Author name code: norton
ADS astronomy entries on 2022-09-14
author:"Norton, Aimee A."
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Title: Dependence of the Continuum Intensities on the Magnetic Fields
at Different Evolution Phases of Sunspots
Authors: Li, Qiaoling; Zhang, Li; Yan, Xiaoli; Norton, Aimee A.;
Wang, Jingcheng; Yang, Liheng; Xue, Zhike; Kong, Defang
Bibcode: 2022ApJ...936...37L
Altcode:
The relationship between the continuum intensities and magnetic
fields for stable and decaying sunspots is analyzed using the
scattered-light-corrected data from the Helioseismic and Magnetic
Imager. From our analysis, the main differences between stable and
decaying sunspots are as follows. In the continuum intensity range from
0.35I qs to 0.65I qs, where I qs is
the continuum intensity of the quiet solar surface, the relationship
between continuum intensity and transverse magnetic field and the
relationship between continuum intensity and inclination display a
much higher scatter during the decaying phase of the sunspots. During
and after the formation of the light bridge, the scatter plots show
a bifurcation that indicates that the two umbrae separated by the
light bridge have different thermodynamic properties. The continuum
intensity of the umbra in a decaying sunspot is brighter than that of
the stable sunspot, indicating that the temperatures in the umbra of
decaying sunspots are higher. Furthermore, our results show that the
mean continuum intensity of the umbra gradually increases during the
decay of the sunspot, but the mean continuum intensity of the penumbra
remains constant. Simultaneously, the vertical and transverse magnetic
field strengths in the umbra gradually decrease, and the vertical
magnetic field strengths in the penumbra gradually increase. The
changes in the umbra occur earlier than the changes in the penumbra of
the decaying sunspot, suggesting that the umbral and penumbral decay
may be an interdependent process during the decay of the sunspot.
Title: On the Hemispheric Bias Seen in Vector Magnetic Field Data
Authors: Liu, Yang; Griñón-Marín, Ana Belén; Hoeksema, Jon T.;
Norton, Aimee A.; Sun, Xudong
Bibcode: 2022SoPh..297...17L
Altcode:
The east-west component of the magnetic field, Bϕ, as
observed in solar magnetograms containing quiet regions, is found to
change its sign when the regions cross the central meridian. It is
seen in both HMI/SDO and VSM/SOLIS full disk vector magnetograms. A
mismatch between the calibrated line-of-sight and transverse fields is
the reason for this hemispheric bias problem. Here mismatch means that
one of the fields is either over-estimated or under-estimated. For HMI
data, the transverse field is over-estimated. This mismatch is caused
ultimately by a filling factor that is not precisely determined when
unresolved structures are present. An updated inversion procedure for
HMI observations, developed recently, is able to derive the filling
factor with reasonable accuracy. The new data show that the hemispheric
bias problem has been mitigated substantially.
Title: Observational evidence of spot-producing magnetic ring's
split during MHD evolution
Authors: Norton, Aimee; Dikpati, Mausumi; McIntosh, Scott; Gilman,
Peter
Bibcode: 2021AGUFMSH55D1876N
Altcode:
Spot-producing toroidal rings of 6-degree latitudinal width, with peak
field of 15 kG, have been found to undergo dynamical splitting due
to nonlinear MHD. Split-time depends on the latitude-location of the
ring. Ring-splitting occurs fastest, within a few weeks, at latitudes
20-25 degrees. Rossby waves work as perturbations to drive instability
of spot-producing toroidal rings. The ring-split is caused by the `mixed
stress' or cross correlations of perturbation velocities and magnetic
fields, which arise due to the interaction of Rossby Waves. Mixed
stress carries magnetic energy and flux from the ring-peak to its
shoulders, eventually leading to the ring-split. The two split-rings
migrate away from each other, the high latitude counterpart slipping
poleward faster, due to migrating mixed stress and magnetic curvature
stress. Broader toroidal bands do not split. Much stronger rings of 35
kG, despite being narrow, don't split, due to rigidity from stronger
magnetic fields within the ring. The analysis of magnetograms from MDI
during solar cycle 23 indicates emergence of active regions sometimes
at the same longitudes but separated in latitude by 20-degrees or more,
which could be evidence of active regions emerging from split-rings,
which consistently contribute to occasional high latitude excursions of
observed butterfly wings during ascending, peak and descending phases of
a solar cycle. In the future, observational studies using much longer
term magnetograms including GONG and SDO/HMI can determine how often
new spots are found at higher latitudes than their lower latitude
counterparts, and how the combinations influence solar eruptions and
space weather events.
Title: Characterizing -sunspots of Solar Cycle 24 using data from
the Helioseismic Magnetic Imager
Authors: Levens, Peter; Norton, Aimee; Linton, Mark; Knizhnik, Kalman
Bibcode: 2021AGUFMSH55D1880L
Altcode:
A classification of sunspots with complex magnetic configuration,
-spots, are defined as regions with both positive and negative
magnetic polarity umbrae within 2 degrees each other and within a
shared penumbra. -spots are disproportionately responsible for the
most energetic flares and eruptions during any given solar cycle,
i.e. while only 8% of Cycle 24 spots were -spots, 80% of the X-class
flares originated from them. A new quantity, the degree of (DoD), is
introduced to characterize the fraction of active region umbral flux
that is participating in the configuration. See the attached figure
showing NOAA 12673 with contours outlining the umbral regions in a
configuration with a DoD of 70%. For sunspot groups in Solar Cycle 24,
we analyze Spaceweather HMI Active Region Patches (SHARPs) to calculate
the temporal variations of DoD, magnetic flux, flux emergence rate,
polarity footpoint separation, tilt angle and rotation rate for -spots
and a control group of sunspots that are not in a configuration. We
report the calculated quantities at the time the region is at the
maximum DoD and also at the time of maximum magnetic flux. Our goal is
to isolate the regions of the -spot which are critical to our space
weather prediction capabilities in order to gain insight into how
-spots form. This work was supported by NASA HSR grant NNH18ZDA001N.
Title: Improvement of the Helioseismic and Magnetic Imager (HMI)
Vector Magnetic Field Inversion Code
Authors: Griñón-Marín, Ana Belén; Pastor Yabar, Adur; Liu, Yang;
Hoeksema, J. Todd; Norton, Aimee
Bibcode: 2021ApJ...923...84G
Altcode: 2021arXiv210909131B; 2021arXiv210909131G
A spectral line inversion code, Very Fast Inversion of the Stokes Vector
(VFISV), has been used since 2010 May to infer the solar atmospheric
parameters from the spectropolarimetric observations taken by the
Helioseismic and Magnetic Imager (HMI) on board the Solar Dynamics
Observatory. The magnetic filling factor, the fraction of the surface
with a resolution element occupied by magnetic field, is set to have
a constant value of 1 in the current version of VFISV. This report
describes an improved inversion strategy for the spectropolarimetric
data observed with HMI for magnetic field strengths of intermediate
values in areas spatially not fully resolved. The VFISV inversion code
has been modified to enable inversion of the Stokes profiles with two
different components: one magnetic and one nonmagnetic. In this scheme,
both components share the atmospheric components except for the magnetic
field vector. In order to determine whether the new strategy is useful,
we evaluate the inferred parameters inverted with one magnetic component
(the original version of the HMI inversion) and with two components (the
improved version) using a Bayesian analysis. In pixels with intermediate
magnetic field strengths (e.g., plages), the new version provides
statistically significant values of filling fraction and magnetic
field vector. Not only does the fitting of the Stokes profile improve,
but also the inference of the magnetic parameters and line-of-sight
velocity are obtained uniquely. The new strategy is also proven to
be effective for mitigating the anomalous hemispheric bias in the
east-west magnetic field component in moderate field regions.
Title: Locating Activity Nests of Sunspots in Solar Cycle 24 using
Data from the Helioseismic Magnetic Imager
Authors: Mendez, Alex; Norton, Aimee; Chen, Ruizhu
Bibcode: 2021AGUFMSH55D1877M
Altcode:
Active region nests are locations on the Sun where sunspots repeatedly
emerge month after month. Other stars show similar nesting behavior
of magnetic activity. The precise physical mechanism that causes
nests is unknown but could be an instability acting on the magnetic
field in the interior of the Sun or star or could be due to flow
fields such as giant convection cells causing preferred locations of
magnetic flux emergence. Activity nests host a great majority of solar
energetic events and as such, are crucial to our understanding of space
weather. We analyze data from the SPEAR (Solar Plage, Ephemeral and
Active Region) Catalogue created from Spaceweather HMI Active Region
Patch (SHARP) data. We identify the nest locations in each hemisphere
during Solar Cycle 24, and record the average lifetime, number of
sunspots and rotation rate of each nest, see figure in which sunspots
associated with unique nests are shown grouped by color and plotted as
a function of longitude and Carrington rotation number. The percentage
of sunspots and magnetic flux contained in the nests is higher than
previously reported. This research is supported by the NSF ASSURE REU
program operated through UC Berkeley Space Sciences Lab and by NASA
Grant 80NSSC20K0602 to Stanford University and beneficial interactions
with the COFFIES team.
Title: Dynamical Splitting of Spot-producing Magnetic Rings in a
Nonlinear Shallow-water Model
Authors: Dikpati, Mausumi; Norton, Aimee A.; McIntosh, Scott W.;
Gilman, Peter A.
Bibcode: 2021ApJ...922...46D
Altcode:
We explore the fundamental physics of narrow toroidal rings during their
nonlinear magnetohydrodynamic evolution at tachocline depths. Using
a shallow-water model, we simulate the nonlinear evolution of
spot-producing toroidal rings of 6° latitudinal width and a peak field
of 15 kG. We find that the rings split; the split time depends on the
latitude of each ring. Ring splitting occurs fastest, within a few
weeks, at latitudes 20°-25°. Rossby waves work as perturbations to
drive the instability of spot-producing toroidal rings; the ring split
is caused by the "mixed stress" or cross-correlations of perturbation
velocities and magnetic fields, which carry magnetic energy and flux
from the ring peak to its shoulders, leading to the ring split. The two
split rings migrate away from each other, the high-latitude counterpart
slipping poleward faster due to migrating mixed stress and magnetic
curvature stress. Broader toroidal bands do not split. Much stronger
rings, despite being narrow, do not split due to rigidity from stronger
magnetic fields within the ring. Magnetogram analysis indicates the
emergence of active regions sometimes at the same longitudes but
separated in latitude by 20° or more, which could be evidence of
active regions emerging from split rings, which consistently contribute
to observed high-latitude excursions of butterfly wings during the
ascending, peak, and descending phases of a solar cycle. Observational
studies in the future can determine how often new spots are found at
higher latitudes than their lower-latitude counterparts and how the
combinations influence solar eruptions and space weather events.
Title: Deciphering the Deep Origin of Active Regions via Analysis
of Magnetograms
Authors: Dikpati, Mausumi; McIntosh, Scott W.; Chatterjee, Subhamoy;
Norton, Aimee A.; Ambroz, Pavel; Gilman, Peter A.; Jain, Kiran;
Munoz-Jaramillo, Andres
Bibcode: 2021ApJ...910...91D
Altcode:
In this work, we derive magnetic toroids from surface magnetograms
by employing a novel optimization method, based on the trust region
reflective algorithm. The toroids obtained in this way are combinations
of Fourier modes (amplitudes and phases) with low longitudinal
wavenumbers. The optimization also estimates the latitudinal width of
the toroids. We validate the method using synthetic data, generated
as random numbers along a specified toroid. We compute the shapes and
latitudinal widths of the toroids via magnetograms, generally requiring
several m's to minimize residuals. A threshold field strength is
chosen to include all active regions in the magnetograms for toroid
derivation, while avoiding non-contributing weaker fields. Higher
thresholds yield narrower toroids, with an m = 1 dominant pattern. We
determine the spatiotemporal evolution of toroids by optimally weighting
the amplitudes and phases of each Fourier mode for a sequence of five
Carrington Rotations (CRs) to achieve the best amplitude and phases for
the middle CR in the sequence. Taking more than five causes "smearing"
or degradation of the toroid structure. While this method applies no
matter the depth at which the toroids actually reside inside the Sun,
by comparing their global shape and width with analogous patterns
derived from magnetohydrodynamic (MHD) tachocline shallow water model
simulations, we infer that their origin is at/near the convection zone
base. By analyzing the "Halloween" storms as an example, we describe
features of toroids that may have caused the series of space weather
events in 2003 October-November. Calculations of toroids for several
sunspot cycles will enable us to find similarities/differences in
toroids for different major space weather events.
Title: Oscillations observed in umbra, plage, quiet-Sun and the
polarity inversion line of active region 11158 using Helioseismic
Magnetic Imager/Solar Dynamics Observatory data
Authors: Norton, A. A.; Stutz, R. B.; Welsch, B. T.
Bibcode: 2021RSPTA.37900175N
Altcode: 2021arXiv210101349N
Using data from the Helioseismic Magnetic Imager, we report on the
amplitudes and phase relations of oscillations in quiet-Sun, plage,
umbra and the polarity inversion line (PIL) of an active region
NOAA#11158. We employ Fourier, wavelet and cross-correlation spectra
analysis. Waves with 5 min periods are observed in umbra, PIL and plage
with common phase values of φ(v, I) = π/2, φ(v, Blos)
= -(π/2). In addition, φ(I, Blos) = π in plage are
observed. These phase values are consistent with slow standing or
fast standing surface sausage wave modes. The line width variations,
and their phase relations with intensity and magnetic oscillations,
show different values within the plage and PIL regions, which may
offer a way to further differentiate wave mode mechanics. Significant
Doppler velocity oscillations are present along the PIL, meaning
that plasma motion is perpendicular to the magnetic field lines, a
signature of Alvènic waves. A time-distance diagram along a section
of the PIL shows Eastward propagating Doppler oscillations converting
into magnetic oscillations; the propagation speeds range between 2
and 6 km s-1. Lastly, a 3 min wave is observed in select
regions of the umbra in the magnetogram data. This article is
part of the Theo Murphy meeting issue `High-resolution wave dynamics
in the lower solar atmosphere'.
Title: Derivation of Toroid Patterns from Analysis of Magnetograms
And Inferring Their Deep-origin
Authors: Chatterjee, S.; Dikpati, M.; McIntosh, S. W.; Norton, A. A.;
Ambroz, P.; Gilman, P.; Jain, K.; Munoz-Jaramillo, A.
Bibcode: 2020AGUFMSH0020013C
Altcode:
We employ a novel optimization method based on Trust Region Reflective
algorithm to derive magnetic toroids from surface magnetograms. Toroids
obtained are combinations of Fourier modes (amplitudes and phases)
with low longitudinal wavenumbers. After validating the method using
synthetic data generated as random numbers along a specified toroid,
we compute shapes and latitudinal-widths of toroids from magnetograms,
usually requiring several m 's to minimize residuals. By comparing
properties of these toroids with patterns produced in the bottom
toroidal band undergoing MHD evolution in a 3D thin-shell shallow-water
type model, we infer their deep origin at/near convention-zone's base
or tachocline. A threshold field-strength is chosen to include all
active regions in magnetograms for toroid derivation, while avoiding
non-contributing weaker fields. Higher thresholds yield narrower
toroids, with m = 1 dominant, implying that stronger active regions
are erupting from the core of the toroids at bottom. We determine the
spatio-temporal evolution of toroids by optimally weighting amplitudes
and phases of each Fourier mode for a sequence of 5 Carrington Rotations
(CRs) to get the best amplitude and phases for the middle CR in the
sequence. Taking more than 5 causes 'smearing' or degradation of toroid
structure. As an example case, we analyze 'Halloween' storms toroids,
and describe the features that might have caused the series of space
weather events in October-November of 2003. We compare features of
these toroids with analogous patterns derived from model-output. To find
similarities/differences in toroids for different major space weather
events, we will analyze long-term magnetograms for several solar cycles.
Title: Properties of Delta Spots Observed with HMI
Authors: Norton, A. A.; Knizhnik, K. J.; Linton, M.; Tarr, L.
Bibcode: 2019AGUFMSH41F3333N
Altcode:
The theory has been promoted that delta-spots are formed by the kink
instability acting on rising flux ropes. Delta-spots are especially
interesting as they are responsible for the majority of explosive
flares. We examine the photospheric properties of delta-spots observed
with HMI between 2011-2018. During this time, 86% of the X-class
flares were produced by active regions classified as deltas at some
point during their disk crossing. We provide an initial examination
of properties, such as rotation and flux emergence rates, of these
regions and consider how these properties relate to their formation.
Title: State of the Profession Considerations for Laboratory
Astrophysics
Authors: Savin, Daniel Wolf; Babb, James F.; Barklem, Paul; Bellan,
Paul M.; Betancourt-Martinez, Gabriele; Blum, Jürgen; Boersma,
Christiaan; Boryta, Mark D.; Brisset, Julie; Brogan, Crystal; Cami,
Jan; Caselli, Paola; Chutjian, Ara; Corrales, Lia; Crabtree, Kyle;
Dominguez, Gerardo; Federman, Steven R.; Fontes, Christopher J.;
Freedman, Richard; Gavilan-Marin, Lisseth; Gibson, Brad; Golub, Leon;
Gorczyca, Thomas W.; Hahn, Michael; Hartmann, Dieter; Hörst, Sarah M.;
Hudson, Reggie L.; Ji, Hantao; Kreckel, Holger; Kuhn, Jeffrey; Lawler,
James E.; Lee, Timothy J.; Leutenegger, Maurice A.; Mancini, Roberto;
Marler, Joan P.; Mashonkina, Lyudmila I.; McCarthy, Michael C.;
McCoustra, Martin; McGuire, Brett A.; Milam, Stefanie N.; Montgomery,
Mike; Murphy, Nicholas A.; Nave, Gillian; Nelson, Robert M.; Nollett,
Kenneth M.; Norton, Aimee A.; Novotný, Oldřich; Papol, Anthony;
Raymond, John C.; Salama, Farid; Sciamma-O'Brien, Ella M.; Smith,
Randall; Sosolik, Chad; Sousa-Silva, Clara; Spyrou, Artemis; Stancil,
Phillip C.; Sung, Keeyoon; Tennyson, Jonathan; Timmes, Frank; Trimble,
Virginia L.; Venot, Olivia; Wahlgren, Glenn; Wargelin, Bradford J.;
Winget, Don; Wood, Michael P.
Bibcode: 2019BAAS...51g...7S
Altcode: 2019astro2020U...7S
Astrophysics advances, in part, through laboratory astrophysics studies
of the underlying processes controlling the observed properties of
the Cosmos. These studies encompass both theoretical and experimental
research. Robust support for laboratory astrophysics is critically
needed to maximize the scientific return of astronomical observations.
Title: Astrophysical Science enabled by Laboratory Astrophysics
Studies in Atomic, Molecular, and Optical (AMO) Physics
Authors: Savin, Daniel Wolf; Babb, James F.; Bellan, Paul M.; Brogan,
Crystal; Cami, Jan; Caselli, Paola; Corrales, Lia; Dominguez, Gerardo;
Federman, Steven R.; Fontes, Chris J.; Freedman, Richard; Gibson,
Brad; Golub, Leon; Gorczyca, Thomas W.; Hahn, Michael; Hartmann,
Dieter; Hörst, Sarah M.; Hudson, Reggie L.; Kuhn, Jeffrey; Lawler,
James E.; Leutenegger, Maurice A.; Marler, Joan P.; McCarthy, Michael
C.; McGuire, Brett A.; Milam, Stefanie N.; Murphy, Nicholas A.; Nave,
Gillian; Norton, Aimee A.; Papol, Anthony; Raymond, John C.; Salama,
Farid; Sciamma-O'Brien, Ella M.; Smith, Randall; Sosolik, Chad;
Sousa-Silva, Clara; Stancil, Phillip C.; Timmes, Frank; Trimble,
Virginia L.; Wargelin, Bradford J.
Bibcode: 2019BAAS...51c..96S
Altcode: 2019astro2020T..96S
We highlight a few of the many astrophysical advances that will become
possible with advances in AMO laboratory astrophysics. This submission
supersedes the previous submission.
Title: Exploring Sunspot Emergence with the Helioseismic and
Magnetic Imager
Authors: Venkatesan, Vidya; Scherrer, Phil; Bogart, Rick; Baldner,
Charles; Norton, AImee
Bibcode: 2019AAS...23335902V
Altcode:
The physics behind sunspot emergence is still not well understood. One
of the goals of the Helioseismic Magnetic Imager (HMI) onboard the
Solar Dynamic Observatory (SDO) is to explore the science behind
active region emergence. With HMI's virtually continuous 45-sec data
sampling, it has become possible for the first time to view the detailed
evolution of active regions at high cadence and with reasonably high
resolution. We have made a series of movies to visualize the initial
phases of sunspot emergence. We found evidence of the classic picture
of magnetic flux tubes developing into sunspots as their tops broke
through the photosphere in some of the data sets. We also found that
spots often appear well before their active regions are identified. With
this and additional data, we hope to extract information leading to
improvements in automated and unbiased detection of spot emergence and
to help understand some of the conundrums of spot emergence, including
their non-random longitudinal distribution which cannot be explained
by visibility alone.
Title: IRIS and SDO Observations of Solar Jetlets Resulting from
Network-edge Flux Cancelation
Authors: Panesar, Navdeep K.; Sterling, Alphonse C.; Moore, Ronald L.;
Tiwari, Sanjiv K.; De Pontieu, Bart; Norton, Aimee A.
Bibcode: 2018ApJ...868L..27P
Altcode: 2018arXiv181104314P
Recent observations show that the buildup and triggering of minifilament
eruptions that drive coronal jets result from magnetic flux cancelation
at the neutral line between merging majority- and minority-polarity
magnetic flux patches. We investigate the magnetic setting of 10
on-disk small-scale UV/EUV jets (jetlets, smaller than coronal X-ray
jets but larger than chromospheric spicules) in a coronal hole by using
IRIS UV images and SDO/AIA EUV images and line-of-sight magnetograms
from SDO/HMI. We observe recurring jetlets at the edges of magnetic
network flux lanes in the coronal hole. From magnetograms coaligned
with the IRIS and AIA images, we find, clearly visible in nine cases,
that the jetlets stem from sites of flux cancelation proceeding at
an average rate of ∼1.5 × 1018 Mx hr-1, and
show brightenings at their bases reminiscent of the base brightenings
in larger-scale coronal jets. We find that jetlets happen at many
locations along the edges of network lanes (not limited to the base
of plumes) with average lifetimes of 3 minutes and speeds of 70 km
s-1. The average jetlet-base width (4000 km) is three
to four times smaller than for coronal jets (∼18,000 km). Based on
these observations of 10 obvious jetlets, and our previous observations
of larger-scale coronal jets in quiet regions and coronal holes, we
infer that flux cancelation is an essential process in the buildup and
triggering of jetlets. Our observations suggest that network jetlet
eruptions might be small-scale analogs of both larger-scale coronal
jets and the still-larger-scale eruptions producing CMEs.
