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Author name code: patsourakos
ADS astronomy entries on 2022-09-14
author:"Patsourakos, Spiros"
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Title: The Low-Corona Evolution of Coronal Mass Ejections: Solar
Truth and Implications for Stellar Coronal Mass Ejections
Authors: Patsourakos, Spiros; Vourlidas, Angelos; Balmaceda, Laura
2022cosp...44.1407P Altcode:
Once a Coronal Mass Ejection (CME) is underway, it sparks a variety
of phenomena in the low corona including dimmings, waves and
shocks. An important finding of multi-viewpoint and high-cadence
imaging observations of the initial stages of CMEs from STEREO and
SDO is that they evolve differently in the lateral compared to the
radial direction. The CME lateral expansion in the low corona is of
particular interest to solar-stellar studies because it occurs in the
region that dominates the emission in stellar observations, and triggers
wave and shock phenomena. With this presentation we will discuss: i)
basic observational aspects of the lateral expansion of CMEs in the
solar corona, and ii) how these may contribute to the hunt for stellar
CMEs. We will show how our understanding of the low lateral expansion
of CMEs in the solar corona may help into deciphering and eventually
modeling of the light-curves of dimmings presumably associated with
stellar CMEs.
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Title: The lower solar atmosphere inside and outside coronal holes
and the base of the Solar Wind
Authors: Gontikakis, Costis; Patsourakos, Spiros; Tsinganos, Kanaris;
Koletti, Myrto
2022cosp...44.1336G Altcode:
In this review, we will present the crucial observations that gave rise
to current concepts on the formation of the solar wind, low in the solar
atmosphere. We will discuss the differences between the fast solar wind
originating from coronal holes and the slow solar wind emanating around
solar streamers and closed solar magnetic structures. Observations
from remote spectrographs that may constitute critical tests for the
different solar wind acceleration models will be emphasized. Phenomena
such as plumes and jets will also be examined. Finally, we will
introduce the most recent SolO and PSP results on the origins and
early stages of the solar wind.
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Title: The impact of virtual mass and magnetic erosion on the
propagation of fast ICMEs
Authors: Stamkos, Sotiris; Patsourakos, Spiros; Daglis, Ioannis A.;
Vourlidas, Angelos
2022cosp...44.1406S Altcode:
In order to enhance our understanding of the dynamic interactions of
Interplanetary Coronal Mass Ejections (ICMEs) with the solar wind
and interplanetary magnetic field, we investigate the effect of
magnetic erosion on the well-known aerodynamic drag force acting on
ICMEs. In particular, we generate empirical equations for the basic
parameters of an ICME assuming a cylindrical morphology. Furthermore,
we examine the impact of the virtual mass on the equation of motion
by essentially studying a variable mass system. We quantify the
effect of the reconnection process, which erodes part of the ICME's
magnetic flux and outer-shell mass, on the drag acting on ICMEs and,
eventually, we determine its impact on the time and speed of arrival
of those transients at 1 AU.
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Title: Assessment of near sun axial CME magnetic field.
Authors: Koya, Shifana; Patsourakos, Spiros; Georgoulis, Manolis K.;
Nindos, Alexander
2022cosp...44.1405K Altcode:
The magnetic origin and the role of magnetic helicity in solar eruptions
are known for several years. Here we present a survey of near-Sun
axial coronal mass ejection (CME) magnetic fields that are obtained
by applying a semi-analytical method that calculates the magnetic
helicity of the source active region relying primarily on photospheric
vector magnetograms. The geometrical parameters of CMEs observed by
STEREO/SECCHI and SOHO/LASCO are obtained by fitting the GCS magnetic
flux rope model. We use the estimated near-Sun CME magnetic fields to
infer ICME magnetic fields and to validate them with existing in-situ
magnetometer observation at L1. We conclude that the proposed method,
including the proposed inferences from the survey, is useful for CME
magnetic field forecasting purposes, solar-stellar connection and
projecting towards potential properties of stellar CMEs.
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Title: When do solar erupting hot magnetic flux ropes form?
Authors: Nindos, Alexander; Zhang, Jie; Patsourakos, Spiros; Cheng,
Xin; Vourlidas, Angelos
2022cosp...44.2419N Altcode:
We investigate the formation times of eruptive magnetic flux ropes
relative to the onset of solar eruptions, which is important for
constraining models of coronal mass ejection (CME) initiation. We
inspected uninterrupted sequences of 131 A images that spanned more than
eight hours and were obtained by the Atmospheric Imaging Assembly on
board the Solar Dynamics Observatory to identify the formation times
of hot flux ropes that erupted in CMEs from locations close to the
limb. The appearance of the flux ropes as well as their evolution toward
eruptions were determined using morphological criteria. Two-thirds
(20/30) of the flux ropes were formed well before the onset of the
eruption (from 51 min to more than eight hours), and their formation
was associated with the occurrence of a confined flare. We also found
four events with preexisting hot flux ropes whose formations occurred
a matter of minutes (from three to 39) prior to the eruptions without
any association with distinct confined flare activity. Six flux ropes
were formed once the eruptions were underway. However, in three of
them, prominence material could be seen in 131 Å images, which may
indicate the presence of preexisting flux ropes that were not hot. The
formation patterns of the last three groups of hot flux ropes did not
show significant differences. For the whole population of events, the
mean and median values of the time difference between the onset of the
eruptive flare and the appearance of the hot flux rope were 151 and 98
min, respectively. Our results provide, on average, indirect support
for CME models that involve preexisting flux ropes; on the other hand,
for a third of the events, models in which the ejected flux rope is
formed during the eruption appear more appropriate.
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Title: Identifying the Terrestrial Exoplanets which Deserve More
Scrutiny for Atmosphere Viability: the mASC method
Authors: Samara, Evangelia; Patsourakos, Spiros; Georgoulis, Manolis K.
2022cosp...44.1395S Altcode:
We introduce a practical and physically intuitive method to assess
whether a given exoplanet is a viable candidate for the existence of
an atmosphere, thanks to an efficient magnetospheric shielding from
intense space weather activity from its host star. Our proposed mASC
(magnetic Atmosphere Sustainability Constraint) relies on a best-case
scenario for a dynamo-generated planetary magnetic field and subsequent
magnetic pressure, and a worst-case scenario for the magnetic pressure
of stellar CMEs. The method estimates a dimensionless ratio R whose
excursion from unity implies accordingly an "atmosphere likely" (R
< 1) or an "atmosphere unlikely" (R > 1) scenario. In this work,
we implement our mASC on six "famous" exoplanets whose discovery was
greeted with praise and hopes of habitability. These are Kepler-438b,
Proxima-Centauri b, and Trappist-1d, -1e, -1f, -1g. We conclude that
for none of them the existence of an atmosphere is likely while our
findings are robust for five out of six cases. We conclude that the
mASC ratio could help set observing priorities and suggest which
exoplanets deserve further scrutiny, possibly toward the ultimate
search of potential biosignatures, among other objectives.
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Title: Investigating possible EUV precursors of major solar flares
Authors: AndrÉ-Hoffmann, Augustin; Patsourakos, Spiros; Georgoulis,
Manolis K.; Nindos, Alexander
2022cosp...44.2481A Altcode:
Large-scale solar eruptions that produce major flares and fast coronal
mass ejections are often associated with precursor activity that
may start several hours before the main event. Such activity may be
observed from the photosphere all the way to the transition region
and corona but it is not clear whether it plays an essential role in
the eruption initiation. To investigate this question we search for
precursor activity in Extreme Ultra-violet (EUV) images obtained by the
Atmospheric Imaging Assembly (AIA) instrument on board Solar Dynamics
Observatory (SDO) within a 24-hour window prior to large eruptive
events and investigate whether they contribute to the restructuring and
overall evolution of the magnetic field that leads to eruptions. We
cross-check our findings by performing the same search in relatively
quiet active regions. By comparing the results from the eruptive and
quiet active regions we attempt to identify possible signatures that
could be useful in both the short-term prediction of major flare events
and an enhanced physical understanding of the preflare phase.
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Title: First detection of metric emission from a solar surge
Authors: Alissandrakis, C. E.; Patsourakos, S.; Nindos, A.; Bouratzis,
C.; Hillaris, A.
2022A&A...662A..14A Altcode: 2022arXiv220301043A
We report the first detection of metric radio emission from a surge,
observed with the Nançay Radioheliograph (NRH), STEREO, and other
instruments. The emission was observed during the late phase of the
M9 complex event SOL2010-02-012T11:25:00, described in a previous
publication. It was associated with a secondary energy release,
also observed in STEREO 304 Å images, and there was no detectable
soft X-ray emission. The triangulation of the STEREO images allowed
for the identification of the surge with NRH sources near the central
meridian. The radio emission of the surge occurred in two phases and
consisted of two sources, one located near the base of the surge,
apparently at or near the site of energy release, and another in the
upper part of the surge; these were best visible in the frequency
range of 445.0 to about 300 MHz, whereas a spectral component of
a different nature was observed at lower frequencies. Sub-second
time variations were detected in both sources during both phases,
with a 0.2-0.3 s delay of the upper source with respect to the lower,
suggesting superluminal velocities. This effect can be explained if
the emission of the upper source was due to scattering of radiation
from the source at the base of the surge. In addition, the radio
emission showed signs of pulsations and spikes. We discuss possible
emission mechanisms for the slow time variability component of
the lower radio source. Gyrosynchrotron emission reproduced the
characteristics of the observed total intensity spectrum at the
start of the second phase of the event fairly well, but failed to
reproduce the high degree of the observed circular polarization or the
spectra at other instances. On the other hand, type IV-like plasma
emission from the fundamental could explain the high polarization
and the fine structure in the dynamic spectrum; moreover, it gives
projected radio source positions on the plane of the sky, as seen from
STEREO-A, near the base of the surge. Taking all the properties into
consideration, we suggest that type IV-like plasma emission with
a low-intensity gyrosynchrotron component is the most plausible
mechanism. <P />Movie associated to Fig. A.2 is available at <A
href="https://www.aanda.org/10.1051/0004-6361/202243169/olm">https://www.aanda.org</A>
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Title: Earth-affecting solar transients: a review of progresses in
solar cycle 24
Authors: Zhang, Jie; Temmer, Manuela; Gopalswamy, Nat; Malandraki,
Olga; Nitta, Nariaki V.; Patsourakos, Spiros; Shen, Fang; Vršnak,
Bojan; Wang, Yuming; Webb, David; Desai, Mihir I.; Dissauer, Karin;
Dresing, Nina; Dumbović, Mateja; Feng, Xueshang; Heinemann, Stephan
G.; Laurenza, Monica; Lugaz, Noé; Zhuang, Bin
2021PEPS....8...56Z Altcode: 2020arXiv201206116Z
This review article summarizes the advancement in the studies of
Earth-affecting solar transients in the last decade that encompasses
most of solar cycle 24. It is a part of the effort of the International
Study of Earth-affecting Solar Transients (ISEST) project, sponsored
by the SCOSTEP/VarSITI program (2014-2018). The Sun-Earth is an
integrated physical system in which the space environment of the
Earth sustains continuous influence from mass, magnetic field, and
radiation energy output of the Sun in varying timescales from minutes to
millennium. This article addresses short timescale events, from minutes
to days that directly cause transient disturbances in the Earth's
space environment and generate intense adverse effects on advanced
technological systems of human society. Such transient events largely
fall into the following four types: (1) solar flares, (2) coronal mass
ejections (CMEs) including their interplanetary counterparts ICMEs,
(3) solar energetic particle (SEP) events, and (4) stream interaction
regions (SIRs) including corotating interaction regions (CIRs). In
the last decade, the unprecedented multi-viewpoint observations of
the Sun from space, enabled by STEREO Ahead/Behind spacecraft in
combination with a suite of observatories along the Sun-Earth lines,
have provided much more accurate and global measurements of the size,
speed, propagation direction, and morphology of CMEs in both 3D and over
a large volume in the heliosphere. Many CMEs, fast ones, in particular,
can be clearly characterized as a two-front (shock front plus ejecta
front) and three-part (bright ejecta front, dark cavity, and bright
core) structure. Drag-based kinematic models of CMEs are developed to
interpret CME propagation in the heliosphere and are applied to predict
their arrival times at 1 AU in an efficient manner. Several advanced
MHD models have been developed to simulate realistic CME events from
the initiation on the Sun until their arrival at 1 AU. Much progress
has been made on detailed kinematic and dynamic behaviors of CMEs,
including non-radial motion, rotation and deformation of CMEs, CME-CME
interaction, and stealth CMEs and problematic ICMEs. The knowledge
about SEPs has also been significantly improved. An outlook of how to
address critical issues related to Earth-affecting solar transients
concludes this article.
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Title: Which Terrestrial Exoplanets Deserve More Scrutiny for
Atmosphere Viability?
Authors: Samara, Evangelia; Patsourakos, Spiros; Georgoulis, Manolis
2021AGUFM.U44B..05S Altcode:
We introduce a practical and physically intuitive method to assess
whether a given exoplanet is a viable candidate for the existence of
an atmosphere thanks to an efficient magnetospheric shielding from
intense space weather activity originating from its host star. Our
proposed mASC (magnetic Atmosphere Sustainability Constraint) relies on
a best-case scenario for the dynamo-generated planetary magnetic field
and subsequent magnetic pressure, and a worst-case scenario for the
magnetic pressure of stellar CMEs. It provides a dimensionless ratio
R whose excursion from unity implies accordingly an atmosphere likely
(R < 1) or an atmosphere unlikely (R > 1) scenario. In this work,
we implement our mASC on six famous exoplanets whose discovery was
greeted with praise and hopes of habitability. These are Kepler-438b,
Proxima-Centauri b, and Trappist-1d, -1e, -1f, -1g. The results show
that for none of them the existence of an atmosphere is likely while
our findings are robust for five out of six cases. We conclude that
the mASC ratio could help set observing priorities and suggest which
exoplanets deserve further scrutiny, possibly toward the ultimate
search of potential biosignatures, among other objectives.
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Title: Multiwavelength observations of a metric type-II event
Authors: Alissandrakis, C. E.; Nindos, A.; Patsourakos, S.; Hillaris,
A.
2021A&A...654A.112A Altcode: 2021arXiv210802855A
We have studied a complex metric radio event that originated in a
compact flare, observed with the ARTEMIS-JLS radiospectrograph on
February 12, 2010. The event was associated with a surge observed at 195
and 304 Å and with a coronal mass ejection observed by instruments on
board STEREO A and B near the eastern and western limbs respectively. On
the disk the event was observed at ten frequencies by the Nançay
Radioheliograph (NRH), in Hα by the Catania observatory, in soft
X-rays by GOES SXI and Hinode XRT, and in hard X-rays by RHESSI. We
combined these data, together with MDI longitudinal magnetograms,
to get as complete a picture of the event as possible. Our emphasis
is on two type-II bursts that occurred near respective maxima in
the GOES light curves. The first, associated with the main peak
of the event, showed an impressive fundamental-harmonic structure,
while the emission of the second consisted of three well-separated
bands with superposed pulsations. Using positional information for the
type-IIs from the NRH and triangulation from STEREO A and B, we found
that the type-IIs were associated neither with the surge nor with the
disruption of a nearby streamer, but rather with an extreme ultraviolet
(EUV) wave probably initiated by the surge. The fundamental-harmonic
structure of the first type-II showed a band split corresponding to
a magnetic field strength of 18 G, a frequency ratio of 1.95 and a
delay of 0.23−0.65 s of the fundamental with respect to the harmonic;
moreover it became stationary shortly after its start and then drifted
again. The pulsations superposed on the second type-II were broadband
and had started before the burst. In addition, we detected another
pulsating source, also before the second type-II, polarized in the
opposite sense; the pulsations in the two sources were out of phase
and hence hardly detectable in the dynamic spectrum. The pulsations
had a measurable reverse frequency drift of about 2 s<SUP>−1</SUP>.
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Title: ALMA observations of the variability of the quiet Sun at
millimeter wavelengths
Authors: Nindos, A.; Patsourakos, S.; Alissandrakis, C. E.; Bastian,
T. S.
2021A&A...652A..92N Altcode: 2021arXiv210604220N
<BR /> Aims: We address the variability of the quiet solar chromosphere
at 1.26 mm and 3 mm with a focus on the study of spatially resolved
oscillations and transient brightenings, which are small, weak
events of energy release. Both phenomena may have a bearing on the
heating of the chromosphere. <BR /> Methods: We used Atacama Large
Millimeter/submillimeter Array (ALMA) observations of the quiet Sun
at 1.26 mm and 3 mm. The spatial and temporal resolution of the data
were 1 − 2″ and 1 s, respectively. The concatenation of light
curves from different scans yielded a frequency resolution in spectral
power of 0.5−0.6 mHz. At 1.26 mm, in addition to power spectra of
the original data, we degraded the images to the spatial resolution
of the 3 mm images and used fields of view that were equal in area
for both data sets. The detection of transient brightenings was made
after the effect of oscillations was removed. <BR /> Results: At both
frequencies, we detected p-mode oscillations in the range 3.6−4.4
mHz. The corrections for spatial resolution and field of view at 1.26 mm
decreased the root mean square (rms) of the oscillations by a factor of
1.6 and 1.1, respectively. In the corrected data sets, the oscillations
at 1.26 mm and 3 mm showed brightness temperature fluctuations of
∼1.7 − 1.8% with respect to the average quiet Sun, corresponding to
137 and 107 K, respectively. We detected 77 transient brightenings at
1.26 mm and 115 at 3 mm. Although their majority occurred in the cell
interior, the occurrence rate per unit area of the 1.26 mm events was
higher than that of the 3 mm events; this conclusion does not change
if we take into account differences in spatial resolution and noise
levels. The energy associated with the transient brightenings ranged
from 1.8 × 10<SUP>23</SUP> to 1.1 × 10<SUP>26</SUP> erg and from 7.2
× 10<SUP>23</SUP> to 1.7 × 10<SUP>26</SUP> erg for the 1.26 mm and
3 mm events, respectively. The corresponding power-law indices of the
energy distribution were 1.64 and 1.73. We also found that ALMA bright
network structures corresponded to dark mottles or spicules that can be
seen in broadband Hα images from the GONG network. <BR /> Conclusions:
The fluctuations associated with the p-mode oscillations represent
a fraction of 0.55−0.68 of the full power spectrum. Their energy
density at 1.26 mm is 3 × 10<SUP>−2</SUP> erg cm<SUP>−3</SUP>. The
computed low-end energy of the 1.26 mm transient brightenings is among
the smallest ever reported, irrespective of the wavelength of the
observation. Although the occurrence rate per unit area of the 1.26
mm transient brightenings was higher than that of the 3 mm events,
their power per unit area is smaller likely due to the detection of
many weak 1.26 mm events.
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Title: Tracking solar wind flows from rapidly varying viewpoints by
the Wide-field Imager for Parker Solar Probe
Authors: Nindos, A.; Patsourakos, S.; Vourlidas, A.; Liewer, P. C.;
Penteado, P.; Hall, J. R.
2021A&A...650A..30N Altcode: 2020arXiv201013140N
<BR /> Aims: Our goal is to develop methodologies to seamlessly track
transient solar wind flows viewed by coronagraphs or heliospheric
imagers from rapidly varying viewpoints. <BR /> Methods: We
constructed maps of intensity versus time and elongation (J-maps)
from Parker Solar Probe (PSP) Wide-field Imager (WISPR) observations
during the fourth encounter of PSP. From the J-map, we built an
intensity on impact-radius-on-Thomson-surface map (R-map). Finally,
we constructed a latitudinal intensity versus time map (Lat-map). Our
methodology satisfactorily addresses the challenges associated with
the construction of such maps from data taken from rapidly varying
viewpoint observations. <BR /> Results: Our WISPR J-map exhibits
several tracks, corresponding to transient solar wind flows ranging
from a coronal mass ejection down to streamer blobs. The latter
occurrence rate is about 4-5 per day, which is similar to the
occurrence rate in a J-map made from ~1 AU data obtained with the
Heliospheric Imager-1 (HI-1) on board the Solar Terrestrial Relations
Observatory Ahead spacecraft (STEREO-A). STEREO-A was radially aligned
with PSP during the study period. The WISPR J-map tracks correspond
to angular speeds of 2.28 ± 0.7°/h (2.49 ± 0.95°/h), for linear
(quadratic) time-elongation fittings, and radial speeds of about
150-300 km s<SUP>−1</SUP>. The analysis of the Lat-map reveals
a bifurcating streamer, which implies that PSP was flying through
a slightly folded streamer during perihelion. <BR /> Conclusions:
We developed a framework to systematically capture and characterize
transient solar wind flows from space platforms with rapidly varying
vantage points. The methodology can be applied to PSP WISPR observations
as well as to upcoming observations from instruments on board the Solar
Orbiter mission. <P />Movie associated to Fig. 8 is available at <A
href="https://www.aanda.org/10.1051/0004-6361/202039414/olm">https://www.aanda.org</A>
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Title: Relative field line helicity of a large eruptive solar
active region
Authors: Moraitis, K.; Patsourakos, S.; Nindos, A.
2021A&A...649A.107M Altcode: 2021arXiv210303643M
Context. Magnetic helicity is a physical quantity of great importance
in the study of astrophysical and natural plasmas. Although a density
for helicity cannot be defined, a good proxy for this quantity is field
line helicity. The appropriate quantity for use in solar conditions
is relative field line helicity (RFLH). <BR /> Aims: This work aims
to study in detail the behaviour of RFLH, for the first time, in a
solar active region (AR). <BR /> Methods: The target AR is the large,
eruptive AR 11158. In order to compute RFLH and all other quantities
of interest, we used a non-linear force-free reconstruction of the AR
coronal magnetic field of excellent quality. <BR /> Results: We find
that the photospheric morphology of RFLH is very different than that
of the magnetic field or electrical current, and this morphology is
not sensitive to the chosen gauge in the computation of RFLH. The
value of helicity experiences a large decrease, that is ∼25% of
its pre-flare value, during an X-class flare of the AR; this change
is also depicted in the photospheric morphology of RFLH. Moreover,
the area of this change coincides with the area that encompasses the
flux rope, which is the magnetic structure that later erupted. <BR />
Conclusions: The use of RFLH can provide important information about
the value and location of the magnetic helicity expelled from the
solar atmosphere during eruptive events.
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Title: A Readily Implemented Atmosphere Sustainability Constraint
for Terrestrial Exoplanets Orbiting Magnetically Active Stars
Authors: Samara, Evangelia; Patsourakos, Spiros; Georgoulis, Manolis K.
2021ApJ...909L..12S Altcode: 2021arXiv210207837S
With more than 4300 confirmed exoplanets and counting, the next
milestone in exoplanet research is to determine which of these
newly found worlds could harbor life. Coronal mass ejections (CMEs),
spawned by magnetically active, superflare-triggering dwarf stars,
pose a direct threat to the habitability of terrestrial exoplanets, as
they can deprive them of their atmospheres. Here we develop a readily
implementable atmosphere sustainability constraint for terrestrial
exoplanets orbiting active dwarfs, relying on the magnetospheric
compression caused by CME impacts. Our constraint focuses on an
understanding of CMEs propagation in our own Sun-heliosphere system
that, applied to a given exoplanet requires as key input the observed
bolometric energy of flares emitted by its host star. Application of our
constraint to six famous exoplanets, Kepler-438b, Proxima Centauri b,
and Trappist-1d, -1e, -1f, and -1g, within or in the immediate proximity
of their stellar host's habitable zones showed that only for Kepler-438b
might atmospheric sustainability against stellar CMEs be likely. This
seems to align with some recent studies that, however, may require far
more demanding computational resources and observational inputs. Our
physically intuitive constraint can be readily and en masse applied, as
is or generalized, to large-scale exoplanet surveys to detect planets
that warrant further scrutiny for atmospheres and, perhaps, possible
biosignatures at higher priority by current and future instrumentation.
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Title: Properties Determining Eruption Initiation and
Planeto-Effectiveness of Eruptive Transients in Magnetically Active
Stars
Authors: Georgoulis, Manolis K.; Patsourakos, Spiros; Zhang, Hongqi;
Nindos, Alexander; Samara, Evangelia; Sadykov, Viacheslav M.
2021cosp...43E.993G Altcode:
We present a combined theoretical and data analysis approach to,
first, understand why magnetic eruptions and corresponding ejecta are
triggered in strong-field regions of the Sun and magnetically active
stars and, second, assess the key physical parameters responsible for
the planeto-effectiveness of these eruptions, both on Earth and in
other (exo-)planets. This approach converges on one physical parameter
besides magnetic energy, at least for stellar coronae of high magnetic
Reynolds numbers allowing this parameter to be conserved even under
confined energy release: magnetic helicity. Helicity, via the magnetic
energy-helicity diagram, should be treated equally with magnetic
energy. Due to magnetic helicity accumulation in solar active regions
and its inverse cascading, solar - and stellar, correspondingly -
eruptions may become inevitable after a certain 'point-of-no-return'
is reached. We identify this critical instant as the time when
magnetic polarity inversion lines in active-region photospheres
accumulate fluxes that generate fields stronger than local equipartition
values. Furthermore, using the conserved helicity budgets we abstractly
model post-eruption flux ropes and their transit through astrospheres,
reaching exoplanets and compressing their magnetospheres via magnetic
pressure effects. A rudimentary validation between the near-Sun and
L1 axial magnetic field values of these data-constrained flux ropes is
encouraging and allows us to further constrain scaling laws appropriate
for the astrospheric transit of these ropes. Importantly, we also find
that exoplanets orbiting magnetically active dwarf stars at orbital
radii that are fractions of an astronomical unit seem to be strong
contenders for eruption-driven atmospheric erosion that may gradually
even deprive them from their atmospheres. Some famous exoplanet cases
are examined under this prism. Future improvements are expected by
widely anticipated space- (Parker Solar Probe and Solar Orbiter)
and ground-based (Daniel K. Inouye Solar Telescope) observations.
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Title: Investigating the circumsolar wind with Parker Solar Probe
near-imaging and in-situ high cadence observations
Authors: Patsourakos, Spiros; Liewer, Paulett; Stenborg, Guillermo;
Howard, Russell; Hess, Phillip; Stevens, Michael; Vourlidas, Angelos;
Kasper, Justin; Nindos, Alexander; Penteado, Paulo; Korreck, Kelly;
Case, Anthony
2021cosp...43E.940P Altcode:
The proposition of the existence of the solar wind and its subsequent
discovery were major milestones at the dawn of the Space Age. Since
then, the solar wind has been extensively observed by in-situ
instruments at various locations in the inner and outer heliosphere
but mainly at 1 AU, and by remote sensing instruments at 1 AU. Despite
significant progress in the characterization and understanding of
the solar wind, important questions about the nature of the solar
wind remain unsettled. These questions include the nature of the
launch and acceleration of the solar wind and whether it is steady,
quasi-steady, periodic or intermittent. The recently launched Parker
Solar Probe (PSP) mission, which has been already plunged several times
in the solar corona, is ideally suited to shed more light into these
lingering questions. We present a coordinated analysis of up-close
and high-cadence imaging observations of the solar wind taken by WISPR
and of in-situ solar-wind observations taken inside the solar corona
by SWEAP during the first solar encounters of PSP. A discussion of
instrumental and orbital aspects of the WISPR observations pertinent to
our analysis is also included. Imaging data of the solar wind from ~
1 AU by COR2 on STEREO-A spacecraft is also analyzed. We submit the
time-series of the imaging and in-situ solar wind data to an array of
methods aiming to map their properties. We conclude with a discussion
of future PSP (WISPR and SWEAP) and Solar Orbiter (SoloHI) observing
and analysis strategies pertinent to our science questions.
