Author name code: habbal
ADS astronomy entries on 2022-09-14
author:"Habbal, Shadia"
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Title: The Solar Minimum Eclipse of 2019 July 2. II. The First
Absolute Brightness Measurements and MHD Model Predictions of Fe X,
XI, and XIV out to 3.4 R ⊙
Authors: Boe, Benjamin; Habbal, Shadia; Downs, Cooper; Druckmüller,
Miloslav
Bibcode: 2022ApJ...935..173B
Altcode: 2022arXiv220610106B
We present the spatially resolved absolute brightness of the Fe X,
Fe XI, and Fe XIV visible coronal emission lines from 1.08 to 3.4 R
⊙, observed during the 2019 July 2 total solar eclipse
(TSE). The morphology of the corona was typical of solar minimum,
with a dipole field dominance showcased by large polar coronal holes
and a broad equatorial streamer belt. The Fe XI line is found to be
the brightest, followed by Fe X and Fe XIV (in disk B ⊙
units). All lines had brightness variations between streamers and
coronal holes, where Fe XIV exhibited the largest variation. However,
Fe X remained surprisingly uniform with latitude. The Fe line
brightnesses are used to infer the relative ionic abundances and
line-of-sight-averaged electron temperature (T e )
throughout the corona, yielding values from 1.25 to 1.4 MK in coronal
holes and up to 1.65 MK in the core of streamers. The line brightnesses
and inferred T e values are then quantitatively compared
to the Predictive Science Inc. magnetohydrodynamic model prediction for
this TSE. The MHD model predicted the Fe lines rather well in general,
while the forward-modeled line ratios slightly underestimated the
observationally inferred T e within 5%-10% averaged over
the entire corona. Larger discrepancies in the polar coronal holes
may point to insufficient heating and/or other limitations in the
approach. These comparisons highlight the importance of TSE observations
for constraining models of the corona and solar wind formation.
Title: Insights into the Source Regions of the Solar Wind from Total
Solar Eclipse Observations
Authors: Habbal, Shadia; Druckmuller, Miloslav; Alzate, Nathalia;
Ding, Adalbert; Boe, Benjamin
Bibcode: 2021AGUFMSH12B..01H
Altcode:
Knowledge of the plasma parameters at the source regions of the
solar wind at the Sun is critical for solar wind models to explore
the fundamental physical processes that drive the different solar
wind streams observed in-situ. At present, total solar eclipse
observations offer outstanding opportunities for the inference of these
parameters. These opportunities arise from the spatial extent of their
field of view, starting from the solar surface out to several solar
radii, and the unique diagnostic tools offered by emission from white
light and coronal forbidden lines within the 400 to 1100 nm wavelength
range. This presentation capitalizes on a unique complement of white
light and multi-wavelength eclipse observations acquired between 2006
and 2020 (i.e. straddling more than a full solar cycle) and in-situ
measurements of Fe ion charge states and proton speeds from ACE in
the ecliptic plane over the same time period, as recently reported
by Habbal et al. (ApJL, 911, L4, 2021). These observations reveal
the existence of a quiescent solar wind flow, dominated by Fe10+
both in the corona and in-situ. These streams, which have speeds
ranging from 300 to 700 km/s, originate ubiquitously in the corona from
sources with a well-constrained electron temperature of 1.2 ± 0.1 MK,
independently of solar activity. This complement of observations also
shows that another type of solar wind, referred to as the dynamic wind,
is characterized by highly variable Fe charge states and solar wind
speeds, driven by prominence and active region activity at the base of
the corona. This complement of remote sensing and in-situ measurements
thus yield new insights into the sources of the solar wind at the
Sun, and provide novel constraints on the plasma parameters at these
sources including the electron temperature and the Fe charge state in
the expanding corona.
Title: The Double-bubble Coronal Mass Ejection of the 2020 December
14 Total Solar Eclipse
Authors: Boe, Benjamin; Yamashiro, Bryan; Druckmuller, Miloslav;
Habbal, Shadia
Bibcode: 2021AGUFMSH35B2062B
Altcode:
We present observations of the full extent of a 'double-bubble'
CME structure from the solar surface out to over 5 solar radii,
as captured in white light during the 2020 December 14 total solar
eclipse in Argentina. Its evolution through the corona was recorded
from two observing sites separated by 13 minutes in their times
of totality. The eclipse observations are complemented by several
space-based observations and we characterize the magnetic field
with a potential field source surface model. This CME event itself
is of particular interest, as it demonstrates interactions between a
prominence channel and an active region that led to the double-bubble
structure. Despite the plethora of space-based observations, only the
eclipse data are able to observe the full extent of the CME from the
solar limb out to several solar radii with a high spatial resolution
and yield a detailed study of this unique CME. This work has been
published as Boe et al. (2021), ApJL 914:L39.
Title: A new color-based method for K- and F-corona extraction
Authors: Boe, Benjamin; Habbal, Shadia; Downs, Cooper; Druckmuller,
Miloslav
Bibcode: 2021AGUFMSH15D2057B
Altcode:
We introduce a novel inversion method to separate emission from the
K-corona (electron) and F-corona (dust) continua using unpolarized
total brightness (tB) observations. We apply the new method to five
0.5 nm bandpass images between 529.5 and 788.4 nm acquired during
the 2019 July 2 Total Solar Eclipse (TSE) in Chile and Argentina. The
wavelength dependence relative to the photosphere (i.e. color) of the
F-corona itself is used to infer the tB of the K- and F-corona for
each line of sight. We compare our K-corona emission results with
the Mauna Loa Solar Observatory (MLSO) K-Cor observations from the
day of the eclipse, and the forward modeled K-corona intensity from
the Predictive Science Inc. (PSI) MHD model prediction. Our results
are generally consistent with earlier studies and match both the MLSO
data and PSI-MHD predictions quite well, supporting the validity of
our approach and of the PSI-MHD model. TSEs continue to provide unique
opportunities to quantify the properties of the elusive 'middle' corona,
as demonstrated here. This work has been published as Boe et al. (2021),
ApJ 912:44.
Title: Solar Filament Channels: Magnetic Forces Shaping Multi-Scale
Coronal Dynamics
Authors: Panasenco, Olga; Habbal, Shadia
Bibcode: 2021AGUFMSH25F2148P
Altcode:
The solar dynamo and plasma convection produce three main observed
structures extending from the solar surface into the corona active
regions, solar filaments (prominences when observed at the limb)
and coronal holes. Each of these three key features is interlinked
with the other two in its evolution and dynamics. Active regions,
often with underlying sunspots, can form clusters of magnetic
activity. When active regions decay, solar filaments form at their
boundaries separating opposite magnetic polarities. Alternatively,
decaying active regions can give rise to coronal holes in the presence
of the magnetic flux imbalance. Accumulation of the magnetic flux
at the coronal hole boundaries also creates conditions for filament
formations. Polar crown filaments are permanently present at the
boundaries of the polar coronal holes. Polar coronal holes and their
equatorial extensions, middle-latitude and equatorial coronal holes
can create coronal pseudostreamers when have the same polarity. The
pseudostreamer bases at the photospheric level are multipolar, often
observed as tripolar magnetic configurations with two neutral lines
where twin solar filaments can form separating coronal holes. Solar
wind properties measured in situ by multiple spacecraft show that the
soar wind from pseudostreamers could be fast, Alfvenic slow, or in
between. The resulting wind type depends on the presence or absence of
solar filament channels with or without filaments at the pseudostreamer
base. Here we discuss the energization of the solar corona at different
temporal and spatial scales. We present observations of the extended
solar corona and corresponding PFSS modeling of the coronal magnetic
field to resolve a mystery of sharp temperature boundaries between
large-scale coronal structures and their link to the presence or
absence of filament channels.
Title: Exploring the Solar Wind from Its Source on the Corona into
the Inner Heliosphere during the First Solar Orbiter-Parker Solar
Probe Quadrature
Authors: Telloni, Daniele; Andretta, Vincenzo; Antonucci, Ester;
Bemporad, Alessandro; Capuano, Giuseppe E.; Fineschi, Silvano;
Giordano, Silvio; Habbal, Shadia; Perrone, Denise; Pinto, Rui F.;
Sorriso-Valvo, Luca; Spadaro, Daniele; Susino, Roberto; Woodham, Lloyd
D.; Zank, Gary P.; Romoli, Marco; Bale, Stuart D.; Kasper, Justin C.;
Auchère, Frédéric; Bruno, Roberto; Capobianco, Gerardo; Case,
Anthony W.; Casini, Chiara; Casti, Marta; Chioetto, Paolo; Corso,
Alain J.; Da Deppo, Vania; De Leo, Yara; Dudok de Wit, Thierry;
Frassati, Federica; Frassetto, Fabio; Goetz, Keith; Guglielmino,
Salvo L.; Harvey, Peter R.; Heinzel, Petr; Jerse, Giovanna; Korreck,
Kelly E.; Landini, Federico; Larson, Davin; Liberatore, Alessandro;
Livi, Roberto; MacDowall, Robert J.; Magli, Enrico; Malaspina, David
M.; Massone, Giuseppe; Messerotti, Mauro; Moses, John D.; Naletto,
Giampiero; Nicolini, Gianalfredo; Nisticò, Giuseppe; Panasenco,
Olga; Pancrazzi, Maurizio; Pelizzo, Maria G.; Pulupa, Marc; Reale,
Fabio; Romano, Paolo; Sasso, Clementina; Schühle, Udo; Stangalini,
Marco; Stevens, Michael L.; Strachan, Leonard; Straus, Thomas; Teriaca,
Luca; Uslenghi, Michela; Velli, Marco; Verscharen, Daniel; Volpicelli,
Cosimo A.; Whittlesey, Phyllis; Zangrilli, Luca; Zimbardo, Gaetano;
Zuppella, Paola
Bibcode: 2021ApJ...920L..14T
Altcode: 2021arXiv211011031T
This Letter addresses the first Solar Orbiter (SO)-Parker Solar
Probe (PSP) quadrature, occurring on 2021 January 18 to investigate
the evolution of solar wind from the extended corona to the inner
heliosphere. Assuming ballistic propagation, the same plasma volume
observed remotely in the corona at altitudes between 3.5 and 6.3
solar radii above the solar limb with the Metis coronagraph on SO
can be tracked to PSP, orbiting at 0.1 au, thus allowing the local
properties of the solar wind to be linked to the coronal source region
from where it originated. Thanks to the close approach of PSP to the
Sun and the simultaneous Metis observation of the solar corona, the
flow-aligned magnetic field and the bulk kinetic energy flux density
can be empirically inferred along the coronal current sheet with an
unprecedented accuracy, allowing in particular estimation of the Alfvén
radius at 8.7 solar radii during the time of this event. This is thus
the very first study of the same solar wind plasma as it expands from
the sub-Alfvénic solar corona to just above the Alfvén surface.
Title: The Double-bubble Coronal Mass Ejection of the 2020 December
14 Total Solar Eclipse
Authors: Boe, Benjamin; Yamashiro, Bryan; Druckmüller, Miloslav;
Habbal, Shadia
Bibcode: 2021ApJ...914L..39B
Altcode: 2021arXiv210604027B
Total solar eclipses (TSEs) continue to provide an invaluable platform
for exploring the magnetic topology of the solar corona and for
studying dynamic events such as coronal mass ejections (CMEs)with a
higher spatial resolution over a larger spatially continuous extent
than is possible to achieve with any other method at present. In this
Letter, we present observations of the full extent of a double-bubble
CME structure from the solar surface out to over 5 solar radii,
as captured during the 2020 December 14 TSE. Its evolution through
the corona was recorded from two observing sites separated by 13
minutes in their times of totality. The eclipse observations are
complemented by a plethora of space-based observations including:
Extreme Ultraviolet observations of the solar disk and low corona from
SDO/AIA and STEREO-A/EUVI, white-light coronagraph observations from
SOHO/LASCO-C2, radio from STEREO-A/WAVES and WIND/WAVES, and X-ray from
GOES-16. We also characterize the magnetic field with a potential field
source surface model. This CME event itself is of particular interest,
as it demonstrates interactions between a prominence channel and an
active region that led to the double-bubble structure. Despite the
plethora of space-based observations, only the eclipse data are able
to provide the proper context to connect these observations and yield
a detailed study of this unique CME.
Title: The Color and Brightness of the F-corona Inferred from the
2019 July 2 Total Solar Eclipse
Authors: Boe, Benjamin; Habbal, Shadia; Downs, Cooper; Druckmüller,
Miloslav
Bibcode: 2021ApJ...912...44B
Altcode: 2021arXiv210302113B
Total solar eclipses (TSEs) provide a unique opportunity to quantify
the properties of the K-corona (electrons), F-corona (dust), and
E-corona (ions) continuously from the solar surface out to a few solar
radii. We apply a novel inversion method to separate emission from
the K- and F-corona continua using unpolarized total brightness (tB)
observations from five 0.5 nm bandpasses acquired during the 2019 July
2 TSE between 529.5 and 788.4 nm. The wavelength dependence relative
to the photosphere (i.e., color) of the F-corona itself is used to
infer the tB of the K- and F-corona for each line of sight. We compare
our K-corona emission results with the Mauna Loa Solar Observatory
(MLSO) K-Cor polarized brightness (pB) observations from the day of the
eclipse, and the forward modeled K-corona intensity from the Predictive
Science Inc. (PSI) magnetohydrodynamic (MHD) model prediction. Our
results are generally consistent with previous work and match both the
MLSO data and PSI-MHD predictions quite well, supporting the validity
of our approach and of the PSI-MHD model. However, we find that the
tB of the F-corona is higher than expected in the low corona, perhaps
indicating that the F-corona is slightly polarized—challenging the
common assumption that the F-corona is entirely unpolarized.
Title: Identifying the Coronal Source Regions of Solar Wind Streams
from Total Solar Eclipse Observations and in situ Measurements
Extending over a Solar Cycle
Authors: Habbal, Shadia R.; Druckmüller, Miloslav; Alzate, Nathalia;
Ding, Adalbert; Johnson, Judd; Starha, Pavel; Hoderova, Jana; Boe,
Benjamin; Constantinou, Sage; Arndt, Martina
Bibcode: 2021ApJ...911L...4H
Altcode: 2021arXiv210302128H
This letter capitalizes on a unique set of total solar eclipse
observations acquired between 2006 and 2020 in white light, Fe XI
789.2 nm (Tfexi = 1.2 ± 0.1 MK), and Fe XIV 530.3 nm
(Tfexiv = 1.8 ± 0.1 MK) emission complemented by in
situ Fe charge state and proton speed measurements from Advanced
Composition Explorer/SWEPAM-SWICS to identify the source regions of
different solar wind streams. The eclipse observations reveal the
ubiquity of open structures invariably associated with Fe XI emission
from Fe10+ and hence a constant electron temperature,
Tc = Tfexi, in the expanding corona. The in
situ Fe charge states are found to cluster around Fe10+,
independently of the 300-700 km s-1 stream speeds,
referred to as the continual solar wind. Thus, Fe10+
yields the fiducial link between the continual solar wind and its
Tfexi sources at the Sun. While the spatial distribution of
Fe XIV emission from Fe13+ associated with streamers changes
throughout the solar cycle, the sporadic appearance of charge states
>Fe11+ in situ exhibits no cycle dependence regardless
of speed. These latter streams are conjectured to be released from hot
coronal plasmas at temperatures ≥Tfexiv within the bulge
of streamers and from active regions, driven by the dynamic behavior
of prominences magnetically linked to them. The discovery of continual
streams of slow, intermediate, and fast solar wind characterized by the
same Tfexi in the expanding corona places new constraints
on the physical processes shaping the solar wind.
Title: Measuring Solar Differential Rotation with an Iterative Phase
Correlation Method
Authors: Hrazdíra, Zdeněk; Druckmüller, Miloslav; Habbal, Shadia
Bibcode: 2021ApJS..252....6H
Altcode:
A reliable inference of the differential rotation rate of the solar
photosphere is essential for models of the solar interior. The
work presented here is based on a novel iterative phase correlation
technique, which relies on the measurement of the local shift, at
the central meridian, between two images separated by a given time
interval. Consequently, it does not require any specific reference
features, such as sunspots or supergranules, nor extended observations
spanning several months. The reliability of the method is demonstrated
by applying it to high spatial and temporal resolution continuum
images of the solar photosphere, at 6173 Å, acquired by the Solar
Dynamics Observatory Helioseismic and Magnetic Imager over one complete
Carrington rotation. The data selected covers the time period of 2020
January 1 to February 2. The method was applied to one day, and to the
full time interval. The differential rotation rate derived using this
feature-independent technique yields values that fall in the middle
of the range of those published to date. Most importantly, the method
is suited for the production of detailed rotation maps of the solar
photosphere. It also enables the visual and quantitative identification
of the north-south asymmetry in the solar differential rotation rate,
when present.
Title: Total Solar Eclipse Observations: A Treasure Trove from the
Source and Acceleration Regions of the Solar Wind
Authors: Habbal, Shadia Rifai
Bibcode: 2020JPhCS1620a2006H
Altcode:
A comprehensive exploration of the inner corona, namely the spatial span
starting from the solar surface out to a few solar radii, is essential
for investigating the physical processes responsible for its quiescent
and dynamic state. Such an exploration encompasses the source regions
of the solar wind, and is thus essential for reliably establishing
their link to in-situ measurements, including those from the more
recent Parker Solar Probe mission. Total solar eclipses are the only
platform available at present to fulfill these requirements, as they
offer a spatially uninterrupted diagnosis of the inner corona through
multi-wavelength imaging and spectroscopy. This review highlights
results from almost two decades of eclipse observations. Particular
emphasis is placed on the discovery of the complexity of coronal
structures, in particular at the source regions of the solar wind,
directly connected to prominences. Complex structures include different
manifestations of waves and plasma instabilities. Imaging in coronal
emission lines yields the only diagnostic tool, known to date, for the
empirical inference of the freeze-in distance of heavy ions. Imaging
also enables the mapping of the electron temperature in the inner
corona, and its changes in response to the passage of a coronal mass
ejection (CME). Furthermore, spectroscopic observations reveal that
cool prominence material associated with a CME, travels in tandem,
unscathed, into interplanetary space. Multi-wavelength imaging and
spectroscopy during total solar eclipses thus yield a treasure trove
from the sources and acceleration regions of the solar wind, which beg
continued exploitation in search of signatures of coronal heating and
solar wind acceleration processes.
Title: Coronal Magnetic Field Topology From Total Solar Eclipse
Observations
Authors: Boe, B.; Habbal, S.; Druckmuller, M.
Bibcode: 2020SPD....5121003B
Altcode:
We present the topology of the coronal magnetic field continuously
between 1 and 6 Rs, as quantitatively inferred for 14 unique eclipse
coronae that span almost two complete solar cycles. The magnetic field
topology was traced automatically in processed white-light eclipse
images using the Rolling Hough Transform (RHT). We find that the
direction of the coronal magnetic field does not become radial until at
least 3 Rs, which challenges the common assumption of a radial field
at 2.5 Rs in source surface driven modeling (i.e. PFSS). In addition,
we find an abundance of field lines which extend continuously from the
solar surface out to several solar radii at all latitudes, regardless
of the presence of coronal holes, and a high variance in radiality
between 1.5 and 3 Rs at different latitudes and phases of the solar
cycle. The most non-radial coronal field topologies are found to occur
above regions with weaker magnetic field strengths in the photosphere,
while stronger photospheric fields are associated with highly radial
field lines in the corona. These results have implications for testing
and constraining coronal magnetic field models, and for linking in
situ solar wind measurements to their sources at the Sun.
Title: Coronal Magnetic Field Topology from Total Solar Eclipse
Observations
Authors: Boe, Benjamin; Habbal, Shadia; Druckmüller, Miloslav
Bibcode: 2020ApJ...895..123B
Altcode: 2020arXiv200408970B
Measuring the global magnetic field of the solar corona remains
exceptionally challenging. The fine-scale density structures observed in
white-light images taken during total solar eclipses are currently the
best proxies for inferring the magnetic field direction in the corona
from the solar limb out to several solar radii (R⊙). We
present, for the first time, the topology of the coronal magnetic
field continuously between 1 and 6 R⊙, as quantitatively
inferred with the rolling Hough transform for 14 unique eclipse
coronae that span almost two complete solar cycles. We find that
the direction of the coronal magnetic field does not become radial
until at least 3 R⊙, with a high variance between 1.5
and 3 R⊙ at different latitudes and phases of the solar
cycle. We find that the most nonradial coronal field topologies occur
above regions with weaker magnetic field strengths in the photosphere,
while stronger photospheric fields are associated with highly radial
field lines in the corona. In addition, we find an abundance of field
lines that extend continuously from the solar surface out to several
solar radii at all latitudes, regardless of the presence of coronal
holes. These results have implications for testing and constraining
coronal magnetic field models, and for linking in situ solar wind
measurements to their sources at the Sun.
Title: Solar physics in the 2020s: DKIST, parker solar probe, and
solar orbiter as a multi-messenger constellation
Authors: Martinez Pillet, V.; Tritschler, A.; Harra, L.; Andretta, V.;
Vourlidas, A.; Raouafi, N.; Alterman, B. L.; Bellot Rubio, L.; Cauzzi,
G.; Cranmer, S. R.; Gibson, S.; Habbal, S.; Ko, Y. K.; Lepri, S. T.;
Linker, J.; Malaspina, D. M.; Matthews, S.; Parenti, S.; Petrie, G.;
Spadaro, D.; Ugarte-Urra, I.; Warren, H.; Winslow, R.
Bibcode: 2020arXiv200408632M
Altcode:
The National Science Foundation (NSF) Daniel K. Inouye Solar Telescope
(DKIST) is about to start operations at the summit of Haleakala
(Hawaii). DKIST will join the early science phases of the NASA
and ESA Parker Solar Probe and Solar Orbiter encounter missions. By
combining in-situ measurements of the near-sun plasma environment and
detail remote observations of multiple layers of the Sun, the three
observatories form an unprecedented multi-messenger constellation to
study the magnetic connectivity inside the solar system. This white
paper outlines the synergistic science that this multi-messenger
suite enables.
Title: Iterative Phase Correlation Algorithm for High-precision
Subpixel Image Registration
Authors: Hrazdíra, Zdenek; Druckmüller, Miloslav; Habbal, Shadia
Bibcode: 2020ApJS..247....8H
Altcode:
Many astrophysical observations and measurement techniques that
rely on data from images include an image registration step. The
results of such techniques thus heavily rely on the precision of
the registration. We present an Iterative Phase Correlation (IPC)
algorithm, which is an extension of the well-known phase correlation
method of image registration and is ideally suited for problems, where
the subpixel registration accuracy plays a crucial role. Furthermore,
a sophisticated and reliable method of optimal IPC parameter estimation
is described. The paper includes examples of such optimized parameters
for Solar Dynamics Observatory (SDO)/Helioseismic and Magnetic
Imager, SDO/Atmospheric Imaging Assembly, and Solar Terrestrial
Relations Observatory A/B Sun Earth Connection Coronal and Heliospheric
Investigation images. The new method (both with or without the parameter
optimization step) significantly outperforms standard image registration
methods, such as (non-iterative) phase correlation or (normalized)
cross correlation in the sense of subpixel accuracy. A step-by-step
pseudocode implementation is also included.
Title: On the Inference of Fe+9 Ion Temperature in the
Solar Corona from the 2019 July 2 Total Solar Eclipse
Authors: Yamashiro, B.; Habbal, S.; Ding, A.; Nassir, M.
Bibcode: 2020AAS...23521002Y
Altcode:
We report here on the first inferences of the Fe+9 ion
temperature derived from spectroscopic observations of the Fe X 637.4nm
emission line, over a heliocentric distance range of 1.075-1.368
R⊙ within two polar coronal holes. The observations
were conducted during the total solar eclipse of 2019 July 2 at the
Cerro Tololo International Observatory. Our inferences are compared
with published values for Mg+9 and O+5 from
ultraviolet observations from UVCS/SOHO. Fe+9 exhibits the
same consistent trend of an increase in ionic temperature as a function
of distance. At the closest distance to the Sun, the Fe+9
temperature is ~1.17×107 K and ~2.31×107 K
at 1.368 R⊙, compared to the 106 K electron
temperature. Such inferences provide critical input parameters
for models exploring the physical mechanisms to heat the corona and
accelerate the solar wind. This work was funded by NSF grant AGS-1834662
and AST-1839436 to the University of Hawaíi at Manoa.
Title: Observations of a Polar Coronal Jet During the 21 August 2017
Total Solar Eclipse
Authors: Constantinou, S. L.; Habbal, S.; Druckmuller, M.; Boe, B.;
Hoderova, J.; Solar Wind Sherpas
Bibcode: 2020AAS...23522003C
Altcode:
During the 21 August 2017 total solar eclipse, the solar corona
was imaged in the Fe XI 789.2 nm and Fe XIV 530.3 nm forbidden
lines, with identical instrumentation at three observing sites. The
geographical span across the sites was 1400 km, corresponding to a
25 minute eclipse time difference between the 1st and 3rd site. A jet
was captured in Fe XIV (T = 1.8 MK), in the south polar coronal hole,
in all three sites. However, it had the longest radial extent at the
first site at 17:25 UT, while its intensity and spatial extent decreased
substantially by the time totality hit the last observing site at 17:50
UT. Ancillary data in X-rays (T = 4MK) from Hinode (XRT), and EUV from
SDO/AIA at 19.3 nm (T = 1MK) and 21.1 nm (T = 2MK) revealed a flaring
event associated with reconnection in a bright point in the south
polar coronal hole. The peak of the activity occurred at 17:16 UT,
i.e. just before the start of the eclipse observations. The maximum
extent of the jet was 0.1 Rs in the EUV. The EUV intensity dimmed
substantially thereafter. The spatial extent of the Fe XIV emission of
a heliocentric distance of 2 Rs at 17:25 UT (site 1) far exceeded its
radial extent observed in the EUV, as a consequence of the excitation
process (collisional versus resonance). However, the subsequent dimming
of the jet in Fe XIV at the 2nd and third sites, reflects a drop in
intensity with time. Simultaneous eclipse observations in Fe XI (T = 1.2
MK), only showed polar plumes with no evidence of the jet. The eclipse
observations thus place limits on the lifetime of polar coronal jets,
and a lower limit on their temperature. This work was funded by NSF
grants AGS-1834662 and AST-1839436.
Title: Thermodynamic Changes in the Corona during the 2017 August
21 Total Solar Eclipse
Authors: Boe, B.; Habbal, S.; Druckmuller, M.; Ding, A.; Hoderova,
J.; Starha, P.
Bibcode: 2020AAS...23535907B
Altcode:
Remote sensing observations of FeXI (789.2 nm) and FeXIV (530.3 nm)
emission acquired at multiple observing sites during the 2017 August
21 Total Solar Eclipse were used to infer thermodynamic changes
in the corona as a result of the fortuitous passage of a CME. The
total distance between sites along the path of totality was 1400 km,
corresponding to a difference of 28 minutes between the times of
totality at the first and last site. The relative abundance of Fe10+
and Fe13+ inferred from the observations was used to compute electron
temperature (Te) via theoretical ionization equilibrium abundance
values. Global changes in the ionic emission and inferred Te between
the sites were found. These results underscore the unique advantage
of multi-site and multi-wavelength total solar eclipse observations
for probing the dynamic and thermodynamic properties of the corona
over an uninterrupted distance range of 1 - 3 Rs.
Title: The South American Total Solar Eclipse of 2 July 2019: An
Opportunity for Undergraduate Engagement in Research
Authors: Arndt, M. B.; Habbal, S. R.; Auriemma, S.; Constantinou,
S.; Hayes-Huer, R.; Smith, D.; Solar Wind Sherpas
Bibcode: 2020AAS...23522002A
Altcode:
On 2 July 2019, a total solar eclipse was visible across South
America. Because the corona is a million times fainter than the
photosphere, total solar eclipses provide vital opportunities to make
coronal observations essential for providing insight into mechanisms
behind coronal heating and the solar wind. An international team of 25
scientists, engineers, technicians and students (The Solar Wind Sherpas)
dispersed into 4 teams across Chile and Argentina to make white light,
spectroscopic, and several narrow band (Ar X, Fe IX, FeX, Fe XI, Fe
XIII, Fe XIV, and Ni XV) observations of the solar corona. With support
from NSF, four undergraduates from underserved populations (one from
the University of Hawai'i and three from Bridgewater State University
(BSU) in Massachusetts) were part of the expedition team. The goal for
including undergraduates was to expose them to field work in eclipse
science, help them network with professionals in the field, and better
prepare them for careers in solar physics. This research experience
has already had a positive impact on these students' opportunities
and preparation for future research work. Eclipse expedition travel
support for students and M. Arndt was provided by NSF AGS-1834662
awarded to the University of Hawaíi, Institute for Astronomy. BSU
Students received summer stipends through BSU's ATP program as well
as the Massachusetts NASA Space Grant Consortium. A BSU CARS grant
provided additional travel support for M. Arndt.
Title: The quiet yet turbulent solar corona during the 2 July 2019
total solar eclipse
Authors: Habbal, S.; Druckmuller, M.; Starha, P.; Hoderova, J.;
Johnson, J.; Ding, A.; Starha, P.; Arndt, M.; Solar Wind Sherpas
Bibcode: 2020AAS...23535905H
Altcode:
Multi-wavelength imaging and spectroscopic observations were acquired
at four observing sites during the 2 July 2019 total solar eclipse in
South America, providing continuous observations over 4.5 minutes. Three
sites were located in Chile and one in Argentina. We report here on
preliminary results from the broadband white light and multi-wavelength
imaging experiments centered on the Fe sequence of Fe IX 435.9 nm, Fe X
637.4 nm, Fe XI 789.2 nm, Fe XIII 1074.7 nm, and Fe XIV 530.3 nm coronal
forbidden lines. White light images revealed a classic solar minimum
corona. With peak ionization temperatures spanning 0.8 to 1.8 MK, each
emission line offered a different view of coronal structures. While the
very well defined polar coronal holes were dominated by Fe X and Fe XI
emission, the streamers were dominated by Fe XIV emission. Emphasis
in this presentation will be placed on the characteristics of the
multi-temperature plasmas in the so-called polar plumes, in contrast to
the turbulent streamers.This work was funded by NSF grants AGS-1834662
and AST-1839436, and NASA grant NNX17AH69G to the University of Hawaíi.
Title: CME-induced Thermodynamic Changes in the Corona as Inferred
from Fe XI and Fe XIV Emission Observations during the 2017 August
21 Total Solar Eclipse
Authors: Boe, Benjamin; Habbal, Shadia; Druckmüller, Miloslav; Ding,
Adalbert; Hodérova, Jana; Štarha, Pavel
Bibcode: 2020ApJ...888..100B
Altcode: 2019arXiv191111222B
We present the first remote sensing observations of the impact from
a Coronal Mass Ejection (CME) on the thermodynamic properties of the
solar corona between 1 and 3 R⊙. Measurements of the Fe XI
(789.2 nm) and Fe XIV (530.3 nm) emission were acquired with identical
narrow-bandpass imagers at three observing sites during the 2017 August
21 Total Solar Eclipse (TSE). Additional continuum imagers were used to
observe K+F corona scattering, which is critical for the diagnostics
presented here. The total distance between sites along the path of
totality was 1400 km, corresponding to a difference of 28 minutes
between the times of totality at the first and last site. These
observations were used to measure the Fe XI and Fe XIV emission
relative to continuum scattering, as well as the relative abundance of
Fe10+ and Fe13+ from the line ratio. The electron
temperature (Te) was then computed via theoretical ionization
abundance values. We find that the range of Te is (1.1-1.2)
× 106 K in coronal holes and (1.2-1.4) × 106
K in streamers. Statistically significant changes of Te
occurred throughout much of the corona between the sites as a result
of serendipitous CME activity prior to the eclipse. These results
underscore the unique advantage of multi-site and multi-wavelength TSE
observations for probing the dynamic and thermodynamic properties of the
corona over an uninterrupted distance range from 1 to 3 R⊙.
Title: CME Induced Thermodynamic Changes in the Corona as Inferred
from Fe XI and Fe XIV Emission Observations during the 2017 August
21 Total Solar Eclipse
Authors: Boe, B.; Habbal, S. R.; Druckmuller, M.; Ding, A.; Hoderova,
J.; Starha, P.
Bibcode: 2019AGUFMSH11C3393B
Altcode:
We present the first remote sensing observations of the impact from a
Coronal Mass Ejection (CME) on the thermodynamic properties of the solar
corona between 1 and 3 Rs. Measurements of the Fe XI (789.2 nm) and Fe
XIV (530.3 nm) emission were acquired with identical narrow-bandpass
imagers at three observing sites during the 2017 August 21 Total
Solar Eclipse. Additional continuum emission observations at 788.0 nm
and 529.0 nm were used to isolate line emission. The total distance
between sites along the path of totality was 1400 km, corresponding
to a difference of 28 minutes between the times of totality at the
first and last site. These observations were used to measure the Fe XI
and Fe XIV emission relative to the background continuum scattering,
as well as the temporal variations of the emission between observing
sites. The relative abundance of Fe10+ and Fe13+ was inferred and
used to compute Te via theoretical ionization equilibrium abundance
values. There were changes throughout much of the corona in the
ionic emission and inferred Te between the sites as a result of the
fortuitous passage of a CME during the eclipse. The Fe XI and Fe XIV
ionic emission commonly changed by a factor >2 along individual
lines of sight, and the inferred Te values were found to change by
up to 0.3 x 10^6 K. These results underscore the unique advantage of
multi-site and multi-wavelength total solar eclipse observations for
probing the dynamic and thermodynamic properties of the corona over
an uninterrupted distance range of 1 - 3 Rs.
Title: CME Induced Thermodynamic Changes in the Corona as Inferred
by Fe XI and Fe XIV Emission Observations from the 2017 August 21
Total Solar Eclipse
Authors: Boe, Benjamin; Habbal, Shadia; Druckmuller, Miloslav; Ding,
Adalbert; Hoderova, Jana; Starha, Pavel
Bibcode: 2019shin.confE.143B
Altcode:
We present remote sensing observations of the impact from a Coronal Mass
Ejection (CME) on the thermodynamic properties of the corona between
1 and 3 Solar Radii (Rs). Measurements of the FeXI (789.2 nm) and
FeXIV (530.3 nm) emission were acquired with identical narrow-bandpass
imagers at three observing sites during the 2017 August 21 Total Solar
Eclipse. The total distance between sites along the path of totality
was 1400 km, corresponding to a difference of 28 minutes between
the times of totality at the first and last site. These observations
were used to infer changes in the FeXI and FeXIV emission relative to
background K and F corona scattering. The relative abundance of Fe10+
and Fe13+ inferred from the observations was used to compute electron
temperature (Te) via theoretical ionization equilibrium abundance
values. Global changes in the ionic emission and inferred Te between
the sites were found as a result of the fortuitous passage of a CME
during the eclipse. These results underscore the unique advantage of
multi-site and multi-wavelength total solar eclipse observations for
probing the dynamic and thermodynamic properties of the corona over
an uninterrupted distance range of 1 - 3 Rs.
Title: First Empirical Determination of the Fe 10+ and Fe 13+
Freeze-in Distances in the Solar Corona
Authors: Boe, Benjamin Reid; Habbal, Shadia; Druckmuller, Miloslav;
Landi, Enrico; Kourkchi, Ehsan; Ding, Adalbert; Starha, Pavel;
Hutton, Joseph
Bibcode: 2018shin.confE..36B
Altcode: 2018arXiv180503211B
Heavy ions are markers of the physical processes throughout the fine
scale magnetic structures that define the shape of the solar corona. One
property of the heavy ions, whose value has yet to be empirically
determined in the corona, is the 'freeze-in' distance (Rf) where
they reach fixed ionization states that are adhered to during their
expansion with the solar wind into interplanetary space. We present
the first empirical inference of Rf for Fe10+ and Fe13+ derived from
multi-wavelength imaging observations of the corresponding Fe XI (Fe10+)
789.2 nm and Fe XIV (Fe13+) 530.3 nm emission acquired during the 2015
March 20 total solar eclipse. We find that the two ions freeze-in at
variable distances, even within the same coronal structures. In polar
coronal holes Rf is around 1.45 Rs for Fe10+ and below 1.25 Rs for Fe
13+. Along open field lines in streamer regions Rf ranges from 1.4 to
2 Rs for Fe10+ and from 1.5 to 2.2 Rs for Fe13+. These first empirical
Rf values: (1) reflect the differing plasma parameters between coronal
holes and streamers and structures within them, including prominences
and Coronal Mass Ejections (CMEs); (2) are well below the currently
quoted values derived from empirical model studies; and (3) place doubt
on the reliability of plasma diagnostics based on the assumption of
ionization equilibrium beyond 1.2 Rs.
Title: A Space Coronal Magnetometry Mission
Authors: Lin, Haosheng; Gibson, Sarah; Savage, Sabrina; Tomczyk,
Steven; Downs, Cooper; Rachmeler, Laurel; Kramar, Maxim; Habbal, Shadia
Bibcode: 2018cosp...42E2020L
Altcode:
Direct measurement of the polarized spectra of forbidden coronal
emission lines (CELs) is the most powerful tool for the study of
the solar coronal magnetic fields. Due to its low optical density,
simultaneous multi-sight-lines observations of the corona from space
are needed for tomographic inversion to disentangle the 3D structure of
the solar corona. This presentation will describe the mission concept
and instrument design of a future space coronal magnetometry mission,
consists of many clusters of small spacecraft in near-sun heliocentric
orbits to observe the sun to enable tomographic determination of
the 3D magnetic and thermodynamic structures of the corona. The
spacecraft will be equipped with a wide field, super achromatic lens
coronagraph equipped with two 100-slit, 4-channel spectropolarimeters
optimized for measurement of the polarized CEL spectra from space. This
instrument is tentatively named 'mxCSM'- the massively-multiplexed
Coronal SpectroMagnetometer. A prototype mxCSM is currently under
construction with funding from a 2017 National Science Foundation
Major Research Instrument program grant. This space coronal space
magnetometry mission will advance our knowledge of the corona and the
physics of energetic coronal eruptions, and ultimately enable accurate
space weather forecast.
Title: The First Empirical Determination of the Fe10+
and Fe13+ Freeze-in Distances in the Solar Corona
Authors: Boe, Benjamin; Habbal, Shadia; Druckmüller, Miloslav; Landi,
Enrico; Kourkchi, Ehsan; Ding, Adalbert; Starha, Pavel; Hutton, Joseph
Bibcode: 2018ApJ...859..155B
Altcode:
Heavy ions are markers of the physical processes responsible
for the density and temperature distribution throughout the
fine-scale magnetic structures that define the shape of the solar
corona. One of their properties, whose empirical determination
has remained elusive, is the “freeze-in” distance (R
f ) where they reach fixed ionization states that are
adhered to during their expansion with the solar wind. We
present the first empirical inference of R f for
{Fe}}{10+} and {Fe}}{13+}
derived from multi-wavelength imaging observations of the
corresponding Fe XI ({Fe}}{10+}) 789.2 nm and
Fe XIV ({Fe}}{13+}) 530.3 nm emission acquired
during the 2015 March 20 total solar eclipse. We find that the two
ions freeze-in at different heliocentric distances. In polar coronal
holes (CHs) R f is around 1.45 R ⊙ for
{Fe}}{10+} and below 1.25 R ⊙ for
{Fe}}{13+}. Along open field lines in streamer
regions, R f ranges from 1.4 to 2 R ⊙ for
{Fe}}{10+} and from 1.5 to 2.2 R ⊙
for {Fe}}{13+}. These first empirical R
f values: (1) reflect the differing plasma parameters between
CHs and streamers and structures within them, including prominences
and coronal mass ejections; (2) are well below the currently quoted
values derived from empirical model studies; and (3) place doubt on the
reliability of plasma diagnostics based on the assumption of ionization
equilibrium beyond 1.2 R ⊙.
Title: Coordinated Multi-site Imaging and Spectroscopic Observations
of the 2017 August 21 Total Solar Eclipse
Authors: Arndt, Martina B.; Habbal, Shadia R.; Ding, Adalbert;
Druckmuller, Miloslav; Johnson, Judd; Aniol, Peter
Bibcode: 2018tess.conf30389A
Altcode:
The path of totality for the solar eclipse of 2017 August 21 spanned
the United States from Oregon down to South Carolina. The shadow
took nearly 90 minutes to make this journey, providing unprecedented
opportunities to not only simply witness the event, but to also make
vital imaging and spectroscopic observations of the solar corona. To
maximize our data collection, we dispersed nearly identical experiments
to 5 different sites along a 1200 mile stretch of the northwest portion
of totality: Mitchell, OR, Mackay ID, Whiskey Mountain, WY, Guernsey,
WY, and Alliance, NE. In this poster, we share data from each of these
sites as well as public outreach and educational activities done at
the Alliance, NE site.
Title: Imprints of Coronal Mass Ejections on Coronal Structures
Authors: Alzate, Nathalia; Habbal, Shadia R.
Bibcode: 2018tess.conf10904A
Altcode:
Coronal mass ejections (CMEs) are major disruptions of the coronal
magnetic fields and, in most cases, are associated with the eruption of
prominences. While their impact on Space Weather has been recognized for
several decades now, their imprint on coronal structures however, has
been poorly documented. In this study, we capitalize on the unsurpassed
quality of total solar eclipse white light images spanning a solar
cycle, to present the different manifestations of the imprint of CMEs,
and their corresponding prominence eruptions. Our results show how these
imprints can last for at least several hours. They also show how some of
them can be readily mistaken for rapidly expanding coronal structures,
akin to coronal holes, or sharply defined rays akin to plumes. The
eclipse observations underscore the limitations of our understanding
of the origin of large-scale coronal structures and their expansion
into interplanetary space.
Title: Plasma Properties of the Corona and Sources of the Solar Wind
as Derived from Total Solar Eclipse Observations
Authors: Habbal, Shadia R.; Druckmuller, Miloslav; Ding, Adalbert;
Starha, Pavel; Landi, Enrico; Arndt, Martina B.; Hoderova, Jana;
Johnson, Judd; Starha, Petr
Bibcode: 2018tess.conf32104H
Altcode:
Total solar eclipses provide unique observing opportunities for the
inference of the plasma properties of the corona and establishing
the sources of the solar wind, starting from the solar surface out
to several solar radii. Properties that are critical for exploring
coronal heating and plasma acceleration processes are the distribution
of the electron temperature in the corona, the ionic composition of
the corona, and the freeze-in distances of different ions in the
solar wind. These properties can be readily inferred from imaging
in coronal forbidden lines in the visible wavelength range. On the
other hand, broad band white light eclipse images, which at present
yield the highest resolution depiction of coronal structures, capture
the sources of the solar wind as well as the dynamics of the coronal
plasma. Examples drawn from our most recent eclipse observations in
broadband white light and narrowband imaging in coronal forbidden
lines will be presented. These observations underscore the urgency
for the next generation of space-based instrumentation to carry out
such measurements, to achieve significant progress in understanding
the coronal heating processes and for uncovering the different origins
of the solar wind.
Title: Unique Diagnostic Properties of Spectroscopy in the Visible:
Results from a Novel Imaging Spectrometer Operated During the 2015
and 2017 Total Solar Eclipses
Authors: Ding, Adalbert; Habbal, Shadia R.; Nassir, Michael; Boe,
Benjamin
Bibcode: 2018tess.conf31301D
Altcode:
High spectral resolution spectroscopic observations carried out during
the 20 March 2015 and 21 August 2017 total solar eclipses revealed for
the first time the presence of neutrals and singly ionized elements
streaming away from the Sun embedded within million-degrees plasma
structures, emitting in spectral lines from highly ionized elements
(e.g. Fe XIV , Ni XIII, ..). Speeds ranging from 100 to 1500 km/s were
captured by Doppler spectroscopy over a distance range of a few solar
radii starting from the solar surface. These are the first measurements
to capture the preservation of the ionic composition of erupting
prominence material leading to a coronal mass ejection. Examples from
both eclipses will show how these novel spectroscopic measurements
in the visible wavelength range were enabled by the innovative design
of an imaging spectrometer, with λ/Δλ = 20,000, operating in 40 to
70th order. By covering a wavelength range of 300 to 1100 nm, spectra
of neutrals to highly ionized elements in the corona could thus be
recorded. Furthermore, the current size, weight and design of the
spectrometer, which has no movable parts, can be readily reduced for
use as a payload on a small satellite to yield critical data regarding
the plasma characteristics of ubiquitous dynamic events in the corona,
in the source regions of the solar wind, currently unavailable from
any other ground- and/or space-based facility.
Title: Solar Coronal Observations from Lunar Orbit
Authors: Cooper, John F.; Habbal, Shadia R.; Stubbs, Timothy John;
Glenar, David A.
