CMEs.
---------------------------------------------------------
Title: Prominence Mass Supply and the Cavity
Authors: Schmit, Donald J.; Gibson, S.; Luna, M.; Karpen, J.; Innes, D.
2013ApJ...779..156S Altcode: 2013arXiv1311.2382S
A prevalent but untested paradigm is often used to describe the
prominence-cavity system: the cavity is under-dense because it
is evacuated by supplying mass to the condensed prominence. The
thermal non-equilibrium (TNE) model of prominence formation offers
a theoretical framework to predict the thermodynamic evolution of
the prominence and the surrounding corona. We examine the evidence
for a prominence-cavity connection by comparing the TNE model with
diagnostics of dynamic extreme ultraviolet (EUV) emission surrounding
the prominence, specifically prominence horns. Horns are correlated
extensions of prominence plasma and coronal plasma which appear
to connect the prominence and cavity. The TNE model predicts that
large-scale brightenings will occur in the Solar Dynamics Observatory
Atmospheric Imaging Assembly 171 Å bandpass near the prominence that
are associated with the cooling phase of condensation formation. In
our simulations, variations in the magnitude of footpoint heating
lead to variations in the duration, spatial scale, and temporal offset
between emission enhancements in the other EUV bandpasses. While these
predictions match well a subset of the horn observations, the range of
variations in the observed structures is not captured by the model. We
discuss the implications of our one-dimensional loop simulations for
the three-dimensional time-averaged equilibrium in the prominence
and the cavity. Evidence suggests that horns are likely caused by
condensing prominence plasma, but the larger question of whether this
process produces a density-depleted cavity requires a more tightly
constrained model of heating and better knowledge of the associated
magnetic structure.
---------------------------------------------------------
Title: Coronal Cavity Survey: Morphological Clues to Eruptive
Magnetic Topologies
Authors: Forland, B. C.; Gibson, S. E.; Dove, J. B.; Rachmeler, L. A.;
Fan, Y.
2013SoPh..288..603F Altcode:
We present a survey on coronal prominence cavities conducted using 19
months of data from the Atmospheric Imaging Assembly (AIA) instrument
aboard the Solar Dynamics Observatory (SDO) satellite. Coronal
cavities are elliptical regions of rarefied density lying above and
around prominences. They can be long-lived (weeks to months) but are
often observed to eventually erupt as part of a coronal mass ejection
(CME). We determine morphological properties of the cavities both
by qualitatively assessing their shape, and quantitatively fitting
them with ellipses. We demonstrate consistency between these two
approaches, and find that fitted ellipses are taller than they are wide
for almost all cavities studied, in agreement with an earlier analysis
of white-light cavities. We examine correlations between cavity shape,
aspect ratio, and propensity for eruption. We find that cavities with
a teardrop-shaped morphology are more likely to erupt, and we discuss
the implications of this morphology for magnetic topologies associated
with CME models. We provide the full details of the survey for broad
scientific use as supplemental material.
---------------------------------------------------------
Title: SDO/AIA Observations of a Partially Erupting Prominence
Authors: Tripathi, Durgesh; Reeves, Katharine K.; Gibson, Sarah E.;
Srivastava, Abhishek; Joshi, Navin C.
2013ApJ...778..142T Altcode: 2013arXiv1310.0162T
We report an observation of a partially erupting prominence and its
associated dynamical plasma processes based on observations recorded
by the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics
Observatory. The prominence first went through a slow rise (SR) phase
followed by a fast rise (FR) phase. The SR phase began after a couple of
small brightenings were seen toward the footpoints. When the prominence
had transitioned from SR to FR, it had already become kinked. The
prominence shows strong brightening at the central kink location during
the start of FR. We interpret this as an internal magnetic reconnection
occurring at a vertical current sheet forming between the two legs of
the erupting prominence (flux rope). The brightening at the central
kink location is seen in all EUV channels of AIA. The contributions of
differential emission at higher temperatures are larger compared to that
for typical coronal temperatures supporting a reconnection scenario at
the central kink location. The plasma above the brightening location
is ejected as a hot plasmoid-like structure embedded in a coronal
mass ejection, and those below the brightening move down in the form
of blobs moving toward the Sun's surface. The unique time resolution
of the AIA has allowed these eruptive aspects, including SR-to-FR,
kinking, central current sheet formation, plasmoid-like eruption,
and filament "splitting," to be observed in a single event, providing
strong and comprehensive evidence in favor of the model of partially
erupting flux ropes.
---------------------------------------------------------
Title: Polarimetric Properties of Flux Ropes and Sheared Arcades in
Coronal Prominence Cavities
Authors: Rachmeler, L. A.; Gibson, S. E.; Dove, J. B.; DeVore, C. R.;
Fan, Y.
2013SoPh..288..617R Altcode: 2013arXiv1304.7594R
The coronal magnetic field is the primary driver of solar dynamic
events. Linear and circular polarization signals of certain infrared
coronal emission lines contain information about the magnetic field,
and to access this information either a forward or an inversion method
must be used. We study three coronal magnetic configurations that
are applicable to polar-crown filament cavities by doing forward
calculations to produce synthetic polarization data. We analyze
these forward data to determine the distinguishing characteristics of
each model. We conclude that it is possible to distinguish between
cylindrical flux ropes, spheromak flux ropes, and sheared arcades
using coronal polarization measurements. If one of these models is
found to be consistent with observational measurements, it will mean
positive identification of the magnetic morphology that surrounds
certain quiescent filaments, which will lead to a better understanding
of how they form and why they erupt.
---------------------------------------------------------
Title: Observations of Coronal Mass Ejections with the Coronal
Multichannel Polarimeter
Authors: Tian, H.; Tomczyk, S.; McIntosh, S. W.; Bethge, C.; de Toma,
G.; Gibson, S.
2013SoPh..288..637T Altcode: 2013arXiv1303.4647T
The Coronal Multichannel Polarimeter (CoMP) measures not only the
polarization of coronal emission, but also the full radiance profiles of
coronal emission lines. For the first time, CoMP observations provide
high-cadence image sequences of the coronal line intensity, Doppler
shift, and line width simultaneously over a large field of view. By
studying the Doppler shift and line width we may explore more of the
physical processes of the initiation and propagation of coronal mass
ejections (CMEs). Here we identify a list of CMEs observed by CoMP
and present the first results of these observations. Our preliminary
analysis shows that CMEs are usually associated with greatly increased
Doppler shift and enhanced line width. These new observations provide
not only valuable information to constrain CME models and probe
various processes during the initial propagation of CMEs in the low
corona, but also offer a possible cost-effective and low-risk means
of space-weather monitoring.
---------------------------------------------------------
Title: Two Novel Parameters to Evaluate the Global Complexity of
the Sun's Magnetic Field and Track the Solar Cycle
Authors: Zhao, L.; Landi, E.; Gibson, S. E.
2013ApJ...773..157Z Altcode:
Since the unusually prolonged and weak solar minimum between solar
cycles 23 and 24 (2008-2010), the sunspot number is smaller and the
overall morphology of the Sun's magnetic field is more complicated
(i.e., less of a dipole component and more of a tilted current sheet)
compared with the same minimum and ascending phases of the previous
cycle. Nearly 13 yr after the last solar maximum (~2000), the monthly
sunspot number is currently only at half the highest value of the
past cycle's maximum, whereas the polar magnetic field of the Sun
is reversing (north pole first). These circumstances make it timely
to consider alternatives to the sunspot number for tracking the Sun's
magnetic cycle and measuring its complexity. In this study, we introduce
two novel parameters, the standard deviation (SD) of the latitude of
the heliospheric current sheet (HCS) and the integrated slope (SL)
of the HCS, to evaluate the complexity of the Sun's magnetic field
and track the solar cycle. SD and SL are obtained from the magnetic
synoptic maps calculated by a potential field source surface model. We
find that SD and SL are sensitive to the complexity of the HCS:
(1) they have low values when the HCS is flat at solar minimum,
and high values when the HCS is highly tilted at solar maximum;
(2) they respond to the topology of the HCS differently, as a higher
SD value indicates that a larger part of the HCS extends to higher
latitude, while a higher SL value implies that the HCS is wavier;
(3) they are good indicators of magnetically anomalous cycles. Based
on the comparison between SD and SL with the normalized sunspot number
in the most recent four solar cycles, we find that in 2011 the solar
magnetic field had attained a similar complexity as compared to the
previous maxima. In addition, in the ascending phase of cycle 24,
SD and SL in the northern hemisphere were on the average much greater
than in the southern hemisphere, indicating a more tilted and wavier
HCS in the north than the south, associated with the early reversal
of the polar magnetic field in the north relative to the south.
---------------------------------------------------------
Title: Morphology and Temperature of a Hot Prominence Cavity Observed
with SDO
Authors: Weber, Mark A.; Reeves, K.; Gibson, S.; Kucera, T. A.
2013SPD....44...39W Altcode:
Prominence cavities appear as circularly shaped voids in coronal
emission over polarity inversion lines where a prominence channel
is straddling the solar limb. The presence of chromospheric material
suspended at coronal altitudes is a common but not necessary feature
within these cavities. These voids are observed to change shape as
a prominence feature rotates around the limb. We apply temperature
diagnostics to SDO data to investigate the thermal structure. We find
significant evidence that the prominence cavity is hotter than the
corona immediately outside the cavity boundary. This investigation
follows upon “Thermal Properties of A Solar Coronal Cavity Observed
with the X-ray Telescope on Hinode” by Reeves et al., 2012, ApJ, in
press. M. Weber and K.K. Reeves are supported under contract NNM07AB07C
from NASA to SAO. T. Kucera is supported by an award from the NASA
SHP Program.
---------------------------------------------------------
Title: FORWARD Codes: Now with Widget!
Authors: Gibson, Sarah; Forland, B.; Kucera, T. A.
2013SPD....44...49G Altcode:
The FORWARD suite of SolarSoft IDL codes converts an analytic
or simulation data cube into a form directly comparable to
observations. Observables such as extreme ultraviolet, soft X-ray,
white light, and polarization images from the Coronal Multichannel
Polarimeter (CoMP) can be reproduced. The observer's viewpoint is
also incorperated in the forward analysis and the codes can output
the results in a variety of forms in order to easily create movies,
Carrington maps, or simply plasma properties at a particular point
in the plane of the sky. We present a newly developed front end to
the FORWARD codes which utilizes IDL widgets. Our ultimate goal is to
provide as useful a tool as possible for a broad range of scientific
applications.Abstract (2,250 Maximum Characters): The FORWARD suite
of SolarSoft IDL codes converts an analytic or simulation data cube
into a form directly comparable to observations. Observables such as
extreme ultraviolet, soft X-ray, white light, and polarization images
from the Coronal Multichannel Polarimeter (CoMP) can be reproduced. The
observer's viewpoint is also incorperated in the forward analysis and
the codes can output the results in a variety of forms in order to
easily create movies, Carrington maps, or simply plasma properties at a
particular point in the plane of the sky. We present a newly developed
front end to the FORWARD codes which utilizes IDL widgets. Our ultimate
goal is to provide as useful a tool as possible for a broad range of
scientific applications.
---------------------------------------------------------
Title: Association of solar wind proton flux extremes with
pseudostreamers
Authors: Zhao, L.; Gibson, S. E.; Fisk, L. A.
2013JGRA..118.2834Z Altcode:
We investigate the characteristics and solar origins of a subpopulation
of the solar wind that possesses extreme values of proton flux. Ulysses
observations including solar wind magnetic flux, proton flux, number
density and velocity, and ionic composition are examined in this
study. We find that the departures of solar wind proton flux from its
constancy occur for time intervals leading up to and encompassing the
past two solar minima, and the extreme-proton-flux wind possesses the
following characteristics: (1) it generally originates from sources
middle-distant from the Heliospheric Current Sheet (HCS); (2) it is
associated with a broad range of velocities and electron temperatures
but excludes very fast/cold wind; (3) it exhibits anticorrelation
between electron temperature and proton velocity, as does the rest
of the solar wind; (4) it has extreme proton density values relative
to the rest of the solar wind; and (5) the extreme-high-proton-flux
wind has radial component of open magnetic flux (Br) greater than the
rest of the solar wind, and both extreme-high and extreme-low wind do
not possess the lowest values of Br flux. Comparing with SOHO EIT 195
Å coronal images, we find the observed extreme-proton-flux wind has
temporal and spatial coincidence with the appearance of low-latitude
coronal holes present in the recent two solar minima; the magnetic
field lines extrapolated by the Potential Field Source Surface model
confirm there are coronal pseudostreamer structures involved. So we
propose that these extreme-proton-flux winds can be associated with mid-
to low-latitude coronal holes and "pseudostreamer" structures.
---------------------------------------------------------
Title: Diagnosing the Prominence-Cavity Connection
Authors: Schmit, Donald J.; Gibson, Sarah
2013ApJ...770...35S Altcode: 2013arXiv1304.7595S
Prominences and cavities are ubiquitously observed together, but
the physical link between these disparate structures has not been
established. We address this issue by using dynamic emission in the
extreme ultraviolet to probe the connections of these structures. The
SDO/AIA observations show that the cavity exhibits excessive emission
variability compared to the surrounding quiet-Sun streamer, particularly
in the 171 Å bandpass. We find that this dynamic emission takes the
form of coherent loop-like brightening structures which emanate from the
prominence into the central cavity. The geometry of these structures,
dubbed prominence horns, generally mimics the curvature of the cavity
boundary. We use a space-time statistical analysis of two cavities in
multiple AIA bandpasses to constrain the energetic properties of 45
horns. In general, we find there is a positive correlation between the
light curves of the horns in the 171 Å and 193 Å bandpasses; however,
the 193 Å emission is a factor of five weaker. There is also a strong
correlation between structural changes to the prominence as viewed in
the He II 304 Å bandpass and the enhanced 171 Å emission. In that
bandpass, the prominence appears to extend several megameters along
the 171 Å horn where we observe co-spatial, co-temporal 304 Å and
171 Å emission dynamics. We present these observations as evidence
of the magnetic and energetic connection between the prominence and
the cavity. Further modeling work is necessary to explain the physical
source and consequences of these events, particularly in the context of
the traditional paradigm: the cavity is underdense because it supplies
mass to the overdense prominence.
---------------------------------------------------------
Title: Association of Solar Wind Proton Flux Extremes with
Pseudostreamers
Authors: Zhao, Liang; Gibson, S. E.; Fisk, L. A.
2013shin.confE..58Z Altcode:
We investigate the characteristics and solar origins of a sub-population
of the solar wind that possesses extreme values of proton flux. Ulysses
observations including solar wind magnetic flux, proton flux, number
density and velocity, and ionic composition are examined in this
study. We find the departures of solar wind proton flux from its
constancy occur for time intervals leading up to and encompassing the
past two solar minima, and the extreme proton-flux wind possesses the
following characteristics: 1) it generally originates from sources
middle-distant from the Heliospheric Current Sheet (HCS); 2) it is
associated with a broad range of velocities and electron temperatures,
but excludes very fast/cold wind; 3) it exhibits anticorrelation
between electron temperature and proton velocity, as does the rest
of the solar wind; 4) it has extreme proton density values relative
to the rest of the solar wind; and 5) the extreme-high-proton-flux
wind has radial component of open magnetic flux (Br) greater than the
rest of the solar wind and both extreme-high and extreme-low wind do
not possess the lowest values of Br flux. Comparing with SOHO EIT 195
Å coronal images, we find the observed extreme proton-flux wind has
temporal and spatial coincidence with the appearance of low latitude
coronal holes present in the recent two solar minima; and the magnetic
field lines extrapolated by the Potential Field Source Surface (PFSS)
model confirm there are coronal pseudostreamer structures involved. So
we propose that these extreme-proton-flux wind can be associated with
mid-to-low-latitude coronal holes and "pseudostreamer" structures.
---------------------------------------------------------
Title: The Magnetic Structure of Solar Prominence Cavities: New
Observational Signature Revealed by Coronal Magnetometry
Authors: Bąk-Stȩślicka, Urszula; Gibson, Sarah E.; Fan, Yuhong;
Bethge, Christian; Forland, Blake; Rachmeler, Laurel A.
2013ApJ...770L..28B Altcode: 2013arXiv1304.7388B
The Coronal Multi-Channel Polarimeter (CoMP) obtains daily full-Sun
above-the-limb coronal observations in linear polarization, allowing,
for the first time, a diagnostic of the coronal magnetic field
direction in quiescent prominence cavities. We find that these cavities
consistently possess a characteristic "lagomorphic" signature in linear
polarization indicating twist or shear extending up into the cavity
above the neutral line. We demonstrate that such a signature may be
explained by a magnetic flux-rope model, a topology with implications
for solar eruptions. We find corroborating evidence for a flux-rope
structure in the pattern of concentric rings within cavities seen in
CoMP line-of-sight velocity.
---------------------------------------------------------
Title: Solar wind proton flux extremes and their association with
pseudostreamers
Authors: Zhao, Liang; Gibson, Sarah E.; Fisk, Lennard A.
2013AIPC.1539...94Z Altcode:
Proton flux, as defined by the product of proton number density and
proton speed, while exhibiting remarkable constancy across heliographic
latitudes from pole to equator as measured by the Ulysses spacecraft,
nevertheless showed obvious departure from this constancy for some
mid-latitude wind and extended to high heliomagnetic latitudes during
the recent two solar minima. We examine the solar wind exclusive
of ICMEs from Ulysses and ACE observations, to analyze the solar
wind in-situ data exhibiting extremes in proton flux. We first find
these extreme-proton-flux winds generally originate in latitudes
middle-distant from the heliospheric current sheet (HCS), and they have
relatively slower speed than the bulk of the solar wind. Then we map the
in-situ ACE observations in Carrington rotation (CR) 1997 back to the
solar surface by using the Potential-Field-Source-Surface (PFSS) model,
in order to consider the coronal properties at the extreme-proton-flux
wind sources. We find there is a clear association between these
extreme-proton-flux solar wind and the mid-latitude coronal holes and
"pseudostreamer" structures.
---------------------------------------------------------
Title: FORWARD Codes: Now with Widgets!
Authors: Forland, B.; Gibson, S. E.; Kucera, T. A.
2013AGUSMSH51A..02F Altcode:
The FORWARD suite of SolarSoft IDL codes converts an analytic
model or simulation data cube into a form directly comparable to
observations. Observables such as extreme ultra violet, soft X-ray,
white light, and polarization images from the Coronal Multichannel
Polarimeter (CoMP) can be reproduced. The observer's viewpoint is
also incorporated in the forward analysis and the codes can output
the results in a variety of forms in order to easily create movies,
Carrington maps, or simply observable information at a particular point
in the plane of the sky. We present a newly developed front end to the
FORWARD codes which utilizes IDL widgets to facilitate ease of use by
the solar physics community. Our ultimate goal is to provide as useful
a tool as possible for a broad range of scientific applications.
---------------------------------------------------------
Title: Magnetic structure and flows in coronal prominence cavities
Authors: Gibson, S. E.; Bak-Steslicka, U.; Forland, B.; Schmit, D. J.
2013AGUSMSH23B..04G Altcode:
Prominence cavities provide deep insight into the storage and release
of magnetic energy in the solar corona. Recent studies have yielded
a variety of observations that provide new constraints on models of
prominences, cavities, and coronal mass ejections. In particular,
a survey of SDO/AIA extreme-ultraviolet cavities has demonstrated
that a tear-shaped morphology is a predictor of impending eruption,
indicating that a change in topology may play a role in their
destabilization. Other studies utilizing extreme-ultraviolet and
infrared observations have shown both circulating plane-of-sky flows
and a "bulls-eye" pattern in line-of-sight flows within cavities,
indicating a central magnetic axis. A comparison of coronal flows
within the cavity and flows associated with the embedded prominence
demonstrate both spatial and temporal correlations, indicating
they are both magnetically and thermodynamically connected. Finally,
coronal magnetometric observations show a characteristic "rabbit-head"
signature in linear polarization within polar-crown-prominence cavities,
indicating twisted or sheared magnetic field at the heart of the
cavity. All of these observations lend credence to the model of the
cavity as a magnetic flux rope: both as a long-lived MHD equilibrium
state and as a key component in the ultimate destabilization and
eruption of coronal mass ejections.
---------------------------------------------------------
Title: Association of Solar Wind Proton Flux Extremes with
Pseudostreamers
Authors: Zhao, L.; Gibson, S. E.; Fisk, L. A.
2013AGUSMSH23A..01Z Altcode:
We investigate the characteristics and solar origins of a sub-population
of the solar wind that possesses extreme values of proton flux. Ulysses
observations including solar wind magnetic flux, proton flux, number
density and velocity, and ionic composition are examined in this
study. We find the departures of solar wind proton flux from its
constancy occur for time intervals leading up to and encompassing the
past two solar minima, and the extreme-proton-flux wind possesses the
following characteristics: 1) it generally originates from sources
middle-distant from the Heliospheric Current Sheet (HCS); 2) it is
associated with a broad range of velocities and electron temperatures,
but excludes very fast/cold wind; 3) it exhibits anticorrelation
between electron temperature and proton velocity, as does the rest
of the solar wind; 4) it has extreme proton density values relative
to the rest of the solar wind; and 5) the extreme-high-proton-flux
wind has radial component of open magnetic flux (Br) greater than the
rest of the solar wind and both extreme-high and extreme-low wind do
not possess the lowest values of Br flux. Comparing with SOHO EIT 195
A coronal images, we find the observed extreme-proton-flux wind has
temporal and special coincidence with the appearance of low latitude
coronal holes present in the recent two solar minima; and the magnetic
field lines extrapolated by the Potential Field Source Surface (PFSS)
model confirm there are coronal pseudostreamer structures involved. So
we propose that these extreme-proton-flux wind can be associated with
mid-to-low-latitude coronal holes and "pseudostreamer" structures.
---------------------------------------------------------
Title: Formation of a hot plasma blob: observations of AIA, CoMP
and MK4
Authors: Tian, Hui; Gibson, Sarah
2013enss.confE.107T Altcode:
Using AIA observations, we found that a hot blob of plasma formed as
a trans-equatorial loop system rose and opened up. The hot blob was
most clearly seen in the AIA 94 passband and not obvious in any other
passbands. A cusp-like structure quickly developed below the hot blob
when the blob left the FOV of AIA 1.5 hours after its formation. This
event was also observed by the CoMP and MK4 instruments in Mauna Loa
Solar Observatory. The CoMP observation reveals a clear "bunny ear"
pattern suggestive of a magnetic flux rope around the AIA blob. The
hot blob observed by AIA seems to coincide with the region of enhanced
linear polarization between the two dark ears. A comparison between
these observations with MHD simulations of flux rope eruption suggest
that the hot blob might be the lower part of, or just below, the
erupted flux rope. In the MK4 data we see a clear three-part CME
propagating outward.
---------------------------------------------------------
Title: Interpreting Coronal Polarization Observations
Authors: Rachmeler, L. A.; Casini, R.; Gibson, S. E.
2012ASPC..463..227R Altcode:
Solar coronal polarization observations are an underused data product
because of the difficulties in interpreting the data and in calculating
an inversion.The physics of the polarization is well understood and
documented in the literature. The purpose of this paper is to present
a general overview on how to interpret polarization signals without
calculating an inversion. This is intended to introduce the data to
those who are unfamiliar to polarization, and in so doing, make the
data more accessible.
---------------------------------------------------------
Title: Preliminary Result from an Observational and Modeling Study
of Coronal Pseudostreamer Structure as a Solar Wind Origin
Authors: Zhao, L.; Gibson, S. E.; Fisk, L. A.
2012AGUFMSH52A..02Z Altcode:
Unlike the polar coronal holes, which are the source of fast, cold
solar wind, or helmet streamers, associated with slow, hot wind, the
so-called "pseudostreamers" are still not well-categorized as a solar
wind source, and the source of the slow- and intermediate- speed solar
wind is still under debate. The solar wind proton mass flux, while
exhibiting remarkable constancy across heliographic latitudes from
pole to equator as measured by the Ulysses spacecraft, nevertheless
showed departure from this constancy for some mid-latitude wind in the
recent two solar minima. Such departures were most obvious during the
23-24 solar minimum and extended to high heliomagnetic latitudes. We
examine the non-transient solar wind from Ulysses and ACE observations
in the recent two solar minima, including solar wind magnetic flux,
proton mass flux and velocity, and ionic composition O7+/O6+ as an
indicator of coronal electron temperature, in order to analyze the
solar wind exhibiting extremes in proton mass flux. The average proton
speed of the extreme-mass-flux wind is in the slow to intermediate
range. By applying potential-field-source-surface (PFSS) model to
track the observed solar wind to the solar surface and comparing
with the solar coronal structures there, we found there is a highly
association between the sources of those slow- to intermediate-speed
extreme-mass-flux solar wind and the low-latitude coronal holes and
pseudostreamers structures. We will also discuss the observational
constraints this study has placed on models of solar wind acceleration.
---------------------------------------------------------
Title: Solar Cycles 23 and 24: Effects in the Heliosphere
Authors: Webb, D. F.; Gibson, S. E.
2012AGUFMSH12A..06W Altcode:
The recent extended minimum was the lowest and longest minimum
in about a century, having weak polar magnetic fields, a complex
corona and heliosphere, and recurrent high speed streams. During this
recent minimum, the solar magnetic field achieved a solar maximum-like
corona and solar wind source situation, but with weak magnetic fields
and associated weak heating. The possibility of a trend in the Sun's
current magnetic cycles towards a grand minimum of solar cycles has been
suggested. Predictions for Cycle 24 tend to predict a weak maximum and
the trend during its rise is tracking along or below the SWPC predicted
curve, which has a maximum sunspot count of ~90 in 2013 or 2014. We
will attempt to characterize the variations in the heliosphere caused
by solar conditions during the declining phase of Cycle 23 through
the minimum state and into the rise of Cycle 24. This will include
discussion of pertinent results from recent meetings involving solar
and stellar magnetic minima and solar cycle variations of solar and
heliospheric parameters.
---------------------------------------------------------
Title: Temperature and Extreme-ultraviolet Intensity in a Coronal
Prominence Cavity and Streamer
Authors: Kucera, T. A.; Gibson, S. E.; Schmit, D. J.; Landi, E.;
Tripathi, D.
2012ApJ...757...73K Altcode:
We analyze the temperature and EUV line emission of a coronal cavity and
surrounding streamer in terms of a morphological forward model. We use a
series of iron line ratios observed with the Hinode Extreme-ultraviolet
Imaging Spectrograph (EIS) on 2007 August 9 to constrain temperature
as a function of altitude in a morphological forward model of the
streamer and cavity. We also compare model predictions to the EIS EUV
line intensities and polarized brightness (pB) data from the Mauna
Loa Solar Observatory (MLSO) Mark 4 K-coronameter. This work builds
on earlier analysis using the same model to determine geometry of
and density in the same cavity and streamer. The fit to the data
with altitude-dependent temperature profiles indicates that both
the streamer and cavity have temperatures in the range 1.4-1.7
MK. However, the cavity exhibits substantial substructure such
that the altitude-dependent temperature profile is not sufficient to
completely model conditions in the cavity. Coronal prominence cavities
are structured by magnetism so clues to this structure are to be found
in their plasma properties. These temperature substructures are likely
related to structures in the cavity magnetic field. Furthermore,
we find that the model overestimates the EUV line intensities by a
factor of 4-10, without overestimating pB. We discuss this difference
in terms of filling factors and uncertainties in density diagnostics
and elemental abundances.
---------------------------------------------------------
Title: A porcupine Sun? Implications for the solar wind and Earth
Authors: Gibson, Sarah E.; Zhao, Liang
2012IAUS..286..210G Altcode:
The recent minimum was unusually long, and it was not just the
case of the “usual story” slowed down. The coronal magnetic field
never became completely dipolar as in recent Space Age minima, but
rather gradually evolved into an (essentially axisymmetric) global
configuration possessing mixed open and closed magnetic structures
at many latitudes. In the process, the impact of the solar wind
at the Earth went from resembling that from a sequence of rotating
“fire-hoses” to what might be expected from a weak, omnidirectional
“lawn-sprinkler”. The previous (1996) solar minimum was a more
classic dipolar configuration, and was characterized by slow wind
of hot origin localized to the heliospheric current sheet, and fast
wind of cold origin emitted from polar holes, but filling most of the
heliosphere. In contrast, the more recent minimum solar wind possessed a
broad range of speeds and source temperatures (although cooler overall
than the prior minimum). We discuss possible connections between these
observations and the near-radial expansion and small spatial scales
characteristic of the recent minimum's porcupine-like magnetic field.
---------------------------------------------------------
Title: The magnetism and dynamics of solar coronal cavities
Authors: Gibson, Sarah
2012cosp...39..618G Altcode: 2012cosp.meet..618G
No abstract at ADS
---------------------------------------------------------
Title: Space climate and the recent unusual solar minimum
Authors: Gibson, Sarah
2012cosp...39..617G Altcode: 2012cosp.meet..617G
Solar minima represent times of low magnetic activity and simple
heliospheres. They are thus excellent targets for interdisciplinary,
system-wide studies of the origins of solar variability and consequent
impacts on planetary systems. The recent solar minimum extended
longer and was "quieter" than any we have observed in the Space Age,
inspiring both scientific and public interest. It was the lowest and
longest minimum in about a century, having weak polar magnetic fields,
a complex corona and heliosphere, and recurrent high-speed streams
impacting the Earth's space environment. I will review scientific
results from Sun to Earth pertaining to the recent minimum, and place
these results in a broad context encompassing historical solar and
stellar minima, theoretical models of generative dynamo mechanisms,
and implications of solar and stellar cyclic behavior for the space
climate around planets.