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Title: Lower atmospheric consequences of Coronal Mass Ejections:
waves, shocks and dimmings
Authors: Patsourakos, Spiros
2021cosp...43E1735P Altcode:
Coronal Mass Ejections (CMEs) is a multi-facet phenomenon significantly
perturbing and interacting with the solar, heliospheric and geospace
environments. As far as the CME impact on the solar atmosphere
is concerned, CMEs are intimately linked with a diverse array of
large-scale and multi-wavelength phenomena including chromospheric
and coronal waves, shocks and coronal dimmings. Characterizing and
understanding these phenomena has important implications for not only
CME physics, but also for coronal physics. We hereby supply a discussion
of the state-of-the art regarding the atmospheric consequences of
CMEs as resulting from observations of chromospheric and coronal
waves and shocks and coronal dimmings. We will cover topics including
their physical properties, their connection with CME expansion and
evolution in the low solar atmosphere, their association with particle
acceleration in the low corona, their use as a diagnostic probe of the
properties of the ambient solar atmosphere, and their potential use
for space-weather applications. Moving to stellar contexts, we discuss
recent work on how coronal dimmings in active dwarfs may be be used
in the detection of stellar CMEs. We finally close with a discussion
of new areas in the research of the solar consequences of CMEs that
could be possible with new instrumentation coming recently on-line
including SolO and DKIST.
---------------------------------------------------------
Title: Decoding the Pre-Eruptive Magnetic Field Configurations of
Coronal Mass Ejections
Authors: Patsourakos, S.; Vourlidas, A.; Török, T.; Kliem, B.;
Antiochos, S. K.; Archontis, V.; Aulanier, G.; Cheng, X.; Chintzoglou,
G.; Georgoulis, M. K.; Green, L. M.; Leake, J. E.; Moore, R.; Nindos,
A.; Syntelis, P.; Yardley, S. L.; Yurchyshyn, V.; Zhang, J.
2020SSRv..216..131P Altcode: 2020arXiv201010186P
A clear understanding of the nature of the pre-eruptive magnetic
field configurations of Coronal Mass Ejections (CMEs) is required
for understanding and eventually predicting solar eruptions. Only
two, but seemingly disparate, magnetic configurations are considered
viable; namely, sheared magnetic arcades (SMA) and magnetic flux ropes
(MFR). They can form via three physical mechanisms (flux emergence,
flux cancellation, helicity condensation). Whether the CME culprit
is an SMA or an MFR, however, has been strongly debated for thirty
years. We formed an International Space Science Institute (ISSI) team to
address and resolve this issue and report the outcome here. We review
the status of the field across modeling and observations, identify
the open and closed issues, compile lists of SMA and MFR observables
to be tested against observations and outline research activities
to close the gaps in our current understanding. We propose that the
combination of multi-viewpoint multi-thermal coronal observations
and multi-height vector magnetic field measurements is the optimal
approach for resolving the issue conclusively. We demonstrate the
approach using MHD simulations and synthetic coronal images.
---------------------------------------------------------
Title: When do solar erupting hot magnetic flux ropes form?
Authors: Nindos, A.; Patsourakos, S.; Vourlidas, A.; Cheng, X.;
Zhang, J.
2020A&A...642A.109N Altcode: 2020arXiv200804380N
<BR /> Aims: We investigate the formation times of eruptive magnetic
flux ropes relative to the onset of solar eruptions, which is
important for constraining models of coronal mass ejection (CME)
initiation. <BR /> Methods: We inspected uninterrupted sequences of
131 Å images that spanned more than eight hours and were obtained
by the Atmospheric Imaging Assembly on board the Solar Dynamics
Observatory to identify the formation times of hot flux ropes that
erupted in CMEs from locations close to the limb. The appearance
of the flux ropes as well as their evolution toward eruptions were
determined using morphological criteria. <BR /> Results: Two-thirds
(20/30) of the flux ropes were formed well before the onset of the
eruption (from 51 min to more than eight hours), and their formation
was associated with the occurrence of a confined flare. We also found
four events with preexisting hot flux ropes whose formations occurred
a matter of minutes (from three to 39) prior to the eruptions without
any association with distinct confined flare activity. Six flux ropes
were formed once the eruptions were underway. However, in three of
them, prominence material could be seen in 131 Å images, which may
indicate the presence of preexisting flux ropes that were not hot. The
formation patterns of the last three groups of hot flux ropes did not
show significant differences. For the whole population of events, the
mean and median values of the time difference between the onset of the
eruptive flare and the appearance of the hot flux rope were 151 and 98
min, respectively. <BR /> Conclusions: Our results provide, on average,
indirect support for CME models that involve preexisting flux ropes; on
the other hand, for a third of the events, models in which the ejected
flux rope is formed during the eruption appear more appropriate. <P
/>Movies attached to Figs. 2, 5, 8, and 10 are available at <A
href="https://www.aanda.org/10.1051/0004-6361/202038832/olm">http://www.aanda.org</A>
---------------------------------------------------------
Title: The Solar Orbiter Science Activity Plan. Translating solar
and heliospheric physics questions into action
Authors: Zouganelis, I.; De Groof, A.; Walsh, A. P.; Williams, D. R.;
Müller, D.; St Cyr, O. C.; Auchère, F.; Berghmans, D.; Fludra,
A.; Horbury, T. S.; Howard, R. A.; Krucker, S.; Maksimovic, M.;
Owen, C. J.; Rodríguez-Pacheco, J.; Romoli, M.; Solanki, S. K.;
Watson, C.; Sanchez, L.; Lefort, J.; Osuna, P.; Gilbert, H. R.;
Nieves-Chinchilla, T.; Abbo, L.; Alexandrova, O.; Anastasiadis, A.;
Andretta, V.; Antonucci, E.; Appourchaux, T.; Aran, A.; Arge, C. N.;
Aulanier, G.; Baker, D.; Bale, S. D.; Battaglia, M.; Bellot Rubio,
L.; Bemporad, A.; Berthomier, M.; Bocchialini, K.; Bonnin, X.; Brun,
A. S.; Bruno, R.; Buchlin, E.; Büchner, J.; Bucik, R.; Carcaboso,
F.; Carr, R.; Carrasco-Blázquez, I.; Cecconi, B.; Cernuda Cangas, I.;
Chen, C. H. K.; Chitta, L. P.; Chust, T.; Dalmasse, K.; D'Amicis, R.;
Da Deppo, V.; De Marco, R.; Dolei, S.; Dolla, L.; Dudok de Wit, T.;
van Driel-Gesztelyi, L.; Eastwood, J. P.; Espinosa Lara, F.; Etesi,
L.; Fedorov, A.; Félix-Redondo, F.; Fineschi, S.; Fleck, B.; Fontaine,
D.; Fox, N. J.; Gandorfer, A.; Génot, V.; Georgoulis, M. K.; Gissot,
S.; Giunta, A.; Gizon, L.; Gómez-Herrero, R.; Gontikakis, C.; Graham,
G.; Green, L.; Grundy, T.; Haberreiter, M.; Harra, L. K.; Hassler,
D. M.; Hirzberger, J.; Ho, G. C.; Hurford, G.; Innes, D.; Issautier,
K.; James, A. W.; Janitzek, N.; Janvier, M.; Jeffrey, N.; Jenkins,
J.; Khotyaintsev, Y.; Klein, K. -L.; Kontar, E. P.; Kontogiannis,
I.; Krafft, C.; Krasnoselskikh, V.; Kretzschmar, M.; Labrosse, N.;
Lagg, A.; Landini, F.; Lavraud, B.; Leon, I.; Lepri, S. T.; Lewis,
G. R.; Liewer, P.; Linker, J.; Livi, S.; Long, D. M.; Louarn, P.;
Malandraki, O.; Maloney, S.; Martinez-Pillet, V.; Martinovic, M.;
Masson, A.; Matthews, S.; Matteini, L.; Meyer-Vernet, N.; Moraitis,
K.; Morton, R. J.; Musset, S.; Nicolaou, G.; Nindos, A.; O'Brien,
H.; Orozco Suarez, D.; Owens, M.; Pancrazzi, M.; Papaioannou, A.;
Parenti, S.; Pariat, E.; Patsourakos, S.; Perrone, D.; Peter, H.;
Pinto, R. F.; Plainaki, C.; Plettemeier, D.; Plunkett, S. P.; Raines,
J. M.; Raouafi, N.; Reid, H.; Retino, A.; Rezeau, L.; Rochus, P.;
Rodriguez, L.; Rodriguez-Garcia, L.; Roth, M.; Rouillard, A. P.;
Sahraoui, F.; Sasso, C.; Schou, J.; Schühle, U.; Sorriso-Valvo, L.;
Soucek, J.; Spadaro, D.; Stangalini, M.; Stansby, D.; Steller, M.;
Strugarek, A.; Štverák, Š.; Susino, R.; Telloni, D.; Terasa, C.;
Teriaca, L.; Toledo-Redondo, S.; del Toro Iniesta, J. C.; Tsiropoula,
G.; Tsounis, A.; Tziotziou, K.; Valentini, F.; Vaivads, A.; Vecchio,
A.; Velli, M.; Verbeeck, C.; Verdini, A.; Verscharen, D.; Vilmer, N.;
Vourlidas, A.; Wicks, R.; Wimmer-Schweingruber, R. F.; Wiegelmann,
T.; Young, P. R.; Zhukov, A. N.
2020A&A...642A...3Z Altcode: 2020arXiv200910772Z
Solar Orbiter is the first space mission observing the solar plasma
both in situ and remotely, from a close distance, in and out of the
ecliptic. The ultimate goal is to understand how the Sun produces
and controls the heliosphere, filling the Solar System and driving
the planetary environments. With six remote-sensing and four in-situ
instrument suites, the coordination and planning of the operations are
essential to address the following four top-level science questions:
(1) What drives the solar wind and where does the coronal magnetic field
originate?; (2) How do solar transients drive heliospheric variability?;
(3) How do solar eruptions produce energetic particle radiation that
fills the heliosphere?; (4) How does the solar dynamo work and drive
connections between the Sun and the heliosphere? Maximising the
mission's science return requires considering the characteristics
of each orbit, including the relative position of the spacecraft
to Earth (affecting downlink rates), trajectory events (such
as gravitational assist manoeuvres), and the phase of the solar
activity cycle. Furthermore, since each orbit's science telemetry
will be downloaded over the course of the following orbit, science
operations must be planned at mission level, rather than at the level
of individual orbits. It is important to explore the way in which those
science questions are translated into an actual plan of observations
that fits into the mission, thus ensuring that no opportunities are
missed. First, the overarching goals are broken down into specific,
answerable questions along with the required observations and the
so-called Science Activity Plan (SAP) is developed to achieve this. The
SAP groups objectives that require similar observations into Solar
Orbiter Observing Plans, resulting in a strategic, top-level view of
the optimal opportunities for science observations during the mission
lifetime. This allows for all four mission goals to be addressed. In
this paper, we introduce Solar Orbiter's SAP through a series of
examples and the strategy being followed.
---------------------------------------------------------
Title: The Solar Orbiter Heliospheric Imager (SoloHI)
Authors: Howard, R. A.; Vourlidas, A.; Colaninno, R. C.; Korendyke,
C. M.; Plunkett, S. P.; Carter, M. T.; Wang, D.; Rich, N.; Lynch,
S.; Thurn, A.; Socker, D. G.; Thernisien, A. F.; Chua, D.; Linton,
M. G.; Koss, S.; Tun-Beltran, S.; Dennison, H.; Stenborg, G.; McMullin,
D. R.; Hunt, T.; Baugh, R.; Clifford, G.; Keller, D.; Janesick, J. R.;
Tower, J.; Grygon, M.; Farkas, R.; Hagood, R.; Eisenhauer, K.; Uhl,
A.; Yerushalmi, S.; Smith, L.; Liewer, P. C.; Velli, M. C.; Linker,
J.; Bothmer, V.; Rochus, P.; Halain, J. -P.; Lamy, P. L.; Auchère,
F.; Harrison, R. A.; Rouillard, A.; Patsourakos, S.; St. Cyr, O. C.;
Gilbert, H.; Maldonado, H.; Mariano, C.; Cerullo, J.
2020A&A...642A..13H Altcode:
<BR /> Aims: We present the design and pre-launch performance of
the Solar Orbiter Heliospheric Imager (SoloHI) which is an instrument
prepared for inclusion in the ESA/NASA Solar Orbiter mission, currently
scheduled for launch in 2020. <BR /> Methods: The goal of this paper
is to provide details of the SoloHI instrument concept, design, and
pre-flight performance to give the potential user of the data a better
understanding of how the observations are collected and the sources
that contribute to the signal. <BR /> Results: The paper discusses
the science objectives, including the SoloHI-specific aspects, before
presenting the design concepts, which include the optics, mechanical,
thermal, electrical, and ground processing. Finally, a list of planned
data products is also presented. <BR /> Conclusions: The performance
measurements of the various instrument parameters meet or exceed the
requirements derived from the mission science objectives. SoloHI is
poised to take its place as a vital contributor to the science success
of the Solar Orbiter mission.
---------------------------------------------------------
Title: Modeling the quiet Sun cell and network emission with ALMA
Authors: Alissandrakis, C. E.; Nindos, A.; Bastian, T. S.; Patsourakos,
S.
2020A&A...640A..57A Altcode: 2020arXiv200609886A
Observations of the Sun at millimeter wavelengths with the Atacama
Large Millimeter/submillimeter Array (ALMA) offer a unique opportunity
to investigate the temperature structure of the solar chromosphere. In
this article we expand our previous work on modeling the chromospheric
temperature of the quiet Sun, by including measurements of the
brightness temperature in the network and cell interiors, from
high-resolution ALMA images at 3 mm (Band 3) and 1.26 mm (Band 6). We
also examine the absolute calibration of ALMA full-disk images. We
suggest that the brightness temperature at the center of the solar disk
in Band 6 is ∼440 K above the value recommended by White et al. (2017,
Sol. Phys., 292, 88). In addition, we give improved results for the
electron temperature variation of the average quiet Sun with optical
depth and the derived spectrum at the center of the disk. We found
that the electron temperature in the network is considerably lower
than predicted by model F of Fontenla et al. (1993, ApJ, 406, 319)
and that of the cell interior considerably higher than predicted by
model A. Depending on the network/cell segregation scheme, the electron
temperature difference between network and cell at τ = 1 (100 GHz)
ranges from ∼660 K to ∼1550 K, compared to ∼3280 K predicted
by the models; similarly, the electron temperature, T<SUB>e</SUB>
ratio ranges from ∼1.10 to 1.24, compared to ∼1.55 of the model
prediction. We also found that the network/cell T<SUB>e</SUB>(τ)
curves diverge as τ decreases, indicating an increase of contrast
with height and possibly a steeper temperature rise in the network
than in the cell interior.
---------------------------------------------------------
Title: Transient brightenings in the quiet Sun detected by ALMA at
3 mm
Authors: Nindos, A.; Alissandrakis, C. E.; Patsourakos, S.; Bastian,
T. S.
2020A&A...638A..62N Altcode: 2020arXiv200407591N
<BR /> Aims: We investigate transient brightenings, that is, weak,
small-scale episodes of energy release, in the quiet solar chromosphere;
these episodes can provide insights into the heating mechanism of the
outer layers of the solar atmosphere. <BR /> Methods: Using Atacama
Large Millimeter/submillimeter Array (ALMA) observations, we performed
the first systematic survey for quiet Sun transient brightenings at 3
mm. Our dataset included images of six 87″ × 87″ fields of view
of the quiet Sun obtained with angular resolution of a few arcsec at
a cadence of 2 s. The transient brightenings were detected as weak
enhancements above the average intensity after we removed the effect
of the p-mode oscillations. A similar analysis, over the same fields
of view, was performed for simultaneous 304 and 1600 Å data obtained
with the Atmospheric Imaging Assembly. <BR /> Results: We detected 184
3 mm transient brightening events with brightness temperatures from
70 K to more than 500 K above backgrounds of ∼7200 - 7450 K. All
events showed light curves with a gradual rise and fall, strongly
suggesting a thermal origin. Their mean duration and maximum area were
51.1 s and 12.3 Mm<SUP>2</SUP>, respectively, with a weak preference
of appearing at network boundaries rather than in cell interiors. Both
parameters exhibited power-law behavior with indices of 2.35 and 2.71,
respectively. Only a small fraction of ALMA events had either 304
or 1600 Å counterparts but the properties of these events were not
significantly different from those of the general population except
that they lacked their low-end energy values. The total thermal
energies of the ALMA transient brightenings were between 1.5 ×
10<SUP>24</SUP> and 9.9 × 10<SUP>25</SUP> erg and their frequency
distribution versus energy was a power law with an index of 1.67 ±
0.05. We found that the power per unit area provided by the ALMA events
could account for only 1% of the chromospheric radiative losses (10%
of the coronal ones). <BR /> Conclusions: We were able to detect, for
the first time, a significant number of weak 3 mm quiet Sun transient
brightenings. However, their energy budget falls short of meeting the
requirements for the heating of the upper layers of the solar atmosphere
and this conclusion does not change even if we use the least restrictive
criteria possible for the detection of transient brightenings.
---------------------------------------------------------
Title: Modeling of the Brightness of the Chromospheric Network Based
on ALMA High Resolution Observations of the Quiet Sun
Authors: Alissandrakis, C. E.; Nindos, A.; Bastian, T.; Patsourakos, S.
2020AAS...23610607A Altcode:
ALMA observations of the Sun at mm-λ offer a unique opportunity
to investigate the temperature/density structure of the solar
chromosphere. In a previous work (Alissandrakis et al 2017, A&A
605, A78) we measured the center-to-limb variation of the brightness
temperature, T<SUB>b</SUB>, using low resolution ALMA full-disk
observations in Band 3 (3mm) and Band 6 (1.26 mm), together with data
at 0.85 mm from Bastian et al. 1993 (ApJ, 415, 364). Combining all
data and inverting the solution of the transfer equation we found
that the electron temperature, T<SUB>e</SUB>, in the range of 0.34
< τ<SUB>100</SUB> < 12, where τ<SUB>100</SUB> is the optical
depth at 100 GHz, was ~5% (~300 K) below the one predicted by model C
(average quiet sun) of FAL93 (Fontenla, Avrett, & Loeser, 1993,
ApJ, 406, 319). Here we expand that work by including measurements
of the brightness temperature in the network and cell interiors,
from high resolution ALMA images in Bands 3 and 6. We found that
the observed T<SUB>b</SUB> in the network is considerably lower
than predicted by the FAL93 model F and that of the cell interior
considerably higher than predicted by the FAL93 model A. The observed
network/cell difference of brightness temperature at the center of the
disk, at 100 GHz is about 920 K, compared to ~3250 K predicted by the
FAL93 models; similarly, the T<SUB>b</SUB>, ratio is ~1.14, against
~1.51 of the model prediction. After inversion of the observed data,
the electron temperature of cell interior at τ<SUB>100</SUB>=1 is
~390 K below the average (~600 K above model A) and of the network
~400 K above the average (~1800 K below model A). The implications of
these results will be discussed. We will also discuss the question of
the normalization of brightness temperature observed by ALMA.
---------------------------------------------------------
Title: Interplanetary Coronal Mass Ejections as the Driver of
Non-recurrent Forbush Decreases
Authors: Papaioannou, Athanasios; Belov, Anatoly; Abunina, Maria;
Eroshenko, Eugenia; Abunin, Artem; Anastasiadis, Anastasios;
Patsourakos, Spiros; Mavromichalaki, Helen
2020ApJ...890..101P Altcode:
Interplanetary coronal mass ejections (ICMEs) are the counterparts of
coronal mass ejections (CMEs) that extend in the interplanetary (IP)
space and interact with the underlying solar wind (SW). ICMEs and their
corresponding shocks can sweep out galactic cosmic rays (GCRs) and thus
modulate their intensity, resulting in non-recurrent Forbush decreases
(FDs). In this work, we selected all FDs that were associated with a
sudden storm commencement (SSC) at Earth, and a solar driver (e.g., CME)
was clearly identified as the ICME's source. We introduce and employ
the t<SUB>H</SUB> parameter, which is the time delay (in hours) of the
maximum strength of the interplanetary magnetic field from the FD onset
(as is marked via the SSC), and consequently derive three groups of
FD events (I.e., the early, medium, and late ones). For each of these
we examine the mean characteristics of the FDs and the associated
IP variations per group, as well as the resulting correlations. In
addition, we demonstrate the outputs of a superposed epoch analysis,
which led to an average time profile of the resulting FDs and the
corresponding IP variations, per group. Finally, we interpret our
results based on the theoretical expectations for the FD phenomenon. We
find that both the shock sheath and the ejecta are necessary for
deep GCR depressions and that the FD amplitude (A0) is larger for
faster-propagating ICMEs. Additionally, we note the importance of the
turbulent shock-sheath region across all groups. Finally, we present
empirical relations connecting A0 to SW properties.
---------------------------------------------------------
Title: Observations of solar chromospheric oscillations at 3 mm
with ALMA
Authors: Patsourakos, S.; Alissandrakis, C. E.; Nindos, A.; Bastian,
T. S.
2020A&A...634A..86P Altcode: 2019arXiv191203480P
<BR /> Aims: We aim to study spatially resolved chromospheric
oscillations of the quiet Sun (QS) in the mm-domain at a resolution
of a few arcsec, typically 2.4″ × 4.5″. <BR /> Methods: We used
Atacama Large millimeter and submillimeter Array (ALMA) time series
of interferometric observations of the QS obtained at 3 mm with a 2-s
cadence and a spatial resolution of a few arcsec. The observations were
performed on March 16, 2017 and seven 80″ × 80″ fields of view
(FoV) going from disk center to limb were covered, each one observed for
10 min, therefore limiting the frequency resolution of the power spectra
to 1.7 mHz. For each FoV, masks for cell and network were derived,
and the averaged power spectral densities (PSDs) for the entire FoV,
cell, and network were computed. The resulting power spectra were
fit with an analytical function in order to derive the frequency
and the root-mean-square (rms) power associated with the peaks. The
same analysis, over the same FoVs and for the same intervals, was
performed for simultaneous Atmospheric Imaging Assembly (AIA) image
sequences in 1600 Å. <BR /> Results: Spatially resolved chromospheric
oscillations at 3 mm, with frequencies of 4.2 ± 1.7 mHz are observed
in the QS, in both cell and network. The coherence length-scale of
the oscillations is commensurate with the spatial resolution of our
ALMA observations. Brightness-temperature fluctuations in individual
pixels could reach up to a few hundred K, while the spatially averaged
PSDs yield rms in the range ≈55-75 K, i.e., up to ≈1% of the
averaged brightness temperatures and exhibit a moderate increase
towards the limb. For AIA 1600 Å, the oscillation frequency is 3.7
± 1.7 mHz. The relative rms is up to 6% of the background intensity,
with a weak increase towards the disk center (cell, average). ALMA
3 mm time-series lag AIA 1600 Å by ≈100 s, which corresponds to
a formation-height difference of ≈1200 km, representing a novel
determination of this important parameter. <BR /> Conclusions: The
ALMA oscillations that we detected exhibit higher amplitudes than those
derived from previous lower (≈10″) resolution observations at 3.5 mm
by the Berkeley-Illinois-Maryland Array. Chromospheric oscillations are,
therefore, not fully resolved at the length-scale of the chromospheric
network, and possibly not even at the spatial resolution of our ALMA
observations. Any study of transient brightenings in the mm-domain
should take into account the oscillations.
---------------------------------------------------------
Title: Magnetic Impact of Propagating Interplanetary Coronal Mass
Ejections in the Solar and Stellar Habitability Zones
Authors: Georgoulis, M. K.; Samara, E.; Patsourakos, S.
2019AGUFMSH43A..05G Altcode:
We recount recent results of a statistical method that assigns an
axial magnetic field to CME flux ropes, inferred via the fundamental
conservation principle of magnetic helicity in solar active region
sources. We then extrapolate the near-Sun CME magnetic field to
1 AU, juxtaposing the extrapolation with tens of magnetic-cloud
observations. Uncertainties given, we manage to statistically
reproduce observations, thereby proposing a simple method that
alleviates unnecessary complexity, while featuring applicability on
a case-by-case basis. At a second level, we generalize CME magnetic
configurations and stellar activity, expanding to flaring M-dwarf
and Sun-like stars. We correlate the magnetic energy of stellar,
assumed eruptive, flares with their helicity and extrapolate again to
stellar habitable zones. From assumed planetary equatorial magnetic
fields we predict atmospheric erosion by CME activity for a number of
recently discovered exoplanets (Keppler 438b; Proxima b; the TRAPPIST
system), thought promising for harboring life. Preliminary results
show that knowledge of the planetary equatorial magnetic field can
impose a valuable constraint for exoplanet habitability. Meanwhile, (1)
terrestrial atmospheric erosion seems unlikely even for unrealistically
intense solar eruptions and (2) the likelihood of absence of atmosphere
due to CME-induced erosion in many of the studied exoplanets seems high.
---------------------------------------------------------
Title: Predicting the geoeffective properties of coronal mass
ejections: current status, open issues and path forward
Authors: Vourlidas, A.; Patsourakos, S.; Savani, N. P.
2019RSPTA.37780096V Altcode:
Much progress has been made in the study of coronal mass ejections
(CMEs), the main drivers of terrestrial space weather thanks to the
deployment of several missions in the last decade. The flow of energy
required to power solar eruptions is beginning to be understood. The
initiation of CMEs is routinely observed with cadences of tens
of seconds with arc-second resolution. Their inner heliospheric
evolution can now be imaged and followed routinely. Yet relatively
little progress has been made in predicting the geoeffectiveness of a
particular CME. Why is that? What are the issues holding back progress
in medium-term forecasting of space weather? To answer these questions,
we review, here, the measurements, status and open issues on the main
CME geoeffective parameters; namely, their entrained magnetic field
strength and configuration, their Earth arrival time and speed, and
their mass (momentum). We offer strategies for improving the accuracy
of the measurements and their forecasting in the near and mid-term
future. To spark further discussion, we incorporate our suggestions
into a top-level draft action plan that includes suggestions for sensor
deployment, technology development and modelling/theory improvements. <P
/>This article is part of the theme issue `Solar eruptions and their
space weather impact'.
---------------------------------------------------------
Title: Sheared Magnetic Arcades and the Pre-eruptive Magnetic
Configuration of Coronal Mass Ejections: Diagnostics, Challenges
and Future Observables
Authors: Patsourakos, Spiros; Vourlidas, A.; Anthiochos, S. K.;
Archontis, V.; Aulanier, G.; Cheng, X.; Chintzoglou, G.; Georgoulis,
M. K.; Green, L. M.; Kliem, B.; Leake, J.; Moore, R. L.; Nindos, A.;
Syntelis, P.; Torok, T.; Yardley, S. L.; Yurchyshyn, V.; Zhang, J.
2019shin.confE.194P Altcode:
Our thinking about the pre-eruptive magnetic configuration of Coronal
Mass Ejections has been effectively dichotomized into two opposing
and often fiercely contested views: namely, sheared magnetic arcades
and magnetic flux ropes. Finding a solution to this issue will have
important implications for our understanding of CME initiation. We
first discuss the very value of embarking into the arcade vs. flux rope
dilemma and illustrate the corresponding challenges and difficulties to
address it. Next, we are compiling several observational diagnostics of
pre-eruptive sheared magnetic arcades stemming from theory/modeling,
discuss their merits, and highlight potential ambiguities that could
arise in their interpretation. We finally conclude with a discussion
of possible new observables, in the frame of upcoming or proposed
instrumentation, that could help to circumvent the issues we are
currently facing.