Title: VizieR Online Data Catalog: Gemini Planet Imager spectra of
HR 8799 c/d/e (Greenbaum+, 2018)
Authors: Greenbaum, A. Z.; Pueyo, L.; Ruffio, J. -B.; Wang, J. J.;
De Rosa, R. J.; Aguilar, J.; Rameau, J.; Barman, T.; Marois, C.;
Marley, M. S.; Konopacky, Q.; Rajan, A.; Macintosh, B.; Ansdell, M.;
Arriaga, P.; Bailey, V. P.; Bulger, J.; Burrows, A. S.; Chilcote,
J.; Cotten, T.; Doyon, R.; Duchene, G.; Fitzgerald, M. P.; Follette,
K. B.; Gerard, B.; Goodsell, S. J.; Graham, J. R.; Hibon, P.; Hung,
L. -W.; Ingraham, P.; Kalas, P.; Larkin, J. E.; Maire, J.; Marchis,
F.; Metchev, S.; Millar-Blanchaer, M. A.; Nielsen, E. L.; Norton, A.;
Oppenheimer, R.; Palmer, D.; Patience, J.; Perrin, M. D.; Poyneer, L.;
Rantakyro, F. T.; Savransky, D.; Schneider, A. C.; Sivaramakrishnan,
A.; Song, I.; Soummer, R.; Thomas, S.; Wallace, J. K.; Ward-Duong,
K.; Wiktorowicz, S.; Wolff, S.
Bibcode: 2018yCat..51550226G
Altcode:
HR 8799 was observed with the GPI Integral Field Spectrograph (IFS)
(Macintosh et al. 2014PNAS..11112661M), using its K1 and K2 filters,
on 2013 November 17 (median seeing 0.97") and November 18 (median
seeing 0.75 arcsec), respectively, during GPI's first light. The data
were acquired with a continuous field-of-view (FOV) rotation near
the meridian transit to achieve maximum FOV rotation suitable for
ADI processing (Marois et al. 2006ApJ...641..556M). Conditions are
described in detail in Ingraham et al. (2014ApJ...794L..15I). During
the last 10 exposures of the K1 observations, cryocooler power was
decreased to 30% to reduce vibration, and the last 14 exposures of the
K2 observations had the cryocooler power decreased. Since commissioning,
linear-quadratic-Gaussian control has been implemented (Poyneer et
al. 2016ApOpt..55..323P) and the cryocooling system has been upgraded
with active dampers to mitigate cryocooler cycle vibrations. HR 8799
was observed again on 2016 September 19 in GPI's H band (median seeing
0.97"), as a part of the GPI Expolanet Survey with the updated active
damping system. Planet b falls outside the FOV in these data. (1
data file).
Title: Precursors of magnetic flux emergence in the moat flows of
active region AR12673
Authors: Attie, Raphael; Kirk, Michael; Thompson, Barbara; Muglach,
Karin; Norton, Aimee
Bibcode: 2018csc..confE..34A
Altcode:
We report on observations of magnetic disturbances in active region
AR12673 between Sep. 1 and Sep. 3, 2017 seen as a disruption of the moat
flow several hours before the onset of strong flux emergence near the
main sunspot. The moat flow is commonly known as a radially oriented
strong outflow of photospheric plasma surrounding sunspots which ends
abruptly and thus shapes an annular pattern around the penumbra. Using
highly accurate methods of tracking this photospheric flow applied
to SDO/HMI data, we are able to describe the evolution of the moat
surrounding the main sunspot of AR 12673. We find that several hours
before the emergence of strong magnetic flux near the main sunspot the
moat boundaries are broken at these very same locations. This behavior
is observed both on Sep. 1st and Sep. 3rd. There is no such behavior
observed in the absence of flux emergence. These observational results
pose the question of how often they occur in other active regions and
whether the disruption of the moat flow might be, like in this case,
an indication of impending enhanced magnetic activity or simply a
coincidental event.
Title: HMI Data Corrected for Scattered Light Compared to Hinode
SOT-SP Data
Authors: Norton, A. A.; Duvall, T. L., Jr.; Schou, J.; Cheung,
M. C. M.; Scherrer, P. H.; Chu, K. C.; Sommers, J.
Bibcode: 2018csc..confE.101N
Altcode:
In March 2018, the Helioseismic Magnetic Imager (HMI) team began
providing full-disk data to the public on a daily basis that were
corrected for scattered light. In addition to the intensity and
magnetogram data, the improved vector magnetic field maps are also
provided. The process uses a Richardson-Lucy algorithm and a known
PSF. The deconvolution results in a few percent decrease in umbral
intensity corresponding to a 200 K decrease in temperature, a doubling
of the intensity contrast of granulation from 3.6 to 7.2%, an increase
in total field strength values (not only line-of-sight B) in plage by
1.4, faculae brightening and network darkening, and a partial correction
for the convective blue-shift. The new data series can be found in
JSOC with names similar to the original but with the qualifying term
'_dcon' or '_dconS' appended (denoting whether the deconvolution
was applied to the filtergrams or Stokes images). Comparisons to
near-simultaneous Hinode SOT-SP data demonstrate that the correction
brings the two instruments into much better agreement, including the
inverted magnetic field parameters. We compare our results to similar
efforts in the literature such as work by Diaz Baso and Asensio Ramos
(2018) in which HMI intensity and magnetogram data was enhanced using
neural networks and super-resolution.
Title: The Extended Solar Cycle: Muddying the Waters of Solar/Stellar
Dynamo Modeling Or Providing Crucial Observational Constraints?
Authors: Srivastava, Abhishek K.; McIntosh, Scott W.; Arge,
N.; Banerjee, Dipankar; Dikpati, Mausumi; Dwivedi, Bhola N.;
Guhathakurta, Madhulika; Karak, B. B.; Leamon, Robert J.; Matthew,
Shibu K.; Munoz-Jaramillo, Andres; Nandy, D.; Norton, Aimee; Upton,
L.; Chatterjee, S.; Mazumder, Rakesh; Rao, Yamini K.; Yadav, Rahul
Bibcode: 2018FrASS...5...38S
Altcode: 2018arXiv180707601S
In 1844 Schwabe discovered that the number of sunspots increased and
decreased over a period of about 11 years, that variation became known
as the sunspot cycle. Almost eighty years later, Hale described the
nature of the Sun's magnetic field, identifying that it takes about 22
years for the Sun's magnetic polarity to cycle. It was also identified
that the latitudinal distribution of sunspots resembles the wings of
a butterfly showing migration of sunspots in each hemisphere that
abruptly start at mid-latitudes (about ±35(o) ) towards the Sun's
equator over the next 11 years. These sunspot patterns were shown
to be asymmetric across the equator. In intervening years, it was
deduced that the Sun (and sun-like stars) possess magnetic activity
cycles that are assumed to be the physical manifestation of a dynamo
process that results from complex circulatory transport processes in
the star's interior. Understanding the Sun's magnetism, its origin
and its variation, has become a fundamental scientific objective
the distribution of magnetism, and its interaction with convective
processes, drives various plasma processes in the outer atmosphere
that generate particulate, radiative, eruptive phenomena and shape the
heliosphere. In the past few decades, a range of diagnostic techniques
have been employed to systematically study finer scale magnetized
objects, and associated phenomena. The patterns discerned became
known as the ``Extended Solar Cycle'' (ESC). The patterns of the ESC
appeared to extend the wings of the activity butterfly back in time,
nearly a decade before the formation of the sunspot pattern, and to
much higher solar latitudes. In this short review, we describe their
observational patterns of the ESC and discuss possible connections
to the solar dynamo as we depart on a multi-national collaboration to
investigate the origins of solar magnetism through a blend of archived
and contemporary data analysis with the goal of improving solar dynamo
understanding and modeling.
Title: Perspectives on Astrophysics Based on Atomic, Molecular,
and Optical (AMO) Techniques
Authors: Savin, Daniel Wolf; Babb, James F.; Bellan, Paul M.; Brogan,
Crystal; Cami, Jan; Caselli, Paola; Corrales, Lia; Dominguez, Gerardo;
Federman, Steven R.; Fontes, Chris J.; Freedman, Richard; Gibson,
Brad; Golub, Leon; Gorczyca, Thomas W.; Hahn, Michael; Hörst, Sarah
M.; Hudson, Reggie L.; Kuhn, Jeffrey; Lawler, James E.; Leutenegger,
Maurice A.; Marler, Joan P.; McCarthy, Michael C.; McGuire, Brett A.;
Milam, Stefanie N.; Murphy, Nicholas A.; Nave, Gillian; Norton, Aimee
A.; Papol, Anthony; Raymond, John C.; Salama, Farid; Sciamma-O'Brien,
Ella M.; Smith, Randall; Sosolik, Chad; Sousa-Silva, Clara; Stancil,
Phillip C.; Timmes, Frank; Trimble, Virginia L.; Wargelin, Bradford J.
Bibcode: 2018arXiv181106157S
Altcode:
About two generations ago, a large part of AMO science was dominated by
experimental high energy collision studies and perturbative theoretical
methods. Since then, AMO science has undergone a transition and is now
dominated by quantum, ultracold, and ultrafast studies. But in the
process, the field has passed over the complexity that lies between
these two extremes. Most of the Universe resides in this intermediate
region. We put forward that the next frontier for AMO science is to
explore the AMO complexity that describes most of the Cosmos.
Title: The Magnetic Response of the Solar Atmosphere to Umbral Flashes
Authors: Houston, S. J.; Jess, D. B.; Asensio Ramos, A.; Grant,
S. D. T.; Beck, C.; Norton, A. A.; Krishna Prasad, S.
Bibcode: 2018ApJ...860...28H
Altcode: 2018arXiv180300018H
Chromospheric observations of sunspot umbrae offer an exceptional
view of magnetoacoustic shock phenomena and the impact they have on
the surrounding magnetically dominated plasma. We employ simultaneous
slit-based spectro-polarimetry and spectral imaging observations of
the chromospheric He I 10830 Å and Ca II 8542 Å lines to examine
fluctuations in the umbral magnetic field caused by the steepening of
magnetoacoustic waves into umbral flashes. Following the application
of modern inversion routines, we find evidence to support the scenario
that umbral shock events cause expansion of the embedded magnetic
field lines due to the increased adiabatic pressure. The large number
statistics employed allow us to calculate the adiabatic index, γ =
1.12 ± 0.01, for chromospheric umbral locations. Examination of
the vector magnetic field fluctuations perpendicular to the solar
normal revealed changes up to ∼200 G at the locations of umbral
flashes. Such transversal magnetic field fluctuations have not been
described before. Through comparisons with nonlinear force-free field
extrapolations, we find that the perturbations of the transverse field
components are oriented in the same direction as the quiescent field
geometries. This implies that magnetic field enhancements produced by
umbral flashes are directed along the motion path of the developing
shock, hence producing relatively small changes, up to a maximum
of ∼8°, in the inclination and/or azimuthal directions of the
magnetic field. Importantly, this work highlights that umbral flashes
are able to modify the full vector magnetic field, with the detection
of the weaker transverse magnetic field components made possible by
high-resolution data combined with modern inversion routines.
Title: Advance detection of strong photospheric flux emergence
revealed by disruption of moat flows
Authors: Attié, Raphael; Thompson, Barbara J.; Muglach, Karin;
Norton, Aimee Ann
Bibcode: 2018tess.conf30602A
Altcode:
We report on observations of precursors of magnetic disturbances in AR
12673 seen as a disruption of the moat flow several hours before the
onset of strong flux emergence near the main sunspot. The moat flow is
commonly known as a radially oriented strong outflow of photospheric
plasma surrounding sunspots which ends abruptly and thus shapes an
annular pattern around the penumbra. Using highly accurate methods of
tracking this photospheric flow applied to SDO/HMI data, we are able
to describe the evolution of the moat surrounding the main sunspot of
AR 12673. We find that several hours before the emergence of strong
magnetic flux near the main sunspot the moat boundaries are broken at
these very same locations. Because we detect this specific behavior both
on Sep. 1st and Sep. 3rd, our observations suggest that the disruption
of the moat flow is a precursor of the enhanced magnetic activity
which, in this case, led to the strong flaring activity starting on
Sep 6th. This study is part of a broader statistical survey that
aims at characterizing emerging active regions. In light of these
new observations, our survey will also determine to what extent such
a disruption of the moat flow is followed by strong flux emergence
around sunspots, i.e., is this a peculiar response specific to AR
12673, or is it a characteristic disturbance defining a subset of
active regions prone to flaring activity?
Title: Tracking algorithms and machine learning for the
characterization of active regions over the solar cycle 24
Authors: Attié, Raphael; Thompson, Barbara J.; Kirk, Mechael S.;
Norton, Aimee Ann
Bibcode: 2018tess.conf31604A
Altcode:
Since the year 2010, SDO is sending more than a terabyte of solar
observations per day. By offering such an unprecedented large
and varied data sets, this mission has propelled the solar physics
community into the era of "Big Data" analytics. As an answer to this
new technical and scientific challenge, we present here a threefold
innovative framework for efficient data mining and analysis of the solar
photosphere using SDO/HMI: (i) A method for tracking the horizontal
photospheric flows uses an improved version of "Balltracking". We will
present the most recent version of this feature tracking algorithm,
its advantage over other more traditional methods like Local
Correlation Tracking (LCT) and how it has been specifically tuned
to handle the massive HMI datastream. Coupled with flow segmentation
algorithms, it offers an unprecedented view of the evolution of the
supergranulation. (ii) A method for tracking the magnetic flux
using HMI data called "Magnetic Balltracking". We will show how it
enables us to accurately track magnetic elements on magnetograms in
the Lagrange reference frame, and systematically derive parameters
such as the position, velocity, and fragments area and how we use
it to automate the detection of flux emergence. (iii) The above
methods define a tracking framework whose output feed databases that
become the input of machine learning algorithms for classification
purposes. We will show how this expands our knowledge-base e.g. on
the properties of large-scale photospheric flows prior to and after
the emergence of active regions, and on how the flows interact with
the magnetic field over large areas and long time scales. Through
these examples we will demonstrate how this framework contributes to
a sensible characterization of the evolution of active regions during
the whole solar cycle.
Title: Update on Stray Light Corrected Data from HMI/SDO
Authors: Norton, Aimee Ann
Bibcode: 2018tess.conf20750N
Altcode:
We provide an update on Helioseismic Magnetic Imager (HMI) data products
that have been corrected for stray light using a Richardson-Lucy
algorithm and a known PSF. The deconvolution results in a few percent
decrease in umbral intensity corresponding to ~200 K cooler, a doubling
of the intensity contrast of granulation from 3.6 to 7.2%, an increase
in field strengths in plage by ~1.4, faculae brightening and network
darkening, and a partial correction for the convective blueshift. All
routine HMI data products will be upgraded for at least one full-disk
image per day, beginning on March 1 2018. The new data series are
named similar to the original but with the qualifying term '_dcon' or
'_dconS' appended (denoting whether the deconvolvution was applied
to the filtergrams or Stokes images). As resources allow, we will
post-process data to produce extended time-series upon request. All
data will be available to the public at the SDO JSOC. Deconvolved
data are particularly advantageous for irradiance modeling, tracking,
co-alignment, plage magnetic field measurement, and helioseismology
around sunspots.
Title: Erratum: “Why Is the Great Solar
Active Region 12192 Flare-rich but CME-poor?” (2015, ApJL, 804,
L28)
Authors: Sun, Xudong; Bobra, Monica G.; Hoeksema, J. Todd; Liu, Yang;
Li, Yan; Shen, Chenglong; Couvidat, Sebastien; Norton, Aimee A.;
Fisher, George H.
Bibcode: 2017ApJ...850L..43S
Altcode:
No abstract at ADS
Title: Super-flaring Active Region 12673 Has One of the Fastest
Magnetic Flux Emergence Ever Observed
Authors: Sun, Xudong; Norton, Aimee A.
Bibcode: 2017RNAAS...1...24S
Altcode: 2017RNAAS...1a..24S; 2017arXiv171108383S
The flux emergence rate of AR 12673 is greater than any values reported
in the literature of which we are aware.
Title: The Emergence of Kinked Flux Tubes as the Source of Delta-Spots
on the Photosphere
Authors: Knizhnik, K. J.; Linton, M.; Norton, A. A.; DeVore, C. R.
Bibcode: 2017AGUFMSH13A2462K
Altcode:
It has been observationally well established that the magnetic
configurations most favorable to producing energetic flaring events
reside in so called delta-spots. These delta-spots are a subclass of
sunspots, and are classified as sunspots which have umbrae (dark regions
in the interior of sunspots) with opposite magnetic polarities that
share a common penumbra. They are characterized by strong rotation and
an extremely compact magnetic configuration, and are observed to follow
an inverse-Hale law. They are also observed to have strong twist. It
has been shown that over 90% of X-class flares that occurred during
solar cycles 22 and 23 originated in delta-spots (Guo, Lin & Deng,
2014). Understanding the origin of delta-spots, therefore, is a crucial
step towards the ultimate goal of space weather forecasting. In this
work, we argue that delta-spots arise during the emergence of kinked
flux tubes into the corona, and that their unique properties are due
to the emergence of knots present in the kink mode of twisted flux
tubes. We present numerical simulations that study the emergence
of both kink-stable and unstable flux tubes into the solar corona,
and demonstrate quantitatively that their photospheric signatures
are drastically different, with the latter flux tubes demonstrating
strong coherent rotation and a very tight flux distribution on the
photosphere. We show that the coronal magnetic field resulting from
the emergence of a kinked flux tube contains more free energy than
the unkinked case, potentially leading to more energetic flares. We
discuss the implications of our simulations for observations. This
work was supported by the Chief of Naval Research through the National
Research Council.
Title: Photometric Properties of Network and Faculae Derived from
HMI Data Compensated for Scattered Light
Authors: Criscuoli, Serena; Norton, Aimee; Whitney, Taylor
Bibcode: 2017ApJ...847...93C
Altcode: 2017arXiv170901593C
We report on the photometric properties of faculae and network,
as observed in full-disk, scattered-light-corrected images from the
Helioseismic Magnetic Imager. We use a Lucy-Richardson deconvolution
routine that corrects an image in less than one second. Faculae are
distinguished from network through proximity to active regions. This is
the first report that full-disk observations, including center-to-limb
variations, reproduce the photometric properties of faculae and
network observed previously only in sub-arcsecond-resolution; small
field-of-view studies, I.e. that network, as defined by distance from
active regions, exhibit higher photometric contrasts. Specifically,
for magnetic flux values larger than approximately 300 G, the network
is brighter than faculae and the contrast differences increase toward
the limb, where the network contrast is about twice the facular one. For
lower magnetic flux values, network appear darker than faculae. Contrary
to reports from previous full-disk observations, we also found that
network exhibits a higher center-to-limb variation. Our results are
in agreement with reports from simulations that indicate magnetic
flux alone is a poor proxy of the photometric properties of magnetic
features. We estimate that the contribution of faculae and network
to Total Solar Irradiance variability of the current Cycle 24 is
overestimated by at least 11%, due to the photometric properties of
network and faculae not being recognized as different. This estimate
is specific to the method employed in this study to reconstruct
irradiance variations, so caution should be paid when extending it to
other techniques.
Title: Stray Light Correction of HMI Data
Authors: Norton, Aimee Ann; Duvall, Thomas; Schou, Jesper; Cheung,
Mark; Scherrer, Philip H.
Bibcode: 2017SPD....4820705N
Altcode:
The point spread function (PSF) for HMI is an Airy function convolved
with a Lorentzian. The parameters are bound by ground-based testing
before launch, then post-launch off-limb light curves, lunar eclipse
and Venus transit data. The PSF correction is programmed in C and runs
within the HMI data processing pipeline environment. A single full-disk
intensity image can be processed in less than one second. Deconvolution
of the PSF on the Stokes profile data (a linear combination of
original filtergrms) is less computationally expensive and is shown
to be equivalent to deconvolution applied at the original filtergram
level. Results include a decrease in umbral darkness of a few percent
(~200 K cooler), a doubling of the granulation contrast in intensity
from 3.6 to 7.2%, an increase in plage field strengths by a factor of
1.5, and a partial correction of the convective blueshift in Doppler
velocities. Requests for data corrected for stray light are welcome
and will be processed by the HMI team.
Title: The Emergence of Kinked Flux Tubes as the Source of Delta-Spots
on the Photosphere
Authors: Knizhnik, Kalman; Linton, Mark; Norton, Aimee Ann
Bibcode: 2017SPD....4830005K
Altcode:
It has been observationally well established that the magnetic
configurations most favorable to producing energetic flaring events
reside in so called delta-spots. These delta-spots are a subclass of
sunspots, and are classified as sunspots which have umbrae (dark regions
in the interior of sunspots) with opposite magnetic polarities that
share a common penumbra. They are characterized by strong rotation and
an extremely compact magnetic configuration, and are observed to follow
an inverse-Hale law. It has been shown that over 90% of X-class flares
that occurred during solar cycles 22 and 23 originated in delta-spots
(Guo, Lin & Deng, 2014). Understanding the origin of delta-spots,
therefore, is a crucial step towards the ultimate goal of space
weather forecasting. In this work, we argue that delta-spots arise
during the emergence of kinked flux tubes into the corona, and that
their unique properties are due to the emergence of knots present in
the kink mode of twisted flux tubes. We present numerical simulations
that study the emergence of both kink-stable and unstable flux tubes
into the solar corona, and demonstrate quantitatively that their
photospheric signatures are dramatically different, with the latter
flux tubes demonstrating strong coherent rotation and a very tight flux
distribution on the photosphere. We show that the coronal magnetic
field resulting from the emergence of a kinked flux tube contains
significantly more free energy than the unkinked case, potentially
leading to more energetic flares. We discuss the implications of our
simulations for observations.
