explanation blue bibcodes open ADS page with paths to full text
Author name code: hoeksema
ADS astronomy entries on 2022-09-14
author:"Hoeksema, Todd"
---------------------------------------------------------
Title: Understanding Solar Cycle Magnetic Evolution with Properties
of Solar Active Regions
Authors: Liu, Y.; Hoeksema, T.; Zhao, J.; DeRosa, M. L.; Sun, X.
2020AGUFMSH0020015L Altcode:
Understanding the solar cycle is a fundamental and important objective
in solar physics. Recent studies have revealed correlations between
variations of the poleward transport of photospheric magnetic fields
with properties of both magnetic field in solar active regions as well
as their decay products. Features such as poleward surges often play
an outsized role in advecting flux away from the activity belts into
polar regions, and therefore affect solar cycle activity. This report
describes our plans and reviews preliminary results investigating the
effects of active region-modified zonal and meridional flows on flux
evolution and the solar cycle.
---------------------------------------------------------
Title: The Solar Orbiter magnetometer
Authors: Horbury, T. S.; O'Brien, H.; Carrasco Blazquez, I.; Bendyk,
M.; Brown, P.; Hudson, R.; Evans, V.; Oddy, T. M.; Carr, C. M.; Beek,
T. J.; Cupido, E.; Bhattacharya, S.; Dominguez, J. -A.; Matthews, L.;
Myklebust, V. R.; Whiteside, B.; Bale, S. D.; Baumjohann, W.; Burgess,
D.; Carbone, V.; Cargill, P.; Eastwood, J.; Erdös, G.; Fletcher,
L.; Forsyth, R.; Giacalone, J.; Glassmeier, K. -H.; Goldstein, M. L.;
Hoeksema, T.; Lockwood, M.; Magnes, W.; Maksimovic, M.; Marsch, E.;
Matthaeus, W. H.; Murphy, N.; Nakariakov, V. M.; Owen, C. J.; Owens,
M.; Rodriguez-Pacheco, J.; Richter, I.; Riley, P.; Russell, C. T.;
Schwartz, S.; Vainio, R.; Velli, M.; Vennerstrom, S.; Walsh, R.;
Wimmer-Schweingruber, R. F.; Zank, G.; Müller, D.; Zouganelis, I.;
Walsh, A. P.
2020A&A...642A...9H Altcode:
The magnetometer instrument on the Solar Orbiter mission is designed
to measure the magnetic field local to the spacecraft continuously
for the entire mission duration. The need to characterise not only
the background magnetic field but also its variations on scales from
far above to well below the proton gyroscale result in challenging
requirements on stability, precision, and noise, as well as magnetic
and operational limitations on both the spacecraft and other
instruments. The challenging vibration and thermal environment has
led to significant development of the mechanical sensor design. The
overall instrument design, performance, data products, and operational
strategy are described.
---------------------------------------------------------
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: 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: Roadmap for Reliable Ensemble Forecasting of the Sun-Earth
System
Authors: Nita, Gelu; Angryk, Rafal; Aydin, Berkay; Banda, Juan;
Bastian, Tim; Berger, Tom; Bindi, Veronica; Boucheron, Laura; Cao,
Wenda; Christian, Eric; de Nolfo, Georgia; DeLuca, Edward; DeRosa,
Marc; Downs, Cooper; Fleishman, Gregory; Fuentes, Olac; Gary, Dale;
Hill, Frank; Hoeksema, Todd; Hu, Qiang; Ilie, Raluca; Ireland,
Jack; Kamalabadi, Farzad; Korreck, Kelly; Kosovichev, Alexander;
Lin, Jessica; Lugaz, Noe; Mannucci, Anthony; Mansour, Nagi; Martens,
Petrus; Mays, Leila; McAteer, James; McIntosh, Scott W.; Oria, Vincent;
Pan, David; Panesi, Marco; Pesnell, W. Dean; Pevtsov, Alexei; Pillet,
Valentin; Rachmeler, Laurel; Ridley, Aaron; Scherliess, Ludger; Toth,
Gabor; Velli, Marco; White, Stephen; Zhang, Jie; Zou, Shasha
2018arXiv181008728N Altcode:
The authors of this report met on 28-30 March 2018 at the New Jersey
Institute of Technology, Newark, New Jersey, for a 3-day workshop
that brought together a group of data providers, expert modelers, and
computer and data scientists, in the solar discipline. Their objective
was to identify challenges in the path towards building an effective
framework to achieve transformative advances in the understanding
and forecasting of the Sun-Earth system from the upper convection
zone of the Sun to the Earth's magnetosphere. The workshop aimed to
develop a research roadmap that targets the scientific challenge
of coupling observations and modeling with emerging data-science
research to extract knowledge from the large volumes of data (observed
and simulated) while stimulating computer science with new research
applications. The desire among the attendees was to promote future
trans-disciplinary collaborations and identify areas of convergence
across disciplines. The workshop combined a set of plenary sessions
featuring invited introductory talks and workshop progress reports,
interleaved with a set of breakout sessions focused on specific topics
of interest. Each breakout group generated short documents, listing
the challenges identified during their discussions in addition to
possible ways of attacking them collectively. These documents were
combined into this report-wherein a list of prioritized activities
have been collated, shared and endorsed.
---------------------------------------------------------
Title: Using the Deep Space Gateway to Build the Next Generation
Heliophysics Research Grid
Authors: Vourlidas, A.; Ho, G. C.; Cohen, I. J.; Korendyke, C. M.;
Tun-Beltran, S.; Plunkett, S. P.; Newmark, J.; St Cyr, O. C.;
Hoeksema, T.
2018LPICo2063.3055V Altcode:
The Heliophysics Research Grid (HRG) consists of in situ and imaging
sensors, distributed in key locations in the heliosphere for research
and to support space exploration needs. The Deep Space Gateway enables
the HRG as a storage and staging hub for HRG launches.