Bibcode: 2018tess.conf21806C
Altcode:
The recent solar eclipse of August 21, 2017 has highlighted the
importance of imaging small scale structures in the solar corona at
high spatial and spectroscopic resolution. Such structures include
vortex rings, twisted helices, expanding loops, faint nested loops,
turbulence structures, and plumes that are manifestations of plasma
instabilities in the immediate neighborhoods of prominences generally
surrounded by the hottest coronal material. Forming close to the
Sun in strong coronal magnetic fields, these features likely expand
in the radially-outward weakening magnetic field and contribute to
the textural inhomogeneity of solar wind structures observed at 1
AU. Tracking outward evolution in size, density, speed, and temperature
of these features, otherwise invisible to currently operating space
coronographs, could inform space weather forecast models for the
geospace environment. Detailed diagnostics of these instabilities, the
bulk heating and acceleration of the solar wind, and the transitions
from closed to open coronal magnetic field lines are available from
the forbidden coronal emission lines at visible to near-infrared
(400 - 1000 nm) wavelengths from heavy coronal ions such as Fe, Ni,
Ar, and S. The spatial evolution of coronal electron temperatures can
for example be determined from ratios of Fe X (Fe+9) - Fe
XIV (Fe+13) line emission. Emission lines from radiative
transitions fall off more slowly with radial distance than those from
collisional transitions and can track evolution of the solar wind
to the collisionless regime where ion charge states and temperatures
become frozen into the values that persist out to 1 AU. Ground-based
solar eclipse observations can only track these diagnostics out to
about 3 Rsun, due to Earth atmospheric light background,
while the upcoming Parker Solar Probe mission will make in-situ plasma
measurements only into its minimum perihelion ~ 10 Rsun. As
first suggested by Habbal et al. (Solar Physics, 2013), this gap could
be filled by a solar VIS-NIR spectroscopic telescope onboard a lunar
orbiting spacecraft that periodically (hourly to daily) images the inner
to outer corona above the dark lunar limb from the nightside of the
Moon. Such observations would provide unprecedented angular resolution
of the inner corona and brightness resolution of the outer corona.
Title: Lunar Solar Origins Explorer (LunaSOX) for the Deep Space
Gateway
Authors: Cooper, J. F.; Habbal, S. R.; Stubbs, T. J.; Glenar, D. A.
Bibcode: 2018LPICo2063.3038C
Altcode:
A solar telescope on Deep Space Gateway in lunar orbit could provide
unprecedented brightness and spatial resolution for measurements of
complex structures and small-scale features in the inner solar corona
by using the lunar limb for occultation.
Title: Preparing a Nation for the Eclipse of a Generation -
Authors: Speck, Angela; Habbal, Shadia; Tresch Fienberg, Richard;
Kentrianakis, Michael; Fraknoi, Andrew; Nordgren, Tyler; Penn,
Matthew; Pasachoff, Jay M.; Bakich, Michael; Winter, Henry; Gay,
Pamela; Motta, Mario
Bibcode: 2018AAS...23122002S
Altcode:
On August 21st 2017, there was a total solar eclipse visible from
a vast swath of the US.In preparation for that event, the American
Astronomical society created a taskforce charged with planning
for the eclipse for the entire nation. The preparations included
interfacing with the public, the media, non-profit organizations and
governmental organizations. Preliminary data suggests that nearly 90%
of American adults watched the eclipse either directly or via live
streams. Moreover, there were no major problems associated with the
event, in spite of valiant attempts from, e.g. imprope solar viewing
materials. The eclipse offered opportunities for many scientific
experiments within and ebyond astronomy. Here we present on the work
of the taskforce, and the lessons learned as well as lesser known
science experiments undertaken during the eclipse.
Title: Observations of the Dynamics and Thermodynamics of the Corona
during the 21 August 2017 Total Solar Eclipse
Authors: Habbal, Shadia Rifai; Ding, Adalbert; Druckmuller, Miloslav;
Solar Wind Sherpas
Bibcode: 2018AAS...23122007H
Altcode:
The visible wavelength range, encompassing forbidden coronal emission
lines, offers unique diagnostic tools for exploring the physics of
the solar corona, such as its chemical composition and the dynamics
of its major and minor constituents. These tools are best exploited
during total solar eclipses, when the field of view spans several solar
radii, starting from the solar surface. This spatial span is currently
untenable from any observing platform. Imaging and spectroscopic
eclipse observations, including the 2017 August 21 event, are shown
to be the first to yield the temperature distribution in the corona
as a function of solar cycle. They are also the first to lead to the
discovery of cool prominence material at less than 10,000 to 50,000
K, within more than a radius above the solar surface, streaming away
from the Sun, while maintaining its compositional identity. These data
underscore the importance of capturing emission from coronal forbidden
lines with the next generation space-based instrumentation to address
the general problem of coronal heating.
Title: The Unique Scientific Assets of Multi-Wavelength Total Solar
Eclipse Observations
Authors: Habbal, S. R.; Druckmuller, M.; Ding, A.
Bibcode: 2017AGUFMSH24A..02H
Altcode:
Total solar eclipses continue to yield new discoveries regarding the
dynamics and thermodynamics of the corona, due to the radial span of
the field of view available during totality, starting from the solar
surface out to several solar radii, and due to the diagnostic potential
provided by coronal emission lines. Scientific highlights from past
eclipse observations as well as from the 21 August 2017 eclipse, now
spanning a solar cycle, will be presented. These include white light
and spectral line imaging as well as imaging spectrometry. Emphasis will
be placed on the unique insights into the origin of dynamic structures
captured in eclipse images, and the temperature distribution in the
corona derived from these eclipse observations. Implications of these
results for the general problem of coronal heating, as well as for
the next generation of space instrumentation will be discussed.
Title: Tethered Prominence-CME Systems Captured during the 2012
November 13 and 2013 November 3 Total Solar Eclipses
Authors: Druckmüller, Miloslav; Habbal, Shadia R.; Alzate, Nathalia;
Emmanouilidis, Constantinos
Bibcode: 2017ApJ...851L..41D
Altcode:
We report on white light observations of high latitude tethered
prominences acquired during the total solar eclipses of 2012 November
13 and 2013 November 3, at solar maximum, with a field of view
spanning several solar radii. Distinguished by their pinkish hue,
characteristic of emission from neutral hydrogen and helium, the four
tethered prominences were akin to twisted flux ropes, stretching
out to the limit of the field of view, while remaining anchored at
the Sun. Cotemporal observations in the extreme ultraviolet from the
Solar Dynamics Observatory (SDO/AIA) clearly showed that the pinkish
emission from the cool (≈ {10}4-{10}5 K)
filamentary prominences was cospatial with the 30.4 nm He II emission,
and was directly linked to filamentary structures emitting at coronal
temperatures ≥slant {10}6 K in 17.1 and 19.3 nm. The
tethered prominences evolved from typical tornado types. Each
one formed the core of different types of coronal mass ejections
(CMEs), as inferred from coordinated LASCO C2, C3, and STEREO A and B
coronagraph observations. Two of them evolved into a series of faint,
unstructured puffs. One was a normal CME. The most striking one
was a “light-bulb” type CME, whose three-dimensional structure
was confirmed from all four coronagraphs. These first uninterrupted
detections of prominence-CME systems anchored at the Sun, and stretching
out to at least the edge of the field of view of LASCO C3, provide the
first observational confirmation for the source of counter-streaming
electron fluxes measured in interplanetary CMEs, or ICMEs.
Title: Dynamics of Coronal Structures Captured During the 2012 and
2013 Total Solar Eclipses
Authors: Alzate, N.; Habbal, S. R.; Druckmuller, M.
Bibcode: 2017AGUFMSH54A..04A
Altcode:
White light eclipse images taken during total solar eclipses provide
a very high dynamic range spanning tens of solar radii starting from
the solar surface. They capture the instantaneous state of the corona,
including dynamic events. We present observations of the 2012 November
13 and 2013 November 3 total solar eclipses, taken by Constantinos
Emmanouilidis, in which we captured high latitude tethered prominences
accompanied by CMEs, as well as several `atypical' large scale
structures, spanning a few solar radii above the solar surface. By
complementing the eclipse observations with co-temporaneous SDO/AIA,
STEREO/EUVI and SOHO/LASCO observations, we show how the shape of the
atypical structures outlines the shape of faint CME shock fronts, driven
by flaring activities. The tethered prominences were imaged from their
anchor at the solar surface out to several solar radii. The SDO/AIA
30.4, 17.1 and 19.3 nm emission clearly show how a direct link between
the cool (104 - 105 K) filamentary emission from prominence material,
and the filamentary structures emitting at coronal temperatures (>
106 K), is unmistakably present. The observed survival of these tethered
systems out to the field of view of LASCO C3, establishes the likely
origin of counter-streaming electrons associated with CMEs observed
in interplanetary space (ICMEs). They also provide new insights for
CME-initiation models associated with prominence eruptions. Our work
highlights the uniqueness of eclipse observations in identifying the
impact of transit events on large-scale coronal structures.
Title: Dynamics of Large-scale Coronal Structures as Imaged during
the 2012 and 2013 Total Solar Eclipses
Authors: Alzate, Nathalia; Habbal, Shadia R.; Druckmüller, Miloslav;
Emmanouilidis, Constantinos; Morgan, Huw
Bibcode: 2017ApJ...848...84A
Altcode:
White light images acquired at the peak of solar activity cycle 24,
during the total solar eclipses of 2012 November 13 and 2013 November
3, serendipitously captured erupting prominences accompanied by
CMEs. Application of state-of-the-art image processing techniques
revealed the intricate details of two “atypical” large-scale
structures, with strikingly sharp boundaries. By complementing
the processed white light eclipse images with processed images from
co-temporal Solar Dynamics Observatory/AIA and SOHO/LASCO observations,
we show how the shape of these atypical structures matches the shape of
faint CME shock fronts, which traversed the inner corona a few hours
prior to the eclipse observations. The two events were not associated
with any prominence eruption but were triggered by sudden brightening
events on the solar surface accompanied by sprays and jets. The
discovery of the indelible impact that frequent and innocuous transient
events in the low corona can have on large-scale coronal structures was
enabled by the radial span of the high-resolution white light eclipse
images, starting from the solar surface out to several solar radii,
currently unmatched by any coronagraphic instrumentation. These
findings raise the interesting question as to whether large-scale
coronal structures can ever be considered stationary. They also point
to the existence of a much larger number of CMEs that goes undetected
from the suite of instrumentation currently observing the Sun.
Title: First Detection of Prominence Material Embedded within
a 2 × 106 K CME Front Streaming away at 100-1500 km
s-1 in the Solar Corona
Authors: Ding, Adalbert; Habbal, Shadia Rifai
Bibcode: 2017ApJ...842L...7D
Altcode:
Coronal mass ejections (CMEs) are the largest and most dynamic
explosions detected in the million degree solar corona, with speeds
reaching up to 3000 km s-1 at Earth’s orbit. Triggered
by the eruption of prominences, in most cases, one of the outstanding
questions pertaining to the dynamic CME-prominence system is the
fate of the cool {10}4{--}{10}5 {{K}} ejected
filaments. We present spectroscopic observations acquired during
the 2015 March 20 total solar eclipse, which captured a plethora
of redshifted plasmoids from Fe xiv emission at 2× {10}6
{{K}}. Approximately 10% of these plasmoids enshrouded the same neutral
and singly ionized plasma below 2× {10}5 {{K}}, observed
in prominences anchored at the Sun at that time. This discovery was
enabled by the novel design of a dual-channel spectrometer and the
exceptionally clear sky conditions on the island of Svalbard during
totality. The Doppler redshifts corresponded to speeds ranging
from under 100 to over 1500 km s-1. These are the first
comprehensive spectroscopic observations to unambiguously detect a 2×
{10}6 {{K}} filamentary CME front with inclusions of cool
prominence material. The CME front covered a projected area of 2.5× 1.5
{R}{{s}}2 starting from the solar surface. These
observations imply that cool prominence inclusions within a CME front
maintain their ionic composition during expansion away from the Sun.
Title: Tracing the path towards totality
Authors: Habbal, Shadia
Bibcode: 2016PhyW...29l..34H
Altcode:
In Sun Moon Earth: the History of Solar Eclipses from Omens of Doom to
Einstein and Exoplanets, author and astronomer Tyler Nordgren charts
the evolving history of the solar eclipse.
Title: Coronal plasma diagnostics from ground-based observations
Authors: Landi, E.; Habbal, S. R.; Tomczyk, S.
Bibcode: 2016JGRA..121.8237L
Altcode:
In this paper we discuss the potential of ground-based visible
observations of the solar corona to address the key open problems in
the physics of the solar atmosphere and of solar activity. We first
compare the diagnostic potential of visible observations with those of
high-resolution spectrometers and narrowband imagers working in the
EUV and X-ray wavelength ranges. We then review the main diagnostic
techniques (and introduce a few new ones) that can be applied to
line and continuum emission in the solar atmosphere, and the physical
problems that they enable us to address. Finally, we briefly review the
main features of ground-based coronographic instrumentation currently
being developed and planned.
Title: The Temperature of the Corona as Derived from Total Solar
Eclipse Observations
Authors: Habbal, Shadia R.; Morgan, Huw; Druckmuller, Miloslav;
Ding, Adalbert
Bibcode: 2016SPD....4730801H
Altcode:
Multiwavelength imaging observations in a suite of coronal forbidden
lines of the corona during total solar eclipses enables the empirical
inference of the spatial distribution of temperature in the solar
corona up to a few solar radii above the limb. The temperature
sensitivity of coronal emission lines is such that temperature
differences of 105 K can be detected in the images. Using
high resolution multiwavelength and white light eclipse images acquired
since 2006, covering almost a solar cycle, we show evidence for (1)
how the distribution of the temperature in the corona is bimodal, with
closed coronal structures dominated by 2 106 K plasma, while
structures streaming away from the Sun are dominated by 106
K emission, (2) prominences are invariably enshrouded by the hottest
material in the corona, and (3) that the dominance of one temperature
versus the other is solar-cycle dependent.
Title: On the Discovery of Fast Chromospheric Ejecta of up to 1500
km/s in the Corona within one Radius above the Solar Surface
Authors: Habbal, Shadia R.; Ding, Adalbert
Bibcode: 2016SPD....4720207H
Altcode:
Using a dual channel imaging spectrograph, centered on the Fe XIV 530.3
nm and Fe XI 789.2 nm coronal forbidden lines, spectral observations
were made during the total solar eclipse of 20 March 2015. The slit of
the spectrograph covered approximately 8 Rs and was positioned parallel
to, and starting at central meridian. The slit scanned the corona out to
approximately 1.5 Rs above the limb throughout the duration of totality
of approximately 2.5 minutes. Concentrations of Doppler redshifted
coronal material ranging from 100 to 1500 km/s, with a spatial extent of
up to 0.5 Rs, were detected at different locations along the slit and
at the different slit positions. Surprisingly, chromospheric material,
characterized by He I 587.6 nm, Mg I triplet 516.7, 517.2 and 518.4
nm, and Fe II 516.9 nm emission, was often associated with the Doppler
shifts detected in Fe XIV. Mapping the location of these concentrations
on the corresponding white light eclipse image renders a distribution
reminiscent of a complex coronal mass ejection front moving away from
the observer. Unfortunately, no STEREO observations were available
during that time. The LASCO/C2 coronagraph showed very faint outflows,
consistent with the bulk of the Doppler-shifted material moving away
from the observer. The presence of cool chromospheric material moving
away from the Sun provides the first corroboration of the solar origin
of reported detection of neutral and low ionization state atoms in
the solar wind.
Title: Unique Insights into the Origin and Expansion of Coronal
Structures from Total Solar Eclipse Observations
Authors: Habbal, S. R.; Morgan, H.; Druckmuller, M.; Ding, A.
Bibcode: 2015AGUFMSH11F..01H
Altcode:
The enigma surrounding the solar corona continues to be the focus of
observations from space and the ground, as well as model studies. The
astounding spatial and temporal resolution of recent space-based imaging
experiments, in particular in the ultraviolet and extreme ultraviolet,
have added significantly to the complexity and dynamics of coronal
structures. Their main limitation, however, is the coverage of the inner
corona over a distance range limited to half a solar radius at best
from the solar surface. They thus fall short in placing the observed
structures within the context of the expanding corona from the solar
surface out into interplanetary space. This presentation will review
the unique advantages of total solar eclipse observations in yielding
novel insights into the bewildering variety of seemingly disparate
coronal structures. This is achieved through the outstanding imaging
and diagnostic potentials of the continuum and spectral line emission
over a distance range range covering a few solar radii starting from
the solar surface, coupled with state of the art image processing tools.
Title: Dynamics and Thermodynamics of the Corona Observed During
the Total Solar Eclipse of 20 March 2015
Authors: Habbal, S. R.; Ding, A.; Druckmuller, M.; Johnson, J.;
Morgan, H.; Arndt, M. B.; Alzate, N.; Hutton, J.
Bibcode: 2015AGUFMSH51C2455H
Altcode:
Total solar eclipse observations are snapshots of the instantaneous
dynamic state of the corona, and each observation never fails to
yield surprises. Occurring at the declining phase of solar cycle 24,
the 20 March 2015 total solar eclipse was no exception. Images taken
through narrow bandpass filters centered on the Fe XIV 530.3 nm and
Fe XI 789.2 nm coronal emission lines, showed a corona dominated by
strong Fe XIV emission, with a peak ionization temperature of 1.8
MK, and with weak Fe XI emission at 1.1 MK, present mostly over the
two poles. Simultaneous imaging spectroscopy through a dual channel
high-resolution spectrometer, centered on these two wavelengths,
revealed Doppler red shifts exceeding 1000 km/s in the extended
corona, covering a distance range of up to 1.5 solar radii above the
solar surface. These redshifts together with the observed Doppler
broadening could be assigned to specific coronal structures, which
were observed simultaneously in high resolution white light images. By
comparing these observations with contemporaneous observations from
SDO, SWAP/Proba2 and LASCO/C2 and C3, the dynamics of the coronal
plasma, as well as its thermodynamics, could be mapped in a region of
space, untenable to present-day observatories. These latest eclipse
observations underscore the unique scientific opportunities accessible
with similar instrumentation during the all-american 21 August 2017
total solar eclipse.
Title: The Total Solar Eclipse on Svalbard 2015
Authors: Sigernes, F.; Ellingsen, P. G.; Holmen, S. E.; Brekke, P.;
Danielsen, A.; Olsen, B.; Syrjäsuo, M.; Chen, X.; Dyrland, M. E.;
Partamies, N.; Baddeley, L. J.; Lorentzen, D. A.; Krogtoft, M. A.;
Dragland, T.; Mortensson, H.; Smistad, L.; Oksavik, K.; Heinselman,
C. J.; Habbal, S. R.
Bibcode: 2015AGUFMSH52A..02S
Altcode:
This work reports the results from a multi-instrumental campaign
that was planned and executed to record the Total Solar Eclipse that
occurred on Friday 20th of March 2015 in Longyearbyen (78oN, 15oE)
on Svalbard, Norway. Both airborne hyperspectral- and ground-based
camera systems were used to image the event. A novel video accumulation
filter technique is presented that reveals small scale chromospheric
features. The result is fused with a High Dynamic Range (HDR) image
of the Corona taken from the old Auroral Station in Adventdalen. The
Kjell Henriksen Observatory (KHO) was also operative, but did not
detect any dayside auroral signatures. The background sky condition
was too bright during totality for the auroral cameras. The airborne
hyperspectral data is used to cluster and classify active solar regions
with prominences from the background continuum.
Title: Coronal plasma diagnostics from eclipse observations
Authors: Landi, E.; Habbal, S. R.; Tomczyk, S.
Bibcode: 2015AGUFMSH51C2456L
Altcode:
In this talk we will discuss the diagnostic potential of observationsof
visible spectral lines formed in the extended solar corona that
canbe obtained during eclipses. We will discuss the possible
diagnosticapplications of visible eclipse observations to measure the
physicalparameters of the extended corona, to understand solar wind
origin andacceleration, and to determine the evolution of Coronal
Mass Ejectionsduring onset.We will first review the mechanisms of
formation of spectral lineintensities, we will then illustrate their
diagnostic applications,and show some results from recent eclipse
observations. We will alsoreview the spectral lines that are most
likely to be observed inthe extended solar corona during the upcoming
2017 eclipse in thecontinental United States.
Title: Dynamics and Thermodynamics of the Solar Corona as Inferred
from Total Solar Eclipse Observations
Authors: Habbal, Shadia; Druckmuller, Miloslav; Morgan, Huw; Ding,
Adalbert
Bibcode: 2015TESS....140906H
Altcode:
Imaging the solar corona during total solar eclipses in broadband
white light and in a number of forbidden emission lines in the visible
continues to yield unique insights into the dynamics and thermodynamics
of the coronal plasma. An overview of recent multiwavelength
eclipse observations, spanning almost a solar cycle, will be
presented. Particular emphasis will be placed on the thermodynamics
of dynamic events such prominence eruptions, plasmoids and CMEs,
that are captured in the eclipse images either as they occurred,
or from the trails they left behind in the corona.
Title: The Corona at Solar Maximum as Imaged during the Total Solar
Eclipses of 2012 November 13-14 and 2013 November 3-4
Authors: Habbal, Shadia R.; Druckmuller, Miloslav; Emmanouilides,
Constantinos; Morgan, Huw
Bibcode: 2015AAS...22511502H
Altcode:
The total solar eclipses of 2012 November 13-14 and 2013 November
3-4 coincided with peaks of activity in solar cycle 24. Despite
challenging observing conditions due to weather patterns in both
Australia and central Africa, respectively for these two eclipses,
white light images were successfully obtained from groups stationed
at different sites along the path of totality on both occasions. We
show here how the corona during these two eclipses was remarkable in
many ways. In 2012, a prominence eruption reflecting a classic example
of a current sheet, with a linear extension of almost 0.25 Rs, ending
in a bubble-shaped cavity, was captured in white light. In 2013, two
plasmoids were observed at more than a solar radius above the solar
limb, both associated with filament eruptions, and one ending in a
classic CME bubble. In addition, the intricate complexity of the corona
at these two eclipses, revealed by state-of-the art image processing,
reflected the ubiquitous presence of large expanding loops, and the
fingerprints of plasma instabilities in the form of twisted helical
structures and vortex rings.
Title: Variable Cascade Dynamics and Intermittency in the Solar Wind
at 1 AU
Authors: Sigernes, F.; Ellingsen, P. G.; Holmen, S. E.; Brekke, P.;
Danielsen, A.; Olsen, B.; Syrjäsuo, M.; Chen, X.; Dyrland, M. E.;
Partamies, N.; Baddeley, L. J.; Lorentzen, D. A.; Krogtoft, M. A.;
Dragland, T.; Mortensson, H.; Smistad, L.; Oksavik, K.; Heinselman,
C. J.; Habbal, S. R.
Bibcode: 2014AGUFMSH52A..02S
Altcode:
This work reports the results from a multi-instrumental campaign
that was planned and executed to record the Total Solar Eclipse that
occurred on Friday 20th of March 2015 in Longyearbyen (78oN, 15oE)
on Svalbard, Norway. Both airborne hyperspectral- and ground-based
camera systems were used to image the event. A novel video accumulation
filter technique is presented that reveals small scale chromospheric
features. The result is fused with a High Dynamic Range (HDR) image
of the Corona taken from the old Auroral Station in Adventdalen. The
Kjell Henriksen Observatory (KHO) was also operative, but did not
detect any dayside auroral signatures. The background sky condition
was too bright during totality for the auroral cameras. The airborne
hyperspectral data is used to cluster and classify active solar regions
with prominences from the background continuum.
Title: Properties of solar prominences as obtained by SDO/AIA and
the associated differential emission measure analysis
Authors: Bains, A. S.; Li, B.; Habbal, S. R.
Bibcode: 2014AGUFMSH13B4100B
Altcode:
Prominences are an inherent component of the solar corona. They are
significantly cooler than the surrounding corona, indicating that they
are thermally isolated. Therefore the prominence-corona transition
region (PCTR) plays an important role to establish an equilibrium
system comprising prominences and the ambient corona. We present a
study on solar prominences, PCTR and the quiet Sun using the SDO/AIA
observations. The intensity profiles of different spectral lines show
that there is an intrinsic temperature variation inside prominences. We
then examine the temperature and density properties of prominences,
PCTR and the quiet Sun by using the differential emission measure(DEM)
analysis whereby the six-passband EUV observations are employed. Our
DEM analysis shows that the temperature of the PCTR varies from
logT∼6.0log T sim 6.0 to logT∼6.2log T sim 6.2.
Title: Bridging EUV and White-Light Observations to Inspect the
Initiation Phase of a "Two-Stage" Solar Eruptive Event
Authors: Byrne, J. P.; Morgan, H.; Seaton, D. B.; Bain, H. M.; Habbal,
S. R.
Bibcode: 2014SoPh..289.4545B
Altcode: 2014arXiv1406.4919B; 2014SoPh..tmp..118B
The initiation phase of coronal mass ejections (CMEs) is a very
important aspect of solar physics, as these phenomena ultimately
drive space weather in the heliosphere. This phase is known to occur
between the photosphere and low corona, where many models introduce an
instability and/or magnetic reconnection that triggers a CME, often
with associated flaring activity. To this end, it is important to
obtain a variety of observations of the low corona to build as clear
a picture as possible of the dynamics that occur therein. Here, we
combine the EUV imagery of the Sun Watcher using Active Pixel System
Detector and Image Processing (SWAP) instrument onboard the Project
for Onboard Autonomy (PROBA2) with the white-light imagery of the
ground-based Mark-IV K-coronameter (Mk4) at Mauna Loa Solar Observatory
(MLSO) to bridge the observational gap that exists between the disk
imagery of the Atmospheric Imaging Assembly (AIA) onboard the Solar
Dynamics Observatory (SDO) and the coronal imagery of the Large Angle
Spectrometric Coronagraph (LASCO) onboard the Solar and Heliospheric
Observatory (SOHO). Methods of multiscale image analysis were applied to
the observations to better reveal the coronal signal while suppressing
noise and other features. This allowed an investigation into the
initiation phase of a CME that was driven by a rising flux-rope
structure from a "two-stage" flaring event underlying an extended
helmet streamer. It was found that the initial outward motion of the
erupting loop system in the EUV observations coincided with the first
X-ray flare peak and led to a plasma pile-up of the white-light CME core
material. The characterized CME core then underwent a strong jerk in its
motion, as the early acceleration increased abruptly, simultaneously
with the second X-ray flare peak. The overall system expanded into
the helmet streamer to become the larger CME structure observed in
the LASCO coronagraph images, which later became concave-outward in
shape. Theoretical models for the event are discussed in light of these
unique observations, and it is concluded that the formation of either a
kink-unstable or torus-unstable flux rope may be the likeliest scenario.
Title: Exploring the Prominence-Corona Connection and its Expansion
into the Outer Corona Using Total Solar Eclipse Observations
Authors: Habbal, Shadia Rifai; Morgan, Huw; Druckmüller, Miloslav
Bibcode: 2014ApJ...793..119H
Altcode:
Prominences constitute the most complex magnetic structures in the
solar corona. The ubiquitous presence of their seemingly confined
dense and cool plasma in an otherwise million-degree environment
remains a puzzle. Using a decade of white light total solar eclipse
observations, we show how these images reveal an intricate relationship
between prominences and coronal structures both in their immediate
vicinity, known as coronal cavities, and in the extended corona out
to several solar radii. Observations of suspended prominences and
twisted helical structures spanning several solar radii are central to
these findings. The different manifestations of the prominence-corona
interface that emerge from this study underscore the fundamental role
played by prominences in defining and controlling the complex expansion
and dynamic behavior of the solar magnetic field in the neighborhood
of magnetic polarity reversal regions. This study suggests that the
unraveling of prominences and the outward expansion of the helical
twisted field lines linked to them could be the solar origin of
twisted magnetic flux ropes detected in interplanetary space, and of
the mechanism by which the Sun sheds its magnetic helicity. This work
also underscores the likely role of the prominence-corona interface
as a source of the slow solar wind.
Title: Imaging Comet ISON C/2012 S1 in the Inner Corona at Perihelion
Authors: Druckmüller, Miloslav; Habbal, Shadia Rifai; Aniol, Peter;
Ding, Adalbert; Morgan, Huw
Bibcode: 2014ApJ...784L..22D
Altcode:
Much anticipation and speculation were building around comet ISON,
or C/2012 S1, discovered on 2012 September 21 by the International
Scientific Optical Network telescope in Russia, and bound for the Sun
on 2013 November 28, with a closest heliocentric approach distance
of 2.7 R ⊙. Here we present the first white light image
of the comet's trail through the inner corona. The image was taken
with a wide field Lyot-type coronagraph from the Mees Observatory on
Haleakala at 19:12 UT, past its perihelion passage at 18:45 UT. The
perfect match between the comet's trail captured in the inner corona
and the trail that had persisted across the field of view of 2-6 R
⊙ of the Solar and Heliospheric Observatory Large Angle
and Spectrometric Coronagraph Experiment/C2 coronagraph at 19:12 UT
demonstrates that the comet survived its perihelion passage.
Title: Discovery of a New Class of Coronal Structures in White Light
Eclipse Images
Authors: Druckmüller, Miloslav; Habbal, Shadia Rifai; Morgan, Huw
Bibcode: 2014ApJ...785...14D
Altcode:
White light images of the solar corona, taken during total solar
eclipses, capture the complex dynamic relationship between the coronal
plasma and the magnetic field. This relationship can be recorded on
timescales of seconds to minutes, within a few solar radii above
the solar surface. Rays, large-scale loops, and streamers, which
are the brightest structures in these images, have shaped current
models of the coronal magnetic field and solar wind flow. We show in
this work how the application of novel image processing techniques
to unique high-resolution white light eclipse images reveals the
presence of a new class of structures, reminiscent of smoke rings,
faint nested expanding loops, expanding bubbles, and twisted helical
structures. These features are interpreted as snapshots of the dynamical
evolution of instabilities developing at prominence-corona interfaces
and propagating outward with the solar wind.
Title: From Forbidden Coronal Lines to Meaningful Coronal Magnetic
Fields
Authors: Judge, P. G.; Habbal, S.; Landi, E.
Bibcode: 2013SoPh..288..467J
Altcode: 2013arXiv1304.3863J
We review methods to measure magnetic fields within the corona using
the polarized light in magnetic-dipole (M1) lines. We are particularly
interested in both the global magnetic-field evolution over a solar
cycle, and the local storage of magnetic free energy within coronal
plasmas. We address commonly held skepticisms concerning angular
ambiguities and line-of-sight confusion. We argue that ambiguities are,
in principle, no worse than more familiar remotely sensed photospheric
vector fields, and that the diagnosis of M1 line data would benefit
from simultaneous observations of EUV lines. Based on calculations and
data from eclipses, we discuss the most promising lines and different
approaches that might be used. We point to the S-like [Fe XI] line
(J=2 to J=1) at 789.2 nm as a prime target line (for the Advanced
Technology Solar Telescope (ATST) for example) to augment the hotter
1074.7 and 1079.8 nm Si-like lines of [Fe XIII] currently observed by
the Coronal Multi-channel Polarimeter (CoMP). Significant breakthroughs
will be made possible with the new generation of coronagraphs, in three
distinct ways: i) through single-point inversions (which encompasses
also the analysis of MHD wave modes), ii) using direct comparisons of
synthetic MHD or force-free models with polarization data, and iii)
using tomographic techniques.
Title: Improved methods for determining the kinematics of coronal
mass ejections and coronal waves
Authors: Byrne, J. P.; Long, D. M.; Gallagher, P. T.; Bloomfield,
D. S.; Maloney, S. A.; McAteer, R. T. J.; Morgan, H.; Habbal, S. R.
Bibcode: 2013A&A...557A..96B
Altcode: 2013arXiv1307.8155B
Context. The study of solar eruptive events and associated phenomena is
of great importance in the context of solar and heliophysics. Coronal
mass ejections (CMEs) and coronal waves are energetic manifestations of
the restructuring of the solar magnetic field and mass motion of the
plasma. Characterising this motion is vital for deriving the dynamics
of these events and thus understanding the physics driving their
initiation and propagation. The development and use of appropriate
methods for measuring event kinematics is therefore imperative.
Aims: Traditional approaches to the study of CME and coronal wave
kinematics do not return wholly accurate nor robust estimates of the
true event kinematics and associated uncertainties. We highlight the
drawbacks of these approaches, and demonstrate improved methods for
accurate and reliable determination of the kinematics.
Methods:
The Savitzky-Golay filter is demonstrated as a more appropriate fitting
technique for CME and coronal wave studies, and a residual resampling
bootstrap technique is demonstrated as a statistically rigorous method
for the determination of kinematic error estimates and goodness-of-fit
tests.
Results: It is shown that the scatter on distance-time
measurements of small sample size can significantly limit the ability
to derive accurate and reliable kinematics. This may be overcome by
(i) increasing measurement precision and sampling cadence; and (ii)
applying robust methods for deriving the kinematics and reliably
determining their associated uncertainties. If a priori knowledge
exists and a pre-determined model form for the kinematics is available
(or indeed any justified fitting-form to be tested against the data),
then its precision can be examined using a bootstrapping technique to
determine the confidence interval associated with the model/fitting
parameters.
Conclusions: Improved methods for determining the
kinematics of CMEs and coronal waves are demonstrated to great effect,
overcoming many issues highlighted in traditional numerical differencing
and error propagation techniques.
Title: Probing the Fundamental Physics of the Solar Corona with
Lunar Solar Occultation Observations
Authors: Habbal, S. Rifai; Morgan, H.; Druckmüller, M.; Ding, A.;
Cooper, J. F.; Daw, A.; Sittler, E. C.
Bibcode: 2013SoPh..285....9H
Altcode: 2012SoPh..tmp..218H
Imaging and spectroscopy of the solar corona, coupled with polarimetry,
are the only tools available at present to capture signatures of
physical processes responsible for coronal heating and solar wind
acceleration within the first few solar radii above the solar limb. With
the recent advent of improved detector technology and image processing
techniques, broad-band white light and narrow-band multi-wavelength
observations of coronal forbidden lines, made during total solar
eclipses, have started to yield new views about the thermodynamic and
magnetic properties of coronal structures. This paper outlines these
unique capabilities, which until present, have been feasible primarily
with observations during natural total solar eclipses. This work also
draws attention to the exciting possibility of greatly increasing
the frequency and duration of solar eclipse observations with Moon
orbiting observatories utilizing lunar limb occultation of the solar
disk for coronal measurements.
Title: Advanced Techniques for Studying Coronal Mass Ejections in
Three-Dimensions
Authors: Byrne, Jason P.; Morgan, Huw; Habbal, Shadia; Gallagher, Peter
Bibcode: 2013shin.confE.161B
Altcode:
As the STEREO mission progresses into 2013, the spacecrafts have moved
into quadrature on the far side of the Sun - a unique perspective in the
context of solar physics. This year also heralds the arrival of solar
maximum, when the solar activity cycle should peak and a multitude
of eruptive events may be observed. Therefore, methods for studying
the dynamical evolution of such phenomena as coronal mass ejections
(CMEs) are crucial for revealing the physics at play in these unique
observations. To this end, we present advanced image processing and
stereoscopic techniques for studying CMEs in an effort to determine
their true 3D nature as they propagate through the solar corona. This
is achieved by first performing a dynamic/quiescent signal separation
to remove the static corona in SECCHI images and applying multiscale
filtering techniques to enhance the observed structures. Then an
elliptical tie-pointing technique is used to generate a 3D surface
characterisation of the observed CME front, in order to reveal its true
morphology as it evolves. A model flux-rope was generated in order to
prove the optimal use of this 3D reconstruction technique, especially
while the spacecraft are in quadrature; and is being used to determine
the uncertainties involved in kinematic and morphological analyses of
candidate events observed during this phase of the STEREO mission.
Title: The Period Ratio for Standing Kink and Sausage Modes in Solar
Structures with Siphon Flow. I. Magnetized Slabs
Authors: Li, Bo; Habbal, Shadia Rifai; Chen, Yanjun
Bibcode: 2013ApJ...767..169L
Altcode: 2013arXiv1303.1689L
In the applications of solar magneto-seismology, the ratio of the period
of the fundamental mode to twice the period of its first overtone,
P 1/2P 2, plays an important role. We examine
how field-aligned flows affect the dispersion properties, and hence
the period ratios, of standing modes supported by magnetic slabs in
the solar atmosphere. We numerically solve the dispersion relations
and devise a graphic means to construct standing modes. For coronal
slabs, we find that the flow effects are significant for the fast
kink and sausage modes alike. For the kink ones, they may reduce P
1/2P 2 by up to 23% compared with the static case,
and the minimum allowed P 1/2P 2 can fall below
the lower limit analytically derived for static slabs. For the sausage
modes, while introducing the flow reduces P 1/2P 2
by typically <~ 5% relative to the static case, it significantly
increases the threshold aspect ratio only above which standing sausage
modes can be supported, meaning that their detectability is restricted
to even wider slabs. In the case of photospheric slabs, the flow effect
is not as strong. However, standing modes are distinct from the coronal
case in that standing kink modes show a P 1/2P 2
that deviates from unity even for a zero-width slab, while standing
sausage modes no longer suffer from a threshold aspect ratio. We
conclude that transverse structuring in plasma density and flow
speed should be considered in seismological applications of multiple
periodicities to solar atmospheric structures.
Title: An Anisotropic-Alfvénic-turbulence-based Solar Wind Model
with Proton Temperature Anisotropy
Authors: Li, B.; Habbal, S. R.
Bibcode: 2013ASPC..474..153L
Altcode: 2012arXiv1211.7136L
How the solar wind is accelerated to its supersonic speed is intimately
related to how it is heated. Mechanisms based on ion-cyclotron resonance
have been successful in explaining a large number of observations, those
concerning the significant ion temperature anisotropy above coronal
holes in particular. However, they suffer from the inconsistency with
turbulence theory which says that the turbulent cascade in a low-beta
medium like the solar corona should proceed in the perpendicular rather
than the parallel direction, meaning that there is little energy in
the ion gyro-frequency range for ions to absorb via ion-cyclotron
resonance. Recently a mechanism based on the interaction between the
solar wind particles and the anisotropic turbulence has been proposed,
where the perpendicular proton energy addition is via the stochastic
heating (Chandran et al. 2011). We extend this promising mechanism by
properly accounting for the effect of proton temperature anisotropy on
the propagation of Alfvén waves, for the radiative losses of electron
energy, and for the field line curvature that naturally accompanies
solar winds in the corona. While this mechanism was shown in previous
studies to apply to the polar fast solar wind, we demonstrate here
for the first time that it applies also to the slow wind flowing along
field lines bordering streamer helmets.
Title: The Role of Prominences in the Dynamics of the Solar Corona
Authors: Habbal, S. R.; Druckmuller, M.; Morgan, H.
Bibcode: 2012AGUFMSH53A2262H
Altcode:
Prominences, with temperatures between 40,000 and 100,000 K, are
the coolest structures extending beyond the limb in the solar
corona. Present at all times, they are known to be associated
with complex and twisted magnetic structures. They often erupt and
trigger the launch of coronal mass ejections. Using white light and
multi-wavelength images taken during total solar eclipses, we show how
prominences are indiscriminately linked to coronal structures spanning
a very broad range of spatial scales. Captured over a few minutes,
these images are snapshots of the quiescent and dynamic states of
the corona. These images cover a distance range of a few solar radii
starting from the solar surface, a range untenable with any other
instruments at present. We show how these observations capture the
omnipresence of plasma instabilities, directly linked to prominences,
in the context of large scale coronal structures. We discuss the
implications for the origin of plasma instabilities and turbulence
in the source region of the solar wind.; White light image of the
solar corona taken during the total solar eclipse of 11 July 2010. The
labels are assigned to special features. [From Habbal et al, ApJ 734,
120, 2011]
Title: Plasma Dynamics at the Prominence—Corona Interface
Authors: Miloch, W. J.; Habbal, S. R.; Esser, R.
Bibcode: 2012ApJ...752...85M
Altcode:
The interface between the cool and dense plasma typical of a
prominence and its tenuous and hot surrounding coronal plasma is
poorly understood. We study the plasma dynamics at this interface
using a three-dimensional particle-in-cell code, which enables us to
carry out simulations on spatial and temporal scales of the order of
the Debye length and plasma period, respectively. The results show
that anomalous Bohm diffusion across magnetic field lines occurs
at the interface, leading to mixing of the two plasmas. It is also
shown that collisions with neutral hydrogen within the prominence
plasma are of little importance for the plasma dynamics in the
prominence-corona transition region. In particular, the temperature
of the prominence plasma crossing the interface into the corona
can become anisotropic due to preferential heating by instabilities
originating from unstable velocity distributions. Our results pertain
to spatial scales significantly smaller than scales commonly used in
magnetohydrodynamic simulations, and they shed light on processes that
are very likely to be present at the interface.
Title: CORIMP CME Catalogue: Automatically Detecting & Tracking
CMEs in Coronagraph Data
Authors: Byrne, Jason Phelim; Morgan, Huw; Habbal, Shadia; Gallagher,
Peter
Bibcode: 2012shin.confE..91B
Altcode:
With the large amounts of CME image data available from the SOHO and
STEREO coronagraphs, manual cataloguing of events can be tedious and
subject to user bias. Therefore automated catalogues, such as CACTus
and SEEDS, have been developed in an effort to produce a robust method
of detection and analysis of events. Here we present the development
of a new CORIMP (coronal image processing) CME detection and tracking
technique that overcomes many of the drawbacks of previous methods. It
works by first employing a dynamic CME separation technique to remove
the static background, and then characterizing CMEs via a multiscale
edge-detection algorithm. This allows the inherent structure of
the CMEs to be revealed in each image, which is usually prone to
spatiotemporal crosstalk as a result of traditional image-differencing
techniques. Thus the kinematic and morphological information on
each event is resolved with higher accuracy than previous catalogues,
revealing CME acceleration and expansion profiles otherwise undetected,
and enabling a determination of the varying speeds attained across
the span of the CME. The potential for a 3D characterization of the
internal structure of CMEs is also demonstrated.
Title: Automatic Detection and Tracking of Coronal Mass
Ejections. II. Multiscale Filtering of Coronagraph Images
Authors: Byrne, Jason P.; Morgan, Huw; Habbal, Shadia R.; Gallagher,
Peter T.
Bibcode: 2012ApJ...752..145B
Altcode: 2012arXiv1207.6125B
Studying coronal mass ejections (CMEs) in coronagraph data can be
challenging due to their diffuse structure and transient nature,
and user-specific biases may be introduced through visual inspection
of the images. The large amount of data available from the Solar and
Heliospheric Observatory (SOHO), Solar TErrestrial RElations Observatory
(STEREO), and future coronagraph missions also makes manual cataloging
of CMEs tedious, and so a robust method of detection and analysis is
required. This has led to the development of automated CME detection
and cataloging packages such as CACTus, SEEDS, and ARTEMIS. Here, we
present the development of a new CORIMP (coronal image processing)
CME detection and tracking technique that overcomes many of the
drawbacks of current catalogs. It works by first employing the
dynamic CME separation technique outlined in a companion paper, and
then characterizing CME structure via a multiscale edge-detection
algorithm. The detections are chained through time to determine the
CME kinematics and morphological changes as it propagates across the
plane of sky. The effectiveness of the method is demonstrated by its
application to a selection of SOHO/LASCO and STEREO/SECCHI images,
as well as to synthetic coronagraph images created from a model corona
with a variety of CMEs. The algorithms described in this article are
being applied to the whole LASCO and SECCHI data sets, and a catalog
of results will soon be available to the public.
Title: Automatically Detecting and Tracking Coronal Mass
Ejections. I. Separation of Dynamic and Quiescent Components in
Coronagraph Images
Authors: Morgan, Huw; Byrne, Jason P.; Habbal, Shadia Rifai
Bibcode: 2012ApJ...752..144M
Altcode:
Automated techniques for detecting and tracking coronal mass ejections
(CMEs) in coronagraph data are of ever increasing importance for
space weather monitoring and forecasting. They serve to remove the
biases and tedium of human interpretation, and provide the robust
analysis necessary for statistical studies across large numbers of
observations. An important requirement in their operation is that
they satisfactorily distinguish the CME structure from the background
quiescent coronal structure (streamers, coronal holes). Many studies
resort to some form of time differencing to achieve this, despite
the errors inherent in such an approach—notably spatiotemporal
crosstalk. This article describes a new deconvolution technique that
separates coronagraph images into quiescent and dynamic components. A
set of synthetic observations made from a sophisticated model corona
and CME demonstrates the validity and effectiveness of the technique
in isolating the CME signal. Applied to observations by the LASCO
C2 and C3 coronagraphs, the structure of a faint CME is revealed in
detail despite the presence of background streamers that are several
times brighter than the CME. The technique is also demonstrated to
work on SECCHI/COR2 data, and new possibilities for estimating the
three-dimensional structure of CMEs using the multiple viewing angles
are discussed. Although quiescent coronal structures and CMEs are
intrinsically linked, and although their interaction is an unavoidable
source of error in any separation process, we show in a companion paper
that the deconvolution approach outlined here is a robust and accurate
method for rigorous CME analysis. Such an approach is a prerequisite
to the higher-level detection and classification of CME structure
and kinematics.
Title: Coordinated Visible, EUV and White Light Observations of the
Extended Corona During the 2010 July 11 Total Solar Eclipse
Authors: Habbal, Shadia R.; Landi, E.; Morgan, H.; Druckmuller, M.;
Ding, A.
Bibcode: 2012AAS...22042303H
Altcode:
Eclipse observations of coronal forbidden lines emitted by highly
ionized elements are unique as they extend the field of view of
space-borne high-resolution EUV spectrometers and narrow-band EUV
imagers up to several solar radii. Furthermore, they combine in one
single dataset the two main features of space-borne instrumentation:
high spatial resolution 2D images of the solar corona and
full temperature resolution and diagnostic potential allowed by
monochromatic imaging of individual spectral lines. The limitation
of the published eclipse results, however, has been the absence of
an absolute calibration. In the present work, we combine the 2010
July 11 eclipse observations with simultaneous observations carried
out with the Hinode/EIS instrument. Such a combination allows us to
calibrate the eclipse images and to use them to carry out detailed
plasma diagnostics in the extended corona out to a few solar radii
using a variety of techniques.
