peter

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Author name code: peter
ADS astronomy entries on 2022-09-14
author:"Peter, Hardi"

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Title: What drives decayless kink oscillations in active region
coronal loops on the Sun?
Authors: Mandal, Sudip; Chitta, Lakshmi P.; Antolin, Patrick; Peter,
Hardi; Solanki, Sami K.; Auchère, Frédéric; Berghmans, David;
Zhukov, Andrei N.; Teriaca, Luca; Cuadrado, Regina A.; Schühle,
Udo; Parenti, Susanna; Buchlin, Éric; Harra, Louise; Verbeeck, Cis;
Kraaikamp, Emil; Long, David M.; Rodriguez, Luciano; Pelouze, Gabriel;
Schwanitz, Conrad; Barczynski, Krzysztof; Smith, Phil J.
2022arXiv220904251M Altcode:
We study here the phenomena of decayless kink oscillations in a system
of active region (AR) coronal loops. Using high resolution observations
from two different instruments, namely the Extreme Ultraviolet Imager
(EUI) on board Solar Orbiter and the Atmospheric Imaging Assembly
(AIA) on board the Solar Dynamics Observatory, we follow these AR
loops for an hour each on three consecutive days. Our results show
significantly more resolved decayless waves in the higher-resolution
EUI data compared with the AIA data. Furthermore, the same system of
loops exhibits many of these decayless oscillations on Day-2, while on
Day-3, we detect very few oscillations and on Day-1, we find none at
all. Analysis of photospheric magnetic field data reveals that at most
times, these loops were rooted in sunspots, where supergranular flows
are generally absent. This suggests that supergranular flows, which
are often invoked as drivers of decayless waves, are not necessarily
driving such oscillations in our observations. Similarly, our findings
also cast doubt on other possible drivers of these waves, such as a
transient driver or mode conversion of longitudinal waves near the loop
footpoints. In conclusion, through our analysis we find that none of
the commonly suspected sources proposed to drive decayless oscillations
in active region loops seems to be operating in this event and hence,
the search for that elusive wave driver needs to continue.

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Title: Reconfiguration and Eruption of a Solar Filament by Magnetic
Reconnection with an Emerging Magnetic Field
Authors: Li, Leping; Peter, Hardi; Pradeep Chitta, Lakshmi; Song,
Hongqiang; Xu, Zhe; Xiang, Yongyuan
2022ApJ...935...85L Altcode: 2022arXiv220704579L
Both observations and simulations suggest that the solar filament
eruption is closely related to magnetic flux emergence. It is thought
that the eruption is triggered by magnetic reconnection between
the filament and the emerging flux. However, the details of such
a reconnection are rarely presented. In this study, we report the
detailed reconnection between a filament and its nearby emerging
fields, which led to the reconfiguration and subsequent partial
eruption of the filament located over the polarity inversion line of
active region 12816. Before the reconnection, we observed repeated
brightenings in the filament at a location that overlies a site of
magnetic flux cancellation. Plasmoids form at this brightening region,
and propagate bidirectionally along the filament. These indicate the
tether-cutting reconnection that results in the formation and eruption
of a flux rope. To the northwest of the filament, magnetic fields
emerge, and reconnect with the context ones, resulting in repeated
jets. Afterwards, other magnetic fields emerge near the northwestern
filament endpoints, and reconnect with the filament, forming the newly
reconnected filament and loops. A current sheet repeatedly occurs at
the interface, with the mean temperature and emission measure of 1.7
MK and 1.1×1028 cm-5. Plasmoids form in the
current sheet, and propagate along it and further along the newly
reconnected filament and loops. The newly reconnected filament then
erupts, while the unreconnected filament remains stable. We propose
that besides the orientation of emerging fields, some other parameters,
such as the position, distance, strength, and area, are also crucial
for triggering the filament eruption.

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Title: A highly dynamic small-scale jet in a polar coronal hole
Authors: Mandal, Sudip; Chitta, Lakshmi Pradeep; Peter, Hardi;
Solanki, Sami K.; Cuadrado, Regina Aznar; Teriaca, Luca; Schühle,
Udo; Berghmans, David; Auchère, Frédéric
2022A&A...664A..28M Altcode: 2022arXiv220602236M
We present an observational study of the plasma dynamics at the base
of a solar coronal jet, using high resolution extreme ultraviolet
imaging data taken by the Extreme Ultraviolet Imager on board Solar
Orbiter, and by the Atmospheric Imaging Assembly on board Solar
Dynamics Observatory. We observed multiple plasma ejection events
over a period of ∼1 h from a dome-like base that is ca. 4 Mm wide
and is embedded in a polar coronal hole. Within the dome below the
jet spire, multiple plasma blobs with sizes around 1−2 Mm propagate
upwards to the dome apex with speeds of the order of the sound speed
(ca. 120 km s−1). Upon reaching the apex, some of these
blobs initiate flows with similar speeds towards the other footpoint
of the dome. At the same time, high speed super-sonic outflows
(∼230 km s−1) are detected along the jet spire. These
outflows as well as the intensity near the dome apex appear to be
repetitive. Furthermore, during its evolution, the jet undergoes
many complex morphological changes, including transitions between
the standard and blowout type eruption. These new observational
results highlight the underlying complexity of the reconnection
process that powers these jets and they also provide insights into
the plasma response when subjected to rapid energy injection. Movies associated to Figs. 1, 2, and 4 are available at <A
href="https://www.aanda.org/10.1051/0004-6361/202243765/olm">https://www.aanda.org</A>