---------------------------------------------------------
Title: Q-Maps: A Synoptic Data Product for Investigating Coronal
Connectivity
Authors: Sun, Xudong; Hoeksema, Todd; Liu, Yang; Mikic, Zoran; Titov,
Viacheslav
2017shin.confE..73S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Achieving Consistent Vector Magnetic Field Measurements
from SDO/HMI
Authors: Schuck, P. W.; Scherrer, Phil; Antiochos, Spiro; Hoeksema,
Todd
2016usc..confE..71S Altcode:
NASA's Solar Dynamics Observatory (SDO) is delivering vector magnetic
field observations of the full solar disk with unprecedented temporal
and spatial resolution; however, the satellite is in a highly inclined
geosynchronous orbit. The relative spacecraft-Sun velocity varies by ±3
km/s over a day which introduces significant orbital artifacts in the
Helioseismic Magnetic Imager (HMI) data. We have recently demonstrated
that the orbital artifacts contaminate all spatial and temporal scales
in the data and developed a procedure for mitigating these artifacts
in the Doppler data obtained from the Milne-Eddington inversions in the
HMI Pipeline. Simultaneously, we have found that the orbital artifacts
may be introduced by inaccurate estimates for the free-spectral ranges
(FSRs) of the optical elements in HMI. We describe our approach and
attempt to minimize orbital artifacts in the hmi.V_720 Dopplergram
series by adjusting the FSRs for the optical elements of HMI within
their measurement uncertainties of ±1%. introduces major orbital
artifacts in the Helioseismic Magnetic Imager (HMI) data. We have
recently demonstrated that the orbital artifacts contaminate all spatial
and temporal scales in the data and developed a procedure for mitigating
these artifacts in the Doppler data obtained from the Milne-Eddington
inversions in the HMI Pipeline. Simultaneously, we have found that
the orbital artifacts may be introduced by inaccurate estimates for
the free-spectral ranges (FSRs) of the optical elements in HMI. We
describe our approach and attempt to minimize orbital artifacts in
the hmi.V_720 Dopplergram series by adjusting the FSRs for the optical
elements in HMI within their measurement uncertainties of ±1%.
---------------------------------------------------------
Title: Unexpectedly Large Lorentz-Force Impulse Observed During a
Solar Eruption
Authors: Sun, Xudong; Fisher, George; Torok, Tibor; Hoeksema, Todd;
Li, Yan; CGEM Team
2016shin.confE.158S Altcode:
For fast coronal mass ejections (CMEs), the acceleration phase takes
place in the low corona; the momentum process is presumably dominated by
the Lorentz force. Using ultra-high-cadence vector magnetic data from
the Helioseismic and Magnetic Imager (HMI) and numerical simulations,
we show that the observed fast-evolving photospheric field can be used
to characterize the impulse of the Lorentz force during a CME. While the
peak Lorentz force concurs with the maximum ejecta acceleration, the
observed total force impulse surprisingly exceeds the CME momentum by
over an order of magnitude. We conjecture that most of the Lorentz force
impulse is "trapped" in the thin layer of the photosphere above the HMI
line-formation height and is counter-balanced by gravity. This implies
a consequent upward plasma motion which we coin "gentle photospheric
upwelling". The unexpected effect dominates the momentum processes,
but is negligible for the energy budget, suggesting a complex coupling
between different layers of the solar atmosphere during CMEs.
---------------------------------------------------------
Title: Predicting the Interplanetary Magnetic Field using Approaches
Based on Data Mining and Physical Models
Authors: Riley, P.; Russell, C. T.; de Koning, C. A.; Biesecker, D. A.;
Linker, J.; Owens, M. J.; Lugaz, N.; Martens, P.; Angryk, R.; Reinard,
A.; Ulrich, R. K.; Horbury, T. S.; Pizzo, V. J.; Liu, Y.; Hoeksema, T.
2015AGUFMSH14A..06R Altcode:
An accurate prediction of the interplanetary magnetic field, and,
in particular, its z-component (Bz) is a crucial capability for any
space weather forecasting system, and yet, thus far, it has remained
largely elusive (a point exemplified by the fact that no prediction
center currently provides a forecast for Bz). In this presentation,
we discuss the various physical processes that can produce non-zero
values of Bz and summarize a selection of promising approaches that may
ultimately lead to reliable forecasts of Bz. We describe the first steps
we have taken to develop a framework for assessing these techniques,
and show preliminary results of their efficacy.
---------------------------------------------------------
Title: Why Is the Great Solar Active Region 12192 CME-Poor?
Authors: Sun, Xudong; Bobra, Monica G.; Hoeksema, Todd; Liu, Yang;
Li, Yan; Shen, Chenglong; Couvidat, Sebastien; Norton, Aimee A.;
Fisher, George H.
2015TESS....140802S Altcode:
Solar active region (AR) 12192 of October 2014 hosts the largest
sunspot group in 24 years. It is the most prolific flaring site of
Cycle 24, but surprisingly produced no coronal mass ejection (CME) from
the core region during its disk passage. Here, we study the magnetic
conditions that prevented eruption and the consequences that ensued. We
find AR 12192 to be "big but mild"; its core region exhibits weaker
non-potentiality, stronger overlying field, and smaller flare-related
field changes compared to two other major flare-CME-productive ARs
(11429 and 11158). These differences are present in the intensive-type
indices (e.g., means) but generally not the extensive ones (e.g.,
totals). AR 12192's large amount of magnetic free energy does not
translate into CME productivity. The unexpected behavior suggests
that AR eruptiveness is limited by some relative measure of magnetic
non-potentiality over the restriction of background field, and that
confined flares may leave weaker photospheric and coronal imprints
compared to their eruptive counterparts.
---------------------------------------------------------
Title: Causes of Major Change in the Heliospheric Field
Authors: Hoeksema, Todd
2015TESS....111002H Altcode:
The fundamental polarity structure of the heliospheric magnetic field is
determined in the solar corona and depends on the photospheric magnetic
field. Most of the time the shape of the field evolves slowly from
one solar rotation to the next. Modest perturbations are caused by
the emergence of new flux, whose configuration generally matches the
large-scale patterns that already exist. However, a few times during
the solar cycle a radical change occurs when new flux permanently
disrupts the large-scale pattern. Such times are often associated with
increased numbers of coronal mass ejections. The new pattern typically
strengthens and can endure for many years. This investigation identifies
the reconfigurations detected in the modeled coronal field during the
last several solar cycles and investigates their photospheric sources
in Cycles 23 and 24 using magnetic field observations from WSO, MDI,
and HMI.