---------------------------------------------------------
Title: Magnetic Structure of Coronal Cavities
Authors: Gibson, Sarah; Bak-Steslicka, Urszula; Bethge, Christian;
de Toma, Giuliana; Dove, Jim; Fan, Yuhong; Forland, Blake; Rachmeler,
Laurel
2012shin.confE.209G Altcode:
Coronal cavities are dark, elliptical regions in which strong
and twisted magnetism dwells. Polar-crown-prominence cavities in
particular are excellent targets for coronal magnetometry, because
they are long-lived (on the order of weeks) and extended along the
line of sight. Using data from the Coronal Multichannel Polarimeter
(CoMP), we show a specific structure in linear polarization that
is very consistent from cavity to cavity, and that matches that of a
forward-modeled flux rope. We discuss how this structure scales with the
size of the cavity, and consider implications for future observations
(e.g., ATST and COSMO) in probing and indeed predicting topological
changes and instabilities leading up to eruptions.
---------------------------------------------------------
Title: Implications of proton mass flux extremes for solar wind
acceleration at cycle minima
Authors: Zhao, Liang; Gibson, Sarah E.; Fisk, Lennard A.
2012shin.confE.106Z Altcode:
The solar wind proton mass flux, while exhibiting remarkable constancy
across heliographic latitudes from pole to equator as measured by the
Ulysses spacecraft, nevertheless showed departure from this constancy
for some mid-latitude wind in the recent two solar minima. Such
departures were most obvious during the 23-24 solar minimum and extended
to high heliomagnetic latitudes. We examine the non-transient solar
wind (exclusive of Interplanetary Coronal Mass Ejections (ICMEs))
from Ulysses observations in the recent two solar minima, including
solar wind magnetic flux, proton mass flux and velocity, and ionic
composition O7+/O6+ as an indicator of coronal electron temperature,
in order to analyze the solar wind exhibiting extremes in proton
mass flux. This study places constraints on models of solar wind
acceleration by demonstrating the following properties of extreme
(low/high) mass-flux solar wind observed during solar minima: 1) They
generally originate in latitudes middle-distant from the heliospheric
current sheet (HCS); 2) They have extreme proton density values relative
to the rest of the solar wind; 3) They possess a range of velocities
and electron temperatures, excluding fast/cold and very slow/hot; 4)
They exhibit anticorrelation between electron temperature and proton
velocity, as does the rest of the solar wind; 5) They do not follow the
anticorrelation trend between proton density and velocity of the rest
of the solar wind; and 6) They likewise depart from the trend for the
bulk of the wind relating mass flux and the normalized radial component
of the heliospheric magnetic field. We discuss the association between
these extreme-mass-flux solar wind and mid-latitude coronal holes and
'pseudostreamers'.
---------------------------------------------------------
Title: Stability of Prominence/Cavity Systems
Authors: de Toma, Giuliana; Gibson, S.; Forland, B.
2012shin.confE.208D Altcode:
Prominence/cavity systems are large scale structures in the solar corona
that can live for many weeks and even month and often end their life
in the form of large prominence/ cavity eruptions. During this phase of
the solar cycle, large coronal cavities are seen at high latitudes and
correspond, in on-disk observations, to the polar crown filaments.We
investigate the stability of these large prominence/cavity systems
in the solar corona and their interaction with the ambient coronal
field using observations from SDO/AIA and SDO/HMI. In particular, we
examine how the decline with height of the external coronal magnetic
field influences the evolution of these systems and their likelihood
to erupt.We will present examples of eruptive and non-eruptive coronal
cavities.
---------------------------------------------------------
Title: Diagnosing the Prominence-Cavity Connection
Authors: Schmit, Donald James; Gibson, Sarah
2012shin.confE.210S Altcode:
Prominences and cavities are ubiquitously observed together, but
the physical link between these disparate structures has not been
established. We address this issue by using dynamic emission in
the EUV to probe the connections of these structures. The SDO/AIA
observations show that the cavity undergoes strong brightenings in
the 171A bandpass. These 171A features take the form of loop-segments
which extend from the prominence into the central cavity. Simultaneous
and partially-cospatial changes in the prominence form 304A-extensions
along the lower regions of these 171A features. The correlated dynamics
of both condensed-plasma and coronal-plasma suggest there is a magnetic
and energetic connection between the cavity and the prominence. We
are now working on explaining the observations in terms of the coronal
energy equation, through 1D hydrodynamic and 3D MHD considerations.
---------------------------------------------------------
Title: Cavity morphology in relation to CMEs
Authors: Forland, Blake; Gibson, Sarah; Dove, James; Rachmeler,
Laurel; Fan, Yuhong
2012shin.confE.204F Altcode:
The magnetic field of the corona is the predominate source of energy
when it comes to coronal mass ejections (CME) and flares. Coronal
prominence cavities are highly visible regions of rarified density when
viewed off limb and are often observed erupting into CMEs. A survey
was conducted over 19 months of data using the Atmospheric Imaging
Assembly (AIA) instrument aboard the Solar Dynamics Observatory (SDO)
satellite in order to create a database that could be used to determine
correlations between cavity characteristics and CMEs. The first six
months of the survey were used for an initial analysis which focused
focused on many different cavity characteristics; morphology, aspect
ratio, center height and sub structure. The major result showed that
cavities with a tear shaped morphology are more likely to erupt. The
analysis of aspect ratio also reinforced the use of cavity morphology
to describe and characterize cavities. Other characteristics of the
analysis were inconclusive, however all characteristics will be used
in the continued analysis of all 19 months.
---------------------------------------------------------
Title: Recent Results from the Coronal Multi-Channel Polarimeter
Authors: Tomczyk, Steven; Bethge, C.; Gibson, S. E.; McIntosh, S. W.;
Rachmeler, L. A.; Tian, H.
2012AAS...22031001T Altcode:
The Coronal Multi-Channel Polarimeter (CoMP) instrument is a
ground-based filter/polarimeter which can image the solar corona at
wavelengths around the emission lines of FeXIII at 1074.7 and 1079.8
nm and the chromospheric emission line of HeI at 1083.0 nm. The
instrument consists of a 20-cm aperture coronagraph followed by a
Stokes polarimeter and a Lyot birefringent filter with a passband
of 0.14 nm width. Both the polarimeter and filter employ liquid
crystals for rapid electro-optical tuning. This instrument measures
the line-of-sight strength of the coronal magnetic field through the
Zeeman effect and the plane-of-sky direction of the magnetic field via
resonance scattering. The line-of-sight velocity can also be determined
from the Doppler shift. The CoMP has obtained daily observations from
the Mauna Loa Solar Observatory for almost one year. We will present
recent measurements of the polarization signatures seen with the
CoMP and a comparison with models that allow us to constrain coronal
structure. We also will present observations of coronal waves taken
with the CoMP and discuss their implications for the heating of the
solar corona and the acceleration of the solar wind.
---------------------------------------------------------
Title: The Magnetism and Dynamics of Solar Coronal Cavities
Authors: Gibson, Sarah
2012AAS...22031002G Altcode:
Magnetism defines the complex and dynamic solar corona. We have
historically been limited by the difficulty of directly measuring
the magnetic fields of the corona, and have turned to observations
of coronal plasma to trace out magnetic structure. In some regimes,
however, it is the lack of plasma that is a significant indicator of the
magnetic field. Such a case is the coronal cavity: a dark, elliptical
region in which strong and twisted magnetism dwells. I will elucidate
these enigmatic features using observations of coronal cavities in
multiple wavelengths and from a variety of observing vantages, and show
how magnetic flux rope models provide a self-consistent picture of the
cavity, its sub-structure, and its dynamic evolution as a CME. Moreover,
I will make use of unprecedented measurements of coronal magnetism,
now being obtained by the Coronal Multichannel Polarimeter (CoMP),
to demonstrate the presence of twisted magnetic fields within cavities.
---------------------------------------------------------
Title: Morphology Of A Hot Prominence Cavity Observed With Hinode/XRT
And SDO/AIA
Authors: Weber, Mark A.; Reeves, K. K.; Gibson, S. E.; Kucera, T. A.
2012AAS...22020205W Altcode:
Prominence cavities appear as circularly shaped voids in coronal
emission over polarity inversion lines where a prominence channel
is straddling the solar limb. The presence of chromospheric material
suspended at coronal altitudes is a common but not necessary feature
within these cavities. These voids are observed to change shape as a
prominence feature rotates around the limb. We use a morphological
model projected in cross-sections to fit the cavity emission in
Hinode/XRT passbands, and then apply temperature diagnostics to
XRT and SDO/AIA data to investigate the thermal structure. We find
significant evidence that the prominence cavity is hotter than the
corona immediately outside the cavity boundary. This investigation
follows upon “Thermal Properties of A Solar Coronal Cavity Observed
with the X-ray Telescope on Hinode” by Reeves et al., 2012, ApJ, in
press. M. Weber and K.K. Reeves are supported under contract NNM07AB07C
from NASA to SAO. T. Kucera is supported by an award from the NASA
SHP Program.
---------------------------------------------------------
Title: Diagnosing the Prominence-Cavity Connection
Authors: Schmit, Donald; Gibson, S.
2012AAS...22052102S Altcode:
Prominences are regions of cool, dense plasma which are suspended
above the solar limb within the much hotter and more rarefied solar
corona. The coronal environment surrounding the prominence is often
observed as a elliptical region of reduced density (compared to the
ambient corona) known as a cavity. To date, the cavity has been a
neglected constraint on the prominence system. In this research,
I probe the magnetic structural connection between the cavity and
prominence and the potential role the cavity plays in the mass
and energy balance of the prominence. Observationally, I use the
Hinode/EIS and SDO/AIA datasets to extract dynamic substructure from the
cavity. The temperature-sensitivities of these data are used to diagnose
the interaction of plasma in the prominence and in the surrounding
corona.These observational dynamics present a viable constraint on
prominence models in two ways. Structurally, the morphology of the
extract substructure can be compared to the 3D models of prominence
support. Energetically, the spatial and temporal signature of EUV
dynamics can be compared to the thermal non-equilibrium model for
prominence mass supply. This joint approach systematically addresses
the two largest questions in prominence research: how is the prominence
mass supported and where does it come from.
---------------------------------------------------------
Title: Temperature Structure of a Coronal Cavity and Streamer
Authors: Kucera, Therese A.; Gibson, S. E.; Schmit, D. J.; Landi,
E.; Tripathi, D.
2012AAS...22052113K Altcode:
We analyze the temperature and EUV line emission of a coronal cavity and
surrounding streamer in terms of a morphological forward model. We use a
series of iron line ratios observed with the Hinode Extreme-ultraviolet
Imaging Spectrograph (EIS) on 2007 Aug. 9 to constrain temperature
as a function of altitude in a morphological forward model of the
streamer and cavity. We also compare model prediction of the EIS EUV
line intensities and polarized brightness (pB) data from the Mauna Loa
Solar Observatory (MLSO) MK4. This work builds on earlier analysis using
the same model to determine geometry of and density in the same cavity
and streamer (Gibson et al. 2010 and Schmit and Gibson 2011). The fit
to the data with altitude dependent temperature profiles indicates that
both the streamer and cavity have temperatures in the range 1.4-1.7
MK. However, the cavity exhibits substantial substructure such that the
altitude dependent temperature profile is not sufficient to completely
model conditions in the cavity. This work is supported in part by the
NASA SHP program
---------------------------------------------------------
Title: Forward modeling of coronal polarization
Authors: Gibson, Sarah E.; Casini, Roberto; Dove, James; Tomczyk, Steve
2012decs.confE...6G Altcode:
Coronal polarization measurements from the Coronal Multichannel
Polarimeter (CoMP) instrument provide quantitative information about the
magnetic field above the solar limb. Inversion of these measurements
is difficult due to the optically thin nature of the plasma. Our
forward technique can be used with both local and global models to
obtain quantitative comparisons between models and observations of
the coronal magnetic field. We have used the forward technique to
study the magnetic nature of quiescent coronal cavities. We present
results from the cavity analysis as well as ways to interpret the
coronal polarization data without calculating inversions.
---------------------------------------------------------
Title: Morphology of a Hot Prominence Cavity Observed with XRT and AIA
Authors: Weber, Mark; Reeves, Katherine K.; Gibson, Sarah E.; Kucera,
Therese A.
2012decs.confE..56W Altcode:
Prominence cavities appear as circularly shaped voids in coronal
emission over polarity inversion lines where a prominence channel
is straddling the solar limb. The presence of chromospheric material
suspended at coronal altitudes is a common but not necessary feature
within these cavities. These voids are observed to change shape as
a prominence feature rotates around the limb. We use a morphological
model projected in cross-sections to fit the cavity emission in XRT
passbands, and then apply temperature diagnostics to XRT and AIA data
to investigate the thermal structure. We find significant evidence that
the prominence cavity is hotter than the corona immediately outside the
cavity boundary. This investigation follows upon “Thermal Properties
of A Solar Coronal Cavity Observed with the X-ray Telescope on Hinode”
by Reeves et al., 2012, ApJ, in press. M. Weber and K.K. Reeves are
supported under contract NNM07AB07C from NASA to SAO. T. Kucera is
supported by an award from the NASA SHP Program.
---------------------------------------------------------
Title: Diagnosing the Prominence-Cavity Connection
Authors: Schmit, Donald; Gibson, Sarah
2012decs.confE...7S Altcode:
Prominences are regions of cool, dense plasma which are suspended
above the solar limb within the much hotter and more rarefied solar
corona. The coronal environment surrounding the prominence is often
observed as an elliptical region of reduced density (compared to
the ambient corona) known as a cavity. The fundamental problems in
prominence physics are the magnetic support of condensed plasma and the
mass-source of those condensations. We use the SDO/AIA dataset to probe
the correlated dynamics in between the cool prominence and the coronal
cavity. These dynamics are explained through the 1D modeling of the
radiative instability. The magnetic field inferred from these dynamics
is also compared to the 3D MHD models of prominence support. Through
this joint approach, the dynamic nature of the prominence system is
brought into sharp focus for the first time.
---------------------------------------------------------
Title: Geomagnetic detection of the sectorial solar magnetic field
and the historical peculiarity of minimum 23-24
Authors: Love, Jeffrey J.; Joshua Rigler, E.; Gibson, Sarah E.
2012GeoRL..39.4102L Altcode: 2012GeoRL..3904102L
Analysis is made of the geomagnetic-activity aa index covering solar
cycle 11 to the beginning of 24, 1868-2011. Autocorrelation shows 27.0-d
recurrent geomagnetic activity that is well-known to be prominent during
solar-cycle minima; some minima also exhibit a smaller amount of 13.5-d
recurrence. Previous work has shown that the recent solar minimum 23-24
exhibited 9.0 and 6.7-d recurrence in geomagnetic and heliospheric data,
but those recurrence intervals were not prominently present during the
preceding minima 21-22 and 22-23. Using annual-averages and solar-cycle
averages of autocorrelations of the historical aa data, we put these
observations into a long-term perspective: none of the 12 minima
preceding 23-24 exhibited prominent 9.0 and 6.7-d aa recurrence. We
show that the detection of these recurrence intervals can be traced to
an unusual combination of sectorial spherical-harmonic structure in the
solar magnetic field and anomalously low sunspot number. We speculate
that 9.0 and 6.7-d recurrence is related to transient large-scale,
low-latitude organization of the solar dynamo, such as seen in some
numerical simulations.
---------------------------------------------------------
Title: Thermal Properties of a Solar Coronal Cavity Observed with
the X-Ray Telescope on Hinode
Authors: Reeves, Katharine K.; Gibson, Sarah E.; Kucera, Therese A.;
Hudson, Hugh S.; Kano, Ryouhei
2012ApJ...746..146R Altcode:
Coronal cavities are voids in coronal emission often observed above
high latitude filament channels. Sometimes, these cavities have areas of
bright X-ray emission in their centers. In this study, we use data from
the X-ray Telescope (XRT) on the Hinode satellite to examine the thermal
emission properties of a cavity observed during 2008 July that contains
bright X-ray emission in its center. Using ratios of XRT filters, we
find evidence for elevated temperatures in the cavity center. The area
of elevated temperature evolves from a ring-shaped structure at the
beginning of the observation, to an elongated structure two days later,
finally appearing as a compact round source four days after the initial
observation. We use a morphological model to fit the cavity emission,
and find that a uniform structure running through the cavity does not
fit the observations well. Instead, the observations are reproduced
by modeling several short cylindrical cavity "cores" with different
parameters on different days. These changing core parameters may be
due to some observed activity heating different parts of the cavity
core at different times. We find that core temperatures of 1.75 MK,
1.7 MK, and 2.0 MK (for July 19, July 21, and July 23, respectively)
in the model lead to structures that are consistent with the data,
and that line-of-sight effects serve to lower the effective temperature
derived from the filter ratio.
---------------------------------------------------------
Title: GALFA-HI: A Targeted Search For Star Formation on the Far
Side of the Milky Way
Authors: Stantzos, Nicholas; Gostisha, M.; Benjamin, R.; Gibson, S.;
Koo, B.; Douglas, K. A.; Kang, J.; Park, G.; Peek, J. E. G.; Korpela,
E. J.; Heiles, C.; Newton, J. H.
2012AAS...21925211S Altcode:
The I-GALFA Survey provides a unique window on the spiral structure
of the Milky Way as it contains three coherent 21 cm features that
have been identified as spiral arms: the Perseus Arm, the Outer Arm,
and the recently discovered Outer Scutum-Centaurus Arm. Moreover,
all three of these arms lie beyond the solar circle (although the
Perseus arm is thought to cross interior to the solar circle for
l< 50 degrees), so this gas does not suffer the kinematic distance
ambiguity encountered in the inner Galaxy. We use this data and the CO
surveys compiled by Dame et al (2001) to target a search for distant
star formation regions seen in the Spitzer Space Telescope/GLIMPSE and
WISE mid-infrared all-sky surveys. We characterize the HI arms, and
present the star formation regions that may be potentially associated
with these three arms. Many of these objects will need spectroscopic
follow-up, but some have been previously identified in the Green Bank
Telescope HII Region Discovery Survey of Anderson et al (2011). The
Inner Galaxy ALFA (I-GALFA) survey is part of the Galactic ALFA HI data
set obtained with the Arecibo L-band Feed Array (ALFA) on the Arecibo
305m telescope. Arecibo Observatory is part of the National Astronomy
and Ionosphere Center, operated sequentially by Cornell University
and Stanford Research Institute under Cooperative Agreement with the
U.S. National Science Foundation.
---------------------------------------------------------
Title: The Global Context of Solar Activity During the Whole
Heliosphere Interval Campaign
Authors: Webb, D. F.; Cremades, H.; Sterling, A. C.; Mandrini, C. H.;
Dasso, S.; Gibson, S. E.; Haber, D. A.; Komm, R. W.; Petrie, G. J. D.;
McIntosh, P. S.; Welsch, B. T.; Plunkett, S. P.
2011SoPh..274...57W Altcode:
The Whole Heliosphere Interval (WHI) was an international observing and
modeling effort to characterize the 3-D interconnected "heliophysical"
system during this solar minimum, centered on Carrington Rotation
2068, March 20 - April 16, 2008. During the latter half of the WHI
period, the Sun presented a sunspot-free, deep solar minimum type
face. But during the first half of CR 2068 three solar active regions
flanked by two opposite-polarity, low-latitude coronal holes were
present. These departures from the quiet Sun led to both eruptive
activity and solar wind structure. Most of the eruptive activity,
i.e., flares, filament eruptions and coronal mass ejections (CMEs),
occurred during this first, active half of the interval. We determined
the source locations of the CMEs and the type of associated region,
such as active region, or quiet sun or active region prominence. To
analyze the evolution of the events in the context of the global solar
magnetic field and its evolution during the three rotations centered
on CR 2068, we plotted the CME source locations onto synoptic maps of
the photospheric magnetic field, of the magnetic and chromospheric
structure, of the white light corona, and of helioseismological
subsurface flows. Most of the CME sources were associated with the
three dominant active regions on CR 2068, particularly AR 10989. Most
of the other sources on all three CRs appear to have been associated
with either isolated filaments or filaments in the north polar crown
filament channel. Although calculations of the flux balance and
helicity of the surface magnetic features did not clearly identify a
dominance of one region over the others, helioseismological subsurface
flows beneath these active regions did reveal a pronounced difference
among them. These preliminary results suggest that the "twistedness"
(i.e., vorticity and helicity) of subsurface flows and its temporal
variation might be related to the CME productivity of active regions,
similar to the relationship between flares and subsurface flows.
---------------------------------------------------------
Title: The Sun-Earth Connection near Solar Minimum: Placing it
into Context
Authors: Bisi, Mario M.; Thompson, Barbara J.; Emery, Barbara A.;
Gibson, Sarah E.; Leibacher, John; van Driel-Gesztelyi, Lidia
2011SoPh..274....1B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The solar wind structure and heliospheric magnetic field in
the solar Cycle 23-24 minimum and in the increasing phase of Cycle 24
Authors: Gibson, S. E.; Zhao, L.; Fisk, L. A.
2011AGUFMSH31D..05G Altcode:
The solar wind structure and the heliospheric magnetic field were
substantially different in the latest solar minimum between solar Cycle
23 and 24 from the previous minimum. Compared with the previous minimum,
in the latest solar minimum, the heliospheric magnetic field strength
was substantially reduced; the streamer-associated-low-temperature
solar wind (streamer-stalk wind) was distributed in a narrower region
relative to the heliospheric current sheet (HCS); the slow-proton-speed
solar wind was scattered in a wider latitudinal region; and there
are more large and steady coronal holes at low latitude. We offer
an explanation for the decreased magnetic-field strength and the
narrowed streamer-stalk wind based on an analysis of the Ulysses and
ACE in-situ observations. Solar-wind composition data are used to
demonstrate that there are two distinct structures of solar wind:
solar wind likely to originate from the stalk of the streamer belt
(the highly elongated loops that underlie the HCS), and solar wind
from outside this region. The region outside the streamer-stalk
region is noticeably larger in the Cycle 23-24 minimum; however,
the increased area can account for the reduction in the heliospheric
magnetic-field strength in that minimum. Thus, the total magnetic
flux contained in this region is the same in the two minima. To have a
further understanding of the solar wind structure and its solar source,
we ballistically map the ACE in-situ observation back along a radial
trajectory from 1 AU to the solar source surface (r = 2.5Rsun) using the
observed proton speeds. Then we track the field line from the source
surface to the solar surface using a potential-field-source-surface
(PFSS) extrapolation model. So the ACE observations, including the
heliospheric magnetic field, the solar wind compositional and dynamic
properties at 1AU, can be connected to their coronal sources on the
solar surface. Synoptic maps showing this connection will be provided,
and based on those maps we will further discuss the evolution of the
solar wind and coronal structures throughout the latest solar minimum
till the increasing phase of the Cycle 24.
---------------------------------------------------------
Title: A Snapshot of the Sun Near Solar Minimum: The Whole Heliosphere
Interval
Authors: Thompson, Barbara J.; Gibson, Sarah E.; Schroeder, Peter C.;
Webb, David F.; Arge, Charles N.; Bisi, Mario M.; de Toma, Giuliana;
Emery, Barbara A.; Galvin, Antoinette B.; Haber, Deborah A.; Jackson,
Bernard V.; Jensen, Elizabeth A.; Leamon, Robert J.; Lei, Jiuhou;
Manoharan, Periasamy K.; Mays, M. Leila; McIntosh, Patrick S.; Petrie,
Gordon J. D.; Plunkett, Simon P.; Qian, Liying; Riley, Peter; Suess,
Steven T.; Tokumaru, Munetoshi; Welsch, Brian T.; Woods, Thomas N.
2011SoPh..274...29T Altcode: 2011SoPh..tmp..413T
We present an overview of the data and models collected for the
Whole Heliosphere Interval, an international campaign to study the
three-dimensional solar-heliospheric-planetary connected system near
solar minimum. The data and models correspond to solar Carrington
Rotation 2068 (20 March - 16 April 2008) extending from below the
solar photosphere, through interplanetary space, and down to Earth's
mesosphere. Nearly 200 people participated in aspects of WHI studies,
analyzing and interpreting data from nearly 100 instruments and
models in order to elucidate the physics of fundamental heliophysical
processes. The solar and inner heliospheric data showed structure
consistent with the declining phase of the solar cycle. A closely
spaced cluster of low-latitude active regions was responsible for an
increased level of magnetic activity, while a highly warped current
sheet dominated heliospheric structure. The geospace data revealed an
unusually high level of activity, driven primarily by the periodic
impingement of high-speed streams. The WHI studies traced the solar
activity and structure into the heliosphere and geospace, and provided
new insight into the nature of the interconnected heliophysical system
near solar minimum.
---------------------------------------------------------
Title: The Whole Heliosphere Interval in the Context of a Long and
Structured Solar Minimum: An Overview from Sun to Earth
Authors: Gibson, S. E.; de Toma, G.; Emery, B.; Riley, P.; Zhao, L.;
Elsworth, Y.; Leamon, R. J.; Lei, J.; McIntosh, S.; Mewaldt, R. A.;
Thompson, B. J.; Webb, D.
2011SoPh..274....5G Altcode: 2011SoPh..tmp..427G
Throughout months of extremely low solar activity during the recent
extended solar-cycle minimum, structural evolution continued to be
observed from the Sun through the solar wind and to the Earth. In
2008, the presence of long-lived and large low-latitude coronal holes
meant that geospace was periodically impacted by high-speed streams,
even though solar irradiance, activity, and interplanetary magnetic
fields had reached levels as low as, or lower than, observed in past
minima. This time period, which includes the first Whole Heliosphere
Interval (WHI 1: Carrington Rotation (CR) 2068), illustrates the
effects of fast solar-wind streams on the Earth in an otherwise quiet
heliosphere. By the end of 2008, sunspots and solar irradiance had
reached their lowest levels for this minimum (e.g., WHI 2: CR 2078),
and continued solar magnetic-flux evolution had led to a flattening
of the heliospheric current sheet and the decay of the low-latitude
coronal holes and associated Earth-intersecting high-speed solar-wind
streams. As the new solar cycle slowly began, solar-wind and geospace
observables stayed low or continued to decline, reaching very low
levels by June - July 2009. At this point (e.g., WHI 3: CR 2085) the
Sun-Earth system, taken as a whole, was at its quietest. In this article
we present an overview of observations that span the period 2008 -
2009, with highlighted discussion of CRs 2068, 2078, and 2085. We show
side-by-side observables from the Sun's interior through its surface and
atmosphere, through the solar wind and heliosphere and to the Earth's
space environment and upper atmosphere, and reference detailed studies
of these various regimes within this topical issue and elsewhere.
---------------------------------------------------------
Title: Cavity magnetic observations: A survey using AIA and CoMP data
Authors: Forland, B.; Rachmeler, L. A.; Gibson, S. E.; Dove, J.
2011AGUFMSH43B1951F Altcode:
The magnetic structure of the corona is the predominate source of energy
when it comes to coronal mass ejections (CMEs) and flares. Coronal
prominence cavities are highly visible regions of rarified density
when viewed off limb that are are known to store magnetic energy and
can erupt causing CMEs. Observing magnetic fields in the corona has
always been difficult, but for the first time daily observations
of linear polarization are being made by the Coronal Multichannel
Polarimeter (CoMP). These observations of the optically-thin corona
are ideal for structure such as cavities which extend along the line
of sight. A survey was conducted over the last 6 months using the
Atmospheric Imaging Assembly (AIA) instrument aboard the Solar Dynamic
Observatory (SDO) satellite in order to create a working database of all
visible cavities. These cavities were then compared to intensity and
linear polarization images obtained by the CoMP telescope. The linear
polarization images were examined for specific structures similar to
those created using forward calculations of CoMP-like observables from
magnetohydrodynamic models.
---------------------------------------------------------
Title: Diagnosing the Prominence-Cavity Connection
Authors: Schmit, D. J.; Gibson, S. E.
2011AGUFMSH43B1947S Altcode:
The magnetic field is thought to play a central role in both the
support of prominence plasma as well as the thermodynamic isolation of
the surrounding cavity. We use the statistical goldmine of the SDO/AIA
dataset to probe for the first time the dynamical link between these
related structures. These observations are compared to the 3D magnetic
geometries predicted by MHD models. The dynamic features are explained
within the context of 1D field-aligned momentum and energy imbalance.
---------------------------------------------------------
Title: Comparing Global Coronal Models to CoMP Data
Authors: Rachmeler, L. A.; Gibson, S. E.; Tomczyk, S.
2011AGUFMSH43B1941R Altcode:
Coronal polarization data is one of the very few available quantitative
measurements of the coronal magnetic field, which makes it extremely
attractive as a means of validating numerical models. Our forward
analysis technique produces synthetic line-of-sight integrated
polarization signals from coronal models. We present initial results
from comparisons of forward calculations of the Potential Field Source
Surface (PFSS) model to polarization data taken with the Coronal
Multichannel Polarimeter (CoMP). This research focuses on validating
the applicability of the PFSS model by determining how much the real
corona deviates from a potential field. The non-potentiality of the
corona not only has applications for testing the PFSS field, but also
for forecasting, and for finding the locations of greatest magnetic
energy storage.