---------------------------------------------------------
Title: Deriving the Near-Sun Magnetic Field of Coronal Mass Ejections
from Magnetic Helicity Conservation
Authors: Patsourakos, Spiros; Georgoulis, M. K.; Petroulea, G.;
Vourlidas, A.; Nieves-Chinchilla, T.
2019shin.confE.222P Altcode:
The near-Sun magnetic field of Coronal Mass Ejections represents
a key parameter for assessing their energetics and structuring, and
additionally, it is a major element of methods/applications/simulations
aiming to predict the magnetic field of Earth-directed CMEs upon
impact at geospace. Diagnostics of CME magnetic fields in the corona
can be achieved via observations in the radio domain, which however,
are currently not available on a regular basis. Therefore, several
methods to infer the CME magnetic field in the corona have recently
emerged. We developed one such method which is based on the magnetic
helicity conservation principle applied to flux rope CMEs. Its
input parameters could be readily retrieved from the analysis of
HMI magnetograms and SOHO/STEREO WL coronagraph images. We present
parametric and case-study applications of this method, and discuss how
it be could be used to predict the CME magnetic field magnitude at 1 AU.
---------------------------------------------------------
Title: ICSF: Intensity Conserving Spectral Fitting
Authors: Klimchuk, James A.; Patsourakos, Spiros; Tripathi, Durgesh
2019ascl.soft03007K Altcode:
ICSF (Intensity Conserving Spectral Fitting) "corrects" (x,y) data in
which the ordinate represents the average of a quantity over a finite
interval in the abscissa. A typical example is spectral data, where
the average intensity over a wavelength bin (the measured quantity)
is assigned to the center of the bin. If the profile is curved, the
average will be different from the discrete value at the bin center
location. ICSF, written in IDL and available separately and as part of
SolarSoft (ascl:1208.013), corrects the intensity using an iterative
procedure and cubic spline. The corrected intensity equals the "true"
intensity at bin center, rather than the average over the bin. Unlike
other methods that are restricted to a single fitting function,
typically a spline, ICSF can be used with any function, such as a
cubic spline or a Gaussian, with slight changes to the code.
---------------------------------------------------------
Title: Modeling of the Sunspot-Associated Microwave Emission Using
a New Method of DEM Inversion
Authors: Alissandrakis, C. E.; Bogod, V. M.; Kaltman, T. I.;
Patsourakos, S.; Peterova, N. G.
2019SoPh..294...23A Altcode: 2018arXiv181205751A
We develope a method to compute the temperature and density structure
along the line of sight by inversion of the differential emission
measure (DEM), under the assumptions of stratification and hydrostatic
equilibrium. We apply this method to the DEM obtained from the
Atmospheric Imaging Assembly (AIA) observations and use the results,
together with potential extrapolations of the photospheric magnetic
field, to compute the microwave emission of three sunspots, which we
compare with observations from the Academy of Sciences Radio Telescope
- 600 (RATAN-600) radio telescope and the Nobeyama Radioheliograph
(NoRH). Our DEM-based models reproduce very well the observations of
the moderate-size spot on October 2011 and within 25% the data of a
similar sized spot on March 2016, but predict too low values for the
big spot of 14 April 2016. The latter is better fitted by a constant
conductive flux atmospheric model which, however, cannot reproduce the
peak brightness temperature of 4.7 ×10<SUP>6</SUP>K and the shape of
the source at the NoRH frequency. We propose that these deviations are
due to the low intensity non-thermal emission associated to a moving
pore and to an opposite polarity light bridge. We also find that the
double structure of the big spot at high RATAN-600 frequencies can be
interpreted in terms of the variation of the angle between the magnetic
field and the line of sight along the sunspot.
---------------------------------------------------------
Title: First high-resolution look at the quiet Sun with ALMA at 3mm
Authors: Nindos, A.; Alissandrakis, C. E.; Bastian, T. S.; Patsourakos,
S.; De Pontieu, B.; Warren, H.; Ayres, T.; Hudson, H. S.; Shimizu,
T.; Vial, J. -C.; Wedemeyer, S.; Yurchyshyn, V.
2018A&A...619L...6N Altcode: 2018arXiv181005223N
We present an overview of high-resolution quiet Sun observations,
from disk center to the limb, obtained with the Atacama Large
millimeter and sub-millimeter Array (ALMA) at 3 mm. Seven quiet-Sun
regions were observed at a resolution of up to 2.5″ by 4.5″. We
produced both average and snapshot images by self-calibrating the ALMA
visibilities and combining the interferometric images with full-disk
solar images. The images show well the chromospheric network, which,
based on the unique segregation method we used, is brighter than the
average over the fields of view of the observed regions by ∼305
K while the intranetwork is less bright by ∼280 K, with a slight
decrease of the network/intranetwork contrast toward the limb. At 3
mm the network is very similar to the 1600 Å images, with somewhat
larger size. We detect, for the first time, spicular structures,
rising up to 15″ above the limb with a width down to the image
resolution and brightness temperature of ∼1800 K above the local
background. No trace of spicules, either in emission or absorption,
is found on the disk. Our results highlight the potential of ALMA for
the study of the quiet chromosphere.
---------------------------------------------------------
Title: Eruptive Flare Initiation and the CME Magnetic Field
Authors: Georgoulis, Manolis K.; Patsourakos, Spiros; Kontogiannis,
Ioannis
2018cosp...42E1180G Altcode:
We recount very recent results on the correlation between photospheric
characteristics of eruptive solar active regions and coronal mass
ejection (CME) occurrence / characteristics. In particular, we
argue that one of the most relevant parameters for CME occurrence
is the non-neutralized electric currents appearing exclusively along
intense, shear-ridden magnetic polarity-inversion lines (PILs) in the
photosphere of eruptive active regions. These currents are simply
lacking in the absence of strong PILs and shear. While the physics
underlying non-neutralized currents is rich and shows far-reaching
ramifications, we will focus on the injection of magnetic helicity
due to non-neutralized currents in the pre-eruption phase, that will
then be bodily transported via the CME. For a conductive plasma of
high magnetic Reynolds number, such as that of the solar corona,
we show how the fundamental helicity conservation principle can lead
to estimates of, first, the CME's axial magnetic field strength and,
second, the anticipated magnetic field strength of the interplanetary
CME (ICME) on the verge of geospace. We discuss how this analysis
can be viewed as a meaningful initial or boundary condition for more
elaborate inner-heliospheric propagation models that further consider
the orientation of the ICME magnetic field, thus leading to an improved
understanding and prediction of ICME geoeffectiveness. Part of this
work has been supported by the EU Horizon-2020 FLARECAST project
(grant agreement no. 640216).
---------------------------------------------------------
Title: A New Spin to Exoplanet Habitability Criteria
Authors: Georgoulis, M. K.; Patsourakos, S.
2017AGUFM.P53E2676G Altcode:
We describe a physically- and statistically-based method to infer
the near-Sun magnetic field of coronal mass ejections (CMEs) and then
extrapolate it to the inner heliosphere and beyond. Besides a ballpark
agreement with in-situ observations of interplanetary CMEs (ICMEs) at
L1, we use our estimates to show that Earth does not seem to be at risk
of an extinction-level atmospheric erosion or stripping by the magnetic
pressure of extreme solar eruptions, even way above a Carrington-type
event. This does not seem to be the case with exoplanets, however,
at least those orbiting in the classically defined habitability
zones of magnetically active dwarf stars at orbital radii of a small
fraction of 1 AU. We show that the combination of stellar ICMEs and
the tidally locking zone of mother stars, that quite likely does not
allow these exoplanets to attain Earth-like magnetic fields to shield
themselves, probably render the existence of a proper atmosphere
in them untenable. We propose, therefore, a critical revision of
habitability criteria in these cases that would limit the number of
target exoplanets considered as potential biosphere hosts.
---------------------------------------------------------
Title: Center-to-limb observations of the Sun with ALMA . Implications
for solar atmospheric models
Authors: Alissandrakis, C. E.; Patsourakos, S.; Nindos, A.; Bastian,
T. S.
2017A&A...605A..78A Altcode:
<BR /> Aims: We seek to derive information on the temperature structure
of the solar chromosphere and compare these results with existing
models. <BR /> Methods: We measured the center-to-limb variation of
the brightness temperature, T<SUB>b</SUB>, from ALMA full-disk images
at two frequencies and inverted the solution of the transfer equation
to obtain the electron temperature, T<SUB>e</SUB> as a function of
optical depth, τ. <BR /> Results: The ALMA images are very similar
to AIA images at 1600 Å. The brightness temperature at the center
of the disk is 6180 and 7250 K at 239 and 100 GHz, respectively,
with dispersions of 100 and 170 K. Plage regions stand out clearly in
the 239/100 GHz intensity ratio, while faculae and filament lanes do
not. The solar disk radius, reduced to 1 AU, is 961.1 ± 2.5” and 964.1
± 4.5” at 239 and 100 GHz, respectively. A slight but statistically
significant limb brightening is observed at both frequencies. <BR />
Conclusions: The inversion of the center-to-limb curves shows that
T<SUB>e</SUB> varies linearly with the logarithm of optical depth for
0.34 <τ<SUB>100 GHz</SUB>< 12, with a slope dT<SUB>e</SUB>/
dlnτ = -608 K. Our results are 5% lower than predicted by the average
quiet Sun model C of Fontenla et al. (1993, ApJ. 406, 319), but do
not confirm previous reports that the mm-λ solar spectrum is better
fitted with models of the cell interior.
---------------------------------------------------------
Title: A Helicity-Based Method to Infer the CME Magnetic Field
Magnitude in Sun and Geospace: Generalization and Extension to
Sun-Like and M-Dwarf Stars and Implications for Exoplanet Habitability
Authors: Patsourakos, S.; Georgoulis, M. K.
2017SoPh..292...89P Altcode: 2017arXiv170703579P
Patsourakos et al. (Astrophys. J.817, 14, 2016) and Patsourakos and
Georgoulis (Astron. Astrophys.595, A121, 2016) introduced a method to
infer the axial magnetic field in flux-rope coronal mass ejections
(CMEs) in the solar corona and farther away in the interplanetary
medium. The method, based on the conservation principle of magnetic
helicity, uses the relative magnetic helicity of the solar source
region as input estimates, along with the radius and length of the
corresponding CME flux rope. The method was initially applied to
cylindrical force-free flux ropes, with encouraging results. We hereby
extend our framework along two distinct lines. First, we generalize
our formalism to several possible flux-rope configurations (linear
and nonlinear force-free, non-force-free, spheromak, and torus) to
investigate the dependence of the resulting CME axial magnetic field
on input parameters and the employed flux-rope configuration. Second,
we generalize our framework to both Sun-like and active M-dwarf stars
hosting superflares. In a qualitative sense, we find that Earth may
not experience severe atmosphere-eroding magnetospheric compression
even for eruptive solar superflares with energies ≈10<SUP>4</SUP>
times higher than those of the largest Geostationary Operational
Environmental Satellite (GOES) X-class flares currently observed. In
addition, the two recently discovered exoplanets with the highest
Earth-similarity index, Kepler 438b and Proxima b, seem to lie in the
prohibitive zone of atmospheric erosion due to interplanetary CMEs
(ICMEs), except when they possess planetary magnetic fields that are
much higher than that of Earth.
---------------------------------------------------------
Title: Evidence for two-loop interaction from IRIS and SDO
observations of penumbral brightenings
Authors: Alissandrakis, C. E.; Koukras, A.; Patsourakos, S.; Nindos, A.
2017A&A...603A..95A Altcode: 2017arXiv170407344A
<BR /> Aims: We investigate small scale energy release events which
can provide clues on the heating mechanism of the solar corona. <BR />
Methods: We analyzed spectral and imaging data from the Interface
Region Imaging Spectrograph (IRIS), images from the Atmospheric
Imaging Assembly (AIA) aboard the Solar Dynamics Observatoty (SDO),
and magnetograms from the Helioseismic and Magnetic Imager (HMI)
aboard SDO. <BR /> Results: We report observations of small flaring
loops in the penumbra of a large sunspot on July 19, 2013. Our main
event consisted of a loop spanning 15”, from the umbral-penumbral
boundary to an opposite polarity region outside the penumbra. It lasted
approximately 10 min with a two minute impulsive peak and was observed
in all AIA/SDO channels, while the IRIS slit was located near its
penumbral footpoint. Mass motions with an apparent velocity of 100 km
s<SUP>-1</SUP> were detected beyond the brightening, starting in the
rise phase of the impulsive peak; these were apparently associated
with a higher-lying loop. We interpret these motions in terms of
two-loop interaction. IRIS spectra in both the C II and Si iv lines
showed very extended wings, up to about 400 km s<SUP>-1</SUP>, first
in the blue (upflows) and subsequently in the red wing. In addition
to the strong lines, emission was detected in the weak lines of Cl
I, O I and C I, as well as in the Mg II triplet lines. Absorption
features in the profiles of the C II doublet, the Si iv doublet and
the Mg II h and k lines indicate the existence of material with a
lower source function between the brightening and the observer. We
attribute this absorption to the higher loop and this adds further
credibility to the two-loop interaction hypothesis. Tilts were
detected in the absorption spectra, as well as in the spectra of Cl I,
O I, and C I lines, possibly indicating rotational motions from the
untwisting of magnetic flux tubes. <BR /> Conclusions: We conclude
that the absorption features in the C II, Si iv and Mg II profiles
originate in a higher-lying, descending loop; as this approached
the already activated lower-lying loop, their interaction gave rise
to the impulsive peak, the very broad line profiles and the mass
motions. <P />Movies associated to Figs. A.1-A.3 are available at <A
href="http://www.aanda.org/10.1051/0004-6361/201730643/olm">http://www.aanda.org</A>
---------------------------------------------------------
Title: Center-to-limb observations of the Sun with ALMA
Authors: Alissandrakis, C. E.; Patsourakos, S.; Nindos, A.; Bastian,
T. S.
2017arXiv170509008A Altcode:
We measured the center-to-limb variation of the brightness temperature,
$T_b$, from ALMA full-disk images at two frequencies and inverted the
solution of the transfer equation to obtain the electron temperature,
$T_e$ as a function of optical depth, $\tau$. The ALMA images are very
similar to AIA images at 1600Å. The brightness temperature at the
center of the disk is 6180 and 7250 K at 239 and 100 GHz respectively,
with dispersions of 100 and 170 K. Plage regions stand out clearly
in the 239/100 GHz intensity ratio, while faculae and filament lanes
do not. The solar disk radius, reduced to 1 AU, is $961.1\pm2.5$
arcsec and $964.1\pm4.5$ arcsec at 239 and 100 GHz respectively. A
slight but statistically significant limb brightening is observed at
both frequencies. The inversion of the center-to-limb curves shows
that $T_e$ varies linearly with the logarithm of optical depth for
$0.34<\tau_{100\,GHz}<12$, with a slope $d\ln T_e/d\tau=-608$
K. Our results are 5% lower than predicted by the average quiet sun
model C of Fontenla et al. (1993), but do not confirm previous reports
that the mm-$\lambda$ solar spectrum is better fitted with models of
the cell interior.
---------------------------------------------------------
Title: Near-Sun and 1 AU magnetic field of coronal mass ejections:
a parametric study
Authors: Patsourakos, S.; Georgoulis, M. K.
2016A&A...595A.121P Altcode: 2016arXiv160900134P
<BR /> Aims: The magnetic field of coronal mass ejections (CMEs)
determines their structure, evolution, and energetics, as well as their
geoeffectiveness. However, we currently lack routine diagnostics of
the near-Sun CME magnetic field, which is crucial for determining the
subsequent evolution of CMEs. <BR /> Methods: We recently presented
a method to infer the near-Sun magnetic field magnitude of CMEs and
then extrapolate it to 1 AU. This method uses relatively easy to deduce
observational estimates of the magnetic helicity in CME-source regions
along with geometrical CME fits enabled by coronagraph observations. We
hereby perform a parametric study of this method aiming to assess its
robustness. We use statistics of active region (AR) helicities and CME
geometrical parameters to determine a matrix of plausible near-Sun CME
magnetic field magnitudes. In addition, we extrapolate this matrix
to 1 AU and determine the anticipated range of CME magnetic fields
at 1 AU representing the radial falloff of the magnetic field in
the CME out to interplanetary (IP) space by a power law with index
α<SUB>B</SUB>. <BR /> Results: The resulting distribution of the
near-Sun (at 10 R<SUB>⊙</SUB>) CME magnetic fields varies in the
range [0.004, 0.02] G, comparable to, or higher than, a few existing
observational inferences of the magnetic field in the quiescent
corona at the same distance. We also find that a theoretically and
observationally motivated range exists around α<SUB>B</SUB> = -1.6
± 0.2, thereby leading to a ballpark agreement between our estimates
and observationally inferred field magnitudes of magnetic clouds (MCs)
at L1. <BR /> Conclusions: In a statistical sense, our method provides
results that are consistent with observations.
---------------------------------------------------------
Title: Solar Coronal Jets: Observations, Theory, and Modeling
Authors: Raouafi, N. E.; Patsourakos, S.; Pariat, E.; Young, P. R.;
Sterling, A. C.; Savcheva, A.; Shimojo, M.; Moreno-Insertis, F.;
DeVore, C. R.; Archontis, V.; Török, T.; Mason, H.; Curdt, W.;
Meyer, K.; Dalmasse, K.; Matsui, Y.
2016SSRv..201....1R Altcode: 2016arXiv160702108R; 2016SSRv..tmp...31R
Coronal jets represent important manifestations of ubiquitous solar
transients, which may be the source of significant mass and energy
input to the upper solar atmosphere and the solar wind. While
the energy involved in a jet-like event is smaller than that of
"nominal" solar flares and coronal mass ejections (CMEs), jets
share many common properties with these phenomena, in particular,
the explosive magnetically driven dynamics. Studies of jets could,
therefore, provide critical insight for understanding the larger,
more complex drivers of the solar activity. On the other side of the
size-spectrum, the study of jets could also supply important clues on
the physics of transients close or at the limit of the current spatial
resolution such as spicules. Furthermore, jet phenomena may hint to
basic process for heating the corona and accelerating the solar wind;
consequently their study gives us the opportunity to attack a broad
range of solar-heliospheric problems.
---------------------------------------------------------
Title: A Robust Method to Predict the Near-Sun and Interplanetary
Magnetic Field Strength of Coronal Mass Ejections: Parametric and
Case Studies
Authors: Patsourakos, Spiros; Georgoulis, Manolis K.
2016cosp...41E1531P Altcode:
Predicting the near-Sun, and particularly the Interplanetary (IP),
magnetic field structure of Coronal Mass Ejections (CMEs) and
interplanetary counterparts (ICMEs) is a topic of intense research
activity. This is because Earth-directed CMEs with strong southward
magnetic fields are responsible for the most powerful geomagnetic
storms. We have recently developed a simple two-tier method to
predict the magnetic field strength of CMEs in the outer corona
and in the IP medium, using as input the magnetic-helicity budget
of the source solar active region and stereoscopic coronagraphic
observations. Near-Sun CME magnetic fields are obtained by utilizing
the principle of magnetic helicity conservation of flux-rope CMEs
for coronagraphic observations. Interplanetary propagation of the
inferred values is achieved by employing power-law prescriptions of the
radial evolution of the CME-ICME magnetic fields. We hereby present a
parametric study of our method, based on the observed statistics of
input parameters, to infer the anticipated range of values for the
near-Sun and interplanetary CME-ICME magnetic fields. This analysis
is complemented by application of our method to several well-observed
major CME-ICME events.
---------------------------------------------------------
Title: The 3D structure of Coronal Mass Ejections
Authors: Patsourakos, Spiros
2016cosp...41E1532P Altcode:
Coronal Mass Ejections (CMEs) represent one of the most powerful
energy release phenomena in the entire solar system and are a major
driver of space weather. Prior to 2006, our observational access to
CMEs was limited to single viewpoint remote sensing observations
in the inner/outer corona, and in-situ observations further away,
e.g. at 1 AU. Taking all these factors together, turned out to be
a major obstacle in our understanding and characterizing of the 3D
structure and evolution of CMEs. The situation improved dramatically
with the availability of multi-viewpoint imaging observations of
CMEs, all way through from the Sun to 1 AU, from the STEREO mission
since 2006, combined with observations from other missions (SOHO,
Hinode, SDO, IRIS). With this talk we will discuss several key recent
results in CME science resulting from the analysis of multi-viewpoint
observations. This includes: (1) shape and structure; (2) kinematics
and energetics; (3) trajectories, deflections and rotations; (4)
arrival times and velocities at 1 AU; (5) magnetic field structure;
(6) relationships with coronal and interplanetary shocks and solar
energetic particles. The implications of these results in terms of
CME theories and models will be also addressed. We will conclude
with a discussion of important open issues in our understanding of
CMEs and how these could be addressed with upcoming (Solar Orbiter,
Solar Probe Plus) and under-study missions (e.g., L5).
---------------------------------------------------------
Title: Coronal Mass Ejections: From Sun to Earth
Authors: Patsourakos, S.
2016Hipp....2m..17P Altcode:
Coronal Mass Ejections (CMEs) are gigantic expulsions of magnetized
plasmas from the solar corona into the interplanetary (IP) space. CMEs
spawn ~ 1015 gr of mass and reach speeds ranging between several hundred
to a few thousand km/s (e.g., Gopalswamy et al. 2009; Vourlidas et
al. 2010). It takes 1-5 days for a CME to reach Earth. CMEs are one
of the most energetic eruptive manifestations in the solar system
and are major drivers of space weather via their magnetic fields and
energetic particles, which are accelerated by CME-driven shocks. In
this review we give a short account of recent, mainly observational,
results on CMEs from the STEREO and SDO missions which include the
nature of their pre-eruptive and eruptive configurations and the CME
propagation from Sun to Earth. We conclude with a discussion of the
exciting capabilities in CME studies that will soon become available
from new solar and heliospheric instrumentation.
---------------------------------------------------------
Title: Multi-viewpoint Observations of a Widely distributed Solar
Energetic Particle Event: The Role of EUV Waves and White-light
Shock Signatures
Authors: Kouloumvakos, A.; Patsourakos, S.; Nindos, A.; Vourlidas,
A.; Anastasiadis, A.; Hillaris, A.; Sandberg, I.
2016ApJ...821...31K Altcode:
On 2012 March 7, two large eruptive events occurred in the same active
region within 1 hr from each other. Each consisted of an X-class flare,
a coronal mass ejection (CME), an extreme-ultraviolet (EUV) wave,
and a shock wave. The eruptions gave rise to a major solar energetic
particle (SEP) event observed at widely separated (∼120°) points
in the heliosphere. From multi-viewpoint energetic proton recordings
we determine the proton release times at STEREO B and A (STB, STA)
and the first Lagrange point (L1) of the Sun-Earth system. Using EUV
and white-light data, we determine the evolution of the EUV waves in
the low corona and reconstruct the global structure and kinematics of
the first CME’s shock, respectively. We compare the energetic proton
release time at each spacecraft with the EUV waves’ arrival times
at the magnetically connected regions and the timing and location
of the CME shock. We find that the first flare/CME is responsible
for the SEP event at all three locations. The proton release at STB
is consistent with arrival of the EUV wave and CME shock at the STB
footpoint. The proton release time at L1 was significantly delayed
compared to STB. Three-dimensional modeling of the CME shock shows
that the particle release at L1 is consistent with the timing and
location of the shock’s western flank. This indicates that at L1
the proton release did not occur in low corona but farther away from
the Sun. However, the extent of the CME shock fails to explain the
SEP event observed at STA. A transport process or a significantly
distorted interplanetary magnetic field may be responsible.
---------------------------------------------------------
Title: The spectroscopic imprint of the pre-eruptive configuration
resulting into two major coronal mass ejections
Authors: Syntelis, P.; Gontikakis, C.; Patsourakos, S.; Tsinganos, K.
2016A&A...588A..16S Altcode: 2016arXiv160203680S
<BR /> Aims: We present a spectroscopic analysis of the pre-eruptive
configuration of active region NOAA 11429, prior to two very fast
coronal mass ejections (CMEs) on March 7, 2012 that are associated
with this active region. We study the thermal components and the
dynamics associated with the ejected flux ropes. <BR /> Methods: Using
differential emission measure (DEM) analysis of Hinode/EIS and SDO/AIA
observations, we identify the emission components of both the flux rope
and the host active region. We then follow the time evolution of the
flux rope emission components by using AIA observations. The plasma
density and the Doppler and non-thermal velocities associated with
the flux ropes are also calculated from the EIS data. <BR /> Results:
The eastern and western parts of the active region, in which the two
different fast CMEs originated during two X-class flares, were studied
separately. In both regions we identified an emission component in the
temperature range of log T = 6.8-7.1 associated with the presence of
flux ropes. The time evolution of the eastern region showed an increase
in the mean DEM in this temperature range by an order of magnitude, 5
h prior to the first CME. This was associated with a gradual rise and
heating of the flux rope as manifested by blue-shifts and increased
non-thermal velocities in Ca xv 200.97 Å, respectively. An overall
upward motion of the flux ropes was measured (relative blue-shifts of
~ 12 km s<SUP>-1</SUP>). The measured electron density was found to
be 4 × 10<SUP>9</SUP>-2 × 10<SUP>10</SUP> cm<SUP>-3</SUP> (using
the ratio of Ca xv 181.90 Å over Ca xv 200.97 Å). We compare our
findings with other works on the same AR to provide a unified picture
of its evolution.
---------------------------------------------------------
Title: Predicting the near-Sun and Interplanetary Magnetic Field of
CMEs using photospheric magnetograms and coronagraph images
Authors: Patsourakos, Spiros; Georgoulis, Manolis
2016EGUGA..18.4784P Altcode:
Earth-directed Coronal Mass Ejections (CMEs) containing a strong
southward magnetic-field component upon arrival at 1 AU statistically
account for the most powerful geomagnetic storms. Unfortunately, though,
we currently lack routine diagnostics of the magnetic field of CMEs
and its evolution in the inner heliosphere and the interplanetary (IP)
medium. We hereby present a simple, yet powerful and easy-to-implement,
method to deduce the near-Sun and IP magnetic field entrained in CMEs,
by using photospheric magnetograms of the solar source regions and
multi-viewpoint coronagraph images of the corresponding CMEs. The
method relies on the principle of magnetic-helicity conservation
in low plasma-beta, flux-rope CMEs and a power-law prescription of
the radial evolution of the CME magnetic field in the IP medium. We
outline a parametric study based on the observed statistics of input
parameters to calculate a matrix of magnetic-field solutions for 10000
synthetic CMEs. The robustness and possible limitations / ramifications
of the method are deduced by a comparison with the distributions of
the predicted CME-ICME magnetic fields at 0.3 and 1 AU using actual
Messenger and ACE published observations.
---------------------------------------------------------
Title: The Major Geoeffective Solar Eruptions of 2012 March 7:
Comprehensive Sun-to-Earth Analysis
Authors: Patsourakos, S.; Georgoulis, M. K.; Vourlidas, A.; Nindos,
A.; Sarris, T.; Anagnostopoulos, G.; Anastasiadis, A.; Chintzoglou,
G.; Daglis, I. A.; Gontikakis, C.; Hatzigeorgiu, N.; Iliopoulos, A. C.;
Katsavrias, C.; Kouloumvakos, A.; Moraitis, K.; Nieves-Chinchilla, T.;
Pavlos, G.; Sarafopoulos, D.; Syntelis, P.; Tsironis, C.; Tziotziou,
K.; Vogiatzis, I. I.; Balasis, G.; Georgiou, M.; Karakatsanis, L. P.;
Malandraki, O. E.; Papadimitriou, C.; Odstrčil, D.; Pavlos, E. G.;
Podlachikova, O.; Sandberg, I.; Turner, D. L.; Xenakis, M. N.; Sarris,
E.; Tsinganos, K.; Vlahos, L.