---------------------------------------------------------
Title: A Multi-Observatory Inter-Comparison of Line-of-Sight Synoptic
Solar Magnetograms
Authors: Riley, P.; Ben-Nun, M.; Linker, J. A.; Mikic, Z.; Svalgaard,
L.; Harvey, J.; Bertello, L.; Hoeksema, T.; Liu, Y.; Ulrich, R.
2014SoPh..289..769R Altcode:
The observed photospheric magnetic field is a crucial parameter
for understanding a range of fundamental solar and heliospheric
phenomena. Synoptic maps, in particular, which are derived from
the observed line-of-sight photospheric magnetic field and built up
over a period of 27 days, are the main driver for global numerical
models of the solar corona and inner heliosphere. Yet, in spite of 60
years of measurements, quantitative estimates remain elusive. In this
study, we compare maps from seven solar observatories (Stanford/WSO,
NSO/KPVT, NSO/SOLIS, NSO/GONG, SOHO/MDI, UCLA/MWO, and SDO /HMI)
to identify consistencies and differences among them. We find that
while there is a general qualitative consensus, there are also some
significant differences. We compute conversion factors that relate
measurements made by one observatory to another using both synoptic
map pixel-by-pixel and histogram-equating techniques, and we also
estimate the correlation between datasets. For example, Wilcox Solar
Observatory (WSO) synoptic maps must be multiplied by a factor of 3 -
4 to match Mount Wilson Observatory (MWO) estimates. Additionally, we
find no evidence that the MWO saturation correction factor should be
applied to WSO data, as has been done in previous studies. Finally,
we explore the relationship between these datasets over more than
a solar cycle, demonstrating that, with a few notable exceptions,
the conversion factors remain relatively constant. While our study
was able to quantitatively describe the relationship between the
datasets, it did not uncover any obvious "ground truth." We offer
several suggestions for how this may be addressed in the future.
---------------------------------------------------------
Title: Hot Spine Loops and the Nature of a Late-Phase Solar Flare
Authors: Sun, Xudong; Hoeksema, Todd; Liu, Yang
2013enss.confE..24S Altcode:
The fan-spine magnetic topology is thought to be responsible for
many curious emission signatures in solar explosive events. A spine
field line links topologically separate flux domains and possibly
their evolutionary trends, but direct observational evidence of such
structure has been rare. Here we report a unique event observed by the
Solar Dynamic Observatory (SDO) where a set of hot coronal loops (over
10 MK) that developed during the rising phase of the flare connected
to a quasi-circular chromospheric ribbon at one end and a remote
brightening at the other. Magnetic field extrapolation suggest these
loops are tracers of the spine field line. The sequential brightening
of the ribbon and the increasing number of hot loops suggest that
continuous slipping and null-point type reconnection were at work,
transferring flux from below the fan dome to the exterior. This event
also features an extreme-ultraviolet (EUV) late phase - a second
emission peak observed in the warm EUV lines (2-7 MK) hours after
the flare. Observations indicate that the initially confined process
transitioned to a fluxrope eruption near the flare peak. The eruption
opened the overlying field and drastically accelerated the energy
release. Slow cooling of the large post-flare arcades naturally explains
the sequential delay of the late-phase peak in increasingly cooler EUV
lines. Our result demonstrates the crucial nature of magnetic coupling
between systems of different sizes - a minor topological change may
lead to violent eruptions on a much larger scale.
---------------------------------------------------------
Title: Using Electric Fields to drive simulations of the solar
coronal magnetic field
Authors: Fisher, George H.; Cheung, Mark; DeRosa, Marc; Kazachenko,
Maria; Welsch, Brian; Hoeksema, Todd; Sun, Xudong
2012shin.confE..47F Altcode:
The availability of high-cadence vector magnetograms and Doppler flow
information measured from the HMI instrument on SDO make it possible to
determine the electric field at the solar photosphere. This electric
field, in turn, can be used to drive time-dependent simulations of
the magnetic field in the solar corona, employing the MHD equations,
or simpler time-dependent models such as the magneto-frictional (MF)
model. Here, we demonstrate these concepts by using electric fields
determined from HMI data to drive a time-dependent MF model of the
solar corona in the volume overlying the photosphere near NOAA AR 11158.
---------------------------------------------------------
Title: A Portrait of the Magnetic Sun: Observation and Modeling at
Global and Active Region Scales
Authors: Sun, Xudong; Hoeksema, T.; Liu, Y.; Zhao, X.; Hayashi, K.
2012AAS...22032206S Altcode:
The solar magnetic field contains a vast amount of energy that powers
the dynamic atmosphere. On the large scale, the dipole-like field
waxes and wanes, reversing polarity in each activity cycle. Its
strength and evolution history strongly modulate solar wind speed,
heliospheric open flux, and their sources. On the smaller scale, active
regions with non-potential kilogauss field often exhibit explosive
behaviors that directly affect space weather conditions. Thanks
to space-borne observatories such as MDI and HMI, it is possible to
monitor the photospheric field constantly. The ability to diagnose the
coronal field is also improving due to the advances of extrapolation
models. This dissertation talk briefly summarizes the large scale
magnetic field and solar wind structures of Cycle 23 based on the
MDI data archive and potential field models. I then focus on a recent
major active region observed by HMI. The vector magnetogram sequence,
complemented by a non-linear force-free field extrapolation, portrays in
detail the 3D current and energy evolution leading to major eruptions
with good spatial and temporal resolution. Future work will include
better constrained coronal field modeling and more accurate estimation
of the energy, as well as the coupling between the small and large
scale fields.