---------------------------------------------------------
Title: Solar Prominence Eruptions and CMEs at the Start of Cycle 24
Authors: de Toma, Giuliana; Gibson, S.; Burkepile, J.; Fan, Y.;
Reinard, A.
2011shin.confE.147D Altcode:
We present the analysis of prominence eruptions and CMEs during the
rising phase of cycle 24. We combine data from the two STEREO and
SDO spacecraft (that are near quadrature) to observe simultaneously
the region where a CME originates and the CME moving outward in the
plane-of-the-sky. This allows us to compute trajectories for the
CME and the associated eruptive prominence and, at the same time, to
study the on-disk CME manifestations such as flares, dimming regions,
and coronal waves with high spatial and temporal resolution.
---------------------------------------------------------
Title: Learning about coronal polarization through forward modeling
Authors: Rachmeler, Laurel Anne; Gibson, Sarah; Dove, James
2011shin.confE..30R Altcode:
We present scientific results from forward modeling of coronal
polarization signals whereby synthetic data is created from coronal
models. We have worked with spheromak and cylindrical-type flux ropes,
and breakout-type sheared arcade. Each of these magnetic configurations
produces distinct polarization signatures. We present the results from
our analysis as well as some of the challenges that we have faced,
and the insight we have gained during the analysis. The goal is to
present the scientific utility as well as the limitations of coronal
polarization data.
---------------------------------------------------------
Title: A Ring of Polarized Light: Evidence for Twisted Coronal
Magnetism in Cavities
Authors: Gibson, Sarah; Dove, James; Rachmeler, Laurel; Tomczyk,
Steve; Judge, Phil
2011shin.confE..28G Altcode:
Coronal prominence cavities may be manifestations of twisted or sheared
magnetic fields capable of storing the energy required to drive solar
eruptions. The Coronal Multi-Channel Polarimeter (CoMP), recently
installed at Mauna Loa Solar Observatory, can measure polarimetric
signatures of current-carrying magnetohydrodynamic (MHD) systems. For
the first time, this instrument offers the capability of daily full-Sun
observations of the forbidden lines of Fe XIII with high enough
spatial resolution and throughput to measure polarimetric signatures of
current-carrying MHD systems. By forward-calculating CoMP observables
from analytic MHD models of spheromak-type magnetic flux ropes, we show
that a predicted observable for such flux ropes oriented along the line
of sight is a bright ring of linear polarization surrounding a region
where the linear polarization strength is relatively depleted. We
present CoMP observations of a coronal cavity possessing such a
polarization ring.
---------------------------------------------------------
Title: Vector Tomography for the 3D Coronal Magnetic Field with CoMP
Authors: Kramar, Maxim; Lin, Haosheng; Inhester, Bernd; Gibson, Sarah
2011shin.confE..29K Altcode:
Magnetic fields in the solar corona dominates the gas pressure
and therefore determine the static and dynamic properties of the
corona. Direct measurement of the coronal magnetic field is one of
the most challenging problems in observational solar astronomy and
recently a significant progress has been achieved here with deployment
of the HAO Coronal Multichannel Polarimeter (CoMP). The instrument
provides polarization measurements of Fe XIII 10747 A forbidden line
emission. The observed polarization depends on magnetic field through
the Hanle and Zeeman effects. However, because the coronal measurements
are integrated over line-of-site (LOS), it is impossible to derive the
configuration of the coronal magnetic field from a single observation
(from a single viewing direction). The vector tomography techniques
based on measurements from several viewing directions has the potential
to resolve the 3D coronal magnetic field structure over LOS. Because
of the non-linear character of the Hanle effect, the reconstruction
result based on such data is not straightforward and depends on the
particular coronal field configuration. Therefore we study here what
is the sensitivity of the vector tomographic inversion to sophisticated
(MHD) coronal magnetic field models. <P />For several important cases of
magnetic field configuration, it has been found that even just Stokes-Q
and -U data (supplied with 3D coronal density and temperature) can be
used in vector tomography to provide a realistic 3D coronal magnetic
field configuration. Effect of noise in the all input data has been
also studied. Inclusion of the Stokes-V data into the inversion will
significantly increase a number of of magnetic field configuration which
are possible to reconstruct. <P />Particularly, the reconstructions
may be used to analyze non-potential pre-CME magnetic configurations
or for improving a potential field model when the field is potential.
---------------------------------------------------------
Title: Forward Modeling Cavity Density: A Multi-instrument Diagnostic
Authors: Schmit, D. J.; Gibson, S. E.
2011ApJ...733....1S Altcode:
The thermodynamic properties of coronal prominence cavities present a
unique probe into the energy and mass budget of prominences. Using
a three-dimensional morphological model, we forward model the
polarization brightness and extreme-ultraviolet (EUV) emission of a
cavity and its surrounding streamer. Using a genetic algorithm, we
find the best-fit density model by comparing the models to Mauna Loa
Solar Observatory MK4 and Hinode EUV Imaging Spectrometer data. The
effect of temperature variations on the derived density is also
measured. We have measured the density inside a cavity down to 1.05 R
<SUB>sun</SUB> with height-dependent error bars. Our forward modeling
technique compensates for optically thin projection effects. This
method provides a complementary technique to traditional line ratio
diagnostics that is useful for diffuse off-limb coronal structures.
---------------------------------------------------------
Title: Temperature Structure of a Coronal Cavity
Authors: Kucera, Therese A.; Gibson, S. E.; Schmit, D. J.
2011SPD....42.1833K Altcode: 2011BAAS..43S.1833K
We analyze the temperature structure of a coronal cavity observed in
Aug. 2007. Coronal cavities are long, low-density structures located
over filament neutral lines and are often seen as dark elliptical
features at the solar limb in white light, EUV and X-rays. When
these structures erupt they form the cavity portions of CMEs. It is
important to establish the temperature structure of cavities in order
to understand the thermodynamics of cavities in relation to their
three-dimensional magnetic structure. <P />To analyze the temperature
we compare temperature ratios of a series of iron lines observed by
the Hinode/EUV Imaging Spectrometer (EIS). We also use those lines
to constrain a forward model of the emission from the cavity and
streamer. The model assumes a coronal streamer with a tunnel-like
cavity with elliptical cross-section and a Gaussian variation of height
along the tunnel length. Temperature and density can be varied as
a function of altitude both in the cavity and streamer. The general
cavity morphology and the cavity and streamer density have already
been modeled using data from STEREO's SECCHI/EUVI and Hinode/EIS
(Gibson et al 2010 and Schmit & Gibson 2011).
---------------------------------------------------------
Title: Vector Tomography Based on Hanle and Zeeman Effects Observed
from Ecliptic Plane
Authors: Kramar, Maxim; Lin, H.; Gibson, S.
2011SPD....42.1830K Altcode: 2011BAAS..43S.1830K
The magnetically sensitive coronal emission lines provide
information about coronal magnetic field via Hanle and Zeeman
effects. As the measured emission are integrated over line-of-sight,
the vector tomography must be used for deriving 3D magnetic field
configuration. The unique solution for any field configuration exists
when observations are done from both ecliptic and out of ecliptic
plane and supplied by photospheric magnetic field measurements. When
observations are only from the ecliptic plane, the number of field
configurations which are possible to reconstruct are reduced. We
study here what types of coronal magnetic field configurations can be
reconstructed based on Hanle and Zeeman effects provided by CoMP and
SOLARC instruments. Effect of noise in the data and uncertainty in 3D
reconstruction of the coronal density and temperature are also studied.
---------------------------------------------------------
Title: A Ring of Polarized Light: Evidence for Twisted Coronal
Magnetism in Cavities
Authors: Dove, J. B.; Gibson, S. E.; Rachmeler, L. A.; Tomczyk, S.;
Judge, P.
2011ApJ...731L...1D Altcode:
Coronal prominence cavities may be manifestations of twisted or sheared
magnetic fields capable of storing the energy required to drive solar
eruptions. The Coronal Multi-Channel Polarimeter (CoMP), recently
installed at Mauna Loa Solar Observatory, can measure polarimetric
signatures of current-carrying magnetohydrodynamic (MHD) systems. For
the first time, this instrument offers the capability of daily full-Sun
observations of the forbidden lines of Fe XIII with high enough
spatial resolution and throughput to measure polarimetric signatures of
current-carrying MHD systems. By forward-calculating CoMP observables
from analytic MHD models of spheromak-type magnetic flux ropes, we show
that a predicted observable for such flux ropes oriented along the line
of sight is a bright ring of linear polarization surrounding a region
where the linear polarization strength is relatively depleted. We
present CoMP observations of a coronal cavity possessing such a
polarization ring.
---------------------------------------------------------
Title: The GALFA-HI Survey: Feeding the Disk via Stellar Feedback
Authors: Putman, Mary E.; Peek, J.; Saul, D.; Grcevich, J.; Begum,
A.; Douglas, K.; Gibson, S.; Heiles, C.; Korpela, E.; Lee, M.;
Stanimirovic, S.
2011AAS...21724101P Altcode: 2011BAAS...4324101P
The contribution of future star formation fuel to a galaxy from evolved
stars remains uncertain. We present a correlation of discrete clouds
of HI gas with evolved variable stars and find a number of cases where
stellar mass-loss is likely to have created the cloud. The results
of this study impact our understanding of both stellar outflows and
galactic gas recycling. This research was partially funded by NSF
grant AST-0917810.
---------------------------------------------------------
Title: The GALFA-HI Survey: Transition from HI to H2 Caught in Action
in the Perseus Molecular Cloud
Authors: Lee, Min-Young; Stanimirovic, S.; Leroy, A.; Douglas, K.; Di
Francesco, J.; Gibson, S.; Knee, L.; Plume, R.; Begum, A.; Grcevich,
J.; Heiles, C.; Korpela, E.; Peek, J.; Pingel, N.; Putman, M.; Saul, D.
2011AAS...21724102L Altcode: 2011BAAS...4324102L
The conversion of atomic gas into molecular gas is a critical process
for star formation. Yet, a deep understanding of fundamental agents
that control the ratio of atomic to molecular gas in molecular clouds
has not been achieved. <P />Recently, Krumholz et al. (2009) provided
theoretical predictions for the ratio of atomic to molecular gas in
galaxies as a function of galactic properties (total gas column density
and metallicity). We test the Krumholz's predictions on sub-parsec
scales by investigating the ratio of atomic to molecular gas across the
Perseus molecular cloud. We estimate the dust column density using the
IRIS 60 and 100 micron maps and derive the H2 column density from the
excess of infrared emission relative to the HI column density. Using the
HI data from the GALFA-HI Survey, we derive the map of R<SUB>H2</SUB>
(H2 surface density / HI surface density) for Perseus. Our comparison
of observational data with the Krumholz's predictions shows that
the model reasonably well describes R<SUB>H2</SUB> as a function
of total gas column density even at sub-parsec scales. We compare
R<SUB>H2 </SUB>for several star-forming and dark clouds in Perseus
to investigate the role of interstellar radiation field in molecule
formation. <P />This research was partially funded by the NSF grant
<P />AST-0707679 and the Research Corporation for Science Advancement.
---------------------------------------------------------
Title: Three-dimensional morphology of a coronal prominence cavity
Authors: Gibson, S. E.; Kucera, T. A.; Rastawicki, D.; Dove, J.; de
Toma, G.; Hao, J.; Hill, S. M.; Hudson, H. S.; Marque, C.; McIntosh,
P. S.; Rachmeler, L.; Reeves, K. K.; Schmieder, B.; Schmit, D. J.;
Sterling, A.; Tripathi, D.; Williams, D. R.; Zhang, M.
2010AGUFMSH51A1667G Altcode:
We present a three-dimensional density model of coronal prominence
cavities, and a morphological fit that has been tightly constrained
by a uniquely well-observed cavity. Observations were obtained as part
of an International Heliophysical Year campaign by instruments from a
variety of space- and ground-based observatories, spanning wavelengths
from radio to soft-X-ray to integrated white light. From these data
it is clear that the prominence cavity is the limb manifestation of
a longitudinally-extended polar-crown filament channel, and that
the cavity is a region of low density relative to the surrounding
corona. As a first step towards quantifying density and temperature
from campaign spectroscopic data, we establish the three-dimensional
morphology of the cavity. This is critical for taking line-of-sight
projection effects into account, since cavities are not localized in the
plane of the sky and the corona is optically thin. We have augmented
a global coronal streamer model to include a tunnel-like cavity with
elliptical cross-section and a Gaussian variation of height along
the tunnel length. We have developed a semi-automated routine that
fits ellipses to cross-sections of the cavity as it rotates past the
solar limb, and have applied it to Extreme Ultraviolet Imager (EUVI)
observations from the two Solar Terrestrial Relations Observatory
(STEREO) spacecraft. This defines the morphological parameters of our
model, from which we reproduce forward-modeled cavity observables. We
find that cavity morphology and orientation, in combination with the
viewpoints of the observing spacecraft, explains the observed variation
in cavity visibility for the east vs. west limbs.
---------------------------------------------------------
Title: Three-dimensional Morphology of a Coronal Prominence Cavity
Authors: Gibson, S. E.; Kucera, T. A.; Rastawicki, D.; Dove, J.; de
Toma, G.; Hao, J.; Hill, S.; Hudson, H. S.; Marqué, C.; McIntosh,
P. S.; Rachmeler, L.; Reeves, K. K.; Schmieder, B.; Schmit, D. J.;
Seaton, D. B.; Sterling, A. C.; Tripathi, D.; Williams, D. R.;
Zhang, M.
2010ApJ...724.1133G Altcode:
We present a three-dimensional density model of coronal prominence
cavities, and a morphological fit that has been tightly constrained
by a uniquely well-observed cavity. Observations were obtained as part
of an International Heliophysical Year campaign by instruments from a
variety of space- and ground-based observatories, spanning wavelengths
from radio to soft X-ray to integrated white light. From these data
it is clear that the prominence cavity is the limb manifestation of
a longitudinally extended polar-crown filament channel, and that the
cavity is a region of low density relative to the surrounding corona. As
a first step toward quantifying density and temperature from campaign
spectroscopic data, we establish the three-dimensional morphology
of the cavity. This is critical for taking line-of-sight projection
effects into account, since cavities are not localized in the plane of
the sky and the corona is optically thin. We have augmented a global
coronal streamer model to include a tunnel-like cavity with elliptical
cross-section and a Gaussian variation of height along the tunnel
length. We have developed a semi-automated routine that fits ellipses
to cross-sections of the cavity as it rotates past the solar limb, and
have applied it to Extreme Ultraviolet Imager observations from the
two Solar Terrestrial Relations Observatory spacecraft. This defines
the morphological parameters of our model, from which we reproduce
forward-modeled cavity observables. We find that cavity morphology
and orientation, in combination with the viewpoints of the observing
spacecraft, explain the observed variation in cavity visibility for
the east versus west limbs.
---------------------------------------------------------
Title: A ring of polarized light: evidence for twisted coronal
magnetism in cavities (Invited)
Authors: Dove, J.; Rachmeler, L.; Gibson, S. E.; Judge, P. G.;
Tomczyk, S.
2010AGUFMSH54A..01D Altcode:
Determining coronal magnetic fields is crucial to modeling the processes
that power and trigger solar flares and coronal mass ejections. Coronal
prominence cavities have been modeled as magnetic flux ropes, and have
been observed to erupt bodily as coronal mass ejections. One promising
technique for establishing the magnetic morphology of cavities is to
use spectropolarimetry of the infrared (IR) forbidden lines of Fe XIII
(at 1074.7 nm and 1079.8 nm). The Coronal Multi-Channel Polarimeter is
currently situated at the Mauna Loa Solar Observatory (MLSO), and has
begun taking daily full-Sun observations of line-of-sight integrated
Stokes parameters for these lines. For a variety of analytic coronal
magnetohydrodynamic models, we have determined forward-calculations
of CoMP observables using the formalism of Judge and Casini (2001). We
show that different MHD models and orientations do yield distinguishing
observational characteristics. In particular, a common characteristic
for spheroidal flux ropes oriented along the observational line of
sight is a ring of linear polarization surrounding a region where
the linear polarization strength is relatively depleted (the heart of
darkness). Such a polarization ring has been found in an observation
of a coronal cavity taken by CoMP in April 2005 from Sacramento
Peak. Cavities are ubiquitous features, particularly at this time of
the solar cycle. The daily observations to be taken by CoMP at MLSO
will allow us to further probe these structures, constraining models
of coronal magnetism and providing a testbed for future capabilities
of the proposed Coronal Solar Magnetism Observatory (COSMO).
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Title: 3D Study of Solar Eruptions Using SDO and STEREO Observations
Authors: de Toma, G.; Reinard, A. A.; Gibson, S. E.; Burkepile, J.;
Fan, Y.; Torok, T.
2010AGUFMSH23A1834D Altcode:
Combination of data from the recently launched SDO and the two STEREO
spacecraft -that are now at about 80deg from the Sun-Earth direction-
offers the unprecedented opportunity to observe simultaneously the
region where a CME originates and the CME moving outward in the
plane-of-the-sky. This allows us to compute trajectories for the
CME and the associated eruptive prominence and, at the same time, to
study the on-disk CME manifestations such as flares, dimming regions,
and coronal waves with very high spatial and temporal resolution. We
present examples of Earth-directed CMEs, when the CME can be traced
from the Sun to the Earth, that take advantage of this unique satellite
configuration.
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Title: Space Based Observations of Coronal Cavities in Conjunction
with the Total Solar Eclipse of July 2010
Authors: Kucera, T. A.; Berger, T. E.; Boerner, P.; Dietzel, M.;
Druckmuller, M.; Gibson, S. E.; Habbal, S. R.; Morgan, H.; Reeves,
K. K.; Schmit, D. J.; Seaton, D. B.
2010AGUFMSH51A1666K Altcode:
In conjunction with the total solar eclipse on July 11, 2010 we
coordinated a campaign between ground and space based observations. Our
specific goal was to augment the ground based measurement of coronal
prominence cavity temperatures made using iron lines in the IR (Habbal
et al. 2010 ApJ 719 1362) with measurements performed by space based
instruments. Included in the campaign were Hinode/EIS, XRT and SOT,
PROBA2/SWAP, SDO/AIA, SOHO/CDS and STEREO/SECCHI/EUVI, in addition
to the ground based IR measurements. We plan to use a combination of
line ratio and forward modeling techniques to investigate the density
and temperature structure of the cavities at that time.
---------------------------------------------------------
Title: Morphology of a hot coronal cavity core as observed by
Hinode/XRT
Authors: Reeves, K. K.; Gibson, S. E.; Kucera, T. A.; Hudson, H. S.
2010AGUFMSH51A1669R Altcode:
We follow a coronal cavity that was observed by Hinode/XRT during the
summer of 2008. This cavity has a persistent area of relatively bright
X-ray emission in its center. We use multifilter data from XRT to
study the thermal emission from this cavity, and find that the bright
center is hotter than the surrounding cavity plasma with temperatures
of about 1.6 MK. We follow the morphology of this hot feature as the
cavity structure rotates over the limb during the several days between
July 19 - 23 2008. We find that the hot structure at first looks fairly
circular, then appears to expand and elongate, and then shrinks again
to a compact circular shape. We interpret this apparent change in shape
as being due to the morphology of the filament channel associated with
the cavity, and the change in viewing angle as the structure rotates
over the limb of the Sun.
---------------------------------------------------------
Title: Density Diagnostics in Cavities: Incorporating and Bypassing
Projection Effects
Authors: Schmit, D. J.; Gibson, S. E.; Kucera, T. A.
2010AGUFMSH51A1668S Altcode:
The highly ionized corona emits strongly in EUV atomic emission
lines. Comparison of relative emission in various lines provides the
temperature and density of the coronal plasma. We use an Fe XII line
ratio to probe the density of a prominence cavity at heights generally
only accessible to spectroscopic instruments. We take a novel approach
in this diagnostic by fully accounting for the 3D structure of the
corona so as to compensate for the projection effects in optical thin
emission. The density inside the cavity and the streamer are constrained
using a forward model where in emission is synthesized with CHIANTI. The
synthetic emission and scattering is compared to Hinode/EIS and MLSO
MKIV data. A least squares minimization is conducted using a genetic
algorithm. In particular, this work addresses the degree to which we
can answer the question, “Is there a density jump at all heights?”.
---------------------------------------------------------
Title: Creating synthetic coronal observational data from MHD models:
the forward technique
Authors: Rachmeler, L. A.; Gibson, S. E.; Dove, J.; Kucera, T. A.
2010AGUFMSH31A1786R Altcode:
We present a generalized forward code for creating simulated
coronal observables off the limb from numerical and analytical MHD
models. This generalized forward model is capable of creating emission
maps in various wavelengths for instruments such as Hinode/XRT,
STEREO/SECCHI/EUVI, and coronagraphs, as well as spectropolarimetric
images and line profiles. The inputs to our code can be analytic MHD or
morphological models (of which four come with the code) or 2.5D and 3D
numerical datacubes. We present some examples of the observable data
created with our code as well as its functional capabilities. This
code is currently available for beta-testing (contact authors), with
the ultimate goal of release as a SolarSoft package.
---------------------------------------------------------
Title: Whole Heliosphere Interval: Overview of JD16
Authors: Webb, David F.; Gibson, Sarah E.; Thompson, Barbara J.
2010HiA....15..471W Altcode:
The Whole Heliosphere Interval is an international observing and
modeling effort to characterize the three-dimensional interconnected
solar-heliospheric-planetary system, i.e., the “heliophysical”
system. WHI was part of the International Heliophysical Year, on the
50th anniversary of the International Geophysical Year, and benefited
from hundreds of observatories and instruments participating in IHY
activities. WHI describes the 3-D heliosphere originating from solar
Carrington Rotation 2068, March 20-April 16, 2008. The focus of IAU JD16
was on analyses of observations obtained during WHI, and simulations
and modeling involving those data and that period. Consideration of
the WHI interval in the context of surrounding solar rotations and/or
compared to last solar minimum was also encouraged. Our goal was to
identify connections and commonalities between the various regions of
the heliosphere.
---------------------------------------------------------
Title: Forward modeling of spectropolarimetric data to interpret
coronal magnetic features
Authors: Rachmeler, Laurel A.; Gibson, S. E.; Dove, J.; Judge, P. G.
2010shin.confE..53R Altcode:
We present a forward model that creates various forms of coronal
observational data from simulated systems. Along with plane of
sky parameter slices and integrated emission images, this model
calculates the full Stokes vectors from forbidden infrared lines. It
is clear that photospheric magnetograph data is not sufficient to
ascertain coronal magnetic fields. The coronal Stokes vectors provide
additional information about the magnetic morphology above the solar
limb, specifically the relative strength of the integrated plane of
sky and line of sight field. Our forward model helps to determine
which physical features can be identified in the observations as a
specific component of a theoretical model, without requiring a full
3D inversion of the Stokes profiles. We have found that flux ropes
are theoretically identifiable in the simulated data, and we use this
technique to explore the disambiguation of pre-CME filament structure.
---------------------------------------------------------
Title: The Whole Heliosphere Interval in the Context of the Current
Solar Minimum
Authors: Gibson, S. E.; Webb, D. F.; Thompson, B. J.
2010ASPC..428..223G Altcode:
The current solar minimum may not be "peculiar" when considered on
scales of a century or more. However, the opportunity for discovery
yielded by its extended nature, in combination with the abundance of
modern observations, cannot be overstated. In this paper, we describe
the Whole Heliosphere Interval (WHI), an in-depth study of the Sun-Earth
system for a solar rotation in March/April 2008. We discuss how WHI
fits within the broader context of the current deep, long, and complex
solar minimum.
---------------------------------------------------------
Title: The Minimum Between Cycle 23 and 24: Is Sunspot Number the
Whole Story?
Authors: de Toma, G.; Gibson, S. E.; Emery, B. A.; Arge, C. N.
2010ASPC..428..217D Altcode:
During recent years we have observed a long and deep solar minimum
with sunspot number in 2008 and 2009 reaching the lowest level in
about a century. In spite of the lack of sunspot activity at the Sun,
observations have shown that a relatively complex corona and heliosphere
persisted for most of the minimum phase. The solar corona did not
reach the simple "dipolar" shape often seen during solar minima, while
low-latitude coronal holes, and their associated corotating high-speed
solar wind streams, persisted to 2008, modulating the solar wind. We
compare the current and previous minima to show how, even during very
quiet times, different magnetic configurations are possible at the Sun
and discuss how these different morphologies can affect the corona,
heliosphere, and even the geospace.
---------------------------------------------------------
Title: Thermal Properties of Coronal Cavities as Observed by the
X-Ray Telescope on Hinode
Authors: Reeves, Kathy; Gibson, S. E.; Kucera, T. A.; Hudson, H. S.;
Tripathi, D.
2010AAS...21640511R Altcode: 2010BAAS...41..891R
Coronal cavities are voids in coronal emission often observed above
high latitude filament channels. Sometimes, these cavities have
areas of bright X-ray emission in their centers (i.e. Hudson et al
<P />1999). In this study, we use data from the X-ray Telescope (XRT)
on Hinode to examine the thermal emission properties of two kinds of
coronal cavities, those with and without enhanced emission at their
centers. For cavities with bright X-ray emission in their centers,
we find evidence for elevated temperatures in the cavity center. We
find no obvious correlation between the presence of <P />bright cavity
cores and filament presence or eruption. <P />This work is part of the
effort of the International Space Science Institute International Team
on Prominence Cavities
---------------------------------------------------------
Title: Geometric Model of a Coronal Cavity
Authors: Kucera, Therese A.; Gibson, S. E.; Rastawicki, D.; Dove, J.;
de Toma, G.; Hao, J.; Hudson, H. S.; Marque, C.; McIntosh, P. S.;
Reeves, K. K.; Schmidt, D. J.; Sterling, A. C.; Tripathi, D. K.;
Williams, D. R.; Zhang, M.
2010AAS...21640510K Altcode: 2010BAAS...41..890K
We observed a coronal cavity from August 8-18 2007 during a
multi-instrument observing campaign organized under the auspices of
the International Heliophysical Year (IHY). Here we present initial
efforts to model the cavity with a geometrical streamer-cavity
model. The model is based the white-light streamer model of Gibson et
al. (2003), which has been enhanced by the addition of a cavity and
the capability to model EUV and X-ray emission. The cavity is modeled
with an elliptical cross-section and Gaussian fall-off in length and
width inside the streamer. Density and temperature can be varied in the
streamer and cavity and constrained via comparison with data. Although
this model is purely morphological, it allows for three-dimensional,
multi-temperature analysis and characterization of the data, which
can then provide constraints for future physical modeling. Initial
comparisons to STEREO/EUVI images of the cavity and streamer show that
the model can provide a good fit to the data. This work is part of the
effort of the International Space Science Institute International Team
on Prominence Cavities.
---------------------------------------------------------
Title: Solar Cycle 23: An Unusual Solar Minimum?
Authors: de Toma, Giuliana; Gibson, Sarah; Emery, Barbara; Kozyra,
Janet
2010AIPC.1216..667D Altcode:
We are currently observing the minimum phase of Cycle 23. Magnetic
activity during the years 2006-2009 has been very weak with sunspot
numbers reaching the lowest values in about 100 years. This long and
extended minimum is characterized by weak polar magnetic fields, small
polar coronal holes, and a relatively complex coronal morphology. This
magnetic configuration at the Sun is remarkably different from the one
observed during the previous two solar minima. We review observations
made at the Sun and in the solar wind during the recent solar minima
and discuss the implications of the observed differences for the
heliosphere and geospace.
---------------------------------------------------------
Title: If the Sun is so quiet, why is the Earth ringing? A comparison
of two solar minimum intervals
Authors: Gibson, S. E.; Kozyra, J. U.; de Toma, G.; Emery, B. A.;
Onsager, T. G.; Thompson, B. J.
2009AGUFMSH11A1501G Altcode:
A system-oriented analysis of new observations from the recent
international Whole Heliosphere Interval (WHI) campaign in comparison
with the equivalent Whole Sun Month (WSM) campaign from last cycle’s
minimum yields new insight into solar quiet intervals and the solar
minimum Sun-Earth system. We use a side-by-side comparison of these
two intervals to demonstrate that sunspot numbers, while providing a
good measure of solar activity, do not provide sufficient information
to gauge solar and heliospheric magnetic complexity and its effect
at the Earth. The present solar minimum is exceptionally quiet, with
sunspot numbers the lowest in 75 years, solar wind density and IMF
strength at the lowest values ever observed, and geomagnetic indices
and solar EUV fluxes the lowest in three solar cycles. Despite, or
perhaps because of this global weakness in the heliospheric magnetic
field, large near-equatorial coronal holes lingered even as the
sunspots disappeared, indicating significant open magnetic flux at low
latitudes. Consequently, for the months surrounding the WHI campaign,
strong, long, and recurring high-speed streams in the solar wind
intercepted the Earth in contrast to the weaker and more sporadic
streams that occurred around the time of the WSM campaign. Since
the speed, duration and southward magnetic field component in wind
streams determine the severity of space weather effects, the geospace
environment responded quite differently to the two solar minimum
heliospheric morphologies. We illustrate this point with the behavior
of relativistic electrons in the Earth’s outer radiation belt, which
were more than three times stronger during WHI than in WSM. The cause
is clear: it is well-known that high-speed streams drive radiation belt
population, and indeed, for the months surrounding WHI, geospace and
upper atmospheric parameters were ringing with the periodicities of
the solar wind in a manner that was absent last cycle minimum. Such
behavior could not have been predicted using sunspot numbers alone,
indicating the importance of considering variation within and between
solar minima in analyzing and predicting space weather responses at
the Earth during solar quiet intervals, as well as in interpreting the
Sun’s past behavior as preserved in geological and historical records.