2016ApJ...817...14P Altcode:
During the interval 2012 March 7-11 the geospace experienced a
barrage of intense space weather phenomena including the second
largest geomagnetic storm of solar cycle 24 so far. Significant
ultra-low-frequency wave enhancements and relativistic-electron dropouts
in the radiation belts, as well as strong energetic-electron injection
events in the magnetosphere were observed. These phenomena were
ultimately associated with two ultra-fast (>2000 km s<SUP>-1</SUP>)
coronal mass ejections (CMEs), linked to two X-class flares launched
on early 2012 March 7. Given that both powerful events originated from
solar active region NOAA 11429 and their onsets were separated by less
than an hour, the analysis of the two events and the determination
of solar causes and geospace effects are rather challenging. Using
satellite data from a flotilla of solar, heliospheric and magnetospheric
missions a synergistic Sun-to-Earth study of diverse observational
solar, interplanetary and magnetospheric data sets was performed. It was
found that only the second CME was Earth-directed. Using a novel method,
we estimated its near-Sun magnetic field at 13 R<SUB>⊙</SUB> to be
in the range [0.01, 0.16] G. Steep radial fall-offs of the near-Sun
CME magnetic field are required to match the magnetic fields of the
corresponding interplanetary CME (ICME) at 1 AU. Perturbed upstream
solar-wind conditions, as resulting from the shock associated with the
Earth-directed CME, offer a decent description of its kinematics. The
magnetospheric compression caused by the arrival at 1 AU of the shock
associated with the ICME was a key factor for radiation-belt dynamics.
---------------------------------------------------------
Title: Intensity Conserving Spectral Fitting
Authors: Klimchuk, J. A.; Patsourakos, S.; Tripathi, D.
2016SoPh..291...55K Altcode: 2015SoPh..tmp..180K
The detailed shapes of spectral-line profiles provide valuable
information about the emitting plasma, especially when the plasma
contains an unresolved mixture of velocities, temperatures, and
densities. As a result of finite spectral resolution, the intensity
measured by a spectrometer is the average intensity across a wavelength
bin of non-zero size. It is assigned to the wavelength position at
the center of the bin. However, the actual intensity at that discrete
position will be different if the profile is curved, as it invariably
is. Standard fitting routines (spline, Gaussian, etc.) do not account
for this difference, and this can result in significant errors when
making sensitive measurements. We have developed an iterative procedure
that corrects for this effect. It converges rapidly and is very
flexible in that it can be used with any fitting function. We present
examples of cubic-spline and Gaussian fits and give special attention
to measurements of blue-red asymmetries of coronal emission lines.
---------------------------------------------------------
Title: EUV Coronal Waves: Atmospheric and Heliospheric Connections
and Energetics
Authors: Patsourakos, S.
2015AGUFMSH22A..03P Altcode:
Since their discovery in late 90's by EIT on SOHO, the study EUV coronal
waves has been a fascinating andfrequently strongly debated research
area. While it seems as ifan overall consensus has been reached about
the nurture and nature of this phenomenon,there are still several
important questions regarding EUV waves. By focusing on the most
recentobservations, we will hereby present our current understanding
about the nurture and nature of EUV waves,discuss their connections
with other atmospheric and heliospheric phenomena (e.g.,flares and
CMEs, Moreton waves, coronal shocks, coronal oscillations, SEP events)
and finallyassess their possible energetic contribution to the overall
budget of relatederuptive phenomena.
---------------------------------------------------------
Title: North-south asymmetry in the magnetic deflection of polar
coronal hole jets
Authors: Nisticò, G.; Zimbardo, G.; Patsourakos, S.; Bothmer, V.;
Nakariakov, V. M.
2015A&A...583A.127N Altcode: 2015arXiv150801072N
Context. Measurements of the sunspots area, of the magnetic field in
the interplanetary medium, and of the heliospheric current sheet (HCS)
position, reveal a possible north-south (N-S) asymmetry in the magnetic
field of the Sun. This asymmetry could cause the bending of the HCS of
the order of 5-10 deg in the southward direction, and it appears to
be a recurrent characteristic of the Sun during the minima of solar
activity. <BR /> Aims: We study the N-S asymmetry as inferred from
measurements of the deflection of polar coronal hole jets when they
propagate throughout the corona. <BR /> Methods: Since the corona is
an environment where the magnetic pressure is greater than the kinetic
pressure (β ≪ 1), we can assume that the magnetic field controls the
dynamics of plasma. On average, jets follow magnetic field lines during
their propagation, highlighting their local direction. We measured
the position angles at 1 R<SUB>⊙</SUB> and at 2 R<SUB>⊙</SUB> of
79 jets, based on the Solar TErrestrial RElations Observatory (STEREO)
ultraviolet and white-light coronagraph observations during the solar
minimum period March 2007-April 2008. The average jet deflection is
studied both in the plane perpendicular to the line of sight and, for
a reduced number of jets, in 3D space. The observed jet deflection is
studied in terms of an axisymmetric magnetic field model comprising
dipole (g<SUB>1</SUB>), quadrupole (g<SUB>2</SUB>), and esapole
(g<SUB>3</SUB>) moments. <BR /> Results: We found that the propagation
of the jets is not radial, which is in agreement with the deflection
due to magnetic field lines. Moreover, the amount of the deflection is
different between jets over the north and those from the south pole. A
comparison of jet deflections and field line tracing shows that a ratio
g<SUB>2</SUB>/g<SUB>1</SUB> ≃ -0.5 for the quadrupole and a ratio
g<SUB>3</SUB>/g<SUB>1</SUB> ≃ 1.6-2.0 for the esapole can describe
the field. The presence of a non-negligible quadrupole moment confirms
the N-S asymmetry of the solar magnetic field for the considered
period. <BR /> Conclusions: We find that the magnetic deflection of
jets is larger in the north than in the south of the order of 25-40%,
with an asymmetry that is consistent with a southward deflection of
the heliospheric current sheet of the order of 10 deg, consistent with
that inferred from other independent datasets and instruments.
---------------------------------------------------------
Title: A tiny event producing an interplanetary type III burst
Authors: Alissandrakis, C. E.; Nindos, A.; Patsourakos, S.;
Kontogeorgos, A.; Tsitsipis, P.
2015A&A...582A..52A Altcode: 2015arXiv150708423A
<BR /> Aims: We investigate the conditions under which small-scale
energy release events in the low corona gave rise to strong
interplanetary (IP) type III bursts. <BR /> Methods: We analyzed
observations of three tiny events, detected by the Nançay Radio
Heliograph (NRH), two of which produced IP type III bursts. We
took advantage of the NRH positioning information and of the high
cadence of AIA/SDO data to identify the associated extreme-UV (EUV)
emissions. We measured positions and time profiles of the metric and
EUV sources. <BR /> Results: We found that the EUV events that produced
IP type III bursts were located near a coronal hole boundary, while the
one that did not was located in a closed magnetic field region. In all
three cases tiny flaring loops were involved, without any associated
mass eruption. In the best observed case, the radio emission at the
highest frequency (435 MHz) was displaced by ~55” with respect to
the small flaring loop. The metric type III emission shows a complex
structure in space and in time, indicative of multiple electron
beams, despite the low intensity of the events. From the combined
analysis of dynamic spectra and NRH images, we derived the electron
beam velocity as well as the height, ambient plasma temperature, and
density at the level of formation of the 160 MHz emission. From the
analysis of the differential emission measure derived from the AIA
images, we found that the first evidence of energy release was at the
footpoints, and this was followed by the development of flaring loops
and subsequent cooling. <BR /> Conclusions: Even small energy release
events can accelerate enough electrons to give rise to powerful IP
type III bursts. The proximity of the electron acceleration site to
open magnetic field lines facilitates the escape of the electrons
into the interplanetary space. The offset between the site of
energy release and the metric type III location warrants further
investigation. <P />The movie is available in electronic form at <A
href="http://www.aanda.org/10.1051/0004-6361/201526265/olm">http://www.aanda.org</A>
---------------------------------------------------------
Title: Formation of Magnetic Flux Ropes during a Confined Flaring
Well before the Onset of a Pair of Major Coronal Mass Ejections
Authors: Chintzoglou, Georgios; Patsourakos, Spiros; Vourlidas, Angelos
2015ApJ...809...34C Altcode: 2015arXiv150701165C
NOAA active region (AR) 11429 was the source of twin super-fast
coronal mass ejections (CMEs). The CMEs took place within an hour
from each other, with the onset of the first taking place in the
beginning of 2012 March 7. This AR fulfills all the requirements for
a “super active region” namely, Hale's law incompatibility and a
δ-spot magnetic configuration. One of the biggest storms of Solar
Cycle 24 to date ({D}<SUB>{st</SUB>}=-143 nT) was associated with
one of these events. Magnetic flux ropes (MFRs) are twisted magnetic
structures in the corona, best seen in ∼10 MK hot plasma emission
and are often considered the core of erupting structures. However,
their “dormant” existence in the solar atmosphere (i.e., prior to
eruptions), is an open question. Aided by multi-wavelength observations
by the Solar Dynamics Observatory (SDO) and by the Solar Terrestrial
Relations Observatory (STEREO) and a nonlinear force-free model for the
coronal magnetic field, our work uncovers two separate, weakly twisted
magnetic flux systems which suggest the existence of pre-eruption MFRs
that eventually became the seeds of the two CMEs. The MFRs could have
been formed during confined (i.e., not leading to major CMEs) flaring
and sub-flaring events which took place the day before the two CMEs
in the host AR 11429.
---------------------------------------------------------
Title: How Common Are Hot Magnetic Flux Ropes in the Low Solar
Corona? A Statistical Study of EUV Observations
Authors: Nindos, A.; Patsourakos, S.; Vourlidas, A.; Tagikas, C.
2015ApJ...808..117N Altcode: 2015arXiv150703766N
We use data at 131, 171, and 304 Å from the Atmospheric Imaging
Assembly on board the Solar Dynamics Observatory to search for hot
flux ropes in 141 M-class and X-class solar flares that occurred at
solar longitudes equal to or larger than 50°. Half of the flares were
associated with coronal mass ejections. The goal of our survey is to
assess the frequency of hot flux ropes in large flares irrespective
of their formation time relative to the onset of eruptions. The flux
ropes were identified in 131 Å images using morphological criteria and
their high temperatures were confirmed by their absence in the cooler
171 and 304 Å passbands. We found hot flux ropes in 45 of our events
(32% of the flares); 11 of them were associated with confined flares
while the remaining 34 were associated with eruptive flares. Therefore
almost half (49%) of the eruptive events involved a hot flux rope
configuration. The use of supplementary Hinode X-Ray Telescope data
indicates that these percentages should be considered as lower limits
of the actual rates of occurrence of hot flux ropes in large flares.
---------------------------------------------------------
Title: Intensity Conserving Spline Interpolation (ICSI): A New Tool
for Spectroscopic Analysis
Authors: Klimchuk, James A.; Patsourakos, Spiros; Tripathi, Durgesh
2015TESS....120309K Altcode: 2015arXiv150608102K
Spectroscopy is an extremely powerful tool for diagnosing astrophysical
and other plasmas. For example, the shapes of line profiles provide
valuable information on the distribution of velocities along
an optically thin line-of-sight and across the finite area of a
resolution element. A number of recent studies have measured the
asymmetries of line profiles in order to detect faint high-speed
upflows, perhaps associated with coronal nanoflares or perhaps
associated with chromospheric nanoflares and type II spicules. Over
most of the Sun, these asymmetries are very subtle, so great care
must be taken. A common technique is to perform a spline fit of the
points in the profile in order to extract information at a spectral
resolution higher than that of the original data. However, a fundamental
problem is that the fits do not conserve intensity. We have therefore
developed an iterative procedure called Intensity Conserving Spline
Interpolation that does preserve the observed intensity within each
wavelength bin. It improves the measurement of line asymmetries and
can also help with the determination of line blends.
---------------------------------------------------------
Title: Intensity Conserving Spline Interpolation (ICSI): A New Tool
for Spectroscopic Analysis
Authors: Klimchuk, J. A.; Patsourakos, S.; Tripathi, D.
2014AGUFMSH13B4109K Altcode:
Spectroscopy is an extremely powerful tool for diagnosing astrophysical
and other plasmas. For example, the shapes of line profiles provide
valuable information on the distribution of velocities along
an optically thin line-of-sight and across the finite area of a
resolution element. A number of recent studies have measured the
asymmetries of line profiles in order to detect faint high-speed
upflows, perhaps associated with coronal nanoflares or perhaps
associated with chromospheric nanoflares and type II spicules. Over
most of the Sun, these asymmetries are very subtle, so great care
must be taken. A common technique is to perform a spline fit of the
points in the profile in order to extract information at a spectral
resolution higher than that of the original data. However, a fundamental
problem is that the fits do not conserve intensity. We have therefore
developed an iterative procedure called Intensity Conserving Spline
Interpolation that does preserve the observed intensity within each
wavelength bin. It improves the measurement of line asymmetries and
can also help with the determination of line blends.
---------------------------------------------------------
Title: CME Expansion as the Driver of Metric Type II Shock Emission
as Revealed by Self-consistent Analysis of High-Cadence EUV Images
and Radio Spectrograms
Authors: Kouloumvakos, A.; Patsourakos, S.; Hillaris, A.; Vourlidas,
A.; Preka-Papadema, P.; Moussas, X.; Caroubalos, C.; Tsitsipis, P.;
Kontogeorgos, A.
2014SoPh..289.2123K Altcode: 2013arXiv1311.5159K
On 13 June 2010, an eruptive event occurred near the solar limb. It
included a small filament eruption and the onset of a relatively narrow
coronal mass ejection (CME) surrounded by an extreme ultraviolet
(EUV) wave front recorded by the Solar Dynamics Observatory's (SDO)
Atmospheric Imaging Assembly (AIA) at high cadence. The ejection was
accompanied by a GOES M1.0 soft X-ray flare and a Type-II radio burst;
high-resolution dynamic spectra of the latter were obtained by the
Appareil de Routine pour le Traitement et l'Enregistrement Magnetique
de l'Information Spectral (ARTEMIS IV) radio spectrograph. The combined
observations enabled a study of the evolution of the ejecta and the
EUV wave front and its relationship with the coronal shock manifesting
itself as metric Type-II burst. By introducing a novel technique,
which deduces a proxy of the EUV compression ratio from AIA imaging
data and compares it with the compression ratio deduced from the
band-split of the Type-II metric radio burst, we are able to infer
the potential source locations of the radio emission of the shock on
that AIA images. Our results indicate that the expansion of the CME
ejecta is the source for both EUV and radio shock emissions. Early in
the CME expansion phase, the Type-II burst seems to originate in the
sheath region between the EUV bubble and the EUV shock front in both
radial and lateral directions. This suggests that both the nose and
the flanks of the expanding bubble could have driven the shock.
---------------------------------------------------------
Title: Rapid CME Cavity Formation and Expansion
Authors: Kliem, Bernhard; Forbes, Terry G.; Patsourakos, Spiros;
Vourlidas, Angelos
2014AAS...22421206K Altcode:
A cavity is supposed to be a general feature of well-developed CMEs at
the stage they can be imaged by white-light coronagraphs (in the outer
corona and solar wind). The cavity is interpreted as the cross section
of the CME flux rope in the plane of sky. Preexisting cavities are
observed around some quiescent erupting prominences, but usually not in
active regions. Observations of CME cavities in the inner corona, where
most of them appear to form, have become possible only with the STEREO
and SDO missions. These reveal a very rapid formation and expansion of
"EUV cavities" in fast and impulsively commencing eruptions early in the
phase of main CME acceleration and impulsive flare rise. Different from
the white-light observations, the EUV cavity initially appears to be
larger than the CME flux rope. However, it evolves into the white-light
cavity subsequently. MHD simulations of flux rope eruptions conform to
this picture of initially larger cavity but subsequently approaching
cavity and flux rope size. The initial expansion of ambient flux can
be understood as a "reverse pinch effect", driven by decreasing flux
rope current as the rope rises.
---------------------------------------------------------
Title: Independent CMEs from a Single Solar Active Region - The Case
of the Super-Eruptive NOAA AR11429
Authors: Chintzoglou, Georgios; Patsourakos, Spiros; Vourlidas, Angelos
2014AAS...22432328C Altcode:
In this investigation we study AR 11429, the origin of the twin
super-fast CME eruptions of 07-Mar-2012. This AR fulfills all the
requirements for the 'perfect storm'; namely, Hale's law incompatibility
and a delta-magnetic configuration. In fact, during its limb-to-limb
transit, AR 11429 spawned several eruptions which caused geomagnetic
storms, including the biggest in Cycle 24 so far. Magnetic Flux Ropes
(MFRs) are twisted magnetic structures in the corona, best seen in
~10MK hot plasma emission and are often considered as the culprit
causing such super-eruptions. However, their 'dormant' existence in
the solar atmosphere (i.e. prior to eruptions), is a matter of strong
debate. Aided by multi-wavelength and multi-spacecraft observations
(SDO/HMI & AIA, HINODE/SOT/SP, STEREO B/EUVI) and by using a
Non-Linear Force-Free (NLFFF) model for the coronal magnetic field,
our work shows two separate, weakly-twisted magnetic flux systems
which suggest the existence of possible pre-eruption MFRs.
---------------------------------------------------------
Title: Core and Wing Densities of Asymmetric Coronal Spectral
Profiles: Implications for the Mass Supply of the Solar Corona
Authors: Patsourakos, S.; Klimchuk, J. A.; Young, P. R.
2014ApJ...781...58P Altcode: 2013arXiv1312.4842P
Recent solar spectroscopic observations have shown that coronal spectral
lines can exhibit asymmetric profiles, with enhanced emissions at their
blue wings. These asymmetries correspond to rapidly upflowing plasmas
at speeds exceeding ≈50 km s<SUP>-1</SUP>. Here, we perform a study
of the density of the rapidly upflowing material and compare it with
that of the line core that corresponds to the bulk of the plasma. For
this task, we use spectroscopic observations of several active regions
taken by the Extreme Ultraviolet Imaging Spectrometer of the Hinode
mission. The density sensitive ratio of the Fe XIV lines at 264.78 and
274.20 Å is used to determine wing and core densities. We compute the
ratio of the blue wing density to the core density and find that most
values are of order unity. This is consistent with the predictions for
coronal nanoflares if most of the observed coronal mass is supplied
by chromospheric evaporation driven by the nanoflares. However,
much larger blue wing-to-core density ratios are predicted if most of
the coronal mass is supplied by heated material ejected with type II
spicules. Our measurements do not rule out a spicule origin for the
blue wing emission, but they argue against spicules being a primary
source of the hot plasma in the corona. We note that only about 40%
of the pixels where line blends could be safely ignored have blue wing
asymmetries in both Fe XIV lines. Anticipated sub-arcsecond spatial
resolution spectroscopic observations in future missions could shed
more light on the origin of blue, red, and mixed asymmetries.
---------------------------------------------------------
Title: North-South Asymmetry in the Magnetic Deflection of Polar
Coronal Jets
Authors: Nisticò, Giuseppe; Zimbardo, Gaetano; Bothmer, Volker;
Patsourakos, Spiros
2014cosp...40E2295N Altcode:
Solar jets observed with the Extreme Ultra-Violet Imager (EUVI) and
CORonagraphs (COR) instruments aboard the STEREO mission provide a tool
to probe and understand the magnetic structure of the corona. Since
the corona is an environment where the magnetic pressure is greater
than the kinetic pressure, the magnetic field controls the dynamics
of plasma and, on average, jets during their propagation trace
the magnetic field lines. We discuss the North-South asymmetry of
the magnetic field of the Sun as inferred from measurements of the
deflection of polar coronal hole jets when they propagate throughout
the corona. We measured the position angle at 1 and at 2 solar radii
for the 79 jets of the catalogue of Nisticò et al. (2009), based on
the STEREO ultraviolet and visible observations, and we found that the
propagation is not radial. The average jet deflection is studied both in
the plane perpendicular to the line of sight, and, for a reduced number
of jets in the three dimensional (3D) space. We find that the magnetic
deflection of jets is larger in the North than in the South, with an
asymmetry which is consistent with the N-S asymmetry of the heliospheric
magnetic field inferred from the Ulysses in situ measurements, and
gives clues to the study of the large scale solar magnetic field.
---------------------------------------------------------
Title: Observations of CMEs-ICMEs: Results from Current Space Missions
and Expectations from Future Instrumentation
Authors: Patsourakos, Spiros
2014cosp...40E2464P Altcode:
Our understanding of the physics of CMEs and ICMEs has been
substantially improved over the last 20 years, thanks particularly
to a stream of space missions. While many questions regarding CMEs
and ICMEs have been resolved there are still some important pending
questions. With this talk we will focus on two important problems of
CME and ICME physics, namely the determination of the CME pre-erupting
structures and the physical processes behind their initiation as
well as the properties of CME-ICME propagation in the IP medium. We
will supply a review of recent results related to these two areas and
discuss specific examples of how progress from future instrumentation
may be expected.
---------------------------------------------------------
Title: Sun-to-Earth Analysis of a Major Solar Eruption
Authors: Patsourakos, Spiros
2014cosp...40E2465P Altcode:
During the interval of 7-10 March 2012, Earth's space environment
experienced a barrage of space weather phenomena. Early during 7
March 2012, the biggest proton event of 2012 took place, while on 8
March 2012, an interplanetary shock and coronal mass ejection (CME)
arrived at 1 AU. This sequence trigerred the biggest geomagnetic
storm of cycle 24 so far. The solar source of these activities
was a pair of homologous, eruptive X-class flares associated with
two ultra-fast CMEs. The two eruptions originated from NOAA active
region 11429 during the early hours of 7 March 2012 and within an
hour from each other. Using satellite data from a flotilla of solar,
heliospheric and magnetospheric missions and monitors, we perform
a synergistic Sun-to-Earth study of various observational aspects
of the event sequences. We will present an attempt to formulate a
cohesive scenario which couples the eruption initiation, interplanetary
propagation, and geospace consequences. Our main focus is on building
a framework that starting from solar and near-Sun estimates of the
magnetic and dynamic content and properties of the Earth-directed
CME assess in advance the subsequent geomagnetic response expected,
once the associated interplanetary CME reaches 1 AU. This research has
been co-financed by the European Union (European Social Fund - ESF)
and Greek national funds through the Operational Program "Education
and Lifelong Learning" of the National Strategic Reference Framework
(NSRF) - Research Funding Program: Thales. Investing in knowledge
society through the European Social Fund.
---------------------------------------------------------
Title: Microwave and EUV Observations of an Erupting Filament and
Associated Flare and Coronal Mass Ejections
Authors: Alissandrakis, Costas E.; Kochanov, Alexey A.; Patsourakos,
Spiros; Altyntsev, Alexander T.; Lesovoi, Sergey V.; Lesovoya, Nadya N.
2013PASJ...65S...8A Altcode: 2013arXiv1309.1703A
A filament eruption was observed with the Siberian Solar Radio Telescope
(SSRT) on 2012 June 23, starting at around 06:40 UT, beyond the west
limb. The filament could be followed in SSRT images to heights above 1
R<SUB>⊙</SUB>, and coincided with the core of the CME, seen in LASCO
C2 images. We briefly discuss the dynamics of the eruption: the top of
the filament showed a smooth acceleration up to an apparent velocity
of ∼ 1100 km s<SUP>-1</SUP>. Images behind the limb from STEREO-A
show a two-ribbon flare and the interaction of the main filament,
located along the primary neutral line, with an arch-like structure,
oriented in the perpendicular direction. The interaction was accompanied
by strong emission and twisting motions. The microwave images show
a low-temperature component, a high-temperature component associated
with the interaction of the two filaments and another high-temperature
component apparently associated with the top of flare loops. We
computed the differential emission measure from the high-temperature
AIA bands and from this the expected microwave brightness temperature;
for emission associated with the top of the flare loops, the computed
brightness was 35% lower than the observed value.
---------------------------------------------------------
Title: Parametric study of drag force acting on interplanetary CME
Authors: Podladchikova, O.; Patsourakos, S.; Nindos, A.
2013hell.confR..22P Altcode:
The interaction of an interplanetary coronal mass ejection (ICME)
with the solar wind leads to an equalisation of the ICME and solar
wind velocities at 1 AU. The forces acting on ICMEs have been
evaluated so far in terms of an empirical drag coefficient C_D ~
1 that describes the aerodynamic drag experienced by a typical ICME
due to its interaction with the ambient solar wind. The consideration
of viscous drag coefficients due to proton-magnetic kink encounters
is more realistic for solar wind turbulence. We compare aerodynamic
and viscous drag description and their impact on ICME propagation in
solar wind. We also consider the impact of ICME distortions to their
kinematics as they propagate in the inner heliosphere.
---------------------------------------------------------
Title: The spatial relationship between coronal mass ejections and
solar flares
Authors: Nikou, E.; Nindos, A.; Patsourakos, S.
2013hell.conf...21N Altcode:
Using 19 well-observed eruptions that gave both coronal mass ejections
(CMEs) and flares, we quantified the spatial relationship between pairs
of CMEs and associated flares. The flare and CME source locations were
identified using images obtained at 174 A by the SWAP instrument aboard
PROBA 2 satellite. The SWAP data are suitable for this study because
flare emission does not saturate much. To reduce saturation even more,
our database did not contain any M-class or X-class flare events. We
selected eruptions that occurred close to disk center, as viewed from
Earth, whereas they appeared as limb events in images obtained by the
EUV Imagers (EUVI) aboard the SECCHI/STEREO spacecraft. The centroids
of the CME-associated EUV dimmings in the SWAP images were used as
proxies for the CME source locations. For each event, we compared the
location of the flare brightenings with the location of the dimmings'
centroid at the time of CME initiation which was determined from
the EUVI data. In six cases the CME location was cospatial with flare
brightenings while in the remaining cases the distance between each pair
of flare-CME locations varied from 4 to 191 arcsecs with a median value
of 71 arcsecs. Furthermore, we investigated the CME source locations
with respect to the underlying magnetic field structures.
---------------------------------------------------------
Title: Particle acceleration and nanoflare heating in coronal loops
Authors: Gontikakis, C.; Patsourakos, S.; Efthymiopoulos, C.;
Anastasiadis, A.; Georgoulis, M.
2013hell.conf...18G Altcode:
We model nanoflare heating of extrapolated active-region coronal loops
via the acceleration of electrons and protons in Harris-type current
sheets. The kinetic energy of the accelerated particles is estimated
using semi-analytical and test-particle-tracing approaches. Vector
magnetograms and photospheric Doppler velocity maps of NOAA active
region 09114, recorded by the Imaging Vector Magnetograph (IVM),
were used for this analysis in order to compute a current-free field
extrapolation of the active-region corona. The corresponding Poynting
fluxes at the footpoints of 5000 extrapolated coronal loops were then
calculated. Assuming that reconnecting current sheets develop along
these loops, we utilized previous results to estimate the kinetic-energy
gain of the accelerated particles and we related this energy to
nanoflare heating and macroscopic loop characteristics. Kinetic
energies of 0.1 to 8~keV (for electrons) and 0.3 to 470~keV (for
protons) were found to cause heating rates ranging from 10^-6 to 1
erg s^-1 cm^-3. Hydrodynamic simulations show that such heating rates
can sustain plasma in coronal conditions inside the loops and generate
plasma thermal distributions which are consistent with active region
observations. We concluded the analysis by computing the form of Xray
spectra generated by the accelerated electrons using the thick target
approach that were found to be in agreement with observed X-ray spectra,
thus supporting the plausibility of our nanoflare-heating scenario. This
work is supported by EU's Seventh Framework Programme via a Marie Curie
Fellowship and by the Hellenic National Space Weather Research Network
(HNSWRN) via the THALIS Programme.