Title: New High-Accuracy Methods for Automatically Detecting &
Tracking CMEs
Authors: Byrne, Jason; Morgan, H.; Habbal, S. R.
Bibcode: 2012AAS...22051503B
Altcode:
With the large amounts of CME image data available from the SOHO and
STEREO coronagraphs, manual cataloguing of events can be tedious and
subject to user bias. Therefore automated catalogues, such as CACTus
and SEEDS, have been developed in an effort to produce a robust method
of detection and analysis of events. Here we present the development
of a new CORIMP (coronal image processing) CME detection and tracking
technique that overcomes many of the drawbacks of previous methods. It
works by first employing a dynamic CME separation technique to remove
the static background, and then characterizing CMEs via a multiscale
edge-detection algorithm. This allows the inherent structure of
the CMEs to be revealed in each image, which is usually prone to
spatiotemporal crosstalk as a result of traditional image-differencing
techniques. Thus the kinematic and morphological information on
each event is resolved with higher accuracy than previous catalogues,
revealing CME acceleration and expansion profiles otherwise undetected,
and enabling a determination of the varying speeds attained across
the span of the CME. The potential for a 3D characterization of the
internal structure of CMEs is also demonstrated.
Title: The US 2017 Total Solar Eclipse Workshops
Authors: Arndt, Martina B.; Habbal, S. R.; Wind Sherpas, Solar
Bibcode: 2012AAS...22020101A
Altcode:
In preparation for the Total Solar Eclipse that will span across the
United States in 2017, multiple eclipse workshops are being planned
to bring together professional and amateur researchers, educators,
and imagers. Our ultimate goal with these workshops is to maximize
the amount and quality of data we can collect during the eclipse as
well as to leverage this exciting event to educate and inspire people
of all ages. Part of the workshops will be dedicated to discussing
the science that can be learned from observing total solar eclipses,
and part of the workshops will be dedicated to strategizing about
how to mobilize and prepare communities in the path of totality. In
this poster, we will share our preliminary results from the inaugural
workshop in Maryland, April 2012.
Title: The CORIMP CME Catalogue: Automatically Detecting and Tracking
CMEs in Coronagraph Data
Authors: Byrne, Jason; Morgan, H.; Habbal, S. R.
Bibcode: 2012AAS...22020005B
Altcode:
Studying CMEs in coronagraph data can be challenging due to their
diffuse structure and transient nature, and user-specific biases may
be introduced through visual inspection of the images. The large
amount of data available from the SOHO and STEREO missions also
makes manual cataloguing of CMEs tedious, and so a robust method of
detection and analysis is required. This has led to the development
of automated CME detection and cataloguing packages such as CACTus,
SEEDS and ARTEMIS. Here we present the development of the CORIMP
(coronal image processing) Catalogue: a new, automated, multiscale,
CME detection and tracking catalogue, that overcomes many of the
drawbacks of current catalogues. It works by first employing a
dynamic CME separation technique to remove the static background,
and then characterizing CME structure via a multiscale edge-detection
algorithm. The detections are chained through time to determine the
CME kinematics and morphological changes as it propagates across the
plane-of-sky. The effectiveness of the method is demonstrated by its
application to a selection of SOHO/LASCO and STEREO/SECCHI images, as
well as to synthetic coronagraph images created from a model corona
with a variety of CMEs. These algorithms are being applied to the
whole LASCO and SECCHI datasets, and a CORIMP catalogue of results
will soon be available to the community.
Title: Advantage of Forbidden Emission Lines Over Extreme Ultraviolet
Lines as Coronal Diagnostic Tools
Authors: Habbal, Shadia R.; Druckmuller, M.; Morgan, H.; Ding, A.
Bibcode: 2012AAS...21922407H
Altcode:
Space-based observations, starting in the late sixties and early
seventies, established the frontier for exploring coronal emission
(from the Sun and stars) in the ultraviolet, extreme ultraviolet and
x-rays. Recently, these wavelengths have been the prime line-up for
imaging experiments on solar and heliospheric space-based observatories,
such as SOHO, Trace, STEREO, Hinode, and SDO. Such is also the case for
the recently approved Solar Orbiter mission. Using recent examples from
total solar eclipses, we show how probing the physics of the corona
is seriously short-changed without the inclusion of coronal forbidden
lines, such as the Fe X 637.4 nm, Fe XI 789.2 nm and Fe XIV 530.3 nm
lines. The diagnostic potential of these spectral lines stems primarily
from the strength of their resonantly excited component compared to
their EUV and X-rays counterparts where it is absent.
Title: Modeling the multi-component solar wind from the surface of
the Sun out to several astronomical units
Authors: Li, B.; Li, X.; Habbal, S. R.
Bibcode: 2011AGUFMSH53A2026L
Altcode:
Intrinsically multi-dimensional and involving the transition from the
collision-dominated to the collisionless regime, the solar wind proves
challenging to model. In this presentation we present a consistent
numerical scheme that treats the two major ion species, namely protons
and alpha particles, on an equal footing, and that readily incorporates
such effects as wave/turbulence heating and field-aligned electron heat
flux. The model uses as input the observation-based boundary conditions
at the solar surface and produces as output the global distribution of
fluid, magnetic field as well as wave/turbulence parameters out to the
Earth orbit and beyond. Several representative results we will present
are: 1) How well does the parallel cascade scenario work in shaping the
proton temperature anisotropy? 2) What is the role of finite-wavelength
(non-WKB) Alfven waves in coupling the two ion species? 3) What is the
role of waves/turbulence in shaping the ion differential streaming? On
the one hand, the available remote-sensing and in situ measurements
provide critical constraints for solar wind heating/acceleration
mechanisms. On the other hand, applying the forward modeling approach
to the model outputs helps us make better use of the remote-sensing
data, those made with SOHO/UVCS in particular.
Title: Exploring the Physics of the Corona with Total Solar Eclipse
Observations
Authors: Habbal, Shadia R.; Cooper, John; Daw, Adrian; Ding, Adalbert;
Druckmuller, Miloslav; Esser, Ruth; Johnson, Judd; Morgan, Huw
Bibcode: 2011arXiv1108.2323H
Altcode:
This white paper is a call for a concerted effort to support total
solar eclipse observations over the next decade, in particular for the
21 August 2017 eclipse which will traverse the US continent. With the
recent advances in image processing techniques and detector technology,
the time is ripe to capitalize on the unique diagnostic tools available
in the visible and near infrared wavelength range to explore the
physics of the corona. The advantage of coronal emission lines in this
wavelength range, over their extreme ultraviolet counterparts, is (1)
the significant radiative component in their excitation process (in
addition to the collisional excitation), which allows for observations
out to a few solar radii, (2) the higher spectral selectivity available
for imaging, giving well-defined temperature responses for each bandpass
(one line as opposed to many), and (3) the capability of polarization
measurements in a number of spectral lines. Consequently, the evolution
of the thermodynamic and magnetic properties of the coronal plasma can
be explored starting from the solar surface out to a few solar radii,
namely the most important region of the corona where the expansion
of the solar magnetic field and the acceleration of the solar wind
occur. Since the planning of eclipse observations will not be possible
without the invaluable NASA-published total solar eclipse bulletins by
Espenak and Andersen, a call is also made to ensure continued support
for these efforts.
Title: Enhancing Coronal Structures with the Fourier
Normalizing-radial-graded Filter
Authors: Druckmüllerová, Hana; Morgan, Huw; Habbal, Shadia R.
Bibcode: 2011ApJ...737...88D
Altcode:
Images of the corona have a high dynamic range which is excellent
for quantitative photometric analysis. To understand the processes
governing the solar corona, it is essential to have information about
the absolute brightness as well as the underlying structure. However,
due to the steep radial gradient of brightness in the images, and
to the fact that structures closer to the solar disk have higher
contrast than structures further from the disk, human vision cannot
view the intricate structure of the corona in such images. The
recently developed normalizing-radial-graded filter (NRGF) is an
effective way for revealing the coronal structure. In this work,
we present a more adaptive filter inspired by the NRGF, which
we call the Fourier normalizing-radial-graded filter (FNRGF). It
approximates the local average and the local standard deviation by a
finite Fourier series. This method enables the enhancement of finer
details, especially in regions of lower contrast. We also show how
the influence of additive noise is reduced by a modification to the
FNRGF. To illustrate the power of the method, the FNRGF is applied to
images of emission from coronal forbidden lines observed during the
2010 July 11 total solar eclipse. It is also successfully applied to
space-based observations of the low corona in the extreme ultraviolet
and to white light coronagraph observations, thus demonstrating the
validity of the FNRGF as a new tool that will help the interpretation
of the information embedded in most types of coronal images.
Title: Observation of High-speed Outflow on Plume-like
Structures of the Quiet Sun and Coronal Holes with Solar Dynamics
Observatory/Atmospheric Imaging Assembly
Authors: Tian, Hui; McIntosh, Scott W.; Habbal, Shadia Rifai; He,
Jiansen
Bibcode: 2011ApJ...736..130T
Altcode: 2011arXiv1105.3119T
Observations from the Atmospheric Imaging Assembly onboard the Solar
Dynamics Observatory reveal ubiquitous episodic outflows (jets)
with an average speed around 120 km s-1 at temperatures
often exceeding a million degree in plume-like structures, rooted in
magnetized regions of the quiet solar atmosphere. These outflows are not
restricted to the well-known plumes visible in polar coronal holes, but
are also present in plume-like structures originating from equatorial
coronal holes and quiet-Sun (QS) regions. Outflows are also visible
in the "inter-plume" regions throughout the atmosphere. Furthermore,
the structures traced out by these flows in both plume and inter-plume
regions continually exhibit transverse (Alfvénic) motion. Our finding
suggests that high-speed outflows originate mainly from the magnetic
network of the QS and coronal holes (CHs), and that the plume flows
observed are highlighted by the denser plasma contained therein. These
outflows might be an efficient means to provide heated mass into the
corona and serve as an important source of mass supply to the solar
wind. We demonstrate that the QS plume flows can sometimes significantly
contaminate the spectroscopic observations of the adjacent CHs—greatly
affecting the Doppler shifts observed, thus potentially impacting
significant investigations of such regions.
Title: The U.S. Eclipse Megamovie in 2017: a white paper on a unique
outreach event
Authors: Hudson, Hugh S.; McIntosh, Scott W.; Habbal, Shadia R.;
Pasachoff, Jay M.; Peticolas, Laura
Bibcode: 2011arXiv1108.3486H
Altcode:
Totality during the solar eclipse of 2017 traverses the entire breadth
of the continental United States, from Oregon to South Carolina. It thus
provides the opportunity to assemble a very large number of images,
obtained by amateur observers all along the path, into a continuous
record of coronal evolution in time; totality lasts for an hour and
a half over the continental U.S. While we describe this event here as
an opportunity for public education and outreach, such a movie -with
very high time resolution and extending to the chromosphere - will also
contain unprecedented information about the physics of the solar corona.
Title: Observation of High-speed Outflow on Plume-like Structures
of the Quiet Sun and Coronal Holes with SDO/AIA
Authors: Tian, Hui; McIntosh, Scott W.; Habbal, Shadia Rifal; He,
Jiansen
Bibcode: 2011shin.confE.161T
Altcode:
Observations from the Atmospheric Imaging Assembly (AIA) onboard the
Solar Dynamics Observatory (SDO) reveal ubiquitous episodic outflows
(jets) with an average speed around 120 km s-1 at temperatures
often exceeding a million degree in plume-like structures, rooted in
magnetized regions of the quiet solar atmosphere. These outflows are not
restricted to the well-known plumes visible in polar coronal holes, but
are also present in plume-like structures originating from equatorial
coronal holes and quiet-Sun regions. Outflows are also visible in
the "interplume" regions throughout the atmosphere. Furthermore, the
structures traced out by these flows in both plume and inter-plume
regions continually exhibit transverse (Alfvéenic) motion. Our finding
suggests that high-speed outflows originate mainly from the magnetic
network of the quiet Sun and coronal holes, and that the plume flows
observed are highlighted by the denser plasma contained therein. These
outflows might be an efficient means to provide heated mass into the
corona and serve as an important source of mass supply to the solar
wind. We demonstrate that the quiet-Sun plume flows can sometimes
significantly contaminate the spectroscopic observations of the adjacent
coronal holes - greatly affecting the Doppler shifts observed, thus
potentially impacting significant investigations of such regions.
Title: A Multiscale Technique for Automatically Detecting &
Tracking CMEs in Coronagraph Data
Authors: Byrne, Jason P.; Morgan, Huw; Habbal, Shadia R.
Bibcode: 2011shin.confE.140B
Altcode:
Studying coronal mass ejections (CMEs) in coronagraph data can be
challenging due to their diffuse structure and transient nature, and
user-specific biases may be introduced through visual inspection of
the images. The large amounts of data available from the SOHO, STEREO,
and future Solar Orbiter missions, also makes manual cataloguing of
CMEs tedious, and so a robust method of detection and analysis is
required. This has led to the development of automated CME detection
and cataloguing packages such as CACTus, SEEDS and ARTEMIS. However,
the main drawbacks of these catalogues are: the CACTus method of
detection fails to resolve CME acceleration profiles; the CACTus and
SEEDS running-difference images suffer from spatiotemporal crosstalk;
and the SEEDS and ARTEMIS detections are limited to only the LASCO/C2
field-of-view. Recently, the benefits of multiscale filtering of
coronagraph data have been demonstrated in an effort to overcome
current cataloguing issues. A multiscale decomposition can be applied
to individual images in order to enhance the structure of CMEs whilst
removing noise and small-scale features like stars. Here we present
the development of a new, automated, multiscale, CME detection &
tracking technique. It works by first separating the dynamic CME signal
from the background corona and then characterising CME structure
via a multiscale edge-detection algorithm. The detections are then
chained through time to determine the CME kinematics and morphological
changes as it propagates across the plane-of-sky. We demonstrate
its application to a sample of LASCO data and prove its efficacy in
detecting and tracking CMEs. This technique is being applied to the
complete LASCO dataset, and it is planned to further develop it for
implementation on the SECCHI/COR dataset in the near future.
Title: Thermodynamics of the Solar Corona and Evolution of the Solar
Magnetic Field as Inferred from the Total Solar Eclipse Observations
of 2010 July 11
Authors: Habbal, Shadia Rifai; Druckmüller, Miloslav; Morgan, Huw;
Ding, Adalbert; Johnson, Judd; Druckmüllerová, Hana; Daw, Adrian;
Arndt, Martina B.; Dietzel, Martin; Saken, Jon
Bibcode: 2011ApJ...734..120H
Altcode:
We report on the first multi-wavelength coronal observations,
taken simultaneously in white light, Hα 656.3 nm, Fe IX 435.9 nm,
Fe X 637.4 nm, Fe XI 789.2 nm, Fe XIII 1074.7 nm, Fe XIV 530.3 nm,
and Ni XV 670.2 nm, during the total solar eclipse of 2010 July 11
from the atoll of Tatakoto in French Polynesia. The data enabled
temperature differentiations as low as 0.2 × 106 K. The
first-ever images of the corona in Fe IX and Ni XV showed that there
was very little plasma below 5 × 105 K and above 2.5 ×
106 K. The suite of multi-wavelength observations also
showed that open field lines have an electron temperature near 1×
106 K, while the hottest, 2× 106 K, plasma
resides in intricate loops forming the bulges of streamers, also known
as cavities, as discovered in our previous eclipse observations. The
eclipse images also revealed unusual coronal structures, in the form
of ripples and streaks, produced by the passage of coronal mass
ejections and eruptive prominences prior to totality, which could
be identified with distinct temperatures for the first time. These
trails were most prominent at 106 K. Simultaneous Fe X
17.4 nm observations from Proba2/SWAP provided the first opportunity
to compare Fe X emission at 637.4 nm with its extreme-ultraviolet
(EUV) counterpart. This comparison demonstrated the unique diagnostic
capabilities of the coronal forbidden lines for exploring the evolution
of the coronal magnetic field and the thermodynamics of the coronal
plasma, in comparison with their EUV counterparts in the distance range
of 1-3 R sun. These diagnostics are currently missing from
present space-borne and ground-based observatories.
Title: Modeling Iron Abundance Enhancements in the Slow Solar Wind
Authors: Byhring, H. S.; Cranmer, S. R.; Lie-Svendsen, Ø.; Habbal,
S. R.; Esser, R.
Bibcode: 2011ApJ...732..119B
Altcode:
We have studied the behavior of Fe ions in the slow solar wind,
using a fluid model extending from the chromosphere to 1 AU. Emphasis
is on elemental "pileup" in the corona, i.e., a region where the Fe
density increases and has a local maximum. We study the behavior of
individual Fe ions relative to each other in the pileup region, where
Fe+10 and Fe+12 have been used as examples. We
find that elemental pileups can occur for a variety of densities
and temperatures in the corona. We also calculate the ion fractions
and obtain estimates for the freezing-in distance of Fe in the slow
solar wind. We find that the freezing-in distance for iron is high,
between 3 and 11 R sun, and that a high outflow velocity,
of order 50-100 km s-1, in the region above the temperature
maximum is needed to obtain ion fractions for Fe+10 and
Fe+12 that are consistent with observations.
Title: The Coronal Imprints of Eruptive Prominences and CMEs as
Revealed by the Total Solar Eclipse Observations of 11 July 2010
Authors: Habbal, Shadia R.; Druckmuller, M.; Morgan, H.; Ding, A.;
Johnson, J.; Druckmullerova, H.; Daw, A.; Arndt, M. B.
Bibcode: 2011SPD....42.1305H
Altcode: 2011BAAS..43S.1305H
Total solar eclipses continue to provide unique opportunities for
observing the corona, due primarily to the exceptional diagnostic
capabilities offered by emission from forbidden lines. Such observations
span the heliocentric distance range of 1 - 3 solar radii, providing
information that is currently inaccessible to any space-borne or
ground-based observatory. Taking advantage of such an opportunity,
the most ambitious multi-wavelength observations to date were made
simultaneously in broadband white light, H alpha 656.3 nm, Fe IX 435.9
nm, Fe X 637.4 nm, Fe XI 789.2 nm, Fe XIII 1074.7 nm, Fe XIV 530.3 nm
and Ni XV 670.2 nm, during the total solar eclipse of 11 July 2010
from Tatakoto, an atoll in French Polynesia. A number of curious
coronal structures, namely ripples, streaks and a structure in the
shape of a hook, were detected in the images. The ripples were most
prominent in emission from spectral lines associated with temperatures
around 106 K. The most prominent streak was associated
with a conical-shaped void in the emission from the coolest line of
Fe IX and from the hottest line of Ni XV. A prominence, which erupted
prior to totality, produced the hook in the cooler lines of Fe X and
Fe XI, spanning 0.5 Rs in extent, centered at 1.3 Rs, with a complex
trail of hot and cool twisted structures connecting it to the solar
surface. These observations show for the first time how the passage of
CMEs and eruptive prominences through the corona leave complex density
trails with distinct temperatures.
Title: A Multiscale Technique for Automatically Detecting and Tracking
CMEs in Coronagraph Data
Authors: Byrne, Jason; Morgan, H.; Habbal, S.
Bibcode: 2011SPD....42.2301B
Altcode: 2011BAAS..43S.2301B
Studying coronal mass ejections (CMEs) in coronagraph data can be
challenging due to their diffuse structure and transient nature, and
user-specific biases may be introduced through visual inspection of
the images. The large amounts of data available from the SOHO, STEREO,
and future Solar Orbiter missions, also makes manual cataloguing of
CMEs tedious, and so a robust method of detection and analysis is
required. This has led to the development of automated CME detection
and cataloguing packages such as CACTus, SEEDS and ARTEMIS. However,
the main drawbacks of these catalogues are: the CACTus method of
detection fails to resolve CME acceleration profiles; the CACTus and
SEEDS running-difference images suffer from spatiotemporal crosstalk;
and the SEEDS and ARTEMIS detections are limited to only the LASCO/C2
field-of-view. Recently, the benefits of multiscale filtering of
coronagraph data have been demonstrated in an effort to overcome
current cataloguing issues. A multiscale decomposition can be applied
to individual images in order to enhance the structure of CMEs whilst
removing noise and small-scale features like stars. Here we present
the development of a new, automated, multiscale, CME detection &
tracking technique. It works by first separating the dynamic CME signal
from the background corona and then characterising CME structure
via a multiscale edge-detection algorithm. The detections are then
chained through time to determine the CME kinematics and morphological
changes as it propagates across the plane-of-sky. We demonstrate
its application to a sample of LASCO data and prove its efficacy in
detecting and tracking CMEs. This technique is being applied to the
complete LASCO dataset, and it is planned to further develop it for
implementation on the SECCHI/COR dataset in the near future.
Title: A new view of coronal structures: implications for the source
and acceleration of the solar wind
Authors: Habbal, S. R.; Morgan, H.; Druckmüller, M.
Bibcode: 2011ASInC...2..259H
Altcode:
We show how the complement of white light and a suite of Fe coronal
forbidden line images taken during total solar eclipses since 2006
have yielded new insights into the physical properties of the coronal
plasma and the role of the magnetic field. The unique properties of
these spectral lines make them ideal diagnostic tools for exploring the
first few solar radii above the photosphere where the expansion of the
corona and the acceleration of the solar wind occur. In particular,
these observations show how: (1) localized enhancements of the ion
densities relative to electrons appear in some magnetic structures,
(2) the transition between a collision-dominated to a collisionless
plasma occurs within a heliocentric distance of 1.2 - 1.6 R_s, (3)
the expanding corona is characterized by an electron temperature of
10^6 K, and (4) prominences are enshrouded by hot 2 × 10^6 K coronal
plasma. We discuss the implications of these observations for the
source and acceleration of the solar wind.
Title: Hot Prominence Shrouds (Invited)
Authors: Habbal, S. R.; Druckmuller, M.; Morgan, H.; Solar Wind Sherpas
Bibcode: 2010AGUFMSH54A..03H
Altcode:
The reduced white light emission often observed at the base of streamers
in coronagraphic or total solar eclipse images is commonly referred to
as a prominence cavity. Using multiwavelength eclipse observations,
we show that these cavities are invariably associated with very
hot material, often exceeding 2 million degrees. These empirical
results provide observational evidence for the early model studies of
prominence environments, which predicted the existence of these hot
envelopes. Their implications for the plasma properties of coronal mass
ejections associated with prominence eruptions will also be discussed.
Title: Space Based Observations of Coronal Cavities in Conjunction
with the Total Solar Eclipse of July 2010
Authors: Kucera, T. A.; Berger, T. E.; Boerner, P.; Dietzel, M.;
Druckmuller, M.; Gibson, S. E.; Habbal, S. R.; Morgan, H.; Reeves,
K. K.; Schmit, D. J.; Seaton, D. B.
Bibcode: 2010AGUFMSH51A1666K
Altcode:
In conjunction with the total solar eclipse on July 11, 2010 we
coordinated a campaign between ground and space based observations. Our
specific goal was to augment the ground based measurement of coronal
prominence cavity temperatures made using iron lines in the IR (Habbal
et al. 2010 ApJ 719 1362) with measurements performed by space based
instruments. Included in the campaign were Hinode/EIS, XRT and SOT,
PROBA2/SWAP, SDO/AIA, SOHO/CDS and STEREO/SECCHI/EUVI, in addition
to the ground based IR measurements. We plan to use a combination of
line ratio and forward modeling techniques to investigate the density
and temperature structure of the cavities at that time.
Title: Tomography and the distribution of streamers in the extended
solar corona: some implications for large-scale MHD models
Authors: Morgan, H.; Habbal, S. R.
Bibcode: 2010AGUFMSH31A1790M
Altcode:
cycle. Streamers are most often shaped as extended, often very narrow,
plasma sheets. At most times outside the height of solar maximum,
there are two separate stable large helmet streamer belts extending
from mid-latitudes (in both North and South). At solar minimum, the
streamers converge and join near the equator, giving the impression
of a single large helmet streamer. Outside of solar minimum, the two
streamers do not join, forming separate high-density sheets in the
extended corona (one in the North, another in the South). At solar
maximum, streamers rise radially from their source regions, whilst
during the ascending and descending activity phases, streamers are
skewed towards the equator. For most of the activity cycle, streamers
share the same latitudinal extent as filaments on the disk, showing
that large-scale stable streamers are closely linked to the same
large-scale photospheric magnetic configuration which give rise to
large filaments. The polewards footpoints of the streamers are often
above crown polar filaments and the equatorial footpoints are above
filaments or active regions (or above the photospheric neutral lines
which underlie these structures). The high-density structures arising
from the equatorial active regions either rise and form the equatorial
footpoints of mid-latitude quiescent streamers, or form unstable
streamers at the equator, not connected to the quiescent streamer
structure at higher latitude (so there are often three streamer sheets
sharing the same extended longitudinal region). Comparison between the
tomography results and a potential field source surface model shows
that streamers are not necessarily associated with a magnetic polarity
reversal, but rather are regions containing field lines arising from
widely-separated sources at the Sun. We call these convergence sheets
(sometimes called 'pseudostreamers'). Large-scale coronal MHD models
could improve their agreement with observation by incorporating the
results of tomography.
Title: Total Solar Eclipse Observations of Hot Prominence Shrouds
Authors: Habbal, S. Rifai; Druckmüller, M.; Morgan, H.; Scholl, I.;
Rušin, V.; Daw, A.; Johnson, J.; Arndt, M.
Bibcode: 2010ApJ...719.1362H
Altcode:
Using observations of the corona taken during the total solar eclipses
of 2006 March 29 and 2008 August 1 in broadband white light and in
narrow bandpass filters centered at Fe X 637.4 nm, Fe XI 789.2 nm, Fe
XIII 1074.7 nm, and Fe XIV 530.3 nm, we show that prominences observed
off the solar limb are enshrouded in hot plasmas within twisted magnetic
structures. These shrouds, which are commonly referred to as cavities
in the literature, are clearly distinct from the overlying arch-like
structures that form the base of streamers. The existence of these
hot shrouds had been predicted by model studies dating back to the
early 1970s, with more recent studies implying their association with
twisted magnetic flux ropes. The eclipse observations presented here,
which cover a temperature range of 0.9 to 2 ×106 K, are
the first to resolve the long-standing ambiguity associated with the
temperature and magnetic structure of prominence cavities.
Title: Hot Prominence Cavities
Authors: Habbal, Shadia R.; Druckmuller, M.; Morgan, H.; Scholl, I.;
Rusin, V.; Daw, A.; Johnson, J.; Arndt, M.
Bibcode: 2010AAS...21630202H
Altcode:
Multiwavelength observations of the solar corona made during the total
solar eclipses of 2006 March 29 and 2008 August 1, are used to study
the thermodynamic properties of prominence cavities. Historically,
cavities have been associated with the base of streamers where the
white light intensity is reduced compared to their surroundings. The
exceptional high spatial resolution close to 1 arcsec in the white
light eclipse images, show that they consist of arch-like envelopes,
extending from 0.1 to 0.3 solar radii above prominences. They are
invariably bright in coronal emission lines, with their brightness
varying with temperature. For most of the cases observed, the cavities
are dominated by emission from the hotter, 2 MK Fe XIII 1074.7 and Fe
XIV 530.3 nm lines, although examples of cavities which were bright
in the cooler 1 MK Fe X 637.4 and Fe XI 789.2 nm lines, and dim in
the hotter lines, were also found. These observations resolve the
long-standing ambiguity associated with the temperature of cavities.
Title: On the Constancy of the Electron Temperature in the Expanding
Corona Throughout Solar Cycle 23
Authors: Habbal, Shadia Rifai; Morgan, Huw; Druckmüller, Miloslav;
Ding, Adalbert
Bibcode: 2010ApJ...711L..75H
Altcode:
A recent analysis of Fe emission lines observed during the total solar
eclipses of 2006 March 29 and 2008 August 1 established the first
empirical link between the electron temperature in the expanding corona
and Fe charge states measured in interplanetary space. In this Letter,
we use this link to infer this temperature throughout solar cycle
23 from in situ charge state measurements from the Solar Wind Ion
Composition Spectrometer (SWICS) on the Advanced Composition Explorer
(ACE) and on Ulysses. The distribution of the SWICS/ACE Fe charge
states, which span cycle 23 from 1998 to 2009, is skewed with a peak
centered on Fe8+, Fe9+, and Fe10+
and a tail spanning Fe12+ to Fe20+. An iterative
process based on this distribution and on the Fe ion fraction as
a function of electron temperature yields a narrow peak at 1.1 ×
106 K. The tail in the measured charge state distribution
is attributed to the sporadic release of material hotter than 2 ×
106 K from closed magnetic structures within the bulges of
streamers. The Fe Ulysses charge state measurements between 1992 and
1997 from cycle 22 peaked at Fe11+, indicative of a slightly
higher temperature of 1.5 × 106 K. The relative constancy
of the electron temperature in the expanding corona throughout solar
cycle 23 points to the presence of an unknown mechanism regulating the
energy input to electrons in the acceleration region of the solar wind
at all latitudes during this cycle.
Title: Observations of the 3D coronal structure over a solar cycle
Authors: Morgan, Huw; Habbal, Shadia
Bibcode: 2010AIPC.1216..691M
Altcode:
Solar rotational tomography is applied to almost eleven years of LASCO
C2/SOHO data, revealing for the first time the structural behavior
of streamers over almost a full solar activity cycle. Streamers
are most often shaped as extended, narrow plasma sheets. The sheets
can be extremely narrow at times (<=0.14×106 km at
4Rsolar). This is over twice their heliocentric angular
thickness at 1 AU. For most of the activity cycle, streamers share
the same latitudinal extent as filaments on the disk, showing
that large-scale stable streamers are closely linked to the same
large-scale photospheric magnetic configuration which give rise
to large filaments. There is considerable differential rotation of
streamers at high latitudes, which makes comparison between disk and
coronal structure complicated. The presence of differential rotation
has implications for many areas of coronal and heliospheric research.
Title: A Method for Separating Coronal Mass Ejections from the
Quiescent Corona
Authors: Morgan, Huw; Habbal, Shadia
Bibcode: 2010ApJ...711..631M
Altcode:
A method for separating coronal mass ejections (CMEs) from the quiescent
corona in white-light coronagraph images is presented. Such a separation
allows the study of CME structure, as well as enabling a study of the
quiescent coronal structure, without contamination by the CME. The
fact that the large-scale quiescent corona is very close to radial,
whilst CMEs are highly non-radial, enables the separation of the
two components. The method is applied to Large Angle Spectrometric
Coronagraph/Solar and Heliospheric Observatory C2 and C3 observations,
and is successful in revealing CME signal, faint CMEs and blobs,
and dark rarefactions within a CME. The success of the separation is
tested at solar minimum, a time when streamers are in general most
non-radial. The technique is also compared to other commonly used
methods. The separation method enables (1) the study of extremely faint
CME structure, down to almost the noise level of the coronagraphs, (2)
paves the way for automated categorization of CME internal structure,
and (3) provides a cleaner basis for tomography of the quiescent corona,
without contamination from CMEs.
Title: Observational Aspects of the Three-dimensional Coronal
Structure Over a Solar Activity Cycle
Authors: Morgan, Huw; Habbal, Shadia Rifai
Bibcode: 2010ApJ...710....1M
Altcode:
Solar rotational tomography is applied to almost eleven years of Large
Angle Spectrometric Coronagraph C2/Solar and Heliospheric Observatory
data, revealing for the first time the behavior of the large-scale
coronal density structures, also known as streamers, over almost a full
solar activity cycle. This study gives an overview of the main results
of this project. (1) Streamers are most often shaped as extended,
narrow plasma sheets. The sheets can be extremely narrow at times
(<=0.14 × 106 km at 4 R sun). This is over
twice their heliocentric angular thickness at 1 AU. (2) At most times
outside the height of solar maximum, there are two separate stable
large helmet streamer belts extending from mid-latitudes (in both
north and south). At solar minimum, the streamers converge and join
near the equator, giving the impression of a single large helmet
streamer. Outside of solar minimum, the two streamers do not join,
forming separate high-density sheets in the extended corona (one in
the north, another in the south). At solar maximum, streamers rise
radially from their source regions, while during the ascending and
descending activity phases, streamers are skewed toward the equator. (3)
For most of the activity cycle, streamers share the same latitudinal
extent as filaments on the disk, showing that large-scale stable
streamers are closely linked to the same large-scale photospheric
magnetic configuration, which give rise to large filaments. (4)
The poleward footpoints of the streamers are often above crown polar
filaments and the equatorial footpoints are above filaments or active
regions (or above the photospheric neutral lines which underlie these
structures). The high-density structures arising from the equatorial
active regions either rise and form the equatorial footpoints of
mid-latitude quiescent streamers, or form unstable streamers at the
equator, not connected to the quiescent streamer structure at higher
latitude (so there are often three streamer sheets sharing the same
extended longitudinal region). (5) Comparison between the tomography
results and a potential field source surface model shows that streamers
are not necessarily associated with a magnetic polarity reversal,
but rather are regions containing field lines arising from widely
separated sources at the Sun. We call these convergence sheets. (6)
There is considerable differential rotation of streamers at high
latitudes, which makes comparison between disk and coronal structure
complicated. The presence of differential rotation has implications
for many areas of coronal and heliospheric research.
Title: Mapping the Distribution of Electron Temperature and Fe Charge
States in the Corona with Total Solar Eclipse Observations
Authors: Habbal, S. Rifai; Druckmüller, M.; Morgan, H.; Daw, A.;
Johnson, J.; Ding, A.; Arndt, M.; Esser, R.; Rušin, V.; Scholl, I.
Bibcode: 2010ApJ...708.1650H
Altcode:
The inference of electron temperature from the ratio of the intensities
of emission lines in the solar corona is valid only when the plasma is
collisional. Once collisionless, thermodynamic ionization equilibrium
no longer holds, and the inference of an electron temperature
and its gradient from such measurements is no longer valid. At the
heliocentric distance where the transition from a collision-dominated to
a collisionless plasma occurs, the charge states of different elements
are established, or frozen-in. These are the charge states which are
subsequently measured in interplanetary space. We show in this study
how the 2006 March 29 and 2008 August 1 eclipse observations of a
number of Fe emission lines yield an empirical value for a distance,
which we call Rt , where the emission changes from being
collisionally to radiatively dominated. Rt ranges from 1.1 to
2.0 R sun, depending on the charge state and the underlying
coronal density structures. Beyond that distance, the intensity of the
emission reflects the distribution of the corresponding Fe ion charge
states. These observations thus yield the two-dimensional distribution
of electron temperature and charge state measurements in the corona
for the first time. The presence of the Fe X 637.4 nm and Fe XI 789.2
nm emission in open magnetic field regions below Rt , such
as in coronal holes and the boundaries of streamers, and the absence
of Fe XIII 1074.7 nm and Fe XIV 530.3 nm emission there indicate
that the sources of the solar wind lie in regions where the electron
temperature is less than 1.2 × 106 K. Beyond Rt
, the extent of the Fe X [Fe9+] and Fe XI emission
[Fe10+], in comparison with Fe XIII [Fe12+] and Fe
XIV [Fe13+], matches the dominance of the Fe10+
charge states measured by the Solar Wind Ion Composition Spectrometer,
SWICS, on Ulysses, at -43° latitude at 4 AU, in March-April 2006, and
Fe9+ and Fe10+ charge states measured by SWICS on
the Advanced Composition Explorer, ACE, in the ecliptic plane at 1 AU,
at the time of both eclipses. The remarkable correspondence between
these two measurements establishes the first direct link between the
distribution of charge states in the corona and in interplanetary space.
Title: Eclipse Observations of the Fe XI 789.2 nm Line
Authors: Daw, Adrian; Habbal, S. R.; Morgan, H.; Druckmuller, M.;
Ding, A.; Johnson, J.; Rusin, V.
Bibcode: 2010AAS...21532203D
Altcode: 2010BAAS...42..323D
The first image of the corona in Fe XI 789.2 nm was taken during
the total solar eclipse of 29 March 2006. It revealed a number
of surprises, primarily an emission extending out to at least 3
Rs and localized regions of enhanced Fe^10+ ion density relative
to electrons. Subsequent observations of this spectral line were
successfully made during the eclipses of 2008 and 2009. These Fe XI
observations will be presented, together with simultaneous eclipse
observations of the more widely observed Fe X 637.4, Fe XIII 1074.7 and
Fe XIV 530.3 nm lines. Particular emphasis will be placed on the new
insights gained by this suite of measurements into the thermodynamic
properties of the inner corona.
Title: Space-time localization of inner heliospheric plasma turbulence
using multiple spacecraft radio links
Authors: Richie-Halford, Adam C.; Iess, L.; Tortora, P.; Armstrong,
J. W.; Asmar, S. W.; Woo, Richard; Habbal, Shadia Rifai; Morgan, Huw
Bibcode: 2009SpWea...712003R
Altcode: 2010arXiv1003.3848R
Radio remote sensing of the heliosphere using spacecraft radio signals
has been used to study the near-Sun plasma in and out of the ecliptic,
close to the Sun, and on spatial and temporal scales not accessible
with other techniques. Studies of space-time variations in the inner
solar wind are particularly timely because of the desire to understand
and predict space weather, which can disturb satellites and systems at
1 AU and affect human space exploration. Here we demonstrate proof of
concept of a new radio science application for spacecraft radio science
links. The differing transfer functions of plasma irregularities to
spacecraft radio uplinks and downlinks can be exploited to localize
plasma scattering along the line of sight. We demonstrate the utility of
this idea using Cassini radio data taken in 2001-2002. Under favorable
circumstances we demonstrate how this technique, unlike other remote
sensing methods, can determine center-of-scattering position to within
a few thousandths of an AU and thickness of scattering region to less
than about 0.02 AU. This method, applied to large data sets and used in
conjunction with other solar remote sensing data such as white light
data, has space weather application in studies of inhomogeneity and
nonstationarity in the near-Sun solar wind.
Title: Multi-instrument Study of the Influence of sunspots Magnetic
Fields on the Outflow from adjacent Coronal Holes
Authors: Al-Haddad, Nada A. M.; Habbal, S. R.; Morgan, H.; Scholl,
I.; Roussev, I. I.
Bibcode: 2009shin.confE..18A
Altcode:
Coronal holes are thought to be the origin of the fast solar wind,
although the exact process of its acceleration is yet unknown. In a
recent study, Habbal et al. (2008) found that the presence of an active
region in the proximity of a coronal hole may cause an increase in the
outflow speed. This conclusion was based on SUMER Doppler shift disk
measurements from which the line of sight outflow was inferred. To
further explore this idea, we combine disk MDI magnetograms with
the corresponding UVCS observations off the limb and in situ solar
wind data from ACE for equatorial coronal holes identified from the
Kitt Peak He I 10830 synoptic maps. The UVCS data provide two proxies
for outflow diagnostics: the line widths and intensity ratios of the
oxygen 1032/1037 doublet. We study the speed associated with several
long-lasting coronal holes (i.e. present for 3 to 10 carrington
rotations) and correlate the speed with the strength of the magnetic
fields in the neighboring sunspots. The outcome of this exploratory
work will be presented, and the possible causes of the association
between the different plasma parameters, such as field strength,
outflow velocity, and line widths will be discussed.
Title: IfA Catalogs of Solar Data Products
Authors: Habbal, Shadia R.; Scholl, I.; Morgan, H.
Bibcode: 2009SPD....40.1411H
Altcode:
This paper presents a new set of online catalogs of solar data
products. The IfA Catalogs of Solar Data Products were developed to
enhance the scientific output of coronal images acquired from ground
and space, starting with the SoHO era. Image processing tools have
played a significant role in the production of these catalogs [Morgan
et al. 2006, 2008, Scholl and Habbal 2008]. Two catalogs are currently
available at http://alshamess.ifa.hawaii.edu/ : 1) Catalog of daily
coronal images: One coronal image per day from EIT, MLSO and LASCO/C2
and C3 have been processed using the Normalizing Radial-Graded-Filter
(NRGF) image processing tool. These images are available individually or
as composite images. 2) Catalog of LASCO data: The whole LASCO dataset
has been re-processed using the same method. The user can search files
by dates and instruments, and images can be retrieved as JPEG or FITS
files. An option to make on-line GIF movies from selected images is
also available. In addition, the LASCO data set can be searched from
existing CME catalogs (CDAW and Cactus). By browsing one of the two CME
catalogs, the user can refine the query and access LASCO data covering
the time frame of a CME. The catalogs will be continually updated as
more data become publicly available.
Title: The Curious Case of the Fe XI 789.2 nm Line
Authors: Habbal, Shadia R.; Daw, A.; Morgan, H.; Johnson, J.;
Druckmuller, M.; Rusin, V.
Bibcode: 2009SPD....40.3204H
Altcode:
The first image of the corona in the Fe XI 789.2 nm line was obtained
during the total solar eclipse of 29 March 2006. Observations of the
same spectral line, in conjunction with other more regularly observed
Fe lines, such as Fe X 637.4, Fe XIII 1074.7 and Fe XIV 530.3 nm,
were made during the eclipse of 1 August 2008. During both eclipses,
the Fe XI emission extended further out in the corona than the other
Fe lines. The other striking features in both Fe XI observations was
the presence of localized enhanced emission when compared to white
light, and coronal structures more readily observed in Fe XI than
in white light. The results from both eclipses will be presented,
with particular emphasis on their implications for coronal heating
mechanisms and the coronal electron temperature.
Title: Mapping the Structure of the Corona Using Fourier
Backprojection Tomography
Authors: Morgan, Huw; Habbal, Shadia Rifai; Lugaz, Noé
Bibcode: 2009ApJ...690.1119M
Altcode:
Estimating the structure, or density distribution, of the solar
corona from a set of two-dimensional white-light images made by
coronagraphs is a critical challenge in coronal physics. This work
describes new data-analysis procedures which are used to create global
maps of the coronal structure at heights where the corona becomes
approximately radial (>= 3 R sun). The technique,
which is named Qualitative Solar Rotational Tomography (QSRT),
uses total brightness white light observations, processed with a
suitable background subtraction and a Normalizing Radial Graded
Filter (NRGF). These observations are made with high frequency by
the Large Angle and Spectrometric Coronagraph Experiment (LASCO)
C2 coronagraph, which allows a standard Fourier-transform-based
tomographical reconstruction. In this paper, we first test the technique
using a model corona. QSRT is then applied to a set of observations
made during Carrington Rotation (CR) 2000-2001 (2003 March 16 to
2003 March 31). Since the maps are constructed from data which are
normalized using the NRGF process, QSRT cannot give electron density
directly. Nevertheless, the tests using the model corona demonstrate
the technique's ability to give a good qualitative reconstruction
of the coronal structure at high latitude, with decreasing but
acceptable accuracy at the equator. These tests also demonstrate QSRT's
insensitivity to noise. For the LASCO C2 observations, good agreement is
found between synthetic images calculated from the reconstructed corona
and the original observations, and good agreement is found between the
distribution of density in a QSRT reconstruction and that found using
a global MHD model. Despite their lack of quantitative information on
absolute electron density, the resulting maps (which are constructed
directly from high-resolution coronal data observed at the appropriate
height), contain useful information on the distribution of density in
the corona.
Title: The Role of Heavy Ions as Coronal Diagnostics: Recent Results
from Total Solar Eclipse Observations
Authors: Habbal, S. R.; Daw, A. N.; Morgan, H.; Johnson, J.;
Druckmuller, M.; Druckmullerova, H.; Scholl, I.; Arndt, M. B.;
Pevtsov, A.
Bibcode: 2008AGUFMSH11A..04H
Altcode:
Recent advancements in coronal imaging capabilities and image processing
techniques, have led to new diagnostic capabilities for the exploration
of the solar atmosphere during total solar eclipses. In particular,
the suite of Fe spectral lines in the visible and near infrared, namely
Fe XIV 5303, Fe X 6374 A, Fe XI 7892 A, and Fe XIII 10747 A, together
with continuum white light emission, continue to unveil the intricate
topology of the magnetic field, density structures and temperature
distribution in the solar corona. These spectral lines are also yielding
new insights into the role of heavy ions as diagnostics of the coronal
plasma. This presentation will focus on the surprising results from the
eclipse observations of 2006 and 2008. With observations in H alpha,
neutral helium He I 5876 A and the Fe lines representing four different
ionization states of iron, it is shown how the distribution of neutrals
and heavy ions in select magnetic structures in the corona, provides
new insights into the physics of the coronal plasma, with implications
for models of coronal heating processes. These observations also shed
light on the source regions and properties of neutrals and minor ions
measured in interplanetary space.
Title: Impact of Active Regions on Coronal Hole Outflows
Authors: Habbal, Shadia Rifai; Scholl, Isabelle F.; McIntosh, Scott W.
Bibcode: 2008ApJ...683L..75H
Altcode:
Establishing the sources of the fast and slow solar wind is important
for understanding their drivers and their subsequent interaction
in interplanetary space. Although coronal holes continue to be
viewed as the main source of the fast solar wind, there is recent
evidence that the quiet Sun provides other spatially concentrated
sources. To identify the underlying physical characteristics of the
outflow from coronal holes, solar disk observations from the Solar
and Heliospheric Observatory (SOHO) are considered. These observations
encompass photospheric line-of-sight magnetic field measurements from
the Michelson Doppler Imager (MDI), Fe X 171 Å passband imaging from
the Extreme-ultraviolet Imaging Telescope (EIT), and Ne VIII 770 Å
spectral observations with outflows inferred from their corresponding
Doppler blueshifts, at solar minimum and maximum and at different
latitudes, from the Solar Ultraviolet Measurement of Emitted Radiation
(SUMER) instrument. The sharp variations of outflows within the SUMER
field of view, referred to as velocity gradients, are introduced
as a new diagnostic. It is shown that, in general, coronal holes
are indistinguishable from the quiet Sun, whether in their outflows
or their gradients. Surprisingly, however, when enhanced unbalanced
magnetic flux from active regions extends into neighboring coronal
holes, both outflows and their gradients become significantly enhanced
within the coronal holes and along their boundaries. The same effect is
observed in the quiet Sun, albeit to a lesser extent. These findings
point to the possibility that active regions can lead to enhanced
plasma outflows in neighboring coronal holes.