---------------------------------------------------------
Title: Are Unusual Solar Wind Conditions in SC23-24 Triggering
Changes in the Geospace Response to High Speed Streams? (Invited)
Authors: Kozyra, J. U.; Brandt, P. C.; Buzulukova, N.; de Zeeuw, D.;
Fok, M. H.; Frey, H. U.; Gibson, S. E.; Ilie, R.; Liemohn, M. W.;
Mende, S. B.; Paxton, L. J.; Rastaetter, L.; Ridley, A. J.; Thomsen,
M. F.
2009AGUFMSH14A..06K Altcode:
In the descent to solar minimum in solar cycle 23-24, the high-speed
streams (HSS) were faster and longer lived than previous cycles but
the average IMF was weaker and the average solar wind density lower
than ever before recorded upstream of the Earth. A simulation of high
speed stream activity on 22-24 January 2005 using the BATS-R-US MHD
model with embedded Rice Convection Model driven by solar wind inputs
indicates that, at least for this event, the interaction between high
speed streams and the magnetosphere has been modified by these unusual
solar wind conditions. Northward IMF in the HSS drove the periodic
capture of solar wind/magnetosheath plasma in the dayside magnetosphere
due to high-latitude reconnection. At times of observed strong
periodic auroral activity, a significant IMF By component produced a
magnetospheric sash configuration in the simulations in which fingers
of enhanced plasma beta were associated with strong field-aligned
currents linking to the nightside auroral region. In agreement with
the simulations, IMAGE HENA observed low energy (less than tens of keV)
hydrogen energetic neutral atoms peaking on the dayside for the 3-days
of the high speed stream activity. IMAGE FUV and TIMED GUVI observed
periodic auroral activations during the HSS that resembled poleward
boundary intensifications (PBIs) rather than the periodic substorms
typically associated with HSS. The locations of the observed PBIs in
the southern hemisphere were consistent with the high-beta fingers
in the near-Earth plasma sheet predicted by the simulation. Particle
injection signatures at LANL geosynchronous satellites accompanied the
PBIs. To our knowledge, these results provide the first evidence in
support of the role of northward IMF in HSS interactions. Based on these
results, a study of energetic neutral atom images from TWINS and IMAGE
HENA along with observations from other missions in the Heliophysics
System Observatory is underway to determine if these characteristics
are typical of HSS interactions in the current unusual solar minimum
and to search for consequences throughout geospace.
---------------------------------------------------------
Title: If the Sun is so quiet, why is the Earth ringing? A comparison
of two solar minimum intervals
Authors: Gibson, S. E.; Kozyra, J. U.; de Toma, G.; Emery, B. A.;
Onsager, T.; Thompson, B. J.
2009JGRA..114.9105G Altcode: 2009JGRA..11409105G
Observations from the recent Whole Heliosphere Interval (WHI) solar
minimum campaign are compared to last cycle's Whole Sun Month (WSM)
to demonstrate that sunspot numbers, while providing a good measure of
solar activity, do not provide sufficient information to gauge solar
and heliospheric magnetic complexity and its effect at the Earth. The
present solar minimum is exceptionally quiet, with sunspot numbers at
their lowest in 75 years and solar wind magnetic field strength lower
than ever observed. Despite, or perhaps because of, a global weakness
in the heliospheric magnetic field, large near-equatorial coronal
holes lingered even as the sunspots disappeared. Consequently, for
the months surrounding the WHI campaign, strong, long, and recurring
high-speed streams in the solar wind intercepted the Earth in contrast
to the weaker and more sporadic streams that occurred around the
time of last cycle's WSM campaign. In response, geospace and upper
atmospheric parameters continued to ring with the periodicities of
the solar wind in a manner that was absent last cycle minimum, and the
flux of relativistic electrons in the Earth's outer radiation belt was
elevated to levels more than three times higher in WHI than in WSM. Such
behavior could not have been predicted using sunspot numbers alone,
indicating the importance of considering variation within and between
solar minima in analyzing and predicting space weather responses at
the Earth during solar quiet intervals, as well as in interpreting the
Sun's past behavior as preserved in geological and historical records.
---------------------------------------------------------
Title: Additive Self-helicity as a Kink Mode Threshold
Authors: Malanushenko, A.; Longcope, D. W.; Fan, Y.; Gibson, S. E.
2009ApJ...702..580M Altcode: 2009arXiv0909.4959M
In this paper, we propose that additive self-helicity, introduced
by Longcope and Malanushenko, plays a role in the kink instability
for complex equilibria, similar to twist helicity for thin flux
tubes. We support this hypothesis by a calculation of additive
self-helicity of a twisted flux tube from the simulation of Fan and
Gibson. As more twist gets introduced, the additive self-helicity
increases, and the kink instability of the tube coincides with the
drop of additive self-helicity, after the latter reaches the value
of H<SUB>A</SUB> /Φ<SUP>2</SUP> ≈ 1.5 (where Φ is the flux of the
tube and H<SUB>A</SUB> is the additive self-helicity). We compare the
additive self-helicity to twist for a thin subportion of the tube
to illustrate that H<SUB>A</SUB> /Φ<SUP>2</SUP> is equal to the
twist number, studied by Berger and Field, when the thin flux tube
approximation is applicable. We suggest that the quantity H<SUB>A</SUB>
/Φ<SUP>2</SUP> could be treated as a generalization of a twist number,
when the thin flux tube approximation is not applicable. A threshold on
a generalized twist number might prove extremely useful studying complex
equilibria, just as the twist number itself has proven useful studying
idealized thin flux tubes. We explicitly describe a numerical method
for calculating additive self-helicity, which includes an algorithm
for identifying a domain occupied by a flux bundle and a method of
calculating potential magnetic field confined to this domain. We also
describe a numerical method to calculate twist of a thin flux tube,
using a frame parallelly transported along the axis of the tube.
---------------------------------------------------------
Title: A Survey of Coronal Cavity Density Profiles
Authors: Fuller, J.; Gibson, S. E.
2009ApJ...700.1205F Altcode:
Coronal cavities are common features of the solar corona that appear
as darkened regions at the base of coronal helmet streamers in
coronagraph images. Their darkened appearance indicates that they are
regions of lowered density embedded within the comparatively higher
density helmet streamer. Despite interfering projection effects of
the surrounding helmet streamer (which we refer to as the cavity rim),
Fuller et al. have shown that under certain conditions it is possible
to use a Van de Hulst inversion of white-light polarized brightness
(pB) data to calculate the electron density of both the cavity and
cavity rim plasma. In this article, we apply minor modifications to
the methods of Fuller et al. in order to improve the accuracy and
versatility of the inversion process, and use the new methods to
calculate density profiles for both the cavity and cavity rim in 24
cavity systems. We also examine trends in cavity morphology and how
departures from the model geometry affect our density calculations. The
density calculations reveal that in all 24 cases the cavity plasma has
a flatter density profile than the plasma of the cavity rim, meaning
that the cavity has a larger density depletion at low altitudes than
it does at high altitudes. We find that the mean cavity density is
over four times greater than that of a coronal hole at an altitude
of 1.2 R <SUB>sun</SUB> and that every cavity in the sample is over
twice as dense as a coronal hole at this altitude. Furthermore, we
find that different cavity systems near solar maximum span a greater
range in density at 1.2 R <SUB>sun</SUB> than do cavity systems near
solar minimum, with a slight trend toward higher densities for systems
nearer to solar maximum. Finally, we found no significant correlation
of cavity density properties with cavity height—indeed, cavities show
remarkably similar density depletions—except for the two smallest
cavities that show significantly greater depletion.
---------------------------------------------------------
Title: Flows and Plasma Properties in Quiescent Cavities
Authors: Schmit, Donald; Gibson, Sarah
2009shin.confE.116S Altcode:
Regions of rarefied density often form cavities above quiescent
prominences. In an attempt to constrain the plasma properties of
---------------------------------------------------------
Title: Large-Scale Flows in Prominence Cavities
Authors: Schmit, D. J.; Gibson, S. E.; Tomczyk, S.; Reeves, K. K.;
Sterling, Alphonse C.; Brooks, D. H.; Williams, D. R.; Tripathi, D.
2009ApJ...700L..96S Altcode:
Regions of rarefied density often form cavities above quiescent
prominences. We observed two different cavities with the Coronal
Multichannel Polarimeter on 2005 April 21 and with Hinode/EIS on 2008
November 8. Inside both of these cavities, we find coherent velocity
structures based on spectral Doppler shifts. These flows have speeds of
5-10 km s<SUP>-1</SUP>, occur over length scales of tens of megameters,
and persist for at least 1 hr. Flows in cavities are an example of
the nonstatic nature of quiescent structures in the solar atmosphere.
---------------------------------------------------------
Title: A novel metric for coronal MHD models
Authors: Schmit, D. J.; Gibson, S.; de Toma, G.; Wiltberger, M.;
Hughes, W. J.; Spence, H.; Riley, P.; Linker, J. A.; Mikic, Z.
2009JGRA..114.6101S Altcode: 2009JGRA..11406101S
In the interest of quantitatively assessing the capabilities of
coronal MHD models, we have developed a metric that compares the
structures of the white light corona observed with SOHO LASCO C2
to model predictions. The MAS model is compared to C2 observations
from two Carrington rotations during solar cycle 23, CR1913 and
CR1984, which were near the minimum and maximum of solar activity,
respectively, for three radial heights, 2.5 R<SUB> $\odot$ </SUB>,
3.0 R<SUB> $\odot$ </SUB>, and 4.5 R<SUB> $\odot$ </SUB>. In addition
to simulated polarization brightness images, we create a synthetic
image based on the field topology along the line of sight in the
model. This open-closed brightness is also compared to LASCO C2 after
renormalization. In general, the model's magnetic structure is a
closer match to observed coronal structures than the model's density
structure. This is expected from the simplified energy equations used
in current global corona MHD models.
---------------------------------------------------------
Title: Density and Morphology of Coronal Prominence Cavities
Authors: Gibson, Sarah; Fuller, J.
2009SPD....40.2604G Altcode:
Coronal prominence cavities are fundamental parts of prominences. They
hold clues to the magnetic structure of pre-CME equilibria, and
better represent the coronal source of the expanding volume in CMEs
and magnetic clouds than a prominence does alone. However, prominence
cavities have not been nearly as comprehensively observed and studied
as prominences. This is in part due to projection effects which
can complicate interpretation of observations, and in part because
spectroscopic diagnostic studies require targeted observations, which
have only recently been attempted. I will present recent work using
white-light observations of cavities to model the morphological and
density properties of polar crown filament cavities, with projection
effects taken into account. I will also comment on recent attempts
to obtain spectral diagnostics of coronal prominence cavities, and
will discuss the implications of all of these observations for cavity
stability and thermal and magnetic properties.
---------------------------------------------------------
Title: Flows and Plasma Properties in Quiescent Cavities
Authors: Schmit, Donald; Gibson, S.; Reeves, K.; Sterling, A.;
Tomczyk, S.
2009SPD....40.1015S Altcode:
Regions of rarefied density often form cavities above quiescent
prominences. In an attempt to constrain the plasma properties of
"equilibrium" cavities we conduct several diagnostics using Hinode/EIS,
STEREO/EUVI, and CoMP. One novel observation is of large scale flows in
cavities. Using different instruments to observe two distinct cavities
off the solar limb in coronal emission lines, we find that spectral
doppler shifts imply LOS velocities within cavities on the order of
1-10 km/s. These flows occur over length scales of several hundred Mm
and persist for hours.
---------------------------------------------------------
Title: Partially-erupting prominences: a comparison between
observations and model-predicted observables
Authors: Tripathi, D.; Gibson, S. E.; Qiu, J.; Fletcher, L.; Liu,
R.; Gilbert, H.; Mason, H. E.
2009A&A...498..295T Altcode: 2009arXiv0902.1228T
Aims: We investigate several partially-erupting prominences to
study their relationship with other CME-associated phenomena and
compare these observations with observables predicted by a model
of partially-expelled-flux-ropes (Gibson & Fan 2006a, ApJ,
637, L65; 2006b, J. Geophys. Res., 111, 12103). <BR />Methods: We
studied 6 selected events with partially-erupting prominences using
multi-wavelength observations recorded by the Extreme-ultraviolet
Imaging Telescope (EIT), Transition Region and Coronal Explorer
(TRACE), Mauna Loa Solar Observatory (MLSO), Big Bear Solar Observatory
(BBSO), and Soft X-ray Telescope (SXT). The observational features
associated with partially-erupting prominences were then compared
with the predicted observables from the model. <BR />Results: The
partially-expelled-flux-rope (PEFR) model can explain the partial
eruption of these prominences, and in addition predicts a variety
of other CME-related observables that provide evidence of internal
reconnection during eruption. We find that all of the partially-erupting
prominences studied in this paper exhibit indirect evidence of internal
reconnection. Moreover, all cases showed evidence of at least one
observable unique to the PEFR model, e.g., dimmings external to the
source region and/or a soft X-ray cusp overlying a reformed sigmoid. <BR
/>Conclusions: The PEFR model provides a plausible mechanism to explain
the observed evolution of partially-erupting-prominence-associated
CMEs in our study.
---------------------------------------------------------
Title: How do galaxies accrete gas and form stars?
Authors: Putman, M. E.; Henning, P.; Bolatto, A.; Keres, D.; Pisano,
D. J.; Rosenberg, J.; Bigiel, F.; Bryan, G.; Calzetti, D.; Carilli,
C.; Charlton, J.; Chen, H. -W.; Darling, J.; Gibson, S.; Gnedin, N.;
Gnedin, O.; Heitsch, F.; Hunter, D.; Kannappan, S.; Krumholz, M.;
Lazarian, A.; Lasio, J.; Leroy, A.; Lockman, F. J.; Mac Low, M.;
Maller, A.; Meurer, G.; O'Neil, K.; Ostriker, J.; Peek, J. E. G.;
Prochaska, J. X.; Rand, R.; Robertson, B.; Schiminovich, D.; Simon,
J.; Stanimirovic, S.; Thilker, D.; Thom, C.; Tinker, J.; Wakker, B.;
Weiner, B.; van der Hulst, J. M.; Wolfe, A.; Wong, O. I.; Young, L.
2009astro2010S.241P Altcode: 2009arXiv0902.4717P
Great strides have been made in the last two decades in determining
how galaxies evolve from their initial dark matter seeds to the complex
structures we observe at z=0. The role of mergers has been documented
through both observations and simulations, numerous satellites that
may represent these initial dark matter seeds have been discovered
in the Local Group, high redshift galaxies have been revealed with
monstrous star formation rates, and the gaseous cosmic web has been
mapped through absorption line experiments. Despite these efforts,
the dark matter simulations that include baryons are still unable
to accurately reproduce galaxies. One of the major problems is our
incomplete understanding of how a galaxy accretes its baryons and
subsequently forms stars. Galaxy formation simulations have been unable
to accurately represent the required gas physics on cosmological
timescales, and observations have only just begun to detect the
star formation fuel over a range of redshifts and environments. How
galaxies obtain gas and subsequently form stars is a major unsolved,
yet tractable problem in contemporary extragalactic astrophysics. In
this paper we outline how progress can be made in this area in the
next decade.
---------------------------------------------------------
Title: Causes of Solar Activity
Authors: Giampapa, Mark S.; Gibson, Sarah; Harvey, J. W.; Hill, Frank;
Norton, Aimee A.; Pevtsov, A.
2009astro2010S..92G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Magnetically driven activity in the solar corona: a path to
understanding the energetics of astrophysical plasmas
Authors: Gibson, Sarah; Bastian, Tim; Lin, Haoscheng; Low, B. C.;
Tomczyk
2009astro2010S..94G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The Whole Heliosphere Interval: Campaign Summaries and
Early Results
Authors: Thompson, B.; Gibson, S. E.; McIntosh, S.; Fuller-Rowell,
T.; Galvin, A. B.; Kozyra, J. U.; Petrie, G.; Schroeder, P.; Strachan,
L.; Webb, D. F.; Woods, T.
2008AGUFMSH21C..01T Altcode:
The Whole Heliosphere Interval (WHI) is an internationally coordinated
observing and modeling effort to characterize the 3-dimensional
interconnected solar-heliospheric-planetary system - a.k.a. the
"heliophysical" system. The heart of the WHI campaign is the study
of the interconnected 3-D heliophysical domain, from the interior
of the Sun, to the Earth, outer planets, and into interstellar
space. WHI observing campaigns began with the 3-D solar structure from
solar Carrington Rotation 2068, which ran from March 20 - April 16,
2008. Observations and models of the outer heliosphere and planetary
impacts extend beyond those dates as necessary; for example, the
solar wind transit time to outer planets can take months. WHI occurred
during solar minimum, which optimizes our ability to characterize the
3-D heliosphere and trace the structure to the outer limits of the
heliosphere. Highlights include the 3-D reconstruction of the solar
wind and complex geospace response during this solar minimum, contrasts
with the past solar minimum, and the effect of transient activity on the
"quiet" heliosphere. Nearly 200 scientists are participated in WHI data
and modeling efforts, ensuring that the WHI integrated observations
and models will give us a "new view" of the heliophysical system. A
summary of some of the key results from the WHI first workshop in
August 2008 will be given.
---------------------------------------------------------
Title: Constructing a Data System to Support Analysis of the Whole
Heliosphere Interval
Authors: Thompson, B. J.; Schroeder, P. C.; Gibson, S. E.
2008AGUFMSH23A1632T Altcode:
The Whole Heliosphere Interval is an internationally coordinated
observing and modeling effort to characterize the 3-dimensional
interconnected solar-heliospheric-planetary system. The WHI observing
campaigns began with the 3-D solar structure from solar Carrington
Rotation 2068, which ran from March 20 to April 16, 2008, and traced
these structures through the heliosphere and into geospace. The WHI
team has developed a data and modeling clearinghouse to create a
unified point of entry into the disparate data sets spanning across
the traditional disciplinary boundaries. Linkages are provided to data
from the special observing programs conducted by many observatories
for the WHI effort, models that looked in detail at the WHI and the
many other data sets and models from the interval. We also explore
the Virtual Observatory landscape and highlight their contributions
to the development of a more complete understanding of the entire
heliophysical system.
---------------------------------------------------------
Title: Partially ejected flux ropes: Implications for interplanetary
coronal mass ejections
Authors: Gibson, S. E.; Fan, Y.
2008JGRA..113.9103G Altcode:
Connecting interplanetary coronal mass ejections (ICMEs) to their
solar pre-eruption source requires a clear understanding of how that
source may have evolved during eruption. Gibson and Fan (2006a) have
presented a three-dimensional numerical magnetohydrodynamic simulation
of a CME, which showed how, in the course of eruption, a coronal flux
rope may writhe and reconnect both internally and with surrounding
fields in a manner that leads to a partial ejection of only part of
the rope as a CME. In this paper, we will explicitly describe how the
evolution during eruption found in that simulation leads to alterations
of the magnetic connectivity, helicity, orientation, and topology of
the ejected portion of the rope so that it differs significantly from
that of the pre-eruption rope. Moreover, because a significant part of
the magnetic helicity remains behind in the lower portion of the rope
that survives the eruption, the region is likely to experience further
eruptions. These changes would complicate how ICMEs embedded in the
solar wind relate to their solar source. In particular, the location
and evolution of transient coronal holes, topology of magnetic clouds
("tethered spheromak"), and likelihood of interacting ICMEs would
differ significantly from what would be predicted for a CME which did
not undergo writhing and partial ejection during eruption.
---------------------------------------------------------
Title: Whole Heliosphere Interval: Overview of Heliospheric
Observations
Authors: Galvin, A. B.; Gibson, S.; Heliosphere Team
2008AGUSMSH53A..07G Altcode:
The Whole Heliosphere Interval (http://ihy2007.org/WHI/) is an
international observing and coordinated modeling effort to characterize
the interconnections of the 3-dimensional sun-heliosphere-planetary
system originating from Carrington Rotation 2068. WHI takes place
one solar cycle after the "Whole Sun Month" campaign of 1996. Both
WSM and WHI covered the sun and heliosphere near solar minimum
conditions, providing a basis for comparison from one solar cycle
to the next. The primary goals for WHI include the characterization
and modeling in 3D of the solar minimum heliosphere, and to trace the
affects of solar structure and activity via the solar wind to Earth,
other planetary systems, and the outer heliosphere. Team participants
address solar, heliospheric, geospace, planetary systems, space
weather, and sun-climate observations and models. In this talk, we
provide a "first results" summary of the heliospheric observations
portion of WHI. At this writing, the heliospheric observations are
expected to include modeling as well as measurements from L1 (ACE,
SOHO, Wind), other solar longitudes near 1 AU (STEREO A, STEREO B),
remote sensing from Earth or near-Earth (Ooty Radio Observatory, SMEI,
EISCAT), out-of-the ecliptic (Ulysses), and from the outer heliosphere
(Voyager, IBEX). For Voyager and IBEX, the observing interval extends
until the affects originating from CR 2068 reach the outer heliosphere,
several months later.
---------------------------------------------------------
Title: Forming tori: Implications and possible origins of a "tethered
spheromak" topology for magnetic clouds
Authors: Gibson, S. E.; Fan, Y.
2008AGUSMSH31C..06G Altcode:
We present a "tethered spheromak" model for magnetic clouds. The
proposed topology differs from previous magnetic cloud models invoking
spheromaks in that large portions of the field remain connected to
the sun. This magnetic configuration may explain observed departures
from the standard magnetic cloud model of a cylindrically-symmetric
magnetic flux rope, such as magnetic fields which rotate more than 180
degrees. It is also topologically complex enough to include intermingled
detached, doubly attached, and apparently open fields in a manner
consistent with observations of sporadic heat flux dropouts within
otherwise bidirectional or unidirectional streaming electrons. We use
a numerical simulation to demonstrate how, for solar eruptions where
the kink instability drives significant rotation of an erupting flux
rope, such a tethered spheromak may form during that rope's partial
ejection. It does so because writhing motions and reconnections create
twist about two distinct axes of rotation: the first associated with
the rotated portion of the original rope axis, and the second formed
in situ via reconnections between the erupting rope and surrounding
coronal arcade fields.
---------------------------------------------------------
Title: Whole Heliosphere Interval: Introduction
Authors: Gibson, S. E.; Thompson, B. J.; Webb, D.
2008AGUSMSH53A..01G Altcode:
The Whole Heliosphere Interval (WHI) is an international coordinated
observing and modeling effort to characterize the three-dimensional
interconnected solar-heliospheric-planetary system at solar minimum,
using observations originating at the Sun during Carrington Rotation
2067: March 20 - April 16, 2008. WHI's science begins with the solar
interior and extends through the heliosphere and interplanetary
space out to the heliopause. WHI is a special campaign period of the
International Heliophysical Year, and involves the participation of
many observatories and researchers around the world. A "synoptic" set
of observations provides baseline measurements of the heliophysical
system, while "targeted" observing campaigns during the WHI interval
focuses on particular sub-regions of the coupled heliospheric system
and address specific scientific questions via day-to-day coordinated
observations. This introductory talk will begin this special session
dedicated to providing a broad description of the heliosphere at solar
minimum by showcasing early results of the WHI campaign.
---------------------------------------------------------
Title: Observing the unobservable? Modeling coronal cavity densities
Authors: Fuller, J.; Gibson, S. E.; Detoma, G.; Fan, Y.
2008AGUSMSP51A..04F Altcode:
Prominence cavities in coronal helmet streamers are readily detectable
in white light coronagraph images, yet their interpretation may be
complicated by projection effects. In order to determine a cavity's
density structure, it is essential to quantify the contribution of
non-cavity features along the line of sight. We model the coronal cavity
as an axisymmetric torus that encircles the Sun at constant latitude,
and fit it to observations of a white light cavity observed by the
Mauna Loa Solar Observatory (MLSO) MK4 coronagraph from January 25-30,
2006. We demonstrate that spurious non-cavity contributions (including
departures from axisymmetry) are minimal enough to be incorporated in
a density analysis as conservatively estimated uncertainties in the
data. We calculate a radial density profile for cavity material and for
the surrounding helmet streamer (which we refer to as the "cavity rim"),
and find that the cavity density is depleted by a maximum of 40 percent
compared to the surrounding helmet streamer at low altitudes (1.18 solar
radii), but is consistently higher (double or more) than in coronal
holes. We also find that the relative density depletion between cavity
and surrounding helmet decreases as a function of height. We show that
both increased temperature in the cavity relative to the surrounding
helmet streamer and a magnetic flux rope configuration might lead to
such a flattened density profile. Finally, our model provides general
observational guidelines that can be used to determine when a cavity is
sufficiently unobstructed to be a good candidate for plasma diagnostics.
---------------------------------------------------------
Title: Observing the Unobservable? Modeling Coronal Cavity Densities
Authors: Fuller, J.; Gibson, S. E.; de Toma, G.; Fan, Y.
2008ApJ...678..515F Altcode:
Prominence cavities in coronal helmet streamers are readily detectable
in white-light coronagraph images, yet their interpretation may be
complicated by projection effects. In order to determine a cavity's
density structure, it is essential to quantify the contribution of
noncavity features along the line of sight. We model the coronal cavity
as an axisymmetric torus that encircles the Sun at constant latitude and
fit it to observations of a white-light cavity observed by the Mauna
Loa Solar Observatory (MLSO) MK4 coronagraph from 2006 January 25 to
30. We demonstrate that spurious noncavity contributions (including
departures from axisymmetry) are minimal enough to be incorporated in
a density analysis as conservatively estimated uncertainties in the
data. We calculate a radial density profile for cavity material and
for the surrounding helmet streamer (which we refer to as the "cavity
rim") and find that the cavity density is depleted by a maximum of 40%
compared to the surrounding helmet streamer at low altitudes (1.18
R<SUB>⊙</SUB>) but is consistently higher (double or more) than in
coronal holes. We also find that the relative density depletion between
cavity and surrounding helmet decreases as a function of height. We
show that both increased temperature in the cavity relative to the
surrounding helmet streamer and a magnetic flux rope configuration
might lead to such a flattened density profile. Finally, our model
provides general observational guidelines that can be used to determine
when a cavity is sufficiently unobstructed to be a good candidate for
plasma diagnostics.
---------------------------------------------------------
Title: Geospace, Heliospheric and Solar Data collected during the
Whole Heliosphere Interval
Authors: Thompson, B. J.; Gibson, S. E.; Webb, D. F.
2008AGUSMSH51A..01T Altcode:
The Whole Heliosphere Interval is a comprehensive observing and
modeling campaign that seeks to connect variations in the Earth's
ionosphere and magnetosphere with structure and energy variations in
the heliosphere and solar corona. Hundreds of researchers from around
the world participated by performing observations and contributing
data from an extensive array of sources. This poster will summarize
the observations taking during WHI, including special observations
performed under the targeted observing campaigns.
---------------------------------------------------------
Title: Multi-wavelength Comparison of Prominence Cavities
Authors: Schmit, D. J.; Gibson, S.; de Toma, G.; Reeves, K.; Tripathi,
D.; Kucera, T.; Marque, C.; Tomczyk, S.
2008AGUSMSP43B..04S Altcode:
Recent observational campaigns have brought together a wealth of
data specifically designed to explore the physical properties and
dynamics of prominence cavities. In particular, STEREO and Hinode
data have provided new perspectives on these structures. In order to
effectively analyze the data in a cohesive manner, we produce overlays
of several distinct and complimentary datasets including SOHO UVCS,
CDS, and EIT, Hinode SOT and EIS, STEREO SECCHI, TRACE, and Nancay
Radioheliograph data as well as new observations of coronal magnetic
fields in cavities from the Coronal Multichannel Polarimeter. We are
thus able to investigate how sensitive morphology is to the wavelength
observed which details the nature of the plasma in the cavity.
---------------------------------------------------------
Title: Whole Heliosphere Interval: Early Science Results
Authors: Gibson, Sarah; Webb, David; Thompson, Barbara
2008cosp...37.1011G Altcode: 2008cosp.meet.1011G
The Whole Heliosphere Interval (WHI) is an international coordinated
observing and modeling effort to characterize the three-dimensional
interconnected solar-heliospheric-planetary system at solar minimum,
using observations originating at the Sun during Carrington Rotation
2067: March 20 - April 16, 2008. WHI's science begins with the solar
interior and extends through the heliosphere and interplanetary
space out to the heliopause. WHI is a special campaign period of the
International Heliophysical Year, and involves the participation of
many observatories and researchers around the world. A "synoptic" set
of observations provides baseline measurements of the heliophysical
system, while "targeted" observing campaigns during the WHI interval
focuses on particular sub-regions of the coupled heliospheric system
and address specific scientific questions via day-to-day coordinated
observations. This talk will showcase early results of the WHI
campaign, and thus provide a broad description of the heliosphere at
solar minimum.