Title: Photometric Properties of Network and faculae derived by HMI
data compensated for scattered-light
Authors: Criscuoli, Serena; Norton, Aimee Ann; Whitney, Taylor
Bibcode: 2017SPD....4820703C
Altcode:
We report on the photometric properties of faculae and network
as observed in full-disk,scattered-light corrected images from
the Helioseismic Magnetic Imager (HMI). We usea Lucy-Richardson
deconvolution routine that corrects a full-disk intensity image in
lessthan one second. Faculae are distinguished from network through
proximity to activeregions in addition to continuum intensity and
magnetogram thresholds. This is the firstreport that full-disk image
data, including center-to-limb variations, reproduce the photometric
properties of faculae and network observed previously only in
sub-arcsecond resolution, small field-of-view studies, i.e. that network
exhibit in general higher photometric contrasts. More specifically,
for magnetic flux values larger than approximately 300 G, the network
is always brighter than faculae and the contrast differences increases
toward the limb, where the network contrast is about twice the facular
one. For lower magnetic flux values, pixels in network regions appear
always darker than facular ones. Contrary to reports from previous
full-disk observations, we also found that network exhibits a higher
center-to-limb variation. Our results are in agreement with reports
from simulations that indicate magnetic flux alone is a poor proxy
of the photometric properties of magnetic features. We estimate
that the facular and network contribution to irradiance variability
of the current Cycle 24 is overestimated by at least 11% due to the
photometric properties of network and faculae not being recognized as
distinctly different.
Title: Joy's Law: a survey of its forms
Authors: Norton, Aimee A.
Bibcode: 2017shin.confE..54N
Altcode:
Any dynamo model worth its salt should be able to reproduce the
observed distribution of tilt angles of bipolar magnetic regions. Since
the progress of a given solar cycle and the amplitude of future
cycles can be affected by the tilt of a single region (see Nagy's
'Rogue Active Region' contribution), tilts are a crucial ingredient
with consequences for the frequency of grand minima and maxima (see
Ölçek's 'Long Term Activity in BL Model' contribution). Average
tilts are commonly described as a simple function of latitude, i.e.,
Joy's law. But tilts have also been explored as a function of flux,
time, toroidal field strength and cycle strength. The scatter about
the mean tilt angle is thought to be a function of the rise time of
the flux rope through the convection zone. I explore the literature to
report on which form best captures the Sun's behavior while inflicting
a minimal amount of pain when incorporated into numerical simulations.
Title: The Emergence of Kinked Flux Tubes as the Source of Delta-Spots
on the Photosphere
Authors: Knizhnik, Kalman Joshua; Linton, Mark G.; Norton, Aimee A.
Bibcode: 2017shin.confE.165K
Altcode:
It has been observationally well established that the magnetic
configurations most favorable to producing energetic flaring events
reside in so called delta-spots. These delta-spots are a subclass of
sunspots, and are classified as sunspots which have umbrae (dark regions
in the interior of sunspots) with opposite magnetic polarities that
share a common penumbra. They are characterized by strong rotation and
an extremely compact magnetic configuration, and are observed to follow
an inverse-Hale law. They are also observed to have strong twist. It
has been shown that over 90% of X-class flares that occurred during
solar cycles 22 and 23 originated in delta-spots (Guo, Lin & Deng,
2014). Understanding the origin of delta-spots, therefore, is a crucial
step towards the ultimate goal of space weather forecasting. In this
work, we argue that delta-spots arise during the emergence of kinked
flux tubes into the corona, and that their unique properties are due
to the emergence of knots present in the kink mode of twisted flux
tubes. We present numerical simulations that study the emergence
of both kink-stable and unstable flux tubes into the solar corona,
and demonstrate quantitatively that their photospheric signatures
are drastically different, with the latter flux tubes demonstrating
strong coherent rotation and a very tight flux distribution on the
photosphere. We show that the coronal magnetic field resulting from the
emergence of a kinked flux tube contains significantly more free energy
than the unkinked case, potentially leading to more energetic flares. We
discuss the implications of our simulations for observations. This
work was supported by the Chief of Naval Research through the National
Research Council.
Title: Magnetic Flux Emergence and Decay Rates for Preceder and
Follower Sunspots Observed with HMI
Authors: Norton, A. A.; Jones, E. H.; Linton, M. G.; Leake, J. E.
Bibcode: 2017ApJ...842....3N
Altcode: 2017arXiv170502053N
We quantify the emergence and decay rates of preceder (p) and
follower (f) sunspots within 10 active regions from 2010 to 2014
using Space-weather Helioseismic Magnetic Imager Active Region
Patch data. The sunspots are small to mid-sized regions and contain
a signed flux within a single polarity sunspot of (1.1{--}6.5)×
{10}21 {Mx}. The net unsigned flux within the regions,
including plage, ranges from (5.1{--}20)× {10}21 {Mx}. Rates
are calculated with and without intensity contours to differentiate
between sunspot formation and flux emergence. Signed flux emergence
rates, calculated with intensity contours, for the p (f) spots average
6.8(4.9)× {10}19 {Mx} hr-1, while decay rates
are -1.9(-3.4)× {10}19 {Mx} hr-1. The mean,
signed flux emergence rate of the regions, including plage, is 7.1×
{10}19 {Mx} hr-1, for a mean peak flux of 5.9×
{10}21 {Mx}. Using a synthesis of these results and others
reported previously, there is a clear trend for larger flux regions to
emerge faster than smaller ones. Observed emergence rates (dφ /{dt},
Mx hr-1) scale with total signed peak flux, {\tilde{φ
}}\max , as a power law with an exponent of 0.36, I.e.,
dφ /{dt}=A{\tilde{φ }}\max 0.36. The observed
rates may assist in constraining the boundary and initial conditions
in simulations which already demonstrate increased rates for flux
tubes with higher buoyancy and twist, or in the presence of a strong
upflow. Overall, the observed emergence rates are smaller than those
in simulations, which may indicate a slower rise of the flux in the
interior than what is captured in simulations.
Title: HMI Data Corrected for Stray Light Now Available
Authors: Norton, A. A.; Duvall, T. L.; Schou, J.; Cheung, M. C. M.;
Scherrer, P. H.
Bibcode: 2016usc..confE..95N
Altcode:
The form of the point spread function (PSF) derived for HMI is an
Airy function convolved with a Lorentzian. The parameters are bound
by observational ground-based testing of the instrument conducted
prior to launch (Wachter et al., 2012), by full-disk data used to
evaluate the off-limb behavior of the scattered light, as well as by
data obtained during the Venus transit. The PSF correction has been
programmed in both C and cuda C and runs within the JSOC environment
using either a CPU or GPU. A single full-disk intensity image can
be deconvolved in less than one second. The PSF is described in more
detail in Couvidat et al. (2016) and has already been used by Hathaway
et al. (2015) to forward-model solar-convection spectra, by Krucker et
al. (2015) to investigate footpoints of off-limb solar flares and by
Whitney, Criscuoli and Norton (2016) to examine the relations between
intensity contrast and magnetic field strengths. In this presentation,
we highlight the changes to umbral darkness, granulation contrast
and plage field strengths that result from stray light correction. A
twenty-four hour period of scattered-light corrected HMI data from
2010.08.03, including the isolated sunspot NOAA 11092, is currently
available for anyone. Requests for additional time periods of interest
are welcome and will be processed by the HMI team.
Title: MHD Waves at Umbral-Penumbral Boundary Observed with
Hinode/SOT-SP and SDO/HMI
Authors: Norton, A. A.; Tarbell, T. D.; Scherrer, P. H.; Baldner, C. S.
Bibcode: 2016usc..confE.114N
Altcode:
The conversion of p-modes and other perturbations in the near-surface
layers into MHD waves that can propagate along and across magnetic field
lines is a topic of interest for energy transport. The photospheric
signatures of MHD waves are weak due to low amplitudes at the
beta=1 equipartion level where mode-conversion occurs. We report on
oscillations observed with Hinode SOT/SP and HMI in which we have time
series for sunspots 12186 (11.10.2014) and 12434 (17.10.2015). In
the Milne-Eddington inversion results from SP, oscillations in the
inclination angle and velocity are found at the umbral-penumbral
boundary with 5 minute periods. HMI data also shows distinct
umbral-penumbral boundary oscillations consistent with the SP data. We
discuss surface versus body modes that might explain these observations.
Title: Observables Processing for the Helioseismic and Magnetic
Imager Instrument on the Solar Dynamics Observatory
Authors: Couvidat, S.; Schou, J.; Hoeksema, J. T.; Bogart, R. S.;
Bush, R. I.; Duvall, T. L.; Liu, Y.; Norton, A. A.; Scherrer, P. H.
Bibcode: 2016SoPh..291.1887C
Altcode: 2016SoPh..tmp..120C; 2016arXiv160602368C
NASA's Solar Dynamics Observatory (SDO) spacecraft was launched
11 February 2010 with three instruments onboard, including the
Helioseismic and Magnetic Imager (HMI). After commissioning, HMI
began normal operations on 1 May 2010 and has subsequently observed
the Sun's entire visible disk almost continuously. HMI collects
sequences of polarized filtergrams taken at a fixed cadence with two
4096 ×4096 cameras, from which are computed arcsecond-resolution maps
of photospheric observables that include line-of-sight velocity and
magnetic field, continuum intensity, line width, line depth, and the
Stokes polarization parameters [I ,Q ,U ,V ]. Two processing pipelines
have been implemented at the SDO Joint Science Operations Center (JSOC)
at Stanford University to compute these observables from calibrated
Level-1 filtergrams, one that computes line-of-sight quantities every
45 seconds and the other, primarily for the vector magnetic field, that
computes averages on a 720-second cadence. Corrections are made for
static and temporally changing CCD characteristics, bad pixels, image
alignment and distortion, polarization irregularities, filter-element
uncertainty and nonuniformity, as well as Sun-spacecraft velocity. We
detail the functioning of these two pipelines, explain known issues
affecting the measurements of the resulting physical quantities,
and describe how regular updates to the instrument calibration impact
them. We also describe how the scheme for computing the observables
is optimized for actual HMI observations. Initial calibration of
HMI was performed on the ground using a variety of light sources and
calibration sequences. During the five years of the SDO prime mission,
regular calibration sequences have been taken on orbit to improve and
regularly update the instrument calibration, and to monitor changes
in the HMI instrument. This has resulted in several changes in the
observables processing that are detailed here. The instrument more
than satisfies all of the original specifications for data quality and
continuity. The procedures described here still have significant room
for improvement. The most significant remaining systematic errors are
associated with the spacecraft orbital velocity.
Title: XIPE: the x-ray imaging polarimetry explorer
Authors: Soffitta, P.; Bellazzini, R.; Bozzo, E.; Burwitz, V.;
Castro-Tirado, A.; Costa, E.; Courvoisier, T.; Feng, H.; Gburek,
S.; Goosmann, R.; Karas, V.; Matt, G.; Muleri, F.; Nandra, K.;
Pearce, M.; Poutanen, J.; Reglero, V.; Sabau Maria, D.; Santangelo,
A.; Tagliaferri, G.; Tenzer, C.; Vink, J.; Weisskopf, M. C.; Zane,
S.; Agudo, I.; Antonelli, A.; Attina, P.; Baldini, L.; Bykov, A.;
Carpentiero, R.; Cavazzuti, E.; Churazov, E.; Del Monte, E.; De
Martino, D.; Donnarumma, I.; Doroshenko, V.; Evangelista, Y.; Ferreira,
I.; Gallo, E.; Grosso, N.; Kaaret, P.; Kuulkers, E.; Laranaga, J.;
Latronico, L.; Lumb, D. H.; Macian, J.; Malzac, J.; Marin, F.; Massaro,
E.; Minuti, M.; Mundell, C.; Ness, J. U.; Oosterbroek, T.; Paltani, S.;
Pareschi, G.; Perna, R.; Petrucci, P. -O.; Pinazo, H. B.; Pinchera,
M.; Rodriguez, J. P.; Roncadelli, M.; Santovincenzo, A.; Sazonov,
S.; Sgro, C.; Spiga, D.; Svoboda, J.; Theobald, C.; Theodorou, T.;
Turolla, R.; Wilhelmi de Ona, E.; Winter, B.; Akbar, A. M.; Allan,
H.; Aloisio, R.; Altamirano, D.; Amati, L.; Amato, E.; Angelakis,
E.; Arezu, J.; Atteia, J. -L.; Axelsson, M.; Bachetti, M.; Ballo, L.;
Balman, S.; Bandiera, R.; Barcons, X.; Basso, S.; Baykal, A.; Becker,
W.; Behar, E.; Beheshtipour, B.; Belmont, R.; Berger, E.; Bernardini,
F.; Bianchi, S.; Bisnovatyi-Kogan, G.; Blasi, P.; Blay, P.; Bodaghee,
A.; Boer, M.; Boettcher, M.; Bogdanov, S.; Bombaci, I.; Bonino, R.;
Braga, J.; Brandt, W.; Brez, A.; Bucciantini, N.; Burderi, L.; Caiazzo,
I.; Campana, R.; Campana, S.; Capitanio, F.; Cappi, M.; Cardillo,
M.; Casella, P.; Catmabacak, O.; Cenko, B.; Cerda-Duran, P.; Cerruti,
C.; Chaty, S.; Chauvin, M.; Chen, Y.; Chenevez, J.; Chernyakova, M.;
Cheung, C. C. Teddy; Christodoulou, D.; Connell, P.; Corbet, R.; Coti
Zelati, F.; Covino, S.; Cui, W.; Cusumano, G.; D'Ai, A.; D'Ammando,
F.; Dadina, M.; Dai, Z.; De Rosa, A.; de Ruvo, L.; Degenaar, N.;
Del Santo, M.; Del Zanna, L.; Dewangan, G.; Di Cosimo, S.; Di Lalla,
N.; Di Persio, G.; Di Salvo, T.; Dias, T.; Done, C.; Dovciak, M.;
Doyle, G.; Ducci, L.; Elsner, R.; Enoto, T.; Escada, J.; Esposito,
P.; Eyles, C.; Fabiani, S.; Falanga, M.; Falocco, S.; Fan, Y.; Fender,
R.; Feroci, M.; Ferrigno, C.; Forman, W.; Foschini, L.; Fragile, C.;
Fuerst, F.; Fujita, Y.; Gasent-Blesa, J. L.; Gelfand, J.; Gendre, B.;
Ghirlanda, G.; Ghisellini, G.; Giroletti, M.; Goetz, D.; Gogus, E.;
Gomez, J. -L.; Gonzalez, D.; Gonzalez-Riestra, R.; Gotthelf, E.; Gou,
L.; Grandi, P.; Grinberg, V.; Grise, F.; Guidorzi, C.; Gurlebeck, N.;
Guver, T.; Haggard, D.; Hardcastle, M.; Hartmann, D.; Haswell, C.;
Heger, A.; Hernanz, M.; Heyl, J.; Ho, L.; Hoormann, J.; Horak, J.;
Huovelin, J.; Huppenkothen, D.; Iaria, R.; Inam Sitki, C.; Ingram,
A.; Israel, G.; Izzo, L.; Burgess, M.; Jackson, M.; Ji, L.; Jiang, J.;
Johannsen, T.; Jones, C.; Jorstad, S.; Kajava, J. J. E.; Kalamkar, M.;
Kalemci, E.; Kallman, T.; Kamble, A.; Kislat, F.; Kiss, M.; Klochkov,
D.; Koerding, E.; Kolehmainen, M.; Koljonen, K.; Komossa, S.; Kong,
A.; Korpela, S.; Kowalinski, M.; Krawczynski, H.; Kreykenbohm, I.;
Kuss, M.; Lai, D.; Lan, M.; Larsson, J.; Laycock, S.; Lazzati, D.;
Leahy, D.; Li, H.; Li, J.; Li, L. -X.; Li, T.; Li, Z.; Linares, M.;
Lister, M.; Liu, H.; Lodato, G.; Lohfink, A.; Longo, F.; Luna, G.;
Lutovinov, A.; Mahmoodifar, S.; Maia, J.; Mainieri, V.; Maitra, C.;
Maitra, D.; Majczyna, A.; Maldera, S.; Malyshev, D.; Manfreda, A.;
Manousakis, A.; Manuel, R.; Margutti, R.; Marinucci, A.; Markoff, S.;
Marscher, A.; Marshall, H.; Massaro, F.; McLaughlin, M.; Medina-Tanco,
G.; Mehdipour, M.; Middleton, M.; Mignani, R.; Mimica, P.; Mineo, T.;
Mingo, B.; Miniutti, G.; Mirac, S. M.; Morlino, G.; Motlagh, A. V.;
Motta, S.; Mushtukov, A.; Nagataki, S.; Nardini, F.; Nattila, J.;
Navarro, G. J.; Negri, B.; Negro, Matteo; Nenonen, S.; Neustroev,
V.; Nicastro, F.; Norton, A.; Nucita, A.; O'Brien, P.; O'Dell, S.
Bibcode: 2016SPIE.9905E..15S
Altcode:
XIPE, the X-ray Imaging Polarimetry Explorer, is a mission dedicated to
X-ray Astronomy. At the time of writing XIPE is in a competitive phase
A as fourth medium size mission of ESA (M4). It promises to reopen
the polarimetry window in high energy Astrophysics after more than 4
decades thanks to a detector that efficiently exploits the photoelectric
effect and to X-ray optics with large effective area. XIPE uniqueness is
time-spectrally-spatially- resolved X-ray polarimetry as a breakthrough
in high energy astrophysics and fundamental physics. Indeed the payload
consists of three Gas Pixel Detectors at the focus of three X-ray
optics with a total effective area larger than one XMM mirror but with
a low weight. The payload is compatible with the fairing of the Vega
launcher. XIPE is designed as an observatory for X-ray astronomers with
75 % of the time dedicated to a Guest Observer competitive program and
it is organized as a consortium across Europe with main contributions
from Italy, Germany, Spain, United Kingdom, Poland, Sweden.
Title: Comparison of Coronal Extrapolation Methods for Cycle 24
Using HMI Data
Authors: Arden, William M.; Norton, Aimee A.; Sun, Xudong; Zhao, Xuepu
Bibcode: 2016ApJ...823...21A
Altcode: 2016arXiv160304385A
Two extrapolation models of the solar coronal magnetic field
are compared using magnetogram data from the Solar Dynamics
Observatory/Helioseismic and Magnetic Imager instrument. The two
models, a horizontal current-current sheet-source surface (HCCSSS)
model and a potential field-source surface (PFSS) model, differ in their
treatment of coronal currents. Each model has its own critical variable,
respectively, the radius of a cusp surface and a source surface, and it
is found that adjusting these heights over the period studied allows
for a better fit between the models and the solar open flux at 1 au
as calculated from the Interplanetary Magnetic Field (IMF). The HCCSSS
model provides the better fit for the overall period from 2010 November
to 2015 May as well as for two subsets of the period: the minimum/rising
part of the solar cycle and the recently identified peak in the IMF
from mid-2014 to mid-2015 just after solar maximum. It is found that an
HCCSSS cusp surface height of 1.7 R ⊙ provides the best fit
to the IMF for the overall period, while 1.7 and 1.9 R ⊙
give the best fits for the two subsets. The corresponding values for
the PFSS source surface height are 2.1, 2.2, and 2.0 R ⊙
respectively. This means that the HCCSSS cusp surface rises as the
solar cycle progresses while the PFSS source surface falls.
Title: On HMI's Mod-L Sequence: Test and Evaluation
Authors: Liu, Yang; Baldner, Charles; Bogart, R. S.; Bush, R.;
Couvidat, S.; Duvall, Thomas L.; Hoeksema, Jon Todd; Norton, Aimee Ann;
Scherrer, Philip H.; Schou, Jesper
Bibcode: 2016SPD....47.0810L
Altcode:
HMI Mod-L sequence can produce full Stokes parameters at a cadence of 90
seconds by combining filtergrams from both cameras, the front camera and
the side camera. Within the 90-second, the front camera takes two sets
of Left and Right Circular Polarizations (LCP and RCP) at 6 wavelengths;
the side camera takes one set of Linear Polarizations (I+/-Q and I+/-U)
at 6 wavelengths. By combining two cameras, one can obtain full Stokes
parameters of [I,Q,U,V] at 6 wavelengths in 90 seconds. In norminal
Mod-C sequence that HMI currently uses, the front camera takes LCP and
RCP at a cadence of 45 seconds, while the side camera takes observation
of the full Stokes at a cadence of 135 seconds. Mod-L should be
better than Mod-C for providing vector magnetic field data because
(1) Mod-L increases cadence of full Stokes observation, which leads
to higher temporal resolution of vector magnetic field measurement;
(2) decreases noise in vector magnetic field data because it uses
more filtergrams to produce [I,Q,U,V]. There are two potential issues
in Mod-L that need to be addressed: (1) scaling intensity of the two
cameras’ filtergrams; and (2) if current polarization calibration
model, which is built for each camera separately, works for the combined
data from both cameras. This presentation will address these questions,
and further place a discussion here.
Title: Relation between Intensity Contrast and Magnetic Field for
Active and Quiet Regions Observed on the Solar Photosphere
Authors: Whitney, Taylor; Criscuoli, Serena; Norton, Aimee Ann
Bibcode: 2016SPD....47.1209W
Altcode:
Current solar modeling techniques assume that active and quiet regions
can be considered in the same manner. However, recent results from
numerical simulations and high-spatial resolution observations indicate
that radiative properties of small magnetic elements depend on whether
they are located in plages, network, or quiet areas. These studies have
been carried out typically at, or close to, disk center. In this study,
data from the Helioseismic Magnetic Imager (HMI) are used to investigate
the differences between magnetic elements located in Network/Quiet and
Active Regions (AR) observed at different positions over the solar disk.
Title: The Processing of Observables Made by the HMI Instrument on SDO
Authors: Hoeksema, Jon Todd; Schou, Jesper; Couvidat, Sebastien;
Bogart, Richard S.; Bush, Rock; Duvall, Thomas L.; Liu, Yang; Norton,
Aimee Ann; Scherrer, Philip H.