---------------------------------------------------------
Title: Sun-to-Earth Analysis of a Major Geoeffective Solar Eruption
within the Framework of the
Authors: Patsourakos, S.; Vlahos, L.; Georgoulis, M.; Tziotziou,
K.; Nindos, A.; Podladchikova, O.; Vourlidas, A.; Anastasiadis, A.;
Sandberg, I.; Tsinganos, K.; Daglis, I.; Hillaris, A.; Preka-Papadema,
P.; Sarris, M.; Sarris, T.
2013hell.conf...10P Altcode:
Transient expulsions of gigantic clouds of solar coronal plasma into
the interplanetary space in the form of Coronal Mass Ejections (CMEs)
and sudden, intense flashes of electromagnetic radiation, solar flares,
are well-established drivers of the variable Space Weather. Given the
innate, intricate links and connections between the solar drivers and
their geomagnetic effects, synergistic efforts assembling all pieces
of the puzzle along the Sun-Earth line are required to advance our
understanding of the physics of Space Weather. This is precisely the
focal point of the Hellenic National Space Weather Research Network
(HNSWRN) under the THALIS Programme. Within the HNSWRN framework,
we present here the first results from a coordinated multi-instrument
case study of a major solar eruption (X5.4 and X1.3 flares associated
with two ultra-fast (>2000 km/s) CMEs) which were launched early
on 7 March 2012 and triggered an intense geomagnetic storm (min Dst
=-147 nT) approximately two days afterwards. Several elements of
the associated phenomena, such as the flare and CME, EUV wave, WL
shock, proton and electron event, interplanetary type II radio burst,
ICME and magnetic cloud and their spatiotemporal relationships and
connections are studied all way from Sun to Earth. To this end, we
make use of satellite data from a flotilla of solar, heliospheric and
magnetospheric missions and monitors (e.g., SDO, STEREO, WIND, ACE,
Herschel, Planck and INTEGRAL). We also present our first steps toward
formulating a cohesive physical scenario to explain the string of the
observables and to assess the various physical mechanisms than enabled
and gave rise to the significant geoeffectiveness of the eruption.
---------------------------------------------------------
Title: Hot coronal loops associated with umbral brightenings
Authors: Alissandrakis, C. E.; Patsourakos, S.
2013A&A...556A..79A Altcode: 2013arXiv1307.3392A
<BR /> Aims: We aim to investigate the association of umbral
brightenings with coronal structures. <BR /> Methods: We analyzed
AIA/SDO high-cadence images in all bands, HMI/SDO data, soft X-ray
images from SXI/GOES-15, and Hα images from the GONG network. <BR
/> Results: We detected umbral brightenings that were visible
in all AIA bands as well as in Hα. Moreover, we identified
hot coronal loops that connected the brightenings with nearby
regions of opposite magnetic polarity. These loops were initially
visible in the 94 Å band, subsequently in the 335 Å band, and
in one case in the 211 Å band. A differential emission measure
analysis revealed plasma with an average temperature of about 6.5
× 10<SUP>6</SUP> K. This behavior suggests cooling of impulsively
heated loops. <P />Two movies are available in electronic from at <A
href="http://www.aanda.org">http://www.aanda.org</A>
---------------------------------------------------------
Title: Where is Coronal Plasma Heated?
Authors: Klimchuk, James A.; Bradshaw, S.; Patsourakos, S.; Tripathi,
D.
2013SPD....4420006K Altcode:
The coupling between the chromosphere and corona is a question of
great current interest. It has long been understood that coronal mass
originates in the chromosphere and that the energy which powers the
corona flows up through the chromosphere. However, the details of
how this happens are now being questioned. In the traditional view,
“mechanical” energy flows into the corona in the form of waves
or gradually increasing magnetic stresses. The waves and stresses
dissipate and heat the plasma. The resulting downward thermal conduction
flux causes material to evaporate from the chromosphere and fill
the corona. If the heating is steady, an equilibrium is established
whereby radiation and thermal conduction balance the energy input. If
the heating is impulsive (a nanoflare), the evaporated plasma cools
and drains, only to reappear during the next event. In either case,
the heating occurs in the corona. A new idea is that the heating
occurs instead in the chromosphere. Cold plasma is directly heated
to coronal temperatures and then flows upward due to expansion and
perhaps also an ejection process. The hot tips of type II spicules
are one example, though spicules need not be involved. I will discuss
these two fundamentally different scenarios and the observational
predictions that they make. A comparison with actual observations
leads to the conclusion that only a small fraction of the hot plasma
in the corona comes from chromospheric heating. Most coronal plasma
is a consequence of heating that occurs in the corona itself.
---------------------------------------------------------
Title: Combining Particle Acceleration and Coronal Heating via
Data-constrained Calculations of Nanoflares in Coronal Loops
Authors: Gontikakis, C.; Patsourakos, S.; Efthymiopoulos, C.;
Anastasiadis, A.; Georgoulis, M. K.
2013ApJ...771..126G Altcode: 2013arXiv1305.5195G
We model nanoflare heating of extrapolated active-region coronal loops
via the acceleration of electrons and protons in Harris-type current
sheets. The kinetic energy of the accelerated particles is estimated
using semi-analytical and test-particle-tracing approaches. Vector
magnetograms and photospheric Doppler velocity maps of NOAA active
region 09114, recorded by the Imaging Vector Magnetograph, were
used for this analysis. A current-free field extrapolation of the
active-region corona was first constructed. The corresponding Poynting
fluxes at the footpoints of 5000 extrapolated coronal loops were then
calculated. Assuming that reconnecting current sheets develop along
these loops, we utilized previous results to estimate the kinetic
energy gain of the accelerated particles. We related this energy
to nanoflare heating and macroscopic loop characteristics. Kinetic
energies of 0.1-8 keV (for electrons) and 0.3-470 keV (for protons)
were found to cause heating rates ranging from 10<SUP>-6</SUP> to 1
erg s<SUP>-1</SUP> cm<SUP>-3</SUP>. Hydrodynamic simulations show
that such heating rates can sustain plasma in coronal conditions
inside the loops and generate plasma thermal distributions that are
consistent with active-region observations. We concluded the analysis
by computing the form of X-ray spectra generated by the accelerated
electrons using the thick-target approach. These spectra were found
to be in agreement with observed X-ray spectra, thus supporting the
plausibility of our nanoflare-heating scenario.
---------------------------------------------------------
Title: Spectral diagnostic of a microflare. Evidences of resonant
scattering in C IV 1548 Å, 1550 Å lines
Authors: Gontikakis, C.; Winebarger, A. R.; Patsourakos, S.
2013A&A...550A..16G Altcode:
<BR /> Aims: We study a microflare, classified as a GOES-A1 after
background subtraction, which was observed in active region NOAA 8541
on May 15, 1999. <BR /> Methods: We used TRACE filtergrams to study
the morphology and time evolution. SUMER spectral lines were used to
diagnose the chromospheric plasma (Si ii 1533 Å), transition region
plasma (C iv 1548, 1550 Å), and coronal plasma (Ne viii 770 Å). <BR
/> Results: In the 171 Å and 195 Å filtergrams, we measure apparent
mass motions along two small loops that compose the microflare from
the eastern toward the western footpoints. In SUMER, the microflare is
detected as a small (47 Mm<SUP>2</SUP>), bright area at the western
footpoints of the TRACE loops. The spectral profiles recorded over
the bright area are complex. The Si ii 1533 Å line is self-reversed
owing to opacity, and the coronal Ne viii line profile is composed of
two Gaussian components, one of them systematically redshifted. The
C iv 1548 Å and 1550 Å profiles are badly distorted because of the
temporary depression of the detector local gain caused by the very
high count rates reached in the flaring region and we can only confirm
the presence of strong blueshifts of ≃ -200 km s<SUP>-1</SUP>. Few,
unaffected C iv profiles show two spectral components. In the northern
part of the bright area, all SUMER spectral lines have at least one
blueshifted spectral component. In the southern region of the bright
area the spectral lines are redshifted. Adjacent to the microflare we
measure, for the first time on the solar disk, an intensity ratio of the
1548 Å line to 1550 Å line with values of three to four, indicating
that resonance scattering prevails in the lines formation. Moreover,
the scattering region is found to be cospatial to a solar pore. <BR />
Conclusions: The blueshifts in the footpoints of the microflare and
the apparent mass motions observed with TRACE can be explained by
a gentle chromospheric evaporation triggered by the microflare. The
redshifted spectral components can be explained as cooling material
that is falling back on the solar surface. The presence of resonant
scattering can be explained by the low electron density expected in the
transition region of a solar pore, combined with the high photon flux
coming from the nearby microflare. We estimate that the lower limit
of the electron density in the pore lies in the range 10<SUP>8</SUP>
cm<SUP>-3</SUP> to 10<SUP>9</SUP> cm<SUP>-3</SUP>.
---------------------------------------------------------
Title: Direct Evidence for a Fast Coronal Mass Ejection Driven by the
Prior Formation and Subsequent Destabilization of a Magnetic Flux Rope
Authors: Patsourakos, S.; Vourlidas, A.; Stenborg, G.
2013ApJ...764..125P Altcode: 2012arXiv1211.7211P
Magnetic flux ropes play a central role in the physics of coronal
mass ejections (CMEs). Although a flux-rope topology is inferred for
the majority of coronagraphic observations of CMEs, a heated debate
rages on whether the flux ropes pre-exist or whether they are formed
on-the-fly during the eruption. Here, we present a detailed analysis
of extreme-ultraviolet observations of the formation of a flux rope
during a confined flare followed about 7 hr later by the ejection of
the flux rope and an eruptive flare. The two flares occurred during
2012 July 18 and 19. The second event unleashed a fast (>1000 km
s<SUP>-1</SUP>) CME. We present the first direct evidence of a fast
CME driven by the prior formation and destabilization of a coronal
magnetic flux rope formed during the confined flare on July 18.
---------------------------------------------------------
Title: On the Nature and Genesis of EUV Waves: A Synthesis of
Observations from SOHO, STEREO, SDO, and Hinode (Invited Review)
Authors: Patsourakos, Spiros; Vourlidas, Angelos
2012SoPh..281..187P Altcode: 2012SoPh..tmp...93P; 2012arXiv1203.1135P
A major, albeit serendipitous, discovery of the SOlar and
Heliospheric Observatory mission was the observation by the Extreme
Ultraviolet Telescope (EIT) of large-scale extreme ultraviolet (EUV)
intensity fronts propagating over a significant fraction of the Sun's
surface. These so-called EIT or EUV waves are associated with eruptive
phenomena and have been studied intensely. However, their wave nature
has been challenged by non-wave (or pseudo-wave) interpretations and
the subject remains under debate. A string of recent solar missions
has provided a wealth of detailed EUV observations of these waves
bringing us closer to resolving the question of their nature. With
this review, we gather the current state-of-the-art knowledge in the
field and synthesize it into a picture of an EUV wave driven by the
lateral expansion of the CME. This picture can account for both wave
and pseudo-wave interpretations of the observations, thus resolving
the controversy over the nature of EUV waves to a large degree but
not completely. We close with a discussion on several remaining open
questions in the field of EUV waves research.
---------------------------------------------------------
Title: LEMUR: Large European module for solar Ultraviolet
Research. European contribution to JAXA's Solar-C mission
Authors: Teriaca, Luca; Andretta, Vincenzo; Auchère, Frédéric;
Brown, Charles M.; Buchlin, Eric; Cauzzi, Gianna; Culhane, J. Len;
Curdt, Werner; Davila, Joseph M.; Del Zanna, Giulio; Doschek, George
A.; Fineschi, Silvano; Fludra, Andrzej; Gallagher, Peter T.; Green,
Lucie; Harra, Louise K.; Imada, Shinsuke; Innes, Davina; Kliem,
Bernhard; Korendyke, Clarence; Mariska, John T.; Martínez-Pillet,
Valentin; Parenti, Susanna; Patsourakos, Spiros; Peter, Hardi; Poletto,
Luca; Rutten, Robert J.; Schühle, Udo; Siemer, Martin; Shimizu,
Toshifumi; Socas-Navarro, Hector; Solanki, Sami K.; Spadaro, Daniele;
Trujillo-Bueno, Javier; Tsuneta, Saku; Dominguez, Santiago Vargas;
Vial, Jean-Claude; Walsh, Robert; Warren, Harry P.; Wiegelmann,
Thomas; Winter, Berend; Young, Peter
2012ExA....34..273T Altcode: 2011ExA...tmp..135T; 2011arXiv1109.4301T
The solar outer atmosphere is an extremely dynamic environment
characterized by the continuous interplay between the plasma and the
magnetic field that generates and permeates it. Such interactions play a
fundamental role in hugely diverse astrophysical systems, but occur at
scales that cannot be studied outside the solar system. Understanding
this complex system requires concerted, simultaneous solar observations
from the visible to the vacuum ultraviolet (VUV) and soft X-rays, at
high spatial resolution (between 0.1” and 0.3”), at high temporal
resolution (on the order of 10 s, i.e., the time scale of chromospheric
dynamics), with a wide temperature coverage (0.01 MK to 20 MK,
from the chromosphere to the flaring corona), and the capability of
measuring magnetic fields through spectropolarimetry at visible and
near-infrared wavelengths. Simultaneous spectroscopic measurements
sampling the entire temperature range are particularly important. These
requirements are fulfilled by the Japanese Solar-C mission (Plan B),
composed of a spacecraft in a geosynchronous orbit with a payload
providing a significant improvement of imaging and spectropolarimetric
capabilities in the UV, visible, and near-infrared with respect to
what is available today and foreseen in the near future. The Large
European Module for solar Ultraviolet Research (LEMUR), described
in this paper, is a large VUV telescope feeding a scientific payload
of high-resolution imaging spectrographs and cameras. LEMUR consists
of two major components: a VUV solar telescope with a 30 cm diameter
mirror and a focal length of 3.6 m, and a focal-plane package composed
of VUV spectrometers covering six carefully chosen wavelength ranges
between 170 Å and 1270 Å. The LEMUR slit covers 280” on the Sun with
0.14” per pixel sampling. In addition, LEMUR is capable of measuring
mass flows velocities (line shifts) down to 2 km s<SUP> - 1</SUP> or
better. LEMUR has been proposed to ESA as the European contribution
to the Solar C mission.
---------------------------------------------------------
Title: On the Role of the Background Overlying Magnetic Field in
Solar Eruptions
Authors: Nindos, A.; Patsourakos, S.; Wiegelmann, T.
2012ApJ...748L...6N Altcode:
The primary constraining force that inhibits global solar eruptions is
provided by the overlying background magnetic field. Using magnetic
field data from both the Helioseismic and Magnetic Imager aboard the
Solar Dynamics Observatory and the spectropolarimeter of the Solar
Optical Telescope aboard Hinode, we study the long-term evolution of
the background field in active region AR11158 that produced three major
coronal mass ejections (CMEs). The CME formation heights were determined
using EUV data. We calculated the decay index -(z/B)(∂B/∂z) of the
magnetic field B (i.e., how fast the field decreases with height, z)
related to each event from the time of the active region emergence until
well after the CMEs. At the heights of CME formation, the decay indices
were 1.1-2.1. Prior to two of the events, there were extended periods
(of more than 23 hr) where the related decay indices at heights above
the CME formation heights either decreased (up to -15%) or exhibited
small changes. The decay index related to the third event increased (up
to 118%) at heights above 20 Mm within an interval that started 64 hr
prior to the CME. The magnetic free energy and the accumulated helicity
into the corona contributed the most to the eruptions by their increase
throughout the flux emergence phase (by factors of more than five and
more than two orders of magnitude, respectively). Our results indicate
that the initiation of eruptions does not depend critically on the
temporal evolution of the variation of the background field with height.
---------------------------------------------------------
Title: EBTEL: Enthalpy-Based Thermal Evolution of Loops
Authors: Klimchuk, J. A.; Patsourakos, S.; Cargill, P. J.
2012ascl.soft03007K Altcode:
Observational and theoretical evidence suggests that coronal heating
is impulsive and occurs on very small cross-field spatial scales. A
single coronal loop could contain a hundred or more individual strands
that are heated quasi-independently by nanoflares. It is therefore
an enormous undertaking to model an entire active region or the
global corona. Three-dimensional MHD codes have inadequate spatial
resolution, and 1D hydro codes are too slow to simulate the many
thousands of elemental strands that must be treated in a reasonable
representation. Fortunately, thermal conduction and flows tend to
smooth out plasma gradients along the magnetic field, so "0D models"
are an acceptable alternative. We have developed a highly efficient
model called Enthalpy-Based Thermal Evolution of Loops (EBTEL) that
accurately describes the evolution of the average temperature, pressure,
and density along a coronal strand. It improves significantly upon
earlier models of this type-in accuracy, flexibility, and capability. It
treats both slowly varying and highly impulsive coronal heating;
it provides the differential emission measure distribution, DEM(T),
at the transition region footpoints; and there are options for heat
flux saturation and nonthermal electron beam heating. EBTEL gives
excellent agreement with far more sophisticated 1D hydro simulations
despite using four orders of magnitude less computing time. It promises
to be a powerful new tool for solar and stellar studies.
---------------------------------------------------------
Title: Nanoflare heating of coronal loops in an active region
triggered by reconnecting current sheets
Authors: Gontikakis, C.; Patsourakos, S.; Efthymiopoulos, C.;
Anastasiadis, A.; Georgoulis, M.
2012hell.conf....7G Altcode:
The purpose of this work is to study the heating of coronal loops,
produced by the acceleration of particles inside reconnecting current
sheets (RCS) which represent nanoflares. We also study the hydrodynamic
response of the loops atmosphere to such a heating event. The RCS are
formed as discontinuities of the loop magnetic field caused by the
photospheric shuffling motions. The coronal loops are represented
by the closed magnetic lines of force calculated by the magnetic
field extrapolation of the active region NOAA 9114 magnetogram. The
photospheric motions at the loops footpoints are measured using local
correlation tracking. The magnetic and electric fields accelerating
particles at the RCS are computed using the loop magnetic fields and
the photospheric motions. We further discuss the question of energy
conservation inside the current sheet, and we present the statistical
distributions of quantities relevant for particles acceleration and
coronal heating for a number of the active region's coronal loops.
---------------------------------------------------------
Title: Arrival Times of Interplanetary CMEs and Shocks into the
Earth's Vicinity: STEREO Observations and Analytical Modeling
Authors: Ontiveros, V.; Patsourakos, S.; Corona-Romero, P.;
Gonzalez-Esparza, J. A.
2012hell.conf....9O Altcode:
Interplanetary Coronal Mass Ejections (ICMEs) are one of the largest
disturbances in the solar system. ICMEs and their associated shocks are
the main cause of intense geomagnetic perturbations, that might affect
satellite orbits and telecommunications among other systems. These
important repercussions in the Space Weather have lead to a continuous
effort to predict the arrival times of the ICMEs and their shocks
into the Earth's vicinity, but still the current accuracy in their
arrival time to Earth of few hours needs further ramification,
in particular for operational purposes. White light images from the
STEREO coronagraphs and heliospheric imagers provide an early detection
of coronal mass ejections (CMEs) and ICMEs. In February 6, 2011,
spacecrafts A and B were 180 degrees apart, each one looking down on a
different hemisphere of the Sun and therefore they view from the side
Earth-directed events, allowing a better determination of the physical
parameters of the events and their kinematics in particular. We take
advantage of this configuration and determine the kinematics of the
CMEs and ICMEs of Feb 15th (01:56), March 7th (19:43) and June 21st
(16:03 UT), 2011. These events have an interplanetary counterpart with
Earth arrivals in Feb 18th (00:40 UT), March 10th (05:45 UT) and Jun
23rd (02:18 UT) respectively, as observed by the ACE spacecraft. We
perform 3D fittings of the CME-ICME-shock systems viewed by COR1, COR2
HI1 and HI2 to deduce their kinematics and we use our measurements to
constrain an analytical model of ICME and shock propagation from the
Sun to Earth and compare with the in-situ arrival times to Earth's
orbit. This model is applied where the dynamic pressure parameter
dominates the solar wind dynamics and it is focused on the role of
the transmission of momentum in the ICME-shock system.
---------------------------------------------------------
Title: Multi-wavelength Observations of a Metric Type-II Event
Authors: Alissandrakis, C.; Nindos, A.; Patsourakos, S.; Hillaris,
Al.; Artemis Group
2012hell.conf....6A Altcode:
We have studied a complex metric radio event,observed with the ARTEMIS
radiospectrogarph on February 12, 2010. The event was associated with
a surge observed at 195 and 304 A and with a coronal mass ejection
observed by STEREO A and B instruments near the East wnd West limbs
respectively. On the disk the event was observed at 10 frequencies by
the Nancay Radioheliograph (NRH), in H-alpha by the Catania observatory
and in soft x-rays by GOES SXI. We combined these data, together with
MDI longitudinal magnetic field, to get as complete a picture of the
event as possible. Our emphasis is on two type-II bursts that occured
near respective maxima in the GOES light curves. The first, associated
with the main peak of the event, showed a clear foundamental-harmonic
structure, while the emission of the second consisted of three
well-separated bands. Using positional infornation for the type-IIs
from the NRH we explore their possible association with the surge,
the coronal front and the CME. We also studied fine structured and
foundamental harmonic structure in the metric dynamic spectrum.
---------------------------------------------------------
Title: Constraining a Model for EUV Wave Formation with SDO and
STEREO Quadrature Observations
Authors: Patsourakos, S.; Vourlidas, A.; Olmedo, O.
2012hell.conf....7P Altcode:
The generation mechanism(s) of large-scale propagating intensity fronts
seen in the EUV, often called EUV waves, in association with impulsive
Coronal Mass Ejection (CMEs) is currently a matter of debate. The strong
lateral expansion which some impulsive CMEs undergo during their early
phases, when they are observed in the inner corona by EUV imagers, is
one possible mechanism for the generation of EUV waves. One impulsive
CME - EUV wave pair was observed during 15 February 2011 in quadrature
by SDO and STEREO. The source active region was close to disk center
as seen by SDO and at the limb as seen by STEREO. This configuration
allowed us to determine the kinematics of the EUV wave and of the
early EUV CME by AIA/SDO and EUVI/STEREO respectively. The detailed
kinematics of the early EUV CME (height and radius evolution of the
erupting flux) were then used to constrain a simple model of EUV wave
formation, invoking the erupting flux as the wave driver. The ground
tracks of the EUV wave as predicted by this data-driven model were
then compared with those of the observed wave.
---------------------------------------------------------
Title: Determination of temperature maps of EUV coronal hole jets
Authors: Nisticò, Giuseppe; Patsourakos, Spiros; Bothmer, Volker;
Zimbardo, Gaetano
2011AdSpR..48.1490N Altcode:
Coronal hole jets are fast ejections of plasma occurring within
coronal holes, observed at Extreme-UltraViolet (EUV) and X-ray
wavelengths. Recent observations of jets by the STEREO and Hinode
missions show that they are transient phenomena which occur at much
higher rates than large-scale impulsive phenomena like flares and
Coronal Mass Ejections (CMEs). In this paper we describe some typical
characteristics of coronal jets observed by the SECCHI instruments
of STEREO spacecraft. We show an example of 3D reconstruction of
the helical structure for a south pole jet, and present how the
angular distribution of the jet position angles changes from the
Extreme-UltraViolet-Imager (EUVI) field of view to the CORonagraph1
(COR1) (height ∼2.0 R<SUB>⊙</SUB> heliocentric distance) field
of view. Then we discuss a preliminary temperature determination for
the jet plasma by using the filter ratio method at 171 and 195 Å and
applying a technique for subtracting the EUV background radiation. The
results show that jets are characterized by electron temperatures
ranging between 0.8 and 1.3 MK. We present the thermal structure of
the jet as temperature maps and we describe its thermal evolution.
---------------------------------------------------------
Title: Euv Imaging Of Shock Formation In The Low Corona With Sdo/aia
Authors: Vourlidas, Angelos; Patsourakos, S.; Kouloumvakos, T.
2011SPD....42.0907V Altcode: 2011BAAS..43S.0907V
Shock generation in the low corona has long been inferred by spectral
observations of drifting so-called type-II radio emission in the
metric wavelengths. Type-IIs occur with coronal mass ejections (CMEs)
and/or flares but not consistently. Therefore, the exact relationship
has been difficult to pin down, mostly because of the lack of radio
imaging capability and of the low cadence of EUV observations in the
low corona during the flare/CME formation. The advent of ultra-high
observations from the AIA imagers has changed all that. In this talk,
we present several direct observations of shock formation in the EUV
and their association to the accompanying type-IIs. We will show that
the coronal expansion driven by the formation of the CME ejecta is
responsible for both EUV and radio emissions.
---------------------------------------------------------
Title: Erratum: "Comprehensive Analysis of Coronal Mass
Ejection Mass and Energy Properties Over a Full Solar Cycle" <A
href="/abs/2010ApJ...722.1522V">(2010, ApJ, 722, 1522)</A>
Authors: Vourlidas, A.; Howard, R. A.; Esfandiari, E.; Patsourakos,
S.; Yashiro, S.; Michalek, G.
2011ApJ...730...59V Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Evidence for a current sheet forming in the wake of a coronal
mass ejection from multi-viewpoint coronagraph observations
Authors: Patsourakos, S.; Vourlidas, A.
2011A&A...525A..27P Altcode: 2010arXiv1010.0323P
Context. Ray-like features observed by coronagraphs in the wake
of coronal mass ejections (CMEs) are sometimes interpreted as the
white light counterparts of current sheets (CSs) produced by the
eruption. The 3D geometry of these ray-like features is largely
unknown and its knowledge should clarify their association to the
CS and place constraints on CME physics and coronal conditions. <BR
/> Aims: If these rays are related to field relaxation behind CMEs,
therefore representing current sheets, then they should be aligned to
the CME axis. With this study we test these important implications for
the first time. <BR /> Methods: An example of such a post-CME ray was
observed by various coronagraphs, including these of the Sun Earth
Connection Coronal and Heliospheric investigation (SECCHI) onboard
the Solar Terrestrial Relations Observatory (STEREO) twin spacecraft
and the Large Angle Spectrometric Coronagraph (LASCO) onboard the
Solar and Heliospheric Observatory (SOHO). The ray was observed in
the aftermath of a CME which occurred on 9 April 2008. The twin STEREO
spacecraft were separated by about 48° on that day. This significant
separation combined with a third “eye” view supplied by LASCO allow
for a truly multi-viewpoint observation of the ray and of the CME. We
applied 3D forward geometrical modeling to the CME and to the ray as
simultaneously viewed by SECCHI-A and B and by SECCHI-A and LASCO,
respectively. <BR /> Results: We found that the ray can be approximated
by a rectangular slab, nearly aligned with the CME axis, and much
smaller than the CME in both terms of thickness and depth (≈0.05
and 0.15 R<SUB>⊙</SUB> respectively). The ray electron density and
temperature were substantially higher than their values in the ambient
corona. We found that the ray and CME are significantly displaced
from the associated post-CME flaring loops. <BR /> Conclusions:
The properties and location of the ray are fully consistent with
the expectations of the standard CME theories for post-CME current
sheets. Therefore, our multi-viewpoint observations supply strong
evidence that the observed post-CME ray is indeed related to a post-CME
current sheet. <P />Movies are only available in electronic form at
<A href="http://www.aanda.org">http://www.aanda.org</A>
---------------------------------------------------------
Title: Constraining the Initiation and Early Evolution of CMEs
Authors: Patsourakos, Spiros
2011sswh.book...73P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The Genesis of an Impulsive CME observed by AIA on SDO
Authors: Patsourakos, S.; Vourlidas, A.; Stenborg, G.