---------------------------------------------------------
Title: Recurrent Eruptions in a Quadrupolar Magnetic Configuration
Observed by SDO
Authors: Sun; Xudong; Hoeksema, Todd; Liu, Yang; Hayashi, Keiji
2012decs.confE..91S Altcode:
The active region AR11158 generated the first X-class flare of the
current solar cycle as well as over a dozen CMEs over the course of a
few days. Interestingly, most of these CMEs originated from a complex
quadrupolar magnetic configuration on the eastern side rather than the
center of the region where a major filament situated. A couple of pores
emerged relatively late during the AR development but rapidly altered
the magnetic connectivities, accumulating a large amount of electric
current and free energy at the eruption site. HMI vector magnetograms
and a non-linear force-free field extrapolation are used to explore
the coronal field structures that favor the subsequent eruptions. AIA
observation of the brightening flare loops and footpoint pairs provides
further evidence for the interpretation.
---------------------------------------------------------
Title: Evolution of Magnetic Field and Energy in A Major Eruptive
Active Region Based on SDO/HMI Observation
Authors: Sun, Xudong; Hoeksema, Todd; Liu, Yang; Wiegelmann, Thomas;
Hayashi, Keiji; Chen, Qingrong; Thalmann, Julia
2011sdmi.confE..63S Altcode:
We report the evolution of magnetic field and its energy in NOAA
AR 11158 based on a vector magnetogram series from the Helioseismic
and Magnetic Imager (HMI). Fast flux emergence and strong shearing
motion created a quadrupolar sunspot complex that produced several
major eruptions, including the first X-class flare of solar cycle
24. Extrapolated non-linear force-free coronal field shows substantial
electric current and free energy increase during early flux emergence
along a newly-formed, low-lying filament with a typical 1000 G field
strength and 0.45 Mm^(-1) alpha-parameter at its center. The computed
magnetic free energy reaches a maximum of 2.62E32 erg, about 50%
stored below 6 Mm. This free energy decreases by 0.33E32 erg within
1 hour of the X-class flare, which is likely an underestimation of
the actual energy loss. During the flare, photospheric field changed
rapidly: the horizontal field was enhanced by 28% in the AR core
region. Such change is consistent with the conjectured coronal field
"implosion", and is in line with both the reconnection signatures
and the coronal loop retraction observed by the Atmospheric Image
Assembly (AIA). Extrapolation indicates that the coronal field relaxes
more rapidly with height after the flare and becomes overall less
energetic. These preliminary results demonstrate the capability to
quantitatively study the AR field topology and energetics using SDO
data- although difficulties still abound.
---------------------------------------------------------
Title: Evolution of Magnetic Field in the Flaring Active Region
11158 Observed by SDO/HMI
Authors: Sun, Xudong; Hoeksema, T.; Liu, Y.; Wiegelmann, T.;
Hayashi, K.
2011SPD....42.2101S Altcode: 2011BAAS..43S.2101S
We report the evolution of the magnetic field in NOAA AR11158 over 5
days (2011 Feb 12-16) using preliminary vector magnetograms from the
Helioseismic and Magnetic Imager (HMI) on board the Solar Dynamic
Observatory (SDO). This region consisted of two pairs of major
sunspots and displayed a complex quadrupolar field topology. It
produced multiple major flares and eruptions, including the first
X-class flare of the current solar cycle. Strong shear motion and flux
emergence were both present, with apparent emergence preceding each
major flare. We reconstruct the coronal field from a series of vector
data using a non-linear force-free (NLFF) extrapolation. The estimated
free magnetic energy shows a great increase during the early emergence
of the current-carrying flux, while a significant, permanent decrease (
0.5e32 erg, or 20%) is found after the X-class flare despite continuous
flux injection. We relate this decrease to a previously reported, sudden
change of the photospheric field after the flare. The extrapolated
coronal field structure correspondingly becomes more "compact": the
low-lying of field appears more sheared and stores more free energy,
and higher-altitude field decays faster with height and becomes more
potential. The coronal field overall becomes less-energetic.
---------------------------------------------------------
Title: HMI: First Results
Authors: Centeno, R.; Tomczyk, S.; Borrero, J. M.; Couvidat,
S. Hayashi, K.; Hoeksema, T.; Liu, Y.; Schou, J.
2011ASPC..437..147C Altcode: 2010arXiv1012.3796C
The Helioseismic and Magnetic Imager (HMI) has just started producing
data that will help determine what the sources and mechanisms of
variability in the Sun's interior are. The instrument measures the
Doppler shift and the polarization of the Fe I 6173 Å line, on the
entire solar disk at a relatively-high cadence, in order to study
the oscillations and the evolution of the full vector magnetic field
of the solar Photosphere. After the data are properly calibrated,
they are given to a Milne-Eddington inversion code (VFISV, Borrero et
al. 2010) whose purpose is to infer certain aspects of the physical
conditions in the Sun's Photosphere, such as the full 3-D topology
of the magnetic field and the line-of-sight velocity at the solar
surface. We will briefly describe the characteristics of the inversion
code, its advantages and limitations -both in the context of the model
atmosphere and the actual nature of the data-, and other aspects of its
performance on such a remarkable data load. Also, a cross-comparison
with near-simultaneous maps from the Spectro-Polarimeter (SP) onboard
Hinode will be made.
---------------------------------------------------------
Title: Understanding Solar Eruptions with SDO/HMI Measuring
Photospheric Flows, Testing Models, and Steps Towards Forecasting
Solar Eruptions
Authors: Schuck, Peter W.; Linton, M.; Muglach, K.; Hoeksema, T.