Bibcode: 2016SPD....47.0808H
Altcode:
The Helioseismic and Magnetic Imager (HMI) acquires sequences of
polarized filtergrams of the Sun from which observable quantities
are computed. The observables include five line-of-sight quantities -
magnetic field, velocity, continuum intensity, line depth, and line
width - as well as Stokes polarization parameters. The process of
turning a set of filtergrams into calibrated measurements is quite
involved. Since May 2010 the streams of data from HMI’s two cameras
have been treated separately. The frame list for the Doppler camera
repeats every 45 seconds and the images are combined to determine
the line-of-sight observables. The Vector camera sequence measures
additional polarizations and so requires 135s; images from ten sequences
are combined every 720s to determine the four Stokes polarization
parameters at each of six wavelengths, as well as the LoS observables. A
variety of calibration corrections are made to the Level-1 filtergrams
to account for distortion, image motion and alignment, polarization,
wavelength and intensity irregularities, camera issues, solar rotation,
and other effects. Residual random variations in the final observables
are consistent with photon noise levels, but systematic errors remain
that have not been fully corrected. Of particular concern are those
associated with the velocity of the instrument relative to the Sun
due to the geosynchronous orbit of the Solar Dynamics Observatory
(SDO) spacecraft. This presentation describes the creation of the
observables, characterizes the residual errors, and indicates plans
for future improvements - including correction for the instrument point
spread function. All HMI data are available at http://jsoc.stanford.edu.
Title: Amplitudes of MHD Waves in Sunspots
Authors: Norton, Aimee Ann; Cally, Paul; Baldner, Charles; Kleint,
Lucia; Tarbell, Theodore D.; De Pontieu, Bart; Scherrer, Philip H.;
Rajaguru, Paul
Bibcode: 2016SPD....47.1009N
Altcode:
The conversion of p-modes into MHD waves by strong magnetic fields
occurs mainly in the sub-photospheric layers. The photospheric
signatures of MHD waves are weak due to low amplitudes at the beta=1
equipartion level where mode-conversion occurs. We report on small
amplitude oscillations observed in the photosphere with Hinode SOT/SP
in which we analyze time series for sunspots ARs 12186 (11.10.2014)
and 12434 (17.10.2015). No significant magnetic field oscillations
are recovered in the umbra or penumbra in the ME inversion. However,
periodicities in the inclination angle are found at the umbral/penumbral
boundary with 5 minute periods. Upward propagating waves are indicated
in the intensity signals correlated between HMI and AIA at different
heights. We compare SP results with the oscillations observed in HMI
data. Simultaneous IRIS data shows transition region brightening above
the umbral core.
Title: Precision tests of the Standard Model with Kaon decays at CERN
Authors: Lamanna, G.; Ambrosino, F.; Antonelli, A.; Anzivino, G.;
Arcidiacono, R.; Baldini, W.; Balev, S.; Batley, J. R.; Behler, M.;
Bifani, S.; Biino, C.; Bizzeti, A.; Bloch-Devaux, B.; Bocquet, G.;
Bolotov, V.; Bucci, F.; Cabibbo, N.; Calvetti, M.; Cartiglia, N.;
Ceccucci, A.; Cenci, P.; Cerri, C.; Cheshkov, C.; Chèze, J. B.;
Clemencic, M.; Collazuol, G.; Costantini, F.; Cotta Ramusino, A.;
Coward, D.; Cundy, D.; Dabrowski, A.; D'Agostini, G.; Dalpiaz, P.;
Damiani, C.; Danielsson, H.; De Beer, M.; Dellacasa, G.; Derré,
J.; Dibon, H.; Di Filippo, D.; DiLella, L.; Doble, N.; Duk, V.;
Engelfried, J.; Eppard, K.; Falaleev, V.; Fantechi, R.; Fidecaro,
M.; Fiorini, L.; Fiorini, M.; Fonseca Martin, T.; Frabetti, P. L.;
Fucci, A.; Gallorini, S.; Gatignon, L.; Gersabeck, E.; Gianoli, A.;
Giudici, S.; Gonidec, A.; Goudzovski, E.; Goy Lopez, S.; Gushchin, E.;
Hallgren, B.; Hita-Hochgesand, M.; Holder, M.; Hristov, P.; Iacopini,
E.; Imbergamo, E.; Jeitler, M.; Kalmus, G.; Kekelidze, V.; Kleinknecht,
K.; Kozhuharov, V.; Kubischta, W.; Kurshetsov, V.; Lamanna, G.;
Lazzeroni, C.; Lenti, M.; Leonardi, E.; Litov, L.; Madigozhin, D.;
Maier, A.; Mannelli, I.; Marchetto, F.; Marel, G.; Markytan, M.;
Marouelli, P.; Martini, M.; Masetti, L.; Massarotti, P.; Mazzucato,
E.; Michetti, A.; Mikulec, I.; Misheva, M.; Molokanova, N.; Monnier,
E.; Moosbrugger, U.; Morales Morales, C.; Moulson, M.; Movchan, S.;
Munday, D. J.; Napolitano, M.; Nappi, A.; Neuhofer, G.; Norton, A.;
Numao, T.; Obraztsov, V.; Palladino, V.; Patel, M.; Pepe, M.; Peters,
A.; Petrucci, F.; Petrucci, M. C.; Peyaud, B.; Piandani, R.; Piccini,
M.; Pierazzini, G.; Polenkevich, I.; Popov, I.; Potrebenikov, Yu.;
Raggi, M.; Renk, B.; Retière, F.; Riedler, P.; Romano, A.; Rubin,
P.; Ruggiero, G.; Salamon, A.; Saracino, G.; Savrié, M.; Scarpa, M.;
Semenov, V.; Sergi, A.; Serra, M.; Shieh, M.; Shkarovskiy, S.; Slater,
M. W.; Sozzi, M.; Spadaro, T.; Stoynev, S.; Swallow, E.; Szleper, M.;
Valdata-Nappi, M.; Valente, P.; Vallage, B.; Velasco, M.; Veltri, M.;
Venditti, S.; Wache, M.; Wahl, H.; Walker, A.; Wanke, R.; Widhalm, L.;
Winhart, A.; Winston, R.; Wood, M. D.; Wotton, S. A.; Yushchenko, O.;
Zinchenko, A.; Ziolkowski, M.; NA48/2 Collaboration; NA62 Collaboration
Bibcode: 2016NPPP..273.1671L
Altcode:
Effects of new physics in flavor could be found both in Flavor Changing
Neutral Current (FCNC) processes and in Lepton Flavor Violation
(LFV) modes. The former offer the possibility to deeply test the
standard model in a clean environment, while the latter are sensitive
to contribution from several models beyond the standard model. In
the Kaon sector both FCNC and LFV will be investigated in the NA62
experiment. In addition the kaons sector is an ideal place where to
look for new particles and tiny effects, in the region of hundreds
of MeV/c2. In this paper prospects for exotic searches in
NA62 will be presented, together with recent results from NA48/2 and
NA62-RK on LFV kaon decays modes.
Title: The Magnetic Classification of Solar Active Regions 1992-2015
Authors: Jaeggli, S. A.; Norton, A. A.
Bibcode: 2016ApJ...820L..11J
Altcode: 2016arXiv160302552J
The purpose of this Letter is to address a blindspot in our knowledge
of solar active region (AR) statistics. To the best of our knowledge,
there are no published results showing the variation of the Mount
Wilson magnetic classifications as a function of solar cycle based
on modern observations. We show statistics for all ARs reported in
the daily Solar Region Summary from 1992 January 1 to 2015 December
31. We find that the α and β class ARs (including all sub-groups,
e.g., βγ, βδ) make up fractions of approximately 20% and 80% of
the sample, respectively. This fraction is relatively constant during
high levels of activity however, an increase in the α fraction to
about 35% and and a decrease in the β fraction to about 65% can
be seen near each solar minimum and are statistically significant
at the 2σ level. Over 30% of all ARs observed during the years of
solar maxima were appended with the classifications γ and/or δ,
while these classifications account for only a fraction of a percent
during the years near the solar minima. This variation in the AR
types indicates that the formation of complex ARs may be due to the
pileup of frequent emergence of magnetic flux during solar maximum,
rather than the emergence of complex, monolithic flux structures.
Title: Tilt Angle and Footpoint Separation of Small and Large Bipolar
Sunspot Regions Observed with HMI
Authors: McClintock, B. H.; Norton, A. A.
Bibcode: 2016ApJ...818....7M
Altcode: 2016arXiv160204154M
We investigate bipolar sunspot regions and how tilt angle and footpoint
separation vary during emergence and decay. The Helioseismic and
Magnetic Imager on board the Solar Dynamic Observatory collects data
at a higher cadence than historical records and allows for a detailed
analysis of regions over their lifetimes. We sample the umbral tilt
angle, footpoint separation, and umbral area of 235 bipolar sunspot
regions in Helioseismic and Magnetic Imager—Debrecen Data with an
hourly cadence. We use the time when the umbral area peaks as time zero
to distinguish between the emergence and decay periods of each region
and we limit our analysis of tilt and separation behavior over time
to within ±96 hr of time zero. Tilt angle evolution is distinctly
different for regions with small (≈30 MSH), midsize (≈50 MSH),
and large (≈110 MSH) maximum umbral areas, with 45 and 90 MSH being
useful divisions for separating the groups. At the peak umbral area,
we determine median tilt angles for small (7.°6), midsize (5.°9),
and large (9.°3) regions. Within ±48 hr of the time of peak umbral
area, large regions steadily increase in tilt angle, midsize regions
are nearly constant, and small regions show evidence of negative
tilt during emergence. A period of growth in footpoint separation
occurs over a 72-hr period for all of the regions from roughly 40 to
70 Mm. The smallest bipoles (<9 MSH) are outliers in that they do
not obey Joy's law and have a much smaller footpoint separation. We
confirm the Muñoz-Jaramillo et al. (2015) results that the sunspots
appear to be two distinct populations.
Title: SDO/HMI Vector Magnetic Field Observations of the Solar
Polar Region
Authors: Sun, X.; Hoeksema, J. T.; Liu, Y.; Norton, A. A.; Sainz Dalda,
A.; Hayashi, K.
Bibcode: 2015AGUFMSH23A2429S
Altcode:
SDO/HMI is now providing full-disk vector magnetograms of the
Sun. Although the instrument is optimized for strong field in active
regions, data from the quieter regions can still provide valuable
diagnostics if treated carefully. Here we present our first attempt at
inferring the vector field in the polar regions. Through deep averaging
(96 min) of the Stokes profiles, we find that many unipolar patches
reach 5-sigma signal-to-noise ratio, so magnetic field can be inferred
with confidence. The inclination of the field in these patches appears
to deviate from the radial direction. We discuss the implications for
global coronal field topology and our next steps of work.
Title: The Sun's Photospheric Convection Spectrum
Authors: Hathaway, David H.; Teil, Thibaud; Norton, Aimee A.;
Kitiashvili, Irina
Bibcode: 2015ApJ...811..105H
Altcode: 2015arXiv150803022H
Spectra of the cellular photospheric flows are determined from
full-disk Doppler velocity observations acquired by the Helioseismic
and Magnetic Imager (HMI) instrument on the Solar Dynamics Observatory
spacecraft. Three different analysis methods are used to separately
determine spectral coefficients representing the poloidal flows, the
toroidal flows, and the radial flows. The amplitudes of these spectral
coefficients are constrained by simulated data analyzed with the same
procedures as the HMI data. We find that the total velocity spectrum
rises smoothly to a peak at a wavenumber of about 120 (wavelength of
about 35 Mm), which is typical of supergranules. The spectrum levels
off out to wavenumbers of about 400, and then rises again to a peak
at a wavenumber of about 3500 (wavelength of about 1200 km), which
is typical of granules. The velocity spectrum is dominated by the
poloidal flow component (horizontal flows with divergence but no curl)
at wavenumbers above 30. The toroidal flow component (horizontal flows
with curl but no divergence) dominates at wavenumbers less than 30. The
radial flow velocity is only about 3% of the total flow velocity at
the lowest wavenumbers, but increases in strength to become about 50%
at wavenumbers near 4000. The spectrum compares well with the spectrum
of giant cell flows at the lowest wavenumbers and with the spectrum
of granulation from a 3D radiative-hydrodynamic simulation at the
highest wavenumbers.
Title: The Coronal Global Evolutionary Model: Using HMI Vector
Magnetogram and Doppler Data to Model the Buildup of Free Magnetic
Energy in the Solar Corona
Authors: Fisher, G. H.; Abbett, W. P.; Bercik, D. J.; Kazachenko,
M. D.; Lynch, B. J.; Welsch, B. T.; Hoeksema, J. T.; Hayashi, K.;
Liu, Y.; Norton, A. A.; Dalda, A. Sainz; Sun, X.; DeRosa, M. L.;
Cheung, M. C. M.
Bibcode: 2015SpWea..13..369F
Altcode: 2015arXiv150506018F
The most violent space weather events (eruptive solar flares and
coronal mass ejections) are driven by the release of free magnetic
energy stored in the solar corona. Energy can build up on timescales
of hours to days, and then may be suddenly released in the form of a
magnetic eruption, which then propagates through interplanetary space,
possibly impacting the Earth's space environment. Can we use the
observed evolution of the magnetic and velocity fields in the solar
photosphere to model the evolution of the overlying solar coronal
field, including the storage and release of magnetic energy in such
eruptions? The objective of CGEM, the Coronal Global Evolutionary Model,
funded by the NASA/NSF Space Weather Modeling program, is to develop
and evaluate such a model for the evolution of the coronal magnetic
field. The evolving coronal magnetic field can then be used as a
starting point for magnetohydrodynamic (MHD) models of the corona,
which can then be used to drive models of heliospheric evolution and
predictions of magnetic field and plasma density conditions at 1AU.
Title: Why Is the Great Solar Active Region 12192 Flare-rich but
CME-poor?
Authors: Sun, Xudong; Bobra, Monica G.; Hoeksema, J. Todd; Liu, Yang;
Li, Yan; Shen, Chenglong; Couvidat, Sebastien; Norton, Aimee A.;
Fisher, George H.
Bibcode: 2015ApJ...804L..28S
Altcode: 2015arXiv150206950S; 2015ApJ...804L..28.
Solar active region (AR) 12192 of 2014 October hosts the largest sunspot
group in 24 years. It is the most prolific flaring site of Cycle 24
so far, 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: The Helioseismic and Magnetic Imager (HMI) Vector Magnetic
Field Pipeline: Magnetohydrodynamics Simulation Module for the Global
Solar Corona
Authors: Hayashi, K.; Hoeksema, J. T.; Liu, Y.; Bobra, M. G.; Sun,
X. D.; Norton, A. A.
Bibcode: 2015SoPh..290.1507H
Altcode: 2015arXiv150405217H; 2015SoPh..tmp...48H
Time-dependent three-dimensional magnetohydrodynamics (MHD) simulation
modules are implemented at the Joint Science Operation Center (JSOC)
of the Solar Dynamics Observatory (SDO). The modules regularly produce
three-dimensional data of the time-relaxed minimum-energy state of the
solar corona using global solar-surface magnetic-field maps created
from Helioseismic and Magnetic Imager (HMI) full-disk magnetogram
data. With the assumption of a polytropic gas with specific-heat
ratio of 1.05, three types of simulation products are currently
generated: i) simulation data with medium spatial resolution using
the definitive calibrated synoptic map of the magnetic field with
a cadence of one Carrington rotation, ii) data with low spatial
resolution using the definitive version of the synchronic frame
format of the magnetic field, with a cadence of one day, and iii)
low-resolution data using near-real-time (NRT) synchronic format of the
magnetic field on a daily basis. The MHD data available in the JSOC
database are three-dimensional, covering heliocentric distances from
1.025 to 4.975 solar radii, and contain all eight MHD variables: the
plasma density, temperature, and three components of motion velocity,
and three components of the magnetic field. This article describes
details of the MHD simulations as well as the production of the input
magnetic-field maps, and details of the products available at the
JSOC database interface. To assess the merits and limits of the model,
we show the simulated data in early 2011 and compare with the actual
coronal features observed by the Atmospheric Imaging Assembly (AIA)
and the near-Earth in-situ data.
Title: Coronal Open Magnetic Flux - Comparing two models to the IMF
at 1 AU
Authors: Arden, William; Norton, Aimee A.
Bibcode: 2015TESS....111101A
Altcode:
We present results of two extrapolation techniques for modeling the
magnitude of solar coronal open magnetic flux at 1 AU: PFSS (Potential
field - source surface) and HCCSSS (Horizontal current - current sheet -
source surface). SDO/HMI photospheric magnetic field data from August
2010 through July 2014 are used as input. We compare the modeling
results to the interplanetary magnetic field (IMF) data contained in
the OMNI database. We discuss temporal variations in magnitude over
the rising part of solar cycle 24.
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.
Bibcode: 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: The Sun's Interior Structure and Dynamics, and the Solar Cycle
Authors: Broomhall, A. -M.; Chatterjee, P.; Howe, R.; Norton, A. A.;
Thompson, M. J.
Bibcode: 2015sac..book..191B
Altcode:
No abstract at ADS
Title: Hemispheric Coupling: Comparing Dynamo Simulations and
Observations
Authors: Norton, A. A.; Charbonneau, P.; Passos, D.
Bibcode: 2015sac..book..251N
Altcode:
No abstract at ADS
Title: Magnetic Helicity, Tilt, and Twist
Authors: Pevtsov, Alexei A.; Berger, Mitchell A.; Nindos, Alexander;
Norton, Aimee A.; van Driel-Gesztelyi, Lidia
Bibcode: 2015sac..book..285P
Altcode:
No abstract at ADS
Title: The Sun's Interior Structure and Dynamics, and the Solar Cycle
Authors: Broomhall, A. -M.; Chatterjee, P.; Howe, R.; Norton, A. A.;
Thompson, M. J.
Bibcode: 2014SSRv..186..191B
Altcode: 2014arXiv1411.5941B
The Sun's internal structure and dynamics can be studied with
helioseismology, which uses the Sun's natural acoustic oscillations
to build up a profile of the solar interior. We discuss how solar
acoustic oscillations are affected by the Sun's magnetic field. Careful
observations of these effects can be inverted to determine the
variations in the structure and dynamics of the Sun's interior as
the solar cycle progresses. Observed variations in the structure and
dynamics can then be used to inform models of the solar dynamo, which
are crucial to our understanding of how the Sun's magnetic field is
generated and maintained.
Title: Re-examining Sunspot Tilt Angle to Include Anti-Hale Statistics
Authors: McClintock, B. H.; Norton, A. A.; Li, J.
Bibcode: 2014ApJ...797..130M
Altcode: 2014arXiv1412.5094M
Sunspot groups and bipolar magnetic regions (BMRs) serve as
an observational diagnostic of the solar cycle. We use Debrecen
Photohelographic Data (DPD) from 1974-2014 that determined sunspot tilt
angles from daily white light observations, and data provided by Li
& Ulrich that determined sunspot magnetic tilt angle using Mount
Wilson magnetograms from 1974-2012. The magnetograms allowed for BMR
tilt angles that were anti-Hale in configuration, so tilt values ranged
from 0 to 360° rather than the more common ±90°. We explore the
visual representation of magnetic tilt angles on a traditional butterfly
diagram by plotting the mean area-weighted latitude of umbral activity
in each bipolar sunspot group, including tilt information. The large
scatter of tilt angles over the course of a single cycle and hemisphere
prevents Joy's law from being visually identified in the tilt-butterfly
diagram without further binning. The average latitude of anti-Hale
regions does not differ from the average latitude of all regions in
both hemispheres. The distribution of anti-Hale sunspot tilt angles
are broadly distributed between 0 and 360° with a weak preference for
east-west alignment 180° from their expected Joy's law angle. The
anti-Hale sunspots display a log-normal size distribution similar
to that of all sunspots, indicating no preferred size for anti-Hale
sunspots. We report that 8.4% ± 0.8% of all bipolar sunspot regions
are misclassified as Hale in traditional catalogs. This percentage
is slightly higher for groups within 5° of the equator due to the
misalignment of the magnetic and heliographic equators.
Title: Systematic Errors and Uncertainties in the HMI Magnetic Data
Authors: Norton, A. A.
Bibcode: 2014AGUFMSH53A4198N
Altcode:
Near-continuous, full-disk measurements of the Stokes I, Q,
U and V profiles with a 40962 camera on-board HMI make possible
the investigation of solar events in new and important ways. We
summarize the uncertainties and systematic errors in the HMI vector
and line-of-sight magnetic field data, including synoptic maps. Some
of these were estimated prior to launch and others were unanticipated
or newly determined. We showcase the NOAA AR 11944 and January 2014
HMI data to illustrate the magnitude of errors and the dependence on
spacecraft parameters (especially orbital velocity) and solar physics
conditions. We estimate the relative importance of the uncertainties
and how these errors propagate through the models for space weather
event analysis.
Title: Hemispheric Coupling: Comparing Dynamo Simulations and
Observations
Authors: Norton, A. A.; Charbonneau, P.; Passos, D.
Bibcode: 2014SSRv..186..251N
Altcode: 2014arXiv1411.7052N; 2014SSRv..tmp...51N
Numerical simulations that reproduce solar-like magnetic cycles can be
used to generate long-term statistics. The variations in north-south
hemispheric solar cycle synchronicity and amplitude produced
in simulations has not been widely compared to observations. The
observed limits on solar cycle amplitude and phase asymmetry show that
hemispheric sunspot area production is no more than 20 % asymmetric for
cycles 17-23 and that phase lags do not exceed 20 % (or two years) of
the total cycle period, as determined from Royal Greenwich Observatory
sunspot data. Several independent studies have found a long-term trend
in phase values as one hemisphere leads the other for, on average, four
cycles. Such persistence in phase is not indicative of a stochastic
phenomenon. We compare these observational findings to the magnetic
cycle found in a numerical simulation of solar convection recently
produced with the EULAG-MHD model. This long "millennium simulation"
spans more than 1600 years and generated 40 regular, sunspot-like
cycles. While the simulated cycle length is too long (∼40 yrs) and
the toroidal bands remain at too high of latitudes (>30°), some
solar-like aspects of hemispheric asymmetry are reproduced. The model
is successful at reproducing the synchrony of polarity inversions and
onset of cycle as the simulated phase lags do not exceed 20 % of the
cycle period. The simulated amplitude variations between the north and
south hemispheres are larger than those observed in the Sun, some up
to 40 %. An interesting note is that the simulations also show that
one hemisphere can persistently lead the other for several successive
cycles, placing an upper bound on the efficiency of transequatorial
magnetic coupling mechanisms. These include magnetic diffusion,
cross-equatorial mixing within latitudinally-elongated convective
rolls (a.k.a. "banana cells") and transequatorial meridional flow
cells. One or more of these processes may lead to magnetic flux
cancellation whereby the oppositely directed fields come in close
proximity and cancel each other across the magnetic equator late
in the solar cycle. We discuss the discrepancies between model and
observations and the constraints they pose on possible mechanisms of
hemispheric coupling.