---------------------------------------------------------
Title: Whole Heliosphere Interval: Origins and characteristics of
the quiet solar wind
Authors: Gibson, Sarah
2008cosp...37.1010G Altcode: 2008cosp.meet.1010G
The Whole Heliosphere Interval (WHI) is an international coordinated
observing and modeling effort to characterize the three-dimensional
interconnected solar-heliospheric-planetary system during solar minimum,
using data originating at the Sun during Carrington Rotation 2067:
March 20 - April 16, 2008. WHI is a special campaign period of the
International Heliophysical Year, and involves the participation of many
participating observatories and researchers around the world. WHI's
science begins with the solar interior and extends through the
heliosphere and interplanetary space out to the heliopause. I will
focus on the origins and characteristics of the quiet solar wind, and
summarize the early results of the WHI campaign in order to provide
a broad description of the heliosphere at solar minimum.
---------------------------------------------------------
Title: Hidden Galactic Accretion: The Discovery of Low-Velocity
Halo Clouds
Authors: Peek, J. E. G.; Putman, M. E.; Sommer-Larsen, J.; Heiles,
C. E.; Stanimirovic, S.; Douglas, K.; Gibson, S.; Korpela, E.
2007AAS...211.1408P Altcode: 2007BAAS...39..760P
High-Velocity Clouds (HVCs) have been thought to be part of the Galactic
accretion process since their discovery more than 40 years ago. Two
modes through which HVCs may be generated and contribute to the ongoing
growth of our Galaxy are (1) the tidal stripping of satellite galaxies
and (2) the fragmented condensation of the Galaxy's hot baryonic
halo. We have run cosmological Tree-SPH simulations of a Milky-Way
sized galaxy, in which we can resolve clouds down to 10^5 M⊙, in an
attempt to probe the cooling halo accretion process. The simulations
show that this HVC generation mechanism can indeed reproduce the
characteristics of observed population of HVCs, including the flux,
velocity and cloud clustering properties. These simulations also
predict an equally large population of halo clouds moving at lower
radial velocities: Low-Velocity Halo Clouds (LVHCs). These clouds would
not be observed as HVCs, but would rather be confused with local disk
gas. Taking advantage of the known empirical result that HVCs have
undetectably low infrared dust flux compared to their 21cm column,
we search for these clouds in the preliminary GALFA-HI survey and
IRAS. We announce the discovery of the first examples of these clouds,
and describe their properties. This work was supported in part by NSF
grant AST 04-06987 and NSF grant AST 07-09347.
---------------------------------------------------------
Title: Onset of coronal mass ejections due to loss of confinement
of coronal flux ropes
Authors: Fan, Y.; Gibson, S.
2007AGUFMSH51C..04F Altcode:
Using MHD numerical simulations in a three-dimensional spherical
geometry, we model the loss of confinement and eruption of a flux
rope emerging quasistatically into a pre-existing coronal arcade
field. Our numerical experiments have investigated two distinct
triggering mechanisms that led to the eruption of the flux rope. In
one case, the overlying arcade field declines with height more slowly
such that the emerging flux rope remains confined until a high amount
of internal twist is built up, with the rope self-helicity normalized
by the square of the rope flux reaching about -1.4, and the flux rope
becomes significantly kinked. The kinking motion causes rotation of
the tube to an orientation that makes it easier for it to rupture
through the arcade field, leading to an eruption. In the second case,
the overlying field is made to decline more rapidly with height and the
emerging flux rope is found to lose equilibrium and erupt via the torus
instability when the flux rope self-helicity normalized by the square
of the rope flux is only -0.63, before it becomes kinked. The values of
the total relative magnetic helicity normalized by the square of the
total anchored flux are, on the other hand, quite close for the two
cases when the eruption takes place. We study the eruptive properties
resulting from the two mechansisms and compare them with observations.
---------------------------------------------------------
Title: Source of Nitrogen Isotope Anomaly in HCN in the Atmosphere
of Titan
Authors: Liang, Mao-Chang; Heays, A.; Lewis, B.; Gibson, S.; Yung, Y.
2007DPS....39.4705L Altcode: 2007BAAS...39R.505L
The<SUP>14</SUP>N/<SUP>15</SUP>N ratio for N<SUB>2</SUB> in the
atmosphere of Titan was recently measured to be a factor of two
higher than the corresponding ratio for HCN. Using a one-dimensional
photochemical model with transport, we incorporate new isotopic
photoabsorption and photodissociation cross sections of N<SUB>2</SUB>,
computed quantum-mechanically, and show that the difference in the
ratio of <SUP>14</SUP>N/<SUP>15</SUP>N between N<SUB>2</SUB> and
HCN can be explained primarily by the photolytic fractionation of
<SUP>14</SUP>N<SUP>14</SUP>N and <SUP>14</SUP>N<SUP>15</SUP>N. The
[HC<SUP>14</SUP>N]/[HC<SUP>15</SUP>N] ratio produced by N<SUB>2</SUB>
photolysis alone is 23. This value, together with the observed ratio,
constrain the flux of atomic nitrogen input from the top of the
atmosphere to be in the range 1-2×10<SUP>9</SUP> atoms cm<SUP>-2</SUP>
s<SUP>-1</SUP>. <P />----- <P />There remains a major challenge to
explain the low <SUP>14</SUP>N/<SUP>15</SUP>N ratio for N<SUB>2</SUB>
in the atmosphere of Titan. In view of our success in explaining
the isotopic composition of HCN, we believe that the resolution of
the nitrogen isotopic fraction lies in (1) the photochemistry of
NH<SUB>3</SUB>, (2) the isotopic fractionation of <SUP>15</SUP>N
in NH<SUB>3</SUB> photolysis, and (3) hydrodynamic escape. It is
conceivable that some of the nitrogen in the primitive Titan might have
been sequestered as HCN subduction to the interior of Titan, followed
by conversion back to N<SUB>2</SUB> which would contribute to the
isotopic enrichment of <SUP>15</SUP>N in the N<SUB>2</SUB> atmosphere.
---------------------------------------------------------
Title: Onset of Coronal Mass Ejections Due to Loss of Confinement
of Coronal Flux Ropes
Authors: Fan, Y.; Gibson, S. E.
2007ApJ...668.1232F Altcode:
Using MHD numerical simulations in a three-dimensional spherical
geometry, we model the loss of confinement and eruption of a flux rope
emerging quasi-statically into a preexisting coronal arcade field. Our
numerical experiments investigated two distinct mechanisms that led
to the eruption of the flux rope. In one case, the overlying arcade
field declines with height slowly such that the emerging flux rope
remains confined until its self-relative magnetic helicity normalized
by the square of the rope's flux reaches -1.4 and the flux rope becomes
significantly kinked. The kinking motion causes rotation of the tube
to an orientation that makes it easier for it to rupture through the
arcade field, leading to an eruption. In the second case, the overlying
field declines more rapidly with height, and the emerging flux rope is
found to lose equilibrium and erupt via the torus instability when its
self-relative magnetic helicity normalized by the square of its flux
is only approximately -0.63, before it becomes kinked. The values of
the total relative magnetic helicity of the entire coronal magnetic
field (including both the flux rope and the arcade field) normalized
by the square of the total magnetic flux are, on the other hand, of
similar magnitudes for the two cases when the eruption takes place. We
compare and contrast the eruptive properties and the posteruption
states resulting from the two cases.
---------------------------------------------------------
Title: Coronal Mass Ejections Due to Loss of Confinement of Coronal
Flux Ropes
Authors: Fan, Yuhong; Gibson, S.
2007AAS...210.2919F Altcode: 2007BAAS...39..140F
Using MHD numerical simulations in a three-dimensional spherical
geometry, we model the loss of confinement and eruption of a flux
rope emerging quasistatically into a pre-existing coronal arcade
field. Our numerical experiments have investigated two distinct cases
that led to the eruption of the flux rope. In one case, the overlying
arcade field declines with height more slowly such that the emerging
flux rope remains confined until a high amount of twist is built up,
with the rope self-helicity normalized by the square of the rope flux
reaching about -1.4, and the flux rope becomes significantly kinked. The
kinking motion causes rotation of the tube to an orientation that makes
it easier for it to rupture through the arcade field, leading to an
eruption. In the second case, the overlying field is made to decline
more rapidly with height and the emerging flux rope is found to lose
equilibrium and erupt via the torus instability when the flux rope
self-helicity normalized by the square of the rope flux is only -0.6,
and before it becomes kinked. The values of the total relative magnetic
helicity normalized by the square of the total magnetic flux are, on the
other hand, quite close for the two cases when eruption takes place. We
compare and contrast the eruptive properties and the post-eruption
states of the two cases, and discuss their observational consequences.
---------------------------------------------------------
Title: Splitting Flux Ropes: Modeling The Eruption Of Magnetic
Structures On The Sun
Authors: Gibson, Sarah; Fan, Y.
2007AAS...210.5806G Altcode: 2007BAAS...39..168G
Coronal mass ejections (CMEs) and their associated space weather
manifestations are routinely interpreted as possessing a helical
magnetic flux rope structure. An ongoing controversy remains, however,
as to whether a precursor flux rope exists as a coronal equilibrium
state prior to eruption, or whether it is formed during eruption. This
is an important question to resolve, since CME initiation models and
space weather predictions depend upon a clear understanding of the
configuration of pre-CME magnetic fields and their evolution during
eruption. We will describe an alternative which lies between the
two extremes of a totally erupting, pre-existing rope, and a rope
that forms completely in situ during eruption, i.e., a precursor flux
rope that splits in two and reconnects with surrounding fields during
eruption. We consider the implications of such a "partially-expelled
flux rope" model for a range of CME-related observations, including
partially-erupting filaments, the evolution of post-flare loops and
flare ribbon morphologies, and transient coronal holes.
---------------------------------------------------------
Title: Food Mobilities
Authors: Gibson, Sarah
2007SpCul..10....4G Altcode:
This article explores how food is good to think mobilities with. Food,
taste, and eating are all implicated in differing mobilities, whether
corporeal, technological, imaginative, or virtual. The space of the
dining car brings together the corporeal mobility of passengers,
the technological mobility of the railways, and the mobility
of food. Through the reflections of eating in the dining car by
E. M. Forster and Roland Barthes, this article explores this particular
experience of eating on the move, before examining how cultures of
food and eating are central to experiences of "traveling-indwelling"
and "dwelling-in-traveling" through the wider connections of food
mobilities.
---------------------------------------------------------
Title: The Evolving Sigmoid: Evidence for Magnetic Flux Ropes in
the Corona Before, During, and after CMES
Authors: Gibson, S. E.; Fan, Y.; Török, T.; Kliem, B.
2007sdeh.book..131G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Coronal prominence structure and dynamics: A magnetic flux
rope interpretation
Authors: Gibson, S. E.; Fan, Y.
2006JGRA..11112103G Altcode:
The solar prominence is an example of a space physics phenomenon
that can be modeled as a twisted magnetic flux tube or magnetic flux
"rope." In such models the prominence is one observable part of
a larger magnetic structure capable of storing magnetic energy to
drive eruptions. We show how a flux rope model explains a range of
observations of prominences and associated structures such as cavities
and soft X-ray sigmoids and discuss in particular the observational
and dynamic consequences of three-dimensional reconnections in and
around the evolving magnetic flux rope. We demonstrate that the
flux rope model can describe the prominence's preeruption structure
and dynamics, loss of equilibrium, and behavior during and after an
eruption in which part of the flux rope is expelled from the corona.
---------------------------------------------------------
Title: The Evolving Sigmoid: Evidence for Magnetic Flux Ropes in
the Corona Before, During, and After CMES
Authors: Gibson, S. E.; Fan, Y.; Török, T.; Kliem, B.
2006SSRv..124..131G Altcode: 2007SSRv..tmp...52G
It is generally accepted that the energy that drives coronal mass
ejections (CMEs) is magnetic in origin. Sheared and twisted coronal
fields can store free magnetic energy which ultimately is released
in the CME. We explore the possibility of the specific magnetic
configuration of a magnetic flux rope of field lines that twist
about an axial field line. The flux rope model predicts coronal
observables, including heating along forward or inverse S-shaped,
or sigmoid, topological surfaces. Therefore, studying the observed
evolution of such sigmoids prior to, during, and after the CME gives
us crucial insight into the physics of coronal storage and release of
magnetic energy. In particular, we consider (1) soft-X-ray sigmoids,
both transient and persistent; (2) The formation of a current sheet
and cusp-shaped post-flare loops below the CME; (3) Reappearance of
sigmoids after CMEs; (4) Partially erupting filaments; (5) Magnetic
cloud observations of filament material.
---------------------------------------------------------
Title: Is Reconnection Necessary for Kinked CME Onset?
Authors: Rachmeler, Laurel; DeForest, C. E.; Gibson, S. E.; Fan, Y.
2006SPD....37.0902R Altcode: 2006BAAS...38..236R
We present initial results from a controlled numerical experiment to
determine whether CME onset requires reconnection or can be driven
primarily by loss of plasma equilibrium. The early onset of the kink
instability proceeds with little reconnection in traditional MHD
simulations, but still at a nonzero rate. After the initial onset
of the instability, reconnection proceeds rapidly across the newly
formed current sheet, contributing to the ejection of the kink. We
have simulated the kink instability driven purely by loss of plasma
equilibrium - in the absence of numerical reconnection - as an early
step to understanding the role of reconnection in CME evolution.
---------------------------------------------------------
Title: Validation Techniques for the MAS Corona Model
Authors: Schmit, D.; Gibson, S.; Detoma, G.; Wiltberger, M.
2006AGUSMSH43A..01S Altcode:
In the interest of making competent predictions about the structure
of the solar corona, we have developed the tools necessary to
quantitatively compare the Magnetohydrodynamics Around a Sphere (MAS)
numerical model to the observed corona. The SAIC coronal modeling
group has written an algorithm that creates a two dimensional
polarization brightness image of the corona from the model density
output by computing the line of sight integral for scattered white
light. Using the tools we developed for the CISM Data Explorer, the
white light intensity is extracted from the image around the full
disk of the Sun at a given radial height. A series of these images,
spanning a Carrington rotation, are processed through this method
into a Carrington Map, which we use for direct comparison against
LASCO C2 polarization brightness data. Our validation will begin with
a chi-squared comparison of model to observations of the latitude of
the streamer belt brightness maximum during the Whole Sun Month.
---------------------------------------------------------
Title: On the Nature of the X-Ray Bright Core in a Stable Filament
Channel
Authors: Fan, Y.; Gibson, S. E.
2006ApJ...641L.149F Altcode:
In a search for the cause of the intense heating revealed by X-ray
emission in filament channels, we have simulated the evolution of
a twisted toroidal flux rope emerging quasi-statically into the
corona. Initially, the simulated flux rope remains confined in
equilibrium as the stored magnetic energy increases. With enough
twist buildup, there is a sudden catastrophic loss of equilibrium
and total expulsion of the flux rope. We focused on the quasi-static
phase in which a current sheet forms within the flux rope cavity,
along the so-called bald-patch separatrix surface (BPSS). This
comprises an envelope of field lines that graze the anchoring lower
boundary, enclosing the detached helical field that supports the
prominence. Significant magnetic energy dissipation and heating are
expected to center around such current sheets. The heating that should
result provides a plausible explanation for the hot X-ray sources,
although they appear to be colocated with cool material. If our
physical picture is correct, then the development of X-ray “bright
cores” or “sigmoids” in a filament channel suggests the presence of
a BPSS separating the helical field of a twisted flux rope in stable
confinement from the surrounding untwisted fields.
---------------------------------------------------------
Title: The Calm before the Storm: The Link between Quiescent Cavities
and Coronal Mass Ejections
Authors: Gibson, S. E.; Foster, D.; Burkepile, J.; de Toma, G.;
Stanger, A.
2006ApJ...641..590G Altcode:
Determining the state of the corona prior to CMEs is crucial to
understanding and ultimately predicting solar eruptions. A common and
compelling feature of CMEs is their three-part morphology, as seen
in white-light observations of a bright expanding loop, followed by
a relatively dark cavity, and finally a bright core associated with
an erupting prominence/filament. This morphology is an important
constraint on CME models. It is also quite common for a three-part
structure of loop, cavity, and prominence core to exist quiescently
in the corona, and this is equivalently an important constraint
on models of CME-precursor magnetic structure. These quiescent
structures exist in the low corona, primarily below approximately
1.6 R<SUB>solar</SUB>, and so are currently observable in white light
during solar eclipses, or else by the Mauna Loa Solar Observatory Mk4
coronameter. We present the first comprehensive, quantitative analysis
of white-light quiescent cavities as observed by the Mk4 coronameter. We
find that such cavities are ubiquitous, as they are the coronal limb
counterparts to filament channels observed on the solar disk. We
consider examples that range from extremely long-lived, longitudinally
extended polar-crown-filament-related cavities to smaller cavities
associated with filaments near or within active regions. The former are
often visible for days and even weeks at a time and can be identified
as long-lived cavities that survive for months. We quantify cavity
morphology and intensity contrast properties and consider correlations
between these properties. We find multiple cases in which quiescent
cavities directly erupt into CMEs and consider how morphological and
intensity contrast properties of these cases differ from the general
population of cavities. Finally, we discuss the implications that these
observations may have for the state of the corona just prior to a CME,
and more generally for the nature of coronal MHD equilibria.
---------------------------------------------------------
Title: The Partial Expulsion of a Magnetic Flux Rope
Authors: Gibson, S. E.; Fan, Y.
2006ApJ...637L..65G Altcode:
We demonstrate the partial expulsion of a three-dimensional magnetic
flux rope, in which an upper, escaping rope is separated from a lower,
surviving rope by cusped, reconnecting loop field lines. We use the
three-dimensional magnetohydrodynamic model recently presented by Fan,
extended to examine the erupting rope's end state. As in that work, the
modeled flux rope in spherical coordinates erupts when enough twist has
emerged to induce a loss of equilibrium. After multiple reconnections at
current sheets that form during the eruption, the rope breaks in two,
so that only a part of it escapes. We consider the details of how this
separation occurs and discuss the observational significance of such
a partially expelled flux rope for partially erupting filaments and
re-forming X-ray sigmoids.
---------------------------------------------------------
Title: The emergence and evolution of twisted coronal magnetic fields:
comparing models and observations
Authors: Gibson, S.; Fan, Y.
2006cosp...36.1839G Altcode: 2006cosp.meet.1839G
We will present new results comparing coronal plasma observations to
observables predicted by MHD models of twisted magnetic structures in
the corona We will focus on their emergence through the photosphere
their subsequent equilibrium states and their eruptive properties We
will show that observations of coronal filaments before during and
after eruptions can be explained In particular we will demonstrate
that the observed relationship between filament filament cavity and
hot X-ray sources such as sigmoids are reproduced for a variety of
twisted magnetic structures in equilibrium We will also demonstrate that
modeled loss of equilibrium and eruption of such magnetic structures
can explain a range of observed behaviors of filaments their cavities
and X-ray sigmoids during and after eruptions These include observations
of partially-erupting filaments and the immediate reformation of X-ray
sigmoids after an eruption
---------------------------------------------------------
Title: Partially-ejected flux ropes: implications for space weather
Authors: Gibson, Sarah E.; Fan, Yuhong
2006IAUS..233..319G Altcode:
The structure and evolution of the sources of solar activity directly
affects the nature of space weather disturbances that reach the
Earth. We have previously demonstrated that the loss of equilibrium and
partial ejection of a coronal magnetic flux rope matches observations
of coronal mass ejections (CMEs) and their precursors.In this paper
we discuss the significance of such a partially-ejected rope for space
weather. We will consider how the evolution and bifurcation of the rope
modifies it from its initial, source configuration. In particular,
we will consider how reconnections and writhing motions lead to an
escaping rope which has an axis rotated counterclockwise from the
original rope axis orientation, and which is rooted in transient
coronal holes external to the original source region.
---------------------------------------------------------
Title: The Emergence and Evolution of Twisted Magnetic Flux Ropes
in the Solar Corona
Authors: Fan, Y.; Gibson, S. E.; Manchester, W.
2005ESASP.596E..26F Altcode: 2005ccmf.confE..26F
No abstract at ADS
---------------------------------------------------------
Title: Evolution of Twisted Magnetic Flux Robes Emerging into the
Solar Corona (Invited)
Authors: Fan, Y.; Gibson, S. E.
2005ESASP.592..241F Altcode: 2005ESASP.592E..36F; 2005soho...16E..36F
No abstract at ADS
---------------------------------------------------------
Title: CME Onset Due to Loss of Confinement of Twisted Magnetic
Flux Ropes
Authors: Fan, Y.; Gibson, S.
2005AGUSMSP23A..08F Altcode:
We present MHD simulations in both 2D axisymmetric and 3D spherical
geometries of the evolution of a twisted magnetic flux rope emerging
into the low-β corona previously occupied by a potential arcade
field. We describe both the initial quasi-static evolution whereby
stable equilibrium structures can form with stored free magnetic
energy, and the eventual loss of confinement or equilibrium of the
twisted magnetic flux rope as sufficient twist is being transported
into the corona, resulting in the onset of a CME. We investigate how
the evolution and the loss of equilibrium for a 3D line-tied flux rope
differ compared to the case of a 2D axisymmetric flux rope.
---------------------------------------------------------
Title: Harvey Prize Lecture: The calm before the storm: the link
between quiescent cavities and CMEs
Authors: Gibson, S. E.
2005AGUSMSP43C..01G Altcode:
Coronal mass ejections (CMEs) are thought to be driven by magnetic
energy, stored in twisted or sheared magnetic fields. Magnetic clouds,
which are interplanetary manifestations of CMEs, are commonly modeled
as flux ropes of twisted magnetic field. It has also become quite
standard to model the erupting CME as a flux rope. However, the
question of whether the flux rope is formed during the eruption,
or whether the flux rope existed prior to the eruption, remains
controversial. CMEs often possess a three-part morphology in white light
observations of a bright front, followed by a relatively dark cavity,
and lastly a bright core associated with an erupting prominence. The
three-part structure of CMEs has been shown in a variety of models to
be a consequence of a magnetic flux rope topology. The same physical
reasons for the presence of the cavity system in eruption hold true in
quiescence, and so it is significant that the three-part structure,
in the form of helmet-streamer/cavity/prominence-core often exists
quiescently in the corona. I will present an analysis of a few case
studies of white light quiescent cavities as observed by the HAO Mauna
Loa Solar Observatory Mk4 coronagraph. In particular I will consider
the 3D structure and evolution of these cavities, and how these are
related to CMEs. Finally, I will discuss the implications that these
observations may have for the state of the corona just prior to a CME,
and more generally for the nature of coronal MHD equilibria.
---------------------------------------------------------
Title: Multialtitude Observations of a Coronal Jet during the Third
Whole Sun Month Campaign
Authors: Ko, Y. -K.; Raymond, J. C.; Gibson, S. E.; Alexander, D.;
Strachan, L.; Holzer, T.; Gilbert, H.; Cyr, O. C. St.; Thompson, B. J.;
Pike, C. D.; Mason, H. E.; Burkepile, J.; Thompson, W.; Fletcher, L.
2005ApJ...623..519K Altcode:
On 1999 August 26, a coronal jet occurred at the northwest limb near
a sigmoid active region (AR 8668) that was the target for a joint
observation plan (SOHO joint observing program 106) during the third
Whole Sun Month Campaign. This jet was observed by several instruments
at the limb (SOHO/CDS, SOHO/EIT, TRACE, and Mauna Loa Solar Observatory
CHIP and PICS) and at 1.64 R<SUB>solar</SUB> (SOHO/UVCS). At the limb,
this jet event displayed both low- and high-temperature components. Both
high- and low-temperature components were evident during the early phase
(first 20 minutes) of the event. However, the low-temperature component
is maintained for ~1 hr after the higher temperature component is
gone. There is a second brightening (a possible second jet) seen by
EIT and TRACE about 50 minutes after the onset of the first jet. The
line-of-sight motion at the limb began with a 300 km s<SUP>-1</SUP>
redshift and evolved to a 200 km s<SUP>-1</SUP> blueshift. At
1.64 R<SUB>solar</SUB>, the intensities of Lyα and Lyβ in the jet
increased by a factor of several hundred compared with the background
corona. The C III λ977 line also brightened significantly. This
indicates low-temperature [~(1-2)×10<SUP>5</SUP> K] emission in the
jet, while the intensities of O VI λ1032 and O VI λ1037 increased
by as much as a factor of 8. The UVCS data show evidence of heating at
the early phase of the event. The Doppler shift in the lines indicates
that the line-of-sight (LOS) velocity in the jet started from ~150
km s<SUP>-1</SUP> in blueshift and ended at ~100 km s<SUP>-1</SUP>
in redshift. This LOS motion seen at 1.64 R<SUB>solar</SUB> was
apparently opposite to what was observed when the jet emerged from the
limb. The Doppler dimming analysis indicates that the radial outflow
speed correlates with the magnitude of the LOS speed. Interestingly,
UVCS observations at 2.33 and 2.66 R<SUB>solar</SUB> show no trace of
the jet and SOHO/LASCO observations also yield no firm detection. We
find that a simple ballistic model can explain most of the dynamical
properties of this jet, while the morphology and the thermal properties
agree well with reconnection-driven X-ray jet models.
---------------------------------------------------------
Title: Observational Consequences of a Magnetic Flux Rope Emerging
into the Corona
Authors: Gibson, S. E.; Fan, Y.; Mandrini, C.; Fisher, G.; Demoulin, P.
2004ApJ...617..600G Altcode:
We show that a numerical simulation of a magnetic flux rope emerging
into a coronal magnetic field predicts solar structures and dynamics
consistent with observations. We first consider the structure,
evolution, and relative location and orientation of S-shaped, or
sigmoid, active regions and filaments. The basic assumptions are that
(1) X-ray sigmoids appear at the regions of the flux rope known as
“bald-patch-associated separatrix surfaces (BPSSs), where, under
dynamic forcing, current sheets can form, leading to reconnection
and localized heating, and that (2) filaments are regions of enhanced
density contained within dips in the magnetic flux rope. We demonstrate
that the shapes and relative orientations and locations of the BPSS
and dipped field are consistent with observations of X-ray sigmoids and
their associated filaments. Moreover, we show that current layers indeed
form along the sigmoidal BPSS as the flux rope is driven by the kink
instability. Finally, we consider how apparent horizontal motions of
magnetic elements at the photosphere caused by the emerging flux rope
might be interpreted. In particular, we show that local correlation
tracking analysis of a time series of magnetograms for our simulation
leads to an underestimate of the amount of magnetic helicity transported
into the corona by the flux rope, largely because of undetectable
twisting motions along the magnetic flux surfaces. Observations of
rotating sunspots may provide better information about such rotational
motions, and we show that if we consider the separated flux rope legs as
proxies for fully formed sunspots, the amount of rotation that would
be observed before the region becomes kink unstable would be in the
range 40°-200° per leg/sunspot, consistent with observations.
---------------------------------------------------------
Title: The Role of Garnet Pyroxenite in High-Fe Mantle Melt
Generation: High Pressure Melting Experiments
Authors: Tuff, J.; Takahashi, E.; Gibson, S.
2004AGUFM.V51B0523T Altcode:
Evidence for the existence of heterogeneous or 'marble cake' convecting
mantle<SUP>1</SUP> is provided recently by rare, high MgO ( ∼ 15
wt.%) primitive magmas with anomalously high abundances of FeO*
( ∼ 13.5 to 16 wt. %<SUP>2,3</SUP>; where FeO* = total Fe as
FeO). These high-Fe mantle melts show a limited occurrence in the
initial stage of magmatism in large igneous provinces (e.g. Deccan,
Ethiopia and Paraná-Etendeka) and some have incompatible trace-element
and radiogenic-isotopic ratios (Sr, Nd and Pb) that resemble those of
ocean-island basalts. This suggests that they are predominantly derived
from the convecting mantle<SUP>2</SUP>. The ferropicrites are mildly- to
sub-alkaline and have low contents of Al<SUB>2</SUB>O<SUB>3</SUB> (<
10 wt.%) and heavy rare-earth elements (e.g. Lu < 0.18ppm) that are
consistent with the increased stability of garnet, due to the high FeO*
content in the ferropicrite mantle source. It has been proposed that
the source of the high FeO* may be garnet-pyroxenite streaks derived
from subducted mafic oceanic crust<SUP>2</SUP>. We have undertaken
melting experiments between 1 atmosphere and 7 GPa in order to determine
the anhydrous phase relations of an uncontaminated ferropicrite lava
from the base of the Early-Cretaceous Paraná-Etendeka continental
flood-basalt province. The sample has high contents of MgO ( ∼ 14.9
wt.%), FeO* (14.9 wt.%) and NiO (0.07 wt.%). Olivine phenocrysts have
maximum Fo contents of 85 and are in equilibrium with the host rock,
assuming a K<SUB>d</SUB> of 0.32 and we believe that the sample is
representative of a primary Fe-rich mantle plume derived melt. In total,
75 experimental runs were carried out. Melting phase relations as well
as compositions and modal proportions of all coexisting phases were
successfully determined in 60 run products. Phase relations indicate
that the ferropicrite melt was generated either at ∼ 2.2 GPa from an
olivine-pyroxene residue or ∼ 5 GPa from a garnet-pyroxene residue. A
low bulk-rock Al<SUB>2</SUB>O<SUB>3</SUB> content (9 wt.%) and high
[Gd/Yb]<SUB>n</SUB> ratio (3.1) are consistent with residual garnet
in the ferropicrite melt source and favour high-pressure melting
of garnet-pyroxenite. The garnet pyroxenite may represent subducted
oceanic lithosphere entrained by the upwelling Tristan mantle plume
starting-head. During adiabatic decompression, intersection of the
garnet pyroxenite solidus at ∼ 5 GPa would occur at mantle potential
temperatures of ∼ 1550° C. Subsequent melting of peridotite at
∼ 4.5 GPa may be restricted by the thick overlying sub-continental
lithosphere such that dilution of the garnet-pyroxenite component
would be significantly less than in intra-plate oceanic settings. This
model accounts for the limited occurrence of ferropicrite magma in the
initial stage of continental large igneous provinces and its absence
in ocean-island basalt successions. <SUP>1</SUP> Allègre et al.,
Philosophical Transactions of the Royal Society of London A297, 447-477
(1980). <SUP>2</SUP> Gibson et al., Earth and Planetary Science Letters
174, 355-374 (2000). <SUP>3</SUP> Gibson, Earth and Planetary Science
Letters 195, 59-74 (2002).