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Title: Linking Small-scale Solar Wind Properties with Large-scale
Coronal Source Regions through Joint Parker Solar Probe-Metis/Solar
Orbiter Observations
Authors: Telloni, Daniele; Zank, Gary P.; Sorriso-Valvo, Luca;
D'Amicis, Raffaella; Panasenco, Olga; Susino, Roberto; Bruno, Roberto;
Perrone, Denise; Adhikari, Laxman; Liang, Haoming; Nakanotani, Masaru;
Zhao, Lingling; Hadid, Lina Z.; Sánchez-Cano, Beatriz; Verscharen,
Daniel; Velli, Marco; Grimani, Catia; Marino, Raffaele; Carbone,
Francesco; Mancuso, Salvatore; Biondo, Ruggero; Pagano, Paolo; Reale,
Fabio; Bale, Stuart D.; Kasper, Justin C.; Case, Anthony W.; de Wit,
Thierry Dudok; Goetz, Keith; Harvey, Peter R.; Korreck, Kelly E.;
Larson, Davin; Livi, Roberto; MacDowall, Robert J.; Malaspina, David
M.; Pulupa, Marc; Stevens, Michael L.; Whittlesey, Phyllis; Romoli,
Marco; Andretta, Vincenzo; Deppo, Vania Da; Fineschi, Silvano; Heinzel,
Petr; Moses, John D.; Naletto, Giampiero; Nicolini, Gianalfredo;
Spadaro, Daniele; Stangalini, Marco; Teriaca, Luca; Capobianco,
Gerardo; Capuano, Giuseppe E.; Casini, Chiara; Casti, Marta; Chioetto,
Paolo; Corso, Alain J.; Leo, Yara De; Fabi, Michele; Frassati,
Federica; Frassetto, Fabio; Giordano, Silvio; Guglielmino, Salvo L.;
Jerse, Giovanna; Landini, Federico; Liberatore, Alessandro; Magli,
Enrico; Massone, Giuseppe; Messerotti, Mauro; Pancrazzi, Maurizio;
Pelizzo, Maria G.; Romano, Paolo; Sasso, Clementina; Schühle, Udo;
Slemer, Alessandra; Straus, Thomas; Uslenghi, Michela; Volpicelli,
Cosimo A.; Zangrilli, Luca; Zuppella, Paola; Abbo, Lucia; Auchère,
Frédéric; Cuadrado, Regina Aznar; Berlicki, Arkadiusz; Ciaravella,
Angela; Lamy, Philippe; Lanzafame, Alessandro; Malvezzi, Marco;
Nicolosi, Piergiorgio; Nisticò, Giuseppe; Peter, Hardi; Solanki,
Sami K.; Strachan, Leonard; Tsinganos, Kanaris; Ventura, Rita; Vial,
Jean-Claude; Woch, Joachim; Zimbardo, Gaetano
2022ApJ...935..112T Altcode:
The solar wind measured in situ by Parker Solar Probe in the very
inner heliosphere is studied in combination with the remote-sensing
observation of the coronal source region provided by the METIS
coronagraph aboard Solar Orbiter. The coronal outflows observed near
the ecliptic by Metis on 2021 January 17 at 16:30 UT, between 3.5 and
6.3 R ⊙ above the eastern solar limb, can be associated
with the streams sampled by PSP at 0.11 and 0.26 au from the Sun,
in two time intervals almost 5 days apart. The two plasma flows
come from two distinct source regions, characterized by different
magnetic field polarity and intensity at the coronal base. It follows
that both the global and local properties of the two streams are
different. Specifically, the solar wind emanating from the stronger
magnetic field region has a lower bulk flux density, as expected,
and is in a state of well-developed Alfvénic turbulence, with low
intermittency. This is interpreted in terms of slab turbulence in the
context of nearly incompressible magnetohydrodynamics. Conversely,
the highly intermittent and poorly developed turbulent behavior of the
solar wind from the weaker magnetic field region is presumably due to
large magnetic deflections most likely attributed to the presence of
switchbacks of interchange reconnection origin.