Title: Magnetic Helicity, Tilt, and Twist
Authors: Pevtsov, Alexei A.; Berger, Mitchell A.; Nindos, Alexander;
Norton, Aimee A.; van Driel-Gesztelyi, Lidia
Bibcode: 2014SSRv..186..285P
Altcode:
Since its introduction to astro- and solar physics, the concept of
helicity has proven to be useful in providing critical insights into
physics of various processes from astrophysical dynamos, to magnetic
reconnection and eruptive phenomena. Signature of helicity was also
detected in many solar features, including orientation of solar active
regions, or Joy's law. Here we provide a summary of both solar phenomena
and consider mutual relationship and its importance for the evolution
of solar magnetic fields.
Title: The Helioseismic and Magnetic Imager (HMI) Vector Magnetic
Field Pipeline: Overview and Performance
Authors: Hoeksema, J. Todd; Liu, Yang; Hayashi, Keiji; Sun, Xudong;
Schou, Jesper; Couvidat, Sebastien; Norton, Aimee; Bobra, Monica;
Centeno, Rebecca; Leka, K. D.; Barnes, Graham; Turmon, Michael
Bibcode: 2014SoPh..289.3483H
Altcode: 2014SoPh..tmp...57H; 2014arXiv1404.1881H
The Helioseismic and Magnetic Imager (HMI) began near-continuous
full-disk solar measurements on 1 May 2010 from the Solar Dynamics
Observatory (SDO). An automated processing pipeline keeps pace
with observations to produce observable quantities, including the
photospheric vector magnetic field, from sequences of filtergrams. The
basic vector-field frame list cadence is 135 seconds, but to reduce
noise the filtergrams are combined to derive data products every 720
seconds. The primary 720 s observables were released in mid-2010,
including Stokes polarization parameters measured at six wavelengths,
as well as intensity, Doppler velocity, and the line-of-sight magnetic
field. More advanced products, including the full vector magnetic field,
are now available. Automatically identified HMI Active Region Patches
(HARPs) track the location and shape of magnetic regions throughout
their lifetime.
Title: The Helioseismic and Magnetic Imager (HMI) Vector Magnetic
Field Pipeline: Optimization of the Spectral Line Inversion Code
Authors: Centeno, R.; Schou, J.; Hayashi, K.; Norton, A.; Hoeksema,
J. T.; Liu, Y.; Leka, K. D.; Barnes, G.
Bibcode: 2014SoPh..289.3531C
Altcode: 2014SoPh..tmp...44C; 2014arXiv1403.3677C
The Very Fast Inversion of the Stokes Vector (VFISV) is a
Milne-Eddington spectral line inversion code used to determine the
magnetic and thermodynamic parameters of the solar photosphere from
observations of the Stokes vector in the 6173 Å Fe I line by the
Helioseismic and Magnetic Imager (HMI) onboard the Solar Dynamics
Observatory (SDO). We report on the modifications made to the original
VFISV inversion code in order to optimize its operation within
the HMI data pipeline and provide the smoothest solution in active
regions. The changes either sped up the computation or reduced the
frequency with which the algorithm failed to converge to a satisfactory
solution. Additionally, coding bugs which were detected and fixed in
the original VFISV release are reported here.
Title: Observations of Beta Pictoris b with the Gemini Planet Imager
Authors: Chilcote, J.; Graham, J.; Barman, T.; Fitzgerald, M.; Larkin,
J.; Macintosh, B.; Bauman, B.; Burrows, A.; Cardwell, A.; De Rosa, R.;
Dillon, D.; Doyon, R.; Dunn, J.; Erikson, D.; Gavel, D.; Goodsell,
S.; Hartung, M.; Hibon, P.; Ingraham, P.; Kalas, P.; Konopacky, Q.;
Maire, J.; Marchis, F.; Marley, M.; Mcbride, J.; Millar-Blanchaer, M.;
Morzinski, K.; Norton, A.; Oppenheimer, B.; Palmer, D.; Patience, J.;
Pueyo, L.; Rantakyro, F.; Sadakuni, N.; Saddlemyer, L.; Savransky,
D.; Serio, A.; Soummer, R.; Sivaramakrishnan, A.; Song, I.; Thomas,
S.; Wallace, K.; Wiktorowicz, S.; Wolff, S.
Bibcode: 2014tybp.confE..27C
Altcode:
Using the recently installed Gemini Planet Imager (GPI), we present
measurements of the planetary companion to the nearby young star
beta Pic. GPI is a facility class instrument located at Gemini South
designed to image and provide low-resolution spectra of Jupiter sized,
self-luminous planetary companions around young nearby stars. We
present the current imaged spectrum and atmospheric models of the
planet based upon GPI's R ∼50 integral field spectrograph. Further,
we present a joint analysis of the GPI and NACO astrometry, and the
Snellen et al. (2014) radial velocity measurement of beta Pic b that
provides the first constraint on the argument of periastron, providing
a causal link to the infalling, evaporating bodies.
Title: Connecting the Dots - Magnetic Field in the Inner Heliosphere
Authors: Hoeksema, Jon Todd; Liu, Yang; Sun, Xudong; Norton, Aimee Ann
Bibcode: 2014AAS...22432364H
Altcode:
At any given time the Earth is connected by a cluster of magnetic field
lines to the solar photosphere. The same holds true for any location
in the heliosphere - be it a solar orbiting spacecraft, region of
particle acceleration, source of southward IMF, flare site, ICME,
co-rotating interaction region, comet, planet, etc. That cluster
of field lines may have a common origin that is relatively easy
to identify, e.g. in the center of a high speed stream originating
in an equatorial coronal hole. More often the geometry is complex -
adjacent field lines may come from widely separated places, the coronal
topology may be convoluted, and the field will have been distorted
during its transit. Furthermore, conditions change and history is
important - foot points move or reconnect, the corona is dynamic -
sometimes dramatically so, and the prior state of the heliosphere
matters. Conversely, a region of interest, e.g. an active region,
coronal hole, reconnection site, or shock, may be linked simply or in a
more complex way to one or many other locations in the heliosphere. We
bring together a variety of coronal and heliospheric modeling tools and
new sources of comprehensive solar data to improve the knowledge of
how points in the heliosphere are connected to each other and to the
photosphere and how those connections evolve in time. Our goal is to
determine not only the useful magnetic connections in the corona and
inner heliosphere, but the implications of the corona's fundamental
skeletal structure for understanding sources of in situ observations.
Title: A "breathing" source surface for cycles 23 and 24
Authors: Arden, W. M.; Norton, A. A.; Sun, X.
Bibcode: 2014JGRA..119.1476A
Altcode:
The potential field source surface (PFSS) model is used to represent
the large-scale geometry of the solar coronal magnetic fields. The
height of the source surface in this model can be taken as a free
parameter. Previous work suggests that varying the source surface height
during periods of solar minimum yields better agreement between PFSS
models and the measured magnitude of the interplanetary magnetic field
(IMF) open flux at 1 AU—in other words, the source surface "breathes"
in and out over the course of the solar cycle. We examine the evolution
of open flux during all of cycle 23 and the first part of cycle 24
using photospheric magnetic field maps from the Solar and Heliospheric
Observatory's Michelson Doppler Imager and Solar Dynamics Observatory's
Helioseismic and Magnetic Imager instruments. We determine the value
of source surface height that provides a best fit to the IMF open flux
at 1 AU (using the OMNI 2 data set) for the time period 1996-2012. The
canonical 2.5 Rs source surface matches the measured IMF
open flux during periods of solar maximum but needs to be raised by
approximately 15-30% in order to match the measured IMF open flux at
the periods of solar minimum.
Title: Recovering Joy's Law as a Function of Solar Cycle, Hemisphere,
and Longitude
Authors: McClintock, B. H.; Norton, A. A.
Bibcode: 2013SoPh..287..215M
Altcode: 2013arXiv1305.3205M
Bipolar active regions in both hemispheres tend to be tilted with
respect to the East-West Equator of the Sun in accordance with
Joy's law, which describes the average tilt angle as a function of
latitude. Mt. Wilson Observatory data from 1917 - 1985 are used to
analyze the active-region tilt angle as a function of solar cycle,
hemisphere, and longitude, in addition to the more common dependence on
latitude. Our main results are as follows: i) We recommend a revision of
Joy's law towards a weaker dependence on latitude (slope of 0.13 - 0.26)
and without forcing the tilt to zero at the Equator. ii) We determine
that the hemispheric mean tilt value of active regions varies with each
solar cycle, although the noise from a stochastic process dominates
and does not allow for a determination of the slope of Joy's law on an
11-year time scale. iii) The hemispheric difference in mean tilt angles,
1.1∘±0.27, over Cycles 16 to 21 was significant to a
three-σ level, with average tilt angles in the Northern and Southern
hemispheres of 4.7∘±0.26 and 3.6∘±0.27,
respectively. iv) Area-weighted mean tilt angles normalized by
latitude for Cycles 15 to 21 anticorrelate with cycle strength for
the southern hemisphere and whole-Sun data, confirming previous
results by Dasi-Espuig et al. (Astron. Astrophys.518, A7, 2010). The
Northern Hemispheric mean tilt angles do not show a dependence on cycle
strength. v) Mean tilt angles do not show a dependence on longitude
for any hemisphere or cycle. In addition, the standard deviation of
the mean tilt is 29 - 31∘ for all cycles and hemispheres,
indicating that the scatter is due to the same consistent process even
if the mean tilt angles vary.
Title: A data-driven time-dependent three-dimensional MHD simulation
of solar active regions with HMI vector magnetic field data
Authors: Hayashi, Keiji; Hoeksema, J. T.; Liu, Y.; Sun, X.; Bobra,
M.; Norton, A. A.
Bibcode: 2013SPD....4430204H
Altcode:
We investigate the dynamics of the solar active regions by means
of our data-driven time-dependent three-dimensional MHD simulation
model using the HMI vector magnetic field data. The simulations start
with pre-emergence phase, or very early phase of the active region so
that the development of the loop structures and other signatures of
the active regions will be traced. We tested several cases, mainly
for AR 11158 of Feb. 2011. Either of the plasma motion or electric
field, inferred from the DAVE4VM (Schuck, 2008) is given to the
solar-surface boundary surface of the simulation box to which the
method of projected normal characteristics (Nakagawa et al. 1987;
Wu and Wang, 1987) is applied to ensure the numerical stability and
consistency in physics. As our first attempt, we choose the ideal MHD
equations without any additional terms except gravity. The results of
the simulation show that the method can trace some signatures of the
solar active regions, such as development of the magnetic-field loop
and (nonlinear) twist. Not having all information at the simulation
initial time, nor all physics processes on the photosphere, at
transition region, and in the solar corona, agreements in plasma
quantities with the other observation such as AIA image data are
limited. No flare-like eruptions were obtained under a simulation
setting we currently test. The temporal sequences of three-component
vector data can give good constraints on the MHD simulation studies of
the sub-Alfvenic region, though, we will need more observations, and
probably assumptions, to fulfill the physics system. The MHD simulation
can be a powerful tool to bridge the measurements and observation,
helping interpretation and giving requirement.
Title: How much more can sunspots tell us about the solar dynamo?
Authors: Norton, Aimee A.; Jones, Eric H.; Liu, Y.; Hayashi, K.;
Hoeksema, J. T.; Schou, Jesper
Bibcode: 2013IAUS..294...25N
Altcode:
Sunspot observations inspired solar dynamo theory and continue
to do so. Simply counting them established the sunspot cycle
and its period. Latitudinal distributions introduced the tough
constraint that the source of sunspots moves equator-ward as the
cycle progresses. Observations of Hale's polarity law mandated
hemispheric asymmetry. How much more can sunspots tell us about
the solar dynamo? We draw attention to a few outstanding questions
raised by inherent sunspot properties. Namely, how to explain sunspot
rotation rates, the incoherence of follower spots, the longitudinal
spacing of sunspot groups, and brightness trends within a given sunspot
cycle. After reviewing the first several topics, we then present new
results on the brightness of sunspots in Cycle 24 as observed with
the Helioseismic Magnetic Imager (HMI). We compare these results
to the sunspot brightness observed in Cycle 23 with the Michelson
Doppler Imager (MDI). Next, we compare the minimum intensities of five
sunspots simultaneously observed by the Hinode Solar Optical Telescope
Spectropolarimeter (SOT-SP) and HMI to verify that the minimum
brightness of sunspot umbrae correlates well to the maximum field
strength. We then examine 90 and 52 sunspots in the north and south
hemisphere, respectively, from 2010 - 2012. Finally, we conclude that
the average maximum field strengths of umbra 40 Carrington Rotations
into Cycle 24 are 2690 Gauss, virtually indistinguishable from the
2660 Gauss value observed at a similar time in Cycle 23 with MDI.
Title: PREFACE: Eclipse on the Coral Sea: Cycle 24 Ascending
Authors: Cally, Paul; Erdélyi, Robert; Norton
Bibcode: 2013JPhCS.440a1001C
Altcode:
A total solar eclipse is the most spectacular and awe-inspiring
astronomical phenomenon most people will ever see in their
lifetimes. Even hardened solar scientists draw inspiration from it. The
eclipse with 2 minutes totality in the early morning of 14 November 2012
(local time) drew over 120 solar researchers (and untold thousands of
the general public) to the small and picturesque resort town of Palm
Cove just north of Cairns in tropical north Queensland, Australia,
and they were rewarded when the clouds parted just before totality
to reveal a stunning solar display. Eclipse photograph The
eclipse was also the catalyst for an unusually broad and exciting
conference held in Palm Cove over the week 12--16 November. Eclipse on
the Coral Sea: Cycle 24 Ascending served as GONG 2012, LWS/SDO-5, and
SOHO 27, indicating how widely it drew on the various sub-communities
within solar physics. Indeed, as we neared the end of the ascending
phase of the peculiar Solar Cycle 24, it was the perfect time to
bring the whole community together to discuss our Sun's errant recent
behaviour, especially as Cycle 24 is the first to be fully observed by
the Solar Dynamics Observatory (SDO). The whole-Sun perspective was a
driving theme of the conference, with the cycle probed from interior
(helioseismology), to atmosphere (the various lines observed by the
Atmospheric Imaging Assemble (AIA) aboard SDO, the several instruments
on Hinode, and other modern observatories), and beyond (CMEs etc). The
quality of the presentations was exceptional, and the many speakers
are to be commended for pitching their talks to the broad community
present. These proceedings draw from the invited and contributed
oral presentations and the posters exhibited in Palm Cove. They give an
(incomplete) snapshot of the meeting, illustrating its broad vistas. The
published contributions are organized along the lines of the conference
sessions, as set out in the Contents, leading off with a provocative
view of Cycle 24 thus far from Sarbani Basu. Other invited papers
presented here include an appreciation of Hinode's view of solar
activity as the cycle rises by Toshifumi Shimizu; a first taxonomy of
magnetic tornadoes and chromospheric swirls by Sven Wedemeyer {\it et
al}; an analysis of Hinode/EIS observations of transient heating events;
a timely re-examination of solar dynamo theory by Paul Charbonneau;
an exciting teaser for the solar potential of the Murchison Widefield
Array now operating in Western Australia by Steven Tingay {\it et al};
an overview and critique of the state of nonlinear force-free magnetic
field extrapolation theory and practice by Mike Wheatland and Stuart
Gilchrist; and a masterful review of atmospheric MHD wave coupling to
the Sun's internal p-mode oscillations by Elena Khomenko and Irantzu
Calvo Santamaria. The many contributed papers published here are no less
exciting. All papers have been refereed to a high standard. The
editors thank all the referees, drawn both from conference attendees
and the wider community, who have taken their tasks very seriously and
provided very detailed and helpful reports. Nearly all contributions
have been substantially improved by the process. We must also thank
our financial sponsors. Both the Global Oscillations Network Group
(GONG) and LWS/SDO were generous in their support, as were the School
of Mathematical Sciences and the Monash Centre for Astrophysics (MoCA)
at Monash University, Melbourne, and the Centre for Astronomy at James
Cook University, Townsville. The Local Organizing Committee and the
many students who assisted before and during the conference also deserve
high praise for facilitating such a memorable meeting. Paul Cally,
Robert Erdélyi and Aimee Norton Conference photograph
Title: How do the magnetic field strengths and intensities of sunspots
vary over the solar cycle?
Authors: Norton, A. A.; Jones, E. H.; Liu, Y.
Bibcode: 2013JPhCS.440a2038N
Altcode:
Many efforts have been made to determine if sunspot umbrae continuum
intensities and magnetic field strengths are different at sunspot
maximum than at sunspot minimum. The results are inconsistent, probably
due to differences in sample size and analysis methodology. However,
five out of six studies reviewed in this paper agree that sunspots are
darker and stronger at sunspot maximum than later in the same cycle,
i.e. sunspots brighten during the declining phase of the sunspot
cycle. The trend during the rising phase is not agreed upon. Better
statistics during the rising phase is crucial to determine if umbrae
exhibit a cyclical or linear brightness trend over the cycle. We further
this work by analyzing the intensities of 179 sunspots observed with
the Helioseismic Magnetic Imager (HMI) for the rising phase of Sunspot
Cycle 24. We find no significant trend in the brightness of sunspot
umbrae in HMI data during Carrington Rotations 2097-2129 in either
hemisphere. Future studies should place limits on sunspots included in
the data sample, i.e. use only the leading sunspot in a bipolar active
region after most of the flux has emerged but prior to sunspot decay,
hopefully separating the effects of surface conditions from those of
the interior where the magnetic flux is generated.
Title: Stray Light Correction for HMI Data
Authors: Norton, A. A.; Duvall, T.; Schou, J.; Cheung, M.
Bibcode: 2013enss.confE..95N
Altcode:
Our goal is to find a deconvolution routine that can remove scattered
light in sunspot umbrae without introducing extraneous power in high
spatial frequencies in helioseismology analysis of the same data. Using
ground-based calibration data, a third-order polynomial fit was obtained
for the instrumental modulation transfer function (MTF). Images of the
solar limb and the limb and disk of Venus during its transit were used
to model stray light. An Airy function and a Lorentzian are used in
combination to model the instrumental point spread function (PSF) for
HMI which is made to be positive definite everywhere and zero above
the ideal optical Nyquist frequency. Deconvolution was carried out
using a Lucy-Richardson algorithm on a graphics processing unit. The
deconvolved image is then compared to the original to determine the
extent of introduced Gibb's phenomenon (ringing) and how the power
changes as a function of spatial frequency.
Title: Motion of magnetic elements at the solar equator observed
by SDO/HMI
Authors: Hayashi, K.; Norton, A.; Liu, Y.; Sun, X.; Hoeksema, J. T.
Bibcode: 2012AGUFMSH41D2129H
Altcode:
Characterizing motions of the solar magnetic field near the solar
equator is important for understanding the symmetry and asymmetry
of large scale structures in the solar interior, solar corona,
and solar wind. The SDO/HMI has been observing the full-disk solar
magnetic field, with a cadence of 12 minutes or 45 seconds, since April
2010. With high-cadence long-term observations of the solar photospheric
magnetic field, we analyze the motion of the magnetic field elements,
specifically latitudinal motion, near the solar equator. The regions
that are divergent, convergent or cross-equatorial and appear, in
general, to be coherent on a spatial scale of ~15 degrees longitude
and last for several days.
Title: The Dynamic Polar Magnetic Field Before Its Polarity Reversal
Authors: Sun, X.; Hoeksema, J. T.; Liu, Y.; Sainz Dalda, A.; Norton,
A.; Hayashi, K.
Bibcode: 2012AGUFMSH41D2130S
Altcode:
We characterize the magnetic field in the Sun's polar region using the
spectropolarimetric measurement from the Helioseismic and Magnetic
Imager (HMI) on board the Solar Dynamics Observatory (SDO). With
HMI's high cadence, continuous time coverage, and moderate spectral and
spatial resolution, we are able to estimate the polar magnetic flux, its
latitudinal distribution, and its temporal variation over three years
(2010-2012) during Cycle 24's rising phase. A comparison with higher
spectral resolution observations from Hinode SOT/SP provides constraints
on the flux estimates. The tracking of individual magnetic element
movements yields new insight on the polar field's dynamic behavior
leading up to the polarity reversal. We compare the result with that
from the HMI line-of-sight data, as well as MDI data for Cycle 23. All
observations indicate an earlier reversal of the northern hemisphere
owing to more solar activity in the rising phase, which resulted in
a significant hemispheric asymmetry.
Title: Evolution of the solar luminosity during solar cycle 23
Authors: Vieira, L. A.; Schrijver, C.; DeRosa, M. L.; Norton, A.;
Dudok de Wit, T.; Da Silva, L.; Vuets, A.
Bibcode: 2012AGUFMSH12A..04V
Altcode:
The effect of the solar activity on the solar luminosity, which is
the total electromagnetic solar output, is one of the fundamental
questions in solar physics. Changes of the solar luminosity can arise
from changes of the energy flux in the convection zone that can also
affects other solar parameters such as the surface temperature, the
apparent radius and shape, and the symmetry of the radiative field
itself. Additionally, understanding the latitudinal distribution of the
flux density is needed to compare the solar variability and its stellar
analogues. Nevertheless, our observations of the solar flux density
are limited to a region near the ecliptic plane, which have provided
just a raw estimate of the variability of the solar luminosity. Here
we present a reconstruction of the solar flux density and solar
luminosity for the solar cycle 23 and ascending phase of cycle 24. The
reconstruction is based on a combination of a state-of-art solar surface
magnetic flux transport model and a semi-empirical total and spectral
irradiance model. The flux transport model is based on assimilation
of MDI/SOHO and HMI/SDO magnetograms. The irradiance model's free
parameters are estimated by minimizing the difference between
the model's output and the PMOD Composite of TSI measurements. We
have obtained a good agreement between the model's output and the
measurements. The distribution of active regions leads to a clear
low latitude brightening during the solar maximum. This brightening
results from the balance of the contributions from bright (faculae and
network) and dark features (sunspots) located in the solar surface,
which peaks near the solar equator. As the effects of dark features
are limited to a narrower region, the variability of the flux density
at the poles is dominated by the evolution of faculae and network. The
preliminary results indicate that the heat flux blocked by sunspots
is lower than the flux leaked by bright features. Consequently, an
increase of the luminosity through the cycle is observed as previously
estimated based on near ecliptic measurements. This work also enables
an assessment of the properties of solar variability when viewed from
out of the ecliptic, i.e., such as we might be viewing other stars of
solar activity level. Finally, the limitations of the model and future
strategies to extend the reconstruction of the flux density and solar
luminosity will be presented.