2010AAS...21640214S Altcode: 2010BAAS...41Q.875S
The Solar Dynamics Observatory (SDO) is carrying the first full-disk
imaging vector magnetograph, the Helioseismic and Magnetic Imager (HMI),
into an inclined geosynchronous orbit. This magnetograph will provide
nearly continuous measurements of photospheric vector magnetic fields
at cadences of 90 seconds to 12 minutes with 1" resolution, precise
pointing, and unfettered by atmospheric seeing. The enormous data
stream of 1.5 Terabytes per day from SDO will provide an unprecedented
opportunity to understand the mysteries of solar eruptions. These
ground-breaking observations will permit the application of a new
technique, the differential affine velocity estimator for vector
magnetograms (DAVE4VM), to measure photospheric plasma flows in active
regions. These measurements will permit, for the first time, accurate
assessments of the coronal free energy available for driving CMEs and
flares. The details of photospheric plasma flows, particularly along
magnetic neutral-lines, are critical to testing models for initiating
coronal mass ejections (CMEs) and flares. Assimilating flows and
fields into state-of-the art 3D MHD simulations that model the highly
stratified solar atmosphere from the convection zone to the corona
represents the next step towards achieving NASA's Living with a Star
forecasting goals of predicting "when a solar eruption leading to a
CME will occur." Our presentation will describe these major science
and predictive advances that will be delivered by SDO/HMI.
---------------------------------------------------------
Title: The magnetic field at the heliospheric base during solar
minimum
Authors: Zhao, X.; Hoeksema, T.
2009AGUFMSH13B1534Z Altcode:
What is the base of the heliosphere? and where is the heliospheric
base located? There appears no generally accepted answer to the
questions. We define the heliospheric base as the spherical surface
where all open magnetic field lines have become radial and start to
gradually wind into Archimedes spirals. Both observationally and in
models it seems clear that all of the coronal magnetic field above the
cusp points of coronal streamers is open. However, except at the cusp
points (located near 2.5 solar radii in most magnetostatic models),
the open field lines are not generally radial. The non-radial coronal
plasma expansion, especially during solar minimum, is supposed to
be caused primarily by the transverse magnetic pressure gradient
[Smith and Balogh, 1995]. The pressure gradient approaches zero at
the Alfven critical point, so the height of the Alfven critical
point, at about 15 solar radii, provides a reasonable estimate
of the above-defined heliospheric base. If the non-radial coronal
expansion is indeed caused mainly by the magnetic pressure gradient,
the open magnetic flux is expected to be uniformly distributed at the
heliospheric base. The fast latitude scans of the inner heliosphere
by the Ulysses spacecraft have confirmed that distribution of open
magnetic flux (i.e., the radial component of the magnetic field, Br,
multiplied by the square of the radial distance) is independent of
latitude [Smith and Balogh, 1995; 2008]. The STEREO A and B spacecraft
in 2007.6-2008.6 were well separated in longitude. We compare the two
sets of rotation-averages of unsigned daily open magnetic flux observed
by the STEREO A and B during this period. We find that statistically the
two sets of observations agree very well, suggesting the absence of a
significant gradient in longitude as well. We calculate the strength
of the radial magnetic field component at 15 solar radii using the
horizontal-current current-sheet source-surface (HCCSSS) coronal field
model applied to photospheric magnetic field observations [Zhao &
Hoeksema, 1995; 2001]. The model successfully reproduces a uniform Br,
the same as observed by Ulysses, STEREO A, and STEREO B. The result
further confirms that the heliospheric base is located at the Alfven
critical point at about 15 solar radii.
---------------------------------------------------------
Title: Spatial Structures of Polar Magnetic Field During the Last
Solar Cycle
Authors: Sun, Xudong; Hoeksema, T.
2009SPD....40.1103S Altcode:
The Sun's polar field is closely related to the large scale coronal
structure. It is important for coronal modeling and greatly affects
the result. However, the polar field is not well observed because the
ecliptic lies near the Sun's equator. In this study, we make use of
the data from various observatories (MDI/WSO/MWO/Hinode) to study its
spatial structures during the last solar cycle. The result is useful
to improve the polar field extrapolation schemes.
---------------------------------------------------------
Title: Distributing space weather monitoring instruments and
educational materials worldwide for IHY 2007: The AWESOME and
SID project
Authors: Scherrer, Deborah; Cohen, Morris; Hoeksema, Todd; Inan,
Umran; Mitchell, Ray; Scherrer, Philip
2008AdSpR..42.1777S Altcode:
The International Heliophysical Year (IHY) aims to advance our
understanding of the fundamental processes that govern the Sun, Earth,
and heliosphere. The IHY Education and Outreach Program is dedicated to
inspiring the next generation of space and Earth scientists as well as
spreading the knowledge, beauty, and relevance of our solar system to
the people of the world. In our Space Weather Monitor project we deploy
a global network of sensors to high schools and universities to provide
quantitative diagnostics of solar-induced ionospheric disturbances,
thunderstorm intensity, and magnetospheric activity. We bring real
scientific instruments and data in a cost-effective way to students
throughout the world. Instruments meet the objectives of being sensitive
enough to produce research-quality data, yet inexpensive enough for
placement in high schools and universities. The instruments and data
have been shown to be appropriate to, and usable by, high school age
and early university students. Data contributed to the Stanford data
center is openly shared and partnerships between groups in different
nations develop naturally. Students and teachers have direct access
to scientific expertise. The result is a world-wide collaboration of
scientists, teachers, and students to investigate the variability of
the ionosphere. The research-quality AWESOME (Atmospheric Weather
Electromagnetic System of Observation, Modeling, and Education)
instruments have been selected as a participating program by the United
Nations Basic Space Science Initiative (UNBSSI). The IHY Committee
for International Education and Public Outreach has designated the
simpler SID (Sudden Ionospheric Disturbance) monitors to be provided
to teacher/student teams in each of the 192 countries of the world.
---------------------------------------------------------
Title: A Determination of the Value and Variability of the Sun's
Open Magnetic Flux using a Global MHD Model
Authors: Riley, P.; Mikic, Z.; Linker, J.; Harvey, J. W.; Hoeksema,
T.; Liu, Y.; Bertello, L.