---------------------------------------------------------
Title: Numerical Simulations of Three-dimensional Coronal Magnetic
Fields Resulting from the Emergence of Twisted Magnetic Flux Tubes
Authors: Fan, Y.; Gibson, S. E.
2004ApJ...609.1123F Altcode:
We present the results of MHD simulations in the low-β regime of the
evolution of the three-dimensional coronal magnetic field as an arched,
twisted magnetic flux tube emerges into a preexisting coronal potential
magnetic arcade. We find that the line-tied emerging flux tube becomes
kink-unstable when a sufficient amount of twist is transported into
the corona. For an emerging flux tube with a left-handed twist (which
is the preferred sense of twist for active region flux tubes in the
northern hemisphere), the kink motion of the tube and its interaction
with the ambient coronal magnetic field lead to the formation of an
intense current layer that displays an inverse-S shape, consistent
with the X-ray sigmoid morphology preferentially seen in the northern
hemisphere. The position of the current layer in relation to the
lower boundary magnetic field of the emerging flux tube is also
in good agreement with the observed spatial relations between the
X-ray sigmoids and their associated photospheric bipolar magnetic
regions. We argue that the inverse-S-shaped current layer formed is
consistent with being a magnetic tangential discontinuity limited by
numerical resolution and thus may result in the magnetic reconnection
and significant heating that causes X-ray sigmoid brightenings.
---------------------------------------------------------
Title: Numerical Simulations of 3D Coronal Magnetic Fields Resulting
from the Emergence of Twisted Magnetic Flux Tubes
Authors: Fan, Y.; Gibson, S. E.
2004AAS...204.1803F Altcode: 2004BAAS...36..682F
We present MHD simulations in the low-β regime of the evolution of
the 3D coronal magnetic field as an arched, twisted magnetic flux
tube is transported into a pre-existing coronal potential magnetic
arcade. It is found that the line-tied emerging flux tube becomes
kink unstable when a sufficient amount of twist is transported into
the corona. For an emerging flux tube with a left-handed twist (which
is the preferred sense of twist for active region flux tubes in the
northern hemisphere), the kink motion of the tube and its interaction
with the ambient coronal magnetic field lead to the formation of an
intense current layer which displays an inverse-S shape, consistent
with the X-ray sigmoid morphology preferentially seen in the northern
hemisphere. Our simulation results may explain the X-ray sigmoid
brightenings that are observed during eruptive flares and confirm the
prediction by previous topological studies that magnetic tangential
discontinuities (or current sheets) should form along the so called
“bald-patch” separatrix surface, across which the connectivity of
the coronal magnetic field with the dense photosphere undergoes a sharp
transition. Finally, we will also present simulations in a 3D spherical
geometry of a CME-like eruption of the coronal magnetic field due to
the kink instability of a twisted magnetic flux rope emerging into
the corona.
---------------------------------------------------------
Title: Multi-Altitude Observations of a Coronal Jet
Authors: Ko, Y. -K.; Raymond, J. C.; Gibson, S. E.; Alexander, D.;
Strachan, L.; Holzer, T.; Gilbert, H.; St. Cyr, O. C.; Thompson,
B. J.; Pike, C. D.; Burkepile, J.; Thompson, W.; Fletcher, L.
2004AAS...204.5413K Altcode: 2004BAAS...36..759K
A coronal jet occurred on August 26, 1999 at the NW limb near a sigmoid
active region (AR8668). This jet was observed by several instruments
at the limb (SOHO/CDS, SOHO/EIT, TRACE, MLSO/CHIP, MLSO/PICS) and
at 1.64 Ro (SOHO/UVCS). At the limb, this jet event has both low and
high temperature components. The high temperature component appeared
at the early phase (first 20 minutes) of the event along with the low
temperature component while the latter seems to last long ( ∼ 1 hour)
after the higher temperature component was gone. The line-of-sight
motion at the limb started with red-shifted (by as much as 300 km/s)
and turned blue-shifted (by as much as 200 km/s). At 1.64 Ro, the
intensities of Lyα , Lyβ in the jet increased by a factor of several
hundreds compared with the background corona. C III λ 977 line also
brightened significantly. This indicates low temperature ( ∼ 1-2×
10<SUP>5</SUP> K) emission in the jet, while the intensities of O VI
λ 1032 and O VI λ 1037 increased by a factor of as large as 8. Both
UVCS and CDS data show evidence of heating at the early phase of the
event. The line-of-sight velocity seen at 1.64 Ro started with ∼ 150
km/sec in blue shift and ended at ∼ 100 km/sec in red shift. This is
apparently opposite to what were observed when the jet emerged from
the limb. The Doppler dimming analysis indicates that the radial
outflow speed correlates with the magnitude of the line-of-sight
speed. Interestingly, UVCS observations at 2.33 and 2.66 Ro show no
trace of the jet and LASCO observations also yield no firm sight of the
jet. In this paper, we present the observations by these instruments
and discuss the dynamical structure and physical properties of this
jet. Y.-K. Ko acknowledges the support by NASA grant NAG5-12865.
---------------------------------------------------------
Title: Twist and Flare: The role of helical magnetic structures in
the solar corona
Authors: Gibson, S.
2004AAS...204.4603G Altcode: 2004BAAS...36..736G
Solar explosive events such as coronal mass ejections (CMEs) and flares
are commonly considered to be driven by the free magnetic energy stored
in current carrying (twisted or sheared) coronal magnetic fields. Since
it is presently not feasible to directly observe coronal magnetic
fields, it is reasonable to turn to observations of flux-frozen
solar plasma for evidence of such twisted magnetic field. Indeed,
apparently twisted structures and rotating motions are not hard to find
on the Sun. We must be cautious, however, in interpreting observations
which are essentially projections of three-dimensional structures,
and which highlight sub-regions of the magnetic field for specific
physical reasons (for example, regions that are particularly dense
or hot). In order to interpret such observations, it is essential
to employ a three-dimensional, physical model that realistically
simulates observable properties of the relationship between plasma
and field. I will demonstrate how a model of a twisted magnetic flux
rope emerging into a coronal magnetic field can be used to explain
observed helical solar structures and dynamics. In particular, I
will consider the structure, evolution, and relative location and
orientation of S-shaped, or sigmoidal active regions and filaments. I
will also discuss how the emerging flux rope can explain observed
rotational and shearing motions at the solar photosphere. Finally,
I will address how the emerging magnetic flux rope injects magnetic
helicity into the corona, and how this drives dramatic coronal dynamics.
---------------------------------------------------------
Title: Three-dimensional coronal density structure: 1. Model
Authors: Gibson, S. E.; Foster, D. J.; Guhathakurta, M.; Holzer, T.;
St. Cyr, O. C.
2003JGRA..108.1444G Altcode:
The three-dimensional (3-D) density structure of the solar corona is a
fundamental boundary condition on the solar wind. Most easily applied
models of the global coronal density have been restricted to date
to axisymmetric 2-D cases. We present here a 3-D model made up of a
superposition of multiple streamers, having distinct gaussian widths in
longitude and latitude and both longitudinal and latitudinal dependence
of the neutral lines implicit beneath the streamer cores. Nonradiality
of streamers and solar B-angle tilt are also explicitly treated. We
show how this simple model can capture many of the general properties
of coronal white light observations and demonstrate how such a model
can assist in the interpretation of the multiple views on coronal
structures such as will be provided by the upcoming STEREO mission.
---------------------------------------------------------
Title: Low Density Magnetic Structures (Cavities) in the Solar Corona
Authors: Foster, D.; Gibson, S.; Burkepile, J.
2003AGUFMSH41A..07F Altcode:
Some helmet streamers in the low corona contain a density depleted
region known as a cavity. Cavities form over magnetic polarity inversion
lines, often referred to as filament channels, which frequently
contain prominences. CMEs often erupt from helmet streamers, and
are well associated with erupting prominences. The most common CME
morpholgy is the well known loop cavity. Models have been proposed
that identify these coronal cavities as low coronal manifestations of
twisted magnetic flux ropes, which are then ejected into the solar wind
as part of a CME. In order to begin to understand the magnetic structure
of coronal cavities, this poster will first examine the frequency of
quiescent cavities in the corona using white light observations from
the Mark IV coronameter and eclipse photographs.
---------------------------------------------------------
Title: Observational consequences of a magnetic flux rope topology
Authors: Gibson, S.; Barnes, G.; Demoulin, P.; Fan, Y.; Fisher, G.;
Leka, K.; Longcope, D.; Mandrini, C.; Metcalf, T.
2003AGUFMSH42B0516G Altcode:
We consider the implications of a magnetic flux rope topology for
the interpretation of observations of sigmoidal active regions. A
region of tangential magnetic discontinuities can be identified
using techniques that determine a bald patch (BP) and corresponding
separatrices or a quasi-separatrix layer (QSL) -- for a flux rope this
region can be S-shaped, or sigmoidal. If such a region is physically
driven, current sheets can form yielding conditions appropriate for
reconnective heating. Using a numerical simulation of an emerging
flux rope driven by the kink instability, Fan and Gibson (ApJL, 2003)
showed that current sheets indeed formed a sigmoidal surface. In this
poster we will demonstrate that the current sheets formed on the BP and
BP separatrices. Moreover, we will use the results of the numerical
simulation as proxies for observations: specifically the simulated
field at the photosphere as proxy for the magnetic boundary condition,
the sigmoidal current sheets as proxy for the X-ray active region
emission, and the location of dipped magnetic field lines as proxy
for a filament. We will then consider to what extent such observations
might be used to understand and constrain the basic properties of the
coronal field.
---------------------------------------------------------
Title: Development of 2D MHD Self-Consistent Empirical Model of the
Corona and Solar Wind
Authors: Sittler, E. C.; Ofman, L.; Gibson, S.; Holzer, T.; Davila,
J.; Guhathakurta, M.
2003AGUFMSH42D..07S Altcode:
We are developing a 2D MHD self-consistent empirical model of
the solar corona and solar wind. We constrain the solution using
empirically determined estimates of the effective pressure for the
momentum equation and effective heat flux for the energy equation
provided from coronagraph data and Ulysses plasma and magnetic field
data. Our solutions are steady state and do not use a polytrope which
we know is not valid in the solar corona. We have been able to achieve
preliminary convergence. We will present the results of an error
analysis. Our results are presently only valid during solar minimum,
but are generalizing so it can be used during the transition toward
solar maximum (i.e., three current sheets). We will also present some
preliminary results which will allow us to apply our solutions to
solar maximum conditions.
---------------------------------------------------------
Title: Development of Multidimensional MHD Model for the Solar Corona
and Solar Wind
Authors: Sittler, E. C.; Ofman, L.; Gibson, S.; Guhathakurta, M.;
Davila, J.; Skoug, R.; Fludra, A.; Holzer, T.
2003AIPC..679..113S Altcode:
We are developing a time stationary self-consistent 2D MHD model of
the solar corona and solar wind that explicitly solves the energy
equation, using a semi-empirical 2D MHD model of the corona to provide
an empirically determined effective heat flux qeff (i.e., the term
effective means the possible presence of wave contributions). But,
as our preliminary results indicate, in order to achieve high
speed winds over the poles we also need to include the empirically
determined effective pressure Peff as a constraint in the momentum
equation, which means that momentum addition by waves above 2 RS are
required to produce high speed winds. At present our calculations do
not include the Peff constraint. The estimates of Peff and qeff come
from the semi-empirical 2D MHD model of the solar corona by Sittler
and Guhathakurta (1999a,2002) which is based on Mk-III, Skylab and
Ulysses observations. For future model development we plan to use SOHO
LASCO, CDS, EIT, UVCS and Ulysses data as constraints for our model
calculations. The model by Sittler and Guhathakurta (1999a, 2002) is
not a self-consistent calculation. The calculations presented here is
the first attempt at providing a self-consistent calculation based on
empirical constraints.
---------------------------------------------------------
Title: The Emergence of a Twisted Magnetic Flux Tube into a
Preexisting Coronal Arcade
Authors: Fan, Y.; Gibson, S. E.
2003ApJ...589L.105F Altcode:
To investigate the dynamic evolution of a coronal magnetic field in
response to the emergence of significantly twisted magnetic structures,
we perform MHD simulations in the low-β regime of the emergence of
a twisted magnetic flux tube into a preexisting coronal potential
magnetic arcade. Our simulation of a twisted flux tube, which when
fully emerged contains a twist of 1.875×2π field-line rotation
about the axis between the anchored footpoints, leads to a magnetic
structure with substantial writhing of the tube axis (with an apex
rotation >90°) as a result of the nonlinear evolution of the kink
instability. For an emerging tube with a left-handed twist (which is the
preferred sense of twist for active regions in the northern hemisphere),
the writhing of the tube is also left-handed, producing a forward-S
shape for the tube axis as viewed from the top, which is opposite to
the inverse-S-shaped X-ray sigmoid structures preferentially seen in
the northern hemisphere. However, we find that the writhing motion of
the tube and its interaction with the ambient coronal magnetic field
also drive the formation of an intense current layer that displays an
inverse-S shape, consistent with the shape of X-ray sigmoids.
---------------------------------------------------------
Title: The Emergence of a Twisted Magnetic Flux Tube into a
Pre-existing Coronal Arcade
Authors: Fan, Y.; Gibson, S. E.
2003SPD....34.0416F Altcode: 2003BAAS...35..813F
To investigate the dynamic evolution of coronal magnetic field in
response to the emergence of significantly twisted magnetic structures,
we perform MHD simulations in the low-β regime of the emergence of
a twisted magnetic flux tube into a pre-existing coronal potential
magnetic arcade. Our simulation of a twisted flux tube, which when
fully emerged, contains a twist of 1.875 x 2 π field-line rotation
about the axis between the anchored footpoints, leads to a magnetic
structure with substantial writhing of the tube axis (apex rotation
> 90<SUP>o</SUP>) as a result of the non-linear evolution of the
kink instability. For an emerging tube with a left-handed twist
(which is the preferred sense of twist for active regions in the
northern hemisphere), the writhing of the tube is also left-handed,
producing a forward S-shape for the tube axis as viewed from the top,
which is opposite to the inverse S-shaped X-ray sigmoid structures
preferentially seen in the northern hemisphere. However we find that
the writhing motion of the tube and its interaction with the ambient
coronal magnetic field also drives the formation of an intense current
layer which displays an inverse S-shape, consistent with the shape
of X-ray sigmoids. We compare the resulting current layer from the
dynamic simulation with an analysis of the separatrix surface between
winding and non-winding fields at various states of emergence. <P
/>The National Center for Atmospheric Research is sponsored by the
National Science Foundation. This work is supported in part by AFOSR
grant F49620-02-0191.
---------------------------------------------------------
Title: The "Whole Sun Month" Campaigns As a Prototype for IHY
Authors: Thompson, B. J.; Biesecker, D. A.; Breen, A. R.; Gibson, S. E.
2003EAEJA....11571T Altcode:
The International Heliophysical Year (IHY) in 2007 will consist of
a series of coordinated observations combining data and models from
an expansive group of international participants. Campaigns will be
planned to target all aspects of heliophysics, including solar and
interplanetary physics, geospace science and the climatary impact
on Earth. These campaigns will require extensive coordination to
ensure that available ground-based and space missions are utilized
to the greatest scientific benefit. The "Whole Sun Month" campaigns
serve as an excellent prototype for IHY. The first Whole Sun Month
campaign (10 August - 8 September 1996) consisted of an entire
month of coordinated solar and heliospheric observations, followed
by workshops which combined the analysis of the campaign data with
the utilization of these data to constrain interpretive 3-D models
solar and heliospheric structure. The subsequent campaigns (in 1998
and 1999) targetted more specific topics, again allowing a broad base
of participants to establish a comprehensive base of observations for
model interpretation. The many scientific successes of the Whole Sun
Month campaigns (publications, workshops, model refinement and ongoing
collaborations) and the framework of campaign coordination provides an
excellent basis for the planning of IHY campaigns. We will discuss the
campaigns in detail and begin an outline for how the campaigns could
be expanded to incorporate more observations and a greater timeline
for IHY.
---------------------------------------------------------
Title: Empirically Constrained Multidimensional MHD Model for the
Solar Corona and Solar Wind
Authors: Sittler, E. C.; Ofman, L.; Gibson, S.; Guthathakurta, M.;
Skoug, R.; Fludra, A.; Davila, J.; Holzer, T.
2002AGUFMSH21A0502S Altcode:
We are developing a time stationary self-consistent 2D MHD model of
the solar corona and solar wind that explicitly solves the energy
equation, using a semi-empirical 2D MHD model of the corona to provide
an empirically determined effective heat flux q<SUB>eff</SUB> (i.e.,
the term effective means the possible presence of wave contributions)
for the energy equation and effective pressure P<SUB>eff</SUB>
for the momentum equation. Preliminary results indicated that in
order to achieve high speed winds over the poles we not only needed
to use q<SUB>eff</SUB> in the energy equation, but also needed to
include the empirically determined effective pressure P<SUB>eff</SUB>
as a constraint in the momentum equation, which means that momentum
addition by waves above 2 R<SUB>S</SUB> are required to produce high
speed winds. A solution which only included q<SUB>eff</SUB> showed high
acceleration over the poles below 2 R<SUB>S</SUB>, but then drooped
above that radial distance indicating we needed momentum addition above
that height to get high speed flows over the poles. We will show new
results which include the added constraint of P<SUB>eff</SUB> in the
momentum equation. This method will allows us to estimate the momentum
addition term due to waves as a function of height and latitude within
the corona. The estimates of P<SUB>eff</SUB> and q<SUB>eff</SUB> come
from the semi-empirical 2D MHD model of the solar corona by Sittler and
Guhathakurta (1999, 2002) which is based on Mk-III, Skylab and Ulysses
observations. For future model development we plan to use SOHO LASCO,
CDS, EIT, UVCS, Spartan 201-05 and Ulysses data as constraints for
our model calculations. The model by Sittler and Guhathakurta (1999,
2002) is not a self-consistent calculation. The calculations presented
here are a continuing effort to provide a self-consistent calculation
based on empirical constraints.
---------------------------------------------------------
Title: Indications and implications of twisted magnetic flux in
the corona
Authors: Gibson, S. E.; Fan, Y.; Jain, R.; Low, B.
2002AGUFMSH52A0446G Altcode:
The question of whether magnetic flux ropes are fundamental to CMEs and
their precursors will be addressed using a combination of analytic and
numerical models, along with coronal observations. We have developed
computational tools for evaluating observable properties of modeled
magnetic flux ropes suspended in the corona, such as separatrix surfaces
and dipped magnetic fields. We have also developed numerical models to
demonstrate how a flux rope emerging into an overlying coronal magnetic
arcade will relax to a force-free configuration, with associated
formation of current sheets. Using the results of these two parallel
studies, we will directly compare separatrix surfaces determined from
an analytic (non-force-free) equilibrium model to the current sheets
formed during numerical force-free relaxation of the same initial field
configuration. We will then consider these in the context of observed
X-ray sigmoid structures. We have also developed mathematical methods
for determining the magnetic free energy in analytic models of both
magnetic flux ropes, as well as sheared field configurations that
contain no rope. We will compare the free energies thus determined
for both sheared and twisted fields, as functions of spatial size,
magnetic field strength, and degree of shear or twist. We will consider
the implications of these results for the energetics of coronal mass
ejections.
---------------------------------------------------------
Title: 3-Dimensional Density Model of the Solar Corona
Authors: Foster, D.; Gibson, S. E.; Holzer, T.; Guhathakurta, M.
2002AGUFMSH52A0448F Altcode:
We present a 3-D density model of the solar corona, determined
from synoptic maps of Carrington Rotations 1942-3 (22 Oct. 1998 -
18 Nov. - 15 Dec. 1998). The rotations we have chosen include the
time period of the SPARTAN 201-05 flight (Nov. 1-3, 1998), which
had unprecedented spatial and temporal coverage of the white light
corona. These rotations are also useful because they occur at a point
in the solar cycle (ascending phase) that is complex enough to exhibit
interesting 3-D structure, yet not so dynamic that a meaningful density
model cannot be constructed using the rotation of the sun to provide
the 3-D information. Along with SPARTAN data, we consider observations
made by the Mark IV instrument in the Mauna Loa Observatory, and also
SOHO/LASCO and EIT observations. Our analytic model, an extension
of the axisymmetric model of Guhathakurta et al (1996), allows
for multiple streamers varying in both latitude and longitude, and
explicitly treats nonradial streamers. Our 3-D model will be useful
for testing analysis techniques for the upcoming STEREO mission. We
will also compare its structure to magnetic field extrapolation models,
coronal hole boundaries, and magnetic neutral lines.
---------------------------------------------------------
Title: Solar Synoptic Maps as a Means to Study the Global Sun
Authors: de Toma, G.; Gibson, S. E.; Jenne, R. L.; Arge, C. N.
2002AGUFMSH51A0432D Altcode:
Solar synoptic maps (often referred as Carrington maps) are maps of
the Sun in latitude versus longitude built by merging together solar
observations taken during one solar rotation. They are an efficient
method to represent the Sun as it appears during a rotation yielding
a global view of solar structures, such as active regions, coronal
holes, and helmet streamers. They provide a clear and effective way to
study evolutionary patterns on the Sun and to compare different solar
datasets over long periods of time. Because of their ability to display
a large number of data in a concise way, solar synoptic maps have been
popular for many years. The availability of modern instruments (both
in space and on the ground) that can provide consistent and calibrated
measurements for many years has renewed the interest in this data
format. We believe there is a need for the solar-terrestrial community
to agree on a standard format for synoptic maps of the Sun. Such a
format should be discussed and defined in parallel with the effort
of the Solar Virtual Observatory. At the High Altitude Observatory
(HAO), we are developing a public database of solar synoptic maps for
the solar observations made at Mauna Loa Solar Observatory (MLSO). The
database will include observations of the solar corona in visible light
and of the solar chromosphere in the HeI 1083nm and Hα lines. In this
paper, we present examples of MLSO solar synoptic maps and compare
them with other solar synoptic maps to illustrate the scientific use
and flexibility of this data format.
---------------------------------------------------------
Title: Magnetic flux ropes: Would we know one if we saw one?
Authors: Gibson, S. E.; Low, B. C.; Leka, K. D.; Fan, Y.; Fletcher, L.
2002ESASP.505..265G Altcode: 2002IAUCo.188..265G; 2002solm.conf..265G
There has been much debate lately about whether twisted magnetic flux
ropes exist in the corona. When asked for observational evidence
of them, the temptation is to show images of apparently twisted
structures. However, we must be very careful of projection effects in
interpreting these observations. Two critical aspects of understanding
how we might observe flux ropes are 1) the 3D nature of the flux rope,
and 2) physically, which bits are visible and for what reasons? In
this paper we will use a simple but physically reasonable 3D analytic
model to address these two issues, and develop techniques that can in
future be used on more general models, both analytic and numerical.
---------------------------------------------------------
Title: The Structure and Evolution of a Sigmoidal Active Region
Authors: Gibson, S. E.; Fletcher, L.; Del Zanna, G.; Pike, C. D.;
Mason, H. E.; Mandrini, C. H.; Démoulin, P.; Gilbert, H.; Burkepile,
J.; Holzer, T.; Alexander, D.; Liu, Y.; Nitta, N.; Qiu, J.; Schmieder,
B.; Thompson, B. J.
2002ApJ...574.1021G Altcode:
Solar coronal sigmoidal active regions have been shown to be precursors
to some coronal mass ejections. Sigmoids, or S-shaped structures,
may be indicators of twisted or helical magnetic structures, having
an increased likelihood of eruption. We present here an analysis of a
sigmoidal region's three-dimensional structure and how it evolves in
relation to its eruptive dynamics. We use data taken during a recent
study of a sigmoidal active region passing across the solar disk
(an element of the third Whole Sun Month campaign). While S-shaped
structures are generally observed in soft X-ray (SXR) emission, the
observations that we present demonstrate their visibility at a range of
wavelengths including those showing an associated sigmoidal filament. We
examine the relationship between the S-shaped structures seen in SXR
and those seen in cooler lines in order to probe the sigmoidal region's
three-dimensional density and temperature structure. We also consider
magnetic field observations and extrapolations in relation to these
coronal structures. We present an interpretation of the disk passage
of the sigmoidal region, in terms of a twisted magnetic flux rope
that emerges into and equilibrates with overlying coronal magnetic
field structures, which explains many of the key observed aspects of
the region's structure and evolution. In particular, the evolving flux
rope interpretation provides insight into why and how the region moves
between active and quiescent phases, how the region's sigmoidicity is
maintained during its evolution, and under what circumstances sigmoidal
structures are apparent at a range of wavelengths.
---------------------------------------------------------
Title: Self-consistent 2D MHD modeling of multi-streamer coronal
structures
Authors: Ofman, L.; Sittler, E. C.; Gibson, S.; Holzer, T. E.;
Guhathakurta, M.
2002AGUSMSH21B..02O Altcode:
Recently, a semi-empirical 2D MHD model of the solar corona was
constructed by Sittler and Guhathakurta [1999]. The model uses an
empirical electron density and empirical magnetic field during solar
minimum as input to the conservation equations of mass, momentum,
and energy to derive an empirical effective heat flux, or empirical
heating function. This semi-empirical model is not a self-consistent
calculation. We explore the possibility of developing a self-consistent
model that uses the empirical heating function as a constraint for the
calculations. This allows us to solve the energy equation without use of
a polytrope which we know does not apply near the Sun. For our initial
attempt we use the empirically derived magnetic field model obtained
from observed streamer topologies and Ulysses boundary conditions to
initialize our self-consistent 2D MHD model of the solar corona. We
solve the thermally conductive energy equations with an empirical
heating function, and obtain 3-streamer structure with self-consistent
magnetic field, current-sheets, solar wind outflow, density, and
temperature. We compare the results of the thermally conductive model
to the polytropic model, and to the empirical model. We find that
the self-consistent magnetic field structure is more realistic then
the empirical model. We find that the thermally conductive streamers
result in more diffuse current-sheets than in the polytropic model. We
also find that the heating function reduces the heliocentric distance
of the streamers' cusp, and produces more rapid acceleration of the
solar wind in the thermally conductive model then in the polytropic
model, consistent with observations. We investigate the effect of
various forms of the heating function, and of an empirically derived
heat flux on the solutions.
---------------------------------------------------------
Title: Emergence of twisted magnetic flux into the corona
Authors: Gibson, S.; Low, B. C.; Fan, Y.; Fletcher, L.
2002AAS...200.3603G Altcode: 2002BAAS...34..693G
The interaction between emerging magnetic structures and preexisting
overlying coronal structures will be addressed using a combination of
observations and physical models that incorporate a range of twisted
magnetic topologies. Solar explosive events such as coronal mass
ejections (CMEs) and flares are commonly considered to be driven by
the free magnetic energy stored in twisted (current carrying) coronal
magnetic fields. Understanding the origin and the three-dimensional
nature of these twisted coronal magnetic structures is a crucial step
towards explaining and predicting CMEs and flares. One possible and
appealing picture is that the twisted coronal magnetic structures
form as a result of the emergence of twisted magnetic flux tubes
from the solar interior. We might imagine a scenario where a flux
rope forms sub-photospherically, emerges through the photosphere,
exists in the corona until it loses its stability and erupts in a
CME which moves out through interplanetary space until ultimately
impacting on the Earth's magnetosphere. Attractively simple as this
picture is, reality is likely to be more complicated since the various
regimes are physically very different and pre-existing structures
would get in the way of our traveling flux rope. We will concentrate
on joining up two of these regimes, by considering how a flux rope
could rise from beneath the photosphere and emerge into the corona,
interacting with pre-existing coronal structures. We will approach this
problem by using a combination of numerical models of the flux rope
emergence from beneath the photosphere, analytic models of coronal
dynamic and equilibrium magnetic structures, and photospheric and
coronal observations of the 3-d structure and evolution of a so-called
"sigmoidal", or S-shaped active region. In so doing we hope to gain
essential insight into how twisted magnetic fields are formed and how
they could be ultimately removed from the solar corona.