Title: Magnetic Helicity in Emerging Active Regions: A Statistical
Study
Authors: Liu, Y.; Hayashi, K.; Hoeksema, J. T.; Norton, A. A.; Schuck,
P. W.; Sun, X.
Bibcode: 2012AGUFMSH53B..03L
Altcode:
Magnetic helicity in emerging active regions in early phase of solar
cycle 24 is studied using HMI vector magnetic field data. Magnetic
helicity in active-region corona is computed from the helicity flux
across the photosphere, which is derived using the measured vector
magnetic field on the photosphere and the velocity field computed from
time-series vector magnetic field data using the algorithm DAVE4VM
(Schuck 2008). It is found that the helicity in the active-region
corona is mainly contributed by the photospheric shear motion while
the emergence only contributes a small fraction, and it also shows
a weak hemisphere preference that is consistent with the so-called
hemisphere helicity rule. Correlation between magnetic flux emergence
and helicity injection into the corona is discussed, and its implication
to occurrence of solar flares is explored.
Title: How the inclination of Earth's orbit affects incoming solar
irradiance
Authors: Vieira, L. E. A.; Norton, A.; Dudok de Wit, T.; Kretzschmar,
M.; Schmidt, G. A.; Cheung, M. C. M.
Bibcode: 2012GeoRL..3916104V
Altcode:
The variability in solar irradiance, the main external energy source
of the Earth's system, must be critically studied in order to place
the effects of human-driven climate change into perspective and allow
plausible predictions of the evolution of climate. Accurate measurements
of total solar irradiance (TSI) variability by instruments onboard
space platforms during the last three solar cycles indicate changes of
approximately 0.1% over the sunspot cycle. Physics-based models also
suggest variations of the same magnitude on centennial to millennia
time-scales. Additionally, long-term changes in Earth's orbit modulate
the solar irradiance reaching the top of the atmosphere. Variations of
orbital inclination in relation to the Sun's equator could potentially
impact incoming solar irradiance as a result of the anisotropy of
the distribution of active regions. Due to a lack of quantitative
estimates, this effect has never been assessed. Here, we show that
although observers with different orbital inclinations experience
various levels of irradiance, modulations in TSI are not sufficient
to drive observed 100 kyr climate variations. Based on our model we
find that, due to orbital inclination alone, the maximum change in
the average TSI over timescales of kyrs is ∼0.003 Wm-2,
much smaller than the ∼1.5 Wm-2 annually integrated change
related to orbital eccentricity variations, or the 1-8 Wm-2
variability due to solar magnetic activity. Here, we stress that
out-of-ecliptic measurements are needed in order to constrain models
for the long-term evolution of TSI and its impact on climate.
Title: On Relationship Between CMEs' Speed and Magnetic Field
Structure in the Corona and Inner Heliosphere
Authors: Liu, Yang; Shen, Chenglong; Hayashi, K.; Hoeksema, J. T.;
Norton, A. A.; Sun, X.
Bibcode: 2012shin.confE..79L
Altcode:
In this study, we search for correlation between the speed of active
region-related haloCMEs and the configuration of the ambient magnetic
fields. Having studied 99 halo CMEsin the period from 2000 to 2004,
we find that CMEs under the heliospheric currentsheet (streamer)
are significantly slower than CMEs situated under unidirectional
openfield structures (pseudo-streamer or coronal hole). The average
speed of the former is883 km s^(-1), while the latter is 1388 km
s^(-1). The effect is not biased by the flareimportance. This implies
that the ambient magnetic field structure plays a role indetermining
the speed of the halo CMEs. We further test this hypothesis by
searching forasymmetry in distribution of CMEs' speed in the North-
and South-hemisphere, becausethe features of the corona and inner
heliosphere, such as streamers, pseudo-streamers andcoronal holes,
are primarily determined by the polar field and distribution of solar
active regions. Both are asymmetric. Consequently, configuration of
large-scale magnetic field (streamer and pseudo-streamer) should have
North-South asymmetry. It is found, based on the data in the NASA CMEs
catalog (http://cdaw.gsfc.nasa.gov/CME_list/) in 1996-2009, that the
(yearly-averaged) CMEs speed is faster in South hemisphere before the
polar field reversal (years 2002-2003) and slower after the reversal. A
test from our 3D MHD simulation also confirms it.
Title: Geomagnetic Indices and the Solar Magnetic Open Flux
Authors: Norton, Aimee Ann; Arden, W. M.
Bibcode: 2012AAS...22020603N
Altcode:
On 23 Jan 2012, an M8.7-class solar flare erupted from Active Region
1402, followed by an Earth-directed coronal mass ejection (CME) which
left the Sun at approximately 750 km/s and triggered a geomagnetic storm
a day later. We examine this event through the change in solar open
magnetic flux computed using a potential field source surface (PFSS)
model based on measurements of the photospheric magnetic field from
the Solar Dynamics Observatory’s Helioseismic and Magnetic Imager
(SDO/HMI). We examine the solar magnetic open flux over a number
of regions on the solar surface (total, northern and southern polar
regions, equatorial region and both hemispheres) and correlate these
with geomagnetic indices. This research is a small step in a larger
project to investigate the long-term (i.e. years) correlation between
open solar flux and geomagnetic activity. This correlation will lead
to an increased understanding of the Sun-Earth magnetic interaction
and should enhance our ability to predict space weather. The latter
is increasingly critical as our terrestrial electrical and electronic
infrastructure becomes more and more sensitive and vulnerable to
large-scale solar activity.
Title: Footpoint Separation and Evershed Flow of Active Regions
Authors: Norton, Aimee Ann; Jones, E. H.
Bibcode: 2012AAS...22020604N
Altcode:
The bipolar nature of active regions and sunspot groups within
the Sun’s photosphere is generally attributed to the emergence
of magnetic flux tubes that originate from shear and turbulent
pumping at the base of the Sun’s convection zone. There is debate,
however, as to exactly how well-connected active regions are to
solar interior. A connection to the solar interior during the ascent
of a flux tube through the convection zone is a requirement within
numerical models designed to describe the observed characteristics of
active regions, e.g. Joy’s law tilt and latitude emergence, however,
these models also predict post-emergence behavior of sunspots that
is not supported observationally (Schussler and Rempel, 1995; Fan,
2009; Toth and Gerlei, 2003). It has been suggested (Rubio et al.,
2008; Schussler and Rempel, 1995) that a bipolar magnetic region might
lose its connection quickly upon emergence. Using data from SDO/HMI,
we examine the footpoint separation and the Evershed flow of a number
of active regions over time to detect the disconnection process of a
sunspot from its magnetic roots.
Title: The Vector Magnetic Fields of Sunspots as Observed with HMI
Authors: Norton, Aimee Ann; H. M. I. Vector Magnetic Field Team
Bibcode: 2012AAS...22020605N
Altcode:
The strongest sunspots yet produced by Cycle 24 are analyzed using an
updated Milne-Eddington inversion code (VFISV, Borrero et al. 2010) with
the full-disk polarimetric filtergram data observed with HMI. We compare
the maximum strengths of the observed sunspots to those reported for
ascending Cycle 23 spots. We note any magnetic field trends during daily
and disk-crossing time periods that may be instrument-dependent. Updates
to the inversion code include a regularization of the minimization
function to bias the solution towards a lower eta0 in the case of
double minima.
Title: A First Look at Magnetic Field Data Products from SDO/HMI
Authors: Liu, Y.; Scherrer, P. H.; Hoeksema, J. T.; Schou, J.; Bai,
T.; Beck, J. G.; Bobra, M.; Bogart, R. S.; Bush, R. I.; Couvidat,
S.; Hayashi, K.; Kosovichev, A. G.; Larson, T. P.; Rabello-Soares,
C.; Sun, X.; Wachter, R.; Zhao, J.; Zhao, X. P.; Duvall, T. L., Jr.;
DeRosa, M. L.; Schrijver, C. J.; Title, A. M.; Centeno, R.; Tomczyk,
S.; Borrero, J. M.; Norton, A. A.; Barnes, G.; Crouch, A. D.; Leka,
K. D.; Abbett, W. P.; Fisher, G. H.; Welsch, B. T.; Muglach, K.;
Schuck, P. W.; Wiegelmann, T.; Turmon, M.; Linker, J. A.; Mikić,
Z.; Riley, P.; Wu, S. T.
Bibcode: 2012ASPC..455..337L
Altcode:
The Helioseismic and Magnetic Imager (HMI; Scherrer & Schou 2011)
is one of the three instruments aboard the Solar Dynamics Observatory
(SDO) that was launched on February 11, 2010 from Cape Canaveral,
Florida. The instrument began to acquire science data on March 24. The
regular operations started on May 1. HMI measures the Doppler velocity
and line-of-sight magnetic field in the photosphere at a cadence of
45 seconds, and the vector magnetic field at a 135-second cadence,
with a 4096× 4096 pixels full disk coverage. The vector magnetic
field data is usually averaged over 720 seconds to suppress the p-modes
and increase the signal-to-noise ratio. The spatial sampling is about
0".5 per pixel. HMI observes the Fe i 6173 Å absorption line, which
has a Landé factor of 2.5. These data are further used to produce
higher level data products through the pipeline at the HMI-AIA Joint
Science Operations Center (JSOC) - Science Data Processing (Scherrer et
al. 2011) at Stanford University. In this paper, we briefly describe the
data products, and demonstrate the performance of the HMI instrument. We
conclude that the HMI is working extremely well.
Title: Polarization Calibration of the Helioseismic and Magnetic
Imager (HMI) onboard the Solar Dynamics Observatory (SDO)
Authors: Schou, J.; Borrero, J. M.; Norton, A. A.; Tomczyk, S.;
Elmore, D.; Card, G. L.
Bibcode: 2012SoPh..275..327S
Altcode:
As part of the overall ground-based calibration of the Helioseismic
and Magnetic Imager (HMI) instrument an extensive set of polarimetric
calibrations were performed. This paper describes the polarimetric
design of the instrument, the test setup, the polarimetric model,
the tests performed, and some results. It is demonstrated that HMI
achieves an accuracy of 1% or better on the crosstalks between Q,
U, and V and that our model can reproduce the intensities in our
calibration sequences to about 0.4%. The amount of depolarization
is negligible when the instrument is operated as intended which,
combined with the flexibility of the polarimeter design, means that
the polarimetric efficiency is excellent.
Title: Design and Ground Calibration of the Helioseismic and Magnetic
Imager (HMI) Instrument on the Solar Dynamics Observatory (SDO)
Authors: Schou, J.; Scherrer, P. H.; Bush, R. I.; Wachter, R.;
Couvidat, S.; Rabello-Soares, M. C.; Bogart, R. S.; Hoeksema, J. T.;
Liu, Y.; Duvall, T. L.; Akin, D. J.; Allard, B. A.; Miles, J. W.;
Rairden, R.; Shine, R. A.; Tarbell, T. D.; Title, A. M.; Wolfson,
C. J.; Elmore, D. F.; Norton, A. A.; Tomczyk, S.
Bibcode: 2012SoPh..275..229S
Altcode:
The Helioseismic and Magnetic Imager (HMI) investigation (Solar
Phys. doi:10.1007/s11207-011-9834-2, 2011) will study the solar
interior using helioseismic techniques as well as the magnetic field
near the solar surface. The HMI instrument is part of the Solar
Dynamics Observatory (SDO) that was launched on 11 February 2010. The
instrument is designed to measure the Doppler shift, intensity, and
vector magnetic field at the solar photosphere using the 6173 Å Fe I
absorption line. The instrument consists of a front-window filter, a
telescope, a set of waveplates for polarimetry, an image-stabilization
system, a blocking filter, a five-stage Lyot filter with one tunable
element, two wide-field tunable Michelson interferometers, a pair
of 40962 pixel cameras with independent shutters, and
associated electronics. Each camera takes a full-disk image roughly
every 3.75 seconds giving an overall cadence of 45 seconds for the
Doppler, intensity, and line-of-sight magnetic-field measurements
and a slower cadence for the full vector magnetic field. This article
describes the design of the HMI instrument and provides an overview of
the pre-launch calibration efforts. Overviews of the investigation,
details of the calibrations, data handling, and the science analysis
are provided in accompanying articles.
Title: First Science Results from the High Speed SAAO
Photo-polarimeter
Authors: Potter, S.; Buckley, D.; O'Donoghue, D.; O'Connor, J.; Fourie,
P.; Evans, G.; Sass, C.; Crause, L.; Butters, O.; Norton, A.; Mukai,
K.; Still, M.
Bibcode: 2011ASPC..449...27P
Altcode:
We report on the completion of a new 2 channel, HIgh speed
Photo-POlarimeter (HIPPO) to be used on the 1.9 m optical telescope of
the South African Astronomical Observatory. The instrument makes use
of rapidly counter-rotating (10 Hz), super-achromatic half and quarter
wave-plates, a fixed Glan-Thompson beamsplitter and two photo-multiplier
tubes that record the modulated O and E beams. Each modulated beam
permits an independent measurement of the polarization and therefore the
capability of simultaneous 2 filter observations. All Stokes parameters
are recorded every 0.1 s and photometry every 1 ms. Post-binning of data
is possible in order to improve the signal. This is ideal for measuring,
e.g., the rapid variability of the optical polarization from magnetic
Cataclysmic Variable stars (mCVs). We will present our first science
results made in February 2008. Specifically the discovery of short
quasi-periodic (∼ 3-5 minutes) variations in the circular polarized
emissions from the recently discovered mCV candidate IGRJ14536-5522.
Title: Sunspot Groups Simultaneously Observed with HMI and MDI
Authors: Norton, A. A.; Schou, J.; Liu, Y.; Hoeksema, J. T.
Bibcode: 2011sdmi.confE..42N
Altcode:
Simultaneous data from HMI and MDI is analyzed for active regions 11084
and 11087. We showcase the improved quality of HMI 45-second magnetogram
data over MDI magnetogram data due to higher spectral and spatial
sampling as well as better optical alignment and a magnetically more
sensitive spectral line. Specifically, HMI magnetogram data contains
less leakage of p-mode signal, umbrae do not show saturation at low
intensities, and HMI flux values are consistent with vector data. We
show comparisons of magnetic time series and power spectra observed
by HMI and MDI for sunspot, plage and quiet-Sun.
Title: Recovering Joy's Law, Tilt Angle as a Function of Longitude,
and Tilt Angle Change during Emergence
Authors: McClintock, Bruce H.; Norton, Aimee A.
Bibcode: 2011sdmi.confE..73M
Altcode:
Bipolar active regions in both hemispheres tend to be tilted with
respect to the East-West equator of the Sun in accordance with Joy’s
law which describes the tilt angle as a function of latitude. Joy's law
can be generalized as: average tilt angle = 2° + 0.2° ´ latitude. Mt
Wilson Observatory (MWO) data from 1917-1985 are used to analyze the
active region tilt angle as a function of hemisphere and longitude,
in addition to the more common dependence on latitude. We determine
the minimum number of sunspot groups needed to recover Joy's law
in any given amount of time. We present hemispheric differences in
Joy's law for cycles 17-21. Sunspot cycle 17 and 19 show a small but
significant dependence of tilt angle on longitude over portions of
the solar cycle. This implies that toroidal fields at the base of the
convection zone are tipped with respect to the solar equatorial plane,
affecting the initial angle at which magnetic field ropes begin their
rise. Finally, we use SDO/HMI data to record the change of tilt angle
over time as a sunspot group emerges.
Title: Polarization in Soft X-ray Intermediate Polars
Authors: Katajainen, S.; Lehto, H. J.; Piirola, V.; Berdyugin, A.;
Norton, A.; Butters, O.
Bibcode: 2010ASPC..435..237K
Altcode:
The evolutionary connection between polars and intermediate polars
(IPs) is not yet well established. Soft X-ray IPs are good candidates
for progenitors of polars, but their magnetic field strengths are
poorly constrained. Only a handful of them are known to be circularly
polarized and converting polarized fractions into magnetic field
strengths is problematic, so it is still unclear whether they are of
comparable magnetic field strength to polars or not. We have performed
a polarimetric survey for a sample of Soft X-ray IPs. Results provide
evidences that some IPs have comparable magnetic field strengths to
some polars and can hence evolve from one to the other as their orbital
period decreases and synchronism is achieved.
Title: The Adaptive Optics Summer School Laboratory Activities
Authors: Ammons, S. M.; Severson, S.; Armstrong, J. D.; Crossfield,
I.; Do, T.; Fitzgerald, M.; Harrington, D.; Hickenbotham, A.; Hunter,
J.; Johnson, J.; Johnson, L.; Li, K.; Lu, J.; Maness, H.; Morzinski,
K.; Norton, A.; Putnam, N.; Roorda, A.; Rossi, E.; Yelda, S.
Bibcode: 2010ASPC..436..394A
Altcode: 2011arXiv1111.2015A
Adaptive Optics (AO) is a new and rapidly expanding field of
instrumentation, yet astronomers, vision scientists, and general AO
practitioners are largely unfamiliar with the root technologies crucial
to AO systems. The AO Summer School (AOSS), sponsored by the Center for
Adaptive Optics, is a week-long course for training graduate students
and postdoctoral researchers in the underlying theory, design, and
use of AO systems. AOSS participants include astronomers who expect
to utilize AO data, vision scientists who will use AO instruments to
conduct research, opticians and engineers who design AO systems, and
users of high-bandwidth laser communication systems. In this article
we describe new AOSS laboratory sessions implemented in 2006-2009 for
nearly 250 students. The activity goals include boosting familiarity
with AO technologies, reinforcing knowledge of optical alignment
techniques and the design of optical systems, and encouraging
inquiry into critical scientific questions in vision science using
AO systems as a research tool. The activities are divided into three
stations: Vision Science, Fourier Optics, and the AO Demonstrator. We
briefly overview these activities, which are described fully in other
articles in these conference proceedings (Putnam et al., Do et al.,
and Harrington et al., respectively). We devote attention to
the unique challenges encountered in the design of these activities,
including the marriage of inquiry-like investigation techniques with
complex content and the need to tune depth to a graduate- and PhD-level
audience. According to before-after surveys conducted in 2008, the vast
majority of participants found that all activities were valuable to
their careers, although direct experience with integrated, functional
AO systems was particularly beneficial.
Title: Solar-Cycle Characteristics Examined in Separate Hemispheres:
Phase, Gnevyshev Gap, and Length of Minimum
Authors: Norton, A. A.; Gallagher, J. C.
Bibcode: 2010SoPh..261..193N
Altcode: 2010arXiv1001.3186N
According to research results from solar-dynamo models, the northern
and southern hemispheres may evolve separately throughout the solar
cycle. The observed phase lag between the northern and southern
hemispheres provides information regarding how strongly the hemispheres
are coupled. Using hemispheric sunspot-area and sunspot-number data
from Cycles 12 - 23, we determine how out of phase the separate
hemispheres are during the rising, maximum, and declining period of
each solar cycle. Hemispheric phase differences range from 0 - 11, 0 -
14, and 2 - 19 months for the rising, maximum, and declining periods,
respectively. The phases appear randomly distributed between zero
months (in phase) and half of the rise (or decline) time of the solar
cycle. An analysis of the sunspot cycle double peak, or Gnevyshev gap,
is conducted to determine if the double-peak is caused by the averaging
of two hemispheres that are out of phase. We confirm previous findings
that the Gnevyshev gap is a phenomenon that occurs in the separate
hemispheres and is not due to a superposition of sunspot indices from
hemispheres slightly out of phase. Cross hemispheric coupling could
be strongest at solar minimum, when there are large quantities of
magnetic flux at the Equator. We search for a correlation between the
hemispheric phase difference near the end of the solar cycle and the
length of solar-cycle minimum, but found none. Because magnetic flux
diffusion across the Equator is a mechanism by which the hemispheres
couple, we measured the magnetic flux crossing the Equator by examining
Kitt Peak Vacuum Telescope and SOLIS magnetograms for Solar Cycles 21 -
23. We find, on average, a surplus of northern hemisphere magnetic flux
crossing during the mid-declining phase of each solar cycle. However,
we find no correlation between magnitude of magnetic flux crossing the
Equator, length of solar minima, and phase lag between the hemispheres.
Title: SOLIS Vector Spectromagnetograph: Status and Science
Authors: Henney, C. J.; Keller, C. U.; Harvey, J. W.; Georgoulis,
M. K.; Hadder, N. L.; Norton, A. A.; Raouafi, N. -E.; Toussaint, R. M.
Bibcode: 2009ASPC..405...47H
Altcode: 2008arXiv0801.0013H
The Vector Spectromagnetograph (VSM) instrument has recorded
photospheric and chromospheric magnetograms daily since August
2003. Full-disk photospheric vector magnetograms are observed
at least weekly and, since November 2006, area-scans of active
regions daily. Quick-look vector magnetic images, plus X3D and FITS
formated files, are now publicly available daily. In the near future,
Milne-Eddington inversion parameter data will also be available and
a typical observing day will include three full-disk photospheric
vector magnetograms. Besides full-disk observations, the VSM is
capable of high temporal cadence area-scans of both the photosphere
and chromosphere. Carrington rotation and daily synoptic maps are
also available from the photospheric magnetograms and coronal hole
estimate images.
Title: Daily Full-Disk SOLIS Inverted Vector Magnetic Field Data
Authors: Streander, Kim; Norton, A. A.; SOLIS Team
Bibcode: 2009SPD....40.0917S
Altcode:
Inverted vector magnetic field data from the SOLIS VSM (Synoptic
Optical Long-term Investigations of the Sun Vector Spectromagnetograph)
instrument are now available at:http://solis.nso.edu/. Both full-disk
and smaller field-of-view data containing active regions are
available. The inversion is based on the least-squares minimization
FORTRAN code developed by the HAO group, initially used with Advanced
Stokes Polarimeter data (Skumanich and Lites, 1987; Auer, Heasley and
House, 1977). The main code modification is that a scattered light,
or quiet-Sun profile, is simulated for every center-to-limb position
on the disk. This simulated profile is used as the scattered light
profile, instead of an observed profile averaged from pixels with low
polarization within a small field of view. The data are inversions of
Stokes I, Q, U and V profiles of the Fe I 630.1 and 630.2 nm lines
using a Milne-Eddington (ME) model atmosphere. Stokes I, Q, U and
V profile weights are 0.01, 1.0, 1.0 and 0.1, respectively. All the
Milne-Eddington inverted data are corrected for the 180º ambiguity
using the Non-Potential Field Calculation (NPFC) method developed by
Manolis Georgoulis (Johns Hopkins). Note that data are only inverted
if the observed polarization signal is above a certain threshold.Data
are available daily (weather permitting) beginning April 1, 2009
onwards. Also available is a sample of data from March 2008 containing
several active regions near the equator.