2008AGUSMSH44A..03R Altcode:
The underlying value and variation of the Sun's open, unsigned magnetic
flux is of fundamental scientific importance, yet its properties remain
poorly known. For example, do long term (on the time-scale of ~ 100
years) changes in the strength of the solar magnetic field exist and
do they persist through the heliosphere? If present, they may have
a direct impact on space climate, including implications for the
transport of cosmic rays (CRs), and as such, may affect technology,
space, and even terrestrial climate. Global MHD models are capable of
reproducing the structure of the large-scale solar and interplanetary
magnetic field (at least in the absence of transient phenomena such as
Coronal Mass Ejections), and should, in principle, be able to address
this topic. However, they rely - and depend crucially - on boundary
conditions derived from observations of the photospheric magnetic
field. In spite of ~ 40 years of measurements, accurate estimates of the
radial component of the photospheric magnetic field remain difficult
to make. In this study, we attempt to find a "ground truth" estimate
of the photospheric magnetic field by carefully comparing both disk
magnetograms and diachronic (previously known as synoptic) maps from
6 different observatories (KPVT, SOLIS, GONG, MDI, WSO, and MWO). We
find that although there is a general consensus between several of
them, there are also some significant discrepancies. Using data from
these observatories, we compute global heliospheric solutions for a
selection of epochs during the last 3 solar cycles and compare the
results with in situ observations. We apply these results to several
topics related to the Sun's open flux.
---------------------------------------------------------
Title: Modeling Solar Wind Using the Newly Calibrated MDI Magnetic
Field: 1996-2008
Authors: Sun, X.; Hoeksema, T.
2008AGUSMSP51A..12S Altcode:
The Wang-Sheeley-Arge (WSA) model is regularly used to predict the
solar wind speed and interplanetary magnetic field polarity (IMF) at 1
AU. As the only input to the model, photospheric magnetic observations
can affect the result to a significant extent. In this paper, we employ
the newly calibrated MDI data (1996-2008) and a reasonable polar field
extrapolation to test an objective scheme for predicting the solar wind
parameters. The results are statistically evaluated and compared with
those based on older MDI data and other sources. In order to study the
model dependence, we use three different models to infer the coronal
field: the potential field source surface (PFSS) model, Schatten current
sheet (SCS) model and horizontal-current current-sheet source-surface
(HCCSSS) model. They sometimes produce different coronal field
structures and perform variously in different phases of the solar cycle.
---------------------------------------------------------
Title: The Sun as the Source of Heliospheric "Space Weather": A CISM
Integrated Model Perspective and STEREO Inspiration
Authors: Luhmann, J. G.; Li, Y.; Lynch, B.; Lee, C. O.; Huttunen, E.;
Liu, Y.; Toy, V.; Odstrcil, D.; Riley, P.; Linker, J.; Mikic, Z.; Arge,
C.; Petrie, G.; Zhao, X.; Liu, Y.; Hoeksema, T.; Owens, M.; Galvin,
A.; Simunac, K.; Howard, R.; Vourlidas, A.; Jian, L. K.; Russell, C. T.
2008AGUSMSH31C..01L Altcode:
Models developed under the Center for Integrated Space weather
Modeling (CISM) represent one effort that is underway to realistically
simulate the Sun's physical controls over interplanetary conditions,
or heliospheric "space weather", in three dimensions. This capability
is critical for interpreting the latest observations from STEREO,
whose goal is to enable connections to be made between what is
observed in the heliosphere via distributed in-situ measurements
and what is observed in the corona and heliosphere via imaging from
separated 1 AU perspectives. The ways in which the CISM models are
enabling the exploitation of STEREO and other observations toward
increased understanding of the solar wind and coronal activity and
its consequences are described. In particular, the models allow the
identification of the sources of structures in the solar wind, and
analyses of how the coronal context of the observed CMEs plays a key
role in determining the ultimate terrestrial (and other planetary)
response .
---------------------------------------------------------
Title: Mechanisms of the solar activity cycle
Authors: Hoeksema, Todd
2006AdSpR..38..831H Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Three-Dimensional Magnetohydrodynamic Simulation of a Global
Solar Corona Using a Temperature Distribution Map Obtained from SOHO
EIT Measurements
Authors: Hayashi, Keiji; Benevolenskaya, Elena; Hoeksema, Todd; Liu,
Yang; Zhao, Xue Pu
2006ApJ...636L.165H Altcode:
The temperature at the base of the solar corona is one of the important
factors in determining the solar coronal structure. In this Letter,
we performed the time-dependent magnetohydrodynamic (MHD) simulation
for the solar corona utilizing the temperature map derived from the
multiwavelength observation by the EUV Imaging Telescope (EIT) on
the Solar and Heliospheric Observatory (SOHO) and the magnetic field
map from the Michelson Doppler Imager (MDI) on SOHO. We analyzed the
difference in three-dimensional magnetic field topology obtained when
the uniform base temperature adopted in standard simulations is replaced
by the observation-based, nonuniform temperature distribution. The
differences in the magnetic field topology obtained as the response of
the solar corona to the changes of the temperature at the coronal base
depict the role of the plasma conditions at the coronal base in the
dynamics of the global solar corona. This work is our first effort to
utilize the data of the solar coronal plasma as the boundary condition
to enhance the MHD simulations of a solar corona.
---------------------------------------------------------
Title: Comparison of Photospheric Footpoints of Open Magnetic Field
Regions using CSSS and PFSS models
Authors: Poduval, B.; Hoeksema, T.; Zhao, X.
2005AGUSMSH13A..10P Altcode:
Comparison of Photospheric Footpoints of Open Magnetic Field Regions
using CSSS and PFSS models The Current--Sheet Source Surface (CSSS)
model developed by Zhao and Hoeksema (1995) assumes a cusp surface at
the cusp point of coronal streamers at around 2.5 Rsun, which divides
the corona into three regions, one bounded by the photosphere and
the cusp surface, the second, between the cusp surface and the source
surface, and the third, the region beyond the source surface. In this
model the source surface can be placed closer to the Alfven critical
point which is a great advantage over the traditional Potential
Field Source Surface (PFSS) models, where it is at 2.5 Rsun. The
source surface magnetic field obtained by CSSS model exhibits little
latitudinal variation, which is consistent with the Ulysses observation
of the interplanetary magnetic field (IMF). On the other hand, the
source surface field computed using the PFSS model shows a latitudinal
structure. We have carried out a comparative study of the photospheric
footpoints of open magnetic fields obtained dusing the two models. The
magnetic neutral line was found to be coinciding in the two models,
as expected. There are significant differences in the locations and
sizes of the open field regions on the photosphere, and they are not
always consistent with the observations of coronal holes. We present
the results of the comparison.