2010AGUFMSH14A..03P Altcode:
Understanding the first moments in the life-time of Coronal Mass
Ejections (CMEs), i.e. their genesis, represents possibly the key to
unlock the physical processes responsible for their initiation. After
this critical interval, which could last as little as few minutes for
the most impulsive events, differences between various CME models become
minimal. The recent launch of the SDO mission and the availability of
high-quality EUV imaging from AIA in particular, opened a new avenue
into CME initiation investigations with its unprecedented image cadence
and multi-wavelength simultaneous coverage. We here report on AIA
observations of an impulsive CME-flare-EUV wave event which took place
during 13 June 2010. All the important dynamics (e.g., rise phase of
the flare, impulsive acceleration of the CME) had a duration of only
10 minutes making this event a perfect showcase event for AIA. Taking
advantage of the unique aspects of AIA data (12 sec cadence and 7
different EUV channels) we present a detailed analysis of this event
which includes: (1) its kinematic behavior (acceleration profile);
(2) radial and expansion speeds; (3) relationships between (1) and (2)
with the flare energy release; (4) multi-temperature evolution of the
early CME. All the above supply new strong constraints for the physics
of impulsive CMEs.
---------------------------------------------------------
Title: The Genesis of an Impulsive Coronal Mass Ejection Observed
at Ultra-high Cadence by AIA on SDO
Authors: Patsourakos, S.; Vourlidas, A.; Stenborg, G.
2010ApJ...724L.188P Altcode: 2010arXiv1010.5234P
The study of fast, eruptive events in the low solar corona is one
of the science objectives of the Atmospheric Imaging Assembly (AIA)
imagers on the recently launched Solar Dynamics Observatory (SDO), which
take full disk images in 10 wavelengths with arcsecond resolution and
12 s cadence. We study with AIA the formation of an impulsive coronal
mass ejection (CME) which occurred on 2010 June 13 and was associated
with an M1.0 class flare. Specifically, we analyze the formation of
the CME EUV bubble and its initial dynamics and thermal evolution in
the low corona using AIA images in three wavelengths (171 Å, 193 Å,
and 211 Å). We derive the first ultra-high cadence measurements
of the temporal evolution of the CME bubble aspect ratio (=bubble
height/bubble radius). Our main result is that the CME formation
undergoes three phases: it starts with a slow self-similar expansion
followed by a fast but short-lived (~70 s) period of strong lateral
overexpansion which essentially creates the CME. Then the CME undergoes
another phase of self-similar expansion until it exits the AIA field of
view. During the studied interval, the CME height-time profile shows a
strong, short-lived, acceleration followed by deceleration. The lateral
overexpansion phase coincides with the deceleration phase. The impulsive
flare heating and CME acceleration are closely coupled. However,
the lateral overexpansion of the CME occurs during the declining
phase and is therefore not linked to flare reconnection. In addition,
the multi-thermal analysis of the bubble does not show significant
evidence of temperature change.
---------------------------------------------------------
Title: Simulations of Overexpanding CME Cavities
Authors: Kliem, B.; Forbes, T.; Vourlidas, A.; Patsourakos, S.
2010AGUFMSH51A1661K Altcode:
Coronal mass ejection (CME) cavities seen in white-light coronagraphs
expand nearly self similarly in the outer corona and inner solar
wind. Little is known about their initial expansion in the inner
corona. A two-phase evolution, consisting of an initial overexpansion
up to a heliocentric front height of about 1.5 solar radii, followed by
nearly self-similar expansion, was recently discovered in STEREO/SECCHI
observations of a fast CME (Patsourakos et al. 2010). The overexpansion
is expressed as a decrease of the cavity aspect ratio (center height
by radius) by at least a factor of 2 during the rise phase of the
main CME acceleration. We present MHD simulations of erupting flux
ropes that show the initial overexpansion of a cavity in line with
the observed evolution. The contributions of ideal-MHD expansion and
of magnetic reconnection to the growth of the flux rope and cavity
in the simulations will be quantified to identify the primary cause
of the overexpansion. This assesses the diagnostic potential of the
overexpansion for the change of flux rope current and the role of
magnetic reconnection in the early evolution of CMEs.
---------------------------------------------------------
Title: The Birth of Coronal Mass Ejections As Seen by STEREO and SDO
Authors: Vourlidas, A.; Patsourakos, S.
2010AGUFMSH21C..07V Altcode:
Despite observations of thousands of coronal mass ejections (CMEs),
the details of their formation still elude us. Impulsive CMEs, in
particular, originate low in the corona, and form within 10-15 mins
while accelerating rapidly. This region of the corona is regularly
observed by EUV imagers but the rapid CME evolution requires high
cadence and relatively large fields of view. Thanks to the operation of
the STEREO and SDO missions, we are currently in a unique position to
address the problem of CME formation. The two missions provide almost
simultaneous observations from three viewpoints with 3 EUV imagers. The
EUV instruments observe in the same (or similar) channels and have
highly complimentary cadences and fields of view. In this paper, we
discuss a coherent picture of the birth of CMEs based on a study of the
first few-minute evolution of several impulsive CMEs. These CMEs seem
to first undergo an non-linear expansion followed by a self-similar
phase. We discuss the implication for CME initiation models.
---------------------------------------------------------
Title: Toward understanding the early stages of an impulsively
accelerated coronal mass ejection. SECCHI observations
Authors: Patsourakos, S.; Vourlidas, A.; Kliem, B.
2010A&A...522A.100P Altcode: 2010arXiv1008.1171P
Context. The expanding magnetic flux in coronal mass ejections (CMEs)
often forms a cavity. Studies of CME cavities have so far been limited
to the pre-event configuration to evolved CMEs at great heights, and
to two-dimensional imaging data. <BR /> Aims: Quantitative analysis of
three-dimensional cavity evolution at CME onset can reveal information
that is relevant to the genesis of the eruption. <BR /> Methods:
A spherical model was simultaneously fit to Solar Terrestrial
Relations Observatory (STEREO) Extreme Ultraviolet Imager (EUVI)
and Inner Coronagraph (COR1) data of an impulsively accelerated CME
on 25 March 2008, which displays a well-defined extreme ultraviolet
(EUV) and white-light cavity of nearly circular shape already at low
heights h ≈ 0.2 R_⊙. The center height h(t) and radial expansion
r(t) of the cavity were obtained in the whole height range of the main
acceleration. We interpret them as the axis height and as a quantity
proportional to the minor radius of a flux rope. <BR /> Results:
The three-dimensional expansion of the CME exhibits two phases in
the course of its main upward acceleration. From the first h and r
data points, taken shortly after the onset of the main acceleration,
the erupting flux shows an overexpansion compared to its rise, as
expressed by the decrease in the aspect ratio from κ = h/r ≈ 3
to κ ≈ (1.5-2). This phase is approximately coincident with the
impulsive rise in the acceleration and is followed by a phase of very
gradual change in the aspect ratio (a nearly self-similar expansion)
toward κ ~ 2.5 at h ~ 10 R_⊙. The initial overexpansion of the CME
cavity can be caused by flux conservation around a rising flux rope
of decreasing axial current and by the addition of flux to a growing,
or by even newly formed, flux rope by magnetic reconnection. Further
analysis will be required to decide which of these contributions is
dominant. The data also suggest that the horizontal component of the
impulsive cavity expansion (parallel to the solar surface) triggers the
associated EUV wave, which subsequently detaches from the CME volume.
---------------------------------------------------------
Title: Comprehensive Analysis of Coronal Mass Ejection Mass and
Energy Properties Over a Full Solar Cycle
Authors: Vourlidas, A.; Howard, R. A.; Esfandiari, E.; Patsourakos,
S.; Yashiro, S.; Michalek, G.
2010ApJ...722.1522V Altcode: 2010arXiv1008.3737V
The LASCO coronagraphs, in continuous operation since 1995, have
observed the evolution of the solar corona and coronal mass ejections
(CMEs) over a full solar cycle with high-quality images and regular
cadence. This is the first time that such a data set becomes available
and constitutes a unique resource for the study of CMEs. In this paper,
we present a comprehensive investigation of the solar cycle dependence
on the CME mass and energy over a full solar cycle (1996-2009) including
the first in-depth discussion of the mass and energy analysis methods
and their associated errors. Our analysis provides several results
worthy of further studies. It demonstrates the possible existence of
two event classes: "normal" CMEs reaching constant mass for >10
R <SUB>sun</SUB> and "pseudo"-CMEs which disappear in the C3 field
of view. It shows that the mass and energy properties of CME reach
constant levels and therefore should be measured only above ~10 R
<SUB>sun</SUB>. The mass density (g/R <SUP>2</SUP> <SUB>sun</SUB>)
of CMEs varies relatively little (< order of magnitude) suggesting
that the majority of the mass originates from a small range in coronal
heights. We find a sudden reduction in the CME mass in mid-2003 which
may be related to a change in the electron content of the large-scale
corona and we uncover the presence of a 6 month periodicity in the
ejected mass from 2003 onward.
---------------------------------------------------------
Title: Observational features of equatorial coronal hole jets
Authors: Nisticò, G.; Bothmer, V.; Patsourakos, S.; Zimbardo, G.
2010AnGeo..28..687N Altcode: 2010arXiv1002.2181N
Collimated ejections of plasma called "coronal hole jets" are commonly
observed in polar coronal holes. However, such coronal jets are not only
a specific features of polar coronal holes but they can also be found
in coronal holes appearing at lower heliographic latitudes. In this
paper we present some observations of "equatorial coronal hole jets"
made up with data provided by the STEREO/SECCHI instruments during
a period comprising March 2007 and December 2007. The jet events
are selected by requiring at least some visibility in both COR1 and
EUVI instruments. We report 15 jet events, and we discuss their main
features. For one event, the uplift velocity has been determined as
about 200 km s<SUP>-1</SUP>, while the deceleration rate appears to
be about 0.11 km s<SUP>-2</SUP>, less than solar gravity. The average
jet visibility time is about 30 min, consistent with jet observed in
polar regions. On the basis of the present dataset, we provisionally
conclude that there are not substantial physical differences between
polar and equatorial coronal hole jets.
---------------------------------------------------------
Title: Extreme Ultraviolet Observations and Analysis of
Micro-Eruptions and Their Associated Coronal Waves
Authors: Podladchikova, O.; Vourlidas, A.; Van der Linden, R. A. M.;
Wülser, J. -P.; Patsourakos, S.
2010ApJ...709..369P Altcode:
The Solar Terrestrial Relations Observatory EUV telescopes have
uncovered small-scale eruptive events, tentatively referred to as
"mini-CMEs" because they exhibit morphologies similar to large-scale
coronal mass ejections (CMEs). Coronal waves and widespread diffuse
dimmings followed by the expansion of the coronal waves are the most
brightly manifestations of large-scale CMEs. The high temporal and
spatial resolution of the EUV data allows us to detect and analyze
these eruptive events, to resolve their fine structure, and to show that
the observed "mini-waves" have a strong similarity to the large-scale
"EIT' waves. Here, we analyze a micro-event observed on 2007 October 17
by the Sun Earth Connection Coronal and Heliospheric Investigation EUV
Imager (EUVI) in 171 Å (Fe IX) with a 2.5 minute cadence. The mini-CME
differs from its large-scale counterparts by having smaller geometrical
size, a shorter lifetime, and reduced intensity of coronal wave and
dimmings. The small-scale coronal wave develops from micro-flaring
sites and propagate up to a distance of 40,000 km in a wide angular
sector of the quiet Sun over 20 minutes. The area of the small-scale
dimming is two orders of magnitude smaller than for large-scale
events. The average speed of the small-scale coronal wave studied is
14 km s<SUP>-1</SUP>. Our observations give strong indications that
small-scale EUV coronal waves associated with the micro-eruptions
propagate in the form of slow mode waves almost perpendicular to the
background magnetic field.
---------------------------------------------------------
Title: The Structure and Dynamics of the Upper Chromosphere and Lower
Transition Region as Revealed by the Subarcsecond VAULT Observations
Authors: Vourlidas, A.; Sanchez Andrade-Nuño, B.; Landi, E.;
Patsourakos, S.; Teriaca, L.; Schühle, U.; Korendyke, C. M.;
Nestoras, I.
2010SoPh..261...53V Altcode: 2009arXiv0912.2272V
The Very high Angular resolution ULtraviolet Telescope (VAULT) is a
sounding rocket payload built to study the crucial interface between
the solar chromosphere and the corona by observing the strongest line
in the solar spectrum, the Ly α line at 1216 Å. In two flights, VAULT
succeeded in obtaining the first ever subarcsecond ( 0.5\hbox{$^”$}
) images of this region with high sensitivity and cadence. Detailed
analyses of those observations contributed significantly to new
ideas about the nature of the transition region. Here, we present
a broad overview of the Ly α atmosphere as revealed by the VAULT
observations and bring together past results and new analyses from the
second VAULT flight to create a synthesis of our current knowledge
of the high-resolution Ly α Sun. We hope that this work will serve
as a good reference for the design of upcoming Ly α telescopes and
observing plans.
---------------------------------------------------------
Title: The nature of micro CMEs within coronal holes
Authors: Bothmer, Volker; Nistico, Giuseppe; Zimbardo, Gaetano;
Patsourakos, Spiros; Bosman, Eckhard
2010cosp...38.2840B Altcode: 2010cosp.meet.2840B
Whilst investigating the origin and characteristics of coronal jets
and large-scale CMEs identi-fied in data from the SECCHI (Sun Earth
Connection Coronal and Heliospheric Investigation) instrument suites
on board the two STEREO satellites, we discovered transient events
that originated in the low corona with a morphology resembling that of
typical three-part struc-tured coronal mass ejections (CMEs). However,
the CMEs occurred on considerably smaller spatial scales. In this
presentation we show evidence for the existence of small-scale CMEs
from inside coronal holes and present quantitative estimates of their
speeds and masses. We interprete the origin and evolution of micro
CMEs as a natural consequence of the emergence of small-scale magnetic
bipoles related to the Sun's ever changing photospheric magnetic flux
on various scales and their interactions with the ambient plasma and
magnetic field. The analysis of CMEs is performed within the framework
of the EU Erasmus and FP7 SOTERIA projects.
---------------------------------------------------------
Title: Heatwaves on the Sun
Authors: Robbrecht, Eva; Wang, Yi-Ming; Vourlidas, Angelos;
Patsourakos, Spiros
2010cosp...38.1791R Altcode: 2010cosp.meet.1791R
Dimmings have been observed for several years now, but their
interpretation is still problematic. A dimming is an observational
effect of diminished brightness with respect to pre-event images, which
is usually interpreted as a density depletion. But not all dimmings are
what they appear to be. In this paper we report on an unusual "dimming
wave" which is not a density depletion but rather a heat wave. Thanks
to the stereoscopic view from the SECCHI/EUVI imagers we are able not
only to uncover the nature of the wave, but also to understand its
three dimensional evolution and its relationship to a quiet sun CME.
---------------------------------------------------------
Title: What Is the Nature of EUV Waves? First STEREO 3D Observations
and Comparison with Theoretical Models
Authors: Patsourakos, S.; Vourlidas, A.; Wang, Y. M.; Stenborg, G.;
Thernisien, A.
2009SoPh..259...49P Altcode: 2009arXiv0905.2189P
One of the major discoveries of the Extreme ultraviolet Imaging
Telescope (EIT) on SOHO was the intensity enhancements propagating
over a large fraction of the solar surface. The physical origin(s)
of the so-called EIT waves is still strongly debated with either
wave (primarily fast-mode MHD waves) or nonwave (pseudo-wave)
interpretations. The difficulty in understanding the nature of EUV waves
lies in the limitations of the EIT observations that have been used
almost exclusively for their study. They suffer from low cadence and
single temperature and viewpoint coverage. These limitations are largely
overcome by the SECCHI/EUVI observations onboard the STEREO mission. The
EUVI telescopes provide high-cadence, simultaneous multitemperature
coverage and two well-separated viewpoints. We present here the first
detailed analysis of an EUV wave observed by the EUVI disk imagers on 7
December 2007 when the STEREO spacecraft separation was ≈ 45°. Both a
small flare and a coronal mass ejection (CME) were associated with the
wave. We also offer the first comprehensive comparison of the various
wave interpretations against the observations. Our major findings are
as follows: (1) High-cadence (2.5-minute) 171 Å images showed a strong
association between expanding loops and the wave onset and significant
differences in the wave appearance between the two STEREO viewpoints
during its early stages; these differences largely disappeared later;
(2) the wave appears at the active region periphery when an abrupt
disappearance of the expanding loops occurs within an interval of 2.5
minutes; (3) almost simultaneous images at different temperatures
showed that the wave was most visible in the 1 - 2 MK range and
almost invisible in chromospheric/transition region temperatures; (4)
triangulations of the wave indicate it was rather low lying (≈ 90
Mm above the surface); (5) forward-fitting of the corresponding CME as
seen by the COR1 coronagraphs showed that the projection of the best-fit
model on the solar surface was inconsistent with the location and size
of the co-temporal EUV wave; and (6) simulations of a fast-mode wave
were found in good agreement with the overall shape and location of the
observed wave. Our findings give significant support for a fast-mode
interpretation of EUV waves and indicate that they are probably
triggered by the rapid expansion of the loops associated with the CME.
---------------------------------------------------------
Title: Characteristics of EUV Coronal Jets Observed with STEREO/SECCHI
Authors: Nisticò, G.; Bothmer, V.; Patsourakos, S.; Zimbardo, G.
2009SoPh..259...87N Altcode: 2009arXiv0906.4407N
In this paper we present the first comprehensive statistical study
of EUV coronal jets observed with the SECCHI (Sun Earth Connection
Coronal and Heliospheric Investigation) imaging suites of the two
STEREO spacecraft. A catalogue of 79 polar jets is presented, identified
from simultaneous EUV and white-light coronagraph observations, taken
during the time period March 2007 to April 2008, when solar activity
was at a minimum. The twin spacecraft angular separation increased
during this time interval from 2 to 48 degrees. The appearances of
the coronal jets were always correlated with underlying small-scale
chromospheric bright points. A basic characterization of the morphology
and identification of the presence of helical structure were established
with respect to recently proposed models for their origin and temporal
evolution. Though each jet appeared morphologically similar in the
coronagraph field of view, in the sense of a narrow collimated outward
flow of matter, at the source region in the low corona the jet showed
different characteristics, which may correspond to different magnetic
structures. A classification of the events with respect to previous
jet studies shows that amongst the 79 events there were 37 Eiffel
tower-type jet events, commonly interpreted as a small-scale (∼35
arc sec) magnetic bipole reconnecting with the ambient unipolar open
coronal magnetic fields at its loop tops, and 12 lambda-type jet events
commonly interpreted as reconnection with the ambient field happening at
the bipole footpoints. Five events were termed micro-CME-type jet events
because they resembled the classical coronal mass ejections (CMEs) but
on much smaller scales. The remaining 25 cases could not be uniquely
classified. Thirty-one of the total number of events exhibited a helical
magnetic field structure, indicative for a torsional motion of the jet
around its axis of propagation. A few jets are also found in equatorial
coronal holes. In this study we present sample events for each of
the jet types using both, STEREO A and STEREO B, perspectives. The
typical lifetimes in the SECCHI/EUVI (Extreme UltraViolet Imager)
field of view between 1.0 to 1.7 R<SUB>⊙</SUB> and in SECCHI/COR1
field of view between 1.4 to 4 R<SUB>⊙</SUB> are obtained, and the
derived speeds are roughly estimated. In summary, the observations
support the assumption of continuous small-scale reconnection as an
intrinsic feature of the solar corona, with its role for the heating of
the corona, particle acceleration, structuring and acceleration of the
solar wind remaining to be explored in more detail in further studies.
---------------------------------------------------------
Title: Estimating the Chromospheric Absorption of Transition Region
Moss Emission
Authors: De Pontieu, Bart; Hansteen, Viggo H.; McIntosh, Scott W.;
Patsourakos, Spiros
2009ApJ...702.1016D Altcode: 2009arXiv0907.1883D
Many models for coronal loops have difficulty explaining the observed
EUV brightness of the transition region, which is often significantly
less than theoretical models predict. This discrepancy has been
addressed by a variety of approaches including filling factors and
time-dependent heating, with varying degrees of success. Here, we
focus on an effect that has been ignored so far: the absorption of
EUV light with wavelengths below 912 Å by the resonance continua
of neutral hydrogen and helium. Such absorption is expected to occur
in the low-lying transition region of hot, active region loops that
is colocated with cool chromospheric features and called "moss" as a
result of the reticulated appearance resulting from the absorption. We
use cotemporal and cospatial spectroheliograms obtained with the Solar
and Heliospheric Observatory/SUMER and Hinode/EIS of Fe XII 1242 Å,
195 Å, and 186.88 Å, and compare the density determination from
the 186/195 Å line ratio to that resulting from the 195/1242 Å line
ratio. We find that while coronal loops have compatible density values
from these two line pairs, upper transition region moss has conflicting
density determinations. This discrepancy can be resolved by taking
into account significant absorption of 195 Å emission caused by
the chromospheric inclusions in the moss. We find that the amount of
absorption is generally of the order of a factor of 2. We compare to
numerical models and show that the observed effect is well reproduced
by three-dimensional radiative MHD models of the transition region
and corona. We use STEREO A/B data of the same active region and find
that increased angles between line of sight and local vertical cause
additional absorption. Our determination of the amount of chromospheric
absorption of TR emission can be used to better constrain coronal
heating models.
---------------------------------------------------------
Title: No Trace Left Behind: STEREO Observation of a Coronal Mass
Ejection Without Low Coronal Signatures
Authors: Robbrecht, Eva; Patsourakos, Spiros; Vourlidas, Angelos
2009ApJ...701..283R Altcode: 2009arXiv0905.2583R
The availability of high-quality synoptic observations of the
extreme-ultraviolet (EUV) and visible corona during the SOHO mission
has advanced our understanding of the low corona manifestations of
coronal mass ejections (CMEs). The EUV imager/white light coronagraph
connection has been proven so powerful, it is routinely assumed that if
no EUV signatures are present when a CME is observed by a coronagraph,
then the event must originate behind the visible limb. This assumption
carries strong implications for space weather forecasting but has not
been put to the test. This paper presents the first detailed analysis
of a frontside, large-scale CME that has no obvious counterparts in
the low corona as observed in EUV and Hα wavelengths. The event was
observed by the SECCHI instruments onboard the STEREO mission. The
COR2A coronagraph observed a slow flux-rope-type CME, while an
extremely faint partial halo was observed in COR2B. The event evolved
very slowly and is typical of the streamer-blowout CME class. EUVI A
171 Å images show a concave feature above the east limb, relatively
stable for about two days before the eruption, when it rises into
the coronagraphic fields and develops into the core of the CME. None
of the typical low corona signatures of a CME (flaring, EUV dimming,
filament eruption, waves) were observed in the EUVI B images, which we
attribute to the unusually large height from which the flux rope lifted
off. This interpretation is supported by the CME mass measurements
and estimates of the expected EUV dimming intensity. Only thanks to
the availability of the two viewpoints we were able to identify the
likely source region. The event originated along a neutral line over
the quiet-Sun. No active regions were present anywhere on the visible
(from STEREO B) face of the disk. Leaving no trace behind on the solar
disk, this observation shows unambiguously that a CME eruption does
not need to have clear on-disk signatures. Also it sheds light on the
question of "mystery" geomagnetic storms, storms without clear solar
origin (formerly called problem storms). We discuss the implications
for space weather monitoring. Preliminary inspection of STEREO data
indicates that events like this are not uncommon, particularly during
the ongoing period of deep solar minimum.
---------------------------------------------------------
Title: "Extreme Ultraviolet Waves" are Waves: First Quadrature
Observations of an Extreme Ultraviolet Wave from STEREO
Authors: Patsourakos, Spiros; Vourlidas, Angelos
2009ApJ...700L.182P Altcode: 2009arXiv0905.2164P
The nature of coronal mass ejection (CME)-associated low corona
propagating disturbances, "extreme ultraviolet (EUV) waves," has been
controversial since their discovery by EIT on SOHO. The low-cadence,
single-viewpoint EUV images and the lack of simultaneous inner corona
white-light observations have hindered the resolution of the debate
on whether they are true waves or just projections of the expanding
CME. The operation of the twin EUV imagers and inner corona coronagraphs
aboard STEREO has improved the situation dramatically. During early
2009, the STEREO Ahead (STA) and Behind (STB) spacecrafts observed
the Sun in quadrature having a ≈90° angular separation. An EUV
wave and CME erupted from active region 11012, on February 13, when
the region was exactly at the limb for STA and hence at disk center
for STB. The STEREO observations capture the development of a CME
and its accompanying EUV wave not only with high cadence but also in
quadrature. The resulting unprecedented data set allowed us to separate
the CME structures from the EUV wave signatures and to determine without
doubt the true nature of the wave. It is a fast-mode MHD wave after all.
---------------------------------------------------------
Title: Spectroscopic Observations of Hot Lines Constraining Coronal
Heating in Solar Active Regions
Authors: Patsourakos, S.; Klimchuk, J. A.
2009ApJ...696..760P Altcode: 2009arXiv0903.3880P
Extreme-ultraviolet observations of warm coronal loops suggest that they
are bundles of unresolved strands that are heated impulsively to high
temperatures by nanoflares. The plasma would then have the observed
properties (e.g., excess density compared with static equilibrium)
when it cools into the 1-2MK range. If this interpretation is correct,
then very hot emission should be present outside of proper flares. It
is predicted to be very faint, however. A critical element for proving
or refuting this hypothesis is the existence of hot, yet faint plasmas
which should be at amounts predicted by impulsive heating models. We
report on the first comprehensive spectroscopic study of hot plasmas
in active regions (ARs). Data from the Extreme-ultraviolet Imaging
Spectrometer on Hinode were used to construct emission measure (EM)
distributions in quiescent ARs in the 1-5 MK temperature range. The
distributions are flat or slowly increasing up to approximately 3 MK
and then fall off rapidly at higher temperatures. We show that AR models
based on impulsive heating can reproduce the observed EM distributions
relatively well. Our results provide strong new evidence that coronal
heating is impulsive in nature.
---------------------------------------------------------
Title: Spectroscopic Observations of Hot Lines Constraining Coronal
Heating in Solar Active Regions
Authors: Patsourakos, Spiros; Klimchuk, J. A.
2009SPD....40.1211P Altcode:
EUV observations of warm coronal loops suggest that they are bundles of
unresolved strands that are heated impulsively to high temperatures by
nanoflares. The plasma would then have the observed properties (e.g.,
excess density compared to static equilibrium) when it cools into
the 1-2 MK range. If this interpretation is correct, then very hot
emission should be present outside of proper flares. It is predicted
to be vey faint, however. A critical element for proving or refuting
this hypothesis is the existence of hot, very faint plasmas which
should be at amounts predicted by impulsive heating. We report on
the first comprehensive spectroscopic study of hot plasmas in active
regions. Data from the EIS spectrometer on Hinode were used to construct
emission measure distributions in quiescent active regions in the 1-5 MK
temperature range. The distributions are flat or slowly increasing up to
approximately 3 MK and then fall off rapidly at higher temperatures. We
show that active region models based on impulsive heating can reproduce
the observed EM distributions relatively well. Our results provide
strong new evidence that coronal heating is impulsive in nature.
---------------------------------------------------------
Title: No trace left behind: STEREO Observation of a Coronal Mass
Ejection Lacking Low Coronal Signatures
Authors: Vourlidas, Angelos; Robbrecht, E.; Patsourakos, S.