Title: Causes of Solar Activity
Authors: Giampapa, Mark S.; Gibson, Sarah; Harvey, J. W.; Hill, Frank;
Norton, Aimee A.; Pevtsov, A.
Bibcode: 2009astro2010S..92G
Altcode:
No abstract at ADS
Title: The Tilted Solar Dipole as Observed and Modeled during the
1996 Solar Minimum
Authors: Norton, A. A.; Raouafi, N. -E.; Petrie, G. J. D.
Bibcode: 2008ApJ...682.1306N
Altcode:
We examine the tilt of the solar magnetic dipole away from the
rotational axis near the 1996 solar minimum. A persistent tilted
dipole may result from an MHD instability acting on the toroidal
bands in the solar interior. Nonaxisymmetric eruption of sunspots
has been predicted by dynamo theory and observed in sunspot location
patterns. The decay of follower spots and the poleward migration of
flux could create polar caps that are slightly misaligned with the
north-south rotational axis. To investigate this, we analyze the coronal
streamer geometry observed with LASCO-C2 and the center of gravity of
the polar caps defined by coronal hole boundaries in EIT images and the
unipolar magnetic regions in KPVT magnetograms. We model the coronal
hole boundaries and neutral line locations by potential field source
surface (PFSS) modeling using Kitt Peak magnetograms. Our results
are consistent with an observed tilt of 5°-10° in the heliospheric
current sheet at solar minimum and the idea of persistent off-axis
magnetic polar caps for CRs 1911-1919. The coronal holes show a stable
azimuthal angle for CRs 1911-1919 with a rotation rate slightly less
than the Carrington rate. The PFSS modeling is able to recreate the
observed coronal hole geometry and predict the maximum extent of the
heliospheric current sheet as observed by streamer locations. A 6°
observed tilt of the polar caps during this time is consistent with
the analytical value provided from the PFSS dipole terms. However,
the determination of a tilt of the magnetic polar caps is dominated
by noise. The LASCO coronal streamer geometry traces out an 10° tilt
of the solar dipole from the equatorial plane during CRs 1915-1919.
Title: Evidence for Polar Jets as Precursors of Polar Plume Formation
Authors: Raouafi, N. -E.; Petrie, G. J. D.; Norton, A. A.; Henney,
C. J.; Solanki, S. K.
Bibcode: 2008ApJ...682L.137R
Altcode: 2008arXiv0806.3045R
Observations from the Hinode/XRT telescope and STEREO/SECCHI/EUVI
are utilized to study polar coronal jets and plumes. The study
focuses on the temporal evolution of both structures and their
relationship. The data sample, spanning 2007 April 7-8, shows that
over 90% of the 28 observed jet events are associated with polar
plumes. EUV images (STEREO/SECCHI) show plume haze rising from the
location of approximately 70% of the polar X-ray (Hinode/XRT) and EUV
jets, with the plume haze appearing minutes to hours after the jet was
observed. The remaining jets occurred in areas where plume material
previously existed, causing a brightness enhancement of the latter after
the jet event. Short-lived, jetlike events and small transient bright
points are seen (one at a time) at different locations within the base
of preexisting long-lived plumes. X-ray images also show instances
(at least two events) of collimated thin jets rapidly evolving into
significantly wider plumelike structures that are followed by the
delayed appearance of plume haze in the EUV. These observations provide
evidence that X-ray jets are precursors of polar plumes and in some
cases cause brightenings of plumes. Possible mechanisms to explain
the observed jet and plume relationship are discussed.
Title: A global SOLIS vector spectromagnetograph (VSM) network
Authors: Streander, K. V.; Giampapa, M. S.; Harvey, J. W.; Henney,
C. J.; Norton, A. A.
Bibcode: 2008SPIE.7014E..7PS
Altcode: 2008SPIE.7014E.251S
Understanding the Sun's magnetic field related activity is far
from complete as reflected in the limited ability to make accurate
predictions of solar variability. To advance our understanding of solar
magnetism, the National Solar Observatory (NSO) constructed the Synoptic
Optical Long-term Investigations of the Sun (SOLIS) suite of instruments
to conduct high precision optical measurements of processes on the Sun
whose study requires sustained observations over long time periods. The
Vector Spectromagnetograph (VSM), the principal SOLIS instrument,
has been in operation since 2003 and obtains photospheric vector data,
as well as photospheric and chromospheric longitudinal magnetic field
measurements. Instrument performance is being enhanced by employing
new, high-speed cameras that virtually freeze seeing, thus improving
sensitivity to measure the solar magnetic field configuration. A major
operational goal is to provide real-time and near-real-time data for
forecasting space weather and increase scientific yield from shorter
duration solar space missions and ground-based research projects. The
National Solar Observatory proposes to build two near-duplicates of
the VSM instrument and place them at international sites to form a
three-site global VSM network. Current electronic industry practice
of short lifetime cycles leads to improved performance and reduced
acquisition costs but also to redesign costs and engineering impacts
that must be minimized. The current VSM instrument status and experience
gained from working on the original instrument is presented herein and
used to demonstrate that one can dramatically reduce the estimated
cost and fabrication time required to duplicate and commission two
additional instruments.
Title: Evidence for polar jets as early stage of polar plume formation
Authors: Raouafi, N. E.; Petrie, G. J. D.; Norton, A. A.; Henney, C. J.
Bibcode: 2008AGUSMSH31A..09R
Altcode:
Observations from the Hinode/XRT telescope and STEREO/SECCHI are
utilized to study polar coronal jets and plumes. The study is
particularly focused on the time evolution of jets and how they
relate to polar plumes. We find that most polar jets are associated
with polar plumes. The data sample used for the present study shows
almost a one-to-one spatial correspondence between jets and plumes
(the inverse correspondence has to be evaluated). EUV images show
plume haze rising from the same location of observed polar x-ray and
EUV jets with a time delay ranging from minutes to hours. A number of
jets occured at the same location of long-lived polar plumes. The latter
brightened after the jet eruption. An instance of rapid evolution from
a jet to a plume state is also recorded by XRT alone. We believe that
x-ray jets represent the early stage of formation of polar plumes and
evaluate different mechanisms leading to the formation of polar plumes
after jet eruption.
Title: The Tilted Solar Dipole: Coronal Streamer and Polar Cap
Geometry Observed Near Solar Minimum
Authors: Norton, A. A.; Raouafi, N. -E.
Bibcode: 2008ASPC..383..405N
Altcode:
We examine the tilt of the solar magnetic dipole away from the
rotational axis near solar minimum. The coronal streamer geometry
as observed with LASCO-C2 at 5 R⊙ traces out an
approximately 10° tilt of the solar dipole from the equatorial
plane during Carrington rotations 1915--1919. We also analyze
the center-of-gravity of the polar caps as defined by coronal hole
boundaries in EIT images. A persistent tilted dipole may result from
an MHD instability acting upon the toroidal magnetic bands in the
solar interior. A non-axisymmetric eruption of sunspots mapping out
an m=1 pattern in longitude has been predicted by dynamo theory and
observed in sunspot location patterns. The decay of the follower spots
and migration of this flux poleward could create polar caps that are
slightly misaligned with the North--South rotational axis. Our results
are consistent with an observed tilt of ≤ 10 ° in the heliospheric
current sheet at solar minimum.
Title: The Solar Oxygen Abundance Determined from Polarimetric
Observations
Authors: Norton, Aimee A.; Socas-Navarro, H.
Bibcode: 2007AAS...210.2502N
Altcode: 2007BAAS...39..131N
In this work we present support for recent claims that advocate a
downward revision of the solar oxygen abundance. Our analysis employs
spatially-resolved spectro-polarimetric observations including the Fe
I lines at 6302 Angstroms, and the O I infrared triplet around 7774
Angstroms, in the quiet Sun. We used the Fe I lines to reconstruct the
three-dimensional thermal and magnetic structure of the atmosphere. The
simultaneous O I observations were then employed to determine the
abundance of oxygen at each pixel, using both LTE and non-LTE (NLTE)
approaches to the radiative transfer. In this manner, we obtain
values of log eo=8.64 (NLTE) and 8.94 (LTE) dex. We find an unsettling
fluctuation of the oxygen abundance over the field of view. This is
likely an artifact indicating that, even with this relatively refined
strategy, important physical ingredients are still missing in the
picture. By examining the spatial distribution of the abundance,
we estimate realistic confidence limits of approximately 0.1 dex.
Title: The Solar Oxygen Crisis: Probably Not the Last Word
Authors: Socas-Navarro, H.; Norton, A. A.
Bibcode: 2007ApJ...660L.153S
Altcode:
In this work we present support for recent claims that advocate a
downward revision of the solar oxygen abundance. Our analysis employs
spatially resolved spectropolarimetric observations including the Fe
I lines at 6302 Å and the O I infrared triplet around 7774 Å in the
quiet Sun. We used the Fe I lines to reconstruct the three-dimensional
thermal and magnetic structure of the atmosphere. The simultaneous
O I observations were then employed to determine the abundance of
oxygen at each pixel, using both LTE and non-LTE (NLTE) approaches
to the radiative transfer. In this manner, we obtain values of
logɛO=8.63 (NLTE) and 8.93 (LTE) dex. We find an unsettling
fluctuation of the oxygen abundance over the field of view. This is
likely an artifact indicating that, even with this relatively refined
strategy, important physical ingredients are still missing in the
picture. By examining the spatial distribution of the abundance,
we estimate realistic confidence limits of approximately 0.1 dex.
Title: A Note on Saturation Seen in the MDI/SOHO Magnetograms
Authors: Liu, Y.; Norton, A. A.; Scherrer, P. H.
Bibcode: 2007SoPh..241..185L
Altcode:
A type of saturation is sometimes seen in sunspot umbrae in MDI/SOHO
magnetograms. In this paper, we present the underlying cause of such
saturation. By using a set of MDI circular polarization filtergrams
taken during an MDI line profile campaign observation, we derive
the MDI magnetograms using two different approaches: the on-board
data processing and the ground data processing, respectively. The
algorithms for processing the data are the same, but the former
is limited by a 15-bit lookup table. Saturation is clearly seen in
the magnetogram from the on-board processing simulation, which is
comparable to an observed MDI magnetogram taken one and a half hours
before the campaign data. We analyze the saturated pixels and examine
the on-board numerical calculation method. We conclude that very low
intensity in sunspot umbrae leads to a very low depth of the spectral
line that becomes problematic when limited to the 15-bit on-board
numerical treatment. This 15-bit on-board treatment of the values
is the reason for the saturation seen in sunspot umbrae in the MDI
magnetogram. Although it is possible for a different type of saturation
to occur when the combination of a strong magnetic field and high
velocity moves the spectral line out of the effective sampling range,
this saturation is not observed.
Title: Magnetic Field Vector Retrieval With the Helioseismic and
Magnetic Imager
Authors: Borrero, J. M.; Tomczyk, S.; Norton, A.; Darnell, T.; Schou,
J.; Scherrer, P.; Bush, R.; Liu, Y.
Bibcode: 2007SoPh..240..177B
Altcode: 2006astro.ph.11565B
We investigate the accuracy to which we can retrieve the solar
photospheric magnetic field vector using the Helioseismic and Magnetic
Imager (HMI) that will fly onboard of the Solar Dynamics Observatory by
inverting simulated HMI profiles. The simulated profiles realistically
take into account the effects of the photon noise, limited spectral
resolution, instrumental polarization modulation, solar p modes, and
temporal averaging. The accuracy of the determination of the magnetic
field vector is studied by considering the different operational modes
of the instrument.
Title: Spectral Line Selection for HMI
Authors: Norton, A. A.; Pietarila Graham, J. D.; Ulrich, R. K.;
Schou, J.; Tomczyk, S.; Liu, Y.; Lites, B. W.; López Ariste, A.;
Bush, R. I.; Socas-Navarro, H.; Scherrer, P. H.
Bibcode: 2006ASPC..358..193N
Altcode:
We present information on two spectral lines, Fe I 6173 Å and Ni I 6768
Å, that were candidates for use in the Helioseismic and Magnetic Imager
(HMI) instrument. Both Fe I and Ni I profiles have clean continuum and
no blends that threaten performance. The higher Landé factor of Fe
I means its operational velocity range in regions of strong magnetic
field is smaller than for Ne I. Fe I performs better than Ni I for
vector magnetic field retrieval. Inversion results show that Fe I
consistently determines field strength and flux more accurately than
the Ni I line. Inversions show inclination and azimuthal errors are
recovered to ≈2° above 600 Mx/cm2 for Fe I and above
1000 Mx/cm2 for Ni I. The Fe I line was recommended, and
ultimately chosen, for use in HMI.
Title: Magnetic Field Vector Retrieval with HMI
Authors: Borrero, J. M.; Tomczyk, S.; Norton, A. A.; Darnell, T.;
Schou, J.; Scherrer, P.; Bush, R. I.; Lui, Y.
Bibcode: 2006ASPC..358..144B
Altcode:
The Helioseismic and Magnetic Imager (HMI), on board the Solar Dynamics
Observatory (SDO), will begin data acquisition in 2008. It will provide
the first full-disk, high temporal cadence observations of the full
Stokes vector with a 0.5 arcsec pixel size. This will allow for a
continuous monitoring of the Solar magnetic-field vector. HMI data will
advance our understanding of the small- and large-scale magnetic field
evolution, its relation to the solar and global dynamic processes,
coronal field extrapolations, flux emergence, magnetic helicity, and
the nature of the polar magnetic fields. We summarize HMI's expected
operation modes, focusing on the polarization cross-talk induced
by the solar oscillations, and how this affects the magnetic-field
vector determination.
Title: Spectral Line Selection for HMI: A Comparison of Fe I 6173
Å and Ni I 6768 Å
Authors: Norton, A. A.; Graham, J. Pietarila; Ulrich, R. K.; Schou,
J.; Tomczyk, S.; Liu, Y.; Lites, B. W.; Ariste, A. López; Bush,
R. I.; Socas-Navarro, H.; Scherrer, P. H.
Bibcode: 2006SoPh..239...69N
Altcode: 2006SoPh..tmp...88N; 2006astro.ph..8124N
We present a study of two spectral lines, Fe I 6173 Å and Ni I 6768 Å,
that were candidates to be used in the Helioseismic and Magnetic Imager
(HMI) for observing Doppler velocity and the vector magnetic field. The
line profiles were studied using the Mt. Wilson Observatory, the
Advanced Stokes Polarimeter and the Kitt Peak-McMath Pierce telescope
and one-meter Fourier transform spectrometer atlas. Both Fe I and Ni
I profiles have clean continua and no blends that threaten instrument
performance. The Fe I line is 2% deeper, 15% narrower, and has a 6%
smaller equivalent width than the Ni I line. The potential of each
spectral line to recover pre-assigned solar conditions is tested
using a least-squares minimization technique to fit Milne-Eddington
models to tens of thousands of line profiles that have been sampled
at five spectral positions across the line. Overall, the Fe I line
has a better performance than the Ni I line for vector-magnetic-field
retrieval. Specifically, the Fe I line is able to determine field
strength, longitudinal and transverse flux four times more accurately
than the Ni I line in active regions. Inclination and azimuthal angles
can be recovered to ≈2° above 600 Mx cm−2
for Fe I and above 1000 Mx cm−2 for Ni I. Therefore, the
Fe I line better determines the magnetic-field orientation in plage,
whereas both lines provide good orientation determination in penumbrae
and umbrae. We selected the Fe I spectral line for use in HMI due to
its better performance for magnetic diagnostics while not sacrificing
velocity information. The one exception to the better performance of the
Fe I line arises when high field strengths combine with high velocities
to move the spectral line beyond the effective sampling range. The
higher geff of Fe I means that its useful range of velocity
values in regions of strong magnetic field is smaller than Ni I.
Title: Analysis and visualization of small-scale structures occurring
in high-resolution MHD simulation
Authors: Norton, A.; Mininni, P.; Clyne, J.; Poquet, A.
Bibcode: 2006AGUFMSH13A0406N
Altcode:
We present methods of combining quantitative and visualization
techniques to identify and analyze structures, such as folds
and current sheets, resulting from three-dimensional MHD flow
simulation. These methods have been applied to the results of direct
numerical simulations with grids up to 15363 points. A desktop suite
of analysis and visualization tools ("Vapor") has been developed at
NCAR for interactive analysis of huge datasets. Simulation data on
very large grids are analyzed and visualized directly from a wavelet
representation, enabling interactive isolation of current sheets and
vortices, and analysis of their time-evolution. Flow integration and
volume rendering are applied to local regions in the grid, combined
with numerical analysis to characterize geometric structures that
result. These techniques enabled the discovery of parallel current
and vorticity sheets, found to form at the same spatial locations,
and the sheets were seen to further destabilize and fold or roll-up
after an initial exponential phase. A self-similar evolution of the
current and vorticity maxima was also identified and characterized
using these methods.
Title: The WASP Project and SuperWASP Camera
Authors: Pollacco, D.; Skillen, I.; Collier Cameron, A.; Christian,
D.; Irwin, J.; Lister, T.; Street, R.; West, R.; Clarkson, W.; Evans,
N.; Fitzsimmons, A.; Haswell, C.; Hellier, C.; Hodgkin, S.; Horne,
K.; Jones, B.; Kane, S.; Keenan, F.; Norton, A.; Osborne, J.; Ryans,
R.; Wheatley, P.
Bibcode: 2006Ap&SS.304..253P
Altcode: 2006Ap&SS.tmp..107P
The WASP project and infrastructure supporting the SuperWASP Facility
are described. As the instrument, reduction pipeline and archive system
are now fully operative we expect the system to have a major impact in
the discovery of bright exo-planet candidates as well in more general
variable star projects.
Title: Saturation Effect Seen In The MDI/SOHO Magnetograms
Authors: Liu, Yang; Norton, A. A.
Bibcode: 2006SPD....37.0715L
Altcode: 2006BAAS...38Q.230L
Saturation phenomenon is sometimes seen in the sunspots' umbrae
in SOHO/MDI magnetograms. In this paper, we present a research on
understanding the cause for this saturation. By using a set of MDI line
profile campaign data, we simulated the MDI measurement of magnetic
field, and compared it with one MDI magnetogram taken some times apart
of this line-profile data set. We found that the saturation areas
shown in the MDI magnetogram don't appear in the simulated magnetogram
from the line-profile data. We conclude that very low intensity in
the sunspots' umbrae that leads to failure of on-board computation,
is the reason causing the saturation.
Title: Recovering Solar Toroidal Field Dynamics from Sunspot Location
Patterns
Authors: Norton, Aimee A.; Gilman, Peter A.
Bibcode: 2005ApJ...630.1194N
Altcode: 2005astro.ph..6025N
We analyze both Kitt Peak magnetogram data and MDI continuum
intensity sunspot data to search for the following solar toroidal
band properties: width in latitude and the existence of a tipping
instability (longitudinal m=1 mode) for any time during the solar
cycle. In order to determine the extent to which we can recover the
toroidal field dynamics, we forward-model artificially generated sunspot
distributions from subsurface toroidal fields that we have assigned
certain properties. Sine-curve fitting of Kitt Peak magnetogram data
provided an upper limit of 15° to the tipping amplitude but could not
adequately separate the tip from the width of the toroidal band. We
then analyzed two sunspot distribution parameters using MDI and model
data: the average latitudinal separation of sunspot pairs as a function
of longitudinal separation and the number of sunspot pairs creating
a given angle with respect to the east-west direction. A toroidal
band of 10° width with a constant tipping of 5° best fits MDI data
early in the solar cycle, when the sunspot band is at high latitudes
(>18.5d). A toroidal band of 20° width with a tipping amplitude
decreasing in time from 5deg to 0deg best fits MDI
data late in the solar cycle when the sunspot band is at low latitudes
(<18.5d). Model data generated by untipped toroidal bands cannot fit
MDI high-latitude data using χ2 goodness-of-fit criteria and
can fit only one sunspot distribution parameter at low latitudes. Tipped
toroidal bands satisfy χ2 criteria at both high and low
latitudes for both sunspot distribution parameters. We conclude that
this is evidence to reject the null hypothesis-that toroidal bands
in the solar tachocline do not experience a tipping instability-in
favor of the hypothesis that the toroidal band experiences an m=1
tipping instability for a significant portion of the solar cycle. Our
finding that the band widens from 10° early in the solar cycle to 20°
late in the solar cycle may be explained in theory by magnetic drag
spreading the toroidal band due to altered flow along the tipped field
lines. Higher m modes, most notably m=2 and 6, are apparent in MDI data,
but further analysis is needed to determine this property in detail.
Title: The 2004 transit of Venus observed from the Open University
observatory
Authors: Chamber, P.; Cooper, A.; Norton, A.; Rix, A.; Stewart, M.;
Tanner, J. D.
Bibcode: 2005JBAA..115..144C
Altcode:
The purpose of this report is to compare the accuracies of five
different techniques for determining contact times. Recordings and
measurements of the transit were taken through four instruments,
the Open University's Meade LX200 for accurate timing of the third
contact, and a Meade ETX 105 for coverage of the whole transit. Both
were recorded on digital videotape. In addition, images were recorded
on a webcam on a 100mm telescope and visual estimates were made with an
ETX125. Analysis of the LX200 tapes gave an accuracy of ±5 seconds for
the time of contact. Methods are compared in the Conclusions. Several
other telescopes were used on campus for public displays of the
event. There was minimal black drop.
Title: Deciphering Toroidal Field Dynamics from Sunspot Statistics
Authors: Norton, A. A.; Gilman, P. A.
Bibcode: 2004AAS...204.5304N
Altcode: 2004BAAS...36..756N
We are interested in what solar surface magnetism can tell us about
the interior toroidal magnetic fields. Because some fraction of
solar surface magnetism must be a direct result of the dynamics of the
interior toroidal field, we feel it is worthwhile to study the patterns
of flux which emerge and attempt to recover the basic properties of
the toroidal bands and their time dependent behavior. New theory
predicts a global instability resulting in a tipping of the toroidal
bands with respect to the equatorial plane. We search for evidence of a
tipped toroidal field for some phases of the solar cycle by examining
the dominant latitude of emerging flux as a function of longitude. In
order to determine the extent to which we can recover the toroidal
field dynamics from observations, we use a model to artificially
generate sunspot distributions from subsurface toroidal fields that
we have assigned certain properties such as latitudinal width, peak
field strength and degree of tipping with respect to the equatorial
plane. Observational studies set an upper limit of 15 degrees to the
tipping angle. Model results which best fit the observed data are
those having a toroidal band with a tipping angle of 10 degrees at
high latitudes (early in the sunspot cycle) gradually decreasing to
0 degrees as the sunspot band migrates towards the equator.