---------------------------------------------------------
Title: Potential Field Source Surface Model and Solar Wind Prediction
Authors: Poduval, B.; Zhao, X.; Hoeksema, T.
2005AGUSMSH23C..03P Altcode:
Various magnetic activities of the Sun causes disturbances in the
near-Earth enviornment as well as on the weather and technology
on Earth. "Addressing these disturbances and predicting them well
in advance are the main task of Space Weather research. Much of the
solar side of Space Weather is concerned with the accurate prediction
of solar wind and its properties which are closely related to the
coronal magnetic field. Since a direct measurement of the coronal
magnetic field is still limited to strong field regions, solar wind
predictions are based on theoretical models of the corona. The primary
prediction scheme of the solar wind speed currently used at SEC is
based on the empirical relationship between the flux tube expansion
(FTE) factor obtained using Potential Field Source Surface (PFSS)
model of the corona and the solar wind speed near the Earth. Though
successful, this scheme has significant discrepancies. We have studied,
using the near-Earth saltellites data as well as near--Sun Helios data,
the possible causes of these discrepancies. In our study, FTE at the
source surface were obtained using two different coronal models: PFSS
model and the Current--Sheet Source Surface (CSSS) model. We present
the results of this investigation and a comparison of the two models.
---------------------------------------------------------
Title: A Solar Wind Source Tracking Concept for Inner Heliosphere
Constellations of Spacecraft
Authors: Luhmann, J. G.; Li, Yan; Arge, C. N.; Hoeksema, Todd;
Zhao, Xuepu
2003AIPC..679..168L Altcode:
During the next decade, a number of spacecraft carrying in-situ
particles and fields instruments, including the twin STEREO spacecraft,
ACE, WIND, and possibly Triana, will be monitoring the solar wind in
the inner heliosphere. At the same time, several suitably instrumented
planetary missions, including Nozomi, Mars Express, and Messenger will
be in either their cruise or orbital phases which expose them at times
to interplanetary conditions and/or regions affected by the solar wind
interaction. In addition to the mutual support role for the individual
missions that can be gained from this coincidence, this set provides
an opportunity for evaluating the challenges and tools for a future
targeted heliospheric constellation mission. In the past few years the
capability of estimating the solar sources of the local solar wind has
improved, in part due to the ability to monitor the full-disk magnetic
field of the Sun on an almost continuous basis. We illustrate a concept
for a model and web-based display that routinely updates the estimated
sources of the solar wind arriving at inner heliospheric spacecraft.
---------------------------------------------------------
Title: g-mode detection: Where do we stand?
Authors: Appourchaux, T.; Andersen, B.; Berthomieu, G.; Chaplin, W.;
Elsworth, Y.; Finsterle, W.; Frölich, C.; Gough, D. O.; Hoeksema,
T.; Isaak, G.; Kosovichev, A.; Provost, J.; Scherrer, P.; Sekii, T.;
Toutain, T.
2001ESASP.464..467A Altcode: 2001soho...10..467A
We review the recent developments in determining the upper limits to
g-mode amplitudes obtained by SOHO instruments, GONG and BiSON. We
address how this limit can be improved by way of new helioseismic
instruments and/or new collaborations, hopefully providing in the not
too distant future unambiguous g-mode detection.
---------------------------------------------------------
Title: Study of the Effect of Active Regions on the Solar Irradiance
During Solar Minimum
Authors: Domingo, V.; Sanchez, L.; Appourchaux, T.; Froehlich, C.;
Wehrli, C.; Hoeksema, T.; Pap, J.
1997SPD....28.0206D Altcode: 1997BAAS...29..893D
We have determined both the size of the area that contributes to the
solar irradiance increase around an active region and the angular
distribution of the radiance excess in it, using data obtained during
about one year around solar minimum (April 1996 - April 1997). During
the solar minimum and the early raising phase of the new maximum it
is possible to study the effect of isolated active regions while there
are few of them. The result of this study will be important to separate
the contribution of the active regions to the solar irradiance change
during the solar cycle from any underlying long term effect, if there
is one. The solar radiance measured by the Low-resolution Oscillations
Imager (LOI) of the VIRGO instrument and by the MDI instrument aboard
SOHO is used to determine the dimension of the radiating area. The
increase in irradance is determined by the Sun Photometers (SPM)
and Radiometers on the VIRGO instrument.
---------------------------------------------------------
Title: Initial Results from SOI/MDI High Resolution Magnetograms
Authors: Title, A.; Tarbell, T.; Frank, Z.; Schrijver, C.; Shine,
R.; Wolfson, J.; Zayer, I.; Scherrer, P.; Bush, R.; Deforest, C.;
Hoeksema, T.
1996AAS...188.6915T Altcode: 1996BAAS...28..938T
The Michelson Doppler Imager (MDI) on SoHO takes magnetogram
s with resolutions of 1.2 (high resolution) and 4 (full disk)
arcseconds. Movies of 16 hour duration have been constructed in full
disk and high resolution mode. High resolution movies of the south
polar region also have been obtained. In sums of nine high resolution
magnetograms it is possible to detect fields as low as 5 gauss and
total fluxes as low as 5 10(1) 6 Mx. In mid latitude regions new flux
is observed to emerge everywhere. At all latitudes below 60 degrees
flux is mixed on the scale of supergranulation. In the polar region
above 60 degrees only fields of a single polarity are observed above
the detection limit.
---------------------------------------------------------
Title: VIRGO: Experiment for Helioseismology and Solar Irradiance
Monitoring
Authors: Fröhlich, Claus; Romero, José; Roth, Hansjörg; Wehrli,
Christoph; Andersen, Bo N.; Appourchaux, Thierry; Domingo, Vicente;
Telljohann, Udo; Berthomieu, Gabrielle; Delache, Philippe; Provost,
Janine; Toutain, Thierry; Crommelynck, Dominique A.; Chevalier,
André; Fichot, Alain; Däppen, Werner; Gough, Douglas; Hoeksema,
Todd; Jiménez, Antonio; Gómez, Maria F.; Herreros, José M.; Cortés,
Teodoro Roca; Jones, Andrew R.; Pap, Judit M.; Willson, Richard C.