Title: On the Automated Detection of Coronal Holes in Space-Based Data
Authors: Scholl, I.; Habbal, S. R.; Paiement, A.
Bibcode: 2008AGUSMSP51A..14S
Altcode:
With the advent of EIT/SOHO, SECCHI/STEREO and XRT/HINODE a fortuitous
opportunity arises to test the robustness of coronal feature detection
techniques. In this study, an image processing method is presented
that allows coronal features, such as coronal holes and filament
cavities on the solar disk, often hidden by the overlying coronal
emission, to be revealed. Application of this method to the images
taken by these three instruments at the same time is not only a test
of the robustness of the technique, but also offers a novel way for
comparing the quality and limitation of each data set. The different
adjustments and processing steps needed for these data sets to yield
consistent results regarding the boundaries of coronal holes at
different wavelengths will be presented.
Title: Identifying the Distinctive Plasma Properties of Coronal Holes
Authors: Habbal, S. R.; Scholl, I.; McIntosh, S.
Bibcode: 2008AGUSMSP31D..08H
Altcode:
Interest in defining the distinguishing properties of coronal holes has
been ongoing for several decades, due in large part to the prevailing
view that they are the main source of the fast solar wind. So far, their
main distinct signature on the solar disk is reduced absorption in the
chromospheric He I 1083 nm line, and significantly reduced emission
in EUV emission lines formed at, or above, a temperature of a million
degrees. In this study, MDI line of sight photospheric magnetic field
measurements are combined with EIT solar disk intensities of the EUV
lines of Fe X 171 and Fe XII 195 A to define the boundaries of coronal
holes, following the technique recently described by Scholl and Habbal
(2007). By complementing this identification with coordinated SUMER Ne
VIII intensity and Doppler measurements, it is shown that coronal holes,
for the most part, are not the sole regions of outflow on the solar
surface. While these results provide a new step in identifying coronal
holes, they show that no single criterion can be used to distinguish a
number of their plasma properties from those of the surrounding quiet
Sun. Their underlying origin remains for the most part a puzzle.
Title: In situ spectroscopy of the solar corona
Authors: Morgan, H.; Fineschi, S.; Habbal, S. R.; Li, B.
Bibcode: 2008A&A...482..981M
Altcode:
Context: Future spacecraft missions, such as the proposed Solar Probe
mission, will venture close to the Sun, allowing spectrometers measuring
emission from heavy ions or neutrals in the solar wind to have radial
lines of sight (LOS) pointing away from the Sun, or indeed in any
direction other than sunwards.
Aims: We show that a radial LOS
gives excellent solar wind diagnostics, with tight constraints on ion
density, outflow velocity, and effective temperature parallel to the
coronal magnetic field. In addition, we present the concept that a
spectrometer onboard a spacecraft reaching the solar corona can yield
measurements somewhat similar to an in situ sampling instrument, in
that the 3D velocity distribution and density of the emitting ions
can be measured.
Methods: The well-studied O VI doublet at
1031.96 and 1037.6 Å and the H Ly-α line at 1215.67 Å are chosen
as examples. Solar wind parameters obtained from a 2D three-fluid
magnetohydrodynamic (MHD) model, and formulations for collisional and
radiative emission along a radial LOS, are used to calculate spectral
line profiles for these lines at various heights within a streamer
and coronal hole.
Results: For O VI, the collisional line
profiles directly measure the ion velocity distribution in the radial
direction, with the general Doppler shift of the profiles related
to the bulk ion outflow velocity and the width of the line related
to the effective ion temperature parallel to the magnetic field. An
obvious skew in the collisional profiles is seen in regions with a
high gradient in outflow velocity and/or temperature. The resonant (or
radiative) line profiles behave very differently from those currently
observed in 90° scattering. They are more closely related to the
profile and distribution of the exciting chromospheric spectrum: the
lines are narrow and are centered at wavelengths mirrored around the
rest wavelength of the ion emission, allowing easy separation of the
collisional and radiative components. Despite the Ly-α line being much
more intense than the O VI lines, the large width and high intensity
of the Ly-α radiative component in comparison to the collisional
component is such that these two components cannot be separated. The
Ly-α line is therefore less suitable for solar wind diagnostics.
Conclusions: The prospect of coronal in situ spectral observations,
combined with simultaneous in situ sampling measurements of the solar
wind and magnetic field will give unsurpassed constraints on models
of solar wind heating and acceleration.
Title: Automatic Detection and Classification of Coronal Holes and
Filaments Based on EUV and Magnetogram Observations of the Solar Disk
Authors: Scholl, Isabelle F.; Habbal, Shadia Rifai
Bibcode: 2008SoPh..248..425S
Altcode:
A new method for the automated detection of coronal holes and filaments
on the solar disk is presented. The starting point is coronal images
taken by the Extreme Ultraviolet Telescope on the Solar and Heliospheric
Observatory (SOHO/EIT) in the Fe IX/X 171 Å, Fe XII 195 Å, and
He II 304 Å extreme ultraviolet (EUV) lines and the corresponding
full-disk magnetograms from the Michelson Doppler Imager (SOHO/MDI)
from different phases of the solar cycle. The images are processed to
enhance their contrast and to enable the automatic detection of the
two candidate features, which are visually indistinguishable in these
images. Comparisons are made with existing databases, such as the
He I 10830 Å NSO/Kitt Peak coronal-hole maps and the Solar Feature
Catalog (SFC) from the European Grid of Solar Observations (EGSO),
to discriminate between the two features. By mapping the features
onto the corresponding magnetograms, distinct magnetic signatures are
then derived. Coronal holes are found to have a skewed distribution
of magnetic-field intensities, with values often reaching 100 - 200
gauss, and a relative magnetic-flux imbalance. Filaments, in contrast,
have a symmetric distribution of field intensity values around zero,
have smaller magnetic-field intensity than coronal holes, and lie
along a magnetic-field reversal line. The identification of candidate
features from the processed images and the determination of their
distinct magnetic signatures are then combined to achieve the automated
detection of coronal holes and filaments from EUV images of the solar
disk. Application of this technique to all three wavelengths does not
yield identical results. Furthermore, the best agreement among all
three wavelengths and NSO/Kitt Peak coronal-hole maps occurs during
the declining phase of solar activity. The He II data mostly fail to
yield the location of filaments at solar minimum and provide only a
subset at the declining phase or peak of the solar cycle. However,
the Fe IX/X 171 Å and Fe XII 195 Å data yield a larger number of
filaments than the Hα data of the SFC.
Title: Erratum: ``Localized Enhancements of Fe+10 Density
in the Corona as Observed in Fe XI 789.2 nm during the 2006 March
29 Total Solar Eclipse'' (ApJ,
663, 598 [2007])
Authors: Habbal, Shadia Rifai; Morgan, Huw; Johnson, Judd; Arndt,
Martina Belz; Daw, Adrian; Jaeggli, Sarah; Kuhn, Jeff; Mickey, Don
Bibcode: 2007ApJ...670.1521H
Altcode:
The eclipse image of Figure 3 was provided to the authors by
Jackob Strikis of the Elizabeth Observatory, Athens, who claimed
authorship. However, shortly after publication the authors discovered
that this eclipse image was in fact a preliminary version of an
image belonging to Prof. Miloslav Druckmüller, taken during the
2006 total solar eclipse from Libya at 30°56.946' N, 24°14.301'
E, and at an altitude of 158 m. This image can be found at ApJ, 663, 598 [2007]. We extend our
gratitude to Prof. Druckmüller, from Brno University of Technology,
Czech Republic, who brought this incident to our attention, and who
has graciously accepted our apology for this unintentional mishap. A
forthcoming article in collaboration with Prof. Druckmüller is in
preparation.
Title: The long-term stability of the visible F corona at heights
of 3-6 R_⊙
Authors: Morgan, H.; Habbal, S. R.
Bibcode: 2007A&A...471L..47M
Altcode:
Context: CMEs can effect the distribution of dust grains in the
corona. The brightness of the visible F corona is expected therefore
to change as the frequency of CMEs varies with solar cycle.
Aims: We search for a variation in the F corona by comparing LASCO
C2 observations from solar minimum and maximum.
Methods:
An established inversion method is used to calculate the visible
F corona brightness from LASCO C2 solar minimum observations made
during 1996/10. Good agreement is found with the F corona brightness
calculated from Skylab observations during 1973/05-1974/02 for
heights of 3-6 R_⊙. The unpolarized brightness, which is dominated
by the unpolarized F corona brightness at these heights, is obtained
by subtracting many pairs of polarized brightness images from total
brightness images and averaging over a solar rotation. We calculate the
unpolarized brightness for both solar activity minimum and maximum.
Results: The unpolarized brightness, and therefore the F corona,
remain virtually unchanged between solar minimum and maximum at heights
above 2.6 R_⊙, despite the large change in the shape and activity
of the corona. Using a simple density model, it is shown that the
small variation in unpolarized brightness seen below 2.6 R_⊙ can
arise from differences in the distribution of electron density, and
therefore cannot be attributed to a variation in the F corona.
Conclusions: Despite the large rise in frequency of CMEs from solar
minimum to maximum, the F coronal brightness, at heights of 3-6 R_⊙
in the visible, remains very stable.
Title: Localized Enhancements of Fe+10 Density in the
Corona as Observed in Fe XI 789.2 nm during the 2006 March 29 Total
Solar Eclipse
Authors: Habbal, Shadia Rifai; Morgan, Huw; Johnson, Judd; Arndt,
Martina Belz; Daw, Adrian; Jaeggli, Sarah; Kuhn, Jeff; Mickey, Don
Bibcode: 2007ApJ...663..598H
Altcode:
The first ever image of the full solar corona in the Fe XI 789.2 nm
spectral line was acquired during the total solar eclipse of 2006
March 29. Several striking features stand out in the processed image:
(1) The emission extended out to at least 3 Rsolar in
streamers. (2) A bubble-like structure, occupying a cone of about 45°
and reaching out to 1 Rsolar above the limb, was observed
southward of a bright active region complex close to the limb. (3)
Localized intensity enhancements were found in different parts of
the corona at heights ranging from 1.2 to 1.5 Rsolar. (4)
Striations extended out to the edge of the field of view above an almost
north-south-oriented prominence. Comparison with the corresponding
white-light image taken simultaneously during the eclipse showed
no evidence for these localized enhancements, and the bubble-like
structure and striations, while present, did not stand out in the same
manner. The extent of the Fe XI emission is attributed to the dominance
of radiative over collisional excitation in the formation of that
spectral line. The localized intensity enhancements, observed only in
Fe XI and not in white light, are a signature of localized increases
in Fe+10 density relative to electron density. These are
the first observations to show direct evidence of localized heavy
ion density enhancements in the extended corona. They point to the
importance of implementing observations of the Fe XI 789.2 nm line with
existing or future coronagraphs for the exploration of the physical
processes controlling the behavior of heavy ions in different source
regions of the solar wind.
Title: Large-scale structure of the fast solar wind
Authors: Bisi, M. M.; Fallows, R. A.; Breen, A. R.; Habbal, S. Rifai;
Jones, R. A.
Bibcode: 2007JGRA..112.6101B
Altcode: 2007JGRA..11206101B
We present the results of a comprehensive study of the fast solar
wind near solar minimum conditions using interplanetary scintillation
(IPS) data taken with the EISCAT system in northern Scandinavia, and
a recent extremely long baseline observation using both EISCAT and
MERLIN systems. The results from IPS observations suggest that the fast
wind inside 100 solar radii (R⊙) can be represented by a
two-mode model in some cases but this distinction is much less clear by
in situ distances beyond 1 astronomical unit (215 R⊙). Two
distinct fast streams are seen in the extremely long baseline IPS
observation; comparison of the IPS line of sight with a synoptic map
of white light indicates the faster mode overlies the polar crown and
the slower fast mode overlies an equatorial extension of the polar
coronal hole.
Title: Mees Imaging Solar Spectrometer
Authors: Lin, Haosheng; Li, J.; Kuhn, J. R.; Mickey, D.; Habbal,
S. R.; Jaeggli, S. S.
Bibcode: 2007AAS...210.9215L
Altcode: 2007BAAS...39R.210L
We propose the construction of a new instrument, the Mees Imaging Solar
Spectrometer (MISS), optimized for spectroscopic study of energetic
solar events such as filament eruptions and solar flares, and their
relationship to coronal mass ejections. MISS is a fiber-optics-based
imaging spectrograph. It will be able to perform simultaneous
spectroscopic observations of selected spectral lines and continuum
over an extended field with high spatial and spectral resolution
and high cadence. It will operate nominally in a low-resolution (20"
per pixel), full-disk patrol mode, and can be rapidly switched to a
high-resolution (1" per pixel) region-of-interest mode of observation
when energetic events are detected. Several spectral lines, from CaII
H & K to HeI 1083 nm can be recorded in rapid succession. These
advanced imaging spectroscopic capabilities make it an ideal instrument
for the study of the rapid change of the physical conditions of the
solar atmosphere during these energetic events.
Title: On VI and H2 Lines in Sunspots
Authors: Labrosse, N.; Morgan, H.; Habbal, S. R.; Brown, D.
Bibcode: 2007ASPC..368..247L
Altcode: 2006astro.ph.11490L
Sunspots are locations on the Sun where unique atmospheric conditions
prevail. In particular, the very low temperatures found above
sunspots allow the emission of H2 lines. In this study
we are interested in the radiation emitted by sunspots in the O VI
lines at 1031.96 Å and 1037.60 Å. We use SOHO/SUMER observations
of a sunspot performed in March 1999 and investigate the interaction
between the O VI lines and a H2 line at 1031.87 Å found in
the Werner band. The unique features of sunspots atmospheres may very
well have important implications regarding the illumination of coronal
O+5 ions in the low corona, affecting our interpretation
of Doppler dimming diagnostics.
Title: Angular Momentum Transport and Proton-Alpha-Particle
Differential Streaming in the Solar Wind
Authors: Li, Bo; Habbal, Shadia Rifai; Li, Xing
Bibcode: 2007ApJ...661..593L
Altcode: 2007astro.ph..2380L
The interplay between the proton-alpha-particle differential flow
speed, vαp, and angular momentum transport in the solar
wind is explored by using a three-fluid model. The force introduced
by the azimuthal components is found to play an important role in the
force balance for ions in interplanetary space, bringing the radial flow
speeds of protons and alpha particles closer to each other. For the fast
solar wind, the model cannot account for the decrease of vαp
observed by Helios between 0.3 and 1 AU. However, it can reproduce the
vαp profile measured by Ulysses beyond 2 AU, if the right
value for vαp is imposed at that distance. In the slow wind,
the effect of solar rotation is more pronounced if one starts with
the value measured by Helios at 0.3 AU: a relative change of 10%-16%
is introduced in the radial speed of the alpha particles between 1
and 4 AU. The model calculations show that, although alpha particles
consume only a small fraction of the energy and linear momentum fluxes
of protons, they cannot be neglected when considering the proton
angular momentum flux Lp. In most examples, it is found that
Lp is determined by vαp for both the fast and
the slow wind. In the slow solar wind, the proton and alpha particle
angular momentum fluxes Lp and Lα can be several
times larger in magnitude than the flux carried by the magnetic stresses
LM. While the sum LP=Lp+Lα
is smaller than LM, for the modeled fast and slow wind alike,
this result is at variance with the Helios measurements.
Title: Coronal Mass Ejections : A Study of Structural Evolution
and Classification
Authors: Lowder, Chris; Habbal, S. R.; Morgan, H.
Bibcode: 2007AAS...210.8803L
Altcode: 2007BAAS...39..201L
Coronal Mass Ejections (or CMEs) are known for their majestic, yet
explosive, outflow from the Sun. Although different criteria are
often used for their classification, this paper seeks to classify
them based on the following factors: (1) The velocity of the CME;
(2) the structure of the CME itself, and (3) the angular separation
of the "legs" of the CME as it expands. Given that the outer edge
and the inner core of the CME move at different velocities, this
difference can track the structural evolution of the outburst. Using
data from solar minimum and maximum, CMEs will be analyzed and a new
classification scheme will be developed based on the characteristics
outlined above. This research was conducted as part of an NSF funded
REU program at the Institute for Astronomy at the University of Hawaii.
Title: Following the Trail of Heavy Ions through the Solar Corona
and into the Solar Wind
Authors: Habbal, Shadia R.
Bibcode: 2007AAS...21011103H
Altcode: 2007BAAS...39..235H
Spectroscopy of the solar corona continues to play a key role
for exploring the physical processes that define the properties
of this optically thin plasma and control the acceleration of the
solar wind. These processes determine the range of observed species
temperatures, flow speeds and densities in different magnetic structures
in the corona. This presentation will focus on the diagnostic power
of spectroscopic observations of different ion species for exploring
these physical processes. Particular emphasis will be placed on the
non-negligible role played by heavy ions. A direct example for their
behavior will be highlighted using results from the recent eclipse
observations of 29 March 2006.
Title: A Correlative Study between Coronal Mass Ejections, Prominences
and Flares
Authors: Rasca, Anthony; Habbal, S. R.; Morgan, H.
Bibcode: 2007AAS...210.9332R
Altcode: 2007BAAS...39..216R
The exact cause of coronal mass ejections (CMEs) remains unsettled
despite three decades of observations since their discovery in the early
1970s. Their association with events at the Sun, such as prominence
eruptions and solar flares, is often established from a near-time
and -position angle coincidence on the solar disk and limb. Using a
list from randomly chosen CMEs in the LASCO/C2 catalog, a comparison
is made of the number of associated events from observations at solar
maximum (1999-2000) and during the declining phase of the solar cycle
(2004-05). Images of the Fe XII and He II lines from SOHO/EIT are
used to locate events associated with the CMEs. The results show solar
maximum CMEs having four times more associated prominence eruptions,
without an associated flare, than at solar minimum (12% vs. 3%). CMEs at
solar minimum have five times the number of flare-associated prominences
(11% vs. 2%), and twice the number of flare-associated active regions
(29% vs. 14%). A histogram of the CMEs speed distribution shows a trend
with a skewed peak in the range of 200-399 km/s at both phases of the
solar cycle. When separated into event-associated cases, a similar
distribution with speed is found with the flare-associated events,
whereas a peak in the percent of CME-associated prominence eruptions
appears in the range of 600-799 km/s. Using this information and
the fact that prominence eruptions were most commonly observed at
the solar limb, we estimate that the mean prominence-associated CME
speed lies within the range of 600-799 km/s and the mean flare-only
associated speed lies in the 200-399 km/s range. Such results point to
the importance of prominence eruptions in fast-propagating CMEs. This work was funded by the NSF through a Research Experience for
Undergraduates position at the University of Hawai'i's Institute
for Astronomy.
Title: Maps of the Coronal Electron Density Distribution at Solar
Maximum - Estimates Based on LASCO Observations
Authors: Morgan, Huw; Habbal, S. R.
Bibcode: 2007AAS...21010503M
Altcode: 2007BAAS...39..231M
Estimating the 3D distribution of electron density from a set of
2D white light observations is a critical challenge in coronal
physics. Such an estimation is difficult during solar maximum due
to rapid structural changes in the corona, and to the frequent
`contamination' of observations by transient event. The primary
aim of this work is to create global maps of electron density for
Carrington Rotation 1953 which provide reasonable agreement with
polarized brightness observed by the LASCO C2 coronagraph. The
technique is based on a solar rotational tomography technique, and
while the densities contained within the initially created maps are
in arbitrary units, we assume that it gives a reasonable estimate of
the 3D spatial distribution, or position, of density structures. A
smaller set of LASCO polarized brightness observations are then used
as a constraint in a least-squares fitting routine to improve the
agreement between observation and model. This step also converts the
density map from arbitrary to electron density units. Given the rapid
structural changes of the solar maximum corona, our static estimate of
electron density gives reasonable agreement with polarized brightness
observations. Improvements to the technique will be discussed.
Title: Are solar maximum fan streamers a consequence of twisting
sheet structures?
Authors: Morgan, H.; Habbal, S. R.
Bibcode: 2007A&A...465L..47M
Altcode:
Context: Fan streamers are often observed at low to mid latitudes
in the corona at solar maximum, appearing narrow in latitudinal
extent near the Sun, and fanning out with height, adopting an
approximately linear, but not necessarily radial, configuration above
~3 R⊙.
Aims: We offer arguments to support the
conjecture that such structures may sometimes consist of high density,
non-uniform sheets, viewed edge-on near the Sun, and twisting to a
more face-on alignment by 3 R⊙.
Methods: EUV and
white light observations of a fan streamer observed on 2000/12/05 are
analyzed. A simple 3D density model is used to recreate the streamer
structure.
Results: EIT images show a thin bright sheet at the
base of the streamer. The continuation of this structure through the
EIT, MLSO MKIV coronameter, and LASCO C2 fields of view, suggests
that this sheet is formed mostly of open magnetic field lines. The
overall large-scale appearance of the streamer is well simulated by a
simple model of a twisting high-density sheet. If the twisting-sheet
conjecture is valid, there is a correlation between the distribution
of enhanced rays within the streamer viewed in white light, and the
distribution of small regions of enhanced brightness seen on the disk
in EIT 171 Å at the position of the streamer base.
Conclusions:
.We suggest that the apparent poleward divergence of equatorial coronal
rays, or threads, seen during solar maximum above active regions,
may sometimes be a consequence of such a twisting sheet topology.
Title: An empirical 3D model of the large-scale coronal structure
based on the distribution of Hα filaments on the solar disk
Authors: Morgan, H.; Habbal, S. R.
Bibcode: 2007A&A...464..357M
Altcode: 2006astro.ph.10219M
Context: Despite the wealth of solar data currently available,
the explicit connection between coronal streamers and features on
the solar disk remains unresolved.
Aims: To reproduce the
large-scale coronal structure starting from the solar surface, an
empirical three-dimensional (3D) model is used to test the assumption
that such structure, namely streamers, is a consequence of twisted
high-density sheets originating from prominences (or, equivalently,
filaments) at the base of the corona.
Methods: A 3D model is
created whereby high-density sheets are placed above filaments on
the solar disk, which twist and merge with height into a final radial
configuration constrained by the oberved position of streamers stalks
higher up in the corona. The observational constraints are provided by
white light observations from the LASCO/C2 data during the declining
phase of solar activity, spanning the end of Carrington Rotation
(CR) 2005 and the start of CR 2006, i.e. July-August 2003, and the
position of filaments from the corresponding Hα synoptic maps of the
Paris-Meudon Observatory.
Results: The 3D model thus derived
yields a reasonable agreement with the observed large-scale coronal
structure, in particular the shape of large helmet streamers.
Conclusions: .These results give confidence in the underlying
assumption that large helmet streamers can be the result of the
convergence of two or more sheet-like structures originating from a
distribution of filaments on the solar disk. The model supports the
view that streamers, during that time of the solar cycle, are often
associated with multiple current sheets.
Title: Understanding coronal heating and solar wind acceleration:
Case for in situ near-Sun measurements
Authors: McComas, D. J.; Velli, M.; Lewis, W. S.; Acton, L. W.;
Balat-Pichelin, M.; Bothmer, V.; Dirling, R. B.; Feldman, W. C.;
Gloeckler, G.; Habbal, S. R.; Hassler, D. M.; Mann, I.; Matthaeus,
W. H.; McNutt, R. L.; Mewaldt, R. A.; Murphy, N.; Ofman, L.; Sittler,
E. C.; Smith, C. W.; Zurbuchen, T. H.
Bibcode: 2007RvGeo..45.1004M
Altcode:
The solar wind has been measured directly from 0.3 AU outward,
and the Sun's atmosphere has been imaged from the photosphere out
through the corona. These observations have significantly advanced our
understanding of the influence of the Sun's varying magnetic field on
the structure and dynamics of the corona and the solar wind. However,
how the corona is heated and accelerated to produce the solar wind
remains a mystery. Answering these fundamental questions requires
in situ observations near the Sun, from a few solar radii (R S
) out to ~20 R S , where the internal, magnetic, and
turbulent energy in the coronal plasma is channeled into the bulk energy
of the supersonic solar wind. A mission to make such observations has
long been a top priority of the solar and space physics community. The
recent Solar Probe study has proven that such a mission is technically
feasible and can be accomplished within reasonable resources.
Title: S olar Orbiter Neutral Solar Wind Detector
Authors: Hilchenbach, M.; Orsini, S.; Hsieh, K. C.; Antonucci, E.;
Barabash, S.; Bamert, K.; Bruno, R.; Collier, M. R.; Czechowski,
A.; D'Amicis, R.; De Angelis, E.; Dandouras, I.; Di Lellis, A. M.;
Esser, R.; Giacalone, J.; Gruntman, M.; Habbal, S. R.; Jokipii, J. R.;
Kallio, E.; Kota, J.; Kucharek, H.; Leoni, R.; Livi, S.; Mann, I.;
Marsch, E.; Massetti, S.; Milillo, A.; Möbius, E.; Mura, A.; Sheldon,
R. B.; Schmidt, W.; Selci, S.; Szego, K.; Woch, J.; Wurz, P.; Zanza,
V.; Zurbuchen, T. H.
Bibcode: 2007ESASP.641E..46H
Altcode:
Neutral hydrogen atoms, which give rise to the prominent so lar Ly-α
corona, are closely coup led to the emerging solar-wind plasma. The
density ratio of neutral hydrogen to protons is minute, ~10-6;
therefore, the neutral atoms are tracers in the solar wind. In-situ
observations of the neutral atoms, their flight paths (imag ing),
density, and velocity distribu tions are a new tool to the understanding
of the Ly-α corona, i.e. setting limits on the plasma velocity
distribution along the solar magnetic field lines. The other goal of
the neutral solar- wind instrumentation is the in-situ observation
of the interactions between solar wind plasma and dust grains near
the Sun. We will discuss the science objectives and the potential
"zero charge" solar-wind instrument envelope onboard Solar Orbiter .
Title: Viewing Structure In Coronal Images
Authors: Morgan, H.; Habbal, S. R.; Fineschi, S.
Bibcode: 2007ESASP.641E..15M
Altcode:
New image processing techniques, applied to white-light, pB , UV
or EUV observations, reveal the fine-scale detail of the corona
whilst accurately depicting the large-scale structure. The images
produced by the techniques give new insights into the structure of
streamers, are useful to unravel the complex topology of the solar
maximum corona, and can help make connections between coronal and
solar disk features. CMEs are seen in striking de- tail out to ∼18R
. The quality of imaging produced by missions such as Solar Orbiter
have a strong influence on the impact of that mission, and the solar
remote sensing instrumentation, in particular the EUV imager and coro-
nagraph, can maximize their scientific effectiveness by employing the
new processing techniques.
Title: Broadband Spectroscopy of the Corona during the Total Solar
Eclipse of March 29, 2006
Authors: Jaeggli, Sarah A.; Habbal, S. R.; Kuhn, J. R.; Nayfeh, M. H.
Bibcode: 2006AAS...209.1601J
Altcode: 2006BAAS...38..918J
We present coronal observations from the total solar eclipse of 29
March 2006 taken near Waw al Namus, Libya. During the 4 minutes and 6
seconds of totality, observations were made with a tracking collecting
mirror and fiber-fed spectrograph. The spectrograph used is a high
quantum efficiency commercial Ocean Optics QE65000 Spectrometer with a
wavelength range of 350 to 1100 nm, and spectral resolution of about
0.75 nm. High quantum efficiency allowed for many short exposures
of the inner (100 msec) and outer (10,000 msec) corona during the
eclipse. Important spectral features, and the difference in color
between the inner and outer corona are identified. Atmospheric
contributions are discussed. Likely candidates for the nature of
dust grains contributing to the F-corona measurements are also
presented. These are compared with laboratory spectra of silicon
nanoparticles.
Title: Polarimetric Imaging and Spectroscopy of the Corona from 400
to 2000 nm during the Total Solar Eclipse of 29 March 2006
Authors: Habbal, S. R.; Kuhn, J.; Mickey, D.; Morgan, H.; Jaeggli,
S.; Johnson, J.; Daw, A.; Arndt, M. B.; Nayfeh, M.; Roussev, I.
Bibcode: 2006AGUFMSH44A..06H
Altcode:
Total solar eclipses continue to offer unique opportunities for
exploring the solar corona, in particular for validating new concepts,
and testing new instrumentation. We report on the results of the
observations taken during the total solar eclipse of 29 March 2006. The
eclipse was observed from Waw AnNamous, Libya, under perfect seeing
conditions. A complement of imaging and spectroscopic polarization
measurements, covering the wavelength range from 400 to 2000 nm, were
used. Among the highlights of the observations were the unexpected
radial extent of the emission from the Fe XI 789.2 nm spectral line,
which has proven to have significant potential for future coronagraphic
measurements, and the appearance of presently unidentified spectral
lines in the visible and near infrared part of the spectrum. The
implications of these results for the coronal magnetic field, and the
near-Sun dust environment will be discussed.
Title: Twisted Sheet Structures and the Appearance of Coronal
Streamers at Solar Maximum
Authors: Morgan, H.; Habbal, S. R.
Bibcode: 2006AGUFMSH23B0352M
Altcode:
LASCO/SOHO white light observations of the solar maximum corona
reveal the structure of some streamers as thin sheets of filamentary
structures. We use EIT/SOHO 171Å\ observations to show the existence
of bright thin sheets at very low heights in the corona. Modeling
streamers as thin twisting sheets, originating from the solar surface
and expanding outwards into the corona, successfully recreates the
appearance of some streamers in observations. Low in the corona, the
position and size of modeled sheets are dictated by the position and
size of filaments (or prominences) observed in Hα on the solar disk,
or by enhanced activity in EIT 171Å\ observations. Such structures
can appear to a distant observer as a helmet streamer or a fan-shaped
streamer depending on the latitude and alignment of the structure,
and/or the solar rotation. We show that rays in a fan-shaped equatorial
streamer extend directly from the brightest regions of EIT 171Å\
images, and that the apparent poleward divergence of equatorial coronal
rays is a natural consequence of a twisting sheet topology. A 3D
density model is constructed where sheet-like structures, originating
from regions surrounding prominences, twist and merge to a height
where the corona becomes radial, close to 3 R\odot. We establish that
large helmet streamers may be created by the convergence of two or
more sheet-like structures from widely separated regions on the Sun.
Title: The Depiction of Coronal Structure in White-Light Images
Authors: Morgan, Huw; Habbal, Shadia Rifai; Woo, Richard
Bibcode: 2006SoPh..236..263M
Altcode: 2006astro.ph..2174M
The very steep decrease in density with heliocentric distance
makes imaging of coronal density structures out to a few solar
radii challenging. The radial gradient in brightness can be reduced
using numerous image processing techniques, thus quantitative data
are manipulated to provide qualitative images. We introduce a new
normalizing-radial-graded filter (NRGF): a simple filter for removing
the radial gradient to reveal coronal structure. Applied to polarized
brightness observations of the corona, the NRGF produces images which
are striking in their detail. Total-brightness, white-light images
include contributions from the F corona, stray light, and other
instrumental contributions which need to be removed as effectively
as possible to properly reveal the electron corona structure. A new
procedure for subtracting this background from LASCO C2 white-light,
total-brightness images is introduced. The background is created from
the unpolarized component of total-brightness images and is found to be
remarkably time-invariant, remaining virtually unchanged over the solar
cycle. By direct comparison with polarized-brightness data, we show
that the new background-subtracting procedure is superior in depicting
coronal structure accurately, particularly when used in conjunction
with the NRGF. The effectiveness of the procedures is demonstrated on
a series of LASCO C2 observations of a coronal mass ejection (CME).
Title: Using Polarimetric Imaging and Spectroscopy of the Corona
from 400 to 1800 nm for Exploring the near Sun Plasma
Authors: Habbal, S. Rifai; Kuhn, J.; Mickey, D.; Jaeggli, S.; Morgan,
H.; Roussev, I.; Johnson, J.; Arndt, M. B.; Daw, A.; Nayfeh, M. H.
Bibcode: 2006spse.conf...27H
Altcode:
No abstract at ADS
Title: Solar Maximum Streamers as Thin Twisting Sheets
Authors: Morgan, H.; Habbal, S. Rifai
Bibcode: 2006spse.conf...93M
Altcode:
No abstract at ADS
Title: Effect of the latitudinal distribution of temperature at the
coronal base on the interplanetary magnetic field configuration and
the solar wind flow
Authors: Li, Bo; Habbal, Shadia Rifai; Li, Xing; Mountford, Chris
Bibcode: 2005JGRA..11012112L
Altcode:
Using a two-dimensional MHD model of the corona and solar wind, we
investigate the role of the temperature distribution with latitude at
the coronal base on the global magnetic field configuration and solar
wind properties at 1 AU. The latitudinal distribution of temperature is
aimed at modeling the transition in electron temperature at the Sun from
a polar coronal hole to the quiet Sun to active regions. The results
of the model calculations illustrate how the variation of temperature
with latitude impacts the coronal magnetic field configuration and the
distribution of wave energy flux in the solar wind and consequently its
thermodynamic properties. The sharp temperature changes at the coronal
base lead to the formation of current sheets in the corona. They
also modify the location of the streamer cusp and the neutral line
originating there. Two different approaches in treating electron heat
flux are also compared, one assumes a Spitzer expression throughout the
computational domain and the other assumes a collisionless expression
beyond some radial distance. Model results thus derived differ little
in terms of proton flux and terminal speed.
Title: Hybrid simulation of ion cyclotron resonance in the solar wind:
Evolution of velocity distribution functions
Authors: Li, Xing; Habbal, Shadia R.
Bibcode: 2005JGRA..11010109L
Altcode:
Resonant interaction between ions (oxygen ions O+5
and protons) and ion cyclotron waves is investigated using a one
dimensional hybrid code. Ion cyclotron waves are self-consistently
generated by an ion cyclotron anisotropy instability. We focus on the
detailed acceleration process of ions. The energization of oxygen ions
due to waves is found to have two stages. During the first stage,
oxygen ions are energized by ion cyclotron waves in the direction
perpendicular to the background magnetic field and can develop extreme
high temperature anisotropies with TO⊥/TO∥
≈ 22 in an initially low beta plasma (beta value at 0.01) with
very little parallel heating. During this stage, oxygen ions do not
show an appreciable bulk acceleration along the background magnetic
field. In the second stage, a large bulk acceleration of oxygen ions as
large as 0.3vA, where vA is the Alfvén speed,
is observed. Ion cyclotron waves are not able to maintain a high
temperature anisotropy as inferred from observations. The nonlinear
nature of wave particle interaction produces highly complex velocity
distribution functions in the oxygen ions. In contrast, the heating
and acceleration behavior of the major species, namely protons, is
quite different. The velocity distribution functions of protons are
less complex than the oxygen velocity distributions. Protons can also
develop a large temperature anisotropy with preferential heating in the
perpendicular direction. A bulk acceleration of protons (much smaller
than the acceleration of oxygen ions) along the background magnetic
field is observed to develop simultaneously with the development of
a proton temperature anisotropy.
Title: Solar Probe: Humanity's First Visit to a Star (Invited)
Authors: McComas, D. J.; Velli, M.; Lewis, W. S.; Acton, L. W.;
Balat-Pichelin, M.; Bothmer, V.; Dirling, R. B.; Eng, D. A.; Feldman,
W. C.; Gloeckler, G.; Guhathakurtha, M.; Habbal, S. R.; Hassler, D. M.;
Mann, I.; Maldonado, H. M.; Matthaeus, W. H.; McNutt, R. L.; Mewaldt,
R. A.; Murphy, N.; Ofman, L.; Potocki, K. A.; Sittler, E. C.; Smith,
C. W.; Zurbuchen, T. H.
Bibcode: 2005ESASP.592..279M
Altcode: 2005ESASP.592E..42M; 2005soho...16E..42M
No abstract at ADS
Title: Hybrid Simulation of Ion Cyclotron Resonance in the Solar Wind:
Ion Velocity Distribution Functions
Authors: Li, X.; Habbal, S. R.
Bibcode: 2005ESASP.592..181L
Altcode: 2005ESASP.592E..28L; 2005soho...16E..28L
No abstract at ADS
Title: The Impact of Sunspots on the Interpretation of Coronal
Observations of the O VI Doublet
Authors: Morgan, H.; Habbal, S. Rifai
Bibcode: 2005ApJ...630L.189M
Altcode: 2006astro.ph..2176M
Due to their high intensity of emission in the O VI λλ1031.9 and
1037.6 lines, even small sunspots on the solar disk can strongly
influence the intensity of the radiative scattering component of
O VI lines in the corona. Observations of O VI disk spectra show a
λ1032/λ1038 line intensity ratio of >2.6 in a sunspot, compared
to quiet-disk values of ~2. The enhancement of the λ1032 line in
comparison to the λ1038 line is likely due to interaction between
molecular hydrogen emission from the sunspot and the chromospheric
O5+. Modeling shows that a contribution from sunspots
increases the coronal O VI λ1032/λ1038 intensity ratio to values
considerably higher than those achieved with a quiet-disk or coronal
hole spectrum. Therefore a reexamination of flow velocities derived
from SOHO UVCS streamer observations must be made. This modeling
demonstrates that the inclusion of sunspots, when present, may lead
to nonzero outflow velocities at lower heights in streamer cores,
in contrast to some existing model results.
Title: Origin and Acceleration of the Slow Solar Wind
Authors: Woo, Richard; Habbal, Shadia Rifai
Bibcode: 2005ApJ...629L.129W
Altcode:
This Letter uses Doppler dimming measurements by SOHO UVCS to elucidate
the origin and acceleration of the slow solar wind. By investigating
plasma flow in the corona over an active region during 2000 May 14-16,
we confirm what has been suggested by the presence of the imprint
of active regions in the solar wind near Earth orbit, that active
regions are a source of slow wind. The observed active region does
not have an associated streamer in the outer corona. We explain how
this implies that any related heliospheric current sheet must be
transverse to the line of sight. It is this favorable geometry of a
transverse heliospheric current sheet that allows the plasma flow over
the active region to be isolated in path-integrated Doppler dimming
measurements. The results also show that acceleration of the slow wind
associated with active regions toward its terminal speed is faster
than that along the heliospheric current sheet. These differences in
acceleration explain why the signatures of the heliospheric current
sheet are dissimilar in velocity, but not in density, between the
corona and solar wind measured near Earth orbit.
Title: Siphon flows and oscillations in long coronal loops due to
Alfvén waves
Authors: Grappin, R.; Léorat, J.; Habbal, S. Rifai
Bibcode: 2005A&A...437.1081G
Altcode:
Using an isothermal axisymmetric MHD model of the solar corona with
transparent boundary conditions, we study how coronal loops with apex
height between one third and two solar radii react to Alfvén waves
generated at the base of the corona. The first response is a steady
increase of the density along the excited loops. Density oscillations
are also observed, along the apex of the longest loops, that is,
those along which waves are substantially damped. Both the steady
and the oscillating component scale as the square of the Alfvén wave
amplitude, and accordingly, the frequency is double that of the mother
wave. Siphon flows may also appear, along short or long loops, depending
on whether both or a single foot-point of the loop system is excited.
Title: UVCS Observations of Slow Plasma Flow in the Corona Above
Active Regions
Authors: Woo, R.; Habbal, S. R.
Bibcode: 2005AGUSMSH31A..04W
Altcode:
The elusive source of slow solar wind has been the subject of ongoing
discussion and debate. Observations of solar wind speed near the Earth
orbit, first with IPS (interplanetary scintillation) and later with
Ulysses in situ measurements, have suggested that some slow solar wind
may be associated with active regions (Kojima & Kakinuma 1987; Woo,
Habbal & Feldman 2004). The ability of SOHO UVCS Doppler dimming
measurements to provide estimates of solar wind speed in the corona
(Kohl et al. 1995) has made it possible to investigate the distribution
of flow near the Sun. In this paper, we will present results confirming
that active regions are one of the sources of slow wind. Insight into
the relationship between coronal streamers, active regions and plasma
flow will also be discussed.
Title: Dissertation Talk: The Impact of Sunspots on Modelling Coronal
UV Observations
Authors: Morgan, H.; Habbal, S. R.
Bibcode: 2005AGUSMSP33A..01M
Altcode:
Existing model studies of O VI 1032 and 1037 A spectral lines from
UVCS/SOHO observations often conclude that O5+ ions in coronal streamers
have no significant outflow velocity at heights below 3 Rs, and large
increases above this height. These observations were modelled with a
typical O VI quiet Sun disk spectrum, and the subsequent results were
interpreted as an indication of different flows arising from closed and
open magnetic field regions within streamers. Given that the O VI solar
disk spectrum emitted from sunspots is very different from the spectrum
emitted from the quiet Sun or coronal holes, we show how the inclusion
of a contribution from sunspots in the incident disk radiation, which
excites the coronal O5+ ions, has a significant impact on the intensity
and intensity ratio of the coronal O VI spectral lines. Such a result
has important implications for the calculation of the outflow velocity
of O5+ ions in streamers. Through the analysis of UVCS observations of a
solar maximum active region streamer with a large sunspot cluster at its
base, we show how the inclusion of a 3% contribution from sunspots in
the modelled quiet disk spectrum allows agreement between the observed
and modeled intensity ratios at lower heights with non-zero outflow
velocities. Such a result cannot be achieved with a standard quiet Sun
disk spectrum. Taking the sunspot contribution into account yields O5+
ions with an outflow velocity of about 80 km/s at a height of 3 Rs,
increasing linearly to 260 km/s at a height of 8 Rs. These results
imply that the presence of sunspots on the solar disk concurrent with
streamer observations requires a revision of published results.
Title: Solar Probe's Inside-Out UV Spectrography of the Solar Wind
Authors: Fineschi, S.; Habbal, S. R.; Morgan, H.
Bibcode: 2005AGUSMSH41A..05F
Altcode:
The Solar Probe will fly through the corona, as close as 3 solar radii
from the photosphere at perihelion. This will provide the unique and
first-ever possibility of remote-sensing observations of ultraviolet
(UV) coronal line-emission from inside-out, that is, along the radial
direction of the solar wind outflow, and away from the Sun. Past UV
spectrographic observations of the corona have been possible only from
a sideways perspective (e.g., UVCS/SOHO). The expected UV spectra of the
OVI doublet, 103.2/103.4 nm, Lyman-alpha HI, 121.6 nm, and HeII, 304 nm,
lines from the Probe's new radial perspective will be presented. The
collisional and resonantly scattered components of the line-emission
when observed radially are spectroscopically separated. This allows a
direct measure of the solar wind outflow speed from the Doppler shift
of the collisional component. The line profiles and intensities of both
components yield information on the unresolved velocity distribution of
ions along the radial direction. This is the predominant direction of
the coronal magnetic field. In the past, sideways, UV spectroscopic
observations of line-emission have yielded information on the
unresolved ion velocity distribution perpendicular to the magnetic
field. Therefore, radial UV spectroscopic observations from Solar
Probe will offer a unique opportunity of investigating the anisotropy
of the unresolved coronal ion velocity distribution for the first time.
Title: Crystalline Si Nanoparticles as Carriers of the Blue
Luminescence in the Red Rectangle Nebula
Authors: Nayfeh, Munir H.; Habbal, Shadia Rifai; Rao, Satish
Bibcode: 2005ApJ...621L.121N
Altcode:
The discovery of a band of blue luminescence in the Red Rectangle
proto-planetary nebula has been recently reported by Vijh et al. These
authors used the hydrogen Balmer lines and the line-depth technique
to extract the intensity of the blue luminescence. This luminescence
was attributed to fluorescence from small neutral polycyclic aromatic
hydrocarbon molecules in the interstellar medium, consisting of three
to four aromatic rings such as anthracene and pyrene. We present in
this Letter evidence of another potential carrier responsible for the
blue luminescence, namely, ultrasmall silicon nanoparticles of 1 nm
in diameter.
Title: Interplanetary Scintillation Observations of the Large-Scale
Structure of the Solar Wind Using EISCAT
Authors: Bisi, M. M.; Breen, A. R.; Habbal, S. R.; Fallows, R. A.
Bibcode: 2004AGUFMSH33B..03B
Altcode:
Measurements of interplanetary scintillation (IPS) taken with the
European Incoherent SCATter radar (EISCAT) in northern Scandinavia
can be used to study the evolution of the solar wind as it expands
through interplanetary space. IPS arises from changes in the apparent
brightness of distant, compact radio sources due to scattering by
density irregularities in the solar wind and can be used to obtain
estimates of the solar wind speed. In this paper we present the results
of a study of the large-scale structure of the fast solar wind under
near solar minimum conditions, using data taken with the EISCAT
system, and the extremely long baseline observations which combine
the EISCAT and MERLIN systems. The latter are the best measurements to
date of meridional components of velocity in the inner solar wind. In
particular, the existence of a gradient in solar wind velocity of the
fast wind over the polar crown, at latitudes corresponding to the x-ray
and ultra-violet coronal hole boundary, as reported by Habbal and Woo
(2001), is also explored.