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Title: Small-scale coronal brightenings as seen by Solar Orbiter
Authors: Peter, Hardi; Berghmans, David; Chitta, Lakshmi Pradeep
2022cosp...44.1323P Altcode:
The corona of the Sun shows variability over a wide range of scales,
in space, time and energy. The power-law-like distributions small-scale
coronal brightenings events have been used to propose self-similarity
of the involved processes. Already during the cruise phase, Solar
Orbiter was close enough to the Sun so that images provided by the
Extreme Ultraviolet Imager (EUI) are among the highest resolution
coronal data acquired so far. The small brightenings found in the
quiet Sun, now often termed campfires, could be considered as the small
end of the distribution of coronal transients. Mostly, these coronal
brightenings occur very low in the atmosphere, essentially just above
the chromosphere. Still they show a variety of morphology, ranging
from dot-like to loop-like with propagating disturbances, small jets,
or miniature flux-rope eruptions. This variety of the phenomenology on
the smallest resolvable scales points towards a conclusion that there is
not one single process that can drive small-scale brightenings. This is
supported by studies relating the EUV brightenings to the underlying
magnetic field: a part of the cases shows a relation to changes of
the surface magnetic flux, while in other cases it is very hard to
find any connection to the magnetic field. In the quiet Sun these
small brightenings are mostly found at the edges of bright elements
of the chromospheric network, which they have in common with another
class of brightenings seen at lower temperatures in the transition
region, namely explosive events. These transients have been proposed
as being due to reconnection, have a similar size and lifetime as
the small brightenings, but mostly seem to lack a component at high
temperatures. It might well be that these explosive events are related
to one particular type of the campfires, e.g. the jet-types, but that
remains to be studied. Modelling work on small brightenings is not
yet very abundant. One 3D MHD model of the quiet Sun shows coronal
brightenings that share properties with the observations. Here the
brightening is caused (mostly) by component reconnection, but also
one case of a twisted flux rope is found in the simulation data,
other (future) models most likely will reveal that also different
processes could produce similar brightenings. Because of timing and
the mission profile, so far remote sensing observations have been
taken mostly in regions of quiet Sun. With the perihelion in March
2022 Solar Orbiter will not only be closer than 0.3 AU from the Sun,
providing coronal observations at even higher resolution than before,
but also active region observations are planned. These might extend
the zoo of the small-scale coronal transients to small features in
active regions that might show properties similar or different from
the quiet Sun coronal brightenings. Either way, this will provide a
challenge for our understanding of the small-scale corona.

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Title: Transient small-scale brightenings in the quiet solar corona:
a model for campfires observed with Solar Orbiter
Authors: Chen, Yajie; Peter, Hardi; Berghmans, David; Tian, Hui;
Auchère, Frédéric; Przybylski, Damien
2022cosp...44.2557C Altcode:
Recent observations by the Extreme Ultraviolet Imager (EUI) on
board Solar Orbiter have revealed prevalent small-scale transient
brightenings in the quiet solar corona termed "campfires". To
understand the generation mechanism of these coronal brightenings,
we constructed a self-consistent and time-dependent quiet-Sun
model extending from the upper convection zone to the lower corona
using a realistic three-dimensional radiation magnetohydrodynamic
simulation. From the model we have synthesized the coronal emission
in the EUI 174 passband. We identified several transient coronal
brightenings similar to those in EUI observations. The size and
lifetime of these coronal brightenings are mostly 0.5-4 Mm and ~2 min,
respectively. These brightenings are generally located at a height of
2-4 Mm above the photosphere, and the local plasma is often heated
above 1 MK. By examining the magnetic field structures before and
after the occurrence of brightenings, we concluded that these coronal
brightenings are generated by component magnetic reconnection between
interacting bundles of magnetic field lines or neighboring field lines
within highly twisted flux ropes. Occurring in the coronal part of
the atmosphere, these events generally reveal no obvious signature
of flux emergence or cancellation in photospheric magnetograms. These
transient coronal brightenings may play an important role in heating
of the local coronal plasma.

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Title: Parallel Plasma Loops and the Energization of the Solar Corona
Authors: Peter, Hardi; Chitta, Lakshmi Pradeep; Chen, Feng; Pontin,
David I.; Winebarger, Amy R.; Golub, Leon; Savage, Sabrina L.;
Rachmeler, Laurel A.; Kobayashi, Ken; Brooks, David H.; Cirtain,
Jonathan W.; De Pontieu, Bart; McKenzie, David E.; Morton, Richard J.;
Testa, Paola; Tiwari, Sanjiv K.; Walsh, Robert W.; Warren, Harry P.
2022ApJ...933..153P Altcode: 2022arXiv220515919P
The outer atmosphere of the Sun is composed of plasma heated to
temperatures well in excess of the visible surface. We investigate
short cool and warm (&lt;1 MK) loops seen in the core of an active
region to address the role of field-line braiding in energizing these
structures. We report observations from the High-resolution Coronal
imager (Hi-C) that have been acquired in a coordinated campaign with
the Interface Region Imaging Spectrograph (IRIS). In the core of the
active region, the 172 Å band of Hi-C and the 1400 Å channel of IRIS
show plasma loops at different temperatures that run in parallel. There
is a small but detectable spatial offset of less than 1″ between
the loops seen in the two bands. Most importantly, we do not see
observational signatures that these loops might be twisted around each
other. Considering the scenario of magnetic braiding, our observations
of parallel loops imply that the stresses put into the magnetic field
have to relax while the braiding is applied: the magnetic field never
reaches a highly braided state on these length scales comparable to
the separation of the loops. This supports recent numerical 3D models
of loop braiding in which the effective dissipation is sufficiently
large that it keeps the magnetic field from getting highly twisted
within a loop.