1995SoPh..162..101F Altcode:
The scientific objective of the VIRGO experiment (Variability of solar
IRradiance and Gravity Oscillations) is to determine the characteristics
of pressure and internal gravity oscillations by observing irradiance
and radiance variations, to measure the solar total and spectral
irradiance and to quantify their variability over periods of days to
the duration of the mission. With these data helioseismological methods
can be used to probe the solar interior. Certain characteristics of
convection and its interaction with magnetic fields, related to, for
example, activity, will be studied from the results of the irradiance
monitoring and from the comparison of amplitudes and phases of the
oscillations as manifest in brightness from VIRGO, in velocity from
GOLF, and in both velocity and continuum intensity from SOI/MDI. The
VIRGO experiment contains two different active-cavity radiometers for
monitoring the solar `constant', two three-channel sunphotometers (SPM)
for the measurement of the spectral irradiance at 402, 500 and 862 nm,
and a low-resolution imager (LOI) with 12 pixels, for the measurement
of the radiance distribution over the solar disk at 500 um. In this
paper the scientific objectives of VIRGO are presented, the instruments
and the data acquisition and control system are described in detail,
and their measured performance is given.
---------------------------------------------------------
Title: P-Mode Frequencies of Degree L = 3 TO 5
Authors: Pantel, A.; Hoeksema, T.; Fossat, E.; Scherrer, P.; Gelly,
B.; Grec, G.; Loudagh, S.; Schmider, F. X.
1995ESASP.376b.381P Altcode: 1995soho....2..381P; 1995help.confP.381P
No abstract at ADS
---------------------------------------------------------
Title: Solar Core Rotation: Latest IRIS Results
Authors: Fossat, E.; Lazrek, M.; Loudagh, S.; Pantel, A.; Gelly, B.;
Grec, G.; Schmider, F. X.; Pallé, P. L.; Régulo, C.; Ehgamberdiev,
S.; Khalikov, S.; Hoeksema, T.
1995ESASP.376b.261F Altcode: 1995help.confP.261F; 1995soho....2..261F
No abstract at ADS
---------------------------------------------------------
Title: Analysis of the heliospheric current sheet at Earth's orbit
and model comparisons
Authors: Lepping, R. P.; Szabo, A.; Peredo, M.; Hoeksema, T.
1995sowi.conf...95L Altcode:
IMP 8 magnetic field data for the first half of the year 1994,
i.e., for about 6 solar rotations, are analyzed around regions of
sector boundary crossings with the purpose of obtaining both gross-
and fine-scale characteristics of the related heliospheric current
sheets separating the observed sectors. For purposes of estimating
the attitudes of the normals to the sector boundaries. analysis
intervals (sometimes 30 min or more in length) allowing the field
to fully complete an excursion of about 180 deg were used in the
study, which consisted of variance analyses of the field within those
intervals. The resulting boundary normals were analyzed and compared
to known (generic) models of projected heliospheric current sheets
and to a coronal field model for the same time period. One of the most
outstanding features of the resulting ensemble of estimated boundary
normals for this period is that they strongly prefer low inclinations,
indicating that the observations do not support a 1 AU model that
predicts a current sheet whose surface is approximately parallel with
the sun's equator, such as the 'sombrero' model. They instead support
a model that predicts a relatively high inclination current sheet at 1
AU. Also the normals assume a surprisingly large range of longitudes,
somewhat favoring those consistent with a Parker model (45 deg and
225 deg) and/or radial alignment (0 deg and 180 deg). These boundary
structures, as defined, are shown typically to be as broad as several
hundred proton gyroradii, but having embedded within them very thin
structures associated with stronger currents. Such thin structures
have normals usually differing markedly from the gross boundary. For
some crossings there are indications of a wave-like structure in the
current sheet as it passed the spacecraft.
---------------------------------------------------------
Title: Inference of 3-dimensional structure underlying large-scale
coronal events observed by YOHKOH and ULYSSES
Authors: Slater, G. L.; Freeland, S. L.; Hoeksema, T.; Zhao, X.;
Hudson, H. S.
1995sowi.confQ..63S Altcode:
The Yohkoh/SXT images provide full-disk coverage of the solar corona,
usually extending before and after one of the large-scale eruptive
events that occur in the polar crown These produce large arcades of
X-ray loops, often with a cusp-shaped coronal extension, and are known
to be associated with coronal mass ejections. The Yohkoh prototype of
such events occurred 12 Nov. 1991. This allows us to determine heights
from the apparent rotation rates of these structures. In comparison v
with magnetic-field extrapolations from Wilcox Solar Observatory. use
use this tool to infer the three dimensional structure of the corona
in particular cases: 24 Jan. 1992, 24 Feb. 1993, 14 Apr. 1994, and 13
Nov. 1994. The last event is a long-duration flare event.
---------------------------------------------------------
Title: The Solar Oscillation Imager-Michelson Doppler Imager for SoHO
Authors: Title, A.; Tarbell, T.; Wolfson, J.; Scherrer, P.; Bush,
R.; Hoeksema, T.
1992AAS...180.0606T Altcode: 1992BAAS...24Q.737T
No abstract at ADS
---------------------------------------------------------
Title: Optical Components of the Solar Oscillations Imager-Michelson
Doppler Imager
Authors: Tarbell, T.; Rosenberg, W.; Pope, T.; Huff, L.; Torgerson,
D.; Title, A.; Wolfson, J.; Scherrer, P.; Bush, R.; Hoeksema, T.
1992AAS...180.0607T Altcode: 1992BAAS...24R.737T
No abstract at ADS
---------------------------------------------------------
Title: Empirically derived solar wind conditions near the sun.
Authors: Suess, S. T.; Dryer, M.; Wilcox, J. M.; Hoeksema, T.;
Henning, H.
1983BAAS...15Q.874S Altcode:
No abstract at ADS