2009SPD....40.2104V Altcode:
The availability of high quality synoptic observations of the EUV and
visible corona during the SOHO mission has advanced our understanding
of the low corona manifestations of CMEs. The EUV imager/White light
coronagraph connection has been proven so powerful, it is routinely
assumed that if no EUV signatures are present when a CME is observed
by a coronagraph, then the event must originate behind the visible
limb. This assumption carries strong implications for space weather
forecasting but has not been put to the test. This paper presents the
first detailed analysis of a frontside, large-scale CME that has no
obvious counterparts in the low corona. The event was observed by the
SECCHI instruments on the STEREO mission. The COR2A coronagraph observed
the event as a typical flux-rope type CME, while an extremely faint
partial halo was observed in COR2B. The event evolved very slowly and
is typical of the streamer-blowout CME class. EUVI-A 171A images show
a concave feature above the east limb, relatively stable for about
two days before the eruption, when it rises into the coronagraphic
fields and develops into the core of the CME. None of the typical low
corona signatures of a CME (flaring, EUV dimming, filament eruption,
waves) were observed. Thanks to the two STEREO viewpoints we were able
to identify the likely source region. The event originated along a
quiet sun neutral line. No active regions were present anywhere on the
visible face of the disk. Leaving no trace behind, this observation
shows unambiguously that a CME eruption does not need to have clear
on-disk signatures. Also it sheds light on the question of `mystery'
geomagnetic storms; storms without clear solar origin. Preliminary
inspection of STEREO data indicates that events like this are not
uncommon, particularly during the ongoing period of deep solar minimum.
---------------------------------------------------------
Title: Quadrature STEREO Observations Determine the Nature of
EUV Waves
Authors: Kliem, Bernhard; Patsourakos, S.; Vourlidas, A.; Ontiveros, V.
2009SPD....40.2603K Altcode:
One of the major discoveries of EIT on SOHO was the observation of
large-scale EUV intensity disturbances which travel over significant
fractions of the solar disk. These `EUV waves' are associated with
CME onsets and can be either an MHD wave triggered by the eruption or
the footprints of the associated CME, which currently is a subject of
intense debate. EUV waves are better observed when their source region
is close to disk center, whereas CME onsets and CMEs in general are
better observed off-limb. Therefore, simultaneous multi-viewpoint
observations of EUV waves are best suited to clarify the nature of
these transients and to determine their true relationship with CMEs. <P
/>We present here the first quadrature STEREO observations of an EUV
wave. The wave was observed on 2009 February 13 by both satellites,
which were at a separation of 90 degrees. The wave originated from
an erupting active region near disk center as seen from SC B and
propagated over almost the entire visible solar disk. For SC A the
active region was at the east limb and showed a small erupting bubble,
expanding impulsively in both radial and lateral directions and inducing
deflections of nearby and remote coronal structures. We present high
cadence EUVI and COR1 measurements of both the wave (SC B), and the
expanding EUV bubble (SC A), and of the resulting white-light CME (SC A;
COR1). These would allow to quantify for the first time the true sizes
and expansion characteristics of both the EUV wave and the associated
CME. <P />Finally, we search for wave-associated features in 3D MHD
simulations of CME onsets based on ideal MHD instabilities. These are
compared with the STEREO observations.
---------------------------------------------------------
Title: STEREO Observations of a post-CME Current Sheet
Authors: Patsourakos, S.; Vourlidas, A.; Stenborg, G.
2008AGUFMSH13B1552P Altcode:
Ray-like features in the wake of Coronal Mass Ejections (CMEs) are
often interpreted as current sheets produced by the eruption. The 3D
geometry of such post-CME current sheets is largely unknown and its
knowledge should place important constraints on CME physics and coronal
conditions. An example of a post-CME current sheet was observed on April
9th 2008, in the aftermath of the 'cartwheel' CME, which was observed
by Hinode, SoHO, STEREO and TRACE. The CME and the corresponding current
sheet were well-observed by both STEREO spacecraft, which were separated
by about 48 degrees the day of the event. We present here an analysis
of the 3D morphology of the current sheet using data from the COR1 and
COR2 coronagraphs from both STEREO spacecraft. We will attempt various
forward models (e.g., slabs, cylinders) of the current sheet as seen by
the COR1 and COR2 coronagraphs from both STEREO spacecraft. This will
characterize the 3D geometry of the current sheet and more precisely
its shape and its real width and length. Our forward modeling will also
supply the radial variation of the density along the current sheet. This
information will supply some estimates of the temperature and magnetic
field distributions in and out the current sheet respectively.
---------------------------------------------------------
Title: First STEREO observation of a quiet sun CME
Authors: Robbrecht, E.; Patsourakos, S.; Vourlidas, A.
2008AGUFMSH13B1560R Altcode:
Streamer-blowouts form a particular class of CMEs characterized by a
slow rise and swelling of the streamer that can last for days. While
they are more massive than the average CME, their slow development
complicates their association with features/activity in the low
corona and hampers studies on their initiation mechanism(s). This
paper reports on the first observation from 2 viewpoints of a streamer
blowout CME. The event was observed by the SECCHI/COR2 A instrument
as a typical flux-rope type CME, while a very faint partial halo was
observed in COR2-B. The CME erupted from the east limb in the COR2 A
field of view. EUVI-171 A images show a bright feature above the limb,
traveling from the southern hemisphere towards the equator after which
it slowly rises into the coronagraphic fields of view developing into
the flux-rope structure CME. At the time of eruption the separation
between the two STEREO spacecraft is sufficiently large (54 deg) to
observe the source region face-on in STEREO-B. However, inspection of
EUVI B data didn't reveal any particular source region, other than the
quiet sun. No flaring activity could be related to the eruption. This
observation shows unambiguously that a CME eruption does not necessarily
have clear on-disk signature. Also it sheds light on the long-standing
question of the necessity of having a flare for producing a CME. This
result supplies strong constraints for CME initiation models. This type
of observation could not have been achieved without the multi-viewpoint
observations by STEREO.
---------------------------------------------------------
Title: Comparison of Automated Flare Location Algorithm Results to
Solar Truth
Authors: Plunkett, S. P.; Newmark, J. S.; Kunkel, V.; Patsourakos,
S.; McMullin, D. R.; Hill, S. M.
2008AGUFMSA51A1534P Altcode:
Accurate and timely detection of solar flares and determination of
their heliocentric coordinates are key requirements for space weather
forecasting. We report the results of a study to compare the results
of multiple algorithms for automated determination of flare locations
to "solar truth". The XFL algorithm determines flare locations in near
real-time using GOES-12 SXI image data, and is triggered by GOES-12 XRS
flare detections. We also consider H-alpha flare locations reported
in the FLA data set, and the Latest Events (LEV) locations produced
by LMSAL, based on GOES-12 SXI or SOHO EIT observations. We compare
the results of each of these algorithms to solar truth heliocentric
flare locations determined from analysis of GOES-12 SXI images of
several hundred flares of C class and higher, during periods of high,
moderate, and low solar activity between 2003 and 2006. We also compare
the relative effectiveness of each of these algorithms for determining
flare locations in near real-time, considering both timeliness and
accuracy of the reported flare locations.
---------------------------------------------------------
Title: Observations and analysis of the April 9, 2008 CME using
STEREO, Hinode TRACE and SoHO data
Authors: Reeves, K. K.; Patsourakos, S.; Stenborg, G.; Miralles, M.;
Deluca, E.; Forbes, T.; Golub, L.; Kasper, J.; Landi, E.; McKenzie,
D.; Narukage, N.; Raymond, J.; Savage, S.; Su, Y.; van Ballegooijen,
A.; Vourlidas, A.; Webb, D.
2008AGUFMSH12A..04R Altcode:
On April 9, 2008 a CME originating from an active region behind the limb
was well-observed by STEREO, Hinode, TRACE and SoHO. Several interesting
features connected to this eruption were observed. (1) The interaction
of the CME with open field lines from a nearby coronal hole appeared
to cause an abrupt change in the direction of the CME ejecta. (2) The
prominence material was heated, as evidenced by a change from absorption
to emission in the EUV wavelengths. (3) Because the active region was
behind the limb, the X-Ray Telescope on Hinode was able to take long
enough exposure times to observe a faint current- sheet like structure,
and it was able to monitor the dynamics of the plasma surrounding this
structure. This event is also being studied in the context of activity
that occurred during the Whole Heliosphere Interval (WHI).
---------------------------------------------------------
Title: Static and Impulsive Models of Solar Active Regions
Authors: Patsourakos, S.; Klimchuk, J. A.
2008ApJ...689.1406P Altcode: 2008arXiv0808.2745P
The physical modeling of active regions (ARs) and of the global corona
is receiving increasing interest lately. Recent attempts to model ARs
using static equilibrium models were quite successful in reproducing AR
images of hot soft X-ray (SXR) loops. They however failed to predict
the bright extreme-ultraviolet (EUV) warm loops permeating ARs: the
synthetic images were dominated by intense footpoint emission. We
demonstrate that this failure is due to the very weak dependence of
loop temperature on loop length which cannot simultaneously account for
both hot and warm loops in the same AR. We then consider time-dependent
AR models based on nanoflare heating. We demonstrate that such models
can simultaneously reproduce EUV and SXR loops in ARs. Moreover, they
predict radial intensity variations consistent with the localized core
and extended emissions in SXR and EUV AR observations, respectively. We
finally show how the AR morphology can be used as a gauge of the
properties (duration, energy, spatial dependence, and repetition time)
of the impulsive heating.
---------------------------------------------------------
Title: 3D Numerical Simulation of a New Model for Coronal Jets
Authors: Pariat, E.; Antiochos, S.; DeVore, C. R.; Patsourakos, S.
2008ESPM...12.3.28P Altcode:
Recent solar observations with STEREO and HINODE have revealed evidence
of twisting motions during the evolution of coronal jets. Furthermore,
the observations indicate that some jets achieve near-Alfvenic
velocities. Most models of jet are not capable of explaining these
new observational features. In addition, the impulsiveness of jets,
manifested as a brief, violent energy release phase in contrast to a
slow, quasi-static energy storage phase storage, is an issue not easily
addressed. <P />We will present the results of 3D numerical simulations
of our model for coronal jets. The simulations were performed with our
state-of-art adaptive mesh MHD solver ARMS. The basic idea of the model
is that a jet is due to the release of magnetic twist when a closed
field region undergoes interchange reconnection with surrounding open
field. The fast reconnection between open and closed field results
in the generation of nonlinear Alfven waves that propagate along
the open field, accelerating plasma upward. We will show how the new
stereoscopically-observed features of jets can be explained by the
results of our numerical simulations
---------------------------------------------------------
Title: Highly Efficient Modeling of Dynamic Coronal Loops
Authors: Klimchuk, J. A.; Patsourakos, S.; Cargill, P. J.
2008ApJ...682.1351K Altcode: 2007arXiv0710.0185K
Observational and theoretical evidence suggests that coronal heating
is impulsive and occurs on very small cross-field spatial scales. A
single coronal loop could contain a hundred or more individual strands
that are heated quasi-independently by nanoflares. It is therefore an
enormous undertaking to model an entire active region or the global
corona. Three-dimensional MHD codes have inadequate spatial resolution,
and one-dimensional (1D) hydrodynamic codes are too slow to simulate
the many thousands of elemental strands that must be treated in
a reasonable representation. Fortunately, thermal conduction and
flows tend to smooth out plasma gradients along the magnetic field,
so zero-dimensional (0D) models are an acceptable alternative. We
have developed a highly efficient model called "enthalpy-based thermal
evolution of loops" (EBTEL), which accurately describes the evolution
of the average temperature, pressure, and density along a coronal
strand. It improves significantly on earlier models of this type—in
accuracy, flexibility, and capability. It treats both slowly varying
and highly impulsive coronal heating; it provides the time-dependent
differential emission measure distribution, DEM(T), at the transition
region footpoints; and there are options for heat flux saturation and
nonthermal electron beam heating. EBTEL gives excellent agreement with
far more sophisticated 1D hydrodynamic simulations despite using 4
orders of magnitude less computing time. It promises to be a powerful
new tool for solar and stellar studies.
---------------------------------------------------------
Title: STEREO SECCHI Stereoscopic Observations Constraining the
Initiation of Polar Coronal Jets
Authors: Patsourakos, S.; Pariat, E.; Vourlidas, A.; Antiochos, S. K.;
Wuelser, J. P.
2008ApJ...680L..73P Altcode: 2008arXiv0804.4862P
We report on the first stereoscopic observations of polar coronal jets
made by the EUVI/SECCHI imagers on board the twin STEREO spacecraft. The
significantly separated viewpoints (~11°) allowed us to infer the 3D
dynamics and morphology of a well-defined EUV coronal jet for the first
time. Triangulations of the jet's location in simultaneous image pairs
led to the true 3D position and thereby its kinematics. Initially the
jet ascends slowly at ≈10-20 km s<SUP>-1</SUP> and then, after an
apparent "jump" takes place, it accelerates impulsively to velocities
exceeding 300 km s<SUP>-1</SUP> with accelerations exceeding the solar
gravity. Helical structure is the most important geometrical feature
of the jet which shows evidence of untwisting. The jet structure
appears strikingly different from each of the two STEREO viewpoints:
face-on in one viewpoint and edge-on in the other. This provides
conclusive evidence that the observed helical structure is real and
does not result from possible projection effects of single-viewpoint
observations. The clear demonstration of twisted structure in polar jets
compares favorably with synthetic images from a recent MHD simulation of
jets invoking magnetic untwisting as their driving mechanism. Therefore,
the latter can be considered as a viable mechanism for the initiation
of polar jets.
---------------------------------------------------------
Title: Hot Spectral Emissions in Quiescent Active Regions and
Nanoflare Heating
Authors: Patsourakos, S.; Klimchuk, J. A.
2008AGUSMSP43C..02P Altcode:
A leading candidate for the heating of active region (AR) coronal loops
is the nanoflare model. This model treats coronal loops as collections
of impulsively heated sub-resolution strands and explains several
key observational aspects of warm (1-2 MK) coronal loops. However,
the basic requirement of this model is that the strands initially reach
very high temperatures of several MK before they cool down to canonical
coronal temperatures. Therefore, the detection of hot plasmas in AR
loops represents a stringest test of the nanoflare model. Previous
work has shown that the best way to observe the postulated hot
plasmas is by the means of spectroscopic observations in hot lines
(T > 3 MK). The emission is predicted to be quite faint, but the
EIS spectrometer onboard Hinode has sufficient sensitivity to allow us
to perform such a test for the first time. We will present an analysis
of the emission characteristics of quiescent coronal loops in a number
of hot lines spanning approximately 3-12 MK (Ni XVII, Ca XV, Fe XVII,
Ca XVII, Fe XXIII). We will show that hot plasmas are ubiquitous over
entire active regions, and we will compare the measured intensities
of both hot and warm lines with predictions of nanoflare models.
---------------------------------------------------------
Title: 3D Numerical Simulation and Stereoscopic Observations of
Coronal Jets
Authors: Pariat, E.; Antiochos, S. K.; Patsourakos, S.; DeVore, C. R.
2008AGUSMSP53A..05P Altcode:
Recent solar observations have revealed that coronal jets are a more
frequent phenomenon than previously believed. It is widely accepted
that magnetic reconnection is the fundamental mechanism that gives
rise to the jets. The improved spatial and temporal resolution of
the STEREO observations in combination with stereoscopy yields new
insights into the origins of coronal jets, and provides detailed data
that can be used to test and refine models. We present the results
of 3D numerical simulations of our model for coronal jets. The
simulations were performed with our state-of-art adaptive mesh MHD
solver ARMS. The basic idea of the model is that a jet is due to
the release of twist as a closed field region undergoes interchange
reconnection with surrounding open field. The photospheric driven
evolution of the structure results in the generation of a non linear
Alfven wave along the open fields. Using stereoscopic EUVI images,
we reveal the presence of such twisted structure in a coronal jet
event. This work was supported, in part, by NASA and ONR.
---------------------------------------------------------
Title: Understanding the Initiation of Polar Coronal Jets with
STEREO/SECCHI Stereoscopic Observations
Authors: Vourlidas, A.; Patsourakos, S.; Pariat, E.; Antiochos, S.
2008AGUSMSH23A..02V Altcode:
Polar coronal jets are collimated transient ejections of plasma
occurring in polar coronal holes. The kinematics and mostly the 3D
morphology of jets place strong constraints on the physical mechanism(s)
responsible for their initiation, and were not accessible before
the STEREO mission. We report on the first stereoscopic observations
of polar coronal jets made by the EUVI/SECCHI imagers on-board the
twin STEREO spacecraft at spacecraft separations of ~ 11° and ~
45°. Triangulations of the jet locations in simultaneous image pairs
led to the true 3D position and thereby their kinematics. The most
important geometrical feature of the observed jets is helical structures
showing evidence of untwisting. The jet structure appear strikingly
different from each of the two STEREO viewpoints: face-on in the
one viewpoint and edge-on in the other. This provides solid evidence
that the observed helical structure is real and not resulting from
possible projection effects of single viewpoint observations. The clear
demonstration of twisted structure in polar jets compares favorably
with synthetic images from a recent MHD simulation of jets invoking
magnetic untwisting as their driving mechanism.
---------------------------------------------------------
Title: Understanding Warm Coronal Loops
Authors: Klimchuk, J. A.; Karpen, J. T.; Patsourakos, S.
2007AGUFMSH51C..05K Altcode:
One of the great mysteries of coronal physics that has come to light
in the last few years is the discovery that warm (~ 1 MK) coronal loops
are much denser than expected for quasi-static equilibrium. It has been
shown that the excess density can be explained if loops are bundles
of unresolved strands that are heated impulsively and quasi-randomly
to very high temperatures. This picture of nanoflare heating predicts
that neighboring strands of different temperature should coexist and
therefore that loops should have multi-thermal cross sections. In
particular, emission should be produced at temperatures hotter than 2
MK. Such emission is sometimes but not always seen, however. We offer
two possible explanations for the existence of over-dense warm loops
without corresponding hot emission: (1) loops are bundles of nanoflare
heated strands, but a significant fraction of the nanoflare energy takes
the form of a nonthermal electron beam rather then direct heating;
(2) loops are bundles of strands that undergo thermal nonequilibrium
that results when steady heating is sufficiently concentrated near
the footpoints. We verify these possibilities with numerical hydro
simulations. Time permitting, we will show FeXVII line profile
observations from EIS/Hinode that support the existence of nanoflare
heating. Work supported by NASA and ONR.
---------------------------------------------------------
Title: Comparison of 3D Numerical Simulations with STEREO Observations
of Coronal Jets
Authors: Pariat, E.; Patsourakos, S.; Antiochos, S. K.; DeVore, C. R.
2007AGUFMSH41B..03P Altcode:
Recent solar observations have revealed that coronal jets are a more
frequent phenomenon than previously believed. It is widely accepted that
magnetic reconnection is the fundamental mechanism that gives rise to
the jets. The improved spatial and temporal resolution of the STEREO
observations in combination with stereoscopy yields new insights into
the origins of coronal jets, and provides detailed data that can be
used to test and refine models. We present the results of a 3D numerical
simulation of our model for coronal jets. The simulations were performed
with our state-of-art adaptive mesh MHD solver ARMS. The basic idea
of the model is that a jet is due to the release of twist as a closed
field region undergoes interchange reconnection with surrounding open
field. We compare the structure and dynamics of the simulated jet with
actual EUVI observations, focusing on how the reconfiguration of the
3D magnetic field explains observed properties of the jet. We also
discuss possible signatures for STEREO of twisted structures within
jets. Finally, we discuss the implications of our simulations for
future stereoscopic observations with STEREO. This work was supported,
in part, by NASA and ONR.
---------------------------------------------------------
Title: Towards a Better Understanding of CME Onsets with SECCHI
on STEREO
Authors: Patsourakos, S.; Vourlidas, A.
2007AGUFMSH32A0779P Altcode:
Observations of the first minutes in the life of Coronal Mass Ejections
(CMEs) represent the main key into identifying the physical mechanism(s)
behind them. Previous observations of CME onsets were limited by factors
such as low cadence, small field of view, single-temperature coverage,
and lack of 3D information. These limitations are significantly
mitigated by the availability of SECCHI observations onboard the
STEREO mission. We analyze a series of high-cadence, multi-temperature
observations of CME onsets taken with the EUVI/SECCHI imagers tied with
high-cadence coronagraphic COR1/SECCHI observations. We discuss how
our perception of well-known features pertinent to CME onsets such as
dimmings, EIT waves and cavities is shaped by the unique characteristics
of SECCHI observations, and of the 3D information available in STEREO
obervations in particular. We finally discuss how the generic elements
of our observations compare with the expectations of CME models in an
attempt to place some constraints on them.
---------------------------------------------------------
Title: The Cross-Field Thermal Structure of Coronal Loops from
Triple-Filter TRACE Observations
Authors: Patsourakos, S.; Klimchuk, J. A.
2007ApJ...667..591P Altcode:
The highly suppressed thermal transport across the magnetic field
in the solar corona makes the determination of the cross-field
thermal distribution within coronal loops a powerful diagnostic
of the properties of the heating process itself. The cross-field
thermal structure is currently being strongly debated. Spectroscopic
observations with high temperature fidelity but low spatial resolution
indicate that some observed loops are multithermal, whereas imaging
observations with high spatial resolution but low temperature fidelity
indicate more isothermal conditions. We report here on triple filter
observations of coronal loops made by the Transition Region and Coronal
Explorer (TRACE), which has the best spatial resolution currently
available. We tested the isothermal hypothesis using the emission
measure loci technique and found that the loops are consistent with
an isothermal plasma near 1.5 MK only if a generous estimate of
the photometric uncertainties is used. A more restrictive estimate
based on discussions with the TRACE experimenters rules out the
isothermal hypothesis. The observations are much better explained by
a multithermal plasma with significant emission measure throughout the
range 1-3 MK. The details of the emission measure distribution are not
well defined, however. Future subarcsecond spectroscopic observations
covering a wide range of temperatures are the most promising means of
unlocking the thermal structure of the corona.
---------------------------------------------------------
Title: The Quiet Sun Network at Subarcsecond Resolution: VAULT
Observations and Radiative Transfer Modeling of Cool Loops
Authors: Patsourakos, S.; Gouttebroze, P.; Vourlidas, A.
2007ApJ...664.1214P Altcode:
One of the most enigmatic regions of the solar atmosphere is the
transition region (TR), corresponding to plasmas with temperatures
intermediate of the cool, few thousand K, chromosphere and the hot,
few million K, corona. The traditional view is that the TR emission
originates from a thin thermal interface in hot coronal structures,
connecting their chromosphere with their corona. This paradigm fails
badly for cool plasmas (~T<10<SUP>5</SUP> K), since it predicts
emission orders of magnitude less than what it is observed. It was
therefore proposed that the “missing” TR emission could originate from
tiny, isolated from the hot corona, cool loops at TR temperatures. A
major problem in investigating this proposal is the very small sizes
of the hypothesized cool loops. Here, we report the first spatially
resolved observations of subarcsecond-scale looplike structures seen
in the Lyα line made by the Very High Angular Resolution Ultraviolet
Telescope (VAULT). The subarcsecond (~0.3") resolution of VAULT allows
us to directly view and resolve looplike structures in the quiet Sun
network. We compare the observed intensities of these structures with
simplified radiative transfer models of cool loops. The reasonable
agreement between the models and the observations indicates that an
explanation of the observed fine structure in terms of cool loops
is plausible.
---------------------------------------------------------
Title: Modeling Active Regions with Steady and Impulsive Heating
Authors: Patsourakos, Spiros; Klimchuk, J.
2007AAS...210.9124P Altcode: 2007BAAS...39..208P
There has been considerable recent interest in constructing physical
models of active regions (ARs) and the global coronal. Models based on
static equilibrium theory are quite successful at reproducing soft X-ray
(SXR) images of active regions. They however fail to predict the warm
( 1 MK) loops that are seen to permeate ARs in the EUV. Instead, the
synthetic EUV images are dominated by intense footpoint emission. We
demonstrate that the failure of static models to predict EUV loops is
associated with the very weak dependence of loop temperature on loop
length in models that are based on a single heating mechanism and
that match the SXR observations. The models predict either SXR loops
or EUV loops, but not both. We therefore consider time-dependent AR
models based on nanoflare heating. We demonstrate that such models
can simultaneously reproduce both SXR and EUV loops. Moreover, they
explain the general tendency for SXR emission to dominate in the cores
of ARs and EUV emission to dominate in the periphery. We finally show
how the properties of nanoflares (energy, duration, spatial dependence,
repetition time) can affect the AR morphology. <P />Research supported
by NASA and ONR.
---------------------------------------------------------
Title: Impulsive Coronal Heating At Sub- Arcsecond Scales: What Is
The Best Diagnostic?
Authors: Patsourakos, S.; Klimchik, J. A.
2007ESASP.641E..22P Altcode:
Significant observational and theoretical evidence suggests that coronal
heating operates at sub- rcsecond, currently unresolved, spatial scales
and is impulsive in time. We demonstrate that the most sensitive
diagnostic for this type of heating is provided by spectroscopic
observations in the early phase of such events. We demonstrate that the
spectra of hot lines ( 5 MK), observed at arcsecond resolution with the
EIS spectrometer onboard the recently launched Hinode mission, hold
the signature of the impulsive heating process via the development
of asymmetric profiles. Solar Orbiter (SolO) will provide a unique
opportunity to directly view the postulated sub-arcsecond impulsive
energy releases. We demonstrate that the superior spatial resolution
of the Orbiter EUV remote sensing instrumentation should be tuned to
high temperature plasmas in order to resolve the individual strands.
---------------------------------------------------------
Title: Nonthermal Spectral Line Broadening and the Nanoflare Model
Authors: Patsourakos, S.; Klimchuk, J. A.
2006ApJ...647.1452P Altcode:
A number of theoretical and observational considerations suggest
that coronal loops are bundles of unresolved, impulsively heated
strands. This “nanoflare” model, as it is sometimes called,
predicts high-speed evaporative upflows, which might be revealed as
nonthermal broadening of spectral line profiles. We have therefore
generated synthetic line profile observations based on one-dimensional
hydrodynamic simulations for comparison with actual observations. The
predicted profiles for Ne VIII (770.4 Å), a transition region line,
and Mg X (624.9 Å), a warm coronal line, have modest broadening that
agrees well with existing observations. The predicted profiles for
Fe XVII (254.87 Å), a hot line that will be observed by the Extreme
Ultraviolet Imaging Spectrometer (EIS) on the Solar-B mission, are
somewhat broader and are also consistent with the limited number of hot
line observations that are currently available. Moreover, depending on
the properties of the assumed nanoflare and other parameters of the
simulation, the Fe XVII profile can have distinctive enhancements in
the line wing. This indicates a powerful diagnostic capability that
can be exploited once Solar-B is launched.
---------------------------------------------------------
Title: Testing Nanoflare Heating in Coronal Loops With Observations
From the Extreme Ultraviolet Imaging Spectrometer On-board the
SOLAR-B Mission
Authors: Patsourakos, Spiros; Klimchuk, J. A.