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Title: Small-scale dynamo in cool stars. I. Changes in stratification
and near-surface convection for main-sequence spectral types
Authors: Bhatia, Tanayveer S.; Cameron, Robert H.; Solanki, Sami K.;
Peter, Hardi; Przybylski, Damien; Witzke, Veronika; Shapiro, Alexander
2022A&A...663A.166B Altcode: 2022arXiv220600064B
Context. Some of the small-scale solar magnetic flux can
be attributed to a small-scale dynamo (SSD) operating in the
near-surface convection. The SSD fields have consequences for
solar granular convection, basal flux, and chromospheric heating. A
similar SSD mechanism is expected to be active in the near-surface
convection of other cool main-sequence stars, but this has not been
investigated thus far. Aims: We aim to investigate changes in
stratification and convection due to inclusion of SSD fields for F3V,
G2V, K0V, and M0V spectral types in the near-surface convection. Methods: We studied 3D magnetohydrodynamic (MHD) models of the four
stellar boxes, covering the subsurface convection zone up to the lower
photosphere in a small Cartesian box, based on the MURaM radiative-MHD
simulation code. We compared the SSD runs against reference hydrodynamic
runs. Results: The SSD is found to efficiently produce magnetic
field with energies ranging between 5% to 80% of the plasma kinetic
energy at different depths. This ratio tends to be larger for larger
Teff. The relative change in density and gas pressure
stratification for the deeper convective layers due to SSD magnetic
fields is negligible, except for the F-star. For the F-star, there is
a substantial reduction in convective velocities due to Lorentz force
feedback from magnetic fields, which, in turn, reduces the turbulent
pressure. Conclusions: The SSD in near-surface convection for
cool main-sequence stars introduces small but significant changes
in thermodynamic stratification (especially for the F-star) due to a
reduction in the convective velocities.

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Title: Abundance diagnostics in active regions with Solar
Orbiter/SPICE
Authors: Giunta, Alessandra; Peter, Hardi; Parenti, Susanna; Buchlin,
Eric; Thompson, William; Auchere, Frederic; Kucera, Therese; Carlsson,
Mats; Janvier, Miho; Fludra, Andrzej; Hassler, Donald M.; Grundy,
Timothy; Sidher, Sunil; Guest, Steve; Leeks, Sarah; Fredvik, Terje;
Young, Peter
2022cosp...44.2583G Altcode:
With the launch of Solar Orbiter in February 2020, we are now able to
fully explore the link between the solar activity on the Sun and the
inner heliosphere. Elemental abundance measurements provide a key tracer
to probe the source regions of the solar wind and to track it from the
solar surface and corona to the heliosphere. Abundances of elements
with low first ionisation potential (FIP) are enhanced in the corona
relative to high-FIP elements, with respect to the photosphere. This is
known as the FIP effect, which is measured as abundance bias (FIP bias)
of low and high FIP elements. This effect is vital for understanding the
flow of mass and energy through the solar atmosphere. The comparison
between in-situ and remote sensing composition data, coupled with
modelling, will allow us to trace back the source of heliospheric
plasma. Solar Orbiter has a unique combination of in-situ and remote
sensing instruments that will help to make such a comparison. In
particular, the SPICE (Spectral Imaging of the Coronal Environment)
EUV spectrometer records spectra in two wavelength bands, 70.4-79.0
nm and 97.3-104.9 nm. SPICE is designed to provide spectroheliograms
using a core set of emission lines arising from ions of both low-FIP
and high-FIP elements such as C, N, O, Ne, Mg, S and Fe. These lines
are formed over a wide range of temperatures from 20,000 K to over 1
million K, enabling the analysis of the different layers of the solar
atmosphere. SPICE spectroheliograms can be processed to produce FIP
bias maps, which can be compared to in-situ measurements of the solar
wind composition of the same elements. During the Solar Orbiter Cruise
Phase, SPICE observed several active regions. We will present some of
these observations and discuss the SPICE diagnostic potential to derive
relative abundances (e.g., Mg/Ne) and the FIP bias in those regions.

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Title: The SPICE spectrograph on Solar Orbiter: an introduction and
results from the first Orbits
Authors: Auchère, Frédéric; Peter, Hardi; Parenti, Susanna; Buchlin,
Eric; Thompson, William; Auchere, Frederic; Teriaca, Luca; Kucera,
Therese; Carlsson, Mats; Janvier, Miho; Fludra, Andrzej; Giunta,
Alessandra; Schuehle, Udo; Hassler, Donald M.; Grundy, Timothy;
Sidher, Sunil; Fredvik, Terje; Plowman, Joseph; Aznar Cuadrado, Regina
2022cosp...44.1338A Altcode:
The Spectral Imaging of the Coronal Environment (SPICE) instrument is
the EUV imaging spectrometer on board the Solar Orbiter mission. With
its ability to derive physical properties of the coronal plasma,
SPICE is a key component of the payload to establish the connection
between the source regions and the in-situ measurements of the solar
wind. The spacecraft was successfully launched in February 2020 and
completed its cruise phase in December 2021. During this period,
the remote sensing instruments were mostly operated during limited
periods of time for 'checkout' engineering activities and synoptic
observations. Nonetheless, several of these periods provided enough
opportunities already to obtain new insights on coronal physics. During
the march 2022 perihelion - close to 0.3 AU - SPICE will provide
its highest spatial resolution data so far. Coordinated observations
between the remote sensing and in-situ instruments will provide the
first opportunity to use the full potential of the Solar Orbiter
mission. We will review the instrument characteristics and present
initial results from the cruise phase and first close encounter.