Title: Role of Closed Magnetic Fields in Solar Wind Flow
Authors: Woo, Richard; Habbal, Shadia Rifai; Feldman, Uri
Bibcode: 2004ApJ...612.1171W
Altcode:
In this paper we demonstrate how closed magnetic fields appear to be
playing a significant role in solar wind flow. Confinement or trapping
of plasma is the physical process, while confinement duration, as
characterized by the first ionization potential (FIP) bias, is the
attribute that divides the fast- and slow-wind regions. The trapped
plasma is released along ubiquitous and predominantly radial open
field lines, presumably by continual reconnection at the base of the
corona, with evidence for this process coming from the appearance of
the imprint of polar coronal holes, quiet Sun, and active regions
in the outer corona and interplanetary space. When trapping is not
long enough to enrich the elemental abundance (FIP bias near 1), the
coronal radial density gradient is steep, coronal temperature is low,
and a fast wind flows in the overlying corona. However, the presence of
closed fields still influences the flow of the fast wind, as revealed
by the fact that flow speed is anticorrelated with, or characterized
by, the density at the base of the corona. When trapping is long
enough to enrich the abundance (FIP bias > 1), a slow wind flows,
and FIP bias characterizes its properties. Enhanced FIP bias gives
rise to a decreased coronal radial density gradient, as manifested
by the extension of coronal streamers in white-light coronal images,
increased coronal temperature, and decreased solar wind speed in the
overlying corona.
Title: Solar wind: The solar wind and the Sun-Earth link
Authors: Habbal, Shadia Rifai; Woo, Richard
Bibcode: 2004A&G....45d..38H
Altcode:
The solar wind fills the space between the Sun and its planets,
shapes the planetary environments and the heliosphere, and comes to a
screeching halt at the heliopause, the boundary with the interstellar
medium. This tenuous medium is a fertile environment for exotic
plasma processes, most of which are not fully understood. It also
holds the intimate secrets of the mechanisms heating the corona that
continue to elude us. As the only accessible space plasma laboratory,
we must continue its exploration in search of the processes that impact
the Earth's environment and govern the evolution of stars and their
planetary systems.
Title: A two-dimensional Alfvén wave-driven solar wind model with
proton temperature anisotropy
Authors: Li, Bo; Li, Xing; Hu, You-Qiu; Habbal, Shadia R.
Bibcode: 2004JGRA..109.7103L
Altcode:
We present the first two-dimensional (2-D) Alfvén wave
turbulence-driven solar wind model which takes the proton temperature
anisotropy into account. While the modeled proton temperature anisotropy
in the fast solar wind is established in the inner corona and yields
Tp∥/Tp⊥ = 0.57 at 1 AU,
which is comparable to measured values, Tp∥
and Tp⊥ are only about half the observed
values. In the slow wind, on the other hand, the modeled values
for Tp∥ and Tp⊥ as
well as their ratio are close to those measured in interplanetary
space. Curiously, the dip in the velocity that develops near the cusp
at the top of the helmet streamer reduces the effect of transverse
expansion and leads to a realistic electron temperature in the slow
wind at 1 AU, although no explicit external heating is applied to
electrons. Comparison with models with and without proton temperature
anisotropy shows that by allowing the proton temperature anisotropy to
develop, the average proton temperature is lower than the isotropic
case primarily because of the cooling in the direction parallel to
the magnetic field. These results imply that ion cyclotron resonance
models with isotropic proton temperature are somewhat optimistic in
assessing the role of Alfvén wave turbulence in driving the fast solar
wind. Inclusion of the temperature anisotropy of protons and proton
thermal conduction are necessary for any physically realistic model.
Title: The Linewidth Ratio of the O VI 1032 and 1037 Å Doublet in
the Quiet Corona.
Authors: Morgan, H.; Habbal, S. R.
Bibcode: 2004AAS...204.2903M
Altcode: 2004BAAS...36..695M
In observations of the quiet Corona with the Ultraviolet Coronagraph
Spectrometer (UVCS) on SoHO the line width of the oxygen O VI 1031.9
Å consistently becomes smaller than the width of the O VI 1037.6 Å
line at distances beyond 3 Rs. A model is used to show that
this difference is due to the pumping of the O VI 1037.6 Å line by the
two chromospheric C II lines at 1037 and 1036.3 Å. The model results
are compared with two examples from observations to demonstrate that
the larger width of the 1037.6 Å line is due to the differing line
of sight contributions of the radiative components to each line. This
study shows that the O VI linewidth ratio is a valuable diagnostic tool,
which when used with the ratio of the intensities of the O VI lines,
enables the inference of the outflow velocity of the oxygen ions in
the inner corona.
Title: Hydrogen Lyα Intensity Oscillations Observed by the Solar
and Heliospheric Observatory Ultraviolet Coronagraph Spectrometer
Authors: Morgan, H.; Habbal, S. Rifai; Li, X.
Bibcode: 2004ApJ...605..521M
Altcode:
We report on a search for significant oscillations in different coronal
structures by applying a wavelet analysis to Solar and Heliospheric
Observatory UVCS observations of the hydrogen Lyα 1216 Å line
intensity taken between 1.5 and 2.2 Rsolar. Significant
periodic oscillations, unlikely to be a result of instrumental
effects, are shown to exist in a coronal hole, the quiet Sun, and a
streamer. Observations made sequentially at different heights but at the
same latitude often share similar power spectra. Neighboring pixels at
the same radial distance also share similar power spectra. These results
indicate both a localized structure to the periodicity and a long-range
preservation of oscillation patterns in the radial expansion of the
solar wind. We show that a preference for significant oscillations with
periods of 7-8 minutes exists in three out of the four observations
presented here. Other bands of preferred periodicity are observed at
different heights.
Title: Investigating the links between the solar surface, corona
and inner heliosphere
Authors: Habbal, S. R.
Bibcode: 2004cosp...35.2026H
Altcode: 2004cosp.meet.2026H
Some of the best-kept secrets of the Sun are imbedded in the solar wind
as it provides the link between the solar surface and interplanetary
space. A review of the conditions at the coronal base that define
the plasma properties of the inner and extended corona, and the inner
heliosphere will be presented. Using a complement of observations and
model results it will be shown how the complexity of the coexistence of
open and closed magnetic structures at the Sun can be used to unravel
some of the secrets of this link.
Title: Transition Region and Coronal Loops Heated by Turbulence
Authors: Li, X.; O'Neill, I.; Habbal, S. R.
Bibcode: 2004ESASP.547..279L
Altcode: 2004soho...13..279L
In a recent paper, we proposed that Alfvén waves damped by a fully
developed turbulent cascade is responsible to produce hot coronal loops
with plasma flows (Li and Habbal, 2003). This paper is an extension of
that work. Two fluid dynamic models of long-lived coronal loops with
various loop lengths are presented. It is assumed that the nonthermal
motions inferred from spectral line observations in the transition
region are due to Alfvén waves. These waves originate below the
chromosphere and are responsible for the coronal heating when they are
dissipated by a turbulent cascade. The cascade process transfers energy
from large scales to high frequency small scales where the wave energy
can be readily absorbed by the proton gas. The Coulomb coupling between
protons and electrons subsequently heats the electron gas. The models
reproduce electron densities of 1 - 4×109 cm-3 , in the range inferred
from observations. The mechanism is able to produce coronal loops with
various lengths. Given the same physical and heating parameters, it is
found that small loops tend to have slow plasma flow, low temperatures
and high densities in the main part of a coronal loop. Steady state
plasma flow speed as fast as 40km/s is easily obtained in large loops.
Title: Origin of the Solar Wind and Open Coronal Magnetic Structures
Authors: Habbal, S. R.; Woo, R.
Bibcode: 2004IAUS..219..587H
Altcode: 2003IAUS..219E.263H
Following Parker's theoretical prediction in 1958 of a
subsonic-supersonic solar wind outflow from the Sun space observations
soon confirmed its presence at Earth's orbit. The first EUV and X-ray
observations of the Sun in the early 1970's revealed the complexity of
coronal structures dominated by arch-like closed magnetic structures
with the exception of dim regions named coronal holes where the EUV
and X-ray emissions were significantly reduced. Based originally
on the chance occurrence of reduced x-ray emission at the Sun with
fast solar wind streams measured at Earth's orbit coronal holes were
soon associated with regions of open magnetic flux and the source of
the fast solar wind despite the absence of coronal magnetic field
measurements. With the advent of radio occultation and white light
measurements the first coronal velocity inferences from UVCS/SOHO
the over-the-poles solar wind plasma measurements by Ulysses and
polarimetric coronal measurements the widely held view that coronal
holes are the sole source of the fast solar wind was revisited. These
observations will be highlighted and evidence for the coexistence
of open and closed magnetic structures throughout the corona and the
implications for the source of the fast and the slow solar wind will
be discussed.
Title: Some Considerations about Inferring Coronal Magnetic Fields
and Other Coronal Properties from Coronal Emission Line Polarization
Authors: Arnaud, J.; Habbal, S. R.; Arndt, M.; Woo, R.
Bibcode: 2003AGUFMSH42B0506A
Altcode:
Ground based studies of Coronal Emission Lines (CEL) linear polarization
had been carried out for the 530.3 nm FeXIV line at Pic du Midi and
for the 1074.7 nm Fe XIII line at Sac Peak in the 1977-1980 period. The
large scale organization of the polarization has clearly revealed the
existence of a large scale structure of the coronal magnetic field. More
recently, the first successful eclipse CEL polarimetric measurements
were made in the 1074.7 nm line during the total solar eclipse of 21
June 2001, confirming earlier results of the predominance of a radial
direction of the coronal magnetic field. A first measurement of the
circular polarization in the 1074.7 nm line has also recently been
performed. Circular polarization gives access to the strength of the
LOS magnetic field while the linear polarization maps the transverse
magnetic field direction. We will use ground based and eclipse 1074.7
nm line polarimetric data to provide examples of the properties (e.g.,
magnetic field, abundances, inhomogeneities) such observations can
help to infer in this 3-D and optically thin medium.
Title: Coronal Loops Heated by Turbulence-driven Alfvén Waves
Authors: Li, Xing; Habbal, Shadia Rifai
Bibcode: 2003ApJ...598L.125L
Altcode:
A two-fluid dynamic model of long-lived coronal loops is presented,
whereby heating of the confined plasma is achieved by turbulence-driven
Alfvén waves. It is assumed that the nonthermal motions inferred
from spectral line observations in the transition region are due to
Alfvén waves. It is also assumed that the turbulence is already
fully developed when the waves are injected at the footpoint of
the loop while the wave/turbulence energy is readily absorbed by
the proton gas. The Coulomb coupling between protons and electrons
subsequently heats the electron gas. The model produces a fairly
uniform electron temperature in the coronal segment of the loop even
though the heating is nonuniform. The model also reproduces electron
densities of (1-4)×109 cm-3, in the range
inferred from observations, as well as a moderate flow speed around
10 km s-1 along the loop. The turbulence heating mechanism
adopted in this Letter, however, cannot produce stable loops with
temperatures T<=1.3×106 K.
Title: The Coronal Magnetic Field, Signatures of Coronal Holes and
Silicon Nanometer Dust Grains
Authors: Habbal, S. R.; Arndt, M. B.; Nayfeh, M.; Arnaud, J.; Woo, R.
Bibcode: 2003AGUFMSH41D..04H
Altcode:
The near-infrared part of the solar spectrum is where some of the
strongest coronal forbidden lines are formed. Polarized emission in
these lines offers the only tool currently known for the inference
of the direction of the coronal magnetic field. The first successful
observations of the polarized emission from the 1074.7 nm Fe XIII
line were made by Eddy, Lee and Emerson during the eclipse of 1966
in a limited region of the corona. The only subsequent polarimetric
observations in this line were carried out with the coronagraph at Sac
Peak from 1977-1980. We report on the first successful polarimetric
measurements of the 1074.7 nm line in a field of view extending out
to 3.5 solar radii which were made during the total solar eclipse
of 21 June 2001. In addition to confirming earlier results of the
predominance of a radial direction of the coronal magnetic field, these
measurements yielded the first polarimetric signature of coronal holes,
and the signature of nanometer size dust grains in the corona. These
observations suggest the existence of a rich coronal spectrum of narrow
lines in the near-infared produced by the fluorescence of silicon
nanometer dust grains in the inner corona. This work was funded by
NSF grant ATM-0003661 and NASA grant NAG5-10873 to the Smithsonian
Astrophysical Observatory.
Title: What do Measurements of Abundance Variations Tell us About
the Origin and Evolution of the Solar Wind
Authors: Woo, R.; Habbal, S. R.; Feldman, U.
Bibcode: 2003AGUFMSH41B0470W
Altcode:
Connections between the Sun and solar wind have recently been made based
on observations of density, velocity, and magnetic field. These have
led to fundamental changes in our understanding of coronal magnetic
topology and the origin and evolution of the solar wind. During solar
minimum, polar coronal holes are neither the only regions of open
magnetic field lines nor the sole source of fast solar wind. Instead,
open magnetic field lines thread the entire corona, and solar wind
flowing along them carries the imprint of coronal holes, quiet Sun, and
active regions into interplanetary space. The purpose of this paper is
to show how measurements of abundance variations in the corona and solar
wind reinforce and complete this picture, providing key insight into
where and how the solar wind, especially the slow wind, is produced.
Title: Are coronal holes the only source of fast solar wind at
solar minimum?
Authors: Hu, Y. Q.; Habbal, S. R.; Chen, Y.; Li, X.
Bibcode: 2003JGRA..108.1377H
Altcode:
A two-dimensional (2-D) MHD model of an Alfvén-wave-driven solar
wind in the heliospheric meridional plane is presented whereby the
consequences of a magnetic field distribution at the Sun that digresses
from the standard dipole structure, often used in 2-D MHD models,
are explored. The latitudinal distribution of open magnetic flux
is specified at the solar surface, with a clear distinction between
the polar coronal hole and the neighboring quiet Sun. The region of
strictly closed magnetic structures at the coronal base is limited in
latitude to ±30°. Alfvén waves are assumed to emanate from the solar
surface above 30° latitude so as to open the field lines anchored
there, as well as heat and accelerate the solar wind. The field lines
anchored at the solar surface below 30° latitude, where the plasma
is thermally conductive, remain closed, resulting in the formation of
the helmet streamer astride the solar equator. The solution obtained
is characterized by a helmet streamer in magnetostatic equilibrium,
centered at the solar equator, and a steady solar wind outside. With the
assumption that the contribution of the polar coronal hole and the quiet
Sun to the interplanetary magnetic flux is evenly split between them
during solar minimum, a fast wind solution is obtained that matches
the latitudinal distribution of the solar wind parameters observed
by Ulysses and SOHO and extends from the pole to 9° latitude. The
larger fraction (≈60%) of the fast wind (above 30° latitude at 1 AU)
emerges from the polar coronal hole, while the remainder is associated
with the quiet Sun. While the actual fraction of the fast solar wind
originating from polar coronal holes relies on an accurate estimate of
the contribution of the open magnetic flux from polar coronal holes
to the total IMF flux, this model shows that extending the source of
open magnetic flux at the Sun beyond the traditionally assumed polar
coronal holes can readily account for the latitudinal distribution of
fast wind measured by Ulysses at solar minimum.
Title: A 2.5-dimensional MHD Alfvén-wave-driven solar wind model
Authors: Hu, Y. Q.; Li, X.; Habbal, S. R.
Bibcode: 2003JGRA..108.1378H
Altcode:
A 2.5-dimensional MHD analysis of Alfvén-wave-driven solar wind in
the heliospheric meridional plane is presented in order to extend the
one-dimensional model proposed by [1967] to the two-dimensional case. In
our model, no energy input is applied to the helmet streamer, while the
solar wind along open field lines is assumed to be driven by Alfvén
waves. The differential rotation of the Sun is considered. The numerical
results obtained essentially match relevant Ulysses observations and
give the spatial distribution of the azimuthal components of the flow
velocity and magnetic field. The effect of the existence of these
azimuthal components on the global properties of the solar wind is
found to be negligible, and the loss rate of the angular momentum of
the Sun due to the solar wind is estimated.
Title: Ubiquitous Open Magnetic Field Lines in the Inner Corona
Authors: Woo, Richard; Habbal, Shadia Rifai
Bibcode: 2003AIPC..679...55W
Altcode:
The notion that density structure reflects magnetic field lines
makes it possible to deduce information on coronal magnetic fields
from density measurements. The purpose of this paper is to summarize
the observational evidence for ubiquitous open magnetic field lines
in the inner corona from density measurements. Based on both global
and filamentary structures, these density measurements explain the
unexpected predominance of the radial component of coronal magnetic
field discovered in polarimetric observations over three decades ago.
Title: Large Amplitude Alfvén Waves In Open And Closed Coronal
Structures
Authors: Grappin, R.; Léorat, J.; Habbal, S. R.
Bibcode: 2003AIPC..679..277G
Altcode:
The time-dependent response of the corona in a spherical shell between
1.8 and 16 Rs to injection of low-frequency Alfvén waves at the
inner boundary is considered in the MHD, isothermal and axisymmetric
framework, without approximation for the wave-wind coupling. The
magnetic field is the sum of an external dipole field assumed to be
produced by the sun and of the field induced by the plasma motion
in the spherical shell. Due to Alfvén wave injection, the wind and
magnetic structure change, leading to an increased overexpansion
of the high-latitudes flows and fields. Some of the factors which
affect these changes: dissipation, and latitudinal distribution of
the waves are explored, and the quantitative relation between wind
speed and wave amplitude are discussed. We conclude that Alfvén waves
alone lead ultimately to the disappearance of the slow wind, and that
other factors, such as transverse structures and compressive waves,
are necessary to explain the observed structure of the solar wind.
Title: On the Detection of the Signature of Silicon Nanoparticle
Dust Grains in Coronal Holes
Authors: Habbal, Shadia Rifai; Arndt, Martina Belz; Nayfeh, Munir
H.; Arnaud, Jean; Johnson, Judd; Hegwer, Steve; Woo, Richard; Ene,
Alexandru; Habbal, Feras
Bibcode: 2003ApJ...592L..87H
Altcode:
We report on polarization measurements in the Fe XIII line at 1074.7
nm made during the total solar eclipse of 2001 June 21, which yielded
the first signature of interplanetary dust in the inner corona. In
the first-ever images at this wavelength, the signature of dust
appears as a tangentially polarized emission in the radial extension
of the low-temperature and low-density coronal holes as opposed to
a predominantly radial polarization direction in the rest of the
corona. The observed emission and polarization are attributed to
fluorescence from silicon nanoparticle dust grains in the inner corona.
Title: The 2001 June 21 Eclipse Polarimetric Observations of the Fe
XIII 1074.7 nm Emission Line
Authors: Habbal, S. R.; Arndt, M. B.; Nayfeh, M. H.; Arnaud, J.;
Johnson, J.; Hegwer, S.; Ene, A.
Bibcode: 2003SPD....34.0409H
Altcode: 2003BAAS...35..812H
Polarimetric measurements of the coronal forbidden lines have been
recognized for quite some time as a diagnostic tool for inferring the
direction of the coronal magnetic field. Following the first successful
measurements by Eddy et al. (1973) during the total solar eclipse
of 1966, an observing campaign using the coronagraph at Sacramento
Peak Observatory was pursued between 1977-1980 (Arnaud and Newkirk,
1987). All these measurements yielded the surprising result that the
direction of polarization implied a predominantly radial coronal
magnetic field. We report on the polarization measurements of the
Fe XIII 1074.7nm line, the strongest of the coronal forbidden lines,
which were obtained during the total solar eclipse of 2001 June 21 from
Zambia. In addition to confirming the earlier results of a predominantly
radial field, the signature of nano-size interplanetary dust in
the inner corona, most likely in the form of silicon nanoparticles,
appeared for the first time in these measurements. The signature of
these particles also coincides with the radial expansion of coronal
holes outwards from the Sun, a signature that has never appeared in
any measurement before. Support for this work was provided by
NSF grant ATM-0003661 and NASA grant NAG5-10873
Title: Effect of solar wind flow geometry on solar wind parameters
at 1 AU for a low-frequency cascade driven solar wind
Authors: Mountford, C. J.; Habbal, S. R.; Li, X.
Bibcode: 2003JGRA..108.1079M
Altcode:
A two-fluid, one-dimensional solar wind model is used to explore how
the change in the expansion of a given flow tube with heliocentric
distance influences the properties of the solar wind. Using a single
driving mechanism, namely ion cyclotron resonance through a nonlinear
Kolmogorov cascade process, for proton heating, the Alfvén wave
amplitude, electron density, and temperature are kept fixed at the
coronal base, while the parameters defining the form and extent of
the expansion are varied. The results of this parameter study show
that it is the variation of the expansion with heliocentric distance
rather than the overall faster than radial expansion of the flow tube
that plays a critical role in determining the asymptotic properties
of the solar wind. These results can be understood in light of the
conclusions derived originally by [1980] with a simple ad hoc heating
function, namely that the mass flux and flow speed at 1 AU depend on
whether most of the energy is deposited in the subsonic or supersonic
region of the flow. With a more complex heating function, such as
the one considered in this study, it is shown how the location of
the critical point changes as a result of the interplay between the
location of resonance interaction and the expansion of the flow tube,
which subsequently affects the energy distribution within that flow
tube. In particular, it is shown that for sharp expansion both enhanced
and inhibited flows can occur depending on the heliocentric distance
of the expansion region.
Title: On the Coexistence of a Radial and Non-radial Component of
the Coronal Magnetic Field
Authors: Habbal, S. R.; Woo, R.; Arndt, M.; Arnaud, J.
Bibcode: 2003ASPC..307..446H
Altcode:
No abstract at ADS
Title: The Origin of the Solar Wind
Authors: Woo, Richard; Habbal, Shadia Rifai
Bibcode: 2002AmSci..90..532W
Altcode:
Nearly 1,400 years ago, Chinese astronomers noticed that comet tails
always point away from the Sun. They concluded that the Sun must have
chi</em>—a basic life force—that blows the tails away. It
wasn't until the middle of the 20th century that scientists understood
that this "force" actually consisted of little pieces of the sun
itself—protons and electrons—blowing out into the solar system as a
"wind" at more than a million kilometers per hour. The traditional view
of the solar wind's origins suggests that it originates from special
regions on the Sun, called coronal holes. Woo and Habbal present new
evidence showing that the wind actually emanates from all regions on
the Sun.
Title: Ion Effective Temperatures in Polar Coronal Holes: Observations
versus Ion-Cyclotron Resonance
Authors: Patsourakos, S.; Habbal, S. R.; Hu, Y. Q.
Bibcode: 2002ApJ...581L.125P
Altcode:
The resonant cyclotron interaction between ion-cyclotron waves and
solar wind species is considered nowadays to be a strong candidate
for heating and acceleration of protons, α-particles, and heavy
ions. A crucial physical parameter for determining the amount and
the location of significant heating and acceleration, which the
different solar wind ions receive from the waves in the frame of the
ion-cyclotron mechanism, is their charge-to-mass ratio q/m. Therefore,
comparisons of ion temperatures derived from spectroscopic observations
and calculated by ion-cyclotron models, for ions that span a broad
range in q/m, would provide a rigorous test for such models. By using
an ion-cyclotron model, we calculate the effective temperatures for
10 different ions that cover the range 0.16-0.37 in q/m. Effective
temperatures correspond to unresolved thermal motions and wave
motions. The good agreement between our calculations, based on the
specific mechanism that we employed here (ion-cyclotron resonance)
and on spectroscopic observations of effective temperatures in polar
coronal holes, provides support that the above mechanism accounts for
the energetics and kinematics of fast solar wind heavy ions. However,
such an agreement does not prove that other potential mechanisms can
be excluded.
Title: Radiative transfer effects on hydrogen (and helium) in the
solar atmosphere
Authors: Labrosse, N.; Li, X.; Habbal, S. R.; Gouttebroze, P.;
Mountford, C. J.
Bibcode: 2002ESASP.506...13L
Altcode: 2002svco.conf...13L; 2002ESPM...10...13L
In this work we present Non-Local Thermodynamic Equilibrium (non-LTE)
computations for hydrogen for a VAL-C model of the Sun's atmosphere. The
solar atmosphere is represented by a one-dimensional plane-parallel
horizontal slab. The purpose of this study is to investigate the effects
of the transfer of radiation in the chromosphere and the transition
region. In particular, we aim at understanding how the radiative
losses in the energy balance for electrons are affected by the non-LTE
radiative transfer, which has to be considered in the regions where
the temperature is less than 25000K. The numerical code used here
allows us to study the properties of, and the spectrum emitted by,
the hydrogen particles. The non-LTE radiative transfer equations (RT)
are solved for all optically thick resonance lines. The solutions of
the RT in the optically thick lines affect all population densities of
atoms and ions through the statistical equilibrium equations (SE). For
the VAL-C atmosphere model there is a peak around 6×103K
in the net radiative cooling rates due to several lines and continua
from hydrogen. To our knowledge this peak has never been considered
when evaluating the radiative losses in the chromosphere in the frame
of solar wind modelling. We mention some consequences for solar wind
models in the description of the chromosphere and the transition
region which is often made under the assumption of full ionization
and optically thin plasma.
Title: Large-amplitude Alfvén waves in open and closed coronal
structures: A numerical study
Authors: Grappin, R.; LéOrat, J.; Habbal, S. Rifai
Bibcode: 2002JGRA..107.1380G
Altcode:
We present the first simulations of the coronal response to Alfvén
wave injection using transparent boundaries in a classical one-fluid,
isothermal axisymmetric model including both closed and open magnetic
field structures. The aim of the work is first to study how Alfvén
waves change the contrast between the equatorial and high-latitude wind,
and second, how they modify the geometry of the wind and its global
stability. We integrate the full time-dependent MHD equations, and
inject large-amplitude (150 km/s), low-frequency (20 min period) waves
at 1.8 Rs, both in open and in closed field line regions,
except within narrow regions around the poles and the equator. The
domain considered extends up to 16 Rs. Our principal
results are the following: (1) The assumption of a latitude-independent
Alfvén wave amplitude compatible with observations leads to a large
acceleration both of the high-latitude and equatorial wind; as a
consequence, the contrast between slow and fast wind speeds at 16
Rs is not as large as the observed values if extrapolated
to 1 AU, a result which could potentially change with the use of
better resolved, less dissipative simulations; (2) an initial delay
in the Alfvén flux onset in one hemisphere generates a stable global
circulation in the closed loops region, which after a long enough time
produces a global north-south asymmetry and changes the structure of
the corona as a whole.
Title: Microphysics of Waves and Instabilities in the Solar Wind
and Their Macro Manifestations in the Corona and Interplanetary Space
Authors: Habbal, Shadia Rifai
Bibcode: 2002STIN...0239994H
Altcode:
A breakthrough resulted from the investigation of plasma heating by
ion-cyclotron waves in rapidly expanding flow tubes, often referred
to as coronal funnels and expected to originate in the low transition
region where the temperature gradient in the solar atmosphere rises
very sharply. The investigation was made using a three-fluid plasma
consisting of protons, electrons and alpha particles. It was found that
these waves heat the solar wind plasma by directly heating the heavier
species, namely the alphas. Although only alpha particles dissipate
the waves, the strong Coulomb coupling between alpha particles and
protons, and between protons and electrons, makes it possible for
protons and electrons to be heated also to more than one million
degrees, i.e. to coronal temperatures. Interestingly, the extreme
heating of the alpha particles, however, is such that they end up
being hotter and faster, and are no longer in thermal equilibrium
with the protons and electrons. once the rapid expansion of the flow
tube is complete, the particles return to thermal equilibrium. The
observational signatures of these results are such that if spectral
lines formed below a million degrees are observed at different heights
in the corona, the inferred outflow velocities may vary by a factor of
5 to 6. In addition, if minor ions are indeed much faster than protons
and electrons at temperatures below a million degrees, then one cannot
reliably determine the bulk outflow velocity of the solar wind in that
region from inferences of minor ion outflow velocities. A detailed
parameter study on the resonant interaction between ion cyclotron waves
and alpha particles and other minor ions is also under way. It is found
that the highest frequency of the waves, or the location of the heating
determines whether a thermal equilibrium can be established between
minor ions and protons. As the maximum frequency is increased, alpha
particles and protons become farther away from thermal equilibrium. As
the maximum frequency becomes smaller, alpha particles and protons
are more likely to be in thermal equilibrium. However, if the maximum
frequency is below a critical value, ion cyclotron resonance occurs
at a greater height and a hot corona cannot be produced.
Title: Polarimetric Imaging of The Solar Corona During The 21 June
2001 Total Solar Eclipse
Authors: Habbal, S. R.; Arnaud, J.; Arndt, M.; Ene, A.; Esser, R.;
Faurobert, M.; Hale, J.; Hegwer, S.; Johnson, J.; Woo, R.
Bibcode: 2002EGSGA..27.6098H
Altcode:
We report on the first successful simultaneous eclipse measurements
of the inten- sity and polarization brightness of the K-Corona and the
near-infrared Fe XIII 1074.7 nm emission line. Those observations were
obtained during the total solar eclipse of 21 June 2001. The technique
used for those observations will be presented. Coronal emission lines
polarization measurements are the only tools to date that can yield
the direction of the coronal magnetic field.
Title: Editorial
Authors: Richmond, Arthur D.; Habbal, Shadia; Lee, Lou-Chuang
Bibcode: 2002JGRA..107.1015R
Altcode:
No abstract at ADS
Title: Damping of fast and ion cyclotron oblique waves in the
multi-ion fast solar wind
Authors: Li, X.; Habbal, S.
Bibcode: 2001AGUFMSH21A0738L
Altcode:
Oblique fast waves in a multi-ion low-beta Vlasov plasma such as the
solar wind is investigated. It is shown that at very oblique propagation
angles, proton fundamental and second harmonic cyclotron damping become
dominant. The property of oblique fast waves can also be significantly
changed in the presence of minor ions. Depending on their abundance and
relative speed with respect to protons, minor ions can change the wave
polarization from right-handed at small wave numbers to left-handed
at larger wave numbers for some propagation angles. Consequently,
a power law spectrum of oblique fast waves originating at the Sun may
preferentially heat and accelerate alpha particles rather than protons
and electrons in the fast solar wind. Furthermore, it is shown that
oblique fast waves can heat minor ions more than oblique Alfvenic ion
cyclotron waves thus making them a potentially more important candidate
for the preferential heating of minor ions in the solar wind than ion
cyclotron waves.
Title: Observational Associations Between the Solar Corona and
Solar Interior
Authors: Woo, R.; Armstrong, J. W.; Habbal, S. R.; Habbal, S. R.
Bibcode: 2001AGUFMSH11B0713W
Altcode:
Generated in the solar interior, magnetic fields make their way
through the solar atmosphere, shaping solar wind flow and determining
solar activity. Although essential for understanding and identifying
the physical processes by which this occurs, there has been a lack
of observational associations between the corona and interior of the
Sun. A direct association was recently demonstrated when the latitudinal
profile of the correlation of coronal density separated in latitude by
20 degrees was found to be similar to that of the alternating slow and
fast zonal bands observed in the outer part of the solar convection zone
(Woo et al., ApJ., 538, L171, 2000). The latter are also evident on the
surface of the Sun where they are known as torsional oscillations. In
this paper, we summarize further results from investigating and
characterizing the morphology of coronal density and its relationship
to surface and subsurface solar flow using measurements by the High
Altitude Observatory Mauna Loa Mk III K-coronameter.
Title: Polarized Intensity Measurements of the Corona during the 21
June 2001 Total Solar Eclipse
Authors: Habbal, S. R.; Arnaud, J.; Johnson, J.; Hegwer, S.; Ene, A.;
Hale, J.; Esser, R.; Arndt, M.; Kohl, J. L.; Daw, A.; Faurobert, M.;
Woo, R.; Habbal, F.; Havasy, R.; Alford, J. N.
Bibcode: 2001AGUFMSH11C0716H
Altcode:
We report on the first successful simultaneous polarimetric measurements
of the brightness of the Thompson-scattered white light and intensity
of the near-infrared Fe XIII 10747 Å line, the strongest of the
coronal iron forbidden lines. These observations which extended out
to 3 Rs in the corona were obtained during the total solar
eclipse of 21 June 2001. The novel technique used to acquire these
measurements will be presented. Polarized intensity measurements of the
resonantly scattered component of coronal emission lines are the only
tools to date that can yield the direction of the coronal magnetic
field. Through these simultaneous measurements, we show how the
direction of the coronal magnetic field can be placed in the context
of coronal density structures. We also discuss the implications of
these simultaneous measurements for the source of the solar wind.
Title: The polar coronal holes and the fast solar wind: Some recent
results
Authors: Patsourakos, S.; Habbal, S. -R.; Vial, J. -C.; Hu, Y. Q.
Bibcode: 2001AIPC..598..299P
Altcode: 2001sgc..conf..299P
We report on recent results on the source regions of the fast solar
wind: the Polar Coronal Holes (PCH). They concern a comparison
between the effective temperatures for a large set of different ions
obtained from observations in the inner corona of PCH and from a fast
wind numerical model based on the ion-cyclotron resonant dissipation
of high-frequency Alfvén waves. We also report on some preliminary
results from our modeling concerning the Fe/O ratio in the inner corona
in PCH. .
Title: On the Predominance of the Radial Component of the Magnetic
Field in the Solar Corona
Authors: Habbal, Shadia Rifai; Woo, Richard; Arnaud, Jean
Bibcode: 2001ApJ...558..852H
Altcode:
Polarimetric measurements of the corona out to 2 Rsolar
in the Fe XIII 10747 Å line, the strongest of the iron forbidden
lines, are placed for the first time in the context of spatially
resolved images of coronal density structures. These measurements,
which are the only tool currently available to yield the direction
of the magnetic field, date to 1980, the only year when they were
available with polarized brightness images of the corona. Through this
comparison, the observed predominance of the radial component of the
coronal magnetic field, discovered over three decades ago from eclipse
observations and established systematically by Arnaud, is shown to point
to the coexistence of two magnetic field components in the corona:
a nonradial field associated with the large-scale structures known
as streamers and a more pervasive radial magnetic field. This finding
suggests that these two components are the coronal counterparts of the
strong- and weak-field components recently observed in the quiet-Sun
photospheric field and supported by recent theoretical investigations
of the solar dynamo.
Title: Physics of the Inner Heliosphere 1-10 Rs: Plasma
Diagnostics and Models
Authors: Habbal, Shadia R.
Bibcode: 2001STIN...0182952H
Altcode:
While the mechanisms responsible for heating the solar corona
and accelerating the fast and slow solar wind streams are still
unknown, model computations offer the only means for exploring
and predicting the properties of such mechanisms in light of the
empirical constraints currently available. During the time covered
by this grant, modeling and data analysis efforts were aimed at: 1)
the study of the propagation and damping of ion-cyclotron waves in
the fast solar wind 2) the exploration of the role of instabilities
in the development of temperature anisotropies in the inner corona 3)
the coupling of neutral hydrogen and protons in the fast solar wind 4)
the morphology of the source region of the solar wind. Summarized are
some of the highlights of these studies. Two PhD theses by Xing Li
and Lorraine Allen were partially supported by this grant.
Title: Damping of fast and ion cyclotron oblique waves in the
multi-ion fast solar wind
Authors: Li, Xing; Habbal, Shadia Rifai
Bibcode: 2001JGR...10610669L
Altcode:
A detailed linear analysis of the behavior of oblique fast waves in a
multi-ion low-beta Vlasov plasma such as the solar wind is presented. It
is shown that at very oblique propagation angles, proton fundamental
and second harmonic cyclotron damping become dominant. The property of
oblique fast waves can also be significantly changed in the presence
of minor ions. Depending on their abundance and relative speed with
respect to protons, minor ions can change the wave polarization from
right-handed at small wave numbers to left-handed at larger wave numbers
for some propagation angles. Consequently, a power law spectrum of
oblique fast waves originating at the Sun may preferentially heat and
accelerate alpha particles rather than protons and electrons in the
fast solar wind. Furthermore, it is shown that oblique fast waves can
heat minor ions more than oblique Alfvénic ion cyclotron waves thus
making them a potentially more important candidate for the preferential
heating of minor ions in the solar wind than ion cyclotron waves.
Title: Photospheric Network as the Energy Source for the quiet-Sun
corona
Authors: Ryutova, M.; Habbal, S.; Woo, R.; Tarbell, T.
Bibcode: 2001SoPh..200..213R
Altcode:
We propose a mechanism for the formation of a magnetic energy avalanche
based on highly dynamic phenomena within the ubiquitous small-scale
network magnetic elements in the quiet photosphere. We suggest that
this mechanism may provide constant mass and energy supply for the
corona and fast wind. Constantly emerging from sub-surface layers,
flux tubes collide and reconnect generating magneto-hydrodynamic shocks
that experience strong gradient acceleration in the sharply stratified
photosphere/chromosphere region. Acoustic and fast magnetosonic
branches of these waves lead to heating and/or jet formation due to
cumulative effects (Tarbell et al., 1999). The Alfvén waves generated
by post-reconnection processes have quite a restricted range of
parameters for shock formation, but their frequency, determined by the
reconnection rate, may be high enough (ω≃0.1-2.5 s−1)
to carry the energy into the corona. We also suggest that the primary
energy source for the fast wind lies far below the coronal heights, and
that the chromosphere and transition region flows and also radiative
transient form the base of the fast wind. The continuous supply of
emerging magnetic flux tubes provides a permanent energy production
process capable of explaining the steady character of the fast wind
and its energetics.
Title: UVCS Observations of Velocity Shear at Streamer Boundaries
in the Corona
Authors: Habbal, Shadia Rifai; Woo, Richard; Vial, Jean-Claude
Bibcode: 2001SSRv...97....5H
Altcode:
Measurements of the intensities of the Ovi 1032 and 1037 Å spectral
lines in the southern solar hemisphere, from 1.5 to 5 R_s, were made
with the SOHO Ultraviolet Coronagraph Spectrometer (UVCS) in May
2000 close to solar maximum. The ratio of the intensity of the two
oxygen lines is used as a proxy for solar wind velocity in the inner
corona. White light images of the corona taken with the SOHO/LASCO-C2
during the same time period, and used to place the UVCS observations
in the context of coronal structures, show streamers extending to
high latitudes. The measured radial and azimuthal gradients of the
intensity ratio reflect strong velocity shears in the corona with the
slowest wind coinciding with the axis of streamers. Comparison of these
results with ratios measured with UVCS during solar minimum indicates
that the transition from fast to slow wind in the inner corona occurs
within 20° of the axis of streamers at both phases of the solar cycle.
Title: Associating the Solar Wind Measured by Ulysses with its Source
at the sun
Authors: Woo, Richard; Habbal, Shadia Rifai
Bibcode: 2001SSRv...97...85W
Altcode:
Radio occultation, ultraviolet, and white-light measurements have
expanded our knowledge of the morphology of density and velocity
in polar coronal holes, and made it possible to carry out the first
systematic comparisons between the Ulysses solar wind measurements and
quantitative white-light observations of the solar corona. This paper
summarizes the rationale and salient features of this new approach
which has been used to relate the solar wind observed by Ulysses
in 1993-1995 to the inner corona. The statistical characteristics
(average, standard deviation, and autocorrelation function) of the
Ulysses density measurements of the fast wind are found to be mirrored
in those of polarized brightness measurements of path-integrated density
made by the High Altitude Observatory (HAO) Mauna Loa K-coronagraph at
1.15 R ⊙. These results reinforce the conclusions from
comparisons between measurements of the outer and inner corona. They
show that the polar coronal hole extends radially into the solar wind,
and that sources of the fast wind are not limited to coronal holes.
Title: On the Coexistence of a Radial Magnetic Field with the Large
Scale Field in the Solar Corona
Authors: Habbal, S. R.; Woo, R.; Arnaud, J.
Bibcode: 2001AGUSM..SH22E06H
Altcode:
Polarimetric measurements of the corona out to 2 Rs in the
Fe XIII 10747 A line, the strongest of the iron forbidden lines, are
placed for the first time in the context of spatially resolved images
of coronal density structures. These measurements, which are the only
tool currently available to yield the direction of the magnetic field,
date to 1980, the only year when they were available with polarized
brightness images of the corona. Through this comparison, the observed
predominance of the radial component of the coronal magnetic field,
discovered over three decades ago from eclipse observations, and
established systematically by Arnaud (1982), is shown to point to
the existence of two components of the coronal magnetic field: a
non-radial component associated with the large scale structures known
as streamers, and the second, more dominant one, a pervasive radial
magnetic field. The coexistence of these two components provides new
information for the distribution of open and closed magnetic flux in
the solar corona.
Title: Associating the Solar Wind Measured by Ulysses with its Source
at the sun
Authors: Woo, Richard; Habbal, Shadia Rifai
Bibcode: 2001SSRv...97...81W
Altcode:
Radio occultation, ultraviolet, and white-light measurements have
expanded our knowledge of the morphology of density and velocity
in polar coronal holes, and made it possible to carry out the first
systematic comparisons between the Ulysses solar wind measurements and
quantitative white-light observations of the solar corona. This paper
summarizes the rationale and salient features of this new approach
which has been used to relate the solar wind observed by Ulysses
in 1993-1995 to the inner corona. The statistical characteristics
(average, standard deviation, and autocorrelation function) of the
Ulysses density measurements of the fast wind are found to be mirrored
in those of polarized brightness measurements of path-integrated density
made by the High Altitude Observatory (HAO) Mauna Loa K-coronagraph at
1.15 R_solar. These results reinforce the conclusions from comparisons
between measurements of the outer and inner corona. They show that
the polar coronal hole extends radially into the solar wind, and that
sources of the fast wind are not limited to coronal holes.
Title: UVCS Observations of Velocity Shear at Streamer Boundaries
in the Corona
Authors: Habbal, Shadia Rifai; Woo, Richard; Vial, Jean-Claude
Bibcode: 2001SSRv...97....8H
Altcode:
Measurements of the intensities of the O vi 1032and 1037 Å spectral
lines in the southern solar hemisphere, from 1.5 to 5 R s,
were made with the SOHO Ultraviolet Coronagraph Spectrometer (UVCS) in
May 2000 close to solar maximum. The ratio of the intensity of the two
oxygen lines is used as a proxy for solar wind velocity in the inner
corona. White light images of the corona taken with the SOHO/LASCO-C2
during the same time period, and used to place the UVCS observations
in the context of coronal structures, show streamers extending to
high latitudes. The measured radial and azimuthal gradients of the
intensity ratio reflect strong velocity shears in the corona with the
slowest wind coinciding with the axis of streamers. Comparison of these
results with ratios measured with UVCS during solar minimum indicates
that the transition from fast to slow wind in the inner corona occurs
within 20° of the axis of streamers at both phases of the solar cycle.
Title: Connecting the Sun and the Solar Wind: Comparison of the
Latitudinal Profiles of Coronal and Ulysses Measurements of the
Fast Wind
Authors: Habbal, Shadia Rifai; Woo, Richard
Bibcode: 2001ApJ...549L.253H
Altcode:
A quantitative comparison of the latitudinal profile of polarized
brightness (pB) measurements nearest the Sun at 1.15 Rsolar
by the Mauna Loa Solar Observatory K-Coronameter and Ulysses
interplanetary measurements of the fast solar wind during its first
south polar pass, at the declining phase of the solar cycle, is made
for the first time to identify the sources of the fast solar wind in
the context of coronal density structure. Both profiles are found to
have the same shape. At the Sun, the minimum coincides with the radial
extension of the coronal hole boundaries. The slight rise and plateau
following this minimum toward lower latitudes are identified with
the coronal extension of the quiet Sun. The corresponding profile
of the in situ measured velocity has a maximum within the angular
extent of the polar coronal hole and decreases gradually beyond its
boundaries. The latitudinal profile of the proton flux mimics the
density profile, implying that the mass-loss rate is lowest within
the angular extent of the polar coronal hole. The association of the
fast wind with a density profile that reflects the polar coronal hole
and the surrounding quiet Sun suggests that the fast wind observed by
Ulysses originates from both regions. That these conclusions differ
from earlier published analyses of the same Ulysses measurements is a
consequence of the quantitative and systematic comparison made between
Ulysses and coronal measurements at 1.15 Rsolar.
Title: Electron kinetic firehose instability
Authors: Li, Xing; Habbal, Shadia Rifai
Bibcode: 2000JGR...10527377L
Altcode:
The linear dispersion equation describing electromagnetic waves
propagating in a homogeneous electron-proton plasma along arbitrary
directions relative to the direction of the background magnetic field
is solved numerically for bi-Maxwellian particle distributions. It
is found that in the presence of an electron temperature anisotropy
T⊥<T∥ and a sufficiently warm plasma
(βe>2), several purely growing modes (zero real
frequency) and a quasi-parallel electron firehose instability
develop. While the quasi-parallel mode is unstable for both parallel
and oblique propagation, the zero frequency modes are unstable only
for oblique propagation. Comparison of these modes further shows that
the propagation angle for maximum growth rate and the maximum growth
rate are larger for the purely growing modes than the quasi-parallel
electron firehose while the threshold is lower. Potential application
of the kinetic electron firehose instability to the slow solar wind
is briefly discussed.
Title: Fast waves, Landau and ion-cyclotron resonance in coronal holes
Authors: Li, X.; Habbal, S. R.