2006SPD....37.0124P Altcode: 2006BAAS...38..219P
A number of theoretical and observational considerations suggest
that coronal loops are bundles of unresolved, impulsively heated
strands. This "nanoflare" model, as it is sometimes called,
predicts high-speed evaporative upflows, which might be revealed as
non-thermal broadening of spectral line profiles. We have therefore
generated synthetic line profile observations based on 1D hydrodynamic
simulations of nanoflare heated loop bundles.We will show that hot lines
(T>5MK) hold the imprints of the heating process via the development
of distinct enhancements in the line wings. These signatures do not
appear in the profiles of cooler lines, which is fully consistent
with existing observations. We will demonstrate how the spectra of hot
lines from the Extreme Ultraviolet Imaging Spectrometer (EIS) on-board
the upcoming SOLAR-B mission can be used to test the basic nanoflare
picture and perhaps even to pinpoint the properties of the nanoflares,
such as their energy content, duration, and spatial dependence. We
will present sample observing programs for studying nanoflare heating
in coronal loops that utilize EIS and other instrumentation on-board
SOLAR-B and STEREO.Research supported by NASA and ONR.
---------------------------------------------------------
Title: Coronal Loop Heating by Nanoflares: The Impact of the
Field-aligned Distribution of the Heating on Loop Observations
Authors: Patsourakos, S.; Klimchuk, J. A.
2005ApJ...628.1023P Altcode:
Nanoflares occurring at subresolution strands with repetition times
longer than the coronal cooling time are a promising candidate
for coronal loop heating. To investigate the impact of the spatial
distribution of the nanoflare heating on loop observables, we compute
hydrodynamic simulations with several different spatial distributions
(uniform, loop top, randomly localized, and footpoint). The outputs
of the simulations are then used to calculate density and temperature
diagnostics from synthetic TRACE and SXT observations. We find that
the diagnostics depend only weakly on the spatial distribution of the
heating and therefore are not especially useful for distinguishing among
the different possibilities. Observations of the very high temperature
plasmas that are present only in the earliest stages of nanoflares
can shed more light on the field-aligned distribution of the heating.
---------------------------------------------------------
Title: Coronal Loop Heating by Nanoflares: Non-thermal Velocities
Authors: Patsourakos, S.; Klimchuk, J. A.
2005AGUSMSP41A..06P Altcode:
Spectroscopic observations show non-negligible non-thermal velocities
under coronal conditions. These motions place tight constraints on any
coronal heating mechanism that should be able to reproduce them. We
calculate the non-thermal velocities predicted by the nanoflare
model. We perform 1D time-dependent hydrodynamic simulations of
nanoflares occurring at sub-resolution strands, that make up the
observed coronal loops and calculate profiles for representative
spectral lines. We show that: (1) the calculated non-thermal velocities
compare favorably with observations of cool and warm spectral
lines and (2) the profiles of hot lines, that would be available in
observations from the Extreme Ultraviolet Imaging Spectrometer (EIS)
spectrometer onboard the SOLAR-B mission, can exhibit significant
blue-wing asymmetries which can be used as a monitor of nanoflare
properties. Research supported by NASA and ONR.
---------------------------------------------------------
Title: Coronal Loop Heating by Nanoflares: The Influence of the
Field-aligned Distribution of the Heating on Observables
Authors: Patsourakos, S.; Klimchuk, J. A.
2005AGUSMSP41A..05P Altcode:
We investigate the effect of the spatial distribution of nanoflare
heating on loop observables. We perform 1D time-dependent hydrodynamic
simulations of nanoflares occurring at sub-resolution strands, that make
up the observed coronal loops. The simulations use different spatial
forms for the nanoflare heating (randomly localized, footpoint, uniform
loop top). The outputs of the simulations are then used to calculate
diagnostics from synthetic TRACE and SXT observations. We find that
the diagnostics depend only weakly on the spatial distribution of the
heating, and therefore are not especially useful for distinguishing
among the different possibilities. We propose that the best way to
study the field-aligned spatial distribution of nanoflare heating is
to observe the very high temperature plasmas that are present only in
the earliest stages of an event. Research supported by NASA and ONR.
---------------------------------------------------------
Title: Highly Efficient Modeling of Dynamic Coronal Loops
Authors: Klimchuk, J. A.; Patsourakos, S.; Cargill, P. J.
2005AGUSMSP14A..03K Altcode:
It now seems clear that many coronal loops, especially those observed
by TRACE and EIT, are inherently dynamic and composed of large numbers
of impulsively-heated strands. Modeling these loops in full detail is
extremely challenging, and modeling entire active regions or the whole
Sun is completely out of the question unless approximate techniques are
used. We have developed a simplified set of equations that is remarkably
accurate at describing the evolution of the thermodynamic variables
(T, P, n, v) averaged along the magnetic field of an individual
strand. The equations can be solved ten thousand times more quickly
than the full 1D hydro equations. This "0D" model relaxes two key
assumptions of Cargill's (1994) nanoflare model: (1) the heating can
have any time-dependent profile and need not be instantaneous; and
(2) thermal conduction cooling and radiation cooling occur together
at all times, in varying proportions. We here describe the essential
features of the model and show examples of how well it works.
---------------------------------------------------------
Title: The Effect of the Spatial Distribution of Nanoflare Heating
on Loop Observables
Authors: Patsourakos, S.; Klimchuk, J. A.
2004ESASP.575..297P Altcode: 2004soho...15..297P
No abstract at ADS
---------------------------------------------------------
Title: A Model for Bright Extreme-Ultraviolet Knots in Solar Flare
Loops
Authors: Patsourakos, S.; Antiochos, S. K.; Klimchuk, J. A.
2004ApJ...614.1022P Altcode:
EUV observations often indicate the presence of bright knots in flare
loops. The temperature of the knot plasma is of the order of 1 MK,
and the knots themselves are usually localized somewhere near the loop
tops. We propose a model in which the formation of EUV knots is due
to the spatial structure of the nonflare active region heating. We
present the results of a series of one-dimensional hydrodynamic,
flare-loop simulations, which include both an impulsive flare heating
and a background, active region heating. The simulations demonstrate
that the formation of the observed knots depends critically on
the spatial distribution of the background heating during the decay
phase. In particular, the heating must be localized far from the loop
apex and have a magnitude comparable to the local radiative losses of
the cooling loop. Our results, therefore, provide strong constraints
on both coronal heating and postflare conditions.
---------------------------------------------------------
Title: Bright EUV Knots in Solar Flare Loops: Constraints on Coronal
Heating
Authors: Patsourakos, S.; Antiochos, S.; Klimchuk, J.
2004AAS...204.8705P Altcode: 2004BAAS...36Q.819P
EUV observations often indicate the presence of bright knots in flare
loops. The temperature of the knot plasma is of order 1MK, and the
knots themselves are usually localized somewhere near the loop tops. We
propose a model in which the formation of EUV knots is due to the
spatial structure of the non-flare active region heating. We present
the results of a series of 1D hydrodynamic, flare-loop simulations,
which include both an impulsive flare heating and a background, active
region heating. The simulations demonstrate that the formation of the
observed knots depends critically on the spatial distribution of the
background heating during the decay phase. In particular, the heating
must: (1) be localized, (2) be situated far from the loop apex and (3)
have a magnitude comparable with the local radiative losses of the
cooling loop. Our results, therefore, provide strong constraints on
both coronal heating and post-flare conditions. <P />Research supported
by NASA and ONR.
---------------------------------------------------------
Title: Mass and Kinetic Energy Distributions of Coronal Mass Ejections
in 1996-2002
Authors: Vourlidas, A.; Patsourakos, S.
2004AAS...204.7303V Altcode: 2004BAAS...36..800V
We present the mass and kinetic energy distributions of coronal mass
ejections observed by LASCO between 1996 and 2002. The sample includes
more than 4000 events. Events with projected widths larger than 120
deg were excluded because of uncertainties in the calculation of the
mass and speed for such large events. <P />We compare the LASCO mass
and energy distribution to similar distributions from Solwind and
soft x-ray flares. In particular, we find that the CME kinetic energy
distribution follows a power law similar to the one found for solar
flares. The implications of our findings are discussed in the paper.
---------------------------------------------------------
Title: The Inability of Steady-Flow Models to Explain the
Extreme-Ultraviolet Coronal Loops
Authors: Patsourakos, S.; Klimchuk, J. A.; MacNeice, P. J.
2004ApJ...603..322P Altcode:
Recent observations from the Transition Region and Coronal Explorer
(TRACE) and the EUV Imaging Telescope (EIT) show that warm (T~1-1.5 MK)
EUV coronal loops in active regions generally have enhanced densities,
enhanced pressure scale heights, and flat filter ratio (temperature)
profiles in comparison with the predictions of static-equilibrium
theory. It has been suggested that mass flows may explain these
discrepancies. We investigate this conjecture using one-dimensional
hydrodynamic simulations of steady flows in coronal loops. The flows
are driven by asymmetric heating that decreases exponentially along
the loop from one footpoint to the other. We find that a sufficiently
large heating asymmetry can produce density enhancements consistent
with a sizable fraction of the observed loops, but that the pressure
scale heights are smaller than the corresponding gravitational scale
heights, and that the filter ratio profiles are highly structured,
in stark contrast to the observations. We conclude that most warm EUV
loops cannot be explained by steady flows. It is thus likely that the
heating in these loops is time dependent.
---------------------------------------------------------
Title: Solar Physics from Space for the Next Solar Cycle
Authors: Vourlidas, Angelos; Patsourakos, Spiros
2004hell.conf...78V Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Coronal Loop Heating by Nanoflares: Some Observational
Implications
Authors: Patsourakos, S.; Klimchuk, J. A.
2004hell.conf...35P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Are All Coronal Loops Heated by Nanoflares?
Authors: Klimchuk, J. A.; Patsourakos, S.; Winebarger, A. R.
2003SPD....34.1006K Altcode: 2003BAAS...35R.825K
Observations from TRACE, SOHO, and Yohkoh have revealed new details
of coronal loops that make them more mysterious than ever. One of
the biggest puzzles concerns the loop density. Hot (> 2 MK) loops
observed by Yohkoh tend to be under dense compared to the predictions
of equilibrium theory, while warm ( 1 MK) loops observed by TRACE
and EIT tend to be over dense. Some over dense loops can be explained
by steady heating that is concentrated near one or both of the loop
legs, but a majority of these loops cannot. <P />We here consider
the possibility that observed loops are comprised of large numbers
of unresolved strands that are heated impulsively and randomly by
nanoflares. The loops appear quasi-steady even though the individual
sub-strands are highly time dependent. When the strands are hot,
they cool primarily by thermal conduction and are under dense, but
when they are warm, they cool primarily by radiation and are over
dense. Since Yohkoh and TRACE are sensitive to different strands,
we might expect them to observe the under and over densities that
they do. <P />To evaluate the feasibility of this universal model
of coronal loops, we have performed 1D hydrodynamic simulations of
impulsively heated strands and compared them with observations from
Yohkoh and TRACE. The results are encouraging in many respects, but
difficulties remain. In this presentation, we discuss the successes
and failures of the model. <P />This work was supported by NASA and ONR.
---------------------------------------------------------
Title: Can Steady-state Mass Flows Explain the Non-hydrostatic Cool
EUV Coronal Loops in Active Regions?
Authors: Patsourakos, S.; Klimchuk, J. A.
2003SPD....34.1009P Altcode: 2003BAAS...35..826P
Recent EIT/TRACE observations of cool (≈ 1-1.5 MK) EUV coronal loops
in active regions showed that these loops are very often characterized
by greatly enhanced pressure scale-heights and densities compared to
the predictions of static equilibrium theory. It has been suggested
that mass flows may explain these over-dense and over-pressure
loops. We investigate this conjecture by the means of 1D hydrodynamic
simulations of steady-state mass flows in coronal loops. The mass flows
in our calculations are driven by asymmetric heating that decreases
exponentially along the loop from one footpoint all way to the
other. By considering several representative cases for the magnitude
and the length scale of the applied asymmetric heating, we determine
how steady-state mass flows affect the thermodynamic structure of
coronal loops and assess whether they can lead to enhanced pressure
scale-heights and densities. Research supported in part by NASA and ONR.
---------------------------------------------------------
Title: Bright Knots in EUV Post-flare Loops : TRACE Observations
and 1D Hydrodynamic Modeling
Authors: Patsourakos, S.; Antiochos, S. K.; Klimchuk, J. A.
2002AGUFMSH21C..04P Altcode:
EUV post-flare loops often possess bright knots along them. Some
examples of such post-flare loops seen by TRACE will be shown, along
with a brief outline of their properties. We will then present the
results of a series of 1D hydrodynamic simulations of flaring loops,
which employ different heating functions for the impulsive and decay
phase of the simulated flares. It will be demonstrated that the creation
of these knots depends crucially on the spatio-temporal distribution of
the heating during the decay phase. This provides strong constraints
on both post-flaring conditions and AR loop heating. We will finally
briefly outline how SDO instrumentation could improve our knowledge
of this topic. Research supported in part by NASA and ONR.
---------------------------------------------------------
Title: Ion Effective Temperatures in Polar Coronal Holes: Observations
versus Ion-Cyclotron Resonance
Authors: Patsourakos, S.; Habbal, S. R.; Hu, Y. Q.
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: Fuzzy hot post-flare loops versus sharp cool post-flare loops
Authors: Patsourakos, S.; Antiochos, S. K.; Klimchuk, J. A.
2002ESASP.505..207P Altcode: 2002solm.conf..207P; 2002IAUCo.188..207P
By using high spatial resolution TRACE EUV observations we show that hot
(≍2 MK) post-flare loops are fuzzier than the cooler (≍1 MK) ones. A
simple 0d model of a cooling loop arcade, where different loops in the
arcade start to cool down at slightly different initial conditions,
is sufficient to reproduce qualitatively the observed behavior of the
EUV post-flare loops.
---------------------------------------------------------
Title: Soho Contribution to Prominence Science
Authors: Patsourakos, Spiros; Vial, Jean-Claude
2002SoPh..208..253P Altcode:
We present the main current issues concerning prominence studies. We
recall the large range of plasma parameters found in prominences
which makes the work of the MHD modeler more difficult. We also
summarize the capabilities of the SOHO instrumentation. We present and
discuss the most recent SOHO results concerning the determination of
temperature, densities, and velocities. We put some emphasis on the
different morphologies observed, the diagnostic capabilities of the
Lyman lines profiles when accompanied by improved non-LTE modeling,
and the information gathered from the first prominence oscillations
measured from space. We also make an account of eruptive prominences. We
finally discuss what could be done with present and future SOHO data
to improve our understanding of prominences.
---------------------------------------------------------
Title: Solar cycle variation of the temperature structure within
the cores of coronal streamers
Authors: Culhane, J. L.; Foley, C. R.; Patsourakos, S.; Mackay, D.
2002ESASP.508..371C Altcode: 2002soho...11..371C
We use the Coronal Diagnostic Spectrometer onboard the Solar and
Heliospheric Observatory (SOHO) to analyze conditions in coronal
streamer structures observed close to solar minimum (1996, July 8) and
near maximum (1999, August 5). From emission line intensities (Fe IX-XV
ions), the line ratio method gives the radial temperature behaviour. The
solar minimum peak values were about 1.4 MK at 1.3 R<SUB>0</SUB>, while
near solar maximum values were consistent with Yohkoh observations at
the last maximum, displaying an asymptotic temperature of around 2.2
MK above 1.2 R<SUB>0</SUB>. We discuss the observations in relation to
possible mechanisms for energy deposition in large coronal structures.
---------------------------------------------------------
Title: Hot versus cool coronal loops
Authors: Patsourakos, S.; Klimchuk, J. A.; Antiochos, S. K.
2002AAS...200.0209P Altcode: 2002BAAS...34..640P
EUV and SXR observations show respectively that cool (1 MK) loops are
finer and maybe more dynamic than hotter (2 MK) ones. Whether this
reflects a fundamental difference in the properties of the heating
mechanism in action in each loop class is not yet clear. We will address
some aspects of this issue by combining EUV and SXR observations of
such loops with eventually hydrodynamic simulations of a nano-flare
heated corona. Research supported in part by ONR and NASA.
---------------------------------------------------------
Title: Intermittent behavior in the transition region and the low
corona of the quiet Sun
Authors: Patsourakos, S.; Vial, J. -C.
2002A&A...385.1073P Altcode:
We present an analysis of light-curves obtained in the O IV and Ne
VIII transition region and low corona lines, that were simultaneously
recorded in a quiet Sun region by SUMER/SOHO. By using the flatness
spectrum of the observed light-curves we searched for intermittency
signatures. It was found that a significant proportion of points
in the observed area exhibit clear indications of intermittency,
irrespectively of their intrinsic intensity. Our findings give favor to
an impulsively heated transition region and corona via intermittent-type
MHD turbulence.
---------------------------------------------------------
Title: What are the Origins of Quiescent Coronal Soft X-Rays?
Authors: Foley, C. R.; Culhane, J. L.; Patsourakos, S.; Yurow, R.;
Moroney, C.; Mackay, D.
2002mwoc.conf..341F Altcode:
We have examined the evolution and modulation of the Sun's atmosphere
from the photosphere up to the outer corona through the decline and
rise of solar cycles 22, and 23 respectfully. For this we have used
Yohkoh soft X-ray telescope (SXT) images, Kitt peak magnetograms and EUV
spectra provided by the Coronal Diagnostic Spectrometer (CDS). We find
as Hara (1996, 1997) found, that there is a modulation of the coronal
brightness which varies annually in the high latitude activity zones,
and that this is linked to the presence and disappearance of active
regions on the sun's disk. We interpret our results with regards to the
emergence and diffusion of magnetic flux. We find that the appearance
of high latitude activity zones may be explained simply by the decay
of diffused active region flux, We also find evidence for a positive
temperature gradient within the corona from the emission profiles in
the different lines.
---------------------------------------------------------
Title: Solar cycle variation of the temperature structure within
the cores of coronal streamers
Authors: Foley, C. R.; Patsourakos, S.; Culhane, J. L.; MacKay, D.
2002A&A...381.1049F Altcode:
We use the Coronal Diagnostic Spectrometer onboard the Solar and
Heliospheric Observatory (SOHO) to analyze conditions in coronal
streamer structures observed close to solar minimum (1996 July 8)
and near maximum (1999 August 5). We measured the intensities of
emission lines from Fe IX-XV ions and found the most intense emission
to be from Fe XI at solar minimum and from Fe XV at solar maximum. We
then used the line ratio method with transitions in selected ions to
extract the radial temperature behavior in the structures. The solar
minimum peak values were about 1.4 MK at 1.3 R<SUB>sun</SUB>, while
values derived close to solar maximum were consistent with the Yohkoh
observations at the last maximum, displaying an apparently asymptotic
temperature of around 2.2 MK above 1.2 R<SUB>sun</SUB>. We discuss the
observations in relation to possible mechanisms for energy deposition
in large coronal structures at different phases of the solar cycle.
---------------------------------------------------------
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.
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: Analysis of a UV Event in a Polar Coronal Hole
Authors: Patsourakos, Spiros; Vial, Jean-Claude
2001SoPh..203...39P Altcode:
We present observations of a UV event which occurred in a polar coronal
hole. They were obtained by SUMER on SOHO in several chromospheric and
transition region spectral lines. Its birth site was about 50 arc sec
inside the limb and in a network lane showing a net outflow before
its initiation. The event had an extension of about 5 arc sec along
the slit, a duration of about 3 min and was characterized by a large
increase of intensity together with a significant line broadening
with, however, downflows of about 50 km s<SUP>−1</SUP> being
dominant. Proper motions with a velocity of about 10 km s<SUP>−1</SUP>
were also observed. The event appeared at middle transition (O vi)
temperatures and it simultaneously showed up in chromospheric (O i,
Ly β) and low transition region (C ii) temperatures. We discuss this
event in view of different scenarios to account for it. Our event could
be a part of the large family of quiet-Sun explosive events observed
by Ryutova and Tarbell (2000) taking place in polar coronal holes that
are triggered by magnetic reconnection in the low solar atmosphere.
---------------------------------------------------------
Title: High-resolution EUV imaging and spectroscopy of the corona
Authors: Patsourakos, Spiros; Vial, J. -C.
2001ESASP.493...13P Altcode: 2001sefs.work...13P
We present a set of imagers and spectrometer which have been proposed as
a strawman payload on board the Solar Orbiter mission. The scientific
requirements of the mission are put in the context of the main issues
presently discussed in solar physics. The on-going successful space
solar missions have evidenced a very fine structuring of the solar
atmosphere and its role in various processes at work for coronal
heating, wind acceleration, flaring activity, etc. This is especially
true for magnetic reconnection which seems to proceed at many different
scales. These results point at the need of observations substantially
improving both the spatial resolution and the multi-temperature
(multi-wavelength) coverage. Solar Orbiter offers a unique opportunity
to analyze this fine structure (e.g. the internal structure of the
thin loops observed by TRACE) in closed and open fields. It will allow
for a diagnostic of regions such as the magnetic network which seems
to play a major role in the wind acceleration, in conjunction with
in-situ observations of the ejected plasma.
---------------------------------------------------------
Title: Searching the source regions of the fast solar wind in polar
coronal holes: some recent SOHO/eclipse results and the potential
of the Solar Orbiter
Authors: Patsourakos, Spiros; Vial, J. -C.
2001ESASP.493..321P Altcode: 2001sefs.work..321P
No abstract at ADS
---------------------------------------------------------
Title: Outflow velocity of interplume regions at the base of Polar
Coronal Holes
Authors: Patsourakos, S.; Vial, J. -C.
2000A&A...359L...1P Altcode:
We report on SUMER/SOHO observations at 1.05 R<SUB>sun</SUB> of a well
identified interplume region in a South Pole Coronal Hole. Combination
of Doppler shifts and Doppler dimming measurements allowed to
determine, for the first time, the total wind outflow velocity (~ 67 km
s<SUP>-1</SUP>) at this height. Our calculations of the outflow velocity
benefit from co-spatial and almost co-temporal observations. This large
outflow velocity is a strong argument in favour of the interplumes
being the main source of the fast solar wind. We find that the mass
flux density through the observed interplume is 4.8 10<SUP>-10</SUP>
g cm<SUP>-2</SUP>s<SUP>-1</SUP> which yields 10<SUP>-15</SUP> g
cm<SUP>-2</SUP>s<SUP>-1</SUP> at 1 AU with an expansion factor of 11.
---------------------------------------------------------
Title: Contribution a l'etude du chauffage de la couronne solaire et
de l'acceleration du vent solaire dans les trous coronaux Title:
Contribution a l'etude du chauffage de la couronne solaire et
de l'acceleration du vent solaire dans les trous coronaux Title:
Investigation of coronal heating and solar wind acceleration in
coronal holes;
Authors: Patsourakos, Spiros
2000PhDT.......234P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Transition-Region Network Boundaries in the Quiet Sun: Width
Variation with Temperature as Observed with CDS on SOHO
Authors: Patsourakos, S.; Vial, J. -C.; Gabriel, A. H.; Bellamine, N.
1999ApJ...522..540P Altcode:
We report here the results of a study of the temperature variation
of the network boundary thicknesses in the quiet-Sun transition
region. A Fourier-based two-dimensional autocorrelation method has
been applied to 240<SUP>”</SUP>×240<SUP>”</SUP> rasters obtained in
several transition-region lines by the CDS spectrometer on SOHO. The
quantitative variation of the network boundary width with temperature
has been obtained for the first time in a full two-dimensional field. It
appears that network boundaries have an almost constant width up to
a temperature of about 10<SUP>5.4</SUP> K and then fan out rapidly at
coronal temperatures. This expansion of the transition-region network
boundaries with temperature is found to be quantitatively in agreement
with earlier theoretical models of the transition region.
---------------------------------------------------------
Title: Coordinated observations between SOHO/SUMER and ground during
the 1998 total eclipse: Non-thermal line broadenings and electron
densities in a polar coronal hole
Authors: Patsourakos, S.; Vial, J. -C.; Gabryl, J. -R.; Koutchmy,
S.; Schühle, U.
1999AIPC..471..285P Altcode: 1999sowi.conf..285P
Alfvén waves represent one of the most prominent ways of heating the
solar corona and accelerating the solar wind. One of their signatures
is to broaden the spectral lines in excess of their thermal width. Here
we aim to combine observations of non-thermal broadenings measured
by SUMER in OVI (1037.6 Å) line and electronic densities derived
from white-light observations during the 1998 total eclipse. After
checking the validity of the frequently-used assumption of equal ion
and electron temperatures, we compute the variation of the non-thermal
velocity as a function of height in an interplume region within the
south polar coronal hole.
---------------------------------------------------------
Title: Outflow Velocities at the Base of a Polar Coronal Hole During
the 1998 Total Eclipse
Authors: Patsourakos, S.; Vial, J. -C.; Gabryl, J. -R.; Koutchmy,
S.; Schühle, U.
1999SSRv...87..291P Altcode:
Polar coronal holes represent the most convincing site from which the
high-speed solar wind originates. Here we report high-accuracy Doppler
shifts measured in the O VI (1037.6 Å) line obtained by SUMER on SOHO
inside an interplume region within the south polar coronal hole. We
infer limits on the outflow velocity and draw hints about the flow
geometry.
---------------------------------------------------------
Title: Solar chromospheric structures observed in UV ressonance
lines : a multivariate analysis approach
Authors: Patsourakos, S.; Bocchialini, K.; Vial, J. -C.
1999CR2...322..337P Altcode:
We present the results of a statistical analysis carried out from a data
base of 6 solar chromospheric emission lines recorded simultaneously
and with high spectral resolution. An empirical and a clustering method
for separating the different solar structures contributions have been
used and been found in a good agreement. Mean profiles corresponding to
the different populations have been built. Correlations of different
parameters for each profile allowed us to deduce different properties
of the solar chromosphere, such as the existence of magnetic canopies
and downflows in active regions.
---------------------------------------------------------
Title: Solar chromospheric structures observed in UV resonance lines:
a multivariate analysis approach.
Authors: Patsourakos, S.; Bocchialini, K.; Vial, J. -C.
1998CRASB.326..337P Altcode:
The authors present the results of a statistical analysis carried out
from a data base of six solar chromospheric emission lines recorded
simultaneously and with high spectral resolution. An empirical and
a clustering method for separating the different solar structure
contributions have been used and found to be in good agreement. Mean
profiles corresponding to the different populations have been
built. Correlations of different parameters for each profile allowed
one to deduce different properties of the solar chromosphere, such as
the existence of magnetic canopies and downflows in active regions.
---------------------------------------------------------
Title: Simulated white-light images of coronal structures as obtained
by the CORI imager on-board a solar probe
Authors: Patsourakos, S.; Vial, J. -C.
1997AIPC..385..129P Altcode: 1997recs.conf..129P
A white-light coronal imager called CORI to be implemented on a solar
probe has been proposed by Habbal et al. (1995). Its scientific
objectives concern the investigation of the solar corona and the
source of the solar wind. It is aimed as a complement to the in-situ
instruments. This paper presents some simulations of the images
that will be recorded when observing solar structures of increasing
complexity during the close encounter phase of the trajectory. These
attempts should be considered as a first step towards the assessment
of the full scientific capabilities of CORI and the definition of the
observing strategy.
---------------------------------------------------------
Title: Low Transition-Region Characteristics of Equatorial Coronal
Holes
Authors: Patsourakos, S.; Bocchialini, K.; Vial, J. -C.
1997ESASP.404..577P Altcode: 1997cswn.conf..577P
No abstract at ADS
---------------------------------------------------------
Title: First Results of SOHO's Joint Observing Programme 40
Authors: Patsourakos, S.; Bocchialini, K.; Vial, J. -C.
1997IAUJD..19E..38P Altcode:
The first results of SOHO's JOP 40 are presented. This program
proposes to study the chromospheric to transition region of equatorial
coronal holes in order to derive parameters such as the temperature,
the density, using different lines formed at different altitudes,
in different places: the boundary of a coronal hole or the central
region, on the disk. The two components of the chromospheric quiet
Sun, network and internetwork, should be observed, in and out of an
equatorial coronal hole.