---------------------------------------------------------
Title: Coronal mass ejection
Authors: Gibson, Sarah
2002bhty.confE..11G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Sigmoidal diagnostics with SOHO/CDS
Authors: Del Zanna, G.; Gibson, S. E.; Mason, H. E.; Pike, C. D.;
Mandrini, C. H.
2002AdSpR..30..551D Altcode:
During the third Whole Sun Month Campaign (August 18 - September 14,
1999), the evolution of the active region NOAA 8668 was followed
during its meridian passage and at the limb (Sigmoid JOP 106),
with simultaneous observations with the Solar and Heliospheric
Observatory (SOHO), and with other instruments, both satellite
and ground-based. On August 21st, a small flare, associated with
a brightening of the sigmoidal structure, occurred. SOHO Coronal
Diagnostic Spectrometer (CDS) observations of this small flare are
presented. Coronal temperatures and densities of the sigmoid are
estimated. High transition region densities (in the range 2.5-7 × 10
<SUP>11</SUP> cm <SUP>-3</SUP>), obtained using O IV, are present in
the brightenings associated with the flare. At coronal level, high
temperatures of at least 8 MK were reached, as shown by strong Fe
XIX emission. After this small flare, relatively strong blue-shifts
(⋍ 30 km/s) are observed in coronal lines, located at the two ends
of a small loop system associated with the sigmoid.
---------------------------------------------------------
Title: Interpreting observations of the three-dimensional coronal
mass ejection
Authors: Gibson, S. E.; Burkepile, J.; deToma, G.
2001AGUFMSH12B0751G Altcode:
The upcoming STEREO mission will provide observations of coronal mass
ejections (CMEs) from multiple points of view, yielding unprecedented
clues to their three-dimensional structure. It is therefore crucial to
develop data analysis tools to interpret these observations. We will
present a description of such a data analysis method. Specifically,
we will approach the "forward problem" by considering density models
of CMEs which can be integrated along different lines of sight to
yield different observable white light distributions. The resulting
white light distributions could in future be compared directly to the
multiple viewpoints of STEREO, but for now will be compared to a range
of existing CME observations in order to gain information on which
density models best reproduce observed features. We will also describe
how genetic algorithm techniques can be applied to efficiently find the
best models and model parameters to match a given set of observations.
---------------------------------------------------------
Title: Global Solar Wind Structure from Solar Minimum to Solar
Maximum: Sources and Evolution
Authors: Gibson, S. E.
2001SSRv...97...69G Altcode:
During the past few years, significant progress has been made in
identifying the coronal sources of structures observed in the solar
wind. This recent work has been facilitated by the relative simplicity
and stability of structures during solar minimum. The challenge now
is to continue to use coordinated coronal/solar wind observations to
study the far more complicated and time-evolving structures of solar
maximum. In this paper I will review analyses that use a wide range
of observations to map out the global heliosphere and connect the
corona to the solar wind. In particular, I will review some of the
solar minimum studies done for the first Whole Sun Month campaign
(WSM1), and briefly consider work in progress modeling the ascending
phase time period of the second Whole Sun Fortnight campaign (WSF)
and SPARTAN 201-05 observations, and the solar maximum third Whole Sun
Month campaign (WSM3). In so doing I hope to demonstrate the increase
in complexity of the connections between corona and heliosphere with
solar cycle, and highlight the issues that need to be addressed in
modeling solar maximum connections.
---------------------------------------------------------
Title: 3-D and twisted: magnetic field topologies of CMEs
Authors: Gibson, S. E.; Low, B.
2001AGUSM..SH41C08G Altcode:
Physical models admitting a range of magnetic topologies within a
coronal mass ejection (CME) will be compared to observations. The
nature of CME magnetic fields and their relationships with their plasma
distributions are largely unknown, because coronal magnetic fields
are not directly observed and the three-dimensional (3D) morphology
of the CME can, at best, be inferred from CME density and temperature
structures observed as projections onto the plane of the sky. Important
insights can be obtained from the relationship between CMEs observed
at the solar limb and those observed projected on the solar disk. To
study this relationship an MHD model of the 3-D CME is required. This
was carried out using a 3-D analytically exact MHD model which treats
the CME magnetic field as a spheromak-type flux rope magnetic field
pushing its way out of a global open magnetic field (Gibson and Low,
ApJ, 493, 460, 1998 & JGR, 105, 18187, 2000). This model shows that
such observed white-light limb features as three-part CMEs and U-shaped
“disconnected” regions, and on-disk structures such as twin dimmings
(also referred to as transient coronal holes), and sigmoidal filaments
and X-ray loops can be self-consistently explained in terms of the
same 3D magnetic morphology and plasma structure viewed in different
projections. Further development in this work, including variations
of the original model to allow for a greater variety of admissible
magnetic topologies, will be reported.
---------------------------------------------------------
Title: Dynamics of Expanding Flux Ropes in Coronal Mass Ejections
Authors: Manchester, W. B.; Gombosi, T. I.; De Zeeuw, D. L.; Powell,
K. G.; Low, B.; Gibson, S. E.
2001AGUSM..SH22A07M Altcode:
We present a three-dimensional numerical ideal magnetohydrodynamics
(MHD) model describing the time-dependent expulsion of a CME form the
solar corona. The CME is driven by a twisted magnetic flux rope that
is anchored at both ends in the photosphere and embedded in a open
bipolar magnetic field. We follow the evolution of the CME from the
low corona as it makes its way through surrounding magnetic fields
anchored to the sun. We explore the dynamics of the expanding flux
rope in 3D space to determine significant MHD effects. This model
employs a variety of initial state similar to that suggested by
Gibson and Low as a means of producing several notable features of
CME's such as a coronal cavity and bright core seen in white-light
coronagraphs.Our numerical model is in contrast to traditional CME
models that incorporate force-free bipolar magnetic fields. The flux
rope configuration offers the advantage of greater magnetic free energy
to drive the CME and produces plasma outflows that qualitatively match
white-light coronagraph observations of CME structure.
---------------------------------------------------------
Title: Source Region of High and Low Speed Wind during the Spartan
201-05 Flight
Authors: Guhathakurta, Madhullika; Sittler, Ed, Jr.; Fisher, Richard;
Kucera, Therese; Gibson, Sarah; McComas, Dave; Skoug, Ruth
2001SSRv...97...45G Altcode:
The large-scale coronal magnetic fields of the Sun are believed to play
an important role in organizing the coronal plasma and channeling the
high and low speed solar wind along the open magnetic field lines of the
polar coronal holes and the rapidly diverging field lines close to the
current sheet regions, as has been observed by the instruments aboard
the Ulysses spacecraft from March 1992 to March 1997. We have performed
a study of this phenomena within the framework of a semi-empirical
model of the coronal expansion and solar wind using Spartan, SOHO,
and Ulysses observations during the quiescent phase of the solar
cycle. Key to this understanding is the demonstration that the white
light coronagraph data can be used to trace out the topology of the
coronal magnetic field and then using the Ulysses data to fix the
strength of the surface magnetic field of the Sun. As a consequence,
it is possible to utilize this semi-empirical model with remote sensing
observation of the shape and density of the solar corona and in situ
data of magnetic field and mass flux to predict values of the solar
wind at all latitudes through out the solar system. We have applied
this technique to the observations of Spartan 201-05 on 1 2 November,
1998, SOHO and Ulysses during the rising phase of this solar cycle and
speculate on what solar wind velocities Ulysses will observe during
its polar passes over the south and the north poles during September
of 2000 and 2001. In order to do this the model has been generalized
to include multiple streamer belts and co-located current sheets. The
model shows some interesting new results.
---------------------------------------------------------
Title: Three-dimensional and twisted: An MHD interpretation of
on-disk observational characteristics of coronal mass ejections
Authors: Gibson, S. E.; Low, B. C.
2000JGR...10518187G Altcode:
A physical interpretation of observed coronal “on-disk” manifestations
of an Earth-directed coronal mass ejection (CME) is presented. The
fundamental question of how the CME's magnetic field and its plasma
distribution are related is largely unanswered, because a crucial piece
of the puzzle, that is the three-dimensional (3-D) morphology of the
CME, remains difficult to ascertain so long as coronal observations
are limited to projections onto a single plane of the sky. In order
to understand the relationship between observations of CMEs projected
at the solar limb and those projected on the solar disk, some sort of
model of the 3-D CME is required. In this paper we address both the
question of the 3-D morphology of the CME and the more fundamental
question of the nature of the plasma-magnetic field relationship,
by comparing the limb and on-disk CME representations of an analytic
3-D MHD model based on a spheromak-type flux rope magnetic field
configuration. In particular, we show that the morphology of twin
dimmings (also referred to as transient coronal holes) observed
in X ray and EUV can be reproduced by the CME model as the on-disk
projection of the prominence cavity modeled for limb CMEs. Moreover,
the bright core of a limb CME, generally corresponding to the material
in an erupting prominence, may be interpreted to be the S-shaped
central core of the modeled on-disk CME, splitting the cavity into
twin dimmings when observed head-on without obstruction. The magnetic
field structure of this central core exhibits many of a filament's
magnetic field features required to match observations. Finally,
we consider the nature of S-shaped filaments and X-ray “sigmoids”
in the context of the model, in terms of localized heating and cooling
acting on the modeled CME magnetic field structure.
---------------------------------------------------------
Title: SOHO/UVCS Observations of a Coronal Jet During the Third
Whole Sun Month Campaign
Authors: Ko, Y. -K.; Raymond, J.; Gibson, S.; Strachan, L.; Alexander,
D.; Fletcher, L.; Holzer, T.; Gilbert, H.; Burkepile, J.; St. Cyr,
C.; Thompson, B.
2000SPD....31.0271K Altcode: 2000BAAS...32R.823K
On August 26 1999, a coronal jet occurred at the north west limb
near a sigmoid active region which has been the target for a joint
observation plan during the third Whole Sun Month Campaign. This jet
was observed by several instruments at the limb (SOHO/CDS, SOHO/EIT,
TRACE, MLSO/CHIP, MLSO/PICS), at 1.7 Ro (SOHO/UVCS), and at the outer
corona (SOHO/LASCO). At 1.7 Ro, the intensities of Lyman alpha, Lyman
beta in the jet increased by as large a factor of 100 compared with the
background corona, while those for O VI 1032 and O VI 1037 increased
by a factor of 2. C III 977 line also brightened significantly. The
line shift in the lines indicates that the line-of-sight velocity in
the jet started from 150 km/sec blue shift and ended at 120 km/sec
red shift. This line-of-sight motion seen at 1.7 Ro apparently was
opposite that observed when the jet emerged from the limb. In this
paper, we present the observation by SOHO/UVCS and discuss the dynamic
structure and physical properties of this jet as it passed through
1.7 Ro. Comparisons will be shown with the observations from other
instruments. This work is supported by NASA Grant number NAG5-7822.
---------------------------------------------------------
Title: Source Region of High and Low Speed Wind During the Flight
of Spartan 201-05
Authors: Guhathakurta, M.; Sittler, E.; Fisher, R.; Gibson, S.;
Kucera, T.
2000SPD....31.0903G Altcode: 2000BAAS...32..841G
The large scale coronal magnetic fields of the Sun are believed to play
an important role in organizing the coronal plasma and channeling the
high and low speed solar wind along the open magnetic field lines of
the polar coronal holes and the rapidly diverging field lines close
to the current sheet regions, as has been observed by the instruments
aboard the Ulysses spacecraft from 3/92-3/97. We have performed a study
of this phenomena within the framework of a semi-empirical model of the
coronal expansion and solar wind using Spartan201-03, September, 1995,
SOHO and Ulysses observations during the quiescent phase of the past
solar cycle. Key to this understanding is the demonstration that the
white light coronagraph data can be used to trace out the topology of
the coronal magnetic field and then using the Ulysses data to fix the
strength of the surface magnetic field of the Sun. As a consequence,
it is possible to utilize this semi-empirical model with remote
sensing observation of the shape and density of the solar corona and
in situ data of magnetic field and mass flux to predict values of the
solar wind at all latitudes throuhtout the solar system. We will apply
this technique to the observations of Spartan 201-05 on 1-2 November,
1998, SOHO and Ulysses during the rising phase of this solar cycle and
speculate on what solar wind velocities Ulysses will observe during
its polar passes over the south and the north poles during September
of 2000 and 2001. This work has been funded by NASA SR & T.
---------------------------------------------------------
Title: The Third Whole Sun Month Campaign - Coronal Synoptic Maps
Authors: Biesecker, D. A.; Gibson, S. E.; Alexander, D.; Fludra, A.;
Hoeksema, J. T.; Panasyuk, A. V.; Thompson, B. J.
2000SPD....31.0239B Altcode: 2000BAAS...32..817B
Observations for the Third Whole Sun Month Campaign were made throughout
Carrington Rotation 1953 (August 18-September 14, 1999). As in the
first campaign; the primary focus is on understanding the large scale
solar corona and the connections to interplanetary space over a full
solar rotation. The fundamental notion of these campaigns is that the
observations are available for anyone to work with. In this poster,
we use synoptic maps to show the morphology of the solar corona during
CR1953 at a variety of wavelengths, heights, and temperatures. Data
are shown from YOHKOH SXT, MLSO Mk4, and SOHO MDI, CDS, UVCS, EIT,
and LASCO. The current campaign differs from the first campaign in that
near solar maximum conditions prevailed. We held one workshop in order
to get organized and begin collaborations. The planned studies will
include determining the plasma parameters in various coronal structures
and in modeling the structure of the coronal magnetic fields. In
addition, we had the opportunity to study how a "sigmoidal" active
region evolved as it crossed the solar disk and affected the global
corona through a series of flares and eruptive events, and to obtain
detailed observations of its structure over a wide range of heights
and temperatures. We will be holding future workshops to analyze the
data and work on models. We invite you to participate in this campaign
or at least see our current plans for data analysis and modeling.
---------------------------------------------------------
Title: Latitudinal dependence of outflow velocities from O VI Doppler
dimming observations during the Whole Sun Month
Authors: Strachan, Leonard; Panasyuk, Alexander V.; Dobrzycka, Danuta;
Kohl, John L.; Noci, Giancarlo; Gibson, Sarah E.; Biesecker, Douglas A.
2000JGR...105.2345S Altcode:
Empirical determinations of outflow velocities in the solar corona
provide a much needed constraint, along with density and temperature
determinations, of the acceleration and heating mechanisms in the
extended corona. Much progress has been made on density determinations
from white light polarized brightness observations but outflow
velocities have been more difficult to determine. We present the
first determinations of outflow velocities versus height and latitude
based on a three-dimensional (3-D) reconstruction of the O VI 1032
and 1037 Å emissivities. The Doppler dimming (and pumping) of the
local emissivities give true localized outflow velocities at the
selected locations in the extended corona from ~ 1.75 to 2.75 solar
radii. The velocities are based on an empirical model of the corona
which is constrained by the reconstructed O VI emissivities derived
from the SOHO Ultraviolet Coronagraph Spectrometer (UVCS) synoptic
observations and by electron density determinations based on white
light measurements from the SOHO Large Angle Spectroscopic Coronagraph
(LASCO) and Mauna Loa Solar Observatory (MLSO) Mk III coronameter.
---------------------------------------------------------
Title: Searching for Sigmoids in SOHO/CDS
Authors: Gibson, Sarah; Mason, Helen; Pike, Dave; Young, Peter
1999ESASP.446..331G Altcode: 1999soho....8..331G
Sigmoidal structures observed in X-rays have been shown to be precursors
to CMEs, existing in some cases for several days before an eruption
(Sterling and Hudson 1997,ApJ,491,L55; Canfield et al, 1999, GRL, 26,
6, 627). While these S-shaped structures are most apparent in X-ray
active region observations, they may be manifestations of a more general
helical magnetic structure having observational signatures at other
wavelengths. We will present preliminary results of a survey search for
sigmoidal structures and other CME tracers in archived SOHO/CDS data
for a series of active regions known to contain erupting sigmoidal
structures in X-ray observations. We are particularly interested in
determining the relative locations and temperatures of these tracers,
and will see to what extent the data answers questions such as,
if S shapes are observed at different wavelengths do they line up,
or is there a spatial displacement and/or rotation of angle of S that
corresponds with height/temperature variation ? How does the appearance
of the region vary over the lifetime of the observed x-ray sigmoidal
structure ? After an eruption, how much if any of the S shape remains,
and at what spatial and spectral locations ? We will use the results of
this comparison survey to consider what the implications are for the
underlying magnetic field structure, and the location and variation
of heating throughout it.
---------------------------------------------------------
Title: The Three-dimensional Coronal Magnetic Field during Whole
Sun Month
Authors: Gibson, S. E.; Biesecker, D.; Guhathakurta, M.; Hoeksema,
J. T.; Lazarus, A. J.; Linker, J.; Mikic, Z.; Pisanko, Y.; Riley, P.;
Steinberg, J.; Strachan, L.; Szabo, A.; Thompson, B. J.; Zhao, X. P.
1999ApJ...520..871G Altcode:
Combining models and observations, we study the three-dimensional
coronal magnetic field during a period of extensive coordinated
solar observations and analysis known as the Whole Sun Month (WSM)
campaign (1996 August 10-September 8). The two main goals of the WSM
campaign are addressed in this paper, namely, (1) to use the field
configuration to link coronal features observed by coronagraphs and
imaging telescopes to solar wind speed variations observed in situ and
(2) to study the role of the three-dimensional coronal magnetic field
in coronal force balance. Specifically, we consider how the magnetic
field connects the two fastest wind streams to the two regions that
have been the main foci of the WSM analysis: the equatorial extension
of the north coronal hole (known as the Elephant's Trunk) and the
axisymmetric streamer belt region on the opposite side of the Sun. We
then quantitatively compare the different model predictions of coronal
plasma and solar wind properties with observations and consider the
implications for coronal force balance and solar wind acceleration.
---------------------------------------------------------
Title: The north-south coronal asymmetry with inferred magnetic
quadrupole
Authors: Osherovich, V. A.; Fainberg, J.; Fisher, R. R.; Gibson,
S. E.; Goldstein, M. L.; Guhathakurta, M.; Siregar, E.
1999AIPC..471..721O Altcode: 1999sowi.conf..721O
The quiet corona at times close to solar minimum shows a striking
north-south asymmetry which suggests that neither dipole-like nor
octupole-like fields are sufficient to describe the global coronal
magnetic field. We believe that such phenomena reflect the asymmetry
of the intrinsic magnetic field of the sun as a star; this weak field
is usually obscured by active regions. Empirical models for spherical
corona (at solar maximum) and for ellipsoidal corona (at solar minimum)
have been established. We extend the existing classification to include
an empirical model for the quiet solar corona with strong north-south
asymmetry. We show examples of such asymmetric corona in the green line
for three different solar minima and evolution of corona from almost
ellipsoidal type to corona with strong north-south asymmetry “bald
man with double beard”). A theoretical model (1984) of Osherovich
et al. (1) relates such asymmetry to the existence of a significant
quadrupole term in the global magnetic field of the sun. According to
this model, the size of northern and southern polar coronal holes is
affected differently by a quadrupole term which creates asymmetry in
the magnetic and thermodynamic parameters as well as in the velocity
of the outflow from the two polar regions.
---------------------------------------------------------
Title: Modeling CMEs in three dimensions using an analytic MHD model
Authors: Gibson, Sarah E.; Alexander, David; Biesecker, Doug; Fisher,
Richard; Guhathakurta, Madhulika; Hudson, Hugh; Thompson, B. J.
1999AIPC..471..645G Altcode: 1999sowi.conf..645G
Because coronal mass ejections (CMEs) are viewed in projection,
it is difficult to determine their three-dimensional nature. We use
an analytic model of CMEs as an example of a fully three-dimensional
magnetic field structure in MHD force balance with an emerging CME. We
present the CME magnetic field and its associated density structure,
seen projected at the limb from two viewing angles perpendicular
to the plane of the sky, and emerging from disk center representing
“earth-directed” CME events. The range of CME structures thus produced
compares well to existing CME white-light coronagraph and full disk
EUV and X-ray observations. In particular, we find that both 3-part
“front-cavity-core” and “U-shaped” white light CMEs, as well as the
twin dimmings (also referred to as transient coronal holes) observed in
X-ray and EUV, can successfully be reproduced by the CME model. All of
these structures are a direct consequence of a single three-dimensional
magnetic field topology, viewed from different directions.
---------------------------------------------------------
Title: Solar minimum streamer densities and temperatures using Whole
Sun Month coordinated data sets
Authors: Gibson, S. E.; Fludra, A.; Bagenal, F.; Biesecker, D.;
del Zanna, G.; Bromage, B.
1999JGR...104.9691G Altcode:
We model electron densities of the simplest, most symmetric solar
minimum streamer structure observed during the Whole Sun Month (WSM)
campaign, using coronal observations of both visible white light and
extreme ultraviolet (EUV) emission. Using white light data from the
SOHO/LASCO/C2 and HAO/Mauna Loa Mark 3 coronagraphs, we determine
electron densities by way of a Van de Hulst inversion. We compare the
white light densities to those determined from the density sensitive
EUV line ratios of Si IX 350/342 Å observed by the SOHO/coronal
diagnostic spectrometer (CDS). Moreover, from the white light density
profiles we calculate hydrostatic temperature profiles and compare
to temperatures derived from the Si XII/Mg X line ratio. We find
the white light and spectral analysis produce consistent density and
temperature information.
---------------------------------------------------------
Title: Properties of Coronal White-Light Transients in the SPARTAN
201/WLC and SOHO/LASCO Coronagraphs
Authors: Biesecker, D. A.; Kucera, T. A.; Fisher, R. R.; Gibson,
S. E.; Guhathakurta, M.; Wang, D.
1999AAS...194.1610B Altcode: 1999BAAS...31..851B
The SPARTAN 201/WLC was used to observe the solar corona from about
20:30 UT on 98/11/01 to about 13:30 UT on 98/11/03. The SOHO/LASCO
coronagraphs were operating continuously throughout this period. The
range of heights in the corona covered by the SPARTAN and LASCO
coronagraphs and the temporal cadence of the data allow the properties
of coronal transients to be examined in greater detail than previously
possible with white light data. The SPARTAN coronagraph observes in
white light brightness and polarized brightness at heights of 1.3
to 5.5 solar radii. The LASCO coronagraphs observe in white light
brightness and polarized brightness at heights of 2.5 to 30 solar
radii. We will measure the velocity and mass of the observed coronal
transients with time. There were at least 4 coronal mass ejections
observed with SOHO/LASCO during the time of the SPARTAN flight. Using
solar disk images as a proxy, we will correct the data for plane of
the sky projection. We will explore the height at which the CME's are
initiated and the heights at which they are accelerated. In addition,
we will determine what fraction of the mass is in a CME when it is
initiated and how much is added throughout the event.
---------------------------------------------------------
Title: Physical properties of a coronal hole from a coronal diagnostic
spectrometer, Mauna Loa Coronagraph, and LASCO observations during
the Whole Sun Month
Authors: Guhathakurta, M.; Fludra, A.; Gibson, S. E.; Biesecker, D.;
Fisher, R.
1999JGR...104.9801G Altcode:
Until recently [Guhathakurta and Fisher, 1998], inference of
electron density distribution in the solar corona was limited by
the field of view of white-light coronagraphs (typically out to 6
R<SUB>s</SUB>). Now, for the first time we have a series of white-light
coronagraphs (SOHO/LASCO) whose combined field of view extends from
1.1-30 R<SUB>s</SUB>. Quantitative information on electron density
distribution of coronal hole and coronal plumes/rays are estimated
by using white-light, polarized brightness (pB) observations from the
SOHO/LASCO/C2 and C3 and HAO/Mauna Loa Mark III coronagraphs from 1.15
to 8.0 R<SUB>s</SUB>. Morphological information on the boundary of
the polar coronal hole and streamer interface is determined from the
white-light observations in a manner similar to the Skylab polar coronal
hole boundary estimate [Guhathakurta and Holzer, 1994]. The average
coronal hole electron density in the region 1-1.15 R<SUB>s</SUB> is
estimated from the density-sensitive EUV line ratios of Si IX 350/342 Å
observed by the SOHO/coronal diagnostic spectrometer (CDS). We combine
these numbers with the estimate from white-light (WL) observations to
obtain a density profile from 1 to 8 R<SUB>s</SUB> for the plumes and
the polar coronal hole. We find that white light and spectral analysis
produce consistent density information. Extrapolated densities inferred
from SOHO observations are compared to Ulysses in situ observations of
density. Like the density inferred from the Spartan 201-03 coronagraph,
the current SOHO density profiles suggest that the acceleration of
the fast solar wind takes place very close to the Sun, within 10-15
R<SUB>s</SUB>. The density information is used to put constraints on
solar wind flow velocities and effective temperatures. Finally, these
results are compared to the recent analysis of the Spartan 201-03
white-light observations.
---------------------------------------------------------
Title: Magnetohydrodynamic modeling of the solar corona during Whole
Sun Month
Authors: Linker, J. A.; Mikić, Z.; Biesecker, D. A.; Forsyth, R. J.;
Gibson, S. E.; Lazarus, A. J.; Lecinski, A.; Riley, P.; Szabo, A.;
Thompson, B. J.
1999JGR...104.9809L Altcode:
The Whole Sun Month campaign (August 10 to September 8, 1996) brought
together a wide range of space-based and ground-based observations
of the Sun and the interplanetary medium during solar minimum. The
wealth of data collected provides a unique opportunity for testing
coronal models. We develop a three-dimensional magnetohydrodynamic
(MHD) model of the solar corona (from 1 to 30 solar radii) applicable
to the WSM time period, using measurements of the photospheric
magnetic field as boundary conditions for the calculation. We compare
results from the computation with daily and synoptic white-light and
emission images obtained from ground-based observations and the SOHO
spacecraft and with solar wind measurements from the Ulysses and WIND
spacecraft. The results from the MHD computation show good overall
agreement with coronal and interplanetary structures, including the
position and shape of the streamer belt, coronal hole boundaries,
and the heliospheric current sheet. From the model, we can infer the
source locations of solar wind properties measured in interplanetary
space. We find that the slow solar wind typically maps back to near
the coronal hole boundary, while the fast solar wind maps to regions
deeper within the coronal holes. Quantitative disagreements between
the MHD model and observations for individual features observed during
Whole Sun Month give insights into possible improvements to the model.
---------------------------------------------------------
Title: The SPARTAN 201 White Light Coronagraph Experiment on STS-95
Authors: Fisher, R. R.; Guhathakurta, M.; Kucera, T.; Gibson, S.;
Johnson, J.; Card, G.; Spartan201 Team
1999AAS...194.1612F Altcode: 1999BAAS...31..851F
The White Light Coronagraph Experiment included in the SPARTAN
201 payload was flown on the STS-95 Space Shuttle mission which was
launched on 29 October 1998. The flight systems and payload instruments
were operated for a total duration of 41 hours from low earth orbit
from 31 October to 2 November. The white light coronagraph experiment
was designed to investigate the physical properties and the physical
processes of the solar corona, and the instrument and spacecraft systems
were configured for flight operations at a time of enhanced solar
activity. The operational performance of the experiment and SPARTAN 201
carrier system are described, and the preliminary scientific topics of
investigations are identified. Comparisons with other types of coronal
data, ground-based K-coronameter and other space coronagraphs, are
briefly reviewed. The data reduction plans and the scientifc goals for
this mission are described. A summary of scientific insights gathered
from this new data set is included in this presentation.
---------------------------------------------------------
Title: Temporal Evolution and Physical Properties of North Polar
Coronal Hole from SPARTAN 201-05, SOHO, TRACE and Mk3
Authors: Guhathakurta, M.; Deforest, C.; Fisher, R. R.; Ofman, L.;
Kucera, T.; Gibson, S.; Spartan201 Team
1999AAS...194.3203G Altcode: 1999BAAS...31..870G
Polar coronal rays/plumes as long lived structures that extend out
to 6 R_sun were first observed during the first flight of SPARTAN 201
spacecraft during April 11-12 of 1993. In this paper we will present
detail observations from the WLC aboard Spartan 201 spacecraft (31
Oct.- 2 Nov.,1998) of the north polar coronal hole and comapre its
physical properties to the past three Spartan missions. We will present
comparisons of the Spartan WL observations with the Mk3 pB observations,
SOHO LASCO and EIT observations, and finally the high resolution TRACE
171 Angstroms observations, to characterize the north polar coronal
hole all the way from the base of the corona out to 30 R_sun. We will
also look for signatures of waves (quasi-period variations) in the
coronal hole plumes and interplume regions in the high cadence Spartan
pB observations obtained during this mission.
---------------------------------------------------------
Title: Synoptic Sun during the first Whole Sun Month Campaign:
August 10 to September 8, 1996
Authors: Biesecker, D. A.; Thompson, B. J.; Gibson, S. E.; Alexander,
D.; Fludra, A.; Gopalswamy, N.; Hoeksema, J. T.; Lecinski, A.;
Strachan, L.