Bibcode: 2000AAS...197.3106L
Altcode: 2000BAAS...32.1447L
Historically, fast waves were believed to be responsible for the solar
wind heating. It was known that fast waves primarily heat electrons
in a low-beta electron/proton plasma, such as the inner corona. They
have been not paid much attention until recently since both in situ
and remote sensing measurements (UVCS/SOHO) found that not only ions
are hotter than electrons, they have more than mass-proportional
temperatures as well. However, at very oblique propagation, proton
fundamental and second harmonic cyclotron damping become dominant. The
property of oblique fast waves can also be changed dramatically
due to the presence of minor ions. Minor ions can change the wave
polarization from left-handed at small wave numbers to right-handed
at larger wave numbers depending on the abundance of of minor ions,
the wave propagation angle, and the relative flow speed between minor
ions and protons. In coronal holes, refraction and velocity shear will
naturally change wave vectors oblique even these waves originally
are parallel. Subsequently, fast branch waves will heat minor ions
preferentially if high frequency fast waves can be generated in coronal
holes. It is possible that fast waves play a role in coronal heating
and the solar wind acceleration.
Title: Solar Wind: Coronal Origins
Authors: Habbal, S.; Woo, R.
Bibcode: 2000eaa..bookE2313H
Altcode: 2001eaa..book.2820H
To establish the coronal origins of the solar wind is to find its source
regions at the Sun. Dominated by electrons and protons, this outflow of
fully ionized atoms also carries traces of neutral hydrogen and heavier
elements, such as alpha particles, oxygen and iron ions. There are two
types of winds detected so far: the fast and the slow (see SOLAR WIND:
GLOBAL PROPERTIES). Since they are disti...
Title: Thermal coupling of protons and neutral hydrogen with
anisotropic temperatures in the fast solar wind
Authors: Allen, Lorraine A.; Habbal, Shadia R.; Li, Xing
Bibcode: 2000JGR...10523123A
Altcode:
The thermal coupling between the neutral hydrogen and protons in the
inner corona is explored by extending the study of Allenet al. [1998]
to include anisotropic proton temperature to determine what the
neutral hydrogen Ly α spectral line measurements reveal about the
proton temperature, temperature anisotropy, and outflow velocity in
the fast solar wind. The anisotropic proton temperature is produced
by ion cyclotron resonant interaction of protons with high-frequency
waves, produced by a nonlinear cascade at the Kolmogorov dissipation
rate from dominant lower-frequency Alfvén waves. As a result of the
coupling between the respective parallel and perpendicular components
of the neutral hydrogen and proton temperatures, a greater temperature
anisotropy in the neutral hydrogen develops as compared to the case
when the proton temperature is isotropic. The neutral hydrogen and
proton effective temperatures (Teff), incorporating both
random and wave motions of the particles, and outflow velocities, are
comparable below ~3Rs. Neutral hydrogen anisotropy ratios,
TH(eff)/T∥, ~4 below 3Rs are readily
attained, in agreement with observations. Below ~3Rs, these
reflect the proton anisotropy ratio. For plasma conditions typical
of the fast solar wind, these results imply that the measured Ly α
spectral line profiles, from which the neutral hydrogen temperature,
anisotropy ratio, and outflow velocity are inferred, are equivalent
to measurements of protons below ~3Rs. Beyond this distance
the width of the measured Ly α spectral lines provides a lower limit
to the proton effective temperature and temperature anisotropy in the
inner corona.
Title: Observed Associations between the Solar Interior, Corona,
and Solar Wind
Authors: Woo, Richard; Armstrong, J. W.; Habbal, Shadia Rifai
Bibcode: 2000ApJ...538L.171W
Altcode:
Using polarized brightness (pB) measurements made by the High
Altitude Observatory (HAO) Mauna Loa Mk III K-coronameter, we
investigate the daily changes of path-integrated density at 1.15
Rsolar. During 1996, when simultaneous pB and helioseismology
data were available, we find that the correlation of pB (at zero time
lag and 20° latitude lag) varies with latitude in the same way that the
subsurface differential rotation inferred from helioseismology does. The
association is such that bands of higher pB correlation are associated
with retrograde subsurface rotation and that lower pB correlation bands
are associated with prograde subsurface rotation. We also show that
polar coronal holes are distinguished by a nonrecurring longitudinal
structure as opposed to a recurring structure in the quiet Sun. In
addition, the levels of pB and standard deviation σpB of pB
are about half of those of the neighboring quiet Sun. These statistical
characteristics of coronal density in polar holes and the quiet Sun
were also present in 1993-1994 and are replicated in the statistics
of the distant solar wind observed by Ulysses. The association of
the density (pB) correlation with subsurface flow (when simultaneous
data were available in 1996), together with the association of the
latitudinal dependence of the statistical characteristics (average,
standard deviation, and autocorrelation function) of the coronal (pB)
and solar wind (Ulysses) density (when simultaneous data were available
in 1993-1994), suggest a correlated variability of subsurface flow,
coronal density, and solar wind density organized by solar latitude.
Title: Connecting the Sun and the solar wind: Source regions of the
fast wind observed in interplanetary space
Authors: Woo, Richard; Habbal, Shadia Rifai
Bibcode: 2000JGR...10512667W
Altcode:
Highly sensitive radio occultation and white light measurements of
path-integrated density have shown that the solar corona comprises
three distinct morphological regions, streamer, quiet Sun, and
polar coronal hole, which except for the streamer region, extend
radially into interplanetary space from 1.15Rs to at least
30Rs. In this paper we build on these results by comparing
solar wind flow speeds observed at the same time as path-integrated
density. Flow speeds are inferred from the Doppler dimming of O VI
lines with the ultraviolet coronagraph spectrometer on the Solar
and Heliospheric Observatory, while the simultaneous polarized
brightness measurements of path-integrated density are from the High
Altitude Observatory Mauna Loa Mk III K-coronameter. The comparison
of global flow speed and density observations in 1997 produces three
new results. First, it shows, that the three distinct morphological
regions, identified earlier in density measurements, are present in the
latitudinal profile of the flow speed in the corona. In particular,
the flow speed measurements provide evidence for the quiet Sun as
an additional source of fast wind. Second, the comparison shows that
flow speed and density are anticorrelated in the solar corona. Third,
it demonstrates that the Mk III pB measurements can readily serve as a
proxy for velocity distribution in the outer corona. The extensive Mk
III data set that spans nearly two solar cycles therefore provides the
framework of near-Sun measurements with which connections with solar
wind measurements in interplanetary space can be made. Specifically,
we show that fast wind regions in the heliosphere, observed directly
by Ulysses and Wind plasma measurements and remotely by Nagoya
interplanetary scintillation measurements, map radially back to fast
wind regions at the Sun identified by the Mk III data.
Title: Temperature, density and magnetic field structure of the
corona during the total eclipse of 1999 August 11
Authors: Habbal, S. R.; Johnson, J.; Nisenson, P.; Woo, R.; Fineschi,
S.; Esser, R.; Wood, C. H.; Hale, J.; Forman, M. A.; Johnson, J. A.;
Jabbour, J.
Bibcode: 2000SPD....31.0235H
Altcode: 2000BAAS...32..817H
The goal of the eclipse expedition of the Harvard-Smithsonian Center
for Astrophysics on 1999 August 11 to Ayn Diwar in Syria was to explore
the temperature, density and magnetic structure of the corona through
simultaneous imaging in the Fe X 6374, XIV 5303 and XI 7892 Angstroms
lines, the Hα 6563 Angstroms line, and the polarized brightness or
white light. Polarization measurements were made in the Fe XIV 5303
Angstroms and Hα 6563 Angstroms lines to yield the direction of the
coronal magnetic field. Inferences of the temperature distribution
were made from the three iron lines, while density profiles were
derived from the polarized brightness measurements. Supporting
space based observations were acquired with LASCO and UVCS on
SOHO. The comprehensive diagnostic resulting from the analysis of the
observations of the close-to-spherically symmetric corona of 1999
August 11 approaching solar maximum will be presented. Funding for
this research was provided by NSF grant ATM 9521733 to the Smithsonian
Astrophysical Observatory. We acknowledge the generous hospitality
and support bestowed upon the team by the Syrian Ministry of Higher
Education to conduct the experiment in Syria. The digitization of
the photographic film was made with the help of Dr. J. Thornton and
S. Sarafian from the Image Science Laboratory at Polaroid Corporation.
Title: Apparent Associations Between the Solar Interior, Corona,
and Solar Wind
Authors: Woo, R.; Armstrong, J. W.; Habbal, S. R.
Bibcode: 2000SPD....31.0230W
Altcode: 2000BAAS...32..816W
Using polarized brightness (pB) measurements made by the High Altitude
Observatory (HAO) Mauna Loa Mk III K-coronameter, we investigate
the daily changes of path-integrated density at 1.15 Ro representing
mainly longitudinal structure but also temporal variations near the
Sun. We relate these coronal features to the interior of the Sun
by comparing them with the subsurface large-scale velocity patterns
associated with torsional oscillations. Specifically, we find that the
latitudinal profile of the correlation of density variations between
latitudes separated by 20 deg is similar to that of the subsurface
zonal variations of the Sun's differential rotation from the same time
period in 1996. From equator to pole, bands of high and low density
correlation appear to be associated with those of slower (retrograde)
and faster (prograde) rotation, respectively. We also show that polar
coronal holes are distinguished by non-recurring longitudinal structure,
as opposed to recurring structure in the neighboring quiet Sun, with
the standard deviation of the longitudinal variations of pB being half
of that of the quiet Sun. These distinct signatures of the longitudinal
structure of coronal density including their dependence on latitude are
also present in 1993-1994, and replicated in the Ulysses proton density
measurements of the distant solar wind during the same time, showing
that polar coronal holes extend radially into the solar wind. Since
polar coronal holes and the quiet Sun are associated with retrograde
rotation, and the polar coronal hole boundary with prograde rotation,
the manifestation of these coronal features in the solar wind also
reflect the association of the solar wind with the dynamics of the
solar interior.
Title: Proton/alpha magnetosonic instability in the fast solar wind
Authors: Li, Xing; Habbal, Shadia Rifai
Bibcode: 2000JGR...105.7483L
Altcode:
A proton/alpha magnetosonic instability is investigated in the
framework of the linear theory of plasma waves for conditions
typical of the fast solar wind. Warm streaming alpha particles with
a differential speed, the speed relative to the major ions/protons,
vα, close to the Alfvén speed, are found to significantly
enhance a magnetosonic instability when their temperature anisotropy
Γi=Ti⊥/Ti∥ is less than 1. Here
Ti∥ and Ti⊥ denote the velocity distribution
parallel and perpendicular to the magnetic field. The possible role of
the instability in limiting the relative speed between alpha particles
and protons in the fast solar wind is discussed.
Title: A four-fluid turbulence-driven solar wind model for
preferential acceleration and heating of heavy ions
Authors: Hu, You Qiu; Esser, Ruth; Habbal, Shadia R.
Bibcode: 2000JGR...105.5093H
Altcode:
We present for the first time a one-dimensional, four-fluid
turbulence-driven solar wind model in order to investigate the
preferential acceleration and heating of heavy ions by the resonant
cyclotron interaction with parallel-propagating left-hand-polarized ion
cyclotron waves. The model contains four species: electrons, protons,
alpha particles, and one species of minor ions. A Kolmogorov type of
cascade effect is introduced to transfer energy from the low-frequency
Alfvén waves to the high-frequency ion cyclotron waves, which are
assumed to be entirely dissipated by the wave-particle interaction. The
quasi-linear theory of the wave-particle interaction is invoked to
distribute the dissipated wave energy among the three ion species based
on a given power law spectrum of the ion cyclotron waves and the cold
plasma dispersion relation. It is found that in terms of the cold plasma
dispersion relation, the dispersion generated by all ion species has an
appreciable influence on both the behavior of the major species and the
preferential acceleration and heating of the minor ions. The larger the
number of species included in the dispersion relation is, the stronger
preferential acceleration and heating produced by the waves for the
heavy ions close to the Sun will be. A detailed comparison is carried
out between two cases, one with and the other without the dispersive
effect of the minor ions. Although the solutions for the two cases
are somewhat different, they predict a more or less similar behavior
of the minor ions, which essentially agrees with recent observations
from SOHO. This indicates that the resonant cyclotron interaction may
be responsible for the preferential acceleration and heating of minor
ions in the fast solar wind. Furthermore, the influence of minor ions on
the proton-alpha solar wind is found to be dominated by the dispersive
effect of the minor ions. Even though such an influence is exaggerated
by the cold plasma dispersion relation, it is still small and remains
within the present observational uncertainties. Therefore minor ions
may be treated approximately as test particles in the solar wind.
Title: Commission 49: Interplanetary Plasma and Heliosphere:
(Plasma Interplanetaire et Heliosphere)
Authors: Verheest, F.; Vandas, M.; Buti, B.; Cramer, N. F.; Dryer, M.;
Habbal, S. R.; Hollweg, J. V.; Huber, M. C. E.; Kojima, M.; Ripken, H.
Bibcode: 2000IAUTA..24...77V
Altcode:
No abstract at ADS
Title: Here Comes Solar Probe!
Authors: Möbius, E.; Gloeckler, G.; Goldstein, B.; Habbal, S.;
McNutt, R.; Randolph, J.; Title, A.; Tsurutani, B.
Bibcode: 2000AdSpR..25.1961M
Altcode:
Despite recent advances, fundamental questions remain about the nature
of the solar corona and the solar wind: 1) What heats the corona and
accelerates the solar wind? 2) Where do the different types of solar
wind originate? 3) Where and how are energetic particles produced and
transported near the Sun? 4) What role do plasma turbulence and waves
play in the corona and solar wind production? 5) What is the nature
of the magnetic field and photospheric structures near the solar
poles? Flying a trajectory perpendicular to the Earth-Sun line during
its perihelion passage, Solar Probe will use in-situ and imaging
instruments to provide the first three dimensional viewing of the
corona, direct observations of solar polar regions, and local sampling
of the solar environment. These primary observations are complemented
by context-setting measurements and Earth-based observations. Solar
Probe is currently scheduled for launch in February 2007 as the third
in the new Outer Planets/Solar Probe mission line of NASA and will
arrive at the Sun in 2010 under solar maximum conditions with a second
closest approach near solar minimum in 2015
Title: Ion cyclotron waves, instabilities and solar wind heating
Authors: Li, Xing; Habbal, Shadia R.
Bibcode: 1999SoPh..190..485L
Altcode:
The effect of alpha particles on the dispersion relation of ion
cyclotron waves and its influence on the heating of the solar
wind plasma are investigated. The presence of alpha particles can
dramatically change the dispersion relation of ion cyclotron waves,
and significantly influence the way that ion cyclotron waves heat
the solar wind plasma. We find that a spectrum of ion cyclotron waves
affects the thermal anisotropy of the solar wind protons and other ions
differently in interplanetary space: When alpha particles have a speed
uα>0.5vA, and both protons and alpha particles
have a thermal anisotropy T⊥/T∥>1, ion
cyclotron waves heat protons in the direction perpendicular to the
magnetic field, cool them in the parallel direction, and exert the
opposite effect on alpha particles.
Title: On the cascade process of Alfvén waves in the fast solar wind
Authors: Hu, You Qiu; Habbal, Shadia Rifai; Li, Xing
Bibcode: 1999JGR...10424819H
Altcode:
We present a numerical study which explores the nonlinear cascade
effect associated with Alfvén waves in the fast solar wind. The set
of one-dimensional, two-fluid equations describing the solar wind
and a power spectrum equation for Alfvén waves, as first proposed
by Tu et al. [1984], are solved simultaneously in a self-consistent
manner. Both Kolmogorov and Kraichnan cascade functions, which vary
as f5/2P3/2 and f3P2,
respectively, and considered. For an Alfvén wave spectrum at the
coronal base, which is flat in the low-frequency range and has a
slope of -1 in the high-frequency range, the Kolmogorov cascade
function reproduces the Alfvén wave spectrum observed beyond 0.29
AU very well. The Kraichnan cascade function, on the other hand,
yields a spectrum that is within the 90% confidence level of the
observed values. Both cascade functions yield a gradually accelerating
fast solar wind in the inner corona, typical of wave acceleration
models. The results of this first solar wind model which describes,
in a self-consistent manner, the evolution of the wave spectrum and
cascade in the inner corona confirm conclusions reached by earlier
studies, namely, that the Kolmogorov process produces a stronger
cascade effect than the Kraichnan process and seems more relevant for
Alfvén waves in the fast solar wind, at least beyond 0.29 AU. The
approach shows that Alfvén waves with periods of hours or shorter,
undergo an appreciable evolution from the solar surface to 1 AU, thus
implying that their spectrum; hence their total energy flux at the Sun
cannot be readily predicted from that observed in interplanetary space.
Title: Resonant acceleration and heating of solar wind ions by
dispersive ion cyclotron waves
Authors: Hu, You Qiu; Habbal, Shadia Rifai
Bibcode: 1999JGR...10417045H
Altcode: 1999JGR...10417045Q
We investigate the preferential acceleration and heating of solar
wind alpha particles by the resonant cyclotron interaction with
parallel-propagating left-hand-polarized ion cyclotron waves. The
Alfvén wave spectrum equation is generalized to multi-ion plasmas and
a Kolmogorov type of cascade effect is introduced to transfer energy
from the low-frequency Alfvén waves to the high-frequency ion cyclotron
waves, which are assumed to be entirely dissipated by the wave-particle
interaction. In order to distribute the dissipated wave energy among
the alphas and protons, the quasi-linear theory of the wave-particle
interaction is used along with the cold plasma dispersion relation,
and a power law spectrum of the ion cyclotron waves is assumed, with the
spectral index as a free parameter of the model. The set of three-fluid
solar wind equations and the Alfvén wave spectrum equation are then
solved in order to find fast solar wind solutions. It is found that
the effect of the alpha particles on the dispersion relation, omitted
in most previous wave-driven solar wind models, has a significant
influence on the preferential acceleration and heating of the alphas,
especially in the region close to the Sun. With this effect included,
the alpha particles can be accelerated to a bulk flow speed faster
than the protons by a few hundred kilometers per second and heated
by the resonant cyclotron interaction to more than mass-proportional
temperature values at several solar radii. However, this mechanism
does not yield a differential speed of the order of an Alfvén speed
and a mass-proportional temperature for the alphas beyond 0.3 AU,
as observed, which confirms the same conclusion reached previously by
Isenberg and Hollweg [1983] for nondispersive ion cyclotron waves.
Title: Radial evolution of density structure in the solar corona
Authors: Woo, Richard; Habbal, Shadia Rifai
Bibcode: 1999GeoRL..26.1793W
Altcode:
White-light measurements made by the SOHO coronagraphs (LASCO for
Large Angle Spectrometric Coronagraph) and the HAO Mauna Loa Mk III
K-coronameter are combined to follow the evolution of path-integrated
density structure in the solar corona overlying both coronal hole and
quiet Sun regions from 1.15 to 5.5 Ro. The global imaging
provided by these two instruments confirms and strengthens earlier
results discovered by spacecraft radio ranging measurements [Woo and
Habbal, 1999], that the imprint of density structure at the Sun —
as manifested in the background latitudinal density profile closest
to the Sun at 1.15 Ro — is carried essentially radially
into interplanetary space with the same density gradient. The only
exceptions are coronal streamers that evolve into the heliospheric
current sheet within a few solar radii of the Sun.
Title: Comparison of Fe λ5303, λ6374 and λ7892 spectral line
observations in a coronal hole and streamer
Authors: Wood, Christine H.; Habbal, Shadia R.; Esser, Ruth; Penn,
Matthew
Bibcode: 1999AIPC..471..293W
Altcode: 1999sowi.conf..293W
We present intensity and line width measurements of the Fe X λ6374,
Fe XI λ7892 and Fe XIV λ5303 lines between 1.03 and 1.4 Rs
in a coronal hole and a streamer. The observations were made at the
National Solar Observatory at Sacramento Peak on 26 February 1998. In
the coronal hole, only the Fe X line was observed; an upper limit
of 106 K for the electron temperature and 28 km/s for the
amplitude of nonthermal motions was inferred from the Fe X measurements
at 1.06 Rs. While all three lines were observed in the
streamer, the unique result was that the width of the Fe XI line
increased with heliocentric distance as opposed to a decrease in the
Fe X and Fe XIV line widths. We interpret this as evidence for the
existence of multitemperature static plasmas, and a solar wind outflow
at the streamer base.
Title: Magnetic energy avalanche as the source of the fast wind
Authors: Ryutova, M. P.; Habbal, S. R.; Woo, R.; Tarbell, T.
Bibcode: 1999AIPC..471..227R
Altcode: 1999sowi.conf..227R
We propose a mechanism for the formation of a magnetic energy avalanche
based on highly dynamic phenomena within the ubiquitous small scale
network magnetic elements in the quiet photosphere. We suggest that
this mechanism may provide constant mass and energy supply for the
origin of the fast wind.
Title: A new view of the origin of the solar wind
Authors: Woo, Richard; Habbal, Shadia Rifai
Bibcode: 1999AIPC..471...71W
Altcode: 1999sowi.conf...71W
This paper uses white-light measurements made by the SOHO LASCO
coronagraph and HAO Mauna Loa Mk III K-coronameter to illustrate
the new view of solar wind structure deduced originally from radio
occultation measurements. It is shown that the density profile
closest to the Sun at 1.15 Ro, representing the imprint of the
Sun, is carried essentially radially into interplanetary space by
small-scale raylike structures that permeate the solar corona and
which have only been observed by radio occultation measurements. The
only exception is the small volume of interplanetary space occupied
by the heliospheric plasma sheet that evolves from coronal streamers
within a few solar radii of the Sun. The radial preservation of the
density profile also implies that a significant fraction of field
lines which extend into interplanetary space originate from the quiet
Sun, and are indistinguishable in character from those emanating from
polar coronal holes. The white-light measurements dispel the long-held
belief that the boundaries of polar coronal holes diverge significantly,
and further support the view originally proposed in (1) that the fast
solar wind originates from the quiet Sun as well as polar coronal holes.
Title: Proton temperature anisotropy in the fast solar wind:
Turbulence-driven dispersive ion cyclotron waves
Authors: Li, Xing; Habbal, Shadia R.; Hollweg, Joseph V.; Esser, Ruth
Bibcode: 1999AIPC..471..531L
Altcode: 1999sowi.conf..531L
The effects of parallel propagating ion cyclotron waves on the solar
wind plasma are investigated in an attempt to reproduce the observed
proton temperature anisotropy. The model calculations presented
here assume that a nonlinear cascade process, at the Kolmogorov rate,
transports energy from low-frequency Alfvén waves to the ion cyclotron
resonant range. The energy is then picked up by the plasma through the
resonant cyclotron interaction. Ion cyclotron waves are found to play
an important role in shaping the proton temperature anisotropy starting
in the inner corona and extending to interplanetary space. Dispersive
ion cyclotron waves are able to cool protons more significantly than
nondispersive ones.
Title: Coronal plumes and the expansion of pressure-balanced
structures in the fast solar wind
Authors: Casalbuoni, Sara; Del Zanna, Luca; Habbal, Shadia R.;
Velli, Marco
Bibcode: 1999JGR...104.9947C
Altcode:
The expansion of a coronal hole filled with a discrete number of
higher-density filaments (plumes) in overall pressure balance with the
ambient medium is described within the thin flux tube approximation. The
resulting solar wind model extends the results of Parker [1964]
and Velli et al. [1994] to nonisothermal temperature profiles and
includes a flux of Alfvén waves propagating both inside and outside
the structures. Remote sensing and solar wind in situ observations
are used to constrain the parameter range of our study. Close to the
Sun, the precise plasma parameters are fundamental in determining the
relative position of the critical points, which are found by means
of an iterative procedure because the flows from the two regions are
coupled. At greater distances the filling factor of the higher-density
regions may vary largely, and streams which are either faster or
slower than the wind arising from the ambient hole may result,
depending on the temperature differences and on the flux of Alfvén
waves assumed in the two regions. Velocity differences of the order
of ~50 kms-1, such as those found in microstreams in the
high-speed solar wind, might be thus easily explained by reasonable
fluctuation amplitudes at the Sun, although the natural candidates
for plumes at large heliocentric distances are more likely to be the
so-called pressure-balanced structures.
Title: Coronal Hole Myth
Authors: Woo, R.; Habbal, S. R.
Bibcode: 1999AAS...194.3201W
Altcode: 1999BAAS...31..870W
White-light measurements made by the SOHO LASCO (Large Angle
Spectrometric Coronagraph) coronagraph and HAO Mauna Loa Mk III
K-coronameter are used to follow path-integrated density structure
in the solar corona as it evolves from 1.15 to 5.5 Ro. Global imaging
confirms and strengthens earlier results from spacecraft radio ranging
measurements [Woo and Habbal, ApJ, 510, L69, 1999], that the imprint
of density structure at the Sun -- as manifested in the background
azimuthal density profile closest to the Sun at 1.15 Ro -- is carried
essentially radially into interplanetary space. The only exception
is the relatively small volume of interplanetary space occupied by
the heliospheric current sheet that evolves from coronal streamers
within a few solar radii of the Sun. These measurements dispel the
long-held belief that the boundaries of polar coronal holes diverge
significantly. They also imply that a significant fraction of field
lines which extend into interplanetary space originate from the quiet
Sun, and are indistinguishable in character from those emanating from
polar coronal holes. These results further support the view originally
proposed by Woo and Habbal [GRL, 24, 1159, 1997] that the fast solar
wind originates from the quiet Sun as well as polar coronal holes. This
paper describes research carried out at JPL/Caltech under a contract
with NASA. Support for S.R. Habbal was provided by NASA grant NAG5-6215.
Title: Relationship between Mass Flux and Coronal Density in the
Fast Solar Wind
Authors: Habbal, S. R.; Woo, R.; Li, X.
Bibcode: 1999AAS...194.3202H
Altcode: 1999BAAS...31..870H
The solar wind mass flux, inferred from in situ measurements of the
density and flow speed, is one of the conserved quantities that provides
an inevitable constraint for solar wind models. In situ measurements
have consistently shown that the mass flux in the fast solar wind
does not vary by more than a factor of two. Typical values range from
1.5 x 10(8) cm(-3) to 3 10(8) cm(-3) for wind speeds at or above 700
km/s. While the density measured in situ can vary by approximately a
factor of two, the flow speed does not vary by more than 10 to 20%
in the fast streams. We show in this paper that the variations in
the mass flux in the fast solar wind are directly related to changes
in the density at the Sun. This finding provides further support for
the view recently proposed by Woo and Habbal that the coronal density
extends almost radially outwards from the Sun, that this extension
is reflected in in situ measurements, and that the quiet Sun is also
a source of the fast solar wind in addition to coronal holes. This
work is supported in part by NASA grant NAG5-6215 to the Smithsonian
Astrophysical Observatory.
Title: Extension of the Polar Coronal Hole Boundary into
Interplanetary space
Authors: Woo, Richard; Habbal, Shadia Rifai; Howard, Russell A.;
Korendyke, Clarence M.
Bibcode: 1999ApJ...513..961W
Altcode:
White-light measurements made by the SOHO LASCO C2 and C3 coronagraphs
and the Mk III Mauna Loa K-coronameter, ranging from 1.15 to 30
Rsolar, have been combined with Kitt Peak daily He I
1083 nm coronal hole maps, and full Sun Yohkoh soft X-ray images,
to show that the boundaries of polar coronal holes, as determined
by measurements of path-integrated density, extend approximately
radially into interplanetary space. These results are in contrast to
the long-standing view that the boundaries of polar coronal holes
diverge significantly beyond radial, evolving around the edges of
streamers. The combined observations also show that the corona is
dominated by raylike structures as small as a few degrees in angular
size with respect to Sun center, originating from both coronal holes
and the quiet Sun. This analysis provides further support for results
originally derived from radio occultation measurements, namely, that
the coronal density projects itself almost radially from the Sun into
the outer corona, implying that open field lines abound in the quiet
Sun from which the fast wind can alsooriginate.
Title: Heating and cooling of protons by turbulence-driven ion
cyclotron waves in the fast solar wind
Authors: Li, Xing; Habbal, Shadia R.; Hollweg, Joseph V.; Esser, Ruth
Bibcode: 1999JGR...104.2521L
Altcode:
The effects of parallel propagating nondispersive ion cyclotron
waves on the solar wind plasma are investigated in an attempt
to reproduce the observed proton temperature anisotropy, namely,
Tp⊥>>Tp∥ in the inner corona and
Tp⊥<Tp∥ at 1 AU. Low-frequency Alfvén
waves are assumed to carry most of the energy needed to accelerate and
heat the fast solar wind. The model calculations presented here assume
that nonlinear cascade processes, at the Kolmogorov and Kraichnan
dissipation rates, transport energy from low-frequency Alfvén waves
to the ion cyclotron resonant range. The energy is then picked up
by the plasma through the resonant cyclotron interaction. While
the resonant interaction determines how the heat is distributed
between the parallel and perpendicular degrees of freedom, the level
of turbulence determines the net dissipation. Ion cyclotron waves
are found to produce a significant temperature anisotropy starting
in the inner corona, and to limit the growth of the temperature
anisotropy in interplanetary space. In addition, this mechanism heats
or cools protons in the direction parallel to the magnetic field. While
cooling in the parallel direction is dominant, heating in the parallel
direction occurs when Tp⊥>>Tp∥. The
waves provide the mechanism for the extraction of energy from the
parallel direction to feed into the perpendicular direction. In
our models, both Kolmogorov and Kraichnan dissipation rates yield
Tp⊥>>Tp∥ in the corona, in agreement
with inferences from recent ultraviolet coronal measurements, and
predict temperatures at 1 AU which match in situ observations. The
models also reproduce the inferred rapid acceleration of the fast
solar wind in the inner corona and flow speeds and particle fluxes
measured at 1 AU. Since this mechanism does not provide direct energy
to the electrons, and the electron-proton coupling is not sufficient
to heat the electrons to temperatures at or above 106K,
this model yields electron temperatures which are much cooler than
those currently inferred from observations.
Title: An Empirical Model of a Polar Coronal Hole at Solar Minimum
Authors: Cranmer, S. R.; Kohl, J. L.; Noci, G.; Antonucci, E.;
Tondello, G.; Huber, M. C. E.; Strachan, L.; Panasyuk, A. V.;
Gardner, L. D.; Romoli, M.; Fineschi, S.; Dobrzycka, D.; Raymond,
J. C.; Nicolosi, P.; Siegmund, O. H. W.; Spadaro, D.; Benna, C.;
Ciaravella, A.; Giordano, S.; Habbal, S. R.; Karovska, M.; Li, X.;
Martin, R.; Michels, J. G.; Modigliani, A.; Naletto, G.; O'Neal,
R. H.; Pernechele, C.; Poletto, G.; Smith, P. L.; Suleiman, R. M.
Bibcode: 1999ApJ...511..481C
Altcode:
We present a comprehensive and self-consistent empirical model
for several plasma parameters in the extended solar corona above
a polar coronal hole. The model is derived from observations
with the SOHO Ultraviolet Coronagraph Spectrometer (UVCS/SOHO)
during the period between 1996 November and 1997 April. We compare
observations of H I Lyα and O VI λλ1032, 1037 emission lines
with detailed three-dimensional models of the plasma parameters and
iterate for optimal consistency between measured and synthesized
observable quantities. Empirical constraints are obtained for
the radial and latitudinal distribution of density for electrons,
H0, and O5+, as well as the outflow velocity
and unresolved anisotropic most probable speeds for H0 and
O5+. The electron density measured by UVCS/SOHO is consistent
with previous solar minimum determinations of the white-light coronal
structure; we also perform a statistical analysis of the distribution
of polar plumes using a long time series. From the emission lines we
find that the unexpectedly large line widths of H0 atoms
and O5+ ions at most heights are the result of anisotropic
velocity distributions. These distributions are not consistent with
purely thermal motions or the expected motions from a combination of
thermal and transverse wave velocities. Above 2 Rsolar,
the observed transverse most probable speeds for O5+ are
significantly larger than the corresponding motions for H0,
and the outflow velocities of O5+ are also significantly
larger than the corresponding velocities of H0. Also, the
latitudinal dependence of intensity constrains the geometry of the
wind velocity vectors, and superradial expansion is more consistent
with observations than radial flow. We discuss the constraints and
implications on various theoretical models of coronal heating and
acceleration.
Title: Plasma Properties in Coronal Holes Derived from Measurements
of Minor Ion Spectral Lines and Polarized White Light Intensity
Authors: Esser, Ruth; Fineschi, Silvano; Dobrzycka, Danuta; Habbal,
Shadia R.; Edgar, Richard J.; Raymond, John C.; Kohl, John L.;
Guhathakurta, Madhulika
Bibcode: 1999ApJ...510L..63E
Altcode:
Recent observations of the Lyα λ1216, Mg X λ625, and O VI λ1038
spectral lines carried out with the Ultraviolet Coronagraph Spectrometer
(UVCS) on board SOHO at distances in the range 1.35-2.1 RS in
the northern coronal hole are used to place limits on the turbulent wave
motions of the background plasma and the thermal motions of the protons
and Mg+9 and O+5 ions. Limits on the turbulent
wave motion are estimated from the measured line widths and electron
densities derived from white light coronagraph observations, assuming
WKB approximation at radial distances covered by the observations. It
is shown that the contribution of the turbulent wave motion to the
widths of the measured spectral lines is small compared to thermal
broadening. The observations show that the proton temperature slowly
increases between 1.35 and 2.7 RS and does not exceed
3×106 K in that region. The temperature of the minor ions
exceeds the proton temperature at all distances, but the temperatures
are neither mass proportional nor mass-to -charge proportional. It is
shown, for the first time, that collision times between protons and
minor ions are small compared to the solar wind expansion times in
the inner corona. At 1.35 RS the expansion time exceeds
the proton Mg+9 collision time by more than an order of
magnitude. Nevertheless, the temperature of the Mg ions is significantly
larger than the proton temperature, which indicates that the heating
mechanism has to act on timescales faster than minutes. When the
expansion time starts to exceed the collision times a rapid increase
of the O+5 ion spectral line width is seen. This indicates
that the heavier and hotter ions lose energy to the protons as long as
collision frequencies are high, and that the ion spectral line width
increases rapidly as soon as this energy loss stops.
Title: Imprint of the Sun on the Solar Wind
Authors: Woo, Richard; Habbal, Shadia Rifai
Bibcode: 1999ApJ...510L..69W
Altcode:
Observations of the inner corona in polarized brightness by the Mauna
Loa Mk III K-coronameter at 1.15 Rsolar and soft X-rays
by Yohkoh at 1.03 Rsolar are combined with 1995 Ulysses
radio occultation measurements of the solar wind to demonstrate that
the signatures of the coronal hole boundary, active regions, and
bright points are present in the heliocentric distance range of 20-30
Rsolar. The existence of these signatures in the brightness
of the corona (observed by ranging measurements) and the contrast of
the small-scale raylike structures comprising the corona (observed by
Doppler scintillation measurements) at such distances can readily be
accounted for by open field lines rooted within the complex magnetic
structures of the quiet Sun, active regions, and bright points. Hence,
with the exception of the small volume of interplanetary space occupied
by the heliospheric current sheet that evolves from coronal streamers
within a few solar radii of the Sun, small-scale raylike structures
carry the imprint of the different density structures of the solar
disk approximately radially into the heliosphere.
Title: Solar Wind Nine
Authors: Habbal, Shadia Rifai; Esser, Ruth; Hollweg, Joseph V.;
Isenberg, Philip A.
Bibcode: 1999AIPC..471.....H
Altcode: 1999sowi.conf.....H
No abstract at ADS
Title: A New View of the Origin of the Solar Wind
Authors: Woo, Richard; Habbal, Shadia Rifai
Bibcode: 1999STIN...0055758W
Altcode:
This paper uses white-light measurements made by the SOHO LASCO
coronagraph and HAO Mauna Loa Mk III K-coronameter to illustrate
the new view of solar wind structure deduced originally from radio
occultation measurements. It is shown that the density profile
closest to the Sun at 1.15 Ro, representing the imprint of the
Sun, is carried essentially radially into interplanetary space by
small-scale raylike structures that permeate the solar corona and
which have only been observed by radio occultation measurements. The
only exception is the small volume of interplanetary space occupied
by the heliospheric plasma sheet that evolves from coronal streamers
within a few solar radii of the Sun. The radial preservation of the
density profile also implies that a significant fraction of field lines
which extend into interplanetary space originate from the quiet Sun,
and are indistinguishable in character from those emanating from polar
coronal holes. The white-light measurements dispel the long-held belief
that the boundaries of polar coronal holes diverge significantly,
and further support the view originally proposed that the fast solar
wind originates from the quiet Sun as well as polar coronal holes.
Title: The Effect of Temperature Anisotropy on Observations of
Doppler Dimming and Pumping in the Inner Corona
Authors: Li, Xing; Habbal, Shadia Rifai; Kohl, John L.; Noci, Giancarlo
Bibcode: 1998ApJ...501L.133L
Altcode: 1998astro.ph..5021L
Recent observations of the spectral line profiles and intensity ratio
of the O VI λλ1032 and 1037.6 doublet by the Ultraviolet Coronagraph
Spectrometer (UVCS) on the Solar and Heliospheric Observatory (SOHO),
made in coronal holes below 3.5 RS, provide evidence
for Doppler dimming of the O VI λ1037.6 line and pumping by the
chromospheric C II λ1037.0182 line. Evidence for a significant kinetic
temperature anisotropy of O5+ ions was also derived from
these observations. We show in this Letter how the component of the
kinetic temperature in the direction perpendicular to the magnetic
field, for both isotropic and anisotropic temperature distributions,
affects both the amount of Doppler dimming and pumping. Taking this
component into account, we further show that the observation of the O
VI doublet intensity ratio less than unity can be accounted for only
if pumping by C II λ1036.3367 in addition to C II λ1037.0182 is in
effect. The inclusion of the C II λ1036.3367 pumping implies that the
speed of the O5+ ions can reach 400 km s-1 around
3 RS, which is significantly higher than the reported UVCS
values for atomic hydrogen in polar coronal holes. These results imply
that oxygen ions flow much faster than protons at that heliocentric
distance.
Title: UVCS/SOHO Empirical Determinations of Anisotropic Velocity
Distributions in the Solar Corona
Authors: Kohl, J. L.; Noci, G.; Antonucci, E.; Tondello, G.; Huber,
M. C. E.; Cranmer, S. R.; Strachan, L.; Panasyuk, A. V.; Gardner,
L. D.; Romoli, M.; Fineschi, S.; Dobrzycka, D.; Raymond, J. C.;
Nicolosi, P.; Siegmund, O. H. W.; Spadaro, D.; Benna, C.; Ciaravella,
A.; Giordano, S.; Habbal, S. R.; Karovska, M.; Li, X.; Martin, R.;
Michels, J. G.; Modigliani, A.; Naletto, G.; O'Neal, R. H.; Pernechele,
C.; Poletto, G.; Smith, P. L.; Suleiman, R. M.
Bibcode: 1998ApJ...501L.127K
Altcode:
We present a self-consistent empirical model for several plasma
parameters of a polar coronal hole near solar minimum, derived from
observations with the Solar and Heliospheric Observatory Ultraviolet
Coronagraph Spectrometer. The model describes the radial distribution of
density for electrons, H0, and O5+ and the outflow
velocity and unresolved most probable velocities for H0
and O5+ during the period between 1996 November and 1997
April. In this Letter, we compare observations of H I Lyα and O
VI λλ1032, 1037 emission lines with spatial models of the plasma
parameters, and we iterate for optimal consistency between measured and
synthesized observable quantities. The unexpectedly large line widths
of H0 atoms and O5+ ions at most radii are the
result of anisotropic velocity distributions, which are not consistent
with purely thermal motions or the expected motions from a combination
of thermal and transverse wave velocities. Above 2 Rsolar,
the observed transverse, most probable speeds for O5+ are
significantly larger than the corresponding motions for H0,
and the outflow velocities of O5+ are also significantly
larger than the corresponding velocities of H0. We discuss
the constraints and implications on various theoretical models of
coronal heating and acceleration.
Title: Comment on: “Polar plumes and fine-scale coronal structures
— On the interpretation of coronal radio sounding data” by
Pätzold and Bird
Authors: Woo, Richard; Habbal, Shadia Rifai
Bibcode: 1998GeoRL..25.1849W
Altcode:
No abstract at ADS
Title: Thermal coupling of protons and neutral hydrogen in the fast
solar wind
Authors: Allen, Lorraine A.; Habbal, Shadia R.; Hu, You Q.
Bibcode: 1998JGR...103.6551A
Altcode:
We investigate the coupling between neutral hydrogen atoms and protons
in the corona for a range of proton temperatures reaching a maximum
of 6×106K, as recently inferred from observations of
the Ly α spectral line profiles by Kohl et al. [1996]. We adopt the
approach used by Olsen et al. [1994], whereby the neutral hydrogen
atoms are treated as test particles in a background electron-proton
solar wind. Charge exchange between neutrals and protons, radiative
recombination, collisional ionization of the neutrals, and the effects
of Alfvén waves, described by a single frequency or a spectrum, are
included in the model. The computations show that an anisotropy in
the neutral hydrogen temperature develops in the directions parallel
and perpendicular to the magnetic field within 2-3 RS
for solar wind conditions, consistent with observational constraints
of the fast wind. Although TH⊥ exceeds
TH∥ (~Tp) in the inner corona, the
anisotropy decreases as the peak proton temperature increases, with
a temperature difference of <8×105K when the protons
reach 6×106K. We find that the effective temperature
TH(eff)⊥, incorporating both random and
wave motions of the neutral hydrogen, and the calculated Ly α line
profile are independent of wave frequency. The dominant contribution
to the profiles comes from TH(eff)⊥ at the
point of closest approach to the Sun along the line of sight (LOS),
although the widths of the profiles are significantly narrowed by
non-90° scattering along the LOS, broadened by outflow velocity,
and narrowed or broadened by steep temperature gradients along the
LOS. The proton and neutral hydrogen effective temperatures and
velocities are comparable below ~3 RS, thus implying
that the measured Ly α profiles are equivalent to measurements
of the velocity distribution of protons in that region. Beyond ~3
RS, however, TH(eff)⊥ is found to
be significantly lower than Tp(eff), and the measurement
of TH(eff)⊥ provides a lower limit for
Tp(eff) there.
Title: Cor-I: a coronal white-light imager for a solar probe
Authors: Vial, J. -C.; Koutchmy, S.; Habbal, S. R.
Bibcode: 1998AdSpR..21..291V
Altcode:
Solar and heliospheric observations acquired over several decades,
have shown that the corona is a highly structured medium. There is
no doubt that these structures reflect the response of the coronal
plasma - confined by the highly inhomogeneous magnetic field - to
different forms of energy input. While in-situ plasma measurements
have provided the characteristic properties of both fast and slow
solar winds, they have fallen short in connecting them to the source
regions of the wind. A near-Sun flyby mission offers an unprecedented
opportunity to explore the solar wind at distances much closer to
the Sun than ever achieved before. However, it is essential that
in-situ measurements be coordinated with simultaneous imaging of
the structures encountered in the corona. We present the concept and
design of a white-light imager called Cor-I, as a key instrument for a
near-Sun flyby mission which makes it possible to distinguish spatial
structures from temporal changes in the plasma parameters. With the
inference of the electron density from the Thomson scattered emission,
white-light measurements are also a very powerful tool for quantitative
studies of the acceleration region of the solar wind. In addition, the
proposed instrument carries the potential for discovery of transient
events and waves in these parts of the acceleration region of fast and
slow solar winds that are inaccessible to in-situ plasma instruments.
Title: Multiscale filamentary structures in the solar corona and
their implications for the origin and evolution of the solar wind
Authors: Woo, R.; Habbal, S. Rifai
Bibcode: 1998PSP....15..351W
Altcode:
No abstract at ADS
Title: The Solar Probe Mission: A search for the Origin of the Solar
Wind and an Unprecedented View of the Solar Surface
Authors: Habbal, S. R.; Gloeckler, G.; McNutt, R. L., Jr.; Tsurutani,
B. T.
Bibcode: 1998ESASP.417...83H
Altcode: 1998cesh.conf...83H
No abstract at ADS
Title: Experimental constraints on pulsed and steady state models
of the solar wind near the Sun
Authors: Feldman, W. C.; Habbal, S. R.; Hoogeveen, G.; Wang, Y. -M.
Bibcode: 1997JGR...10226905F
Altcode:
Ulysses observations of the high-latitude solar wind were combined with
Spartan 201 observations of the corona to investigate the nature and
extent of uncertainties in our knowledge of solar wind structure near
the Sun. In addition to uncertainties stemming from the propagation of
errors in density profiles inferred from coronagraph observations [see,
e.g., Lallement et al., 1986], an assessment of the consequences of
choosing different analysis assumptions reveals very large, fundamental
uncertainties in our knowledge of even the basics of coronal structure
near the Sun. In the spirit of demonstrating the nature and extent
of these uncertainties we develop just one of a generic class of
explicitly time-dependent and filamentary models of the corona that is
consistent with the Ulysses and Spartan 201 data. This model provides a
natural explanation for the radial profiles of both the axial ratios
and apparent radial speeds of density irregularities measured at
radial distances less than 10RS using the interplanetary
scintillation technique.
Title: Electron Temperature Distribution in Coronal Holes
Authors: Halas, C. D.; Habbal, S. R.; Penn, M.; Uitenbroek, H.; Esser,
R.; Altrock, R.; Guhathakurta, M.