Title: Magnetic Field-Minimum Intensity Correlation in Sunspots:
A Tool for Solar Dynamo Diagnostics
Authors: Norton, Aimee A.; Gilman, Peter A.
Bibcode: 2004ApJ...603..348N
Altcode:
Within a sunspot umbra, the continuum intensity is known to be
inversely proportional to the magnetic field strength. Studied less
is the relationship between the minimum continuum intensity and the
maximum field strength of different sunspots. We conduct a test of this
global relationship, using brightness ratios and magnetic field data
from the Advanced Stokes Polarimeter and the Michelson Doppler Imager
(MDI) for 10 sunspot umbrae of various sizes observed 1998 May-2003
June. We determine that the peak field strengths of sunspots can be
ascertained from a fit to their corresponding brightness ratios with
an accuracy of ~100 G, nearly twice the accuracy that a fit to the MDI
magnetogram values can provide. We then analyze continuum intensity
data from the MDI to characterize the distribution of sunspots as a
function of latitude. We hand-select 331 and 321 umbrae, respectively,
in the northern and southern hemispheres during Carrington rotations
1910-2003. Although the average location of sunspot eruption moves
equatorward throughout the solar cycle, the northern hemisphere shows
darker umbrae located systematically closer to the equator, while
brighter umbrae are found at higher latitudes. These findings confirm
the results of simulations that show strong flux emerging radially
while weak flux emerges nonradially, causing weak flux to emerge
poleward of its original toroidal field position. The average umbral
intensity decreased in the north through the solar cycle, reaching
a minimum intensity around sunspot maximum, possible evidence of the
toroidal field strength peaking at solar maximum. This finding is in
opposition to previous observations suggesting an increase late in
the cycle. The southern hemisphere umbral distribution appears more
disorganized and periodic in nature.
Title: Acceleration Effects in MDI Magnetogram Data
Authors: Norton, A.; Settele, A.
Bibcode: 2003SoPh..214..227N
Altcode:
Acceleration effects are found in the Michelson Doppler Imager
(MDI) magnetogram data because changes in the line profiles during
the 30-s measurement are introduced by underlying p-mode velocity
variations. This imparts an oscillatory component to the magnetic flux
signal. Simulated profiles using Maltby M and Harvard Smithsonian
Reference Atmospheres (HSRA) are shifted in accordance with a given
velocity amplitude and period and the MDI algorithm for data measurement
is applied. The simulated oscillatory component to the magnetic flux
density always has a phase difference with respect to the underlying
velocity of −90°. The maximum introduced RMS amplitude is a function
of velocity amplitude and field strength, but realistic errors are
on the order of 5/2000 G, or 0.25% of field strength. Comparison
of simulations with observations shows RMS amplitudes of MDI flux
density are much greater than predicted by this effect. A 2-component
HSRA model, tested to determine if stronger fields with smaller fill
factors could fit the data, still can not reproduce the observations. It
is concluded that oscillatory amplitudes of magnetic flux density
measured with MDI are not due to acceleration effects, although the
effect could contribute up to 25% of the measured amplitude. Attempts
to remove acceleration effects from the magnetic flux signal are not
successful. Also, we confirm that velocities measured in linearly
polarized light in the vicinity of a strong magnetic field contain
larger errors than velocities measured in circularly polarized light
(Yang and Norton, 2001).
Title: The Search for a Tipped Toroidal Field
Authors: Norton, A. A.; Gilman, P. A.; Henney, C. J.; Cally, P. S.
Bibcode: 2003SPD....34.1903N
Altcode: 2003BAAS...35..842N
A magnetic tipping instability of the tachocline toroidal field has
been predicted (Cally et al., 2003) that could produce a toroidal
field tipped with respect to the equatorial axis. One result of a
tipped toroidal band is the eruption of magnetic flux over a range of
latitudes from the same toroidal ring. The longitudinal dependence
of this flux emergence would contribute to non-axisymmetry of the
whole flux emergence pattern by giving it a longitudinal wavenumber
m=1 dependence. We search for evidence (or lack thereof) of a tipped
toroidal field for some phases of the solar cycle by examining the
dominant latitude of emerging flux as a function of longitude. We use
the existing observational data from Kitt Peak synoptic Carrington
Rotation magnetograms to identify the location of strong flux,
independently in each hemisphere, and test whether the location of
the flux reveals a pattern compatible with the tipping instability m=1.
Title: Observing MHD Oscillations in Sunspot
Authors: Norton, A. A.; Uitenbroek, H.
Bibcode: 2003PADEU..13..109N
Altcode:
Attempts to detect magnetohydrodynamic waves in the solar photosphere by
identifying oscillations in the magnetic field have proved problematic
due to suspected contributions from systematic temperature and density
fluctuations causing the spectral line formation height to vary, which
in turn samples a vertical gradient in the magnetic field strength. We
investigate this effect in sunspot umbrae and penumbrae through the
analysis of data obtained with the Advanced Stokes Polarimeter in
spectral lines with notoriously different temperature sensitivities. The
temporal behavior of the magnetic field strength in sunspot is presented
with special consideration to line formation physics occurring in
the dynamic solar atmosphere. These results are compared to forward
modeling of Stokes profiles with a radiative transfer code given a
sunspot atmosphere perturbed by an MHD oscillation.
Title: The Helioseismic and Magnetic Imager (HMI) on SDO: Full Vector
Magnetography with a Filtergraph Polarimeter
Authors: Graham, J. D.; Norton, A.; López Ariste, A.; Lites, B.;
Socas-Navarro, H.; Tomczyk, S.
Bibcode: 2003ASPC..307..131G
Altcode:
No abstract at ADS
Title: Vector Magnetic Field Measurement Capabiliity of the
Helioseismic and Magnetic Imager on SDO
Authors: Bush, R.; Scherrer, P.; Schou, J.; Liu, Y.; Tomczyk, S.;
Graham, J.; Norton, A.
Bibcode: 2002AGUFMSH52A0464B
Altcode:
The Helioseismic and Magnetic Imager (HMI) instrument has been selected
as part of the payload complement of the Solar Dynamics Observatory
Spacecraft. In this poster we describe the observing technique for
measuring solar vector magnetic fields. The expected performance of
the HMI instrument will be discussed including results of modeling
the observing lines and instrument.
Title: Observing MHD oscillations: the effects of vertical magnetic
gradients and thermodynamic fluctuations
Authors: Norton, A. A.; Uitenbroek, H.
Bibcode: 2002ESASP.505..281N
Altcode: 2002solm.conf..281N; 2002IAUCo.188..281N
Attempts to detect magnetohydrodynamic waves in the solar photosphere by
identifying oscillations in the magnetic field have proved problematic
due to suspected contributions from systematic temperature and density
fluctuations causing the spectral line formation height to vary, which
in turn samples a vertical gradient in the magnetic field strength. We
investigate this effect through the analysis of data obtained with the
Advanced Stokes Polarimeter in spectral lines with notoriously different
temperature sensitivities. The temporal behavior of the magnetic field
strength in sunspot and plage is presented with special consideration to
line formation physics occurring in the dynamic solar atmosphere. These
results are compared to forward modeling of Stokes profiles with a
radiative transfer code given a sunspot atmosphere perturbed by an MHD
oscillation. The possibility of a thermodynamic diagnostic is discussed.
Title: Inference of Solar Vector Magnetic Fields with Filtergraph
Instruments
Authors: Graham, J. D.; Lites, B. W.; López Ariste, A.; Norton, A.;
Socas-Navarro, H.; Tomczyk, S.
Bibcode: 2002AAS...200.5611G
Altcode: 2002BAAS...34..736G
We investigate the diagnostic potential of polarimetric measurements
with filtergraph instruments. Numerical simulations are used to
explore the possibility of inferring the magnetic field vector, its
filling factor, and the thermodynamics of model atmospheres when
only a few wavelength measurements are available. The simulations
assume the magnetic sun to be represented by Milne-Eddington (ME)
atmospheres. The results indicate that two wavelength measurements
are insufficient to reliably determine the magnetic parameters,
regardless of whether magnetograph techniques or least-squares fitting
inversions are used. However, as few as four measurements analyzed
with the inversion technique provide enough information to retrieve the
intrinsic magnetic field with an accuracy better than 10 generated by
more general models and ASP data passed through a simulated filtergraph.
Title: Systematic errors in measuring solar magnetic fields with a
FPI spectrometer and MDI
Authors: Settele, A.; Carroll, T. A.; Nickelt, I.; Norton, A. A.
Bibcode: 2002A&A...386.1123S
Altcode:
We will show the potential errors of observations using instruments,
where a line spectrum is obtained not instantly but by scanning through
the spectral line in time. We give two examples in simulations of
a sunspot observation with the measuring procedure of a typical
Fabry-Perot interferometer (FPI) spectrometer and the Michelson
Doppler Imager (MDI) on board of the Solar and Heliospheric Observatory
(SOHO). The effect described is inherent for observations with a low
intensity input signal, where the accumulation time for one image and
therefore the whole process of measuring a spectrum is relatively high
compared to the timescale of the underlying physical processes. We show
that our simulated data produce an error in magnetic field strength and
- in a time series - result in an apparent oscillation of the magnetic
field strength, while the input contained only velocity oscillations. As
the FPI spectrometer is being used more and more widely, one has to
be aware of the disadvantages and potential errors when interpreting
its data. We encourage every observer to do the simple simulation as
described for every specific setup used.
Title: Microquasars
Authors: Chadwick, P.; Norton, A.
Bibcode: 2001Obs...121..361C
Altcode:
No abstract at ADS
Title: Center-to-Limb Angle Dependence of Phases (v, δ|B|) Observed
with the Michelson Doppler Imager
Authors: Norton, A. A.; Ulrich, R. K.; Liu, Y.
Bibcode: 2001ApJ...561..435N
Altcode:
We test the hypothesis that phases between line-of-sight magnetic
and velocity signals depend upon center-to-limb angle if the magnetic
response to photospheric velocity perturbations is both magneto-acoustic
and Alfvénic. The Michelson Doppler Imager observes two bipolar active
regions. Sunspots exhibit the predicted shift toward phase angles
of 0° at the limb. Phases for the first sunspot group are -100°,
-55°, and -31° for data at center-to-limb angles of 14°, 41°,
and 60°. Phases for the second sunspot group are -107°, -66°, and
-14° for data at center-to-limb angles of 16°, 29°, and 57°. The
systematic march from ~-90° phase angles at disk center toward 0°
at the limb could be interpreted that Alfvén waves are more easily
observed at the limb. Unexpectedly, leading sunspot phases split
into positive and negative values as the far side sunspot fields turn
away from the observer. This cannot be explained mathematically by the
change of positive to negative field because phase angles are calculated
using δ|B|. Consistent wave propagation direction, or motion guided by
field lines, is implied since matter moving away from an observer along
negative lines must simultaneously move toward the observer on positive
lines to produce this result. Plage behavior is consistent with the
observed splitting of phases in the leading sunspot. All plage phases
are ~-90° at disk center but split into positive and negative groups
near the limb. Limbward plage phases are 17° for negative polarity
and -95° for positive polarity. Field configurations calculated from
the potential field model show phases differ between open loops, where
outgoing waves could exist, and closed loops whose finite length may
trap waves.
Title: Observed Phases (v, δB) as a Function of Center to Limb Angle
Authors: Norton, A. A.; Liu, Y.; Ulrich, R. K.
Bibcode: 2001ASPC..236..305N
Altcode: 2001aspt.conf..305N
No abstract at ADS
Title: Measuring Magnetic Oscillations in the Solar Photosphere:
Coordinated Observations with MDI, ASP and MWO
Authors: Norton, A. A.; Ulrich, R. K.
Bibcode: 2000SoPh..192..403N
Altcode:
A comprehensive observing effort was undertaken to simultaneously obtain
full Stokes profiles as well as longitudinal magnetogram maps of a
positive plage region on 8 December, 1998 with the Michelson Doppler
Imager, the Advanced Stokes Polarimeter and Mt. Wilson Observatory
magnetograph. We compare 1.2'' spatially-averaged signals of velocities
as well as filter magnetograph longitudinal flux signals with Stokes
determined fluctuations in filling factor, field inclination, magnetic
flux and field strength. The velocity signals are in excellent
agreement. Michelson Doppler Imager magnetic flux correlates best
with fluctuations in the Advanced Stokes Polarimeter filling factor,
not inclination angle or field strength. A correlated flux and filling
factor change in the absence of a field strength fluctuation can be
understood in terms of internally unperturbed flux tubes being buffeted
by external pressure fluctuations. The 12.5'' square aperture spatially
averaged Mt. Wilson magnetograph signals are compared with Michelson
Doppler Imager signals from the corresponding observing area. Velocity
signals are in superb agreement. Magnetic signals exhibit similar
oscillatory behavior. Lack of Advanced Stokes Polarimeter data for this
time excludes interpretation of magnetic fluctuations as due to filling
factor or field inclination angle. Mt. Wilson Observatory simultaneous
sampling of the nickel and sodium spectral line profiles with several
wing pairs allowed inter-comparison of signals from different heights
of formation. Slight phase shifts and large propagation speeds for the
velocity signals are indicative of modified standing waves. Phase speeds
associated with magnetic signals are characteristic of photospheric
Alfvén speeds for plage fields. The phase speed increase with height
agrees with the altitude dependence of the Alfvén speed. The observed
fluctuations and phases are interpreted as a superposition of signatures
from the horizontal component of the driving mechanism sweeping the
field lines in/out of the resolution area and the magnetic response
of the flux tube to this buffeting.
Title: Commission 46: Teaching of Astronomy: (Enseignement de
L'astronomie)
Authors: Fierro, Julieta; Isobe, Syuzo; Jones, B.; Batten, A.;
Arellano, A.; Gervaldi, M.; Guinan, E.; Tush, W.; Hoff, D.; Martinez,
P.; McNally, D.; Norton, A.; Narlikar, J.; Pasachoff, J.; Percy, J.;
Wentzel, D.
Bibcode: 2000IAUTA..24..423F
Altcode:
No abstract at ADS
Title: Study of solar photospheric MHD oscillations: Observations
with MDI, ASP and MWO
Authors: Norton, Aimee Ann
Bibcode: 2000PhDT........90N
Altcode:
Magnetodydrodynamical waves are expected to be an important energy
transport mechanism in the solar atmosphere. This thesis uses data
from a spectro-polarimeter and longitudinal magnetographs to study
characteristics of magneto-hydrodynamical oscillations at photospheric
heights. Significant oscillatory magnetic power is observed with the
Michelson Doppler Imager in three frequency regimes: 0.5--1.0, 3.0--3.5
and 5.5--6.0 mHz corresponding to timescales of magnetic evolution,
p-modes and the three minute resonant sunspot oscillation. Spatial
distribution of magnetogram oscillatory power exhibits the same general
features in numerous datasets. Low frequency magnetogram power is found
in rings with filamentary structure surrounding sunspots. Five minute
power peaks in extended regions of plage. Three minute oscillations
are observed in sunspot umbra. Phase angles between velocity and
magnetic fluctuations are found to be approximately -90°, a signature
of magnetoacoustic waves, in disk-center active region data. Phase
dependence upon observation angle is established through sunspot
values decreasing from -100° at disk-center towards -31° at the
limb, confirming greater Alfen wave visibility at the limb. Consistent
propagation direction or field-aligned velocities explain an unexpected
phase jump from negative to positive values for divergent sunspot
fields observed away from disk-center. Simultaneously obtained Stokes
profiles and longitudinal magnetogram maps of a positive plage region
provide time series which could be compared. The velocity signals are in
excellent agreement. Magnetic flux correlates best with fluctuations in
filling factor, not inclination angle or field strength, implying the
responsible physical mechanism is internally unperturbed flux tubes
being buffeted by external pressure fluctuations. Sampling signals
from different heights of formation provides slight phase shifts
and large propagation speeds for velocity, indicative of modified
standing waves. Phase speeds associated with magnetic signals are
characteristic of photospheric Alfven speeds for plage fields. The
phase speed increase with height agrees with the altitude dependence of
the Alfven speed. Observed fluctuations, phase angles and phase lags
are interpreted as a superposition of signatures from the horizontal
component of the driving mechanism sweeping the field lines in/out
of the resolution area and the magnetic response of the flux tube to
this buffeting.
Title: Characteristics of MHD Oscillations Observed with MDI
Authors: Norton, A. A.; Ulrich, R. K.; Bush, R. I.; Tarbell, T. D.
Bibcode: 1999ASPC..184..136N
Altcode:
We report on the spatial distribution of magnetic oscillatory power and
phase angles between velocity and magnetic signals as observed with the
Michelson Doppler Imager. The dataset is 151.25arcsec x 151.25arcsec
containing sunspot from Dec 2, 1997 with a temporal sampling interval
of 60 seconds and spatial sampling of 0.605arcsec. Simultaneously
observed continuum intensity and surface velocity accompany the magnetic
information. We focus on three frequency regimes: 0.5-1.0, 3.0-3.5 and
5.5-6.0 mHz corresponding roughly to timescales of magnetic evolution,
p-modes and the 3 minute resonant sunspot oscillation. Significant low
frequency magnetic power is found in lower flux pixels, 100-300 Gauss,
in a striking ring with filamentary structure surrounding sunspot. Five
minute oscillatory magnetic power peaks in extended regions of flux
600-800 Gauss. The 3 minute oscillation is observed in sunspot umbra
in pixels whose flux measures 1300-1500 Gauss. Phase angles of -90°
between velocity and magnetic flux in the 3.0-3.5 and 5.5-6.0 mHz
regimes suggest the MHD oscillations are magnetoacoustic in nature.
Title: Characteristics of Magnetohydrodynamic Oscillations Observed
with the Michelson Doppler Imager
Authors: Norton, A. A.; Ulrich, R. K.; Bush, R. I.; Tarbell, T. D.
Bibcode: 1999ApJ...518L.123N
Altcode: 1999astro.ph..7256N
We report on the spatial distribution of the magnetogram oscillatory
power and the phase angles between velocity and magnetogram signals
as observed with the Michelson Doppler Imager. The data set is
151.25" × 151.25", containing the sunspot from 1997 December 2
with a temporal sampling interval of 60 s and spatial sampling of
0.605". The simultaneously observed continuum intensity and surface
velocity accompany the magnetic information. We focus on three frequency
regimes: 0.5-1.0, 3.0-3.5, and 5.5-6.0 mHz, corresponding roughly to
timescales of magnetic evolution, p-modes, and the 3 minute resonant
sunspot oscillation. Significant low-frequency magnetogram power
is found in lower flux pixels, 100-300 G, in a striking ring with
filamentary structure surrounding the sunspot. The 5 minute magnetogram
power peaks in extended regions of flux that measure 600-800 G. The
3 minute oscillation is observed in the sunspot umbra in pixels whose
flux measures 1300-1500 G. Phase angles of approximately -90° between
velocity and magnetic flux in the 3.0-3.5 and 5.5-6.0 mHz regimes are
found in regions of significant cross amplitude.
Title: MHD Wave Search: Coordinated ASP/MDI Observations
Authors: Norton, A. A.; Ulrich, R. K.
Bibcode: 1999soho....9E..75N
Altcode:
We search for the signature of MHD waves in data obtained during
coordinated observations with the Advanced Stokes Polarimeter and the
Michelson Doppler Imager on Dec 8, 1998. MDI observed a small sunspot
and surrounding plage in the hi-resolution field of view for roughly
five hours. During this time, the 84.7'' ASP slit repeatedly scanned
a 4.2'' area within the MDI field of view observing plage and sunspot
for 45 minutes each. We compare the MDI filtergram signals to the full
Stokes data of the ASP. The spatial distribution of MDI magnetogram
power is presented in grayscale plots to provide contextual information
regarding ASP slit placement.
Title: MHD oscillations observed in the solar photosphere with the
Michelson Doppler Imager
Authors: Norton, A.; Ulrich, R. K.; Bogart, R. S.; Bush, R. I.;
Hoeksema, J. T.
Bibcode: 1998IAUS..185..453N
Altcode:
Magnetohydrodynamic oscillations are observed in the solar photosphere
with the Michelson Doppler Imager (MDI). Images of solar surface
velocity and magnetic field strength with 4'' spatial resolution
and a 60 second temporal resolution are analyzed. A two dimensional
gaussian aperture with a FWHM of 10'' is applied to the data in
regions of sunspot, plage and quiet sun and the resulting averaged
signal is returned each minute. Significant power is observed in the
magnetic field oscillations with periods of five minutes. The effect
of misregistration between MDI's left circularly polarized (LCP) and
right circularly polarized (RCP) images has been investigated and is
found not to be the cause of the observed magnetic oscillations. It is
assumed that the large amplitude acoustic waves with 5 minute periods
are the driving mechanism behind the magnetic oscillations. The nature
of the magnetohydrodynamic oscillations are characterized by their
phase relations with simultaneously observed solar surface velocity
oscillations.
Title: Long Term Multiwavelength Monitoring of High Mass X-ray
Binaries
Authors: Roche, P.; Coe, M.; Everall, C.; Fabregat, J.; Reglero, V.;
Prince, T.; Chakrabarty, D.; Bildsten, L.; Norton, A.; Unger, S.;
Buckley, D.
Bibcode: 1994AIPC..308..487R
Altcode: 1994exrb.conf..487R
We present a summary of the Southampton/Valencia/Caltech/SAAO campaign
for long-term, multiwavelength monitoring of high mass x-ray binaries. A
number of sources have been observed in unusual states, including
detailed studies of the Be/x-ray transients X Persei (4U0352+309: disk
loss state, 1988-1990), 3A1118-616 (transient outburst, Jan. 1991),
GX 1+4 (outburst Sept. 1993) and EXO2030+375 (periastron passsage,
June 1993).
Title: The Identification of Potential Counterparts to X-Ray Binaries
Using Cosmos
Authors: Roche, P.; Norton, A.
Bibcode: 1992ASSL..174..431R
Altcode: 1992doss.conf..431R
No abstract at ADS