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Title: Observation of Magnetic Switchback in the Solar Corona
Authors: Telloni, Daniele; Zank, Gary P.; Stangalini, Marco;
Downs, Cooper; Liang, Haoming; Nakanotani, Masaru; Andretta,
Vincenzo; Antonucci, Ester; Sorriso-Valvo, Luca; Adhikari, Laxman;
Zhao, Lingling; Marino, Raffaele; Susino, Roberto; Grimani, Catia;
Fabi, Michele; D'Amicis, Raffaella; Perrone, Denise; Bruno, Roberto;
Carbone, Francesco; Mancuso, Salvatore; Romoli, Marco; Da Deppo, Vania;
Fineschi, Silvano; Heinzel, Petr; Moses, John D.; Naletto, Giampiero;
Nicolini, Gianalfredo; Spadaro, Daniele; Teriaca, Luca; Frassati,
Federica; Jerse, Giovanna; Landini, Federico; Pancrazzi, Maurizio;
Russano, Giuliana; Sasso, Clementina; Berghmans, David; Auchère,
Frédéric; Aznar Cuadrado, Regina; Chitta, Lakshmi P.; Harra, Louise;
Kraaikamp, Emil; Long, David M.; Mandal, Sudip; Parenti, Susanna;
Pelouze, Gabriel; Peter, Hardi; Rodriguez, Luciano; Schühle, Udo;
Schwanitz, Conrad; Smith, Phil J.; Verbeeck, Cis; Zhukov, Andrei N.
2022arXiv220603090T Altcode:
Switchbacks are sudden, large radial deflections of the solar wind
magnetic field, widely revealed in interplanetary space by the Parker
Solar Probe. The switchbacks' formation mechanism and sources are still
unresolved, although candidate mechanisms include Alfvénic turbulence,
shear-driven Kelvin-Helmholtz instabilities, interchange reconnection,
and geometrical effects related to the Parker spiral. This Letter
presents observations from the Metis coronagraph onboard Solar Orbiter
of a single large propagating S-shaped vortex, interpreted as first
evidence of a switchback in the solar corona. It originated above
an active region with the related loop system bounded by open-field
regions to the East and West. Observations, modeling, and theory provide
strong arguments in favor of the interchange reconnection origin of
switchbacks. Metis measurements suggest that the initiation of the
switchback may also be an indicator of the origin of slow solar wind.

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Title: Doppler shifts of spectral lines formed in the solar transition
region and corona
Authors: Chen, Yajie; Peter, Hardi; Przybylski, Damien; Tian, Hui;
Zhang, Jiale
2022A&A...661A..94C Altcode: 2022arXiv220304691C
Context. Emission lines formed in the transition region and corona
dominantly show redshifts and blueshifts, respectively. Aims: We investigate the Doppler shifts in a 3D radiation
magnetohydrodynamic (MHD) model of the quiet Sun and compare these
to observed properties. We concentrate on Si IV 1394 Å originating
in the transition region and examine the Doppler shifts of several
other spectral lines at different formation temperatures. 
Methods: We constructed a radiation MHD model extending from the upper
convection zone to the lower corona using the MURaM code. In this
quiet Sun model, the magnetic field is self-consistently maintained
by the action of a small-scale dynamo in the convection zone, and it
is extrapolated to the corona as an initial condition. We synthesized
the profiles of several optically thin emission lines, which formed at
temperatures from the transition region into the corona. We investigated
the spatial structure and coverage of redshifts and blueshifts and how
this changes with the line-formation temperature. Results: The
model successfully reproduces the observed change of average net Doppler
shifts from redshifted to blueshifted from the transition region into
the corona. In particular, the model shows a clear imbalance of area
coverage of redshifts versus blueshifts in the transition region of
ca. 80% to 20%, even though it is even a bit larger on the real Sun. We
determine that (at least) four processes generate the systematic Doppler
shifts in our model, including pressure enhancement in the transition
region, transition region brightenings unrelated to coronal emission,
boundaries between cold and hot plasma, and siphon-type flows. Conclusions: We show that there is not a single process that is
responsible for the observed net Doppler shifts in the transition
region and corona. Because current 3D MHD models do not yet fully
capture the evolution of spicules, which is one of the key ingredients
of the chromosphere, most probably these have yet to be added to the
list of processes responsible for the persistent Doppler shifts.