1999JGR...104.9679B Altcode:
A large number of synoptic maps from a variety of instruments are used
to show the general morphology of the Sun at the time of the First
Whole Sun Month Campaign. The campaign was conducted from August 10 to
September 8, 1996. The synoptic maps cover the period from Carrington
rotation 1912/253° to Carrington rotation 1913/45°. The synoptic maps
encompass both on-disk data and limb data from several heights in the
solar atmosphere. The maps are used to illustrate which wavelengths and
data sets show particular features, such as active regions and coronal
holes. Of particular interest is the equatorial coronal hole known as
the “elephant's trunk,” which is clearly evident in the synoptic
maps of on-disk data. The elephant's trunk is similar in appearance
to the Skylab-era, “Boot of Italy,” equatorial coronal hole. The
general appearance of the limb maps is explained as well. The limb
maps also show evidence for equatorial coronal holes.
---------------------------------------------------------
Title: Comparison of Coronal Data between the SPARTAN 201/WLC,
SOHO/LASCO, and the MARK 3 Coronagraph
Authors: Kucera, T. A.; Wang, D.; Lecinski, A.; Biesecker, D. A.;
Fisher, R. R.; Gibson, S. E.; Guhathakurta, M.
1999AAS...194.1611K Altcode: 1999BAAS...31..851K
We compare coronal data from three different coronagraphs operating
during the flight of SPARTAN 201-5 on Nov 1-3, 1998. The SPARTAN
201/White Light Coronagraph provides reliable data from 1.5--4.0
solar radii, bridging a gap in the radial coverage between the Mark
3 Coronagraph (which has reliable data from 1.16--1.8 solar radii)
and the SOHO/LASCO C2 (2.5--6 solar radii). We will compare the
radial brightness profiles of different coronal features as seen by
the three different instruments, comparing the apparent structures in
total white-light and polarized brightness.
---------------------------------------------------------
Title: Constraints on Coronal Outflow Velocities Derived from UVCS
Doppler Dimming Measurements and in-Situ Charge State Data
Authors: Strachan, L.; Ko, Y. -K.; Panasyuk, A. V.; Dobrzycka, D.;
Kohl, J. L.; Romoli, M.; Noci, G.; Gibson, S. E.; Biesecker, D. A.
1999SSRv...87..311S Altcode:
We constrain coronal outflow velocity solutions, resolved along the
line-of-sight, by using Doppler dimming models of H I Lyman alpha and
O VI 1032/1037 Å emissivities obtained with data from the Ultraviolet
Coronagraph Spectrometer (UVCS) on SOHO. The local emissivities, from
heliocentric heights of 1.5 to 3.0 solar radii, were determined from 3-D
reconstructions of line-of-sight intensities obtained during the first
Whole Sun Month Campaign (10 August to 8 September 1996). The models use
electron densities derived from polarized brightness measurements made
with the visible light coronagraphs on UVCS and LASCO, supplemented
with data from Mark III at NCAR/MLSO. Electron temperature profiles
are derived from 'freezing-in' temperatures obtained from an analysis
of charge state data from SWICS/Ulysses. The work concentrates on
neutral hydrogen outflow velocities which depend on modeling the
absolute coronal H I Lyα emissivities. We use an iterative method to
determine the neutral hydrogen outflow velocity with consistent values
for the electron temperatures derived from a freezing-in model.
---------------------------------------------------------
Title: The Canadian Galactic plane survey.
Authors: Taylor, A. R.; Gibson, S.; Leahy, D.; Peracaula, M.;
Dougherty, S.; Carignan, C.; St-Louis, N.; Fich, M.; Ghazzali, N.;
Joncas, G.; Pineault, S.; Mashchenko, S.; Irwin, J.; English, J.;
Heiles, C.; Normandeau, M.; Martin, P.; Johnstone, D.; Basu, S.;
McCutcheon, W.; Routledge, D.; Vaneldik, F.; Dewdney, P.; Galt, J.;
Gray, A.; Higgs, L.; Knee, L.; Landecker, T.; Purton, C.; Roger,
R. S.; Tapping, K.; Wallace, B.; Willis, T.; Beichman, C.; Duric,
N.; Green, D.; Heyer, M.; Wendker, H.; Zhang, Xizhen
1998JRASC..92R.319T Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Empirical modeling of the solar corona using genetic algorithms
Authors: Gibson, S. E.; Charbonneau, P.
1998JGR...10314511G Altcode:
Many remote sensing applications encountered in astronomy and space
science involve the solution of nonlinear inverse problems. These
are often difficult to solve because of nonlinearities, ill-behaved
integration kernels, and amplification of data noise associated
with the inversion of the integral operator. In some cases these
difficulties are severe enough to warrant repeated evaluations of the
forward problem as an alternate approach to formal inversion. Because
a forward approach is intrinsically repetitive and time consuming, an
efficient and flexible forward technique is required for this avenue
to be practical. We show how a forward technique based on a genetic
algorithm allows us to fit magnetostatic models of the solar minimum
corona to observations in white light to a degree that would otherwise
have been computationally prohibitive. In addition, and perhaps equally
important, the method also allows the determination of global error
estimates on the model parameters defining the best fit solution.
---------------------------------------------------------
Title: Coronal Outflow Velocities in a 3D Coronal Model Determined
from UVCS Doppler Dimming Observations
Authors: Strachan, L.; Panasyuk, A. V.; Dobrzycka, D.; Gibson, S.;
Biesecker, D. A.; Ko, Y. -K.; Galvin, A. B.; Romoli, M.; Kohn, J. L.
1998EOSTr..79..278S Altcode:
We constrain coronal outflow velocity solutions, resolved along
the line-of-sight, by using Doppler dimming models of H I Lyman
alpha and O VI 1032/1037 Angstrom emissivities obtained with data
from the Ultraviolet Coronagraph Spectrometer (UVCS) on SOHO. The
local emissivities, from heliocentric heights of 1.5 to 3.0
radii, were determined from 3-D reconstructions of line-of-sight
intensities obtained during the Whole Sun Month Campaign (10 Aug. --
8 Sep. 1996). The models use electron densities derived from polarized
brightness measurements made with the visible light coronagraphs on UVCS
and LASCO, supplemented with data from Mark III at NCAR/MLSO. Electron
temperature profiles are derived from `freezing-in' temperatures
obtained from an analysis of charge state data from SWICS/Ulysses. The
work concentrates on O5+ outflow velocities which are determined from an
analysis of the the O VI line ratios. This analysis is less sensitive
to the uncertainties in the electron density and independent of the
ionization balance and elemental abundance than the analyses which
use individual spectral lines. This work is supported in part by NASA
under grant NAG-3192 to the Smithsonian Astrophysical Observatory,
by the Italian Space Agency and by Swiss funding agencies.
---------------------------------------------------------
Title: Empirical Models of Temperature, Densities, and Velocities
in the Solar Corona
Authors: Fludra, A.; Strachan, L.; Alexander, D.; Bagenal, F.;
Biesecker, D. A.; Dobrzycka, D.; Galvin, A. B.; Gibson, S.; Hassler,
D.; Yo, Y. -K.; Panasyuk, A. V.; Thompson, B.; Warren, H.; del Zanna,
G.; Zidowitz, S.; Antonucci, E.; Bromage, B. J. I.; Giordano, S.
1998EOSTr..79..278F Altcode:
We present empirical results for temperatures, densities, and outflow
velocities of constituents of the solar corona from 1 to 3 Ro in
polar coronal holes and an equatorial streamer. Data were obtained
from a variety of space and ground-based instruments during August
1996 as part of the SOHO Whole Sun Month Campaign. From white light
data obtained with the SOHO/LASCO/C2 and HAO/Mauna Loa coronagraphs,
we determine electron densities and compare them to those determined
from the density-sensitive EUV line ratio of Si IX 350/342 Angstroms
observed by the SOHO/Coronal Diagnostic Spectrometer (CDS). Moreover,
from the white light density profiles we calculate temperature profiles
and compare to temperature diagnostic information from EUV lines and
soft X-ray images from Yohkoh. H I Ly alpha and O VI 1032/1037 Angstrom
intensities from the SOHO Ultraviolet Coronagraph Spectrometer (UVCS)
are used to estimate both the direction and magnitude of plasma outflow
velocities in coronal holes and streamers above 1.5 Ro. The velocities
are derived using densities from white light coronagraph data and
coronal electron temperature estimates derived from Ulysses/SWICS
ion composition data. Near the base of the corona we find the white
light and spectral analysis produce consistent density and temperature
information. In the extended corona we find results consistent with
high outflow velocities and a superradial outflow geometry in polar
coronal holes.
---------------------------------------------------------
Title: The Canadian Galactic Plane Survey.
Authors: Gibson, S.; Taylor, A. R.; Leahy, A.; Dougherty, S.;
Carignan, C.; St. -Louis, N.; Fich, M.; Ghazzali, N.; Joncas, G.;
Pineault, S.; Normandeau, M.; Heiles, C.; Irwin, J.; English, J.;
Martin, P.; Johnstone, D.; Basu, S.; McCutcheon, W.; Routledge, D.;
Vaneldik, F.; Dewdney, P.; Galt, J.; Gray, A.; Higgs, L.; Knee, L.;
Landecker, T.; Purton, C.; Roger, R. S.; Tapping, K.; Willis, T.;
Moriarty-Schieven, G.; Beichman, C.; Terebey, S.; Duric, N.; Green,
D.; Heyer, M.; Wendker, H.; Zhang, Xizhen
1998JRASC..92...28G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: A Time-Dependent Three-Dimensional Magnetohydrodynamic Model
of the Coronal Mass Ejection
Authors: Gibson, S. E.; Low, B. C.
1998ApJ...493..460G Altcode:
We present a theoretical magnetohydrodynamic (MHD) model describing the
time-dependent expulsion of a three-dimensional coronal mass ejection
(CME) out of the solar corona. The model relates the white-light
appearance of the CME to its internal magnetic field, which takes the
form of a closed bubble, filled with a partly anchored, twisted magnetic
flux rope, and embedded in an otherwise open background field. The model
is constructed by solving in closed form the time-dependent ideal MHD
equations for a γ = 4/3 polytrope making use of a similarity assumption
and the application of a mathematical stretching transformation in order
to treat a complex field geometry with three-dimensional variations. The
density distribution frozen into the expanding CME magnetic field
is obtained. The scattered white light integrated along the line of
sight shows the conspicuous three features often associated with CMEs
as observed with white-light coronagraphs: a surrounding high-density
region, an internal low-density cavity, and a high-density core. We
also show how the orientation of this three-dimensional structure
relative to the line of sight can give rise to a variety of different
geometric appearances in white light. These images generated from a CME
model in a realistic geometry offer an opportunity to directly compare
theoretical predictions on CME shapes with observations of CMEs in
white light. The mathematical methods used in the model construction
have general application and are described in the Appendices.
---------------------------------------------------------
Title: The ElectronTemperature Profile in the North Polar Coronal
Hole During the WSM Inferred by SWICS/Ulysses,LASCO and UVCS data
Authors: Ko, Y. -K.; Galvin, A. B.; Gibson, S.; Strachan, L.
1998EOSTr..79..283K Altcode:
The solar wind ionic charge states are frozen-in in the inner solar
corona within 5 solar radii. The freeze-in process, thus the frozen-in
ionic charge states, depends on the electron temperature, electron
density and the ion velocity in the ion's freeze-in region. Therefore
the observed solar wind ionic charge states can be used to infer
the physical properties in the inner solar corona where important
solar wind heating and acceleration mechanisms are believed to take
place. During the SOHO Whole Sun Month Campaign, Ulysses observed high
speed solar wind from the north polar coronal hole. With the electron
density profile derived from the LASCO/C2 and HAO/Mark 3 coronagraphs
and the outflow velocities derived from the UVCS instrument, we model
the electron temperature profile in the north polar coronal hole
constrained by the above and the solar wind ionic charge states data
observed by the SWICS instrument onboard Ulysses.
---------------------------------------------------------
Title: Self-similar Time-dependent MHD in Three-dimensional Space
Authors: Low, B. C.; Gibson, S. E.
1997AAS...19112006L Altcode: 1997BAAS...29.1403L
A general class of self-similar exact solutions to the time-dependent
ideal MHD equations was discovered in the early eighties (Low 1982 ApJ
254, 796; Low 1984 ApJ 281, 392). These solutions describe exploding or
imploding atmospheres in the polytropic approximation with a 4/3 index
and in the presence of Newtonian gravity. A full range of accelerating,
decelerating, or inertial explosions or implosions are possible. A novel
feature of these solutions is that they allow for full variation in
three dimensional space unstricted by any spatial symmetry, presenting
an opportunity for generating models of exploding or imploding
atmospheres in realistic geometry. The reduction of the problem from
four dimensional space-time to the three-dimensional similarity space
leads to governing equations which are still highly non-trivial to
solve. This paper presents the results of a method of solution which
yields a three-dimensional, analytic model of a coronal mass ejection
carrying a ball of twisted magnetic fields pushing its way through
surrounding open magnetic fields in a time-dependent expulsion out of
the solar corona (Gibson and Low 1998 ApJ, in press). This method may
be useful in other astrophysical applications. The National Center for
Atmospheric Research is sponsored by the National Science Foundation.
---------------------------------------------------------
Title: Fitting a 3-D Analytic Model of the Coronal Mass Ejection
to Observations
Authors: Gibson, S. E.; Biesecker, D.; Fisher, R.; Howard, R. A.;
Thompson, B. J.
1997ESASP.415..111G Altcode: 1997cpsh.conf..111G
No abstract at ADS
---------------------------------------------------------
Title: Fitting a 3-d analytic model of the Coronal Mass Ejection
to observations
Authors: Gibson, Sarah; Fisher, Richard; Howard, Russ; Thompson,
Barbara
1997SPD....28.0110G Altcode: 1997BAAS...29..880G
We present the application of an analytic magnetohydrodynamic model
(Gibson and Low, 1997) to observations of the time-dependent expulsion
of three-dimensional Coronal Mass Ejections (CMEs) out of the solar
corona. The model relates the white-light appearance of the CME to
its internal magnetic field, which takes the form of a closed bubble,
filled with a partly anchored, twisted magnetic flux rope and embedded
in an otherwise open background field. The density distribution frozen
into the expanding CME magnetic field is fully three-dimensional, and
can be integrated along the line of sight to reproduce observations of
scattered white light. The model is able to reproduce the conspicuous
three features often associated with CMEs as observed with white-light
coronagraphs: a surrounding high-density region, an internal low-density
cavity, and a high-density core. By varying the model parameters,
including the location and orientation of the CME magnetic axis relative
to the limb, we are able to fit the model directly to examples of CMEs
observed by the HAO/SMM Coronagraph, the HAO/Mark III K-Coronameter,
and also to an event observed both by the SOHO/LASCO coronagraphs and
the SOHO/EIT EUV coronal imager.
---------------------------------------------------------
Title: Results from the "Whole Sun Month" campaign
Authors: Gibson, Sarah; Biesecker, Doug
1997SPD....28.0401G Altcode: 1997BAAS...29..907G
From August 10 - September 8, 1996, a coordinated set of observations
were taken as part of the "Whole Sun Month" (WSM) campaign. This
campaign involved many ground- and space-based instruments (including
most of those on board the SOHO satellite), and was coordinated with
the IACG Campaign IV. The goal of the WSM campaign was to gather and
model coronal observations of the large-scale, stable solar minimum
corona, and to link these observations to in situ observations of the
solar wind. The presence of a large equatorial coronal hole extension
(dubbed "the elephant's trunk") during the WSM rotation facilitates the
connection between coronal and in situ wind observations, as it can be
directly linked to the appearance of high speed solar wind streams. We
will present an overview of the observations taken, along with some
of the preliminary results of collaborative modeling efforts. The
purpose of the modeling is to quantify the physical properties of
the 3-dimensional, large scale, stable solar minimum corona during
the WSM period, between approximately 1 and 3 solar radii, and to
test and use this information with models connecting the corona to
in situ observations of the solar wind. Further information on the
WSM campaign, the observations that have been taken, and the modeling
efforts that are being planned can be found at the WSM home page at
http://serts.gsfc.nasa.gov/whole_sun.
---------------------------------------------------------
Title: SOHO EIT Carrington Maps from Synoptic Full-Disk Data
Authors: Thompson, B. J.; Newmark, J. S.; Gurman, J. B.;
Delaboudiniere, J. P.; Clette, F.; Gibson, S. E
1997ESASP.404..779T Altcode: 1997cswn.conf..779T
No abstract at ADS
---------------------------------------------------------
Title: A Search for the Coronal Origins of Fast Solar Wind Streams
During the Whole Sun Month Period
Authors: Lazarus, A. J.; Steinberg, J. T.; Biesecker, D. A.; Forsyth,
R. J.; Galvin, A. B.; Ipavich, F. M.; Gibson, S. E.; Lecinski, A.;
Hassler, D. M.; Hoeksema, J. T.; Riley, P.; Strachan, L., Jr.; Szabo,
A.; Lepping, R. P.; Ogilvie, K. W.; Thompson, B. J.
1997ESASP.404..511L Altcode: 1997cswn.conf..511L
No abstract at ADS
---------------------------------------------------------
Title: Polar Coronal Hole Density and its Solar Wind Consequences
using LASCO Observations
Authors: Guhathakurta, M.; Biesecker, D.; Gibson, S.; Fisher, R.
1997ESASP.404..421G Altcode: 1997cswn.conf..421G
No abstract at ADS
---------------------------------------------------------
Title: Modeling a Simple Coronal Streamer during Whole Sun Month
Authors: Gibson, S. E.; Bagenal, F.; Biesecker, D.; Guhathakurta,
M.; Hoeksema, J. T.; Thompson, B. J.
1997ESASP.404..407G Altcode: 1997cswn.conf..407G
No abstract at ADS
---------------------------------------------------------
Title: Applications of Genetic Algorithms to Solar Coronal Modeling
Authors: Gibson, S.; Charbonneau, P.
1996AAS...188.3622G Altcode: 1996BAAS...28..876G
Genetic algorithms are efficient and flexible means of attacking
optimization problems that would otherwise be computationally
prohibitive. Consider a model that represents an observable quantity in
terms of a few parameters, with an associated chi (2) measuring goodness
of fit with respect to data. If the modeled observable is non-linear
in the parameters, there can exist a degeneracy of minimum chi (2)
in parameter space. It is then essential to understand the location
and extent of this degeneracy in order to find the global optimum
and quantify the degeneracy error around it. Traditional methods of
spanning parameter space such as a grid search or a Monte Carlo approach
scale exponentially with the number of parameters, and waste a great
deal of computational time looking at “un-fit” solutions. Genetic
algorithms, on the other hand, converge rapidly onto regions of
minimum chi (2) while continuously generate “mutant solutions”,
allowing an efficient and comprehensive exploration of parameter
space. Our aim has been to develop an approach that simultaneously
yields a best fit solution and global error estimates, by modifying
and extending standard genetic algorithm-based techniques. We fit two
magnetostatic models of the solar minimum corona to observations in
white light. The first model allows horizontal bulk currents and the
second also allows sheet currents enclosing and extending out from the
equatorial helmet streamer. Using our genetic algorithm approach, we
map out the degeneracy of model parameters that reproduce observations
well. The flexibility of genetic algorithms facilitates incorporating
the additional observational constraint of photospheric magnetic
flux, reducing the degeneracy of solutions to a range represented
by reasonable error bars on the model predictions. By using genetic
algorithms we are able to identify and constrain the degeneracy inherent
to the models, a task, which, particularly for the more complex second
model, would be impractical using a traditional technique. The ultimate
result is a greater understanding of the large scale structure of the
solar corona, providing clues to the mechanisms heating the corona
and accelerating the solar wind.
---------------------------------------------------------
Title: Current sheets in the solar minimum corona
Authors: Gibson, S. E.; Bagenal, F.; Low, B. C.
1996JGR...101.4813G Altcode:
We analytically combine stress-free current sheets with a coronal
magnetostatic bulk current model. We begin by imposing a current sheet
at the equator as an upper boundary condition on the modeled coronal
field. We find that in order to reproduce the sharp gradients across
the boundaries of helmet streamers, we also have to add current sheets
along the interface between open and closed field lines. We find a
description of coronal magnetic field and density in the presence
of both bulk and sheet currents that matches both white light and
photospheric magnetic flux observations.
---------------------------------------------------------
Title: The Large-Scale Structure of the Solar Minimum Corona
Authors: Gibson, Sarah
1995AAS...18712204G Altcode: 1995BAAS...27R1454G
I will present the results of my Ph.D. thesis, the goal of which
was to find a quantitative description of the large-scale structure
of magnetic field and density in the solar minimum corona that was
consistent with observations of both white light intensity and the
magnetic field at the photosphere. We used white light images from
NASA's Solar Maximum Mission (SMM) Coronagraph/Polarimeter and the
High Altitude Observatory Mark III (MkIII) K-coronameter, along with
photospheric field measurements from Stanford's Wilcox Solar Observatory
(WSO), as constraints on the magnetostatic model of Bogdan and Low
(B&L) [\markcite{1986}]. We found a solution to the B&L model
that reproduced observations of white light and photospheric flux to
within quantifiable model and observational limits, and calculated
the physical plasma properties of density, pressure, magnetic field,
and temperature that corresponded to these parameters. Further,
we extended the model to include current sheets at the equator and
around the coronal helmet streamer, and showed that by doing so we
improved the fit to white light data and to a lesser extent to the
photospheric flux. Moreover, by including current sheets in the model,
we produced a magnetic field line structure which better matched the
underlying coronal white light structure, and which was more consistent
with a solar wind accelerating along the open field lines. This work
was partially funded by NASA GSRP grant number 50916.
---------------------------------------------------------
Title: Large-scale magnetic field and density distribution in the
solar minimum corona
Authors: Gibson, S. E.; Bagenal, F.
1995JGR...10019865G Altcode:
We seek a quantitative description of the large-scale structure
of magnetic field and density in the solar minimum corona that is
consistent with observations of both white light intensity and the
magnetic field at the photosphere. We use white light images from
NASA's Solar Maximum Mission (SMM) Coronagraph/Polarimeter and the
High-Altitude Observatory Mark III (MkIII) K-coronameter, along with
photospheric field measurements from Stanford's Wilcox Solar Observatory
(WSO), as constraints on the magnetostatic model of Bogdan and Low
[1986] (B&L). <P />We find a family of solutions to the B&L
model that reproduce observations of white light quite well, each
with a different magnetic field structure. We show that the observed
photospheric field cannot be used as an exact boundary condition on the
B&L model, but we can limit the white light solutions by matching
the total observed photospheric magnetic flux. We find a set of model
parameters that reproduces white light and photospheric field to within
quantifiable model and observational limits and calculate the physical
plasma properties corresponding to these parameters. We conclude that
this fit represents a self-consistent description of the solar minimum
coronal magnetic field and density.
---------------------------------------------------------
Title: The Large-Scale Structure of the Solar Minimum Corona
Authors: Gibson, Sarah Elizabeth
1995PhDT........21G Altcode:
The goal of this thesis is to find a quantitative description of
the large-scale structure of magnetic field and density in the solar
minimum corona that is consistent with observations of both white light
intensity and the magnetic field at the photosphere. We use white light
images from NASA's Solar Maximum Mission (SMM) Coronagraph/Polarimeter
and the High Altitude Observatory Mark III (MkIII) K-coronameter,
along with photospheric field measurements from Stanford's Wilcox Solar
Observatory (WSO), as constraints on the magnetostatic model of Bogdan
and Low (B&L) (1986). We find a family of solutions to the B&L
model that reproduce observations of white light quite well, each
with a different magnetic field structure. We show that the observed
photospheric field cannot be used as an exact boundary condition on the
B&L model, but we can limit the white light solutions by matching
the total observed photospheric magnetic flux. We find a set of seven
model parameters that reproduces white light and photospheric field
to within quantifiable model and observational limits, and calculate
the physical plasma properties of density, pressure, magnetic field,
and temperature that correspond to these parameters. We extend the
model to include current sheets at the equator and around the coronal
helmet streamer, and show that by doing so we improve the fit to white
light data and to a lesser extent to the photospheric flux. Moreover,
by including current sheets in the model, we produce a magnetic
field line structure which better matches the underlying coronal
white light structure, and which is more consistent with a solar wind
accelerating along the open field lines. We use the magnetic field
structure determined from our bulk current/current sheet model to
calculate expansion factors, which can be used as essential inputs
to solar wind models. Finally, we determine that the temperature
structure predicted by our model is not in thermal equilibrium. We
present a preliminary comparison of this temperature structure to
independent emission line temperature diagnostics, and discuss how we
hope in future to use such analyses to produce a more energetically
consistent temperature distribution.
---------------------------------------------------------
Title: Large-Scale Coronal Magnetic Field and Density Structures
Authors: Gibson, S.; Bagenal, F.
1994scs..conf..155G Altcode: 1994IAUCo.144..155G
The authors have modelled the large-scale magnetic field and density
structures in the corona using the magnetostatic model of Bogdan and
Low (1986) and white light images from both NASA's SMM and the High
Altitude Observatory Mark III. They calculated the magnetic field,
density, pressure, and temperature distribution in the corona.
---------------------------------------------------------
Title: A Multi-wavelength Study of the Pleiades Region in Conjunction
with WISP
Authors: Gibson, S.; Nordsieck, K. H.; Afflerbach, A.; Anderson,
C. M.; Jaehnig, K. P.; Michalski, P. E.
1994ASPC...58...78G Altcode: 1994icdi.conf...78G
No abstract at ADS
---------------------------------------------------------
Title: The Large Scale Structure of the Solar Corona
Authors: Gibson, S.; Bagenal, F.
1993BAAS...25.1211G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Modelling the large scale structure of the solar corona.
Authors: Gibson, Sarah; Bagenal, F.
1992ESASP.348..101G Altcode: 1992cscl.work..101G
The authors find a quantitative description of the large scale
structure of magnetic field and density distribution in the coronal
plasma. They use the magnetostatic model of Bogdan and Low and white
light images from both NASA's SMM Coronagraph/Polarimeter and the High
Altitude Observatory Mark III K-coronameter. By combining the SMM and
MkIII datasets the authors were able to more accurately determine
a density distribution that matched the white light images of the
corona. The model then allows to calculate the magnetic field and
plasma characteristics (such as the coronal temperature structure)
which are essential for understanding the mechanisms that heat the
corona and drive the solar wind.
---------------------------------------------------------
Title: Modelling the Large Scale Structure of the Solar Corona
Authors: Gibson, S.; Bagenal, F.
1992AAS...180.1207G Altcode: 1992BAAS...24..748G
We report on recent attempts to find a quantitative description of
both the magnetic field and the distribution of plasma in the lower
corona that matches the white light images of the K-corona. We use the
magnetostatic model of Bogdan and Low and data obtained by the High
Altitude Observatory K-Coronameter (1.2 - 2.3 Rsun) and the Solar
Maximum Mission Coronameter/Polarimeter (1.5 - 4 Rsun). By varying
parameters in the Bogdan and Low model we are able to quantitatively
match the general characteristics of the lower corona at solar minimum:
power law radial profiles of coronal brightness: enhanced brightness
at the equator; uniform density depletion at the pole. Further, we
use the best fit model to determine a temperature distribution in the
corona and investigate the implications this has for solar wind theory.
---------------------------------------------------------
Title: Modeling the large-scale structure of the solar corona
Authors: Bagenal, F.; Gibson, S.
1992sws..coll..135B Altcode:
The aim of this study is to find a quantitative description of both the
magnetic field and the distribution of plasma in the lower corona that
matches the white light images of the K-corona. We use the magnetostatic
model of Bogdan and Low (1986) and data obtained by the High Altitude
Observatory Mark III K-Coronameter stationed at Mauna Loa, Hawaii. To
start with, we take the simplest, solar minimum case when the corona is
approximately longitudinally symmetric. By varying parameters in the
Bogdan and Low model we are able to quantitatively match the general
characteristics of the lower corona at solar minimum: power law radial
profiles of coronal brightness; enhanced brightness at the equator;
uniform density depletion at the pole.
---------------------------------------------------------
Title: Modeling the large-scale structure of the solar corona
Authors: Bagenal, F.; Gibson, S.
1991JGR....9617663B Altcode:
The aim of this study is to find a quantitative description of both the
magnetic field and the distribution of plasma in the lower corona that
matches the white light images of the K-corona. We use the magnetostatic
model of Bogdan and Low (1986) and data obtained by the High Altitude
Observatory Mark III K-Coronameter stationed at Mauna Loa, Hawaii. To
start with, we take the simplest, solar minimum case when the corona is
approximately longitudinally symmetric. By varying parameters in the
Bogdan and Low model we are able to quantitatively match the general
characteristics of the lower corona at solar minimum: power law radial
profiles of coronal brightness; enhanced brightness at the equator;
uniform density depletion at the pole. Further, we find the set of
parameters that best fit the data and investigate how well the model
parameters are resolved by the data.
---------------------------------------------------------
Title: Modelling the Large-Scale Structure of the Corona
Authors: Bagenal, F.; Gibson, S.
1991BAAS...23.1058B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Modeling the Solar Corona at Solar Minimum
Authors: Bagenal, F.; Gibson, S.
1990BAAS...22..869B Altcode:
No abstract at ADS