Bibcode: 1997AAS...191.7413H
Altcode: 1997BAAS...29Q1326H
Knowledge of the electron temperature within coronal holes is extremely
important for constructing solar wind models and for understanding
the coronal heating process. We report on the two-dimensional CCD
observations of the Fe IX 4585, Fe X 6374, Fe XI 7892 and Fe XIV 5303
{ Angstroms} emission lines made using a coronagraph at the National
Solar Observatory at Sacramento Peak. These iron lines, which have
a peak formation temperature of 5 10(5) , 10(6) , 1.2 10(6) , and 2
10(6) K, respectively, allow the examination of different temperature
plasmas within the same large scale magnetic structure. To account for
possible line of sight ambiguities from hot material in the foreground
or background of the coronal hole, Yohkoh data were used to determine
the extent of the coronal hole along the line of sight. Intensities and
widths of these spectral lines as a function of heliocentric distance
out to 1.15 R_s will be presented. A comparison will be made between
coronal hole and streamer observations.
Title: New Understanding of the Solar Wind: the Impact of ULYSSES
and SOHO Measurements
Authors: Habbal, S. R.
Bibcode: 1997AAS...19110102H
Altcode: 1997BAAS...29.1371H
Despite the complex interaction between magnetic fields and plasma,
the solar wind manages to escape into interplanetary space in two
remarkably well-defined states: the fast wind exceeding 700 km/s and
the slow wind coasting at 300 - 400 km/s. These two states are also
distinguished by their ion composition and temporal variability. An
unprecedented view of the solar wind phenomenon is emerging from in situ
and remote sensing observations. Local properties of the solar wind
plasma characteristics spanning the heliosphere beyond Earth's orbit
continue to be measured by Ulysses, while the source and acceleration
regions of the solar wind are being probed by the Solar and Heliospheric
Observatory (SOHO). Diagnostic tools made possible with the Ultraviolet
Coronagraph Spectrometer (UVCS) on SOHO are providing the most direct
witness of the physical processes defining the solar wind. This review
highlights the most outstanding facts and puzzles pertaining to the
physical characteristics and origin of the fast and slow solar wind to
emerge from the complement of in situ and remote sensing observations.
Title: Origins of the Slow and the Ubiquitous Fast Solar Wind
Authors: Habbal, S. R.; Woo, R.; Fineschi, S.; O'Neal, R.; Kohl, J.;
Noci, G.; Korendyke, C.
Bibcode: 1997ApJ...489L.103H
Altcode: 1997astro.ph..9021H
We present in this Letter the first coordinated radio occultation
measurements and ultraviolet observations of the inner corona below
5.5Rs, obtained during the Galileo solar conjunction in
1997 January, to establish the origin of the slow solar wind. Limits
on the flow speed are derived from the Doppler dimming of the
resonantly scattered component of the oxygen 1032 and 1037.6 Å
lines as measured with the ultraviolet coronagraph spectrometer
(UVCS) on the Solar and Heliospheric Observatory (SOHO). White light
images of the corona from the large-angle spectroscopic coronagraph
(LASCO) on SOHO taken simultaneously are used to place the Doppler
radio scintillation and ultraviolet measurements in the context of
coronal structures. These combined observations provide the first
direct confirmation of the view recently proposed by Woo & Martin
that the slow solar wind is associated with the axes, also known as
stalks, of streamers. Furthermore, the ultraviolet observations also
show how the fast solar wind is ubiquitous in the inner corona and
that a velocity shear between the fast and slow solar wind develops
along the streamer stalks.
Title: Influence of heavy ions on the high-speed solar wind
Authors: Li, Xing; Esser, Ruth; Habbal, Shadia R.; Hu, You-Qiu
Bibcode: 1997JGR...10217419L
Altcode:
We present the results of a parameter study of the influence of heavy
ions on the background solar wind, choosing doubly ionized helium, or
alpha particles, and O+6, as examples. Using a three-fluid
solar wind model, we keep the input parameters to the electrons and
protons unchanged and investigate the effects of changing the input
energy flux to the heavy ions and their coronal abundance, i.e.,
their abundance at 1 Rs, on the background electron-proton
solar wind. Our results confirm earlier studies that alpha particles
can have a dramatic effect on the thermodynamic and flow properties of
the protons in the solar wind. The maximum coronal abundance for which
the changes in the energy input to the heavy ions has no effect on the
protons is 5×10-4 for the alphas and 5×10-5
for the oxygen ions, which are well below the photospheric values. For
larger coronal abundances, the sensitivity of the changes of the
flow speed and proton mass flux to changes in the energy input to
the heavy ions increases sharply with increasing abundance. When the
heavy ions are not heated, the increase in the coronal abundance leads
to an increase in flow speed, a decrease in proton mass flux, and an
increase in proton temperature at 1 AU. However, as the heat input to
the heavy ions increases, the dependence of these parameters on the
abundance goes through a transition and starts to follow the opposite
pattern, namely a decrease in flow speed and proton temperature at
1 AU, and an increase in proton mass flux. This study shows that,
for currently known photospheric elemental abundances, the flow
properties of heavy ions cannot be investigated independently of those
of the bulk proton-electron solar wind. The effect of heavy ions on
the electron-proton bulk solar wind is determined primarily by the
collisions occurring very close to the coronal base. Hence including
physical processes responsible for the preferential heating of heavy
ions to temperatures exceeding those of protons in the inner corona
cannot be done without considering the subsequent implications for
the protons and electrons in a self-consistent manner.
Title: A fast solar wind model with anisotropic proton temperature
Authors: Hu, Y. Q.; Esser, R.; Habbal, S. R.
Bibcode: 1997JGR...10214661H
Altcode:
We explore the energy requirements for the fast solar wind when the
anisotropy in the proton temperature is taken into account. Using a
one-dimensional, two-fluid model with anisotropic proton temperature,
we present high-speed solar wind solutions which meet most of the
empirical constraints currently available from in situ measurements in
interplanetary space and very recent remote sensing observations of the
inner corona. Included in the model is the momentum exerted on the flow
by Alfvén waves, as well as heating due to their damping. However,
to produce solutions consistent with these empirical constraints,
additional heat input to both electrons and protons, as well as momentum
addition to the protons, are found to be needed. These are described
by ad hoc functions with adjustable parameters. While classical thermal
conduction is adopted for both electrons and protons in the inner corona
in the model computations, the corresponding heat fluxes in the outer
corona are limited to values comparable to current observations. The
fast solar wind solutions thus obtained differ from each other mainly
in their thermal properties within 0.3 AU from the Sun, a region that
is still poorly probed by in situ and remote sensing measurements. To
satisfy observational constraints, we find that the inclusion of a
proton temperature anisotropy in the modeling of the solar wind requires
that either the protons be highly anisotropic in the inner corona
or that there exist a mechanism, in addition to adiabatic expansion,
to cool them in the direction parallel to the magnetic field. Given
these observational constraints and in the absence of knowledge of
an efficient cooling mechanism, our model computations imply that
the maximum temperature of the protons in the parallel direction has
to be limited to 106K in the corona. Furthermore, because
of the strong coupling between electrons and protons, and between the
parallel and perpendicular motions, at the coronal base, the electron
temperature as well as the perpendicular proton temperature cannot be
much higher than 106K there. Although thermal anisotropy
of the protons is found to have little influence on the dynamics of
the fast solar wind, its inclusion imposes new requirements on the
unknown coronal heating mechanisms.
Title: Extension of coronal structure into interplanetary space
Authors: Woo, Richard; Habbal, Shadia Rifai
Bibcode: 1997GeoRL..24.1159W
Altcode:
We investigate the extension and evolution of the solar corona into
interplanetary space by comparing 1995 Ulysses radio occultation
measurements of path-integrated electron density and density
fluctuations measured between 21 and 32 Ro, with simultaneous
white-light measurements made by the HAO Mauna Loa K-coronameter below
2.5 Ro. The surprising picture of the extended corona to
emerge from this comparison is one in which stalks of streamers,
occupying a small fraction of volume in interplanetary space, are
superimposed on a background corona distinguished by a plethora of ray
like structures, often referred to as plumes in polar coronal holes. The
radial preservation of the boundary between polar coronal holes and the
base of streamers implies that the solar wind from polar coronal holes
expands radially rather than undergoing any significant divergence
as previously thought. Combining this picture of the extended corona
with in situ velocity measurements made by Ulysses throughout its two
polar passages, we conclude that the raylike structures, except for
the stalks of streamers, seem to be the source of the fast wind. The
existence of the fast wind at low latitudes can be attributed to these
raylike structures, rather than the expansion of the boundaries of
polar coronal holes to low latitudes.
Title: Model Computations of the Line Profiles of O VI 1032 and 1037
Angstroms in the Fast Solar Wind and Comparison with UVCS Observations
Authors: Li, X.; Habbal, S. R.; Esser, R.
Bibcode: 1997SPD....28.0123L
Altcode: 1997BAAS...29..883L
The profiles of the O VI 1032 and 1037 Angstroms spectral lines are
calculated for the fast solar wind. The computed theoretical line
profiles are based on high speed solar wind models where the O(+5)
ions are treated as test particles in a three-fluid (electrons,
protons and alphas) background solar wind flow. The background solar
wind model matches the observational constraints of particle flux,
flow speeds and temperatures at 1 AU, and the electron density
profiles in the inner corona. Line of sight effects are included
in the calculations of the line profile. Preferential heating is
applied to the oxygen ions to produce an ion temperature in the inner
corona around 2 x 10(8) K, as inferred from the UVCS observations on
SOHO, and a flow speed exceeding that of the protons beyond several
solar radii. Both resonantly scattered and collisionally excited
components of the oxygen 1032 and 1037 Angstroms lines are computed. We
find that for flow speeds below 100 km/s, the two components have
approximately the same width. However, once the speed exceeds 150
km/s, the collisionally excited component becomes much wider than the
resonantly scattered component. This effect can be explained by the
strong Doppler dimming of the resonantly scattered component as the
flow speed increases. Consequently, when the integration along the line
of sight is taken into account, ions traveling along trajectories away
from the plane of the sky will contribute to the the broadening of the
collisionally excited component and to the dimming of the resonantly
scattered component. The model computations thus suggest that the
broad oxygen line profiles observed by the UVCS instrument on SOHO
reflect the existence of very high oxygen flow speeds very close to
the coronal base, in addition to the high kinetic temperatures.
Title: Thermal Coupling of Protons and Neutral Hydrogen in the Fast
Solar Wind
Authors: Allen, L.; Habbal, S. R.
Bibcode: 1997SPD....28.0402A
Altcode: 1997BAAS...29..907A
Motivated by the recent Spartan and UVCS observations [Kohl et al. 1996]
of hot protons with temperatures exceeding 4 x 10(6) K below 3.5 R_s
in coronal holes, as inferred from the measured broadening of the
Lyman alpha spectral line profile, we studied the thermal coupling of
neutral hydrogen to protons in the presence of Alfven waves in the
solar wind. The approach used is adopted from Olsen et al. [1994]
in which the neutral hydrogen atoms are treated as test particles
in a background electron-proton solar wind. The model computations
show that an anisotropy in the neutral hydrogen temperature in the
directions parallel and perpendicular to the magnetic field develops in
the inner corona well below 5 R_s for background solar wind solutions
consistent with observational constraints of the high speed wind. In
particular, we find that the neutral hydrogen temperature parallel
to the magnetic field direction remains strongly coupled to the
proton temperature, T_p, while the perpendicular neutral hydrogen
temperature exceeds this by ~ 10(6) K for a wide range of proton flow
speeds, densities and temperatures for a spectrum of Alfven waves. The
neutral hydrogen effective temperature, T_{H(eff)}(perpendicular to
) , incorporating both random thermal motion and wave motion of the
particles, is found to be independent of frequency and significantly
less than the proton effective temperature, T_{p(eff)}, in the inner
corona. Thus, without additional information about the waves, which
would allow T_H(perpendicular to ) and T_p to be extracted from the
models, T_{H(eff)}(perpendicular to ) provides an upper limit on T_p
and a lower limit on T_{p(eff)}. However, with increasing proton
temperature, the anisotropy in the inner corona decreases, with a
temperature difference of < 8 x 10(5) K between the protons and
neutrals below 3 R_s when the latter reach 6 x 10(6) K.
Title: The Solar Probe Mission
Authors: Habbal, S. R.
Bibcode: 1997SPD....28.1104H
Altcode: 1997BAAS...29..915H
Designed for the first close encounter with the Sun, the Solar Probe
mission will fly a spacecraft, instrumented for both in-situ and remote
sensing measurements, exploring the distance of between 110 and 3 solar
radii above the Sun's surface. The Solar Probe will directly sample the
solar corona, one of the last unexplored regions of the solar system,
crossing over the polar coronal hole and reaching the equator in a
trajectory perpendicular to the ecliptic. This mission will provide
the first view of the Sun's polar regions, and the first close flyby of
a star. The Solar Probe will also provide the first three-dimensional
view of the corona with the same suite of instruments. The scientific
focus of the Solar Probe mission will be to unravel the mysteries of the
coronal heating processes and solar wind acceleration. Solar Probe's
in-situ instrumentation will provide the first direct measurements of
the plasma distribution function, energetic particle fluxes, magnetic
fields, and plasma waves in the solar corona. The remote-sensing
instruments will provide close-up views of the Sun not possible from
Earth orbit, resolving the smallest visible magnetic structures.
Title: Hot protons in the inner corona and their effect on the flow
properties of the solar wind
Authors: Esser, Ruth; Habbal, Shadia R.; Coles, William A.; Hollweg,
Joseph V.
Bibcode: 1997JGR...102.7063E
Altcode:
Following recent observations which indicate the
presence of extremely high flow speeds in the inner
corona, 700-800kms-1 below 10RS,
and the possible presence of very high proton temperatures,
3×106<=Tp<=8.5×106K,
we present a parameter study which shows that if the high proton
temperatures in the inner corona are genuine, then flow speeds of
700 to 800kms-1 can readily be achieved at 10S
or even closer to the coronal base. If one allows for both heat and
momentum deposition in the inner corona, the rapid acceleration close
to the coronal base can be achieved with proton temperatures well
below the upper limit placed by the observations.
Title: Imaging the source regions of the solar wind
Authors: Habbal, Shadia Rifai
Bibcode: 1997AIPC..385..105H
Altcode: 1997recs.conf..105H; 1997AIPC..385..105R
Remote sensing of the solar corona in the extreme ultraviolet and white
light is an indispensable tool for probing the source and acceleration
regions of the solar wind which are inaccessible to in situ plasma,
particles and fields experiments. Imaging the solar disk and corona
from the unique vantage point of the trajectory and the proximity of
the Solar Probe spacecraft will provide the first ever opportunity to
explore the small scale structures within coronal holes and streamers
from viewing angles and with spatial resolutions never attained
before. The extreme ultraviolet and white light wavelength ranges
offer a powerful tool for diagnostic studies of this region.
Title: Remote sensing measurements of the corona with the Solar Probe
Authors: Habbal, Shadia Rifai; Woo, Richard
Bibcode: 1997AIPC..385...77H
Altcode: 1997recs.conf...77H; 1997AIPC..385...77R
Remote sensing measurements of the solar corona are indispensable for
the exploration of the source and acceleration regions of the solar
wind which are inaccessible to in situ plasma, particles and fields
experiments. Furthermore, imaging the solar disk and corona from the
unique vantage point of the trajectory and the proximity of the Solar
Probe spacecraft, will provide the first ever opportunity to explore the
small scale structures within coronal holes and streamers from viewing
angles and with spatial resolutions never attained before. Imaging will
also provide the essential context for the in situ measurements. The
scientific advantages of different proposed imagers are summarized
here. Both disk and limb observations are recommended. Given the power,
weight and telemetry limitations of the Solar Probe, the optimal choice
of imagers could not be provided at the time of the workshop. Further
concentrated studies were highly recommended.
Title: Finest Filamentary Structures of the Corona in the Slow and
Fast Solar Wind
Authors: Woo, Richard; Habbal, Shadia Rifai
Bibcode: 1997ApJ...474L.139W
Altcode:
Recent progress in our understanding of electron density fluctuations
observed by radio occultation measurements has demonstrated that a
break in the vicinity of 1 Hz in the temporal frequency spectrum of
the density fluctuations provides a measure of the size of the finest
filamentary structures in the solar corona. Breaks in frequency
have been inferred from the density spectra deduced by Coles et
al. from 1979-1980 Voyager phase scintillation and spectral broadening
measurements. These results show that the finest filamentary structures
are found in the extensions or stalks of coronal streamers--the likely
sources of the slow solar wind--and are over a factor of 3 smaller
than those in the fast wind emanating from coronal holes. The inferred
sizes of the finest filamentary structures are approximately 6 km in
the slow wind at 8 Rsolar and 22 km in the fast wind at
9.1 Rsolar.
Title: Coronal Holes and the Solar Wind
Authors: Esser, R.; Habbal, S. R.
Bibcode: 1997cwh..conf..297E
Altcode: 2006mslp.conf..297E
No abstract at ADS
Title: Robotic Exploration Close to the Sun: Scientific Basis
Authors: Habbal, Shadia Rifai
Bibcode: 1997AIPC..385.....H
Altcode: 1997recs.conf.....H
No abstract at ADS
Title: Radio, visible, and X ray emission preceding and following
a coronal mass ejection
Authors: Habbal, Shadia R.; Mossman, Amy; Gonzalez, Raymond; Esser,
Ruth
Bibcode: 1996JGR...10119943H
Altcode:
This study uses both disk and limb observations to examine the changing
conditions of the low solar corona, below 1.5 Rs, preceding
and following a coronal mass ejection observed on the west limb on
April 12, 1993. The disk observations comprise 90 cm (333 MHz) radio
and daily Yohkoh soft X ray measurements, while the limb observations
include measurements of emission from X rays, Fe X 637.4 nm and Fe
XIV 530.3 nm coronal lines, and broadband Thomson-scattered white
light. The analysis of the disk and limb observations shows that
throughout the 3 days of consecutive observations, the occurrence
and persistence of nonthermal emission at 90 cm, also known as type
I noise storm emission, were associated with large-scale magnetic
structures where the coronal mass ejection eventually occurred. Other
than a subsequent flare observed in X rays at the limb, the changes
in the coronal emission preceding and following the event were not
markedly different from changes in other neighboring structures. The
analysis of this novel combination of data supports the current view
that coronal mass ejections are a cause rather than a consequence of the
``classical'' solar activity in the low corona. The radio observations,
on the other hand, suggest that a connection between a noise storm
and a coronal mass ejection exists. However, they do not necessarily
imply that the noise storm actually initiates the event.
Title: Solar Wind Eight
Authors: Winterhalter, D.; Gosling, J. T.; Habbal, S. R.; Kurth,
W. S.; Neugebauer, M.
Bibcode: 1996AIPC..382.....W
Altcode: 1996sowi.conf.....W
No abstract at ADS
Title: Flow properties of the solar wind obtained from white light
data, Ulysses observations and a two-fluid model
Authors: Habbal, Shadia Rifai; Esser, Ruth; Guhathakurta, Madhulika;
Fisher, Richard
Bibcode: 1996AIPC..382..129H
Altcode:
We derive the flow properties of the solar wind using a two-fluid
model constrained by the density gradients inferred from white
light observations of a south polar coronal hole on 11 April 1993
during the SPARTAN 201-1 flight, and interplanetary observations,
e.g. from Ulysses' south polar passage. We present the results of
model computations for which we get the best fit to these data. One
of the main results of this study is that, for the same energy input
to electrons and protons, the proton temperature can be significantly
higher than the electron temperature in the inner corona. In addition,
we show that different functional forms of the energy addition with
the same total energy input can yield different solar wind parameters
at 1AU.
Title: Demonstrating the limitations of line ratio temperature
diagnostic using Fe X and Fe XIV spectral line intensity observations
Authors: Esser, Ruth; Brickhouse, Nancy S.; Habbal, Shadia R.;
Mossman, Amy
Bibcode: 1996AIPC..382..173E
Altcode: 1996sowi.conf..173E
The electron temperature in the inner corona can be derived from
spectral line intensity measurements by comparing the ratio of the
measured intensities of two spectral lines to the ratio calculated from
theoretical models. In a homogeneous plasma the line ratio technique can
be used for any two lines if the ratio of the intensities is independent
of the density. The corona, however, is far from homogeneous and usually
several distinct structures are present along the line-of-sight. For
example, even the large polar coronal holes at solar minimum can
be partly or completely obscured by emission from hotter and denser
surrounding regions. In this case the structures that contribute to the
line intensity do not occupy the same volume if the peak temperature of
the spectral lines are too widely separated. We demonstrate this effect
for the southern polar coronal hole, using daily intensity measurements
of the Fe XIV 5303 Å and Fe X 6374 Å spectral lines from the National
Solar Observatory at Sacramento Peak (NSO/SP), X-ray emission from daily
YOHKOH observations, and polarization brightness measurements from the
HAO white light coronagraph at Mauna Loa Solar Observatory. We then show
that the temperature in the southern coronal hole derived from the ratio
of the two Fe spectral lines, varies by more than 0.8×106
K due to the changing contribution from surrounding regions.
Title: Modeling high flow speeds in the inner corona
Authors: Esser, Ruth; Habbal, Shadia Rifai
Bibcode: 1996AIPC..382..133E
Altcode: 1996sowi.conf..133E
Following recent observations which indicate the possibility
of extremely high flow speeds in the inner corona, 700-800 km
s-1 below 10 RS, and the possibility of very
high proton temperatures, Tp<=8.5×106 K,
we present a new approach to solar wind modeling. In this approach
we show that if the high proton temperatures in the inner corona are
genuine, then flow speeds of 700 to 800 km s-1 can readily
be achieved at 10 RS or even closer to the coronal base.
Title: Exploring the temperature structure of coronal holes with a
novel combination of visible Fe lines
Authors: Habbal, Shadia Rifai; Brickhouse, Nancy S.; Esser, Ruth
Bibcode: 1996AIPC..382..177H
Altcode: 1996sowi.conf..177H
Establishing the temperature structure and temperature gradient
in the source region of the solar wind, from limb observations,
is often exacerbated by the interception along the line of sight of
hotter and denser material originating from the boundaries of coronal
holes. Probing coronal holes, however, can be optimized with a judicious
choice of spectral lines, such as the visible forbidden iron lines of
Fe IX 3801, Fe X 6374 and Fe XI 7892 Å, which are sensitive to electron
temperatures around 106 K. In addition observations made with
the Fe XIV 5303 Å line should yield information about any hot material
intercepting the line of sight. The combination of these Fe lines
offers a very powerful diagnostic tool for the electron temperature
within coronal holes and the structures embedded within them.
Title: Finest Filamentary Structures of the Inner Corona in the Slow
and Fast Solar Wind
Authors: Woo, R.; Habbal, S. R.
Bibcode: 1996AAS...188.8002W
Altcode: 1996BAAS...28R.956W
Recent progress in the interpretation of angular scattering measurements
has shown that a break in the vicinity of 1 Hz in the temporal frequency
spectrum of electron density fluctuations provides a measure of the size
of the finest filamentary structures in the solar corona. Using density
spectra deduced from 1979-1980 Voyager joint phase scintillation and
spectral broadening measurements by Coles et al. [1991], it is shown
that the finest filamentary structures are found in the extensions or
stalks of coronal streamers - the apparent sources of the slow solar
wind - and are over a factor of three smaller than those in the fast
wind emanating from coronal holes. The measured sizes of the finest
filamentary structures are approximately 6 km in the slow wid at 8 Ro
and 22 km in the fast wind at 9.1 Ro.
Title: Inferences of Plasma Parameters from Coronal Hole Observations
Authors: Habbal, Shadia Rifai
Bibcode: 1996Ap&SS.243...49H
Altcode: 1996IAUCo.154...49H
The temperature in the acceleration region of the solar wind remains one
of the most elusive parameters to measure. Knowledge of the temperature
as well as its gradient in the inner corona is fundamental for placing
constraints on physical mechanisms thought to be responsible for
the coronal heating process, as well as for understanding the flow
properties of the solar wind. Estimates of the helium abundance is
essential for understanding the puzzling behavior of heavier ions in the
solar wind. As an illustration of the difficulties and uncertainties
involved in the inferences of plasma parameters in the wolar wind
acceleration region, The inference of electron temperature and helium
abundance will be described. Prospects for future observations will
be briefly discussed.
Title: High Resolution Studies of the Structure of the Solar
Atmosphere
Authors: Habbal, Shadia R.
Bibcode: 1996sao..reptV....H
Altcode:
Our approach has focused on exploring the physical characteristics of
the coronal heating mechanisms, as manifested in coronal holes, quiet
regions and active regions, using different data sets, data analysis
techniques and image processing tools. The main results from these
studies can be summarized as follows: (1) Temperature inferences in
different coronal structures rely on the spectral lines used. Their
judicious choice is particularly crucial for reliable inferences
in coronal holes. (2) Limits on the helium abundance in the inner
corona can be inferred from knowledge of the temperature and density,
and their gradients in that region. (3) There exists a characteristic
spatial separation of 10"-15" between the substructures within coronal
holes, that is independent of the temperature of the emitting plasma,
or the large scale overlying magnetic field. (4) Different temperature
plasmas coexist at coronal heights regardless of the overlying large
scale structure, such as active regions, quiet regions or coronal
holes, and within these structures. (5) The spatial distribution of
the temporal variability of the coronal emission has a very distinct
temperature dependence, with a peak at 100,000 K, and is independent
of the structure of the overlying large scale magnetic field. (6) In
regard to some of the most spectacular forms of dynamic magnetic events,
namely corona mass ejections, nonthermal emission as manifested in the
form of type I noise storms observed at 90 cm, can serve as predictors
for the occurrence of these events.
Title: FY91 AASERT: Implications of the Small Scale Structure in
the Quiet Sun for the Solar Wind Flow
Authors: Habbal, Shadia R.
Bibcode: 1996sao..reptT....H
Altcode:
The AASERT Program was established to provide training for graduate
and undergraduate student in the field of research complementing a
program sponsored by the Department of Defense.The main focus of this
program was to explore the physical characteristics of the fine scale
magnetic structure in coronal holes which a believe to be the source
region of the fast solar wind.
Title: The Ultraviolet Coronagraph Spectrometer for the Solar and
Heliospheric Observatory
Authors: Kohl, J. L.; Esser, R.; Gardner, L. D.; Habbal, S.; Daigneau,
P. S.; Dennis, E. F.; Nystrom, G. U.; Panasyuk, A.; Raymond, J. C.;
Smith, P. L.; Strachan, L.; Van Ballegooijen, A. A.; Noci, G.;
Fineschi, S.; Romoli, M.; Ciaravella, A.; Modigliani, A.; Huber,
M. C. E.; Antonucci, E.; Benna, C.; Giordano, S.; Tondello, G.;
Nicolosi, P.; Naletto, G.; Pernechele, C.; Spadaro, D.; Poletto, G.;
Livi, S.; Von Der Lühe, O.; Geiss, J.; Timothy, J. G.; Gloeckler,
G.; Allegra, A.; Basile, G.; Brusa, R.; Wood, B.; Siegmund, O. H. W.;
Fowler, W.; Fisher, R.; Jhabvala, M.
Bibcode: 1995SoPh..162..313K
Altcode:
The SOHO Ultraviolet Coronagraph Spectrometer (UVCS/SOHO) is composed of
three reflecting telescopes with external and internal occultation and
a spectrometer assembly consisting of two toric grating spectrometers
and a visible light polarimeter. The purpose of the UVCS instrument is
to provide a body of data that can be used to address a broad range
of scientific questions regarding the nature of the solar corona and
the generation of the solar wind. The primary scientific goals are
the following: to locate and characterize the coronal source regions
of the solar wind, to identify and understand the dominant physical
processes that accelerate the solar wind, to understand how the coronal
plasma is heated in solar wind acceleration regions, and to increase the
knowledge of coronal phenomena that control the physical properties of
the solar wind as determined byin situ measurements. To progress toward
these goals, the UVCS will perform ultraviolet spectroscopy and visible
polarimetry to be combined with plasma diagnostic analysis techniques
to provide detailed empirical descriptions of the extended solar corona
from the coronal base to a heliocentric height of 12 solar radii.
Title: Ultraviolet Coronagraph Spectrometer for the Solar and
Heliospheric Observatory: instrument description and calibration
overview
Authors: Kohl, J. L.; Esser, R.; Gardner, Larry D.; Habbal, S.;
Daigneau, P. S.; Nystrom, George U.; Raymond, John C.; Strachan,
Leonard; van Ballegooijen, A. A.; Noci, G.; Fineschi, Silvano; Romoli,
Marco; Ciaravella, A.; Modigliani, A.; Huber, Martin C.; Antonucci, E.;
Benna, C.; Giordano, S.; von der Luehe, Oskar; Tondello, Giuseppe;
Nicolosi, Piergiorgio; Naletto, Giampiero; Pernechele, Claudio;
Geiss, J.; Gloeckler, G.; Poletto, G.; Spadaro, D.; Allegra, A.;
Basile, G.; Brusa, R.; Wood, B.; Siegmund, Oswald H.
Bibcode: 1995SPIE.2517...40K
Altcode:
The SOHO ultraviolet coronagraph spectrometer (UVCS/SOHO) is
composed of three reflecting telescopes with external and internal
occultation and a spectrometer assembly consisting of two toric grating
spectrometers and a visible light polarimeter. The UVCS will perform
ultraviolet spectroscopy and visible polarimetry to be combined with
plasma diagnostic analysis techniques to provide detailed empirical
descriptions of the extended solar corona from the coronal base to a
heliographic height of 12 R. In this paper, the salient features of
the design of the UVCS instrument are described. An overview of the
UVCS test and calibration activities is presented. The results from
the calibration activity have demonstrated that the UVCS can achieve
all its primary scientific observational goals.
Title: Using Fe X 6374 Å and Fe XIV 5303 Å spectral line
intensities to study the effect of line of sight integration on
coronal temperature inferences
Authors: Esser, R.; Brickhouse, N. S.; Habbal, S. R.; Altrock, R. C.;
Hudson, H. S.
Bibcode: 1995JGR...10019829E
Altcode:
Polar coronal holes are relatively stable structures persisting
over many solar rotations. The appearance of coronal holes in
remote observations, however, can change on a daily basis due to
variations of the denser and hotter plasma surrounding them. We
explore the effect of these denser and hotter surrounding regions on
coronal hole observations, using daily intensity measurements at 1.15
RS of the green Fe XIV 5303 Å and red Fe X 6374 Å spectral
lines. The observations, which were carried out at the National Solar
Observatory a Sacramento Peak, New Mexico, cover at time period of
about four solar rotations. We show that the ``coronal hole''
temperatures derived using the line ratio technique, vary by more than
0.8×106 K over the time interval considered here. We also
provide a short discussion of the expected accuracy of the atomic data
for these two iron spectral lines. Using intensity measurements as a
function of distance from the Sun, we briefly discuss how the regions
surrounding the coronal holes might influence the inference of the
temperature gradient in the coronal holes. The line of sight effect
on the temperature gradient should be explored in more detail in the
future using daily observations of the line intensities as a function
of distance. These observations could be provided by ground-based
coronagraphs and by instruments on board SOHO.
Title: Coronal heating and plasma parameters at 1 AU
Authors: Esser, Ruth; Habbal, Shadia Rifai
Bibcode: 1995GeoRL..22.2661E
Altcode:
A three-fluid description of the solar wind is used to investigate
the mass flux, helium abundance and flow speeds at 1 AU as a function
of heat input in the inner corona. The solar wind model includes
continuity, momentum and energy equations for each of the three species,
electrons, protons, and alpha particles. The energy equations contain
parameterized heat sources for any of the three species. The energy
equation for the electrons also includes radiation losses in the
transition region. We study the effect of heating different particle
species. We show that for a given set of plasma parameters at the
coronal base, heating the electrons, protons and alpha particles, or
all three species, can result in the same mass flux, helium abundance
and proton flow speed at 1 AU, yet very different plasma properties in
the inner corona. The plasma parameters we consider are characteristic
of the high speed solar wind.
Title: The Effects on Mass Flows on the Dissipation of Alfven Waves
in the Upper Layers of the Solar Atmosphere
Authors: Ryutova, Margarita P.; Habbal, Shadia R.
Bibcode: 1995ApJ...451..381R
Altcode:
The influence of parallel plasma flows on the propagation of shear
Alfvén waves along magnetic structures is considered. It is shown that
even in a simple case of regular mass flows directed along the magnetic
field, their presence considerably modifies the dissipation of shear
Alfvén waves, affecting both the magnitude and the height of maximum
dissipation. The strongest effect occurs in the case of downflows when
the flow velocity at a certain height becomes equal to the Alfvén
velocity. Near that point, the wave comes to extinction and gives
off its energy completely. The axial extent of the absorption region
is evaluated. This effect can be directly associated with observed
high-velocity downflows in the transition region, and, in particular,
can serve as a qualitative explanation for the high variability of the
emission observed near 105 K. In the presence of upward
mass flows and moderate downflows, the dissipation of phase-mixed
Alfvén waves is accompanied by the radial redistribution of the
energy input across the magnetic structure, thus creating a mosaic
pattern in the emitting regions. The flow velocities are assumed to
be below the thresholds which correspond to the onset of hydrodynamic
and dissipative instabilities.
Title: Exploring the temperature structure of coronal holes with a
novel combination of visible Fe lines
Authors: Habbal, Shadia Rifai; Brickhouse, Nancy; Esser, Ruth
Bibcode: 1995sowi.confR..69H
Altcode:
The difficulty in establishing the temperature structure and temperature
gradient within coronal holes from limb observations is due to the
frequent veiling of coronal holes by hotter and denser quiet regions
often surrounding them and shaping their boundaries. Nevertheless
probing the coronal hole medium itself can be made with a judicious
choice of spectral lines. We show how a set of visible forbidden Fe
lines, namely Fe IX 3801, Fe X 6374 and Fe Xl 7892 A which are sensitive
to plasma temperatures less than or equal to 106 K can
achieve this purpose. We propose to use these lines in a coordinated
manner with coronagraph observations. In addition observations made
with the Fe XIV 5303 A line should yield information about any hot
material intercepting the line of sight. The proposed combination of
these Fe lines offers a very powerful diagnostic tool for coronal hole
temperatures and structures.
Title: Demonstrating the limitations of line ratio temperature
diagnostic using Fe X and Fe XIV spectral line intensity observations
Authors: Brickhouse, Nancy; Esser, Ruth; Habbal, Shadia R.
Bibcode: 1995sowi.conf...69B
Altcode:
The electron temperature in the inner corona can be derived from
spectral line intensity measurements by comparing the ratio of the
measured intensities of two spectral lines to the ratio calculated from
theoretical models. In a homogeneous plasma the line ratio technique can
be used for any two lines if the ratio of the intensities is independent
of the density. The corona, however, is far from homogeneous. Even large
coronal holes present at the solar poles at solar minimum can be partly
or completely obscured by emission from hotter and denser surrounding
regions. In this paper we investigate the effect of these surrounding
regions on coronal hole temperatures. using daily intensity measurements
at 1.15 Rs of the Fe XIV 5303 A and Fe X 6374 A spectral lines carried
out at the National Solar Observatory at Sacramento Peak. We show that
the temperatures derived using the line ratio technique for these two
spectral lines can vary by more than 0.8 x 106 K due to the
contribution from surrounding regions. This example demonstrates the
inadequacy of spectral lines with widely separate peak temperatures
for temperature diagnostic.
Title: Flow properties of the solar wind derived from a two-fluid
model with constraints from white light and in situ interplanetary
observations
Authors: Habbal, Shadia Rifai; Esser, Ruth; Guhathakurta, Madhulika;
Fisher, Richard R.
Bibcode: 1995GeoRL..22.1465H
Altcode: 1995GeoRL..22.1465R
We derive the flow properties of the solar wind in coronal holes
using a two-fluid model constrained by density profiles inferred from
simultaneous space-based SPARTAN 201-01 and ground-based Mauna Loa
White Light coronagraph observations, and by in situ interplanetary
measurements. Also used as a guide is the hydrostatic temperature
profile derived from the density gradient. Density profiles are inferred
between 1.16 and 5.5 Rs, for two different density structures
observed along the line of sight in a polar coronal hole. The model
computations that fit remarkably well the empirical constraints yield a
supersonic flow at 2.3 Rs for the less dense ambient coronal
hole, and at 3.4 Rs for the denser structures. The novel
result that emerges from these fits is a proton temperature twice as
large as the electron temperature in the inner corona, reaching a peak
of 2 × 106 K at 2 Rs.
Title: Flow properties of the solar wind obtained from white light
data, ULYSSES observations and a two-fluid model
Authors: Habbal, Shadia Rifai; Esser, Ruth; Guhathakurta, Madhulika;
Fisher, Richard
Bibcode: 1995sowi.conf...64H
Altcode:
Using the empirical constraints provided by observations in the inner
corona and in interplanetary space. we derive the flow properties
of the solar wind using a two fluid model. Density and scale height
temperatures are derived from White Light coronagraph observations on
SPARTAN 201-1 and at Mauna Loa, from 1.16 to 5.5 R, in the two polar
coronal holes on 11-12 Apr. 1993. Interplanetary measurements of the
flow speed and proton mass flux are taken from the Ulysses south
polar passage. By comparing the results of the model computations
that fit the empirical constraints in the two coronal hole regions,
we show how the effects of the line of sight influence the empirical
inferences and subsequently the corresponding numerical results.
Title: Determining coronal electron temperatures from observations
with UVCS/SOHO
Authors: Fineschi, S.; Esser, R.; Habbal, S. R.; Karovska, M.; Romoli,
M.; Strachan, L.; Kohl, J. L.; Huber, M. C. E.
Bibcode: 1995sowi.confQ..68F
Altcode:
The electron temperature is a fundamental physical parameter of the
coronal plasma. Currently, there are no direct measurements of this
quantity in the extended corona. Observations with the Ultraviolet
Coronagraph Spectrometer (UVCS) aboard the upcoming Solar and
Heliospheric Observatory (SOHO) mission can provide the most direct
determination of the electron kinetic temperature (or, more precisely,
the electron velocity distribution along the line of sight). This
measurement is based on the observation of the Thomson-scattered Lyman
alpha (Ly-alpha) profile. This observation is made particularly
challenging by the fact that the integrated intensity of the
electron-scattered Ly-alpha line is about 103 times fainter
than that of the resonantly-scattered Ly-alpha component. In addition,
the former is distributed across 50 A (FWHM), unlike the latter that
is concentrated in 1 A. These facts impose stringent requirements on
the stray-light rejection properties of the coronagraph/spectrometer,
and in particular on the requirements for the grating. We make use of
laboratory measurements of the UVCS Ly-alpha grating stray-light, and of
simulated electron-scattered Ly-alpha profiles to estimate the expected
confidence levels of electron temperature determination. Models of
different structures typical of the corona (e.g., streamers, coronal
holes) are used for this parameter study.
Title: Three-fluid solar wind model with Alfven waves
Authors: Esser, Ruth; Habbal, Shadia R.; Hu, You Q.
Bibcode: 1995sowi.conf...64E
Altcode:
We present a study of a three-fluid solar wind model. with continuity,
momentum and separate energy equations for protons. alpha particles
and electrons. Allowing separate coronal heat sources for all three
species, we study the flow properties of the solar wind as a function
of heat input, Alfven wave energy input, and alpha particle abundance.
Title: Coronal magnetic field diagnostics via the Hanle effect of
Lyman series lines
Authors: Fineschi, S.; Habbal, S. R.
Bibcode: 1995sowi.confR..68F
Altcode:
The magnetic field plays a major role in the physics of the solar
corona. However, there are no direct measurements of this physical
parameter. We describe a method that can provide the most direct
determination of the vector magnetic field in the extended corona
(i.e., at heliocentric heights between 1.2 R(solar radius) and 2.0
R(solar radius)). The method is based on polarimetric observations of
UV lines of the Lyman series, that is, Lyman alpha (Ly-alpha), lambda
1216 A, Lyman beta (Ly-beta), lambda 1025 A, and Lyman gamma (Ly-gamma),
lambda 972 A. These lines have a collisional and a resonantly scattered
component. Linear polarization is induced in the resonant component by
the anisotropy in the chromospheric radiation field that illuminates the
corona. Magnetic fields can be suitably determined through the effects
that they induce on this resonance polarization (Hanle effect). The
Hanle effect of the Ly-alpha is sensitive to field strengths in the 10
- 100 gauss range. The resonance polarization of Ly-beta and Ly-gamma
is sensitive, through the Hanle effect, to fields with strengths
between 3 - 30 gauss, and 0.3 - 6 gauss, respectively. We describe a
new method for separating the resonant from the collisional component
of the Ly-beta and Ly-gamma; the method is based on the approximation,
valid within 10%, that the collisional component of the Ly-alpha is
negligible, in typical coronal conditions. From the intensity and
the polarization of the resonant components of these Lyman lines, the
strength and direction of coronal fields can be determined. We model
the sensitivity of Hanle-effect diagnostics for different coronal
structures (e.g., coronal holes and loops).
Title: On the derivation of empirical limits on the helium abundance
in coronal holes below 1.5R s
Authors: Habbal, Shadia Rifai; Esser, Ruth
Bibcode: 1995SSRv...72...39H
Altcode:
We present a simple technique describing how limits on the helium
abundance, α, the ratio of helium to proton number density, can be
inferred from measurements of the electron density, temperature and
their gradients below 1.5R s. As an illustration, we apply
this technique to emission line intensities in the extreme ultraviolet,
measured in polar coronal holes. The example indicates that α can
be significantly large in the inner corona. This technique could be
applicable to the more extensive data to be obtained from coordinated
ground and space-based observations during the Ulysses south polar
passage and the Spartan flight, and subsequently during the SOHO
mission. Limits on the helium abundance in the solar wind can thus be
derived from its source region and compared to interplanetary values.
Title: Changes in the plasma characteristics of the corona associated
with the occurrence of a coronal mass ejection
Authors: Habbal, S. R.; Mossman, A.; Esser, R.; Gonzalez, R.
Bibcode: 1995SPD....26..713H
Altcode: 1995BAAS...27..968H
No abstract at ADS
Title: The Ultraviolet Coronagraph Spectrometer for the Solar and
Hellospheric Observatory
Authors: Raymond, J. C.; Kohl, J. L.; Esser, R.; Gardner, L. D.;
Habbal, S.; Strachan, L.; van Ballegooijen, A. A.; Noci, G.; Fineschi,
S.; Romoli, M.; Huber, M. C. E.; Antonucci, E.; Benna, C.; von der
Luhe, O.; Naletto, G.; Nicolosi, P.; Pernechele, C.; Tondello, G.;
Geiss, J.; Gloeckler, G.; Spadaro, D.; Daigneau, P. S.; Nystrom,
G. U.; Allegra, A.; Basile, G.; Brusa, R.; Wood, B.; Siegmund, O. H. W.
Bibcode: 1995SPD....26..720R
Altcode: 1995BAAS...27..970R
No abstract at ADS
Title: Dynamical Evolution of EUV Structures at the Limb in a
Coronal Hole
Authors: Karovska, M.; Habbal, S. R.
Bibcode: 1995SPD....26..711K
Altcode: 1995BAAS...27..968K
No abstract at ADS
Title: On the Derivation of Empirical Limits on the Helium Abundance
in Coronal Holes Below 1.5 RS
Authors: Habbal, S. R.; Esser, R.
Bibcode: 1995hlh..conf...39H
Altcode:
No abstract at ADS
Title: Recovering the fine structures in solar images
Authors: Karovska, M.; Habbal, S. R.; Golub, L.; DeLuca, E.; Hudson, H.
Bibcode: 1994ESASP.373..183K
Altcode: 1994soho....3..183K
No abstract at ADS
Title: Flow properties of the solar wind obtained from white light
data and a two-fluid model
Authors: Habbal, S. R.; Esser, Ruth; Guhathakurta, Madhulika; Fisher,
Richard
Bibcode: 1994ESASP.373..211H
Altcode: 1994soho....3..211H
No abstract at ADS
Title: Small scale structures in the solar corona
Authors: Habbal, S. R.
Bibcode: 1994SSRv...70...37H
Altcode:
The observational characteristics of the small scale magnetic structures
are summarized. The temperature structure and temporal variability of
the emission from coronal bright points, that pervade the source region
of the solar wind in coronal holes and the quiet sun, and from active
regions are shown to be remarkably similar. Particular emphasis is given
to observations, potentially feasible with SOHO, that could resolve some
of the outstanding issues regarding the role of the small scale magnetic
structures in the energy balance and properties of the solar wind.
Title: Coronal plumes and final scale structure in high speed solar
wind streams
Authors: Velli, M.; Habbal, S. R.; Esser, R.
Bibcode: 1994SSRv...70..391V
Altcode:
We present a solar wind model which takes into account the possible
origin of fast solar wind streams in coronal plumes. We treat coronal
holes as being made up of essentially 2 plasma species, denser,
warmer coronal plumes embedded in a surrounding less dense and cooler
medium. Pressure balance at the coronal base implies a smaller magnetic
field within coronal plumes than without. Considering the total coronal
hole areal expansion as given, we calculate the relative expansion
of plumes and the ambient medium subject to transverse pressure
balance as the wind accelerates. The magnetic flux is assumed to
be conserved independently both within plumes and the surrounding
coronal hole. Magnetic field curvature terms are neglected so the
model is essentially one dimensional along the coronal plumes, which
are treated as thin flux-tubes. We compare the results from this
model with white-light photographs of the solar corona and in-situ
measurements of the spaghetti-like fine-structure of high-speed winds.