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Title: The magnetic drivers of campfires seen by the Polarimetric
and Helioseismic Imager (PHI) on Solar Orbiter
Authors: Kahil, F.; Hirzberger, J.; Solanki, S. K.; Chitta, L. P.;
Peter, H.; Auchère, F.; Sinjan, J.; Orozco Suárez, D.; Albert,
K.; Albelo Jorge, N.; Appourchaux, T.; Alvarez-Herrero, A.; Blanco
Rodríguez, J.; Gandorfer, A.; Germerott, D.; Guerrero, L.; Gutiérrez
Márquez, P.; Kolleck, M.; del Toro Iniesta, J. C.; Volkmer, R.;
Woch, J.; Fiethe, B.; Gómez Cama, J. M.; Pérez-Grande, I.; Sanchis
Kilders, E.; Balaguer Jiménez, M.; Bellot Rubio, L. R.; Calchetti,
D.; Carmona, M.; Deutsch, W.; Fernández-Rico, G.; Fernández-Medina,
A.; García Parejo, P.; Gasent-Blesa, J. L.; Gizon, L.; Grauf, B.;
Heerlein, K.; Lagg, A.; Lange, T.; López Jiménez, A.; Maue, T.;
Meller, R.; Michalik, H.; Moreno Vacas, A.; Müller, R.; Nakai,
E.; Schmidt, W.; Schou, J.; Schühle, U.; Staub, J.; Strecker, H.;
Torralbo, I.; Valori, G.; Aznar Cuadrado, R.; Teriaca, L.; Berghmans,
D.; Verbeeck, C.; Kraaikamp, E.; Gissot, S.
2022A&A...660A.143K Altcode: 2022arXiv220213859K
Context. The Extreme Ultraviolet Imager (EUI) on board the Solar Orbiter
(SO) spacecraft observed small extreme ultraviolet (EUV) bursts,
termed campfires, that have been proposed to be brightenings near the
apexes of low-lying loops in the quiet-Sun atmosphere. The underlying
magnetic processes driving these campfires are not understood. Aims: During the cruise phase of SO and at a distance of 0.523
AU from the Sun, the Polarimetric and Helioseismic Imager on Solar
Orbiter (SO/PHI) observed a quiet-Sun region jointly with SO/EUI,
offering the possibility to investigate the surface magnetic field
dynamics underlying campfires at a spatial resolution of about 380
km. Methods: We used co-spatial and co-temporal data of the
quiet-Sun network at disc centre acquired with the High Resolution
Imager of SO/EUI at 17.4 nm (HRIEUV, cadence 2 s) and the
High Resolution Telescope of SO/PHI at 617.3 nm (HRT, cadence 2.5
min). Campfires that are within the SO/PHI−SO/EUI common field
of view were isolated and categorised according to the underlying
magnetic activity. Results: In 71% of the 38 isolated events,
campfires are confined between bipolar magnetic features, which seem to
exhibit signatures of magnetic flux cancellation. The flux cancellation
occurs either between the two main footpoints, or between one of the
footpoints of the loop housing the campfire and a nearby opposite
polarity patch. In one particularly clear-cut case, we detected the
emergence of a small-scale magnetic loop in the internetwork followed
soon afterwards by a campfire brightening adjacent to the location
of the linear polarisation signal in the photosphere, that is to
say near where the apex of the emerging loop lays. The rest of the
events were observed over small scattered magnetic features, which
could not be identified as magnetic footpoints of the campfire hosting
loops. Conclusions: The majority of campfires could be driven
by magnetic reconnection triggered at the footpoints, similar to the
physical processes occurring in the burst-like EUV events discussed
in the literature. About a quarter of all analysed campfires, however,
are not associated to such magnetic activity in the photosphere, which
implies that other heating mechanisms are energising these small-scale
EUV brightenings.

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Title: Spectroscopic observation of a transition region network jet
Authors: Gorman, J.; Chitta, L. P.; Peter, H.
2022A&A...660A.116G Altcode: 2022arXiv220211375G
 Aims: Ubiquitous transition region (TR) network jets are
considered to be substantial sources of mass and energy to the corona
and solar wind. We conduct a case study of a network jet to better
understand the nature of mass flows along its length and the energetics
involved in its launch. Methods: We present an observation of a
jet with the Interface Region Imaging Spectrograph (IRIS), while also
using data from the Solar Dynamics Observatory (SDO) to provide further
context. The jet was located within a coronal hole close to the disk
center. Results: We find that a blueshifted secondary component
of TR emission is associated with the jet and is persistent along its
spire. This component exhibits upward speeds of approximately 20-70 km
s−1 and shows enhanced line broadening. However, plasma
associated with the jet in the upper chromosphere shows downflows of
5-10 km s−1. Finally, the jet emanates from a seemingly
unipolar magnetic footpoint. Conclusions: While a definitive
magnetic driver is not discernible for this event, we infer that
the energy driving the network jet is deposited at the top of the
chromosphere, indicating that TR network jets are driven from the
mid-atmospheric layers of the Sun. The energy flux associated with the
line broadening indicates that the jet could be powered all the way into
the solar wind. Movie associated with Fig. 3 is available at <A
href="https://www.aanda.org/10.1051/0004-6361/202142995/olm">https://www.aanda.org</A>

---------------------------------------------------------
Title: Anisotropic nonthermal motions in the transition region of
solar active regions
Authors: Mou, Chaozhou; Peter, Hardi; Xia, Lidong; Huang, Zhenghua
2022A&A...660A...3M Altcode:
Context. We study the nonthermal motions in the transition region
of active regions (ARs) using center-to-limb observations of Si
IV 1394 Å and 1403 Å lines. Aims: The aim of this study
is to investigate the characteristics of nonthermal motions in the
transition region of ARs using the center-to-limb measurement. Methods: We used Interface Region Imaging Spectrograph (IRIS)
observations of the Si IV doublet lines 1393.78 Å and 1402.77 Å from
the transition region of ARs to analyze nonthermal motions. We compared
our analyzed data to similar data for the quiet Sun (QS) regions. We
derive the nonthermal width by performing a single Gaussian fitting
on the average spectral line profiles of Si IV doublet lines. We
carried out a statistical analysis of the nonthermal width using the
center-to-limb measurement. Results: We find that the nonthermal
motions are clearly decreasing on the disk with increasing distance
from disk center. Only close to the limb, clearly beyond μ = 0.4,
does the nonthermal broadening increase again towards the limb. The
decrease in the nonthermal broadening in ARs away from disk center is
markedly different from what is seen in the QS. Conclusions:
We conclude that nonthermal motions are anisotropic in ARs, with the
vertical component being greater than the horizontal one. In contrast,
we find the situation in the QS to be consistent with the findings of
previous studies; only opacity effects are responsible for the increase
in the nonthermal widths towards the limb, and nonthermal motions are
isotropic in the QS.

---------------------------------------------------------
Title: Coronal condensation as the source of transition-region
supersonic downflows above a sunspot
Authors: Chen, Hechao; Tian, Hui; Li, Leping; Peter, Hardi; Chitta,
Lakshmi Pradeep; Hou, Zhenyong
2022A&A...659A.107C Altcode: 2021arXiv211201354C
Context. Plasma loops or plumes rooted in sunspot umbrae often harbor
downflows with speeds of 100 km s−1. These downflows
are supersonic at transition region temperatures of ∼0.1 MK. The
source of these flows is not well understood. Aims: We aim
to investigate the source of sunspot supersonic downflows (SSDs)
in active region 12740 using simultaneous spectroscopic and imaging
observations. Methods: We identified SSD events from multiple
raster scans of a sunspot by the Interface Region Imaging Spectrograph,
and we calculated the electron densities, mass fluxes, and velocities
of these SSDs. The extreme-ultraviolet (EUV) images provided by the
Atmospheric Imaging Assembly onboard the Solar Dynamics Observatory and
the EUV Imager onboard the Solar Terrestrial Relations Observatory were
employed to investigate the origin of these SSDs and their associated
coronal rain. Results: Almost all the identified SSDs appear
at the footpoints of sunspot plumes and are temporally associated
with the appearance of chromospheric bright dots inside the sunspot
umbra. Dual-perspective EUV imaging observations reveal a large-scale
closed magnetic loop system spanning the sunspot region and a remote
region. We observed that the SSDs are caused by repeated coronal
rain that forms and flows along these closed magnetic loops toward the
sunspot. One episode of coronal rain clearly indicates that reconnection
near a coronal X-shaped structure first leads to the formation of
a magnetic dip. Subsequently, hot coronal plasma catastrophically
cools from ∼2 MK in the dip region via thermal instability. This
results in the formation of a transient prominence in the dip, from
which the cool gas mostly slides into the sunspot along inclined
magnetic fields under the gravity. This drainage process manifests
as a continuous rain flow, which lasts for ∼2 h and concurrently
results in a nearly steady SSD event. The total mass of condensation
(1.3 × 1014 g) and condensation rate (1.5 × 1010
g s−1) in the dip region were found to be sufficient to
sustain this long-lived SSD event, which has a mass transport rate of
0.7 − 1.2 × 1010 g s−1. Conclusions:
Our results demonstrate that coronal condensation in magnetic dips
can result in the quasi-steady sunspot supersonic downflows. Movies associated to Figs. 1, 3, 6, 7, and 11 are available at <A
href="https://www.aanda.org/10.1051/0004-6361/202142093/olm">https://www.aanda.org</A>

---------------------------------------------------------
Title: peterpeterp/tc_emulator: version 3
Authors: Peter
2022zndo...6223723P Altcode:
scripts for the third submission at WCD

---------------------------------------------------------
Title: A solar coronal loop in a box: Energy generation and heating
Authors: Breu, C.; Peter, H.; Cameron, R.; Solanki, S. K.; Przybylski,
D.; Rempel, M.; Chitta, L. P.
2022A&A...658A..45B Altcode: 2021arXiv211211549B
Context. Coronal loops are the basic building block of the upper solar
atmosphere as seen in the extreme UV and X-rays. Comprehending how
these are energized, structured, and evolve is key to understanding
stellar coronae. Aims: Here we investigate how the energy
to heat the loop is generated by photospheric magneto-convection,
transported into the upper atmosphere, and how the internal
structure of a coronal magnetic loop forms. Methods: In a 3D
magnetohydrodynamics model, we study an isolated coronal loop rooted
with both footpoints in a shallow layer within the convection zone
using the MURaM code. To resolve its internal structure, we limited
the computational domain to a rectangular box containing a single
coronal loop as a straightened magnetic flux tube. Field-aligned heat
conduction, gray radiative transfer in the photosphere and chromosphere,
and optically thin radiative losses in the corona were taken into
account. The footpoints were allowed to interact self-consistently
with the granulation surrounding them. Results: The loop is
heated by a Poynting flux that is self-consistently generated through
small-scale motions within individual magnetic concentrations in
the photosphere. Turbulence develops in the upper layers of the
atmosphere as a response to the footpoint motions. We see little
sign of heating by large-scale braiding of magnetic flux tubes
from different photospheric concentrations at a given footpoint. The
synthesized emission, as it would be observed by the Atmospheric Imaging
Assembly or the X-Ray Telescope, reveals transient bright strands that
form in response to the heating events. Overall, our model roughly
reproduces the properties and evolution of the plasma as observed
within (the substructures of) coronal loops. Conclusions:
With this model we can build a coherent picture of how the energy
flux to heat the upper atmosphere is generated near the solar surface
and how this process drives and governs the heating and dynamics of
a coronal loop. Movie associated to Fig. 2 is available at <A
href="https://www.aanda.org/10.1051/0004-6361/202141451/olm">https://www.aanda.org</A>