Title: Dynamical Structure of Extreme Ultraviolet Macrospicules
Authors: Karovska, Margarita; Habbal, Shadia Rifai
Bibcode: 1994ApJ...431L..59K
Altcode:
We describe the substructures forming the macrospicules and their
temporal evolution, as revealed by the application of an image
enhancement algorithm to extreme ultraviolet (EUV) observations of
macrospicules. The enhanced images uncover, for the first time,
the substructures forming the column-like structures within the
macrospicules and the low-lying arches at their base. The spatial and
temporal evolution of macrospicules clearly show continuous interaction
between these substructures with occasional ejection of plasma following
a ballistic trajectory. We comment on the importance of these results
for planning near future space observations of macrospicules with
better temporal and spatial resolution.
Title: Exploring the Fine Structure at the Limb in Coronal Holes
Authors: Karovska, Magarita; Blundell, Solon F.; Habbal, Shadia Rifai
Bibcode: 1994ApJ...428..854K
Altcode:
The fine structure of the solar limb in coronal holes is explored
at temperatures ranging from 104 to 106 K. An
image enhancement algorithm orignally developed for solar eclipse
observations is applied to a number of simultaneous multiwavelength
observations made with the Harvard Extreme Ultraviolet Spectrometer
experiment on Skylab. The enhanced images reveal the presence of
filamentary structures above the limb with a characteristic separation
of approximately 10 to 15 sec . Some of the structures extend from the
solar limb into the corona to at least 4 min above the solar limb. The
brightness of these structures changes as a function of height above
the limb. The brightest emission is associated with spiculelike
structures in the proximity of the limb. The emission characteristic
of high-temperature plasma is not cospatial with the emission at lower
temperatures, indicating the presence of different temperature plasmas
in the field of view.
Title: Standing shocks in a two-fluid solar wind
Authors: Habbal, Shadia R.; Hu, You Qiu; Esser, Ruth
Bibcode: 1994JGR....99.8465H
Altcode:
We present a numerical study of the formation of standing shocks in
the solar wind using a two-fluid time-dependent model in the presence
of Alfvén waves. Included in this model is the adiabatic cooling
and thermal conduction of both electrons and protons. In this study,
standing shocks develop in the flow when additional critical points form
as a result of either localized momentum addition or rapid expansion of
the flow tube below the existing sonic point. While the flow speed and
density exhibit the same characteristics as found in earlier studies
of the formation of standing shocks, the inclusion of electron and
proton heat conduction produces different signatures in the electron
and proton temperature profiles across the shock layer. Owing to the
strong heat conduction, the electron temperature is nearly continuous
across the shock, but its gradient has a negative jump across it,
thus producing a net heat flux out of the shock layer. The proton
temperature exhibits the same characteristics for shocks produced by
momentum addition but behaves differently when the shock is formed
by the rapid divergence of the flow tube. The adiabatic cooling
in a rapidly diverging flow tube reduces the proton temperature so
substantially that the proton heat conduction becomes negligible in
the vicinity of the shock. As a result, protons experience a positive
jump in temperature across the shock. While Alfvén waves do not affect
the formation of standing shocks, they contribute to the change of the
momentum and energy balance across them. We also find that for this
solar wind model the inclusion of thermal conduction and adiabatic
cooling for the electrons and protons increases significantly the
range of parameters characterizing the formation of standing shocks
over those previously found for isothermal and polytropic models.
Title: The Discrete and Localized Nature of the Variable Emission
from Active Regions
Authors: Arndt, Martina Belz; Habbal, Shadia Rifai; Karovska, Margarita
Bibcode: 1994SoPh..150..165A
Altcode: 1994SoPh..150..165B
Using data from the Extreme Ultraviolet (EUV) Spectroheliometer
onSkylab, we study the empirical characteristics of the variable
emission in active regions. These simultaneous multi-wavelength
observations clearly confirm that active regions consist of a complex
of loops at different temperatures. The variable emission from this
complex has very well-defined properties that can be quantitatively
summarized as follows: (1) It is localized predominantly around the
footpoints where it occurs at discrete locations. (2) The strongest
variability does not necessarily coincide with the most intense
emission. (3) The fraction of the area of the footpoints,δn/N, that
exhibits variable emission, varies by ±15% as a function of time,
at any of the wavelengths measured. It also varies very little from
footpoint to footpoint. (4) This fractional variation is temperature
dependent with a maximum around 105 K. (5) The ratio of
the intensity of the variable to the average background emission,
δI/Ī, also changes with temperature. In addition, we find that these
distinctive characteristics persist even when flares occur within the
active region.
Title: The Discrete Nature of the Variable Emission in Active
Region Loops
Authors: Habbal, Shadia Rifai; Arndt, Martina Belz; Karovska, Margarita
Bibcode: 1994ASPC...68..314H
Altcode: 1994sare.conf..314H
No abstract at ADS
Title: Characteristic Signatures of Solar Activity from the Small
Scale Magnetic Field.
Authors: Habbal, S. R.
Bibcode: 1994ASPC...64..309H
Altcode: 1994csss....8..309H
No abstract at ADS
Title: On the Derivation of Empirical Limits on the Helium Abundance
in Coronal Holes below 1.5 R sub sun
Authors: Habbal, Shadia Rifai; Esser, Ruth
Bibcode: 1994ApJ...421L..59H
Altcode:
We present a simple technique describing how limits on the helium
abundance, alpha, defined as the ratio of helium to proton number
density, can be inferred from measurements of the electron density and
temperature below 1.5 solar radius. As an illustration, we apply this
technique to two different data sets: emission-line intensities in the
extreme ultraviolet (EUV) and white-light observations, both measured
in polar coronal holes. For the EUV data, the temperature gradient is
derived from line intensity ratios, and the density gradient is replaced
by the gradient of the line intensity. The lower limit on alpha derived
from these data is 0.2-0.3 at 1 solar radius and drops very sharply to
interplanetary values of a few percent below 1.06 solar radius. The
white-light observations yield density gradients in the inner corona
beyond 1.25 solar radius but do not have corresponding temperature
gradients. In this case we consider an isothermal atmosphere, and derive
an upper limit of 0.2 for alpha. These examples are used to illustrate
how this technique could be applicable to the more extensive data to be
obtained with the upcoming SOHO mission. Although only ranges on alpha
can be derived, the application of the technique to data currently
available merely points to the fact that alpha can be significantly
large in the inner corona.
Title: Overestimating the Coronal Density and Its Effect on the
Velocities Derived from Ly-alpha Doppler Dimming.
Authors: Esser, Ruth; Habbal, Shadia R.
Bibcode: 1993SoPh..147..241E
Altcode:
It is shown that relatively small errors of the order of 10% in the
electron densities, for example derived from polarization brightness
measurements, might lead to large errors in the velocities inferred
from intensity measurements of the Lα HI λ 1216 spectral line in
the inner corona. It is demonstrated that in some cases this effect
can result in very high velocities close to the coronal base with
subsequent small acceleration with heliocentric distance. It is also
pointed out that the errors in the deduced velocities can be reduced
if simultaneous observations that place constraints on the mass flux
are available, and by ensuring that the mass flux computed from the
derived velocities and densities is constant.
Title: How Reliable are Coronal Hole Temperatures Deduced from
Observations?
Authors: Habbal, S. R.; Esser, R.; Arndt, M. B.
Bibcode: 1993ApJ...413..435H
Altcode:
Given the importance of the temperature at the base of the corona for
the modeling of the solar wind, we investigate the range of temperatures
which have been deduced from remote measurements in coronal holes,
within a heliocentric distance of 1.6 solar radii, and the accuracy to
which these temperatures have been inferred. Results are presented from
an analysis of EUV observations made simultaneously in three spectral
lines at the limb in a polar coronal hole, with little contamination
from quiet region emission. A temperature range of 7.8-9.3 x 10 exp 5
K is obtained, between 1.02 to 1.07 solar radii for the coronal hole,
with a very different temperature range of 9.4 x 10 exp 5 - 1.2 x 10
exp 6 K for the quiet regions bordering it. Inhomogeneities within
the coronal hole contribute to a 14 percent variation in inferred
temperature. The elemental abundance, which is one of the parameters
that influence the temperature inference, can in turn be significantly
constrained when intensity ratios from three spectral lines are used.
Title: High resolution studies of the structure of the solar
atmosphere
Authors: Habbal, Shadia R.
Bibcode: 1993sao..reptS....H
Altcode:
During this second year we pursued the analysis, image enhancement, and
processing of an extensive set of the EUV/Skylab data for the search of
empirical characteristics of coronal heating in different scale magnetic
regions on the Sun. Student involvement in our research projects
included Martina Arndt, Gretchen McPhee and Jennifer Yeh. During
this funding period we published three papers in refereed journals,
one in a conference proceedings, submitted three papers to refereed
journals, and have several manuscripts under preparation. We have also
made two conference presentations and given three invited talks. Our
future projects are continuations of our ongoing long term projects
and include the following: (1) The comparison of the temperature in
coronal holes and the quiet sun--the implication for solar wind models;
(2) The energy spectrum of the variability of the emission in active
regions, the quiet sun, and coronal holes; (3) Studies of the fine
scale structure in the quiet sun and active regions; and (4) Modeling
the radio emission in the presence of structure in the quiet sun and
active regions.
Title: Double shock pairs in the solar wind
Authors: Hu, Y. Q.; Habbal, S. R.
Bibcode: 1993JGR....98.3551H
Altcode:
This paper presents a numerical study of the evolution of a velocity
enhancement disturbance in the solar wind in terms of a one-dimensional,
isentropic MHD flow model. It is shown that the disturbance steepens
and evolves into a double shock pair while propagating outward away
from the Sun. The double shock pair consists of a reverse fast shock,
a reverse slow shock, and a forward fast shock in order of distance
away from the Sun. The formation time of the double shock pair is
nearly inversely proportional to the average velocity gradient of
the disturbance. When the double shock pair is fully developed, the
strength of the fast shocks is essentially determined by the disturbance
amplitude, while the slow shocks behave differently. Their strength
increases first with the disturbance amplitude but starts to decrease
once the disturbance amplitude exceeds a certain value. However,
the fully developed slow shocks will retain their identity up to
1 AU and even farther, though their propagation speed in the solar
wind frame and the jump in velocity and total pressure across them
decrease substantially with heliocentric distance. Theoretically,
double shock pairs would occur frequently in the inner heliosphere,
since the solar wind there is characterized by various large-scale
structures and disturbances, which provide an appropriate ground for
the formation of double shock pairs. Such a prediction remains to be
confirmed by observations and data interpretation.
Title: Interaction between perpendicular magnetohydrodynamic shocks
Authors: Hu, Y. Q.; Habbal, S. R.
Bibcode: 1993PhFlB...5..732H
Altcode:
A general analysis is made of the collision and merging of perpendicular
shocks as well as the interaction between a shock and a tangential
discontinuity. It is found that two head-on shocks diminish both in
strength after collisions and a tangential discontinuity forms between
them. The property of the discontinuity depends on the relative strength
of the two shocks. No discontinuity occurs if the shocks are equal in
strength. The emerging of two shocks propagating in the same direction
results in a strong shock followed by a tangential discontinuity
and a reverse wave. The reverse wave is a rarefaction wave if one or
both of the shocks are strong. If the shocks are both weak, a critical
adiabatic index (CAI) exists. The reverse wave is a rarefaction wave if
the wavelength is less than the CAI and a shock exists if the wavelength
is greater than the CAI. As a wake shock enters from a medium of higher
wave impedance into that of lower wave impedance, the reflected wave
is a rarefaction wave and the total pressure ratio decreases and the
velocity jump increases after the shock passes through the border.
Title: Temperature measurements in the inner corona.
Authors: Esser, Ruth; Habbal, S. R.; Arndt, M. B.
Bibcode: 1992ESASP.348..277E
Altcode: 1992cscl.work..277E
To increase the understanding of the acceleration of the solar wind it
is necessary to combine observations and theoretical approaches. The
authors demonstrate the importance of coordinated measurements in the
inner corona and interplanetary space to place constraints on solar
wind models. Given the fact that the temperature in the inner corona
is the most important parameter in solar wind modeling, observations
from which reliable temperatures can be deduced are crucial for
such coordinated approaches. The authors address how temperatures
in the inner corona have been derived in the past, as well as which
assumptions and models are inherent in the temperatures derived using
different observational techniques. Finally they choose two examples
of EUV observations to demonstrate problems that can arise in the
interpretation of measurements.
Title: Fine Structure at the Limb in a Coronal Hole
Authors: Karovska, M.; Habbal, S. R.; Blundell, F.
Bibcode: 1992AAS...181.8110K
Altcode: 1992BAAS...24R1253K
No abstract at ADS
Title: High resolutions studies of the structure of the solar
atmosphere
Authors: Habbal, Shadia R.
Bibcode: 1992sao..reptR....H
Altcode:
During this first year, we have concentrated on the analysis, and the
image enhancement and processing of an extensive set of the EUV/Skylab
data for the search of empirical characteristics of coronal heating
in different scale magnetic regions on the Sun. Student involvement
in our research projects has been quite successful.
Title: Temperatures and Densities in the Inner Corona
Authors: Habbal, S. R.; Esser, R.
Bibcode: 1992AAS...180.5204H
Altcode: 1992BAAS...24Q.816H
No abstract at ADS
Title: The SPARTAN Ultraviolet Coronagraph
Authors: Gardner, L. D.; Esser, R.; Habbal, S. R.; Hassler, D. M.;
Raymond, J. C.; Strachan, L.; van Ballegooijen, A. A.; Kohl, J. L.;
Fineschi, S.
Bibcode: 1992AAS...180.5202G
Altcode: 1992BAAS...24..815G
An ultraviolet coronagraph (UVC) is being prepared for a series of
orbital flights on NASA's Spartan 201 which is deployed and retrieved
by Shuttle. The Spartan 201 payload consists of the UVC and a white
light coronagraph developed by the High Altitude Observatory. Spartan
is expected to provide 26 orbits of solar observations per flight. The
first flight is scheduled for May 1993 and subsequent flights
are planned to occur at each polar passage of Ulysses (1994 and
1995). The UVC measures the intensity and spectral line profile of
resonantly scattered H I Ly-alpha and the intensities of O VI lambda
1032 and lambda 1037 at heliocentric heights between 1.3 and 3.5 solar
radii. A description of the UVC instrument, its characteristics, and the
observing program for the first flight will be presented. The initial
scientific objective is to determine the random velocity distribution
and bulk outflow velocity of coronal protons and the density and outflow
velocity of O(5+) in polar coronal holes and adjoining high latitude
streamers. This work is supported by NASA under Grant No. NAG5-613 to
the Smithsonian Astrophysical Observatory.
Title: Coronal energy distribution and X-ray activity in the small
scale magnetic field of the quiet sun.
Authors: Habbal, S. R.
Bibcode: 1992AnGeo..10...34H
Altcode:
The author discusses the energy distribution in the small scale
magnetic field that pervades the solar surface, and its relationship
to X-ray/coronal activity. The observed emission from the small scale
structures, at temperatures characteristic of the chromosphere,
transition region and corona, emanates from the boundaries of
supergranular cells, within coronal bright points. This emission is
characterized by a strong temporal and spatial variability with no
definite pattern. The analysis of simultaneous, multiwavelength EUV
observations shows that the spatial density of the enhanced as well as
variable emission from the small scale structures exhibits a pronounced
temperature dependence with significant maxima at 105K and
106K. The radiative energy losses computed from the variable
and enhanced components of the emission from the small scale structures
are much smaller than those from the background quiet Sun. With data
available at present, the observed variability in the small scale
structure cannot account for the coronal heating of the quiet Sun. The
characteristics of their emission are more likely to be an indicator
of the coronal heating mechanisms.
Title: Variable EUV emission in the quiet sun and coronal heating
Authors: Habbal, S. R.
Bibcode: 1992sws..coll...41H
Altcode:
We review the characteristics of the variable emission from the small
scale structure in the quiet sun, in view of the recent theoretical
proposals that microflares are responsible for the heating of the
corona and the solar wind. We consider the observational properties of
the variable emission in quiet regions and coronal holes. Our results
are based primarily on simultaneous multiwavelength EUV observations,
supplemented by combinations of simultaneous cm radio, He I 10830 A,
X-ray and line of sight photospheric magnetic field measurements. We
show that the variable emission from the small-scale structure has
surprisingly well-defined properties. Yet, within the limit of the
temporal and spatial resolution of data currently available, the
radiative losses, from this component of the emission, are a factor of
ten smaller than that in the quiet sun. Hence, the theory of microflare
heating cannot rely on these observations for support.
Title: The Connection between Coronal Bright Points and the
Variability of the Quiet-Sun Extreme-Ultraviolet Emission
Authors: Habbal, Shadia R.; Grace, Edmund
Bibcode: 1991ApJ...382..667H
Altcode:
An analysis of the EUV/Skylab data recorded at six wavelengths
simultaneously and scanning the chromosphere to the corona is
reported. The results show that, whether in a coronal hole or a
quiet region, the significant variable emission in the quiet sun
is preferentially localized in the enhanced emission produced by EUV
bright points in the boundaries of network cells. The spatial density
of the variable and enhanced emission varies with temperature, with
a minimum at 3 x 10 exp 5 K which indicates two favored temperature
distributions of small-scale loops in the quiet sun, one below 3 x
10 exp 5 K and one at coronal temperatures. The enhanced emission
occupies between 10 and 25 percent of the solar surface, depending on
the temperature, while the variable emission covers between 5 and 15
percent. For a given region, the spatial density at a given temperature
does not vary in time by more than 10 percent about its mean value.
Title: First Observations of Macrospicules at 4.8 GHz at the Solar
Limb in Polar Coronal Holes
Authors: Habbal, Shadia R.; Gonzalez, Raymond D.
Bibcode: 1991ApJ...376L..25H
Altcode: 1991ApJ...376L..25R
VLA observations at 4.8, 8.5, and 15 GHz have led to the detection of
macrospicules in solar coronal holes. The limb was sharply defined at
all three frequencies. The brightness temperatures obtained for the
macrospicules lead to an empirical model in which a cool 8000-K core
is surrounded by a thin, hotter sheath of 100,000-200,000 K; these
features are virtually identical to those derived from EUV observations
over 10 years ago. A pinching-off and ballooning is noted at the top
of the macrospicules' magnetic structure which may lead to the escape
of some of the plasma from the macrospicules' locations.
Title: High-Resolution Studies of the Structure of the Solar
Atmosphere Using a New Imaging Algorithm
Authors: Karovska, Margarita; Habbal, Shadia Rifai
Bibcode: 1991ApJ...371..402K
Altcode:
The results of the application of a new image restoration algorithm
developed by Ayers and Dainty (1988) to the multiwavelength EUV/Skylab
observations of the solar atmosphere are presented. The application
of the algorithm makes it possible to reach a resolution better than 5
arcsec, and thus study the structure of the quiet sun on that spatial
scale. The results show evidence for discrete looplike structures in
the network boundary, 5-10 arcsec in size, at temperatures of 100,000 K.
Title: First Observations of Macrospicules at 4.8 GHz at the Solar
Limb in Polar Coronal Holes
Authors: Habbal, S. R.; Gonzalez, R. D.
Bibcode: 1991BAAS...23.1062H
Altcode:
No abstract at ADS
Title: Observations of Coronal Bright Points and Implications for
Coronal Heating Mechanisms (With 3 Figures)
Authors: Habbal, S. R.
Bibcode: 1991mcch.conf..127H
Altcode:
No abstract at ADS
Title: Characteristics of the Variable Quiet Sun EUV Emission
Authors: Habbal, S. R.
Bibcode: 1990BAAS...22.1199H
Altcode:
No abstract at ADS
Title: Exploring the Structure of the Quiet Sun with a New Imaging
Algorithm
Authors: Karovska, M.; Habbal, S. R.
Bibcode: 1990BAAS...22.1199K
Altcode:
No abstract at ADS
Title: Spectral Line and White-Light Intensities in the Coronal in
the Presence of Propagating or Standing Shocks
Authors: Esser, Ruth; Habbal, Shadia Rifai
Bibcode: 1990SoPh..129..153E
Altcode:
The effect of a propagating shock on the HI Lα line and
the polarization brightness in the inner solar wind region is
investigated. We find that the shock produces measurable changes
in both and, provided the measurements are made simultaneously,
the alteration of the density and velocity across the shock can be
derived. For a standing shock the effect on the Lα line and the
white-light radiation is much smaller.
Title: Polar Plumes and the Solar Wind
Authors: Withbroe, G. L.; Habbal, S. R.
Bibcode: 1990BAAS...22..851W
Altcode:
No abstract at ADS
Title: A Comparison between Bright Points in a Coronal Hole and a
Quiet-Sun Region
Authors: Habbal, Shadia Rifai; Dowdy, James F., Jr.; Withbroe,
George L.
Bibcode: 1990ApJ...352..333H
Altcode:
A comparison is made of the morphological structure and temporal
behavior of the emission from coronal bright points in a coronal hole
and a quiet region, using data from the Harvard EUV experiment on
Skylab. It is found that, in both regions, coronal bright points are
located at network boundaries and cover a range of sizes from 10 to
40 in in linear extent. In a given bright pint, the peaks of emission
in the six different lines, measured simultaneously through the same
instrument slit, are not always cospatial, implying that bright points
consist of a complex of small-scale loops at different temperatures. The
intensity of bright points in both regions is also characterized by a
significant temporal variability in all the wavelengths measured. This
variability exhibits no regular periodicity. Yet the ratio of the
varying (ac) to the constant (dc) components of the emission, in all
the bright points studied, has a local maximum at 1-2 x 10 to the 5th
k which coincides with the peak of the radiative loss function, and
another local maximum at Mg x (1.4 x 10 to the 6th K). It is found
that coronal bright points in a coronal hole or a quiet region are
indistinguishable structures, and, therefore, conclude that they are
independent of the overlying background corona.
Title: Synthesis Mapping of a Solar Type I Storm Simultaneously at
90 and 20 Centimeters with the VLA
Authors: Habbal, Shadia Rifai; Ellman, Nancy E.; Gonzalez, Raymond
Bibcode: 1989ApJ...342..594H
Altcode:
A type I radio storm was observed simultaneously at 20 and 90 cm
in November 1986. The characteristic signatures of the storm are
detected at 90 cm only. The results indicate that the noise storm
is unambiguously associated with an active region at the sun center,
and that the distribution of energetic electrons responsible for the
storm emission reaches low coronal heights. Polarization measurements
and storm source location results suggest that the 90-cm emission
is fundamental plasma radiation and that the 20-cm measurements are
characteristic of free-free emission.
Title: Comparison between Bright Points in a Coronal Hole and the
Quiet Sun
Authors: Habbal, S. R.; Withbroe, G. L.; Dowdy, J., Jr.
Bibcode: 1989BAAS...21R.840H
Altcode:
No abstract at ADS
Title: Three-Dimensional Models of the Solar Atmosphere
Authors: van Ballegooijen, A. A.; Habbal, S. R.; Dowdy, J. F.
Bibcode: 1989BAAS...21..836V
Altcode:
No abstract at ADS
Title: Spatial and Temporal Variations of EUV Coronal Bright Points
Authors: Habbal, S. R.; Dowdy, J. F., Jr.; Withbroe, G. L.
Bibcode: 1988BAAS...20Q.977H
Altcode:
No abstract at ADS
Title: Spatial and Temporal Variations of Coronal Heating in Small
Active Regions
Authors: Withbroe, G. L.; Dowdy, J. F., Jr.; Habbal, S. R.
Bibcode: 1988BAAS...20..977W
Altcode:
No abstract at ADS
Title: Simultaneous Observations of 20 Centimeter Bright Points and
He i 10830 Angstrom Dark Points in the Quiet Sun
Authors: Habbal, Shadia R.; Harvey, Karen L.
Bibcode: 1988ApJ...326..988H
Altcode:
The authors present the results of the first simultaneous observations
of the quiet Sun made at the 20 cm radio wavelength and in the He
I λ10830 line. Simultaneous magnetic field measurements were also
obtained with lower time resolution during the five consecutive
hours of observations. In the 512arcsec×512arcsec common observing
field of view the authors find that the 20 cm radio emisison, which
originates from the low corona-transition region, is always associated
with regions of enhances He I absorption; yet, it does not always
coincide with strong He I λ10830 absorption regions known as He I
"dark points". The temporal changes of the 20 cm emission and the
underlying He I absorption are also studied.
Title: Dynamic Nature of coronal heating
Authors: Habbal, S. R.; Harvey, K. L.
Bibcode: 1988ASSL..143..215H
Altcode: 1988acse.conf..215H
The authors present the results of the first simultaneous observations
of the quiet sun made at 20 cm with the VLA and in He I 10830 Å,
together with the line of sight component of the photospheric magnetic
field. The nature of the correlation found between changes in He I dark
points and the 20 cm radio sources, as well as with the underlying
magnetic field, suggest that topological changes in the underlying
magnetic field are playing an important role in the transient coronal
heating process.
Title: Dynamic Changes in an Active Region Observed Simultaneously
at 20 and 90 cm Radio Wavelengths with the VLA
Authors: Habbal, S. R.; Ellman, N. E.; Gonzalez, R.
Bibcode: 1987BAAS...19..942H
Altcode:
No abstract at ADS
Title: Simultaneous observations of changes in coronal bright point
emissionat the 20 cm radio and He I λ10830 wavelengths.
Authors: Habbal, Shadia R.; Harvey, Karen L.
Bibcode: 1986NASCP2442..343H
Altcode: 1986copp.nasa..343H
Preliminary results of observations of solar coronal bright points
acquired simultaneously from ground based observatories at the radio
wavelength of 20 cm and in the He I wavelength 10830 line on September
8, 1985, are reported. The impetus for obtaining simultaneous radio and
optical data is to identify correlations, if any, in changes of the low
transition-coronal signatures of bright points with the evolution of
the magnetic field, and to distinguish between intermittent heating
and changes in the magnetic field topology. Although simultaneous
observations of H alpha emission and the photospheric magnetic field
at Big Bear were also made, as well as radio observations from Owen
Valley Radio Interferometer and Solar Maximum Mission (SSM) (O VIII
line), only the comparison between He 10830 and the Very Large Array
(VLA) radio data are presented.
Title: Simultaneous Observations of Coronal Bright Point Emission
at 20 cm Radio and He 10830 Å Wavelengths
Authors: Harvey, K. L.; Habbal, S. R.
Bibcode: 1986BAAS...18R.901H
Altcode:
No abstract at ADS
Title: Simultaneous Observations of the Quiet Sun at 90 and 20 cm
Radio and He 10830 Å Wavelengths
Authors: Habbal, S. R.; Gonzalez, R.; Harvey, K. L.
Bibcode: 1986BAAS...18..932H
Altcode:
No abstract at ADS
Title: Solar Coronal Bright Points Observed with the VLA
Authors: Habbal, S. R.; Ronan, R. S.; Withbroe, G. L.; Shevgaonkar,
R. K.; Kundu, M. R.
Bibcode: 1986ApJ...306..740H
Altcode:
The first observations of solar coronal bright points made at 20-cm
wavelength with the VLA are reported. The brightness temperature of
the sources observed varies between 1 and 5 x 10 to the 5th K. The
observations indicate that significant fluctuations in the brightness
temperature as well as in the spatial extent of these sources can occur
over a few minutes. These fluctuations are shown to be due to density
and temperature fluctuations at transition region heights combined
with either plasma motions along magnetic field lines or changes in
magnetic field topology, or both.
Title: A two-fluid solar wind model with Alfven waves: parameter
study and application to observations
Authors: Esser, Ruth; Leer, Egil; Habbal, Shadia R.; Withbroe,
George L.
Bibcode: 1986JGR....91.2950E
Altcode:
The effects of Alfven waves from the inner corona on the solar wind
density profile, flow velocity and on the random motion of protons
are studied. Different base densities, temperatures, and wave velocity
amplitudes, as well as different flow geometries, are considered. The
model calculations are compared to simultaneous observations of the
electron density profile and the resonantly scattered Lyman alpha
line. Present observations, out to 4 solar radii, can be used to
place limits on the coronal base density and temperature, and put
an upper limit on the wave amplitude. It is pointed out that future
observations of the electron density and the Lyman alpha line, out
to larger heliocentric distances, and of lines from heavier elements,
should be used to place more stringent constraints on the amplitudes
of MHD waves in the corona.
Title: Spatial and Temporal Variations of Solar Coronal Loops
Authors: Habbal, S. R.; Ronan, R.; Withbroe, G. L.
Bibcode: 1985SoPh...98..323H
Altcode:
Skylab EUV observations of an active region near the solar limb
were analyzed. Both cool (T < 106 K) and hot (T >
106 K) loops were observed in this region. For the hot loops
the observed intensity variations were small, typically a few percent
over a period of 30 min. The cool loops exhibited stronger variations,
sometimes appearing and disappearing in 5 to 10 min. Most of the cool
material observed in the loops appeared to be caused by the downward
flow of coronal rain and by the upward ejection of chromospheric
material in surges. The frequent EUV brightenings observed near the loop
footpoints appear to have been produced by both in situ transient energy
releases (e.g. subflares) and the infall/impact of coronal rain. The
physical conditions in the loops (temperatures, densities, radiative
and conducting cooling rates, cooling times) were determined. The mean
energy required to balance the radiative and conductive cooling of the
hot loops is approximately 3 × 10−3 erg cm−3
s−1. One coronal heating mechanism that can account for
the observed behavior of the EUV emission from McMath region 12634 is
heating by the dissipation of fast mode MHD waves.
Title: Impulsive Phenomena in a Small Active Region
Authors: Withbroe, G. L.; Habbal, S. R.; Ronan, R.
Bibcode: 1985SoPh...95..297W
Altcode:
The temporal and spatial variations of EUV emission from a small
growing active region were investigated. Frequent localized short
term (∼ few minutes) fluctuations in EUV emission were observed
throughout the 7.2 hr interval when the most continuous observations
were acquired. Approximately 20% of the 5 ″ x 5 ″ pixels had
intensity variations exceeding a factor of 1.3 for the chromospheric
Lα line, a factor of 1.5 for lines formed in the chromospheric-coronal
transition region and a factor of 1.4 for the coronal Mg x line. A
subflare in the region produced the largest intensity enhancements,
ranging from a factor of ∼ 2.3 for the chromospheric Lα line to ∼
8 for the transition region and coronal lines. The EUV fluctuations
in this small active region are similar to those observed in coronal
bright points, suggesting that impulsive heating is an important,
perhaps dominant form of heating the upper chromospheric and lower
coronal plasmas in small magnetic bipolar regions. The responsible
mechanism most likely involves the rapid release of magnetic energy,
possibly associated with the emergence of magnetic flux from lower
levels into the chromosphere and corona.
Title: The formation of a standing shock in a polytropic solar wind
model within 1-10 Rs
Authors: Habbal, S. R.
Bibcode: 1985JGR....90..199H
Altcode:
We show how a one-fluid polytropic solar wind model exhibits properties
similar to an isothermal wind when localized momentum addition and/or
rapid area divergence produce multiple critical points in the flow. In
particular, we show that when the sonic transition in the flow occurs
closer to the coronal base, multiple steady solutions can exist. These
multiple steady solutions consist of a continuous solution passing
through the innermost critical point and other steady solutions
involving a steady shock transition. By following the temporal
evolution of the solar wind from a steady state with one critical
point to a steady state with three critical points, we show that a
standing shock solution is more likely to develop than a continuous
solution when momentum deposition occurs close to the coronal base and
the equation of motion admits multiple steady solutions. This result
is particularly relevant to the solar wind when momentum deposition
occurs as a result of a rapidly diverging coronal hole geometry.
Title: Temporal and Spatial Variations of Solar Coronal Bright Points
Observed with the VLA
Authors: Habbal, S. R.; Cowell, A.; Ronan, R.; Withbroe, G. L.;
Shevgaonkar, R.; Kundu, M.
Bibcode: 1984BAAS...16..929H
Altcode:
No abstract at ADS
Title: Fast-mode magnetohydrodynamic waves in coronal holes and the
solar wind
Authors: Fla, T.; Habbal, S. R.; Holzer, T. E.; Leer, E.
Bibcode: 1984ApJ...280..382F
Altcode:
Fast-mode MHD waves in the solar corona can propagate in any direction
relative to the background magnetic field. In coronal holes, they
refract into regions of low Alfven speed and are relatively difficult
to damp. These characteristics lead to the possibility that fast-mode
waves transport energy from magnetically closed coronal regions into
coronal holes, that they are refracted into the central regions of
coronal holes, and that they deposit most of their energy in the
region of supersonic flow of high-speed solar wind streams emanating
from coronal holes. To investigate whether this possibility might be
realized and fast-mode waves might play a significant role in driving
high-speed streams, a parameter study is carried out to examine the
propagation and damping of fast-mode waves in various coronal hole
models. This study indicates a broad range of coronal hole parameters
for which fast-mode waves can play such a role and emphasizes the need
for an improved knowledge of large-scale coronal magnetic structure,
which is required before any firm conclusions can be drawn.
Title: Impulsive Phenomena in a Small Active Region
Authors: Withbroe, G. L.; Habbal, S. R.; Ronan, R.
Bibcode: 1984BAAS...16R.528W
Altcode:
No abstract at ADS
Title: Spatial and Temporal Variations of Solar Coronal Loops
Authors: Ronan, R. S.; Habbal, S. R.; Withbroe, G. L.
Bibcode: 1984BAAS...16..529R
Altcode:
No abstract at ADS
Title: The Formation of a Standing Shock in a Polytropic Wind Model
Within 1-10 R5
Authors: Habbal, S. R.
Bibcode: 1984BAAS...16R.533H
Altcode:
No abstract at ADS
Title: A wind-type model for the generation of astrophysical jets
Authors: Ferrari, A.; Habbal, S. R.; Rosner, R.; Tsinganos, K.
Bibcode: 1984ApJ...277L..35F
Altcode:
Wind-type solutions are discussed for the generation of astrophysical
jets from active galactic nuclei and stellar sources such as
those associated with SS433 and protostellar objects. Acceleration,
collimation, and morphology are consistently interpreted in terms of
a flow starting from the galactic or stellar core inside the "throat"
of a thick accretion disk.
Title: Temporal evolution of the solar wind and the formation of a
standing shock
Authors: Habbal, Shadia Rifai; Rosner, Robert
Bibcode: 1984JGR....8910645H
Altcode: 1984JGR....8910645R
The temporal evolution of the solar wind from one steady state to
another is explored when momentum deposition produces multiple critical
points in the flow. We show that the wind always evolves in time to
a new steady state compatible with the solution of the steady state
equation of motion. However, for the same initial state and identical
asymptotic momentum deposition rate the temporal evolution pattern of
the wind depends on the detailed time history of momentum addition
and is therefore not unique. This feature plays an important role
in the particular case when multiple (three in this study) steady
states exist for identical boundary conditions; each one of these
solutions is thus shown to be physically accessible. The details
of the temporal evolution pattern of the wind reveal the formation
of a shock discontinuity whenever the flow becomes supersonic at a
critical point upstream from the initial critical point. If the flow
remains supersonic at that inner critical point, the shock can become
a standing one, depending on the strength and the temporal history of
momentum addition. The results of this study indicate that the time
scale required for the solar wind to evolve between steady states
is of the order of 30-60 hours. Furthermore, the results also reveal
the interesting and novel phenomenon that a standing shock is likely
to develop in the inner solar wind flow within this time frame, in
particular, in coronal hole regions with rapidly diverging geometries.
Title: Multiple transonic solutions and a new class of shock
transitions in solar and stellar winds.
Authors: Habbal, S. R.; Tsinganos, K.; Rosner, R.
Bibcode: 1983NASCP.2280.213H
Altcode: 1983sowi.conf..213H
The steady isothermal solar wind equations are shown to admit,
under certain circumstances, mutliple transonic solutions when,
for example, momentum deposition gives rise to multiplee critical
points in the flow. These multiple solutions consist of a continuous
solution and solutions which involve shock transitions between critical
solutions. The ambiguity arising from the multiplicity of the solutions
can be resolved by following the time evolution of a wind profile
with one critical point. Results of the numerical integration of the
time-dependent equations with momentum addition show that each of these
multiple solutions is physically accessible and depends on the rate
of change of momentum deposition. These results suggest that standing
shocks are likely to be present in the inner solar wind flow.
Title: Formation of standing shocks in stellar winds and related
astrophysical flows.
Authors: Tsinganos, K.; Habbal, S. R.; Rosner, R.
Bibcode: 1983NASCP.2280.289T
Altcode: 1983sowi.conf..289T
Stellar winds and other analogous astrophysical flows can be described,
to lowest order, by the familiar one dimensional hydrodynamic equations
which, being nonlinear, admit in some instances discontinuous as
well as continuous transonic solutions for identical inner boundary
conditions. The characteristics of the time dependent differential
equations of motion are described to show how a perturbation changes
profile in time and, under well defined conditions, develops into a
stationary shock discontinuity. The formation of standing shocks in
wind type astrophysical flows depends on the fulfillment of appropriate
necessary conditions, which are determined by the conservation of mass,
momentum and energy across the discontinuity, and certain sufficient
conditions, which are determined by the flow's history.
Title: Multiple transonic solutions with a new class of shock
transitions in steady isothermal solar and stellar winds
Authors: Habbal, S. R.; Tsinganos, K.
Bibcode: 1983JGR....88.1965H
Altcode:
A new class of shock transitions are shown to arise in the transonic
solutions of the steady isothermal solar wind equations when, for
example, momentum deposition gives rise to multiple critical points
in the flow. These shock transitions between critical solutions occur
for a certain range of the parameters characterizing the momentum
deposition function. In the presence of such shock transitions, the
isothermal wind equations admit multiple transonic solutions, namely
a continuous solution passing through an inner critical point and
solutions involving a shock transition between critical solutions. These
multiple transonic solutions have the same flow speed at the base
but different supersonic flow speeds at infinity. An additional
interesting feature of the isothermal equations is the equivalence
of nonradial flow tube divergence and momentum addition in giving
rise to multiple critical points and hence to multiple transonic
solutions with shock transitions. The physical relevance of these
properties for astrophysical systems such as the inner solar wind,
flows in extragalactic jets and accretion discs are discussed.
Title: Rapid magnetic energy release, its possible role in coronal
heating and solar wind acceleration
Authors: Withbroe, G. L.; Habbal, S. R.
Bibcode: 1983sao..reptR....W
Altcode:
Studies of the EUV emission from coronal bright points, active
regions and apicules suggest that stochastic mechanisms may plan an
important role in heating the solar atmosphere at chromospheric and
coronal levels. In small magnetic bipolar regions (spatial extent
< 1') the observed EUV variations suggest that impulsive heating
at chromospheric and coronal levels appears to be very important,
possibly the dominant form of heating. The mechanism most likely
involves rapid release of magnetic energy, possibly associated with the
emergence of magnetic flux from lower levels into the chromosphere
and corona. In larger scale (> 1') magnetic bipolar regions,
there is evidence for both quasi-steady and impulsive heating,
with quasi-steady heating dominating. This heating could be caused
by either a mechanism such as steady-state current dissipation, or
by a stochastic process whose integrated effect (resulting from the
smoothing caused by finite radiative and conductive cooling times)
yields a nearly constant radiative output. The widespread variability of
the emission in spectral lines formed at transition region temperatures
(100000 < T < 1000000 K) provides evidence that impulsive energy
releases are a common, nearly continuous phenomenon in bipolar magnetic
regions. However, at the present time we do not know what fraction of
the total energy deposition in the atmosphere (chromosphere and low
corona) originates in impulsive phenomena.
Title: Time Evolution of the Solar Wind Flow with Momentum Addition
and the Formation of Standing Shocks
Authors: Habbal, S. R.; Tsinganos, K.; Rosner, R.
Bibcode: 1982BAAS...14R.939H
Altcode:
No abstract at ADS
Title: A New Class of Standing Shocks in Astrophysical Jets and
Accretion Flows
Authors: Tsinganos, K.; Habbal, S.; Rosner, R.
Bibcode: 1982BAAS...14..871T
Altcode:
No abstract at ADS
Title: Stellar Winds with Multiple Critical Points and Shock
Transitions
Authors: Habbal, S. R.; Tsinganos, K. C.
Bibcode: 1982BAAS...14Q.608H
Altcode:
No abstract at ADS
Title: Electron heating by fast mode magnetohydrodynamic waves in
the solar wind emanating from coronal holes
Authors: Habbal, S. R.; Leer, E.
Bibcode: 1982ApJ...253..318H
Altcode:
It is shown that fast mode magnetohydrodynamic waves, propagating
outwards from the sun in coronal hole regions, will dissipate primarily
through collisionless interaction with electrons rather than with
protons. This dissipation can lead to higher electron than proton
temperatures in the accelerating region of the solar wind, provided
the waves carry a sufficiently large energy flux.
Title: Spatial and Temporal Variations of EUV Coronal Bright Points
Authors: Habbal, S. R.; Withbroe, G. L.
Bibcode: 1981SoPh...69...77H
Altcode:
This paper reports results of an analysis of Skylab observations
of coronal bright points made in EUV spectral lines formed in the
chromosphere, chromospheric-coronal transition region and corona. The
most important result is that the observed bright points exhibited
large variations in EUV emission over time scales as short as 5.5 min,
the temporal resolution of the data. In most cases strong enhancements
in the coronal line were accompanied by strong enhancements in the
chromospheric and transition region lines. The intensity variations
appear to take place within substructures of the bright points, which
most likely consist of miniature loops evolving on time scales of a few
minutes. Coronal cooling times derived from the data are consistent with
an intermittent, impulsive coronal heating mechanism for bright points.
Title: Heating of Coronal Loops by Fast-Mode Magnetohydrodynamic Waves
Authors: Habbal, Shadia Rifai; Leer, Egil; Holzer, Thomas E.
Bibcode: 1979SoPh...64..287H
Altcode:
A possible mechanism for the formation and heating of coronal loops
through the propagation and damping of fast mode waves is proposed
and studied in detail. Loop-like field structures are represented by
a dipole field with the point dipole at a given distance below the
solar surface. The density of the medium is determined by hydrostatic
equilibrium along the field lines in an isothermal atmosphere. The
fast mode waves propagating outward from the coronal base are refracted
into regions with a low Alfvén speed and suffer collisionless damping
when the gas pressure becomes comparable to the magnetic pressure. The
propagation and damping of these waves are studied for three different
cases: a uniform density at the coronal base, a density depletion
within a given flux tube, and a density enhancement within a given flux
tube. The fast mode waves are found to be important in the formation
and heating of the loops if the wave energy flux density is of the order
105 ergs cm-2 s-1 at the coronal base.
Title: Thermal instabilities in magnetically confined plasmas -
Solar coronal loops
Authors: Habbal, S. R.; Rosner, R.
Bibcode: 1979ApJ...234.1113H
Altcode:
The thermal stability of confined solar coronal structures ('loops') is
investigated, following both normal mode and a new, global instability
analysis. It is demonstrated that: (1) normal mode analysis shows
modes with size scales comparable to that of loops to be unstable,
but to be strongly affected by the loop boundary conditions; (2) a
global analysis, based upon variation of the total loop energy losses
and gains, yields loop stability conditions for global modes dependent
upon the coronal loop heating process, with magnetically coupled heating
processes giving marginal stability. The connection between the present
analysis and the minimum flux corona of Hearn is also discussed.
Title: Plan MHD flows in a hyperbolic magnetic field: implications
for the problem of magnetic field line reconnexion
Authors: Habbal, S. R.; Tuan, T. -F.
Bibcode: 1979JPlPh..21...85H
Altcode:
This paper examines the nature of plane, steady, incompressible MHD
flow in a purely hyperbolic magnetic field. It is shown that in such
a magnetic field the MHD equations can yield exact analytic solutions
for the plasma flow. The flow has the following properties. In the far
region where the conductivity is assumed to be sufficiently high so
that the plasma is effectively ‘ frozen ’ to the magnetic field,
the flow pattern is radial. The plasma motion is directed towards the
neutral line in the incident ‘ sectors ’ and away from it in the
outgoing ‘ sectors ’ with a consequent reversal in direction across
the magnetic separatrices where the solution becomes singular. The
plasma pressure and density in this flow are calculated and it is
shown that the latter remains constant along a streamline. It is
further shown that a uniform finite conductivity is not compatible
with a stagnation point at the magnetic null point. However, for a
parabolic increase of conductivity with increasing distance from that
point, plasma flow with uniform density along hyperbolic streamlines
is shown to be possible. The relevance of these flows to the magnetic
field merging problem is discussed.
Title: Heating of Coronal Loops by Fast Mode Mhd-Waves
Authors: Habbal, S. R.; Holzer, T. E.; Leer, E.
Bibcode: 1979phsp.coll..228H
Altcode: 1979phsp.conf..228H; 1979IAUCo..44..228H
This paper discusses the formation and heating of solar coronal loops
by fast mode MHD waves which, unlike Alfven waves, have an acoustic
component. These fast mode waves can carry a substantial energy flux
along the wave normal only in coronal regions with a strong magnetic
field. The propagation and damping of these waves in a two dimensional
solar atmosphere is considered. It is noted that the damping occurs
mainly in the region where beta = 2nkT/(B-squared/8pi) is larger than
0.05, and that most of the energy is transferred to the plasma in the
region where beta approximately equals 0.2. In this case the plasma
in the flux tube with a height approximately equal to 0.2R is heated
most, and the wave energy flux from the base deposits more energy
in this tube than is lost by radiation and heat conduction at the
footpoints. Therefore, density and temperature perturbations across the
field lines will develop and 'loops' may be formed. Heating mechanisms
of the surrounding plasma in both large density and low density loops
are then described.