---------------------------------------------------------
Title: JuliaData/DataFrames.jl: v1.3.2
Authors: Kamiński, Bogumił; Myles White, John; Powerdistribution;
Bouchet-Valat, Milan; Garborg, Sean; Quinn, Jacob; Kornblith, Simon;
Cjprybol; Stukalov, Alexey; Bates, Douglas; Short, Tom; DuBois, Chris;
Harris, Harlan; Squire, Kevin; Pdeffebach; Arslan, Alex; Anthoff,
David; Kleinschmidt, Dave; Noack, Andreas; Shah, Viral B.; Mellnik,
Alex; Arakaki, Takafumi; Mohapatra, Tanmay; Peter; Karpinski, Stefan;
Lin, Dahua; Timema; ExpandingMan; Oswald, Florian; Arraes Jardim
Chagas, Ronan
2022zndo...3376177K Altcode: 2021zndo...3376177M
DataFrames v1.3.2 Diff since v1.3.1 Closed issues: Variance in
runtime reduction functions (#2956) use of map in ByRow (#2957)
Replace and Missing Values (#2976) Subset and Missing Values (#2977)
copying of columns in select! and transform! (#2978) Unexpected
Behavior of Combined Column Selection (#2980) Merged pull requests:
Add a note about df.col .= v broadcasting changes (#2971) (@bkamins)
Update working_with_dataframes.md (#2973) (@alfaromartino) Clean up
join code (#2975) (@bkamins) Add links to docs, rephrase a bit (#2979)
(@nalimilan) fix aliasing detection in sort! (#2981) (@bkamins) make
sure ByRow invokes generic map (#2982) (@bkamins) make sure we use
source column only once (#2983) (@bkamins) Update subset to handle
large number of selectors better (#2989) (@bkamins)

---------------------------------------------------------
Title: Transient small-scale brightenings in the quiet solar corona:
A model for campfires observed with Solar Orbiter
Authors: Chen, Yajie; Przybylski, Damien; Peter, Hardi; Tian, Hui;
Auchère, F.; Berghmans, D.
2021A&A...656L...7C Altcode: 2021arXiv210410940C
Context. Recent observations by the Extreme Ultraviolet Imager (EUI) on
board Solar Orbiter have characterized prevalent small-scale transient
brightenings in the corona above the quiet Sun termed campfires. 
Aims: In this study we search for comparable brightenings in a numerical
model and then investigate their relation to the magnetic field and the
processes that drive these events. Methods: We used the MURaM
code to solve the 3D radiation magnetohydrodynamic equations in a box
that stretches from the upper convection zone to the corona. The model
self-consistently produces a supergranular network of the magnetic
field and a hot corona above this quiet Sun. For the comparison with
the model, we synthesized the coronal emission as seen by EUI in its
174 Å channel, isolated the seven strongest transient brightenings,
and investigated the changes of the magnetic field in and around these
in detail. Results: The transients we isolated have a lifetime of
about 2 min and are elongated loop-like features with lengths around 1
Mm to 4 Mm. They tend to occur at heights of about 2 Mm to 5 Mm above
the photosphere, a bit offset from magnetic concentrations that mark
the bright chromospheric network, and they reach temperatures of above
1 MK. As a result, they very much resemble the larger campfires found
in observations. In our model most events are energized by component
reconnection between bundles of field lines that interact at coronal
heights. In one case, we find that untwisting a highly twisted flux
rope initiates the heating. Conclusions: Based on our study, we
propose that the majority of campfire events found by EUI are driven
by component reconnection and our model suggests that this process
significantly contributes to the heating of the corona above the quiet
Sun. Movies associated to Figs. 2, 4, 5, and A1 are available at <A
href="https://www.aanda.org/10.1051/0004-6361/202140638/olm">https://www.aanda.org</A>

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Title: Campfires observed by EUI: What have we learned so far?
Authors: Berghmans, David; Auchere, F.; Zhukov, Andrei; Mierla,
Marilena; Chen, Yajie; Peter, Hardi; Panesar, Navdeep; Chitta, Lakshmi
Pradeep; Antolin, Patrick; Aznar Cuadrado, Regina; Tian, Hui; Hou,
Zhenyong; Podladchikova, Olena
2021AGUFMSH21A..02B Altcode:
Since its very first light images of the corona, the EUI/HRIEUV
telescope onboard Solar Orbiter has observed small localised
brightenings in the Quiet Sun. These small localised brightenings,
have become known as campfires, and are observed with length scales
between 400 km and 4000 km and durations between 10 sec and 200
sec. The smallest and weakest of these HRIEUV brightenings have
not been previously observed. Simultaneous observations from the
EUI High-resolution Lyman- telescope (HRILYA) do not show localised
brightening events, but the locations of the HRIEUV events clearly
correspond to the chromospheric network. Comparisons with simultaneous
AIA images shows that most events can also be identified in the
17.1 nm, 19.3 nm, 21.1 nm, and 30.4 nm pass-bands of AIA, although
they appear weaker and blurred. Some of the larger campfires have
the appearance of small interacting loops with the brightening
expanding from the contact point of the loops. Our differential
emission measure (DEM) analysis indicated coronal temperatures. We
determined the height for a few of these campfires to be between 1
and 5 Mm above the photosphere. We interpret these events as a new
extension to the flare-microflare-nanoflare family. Given their low
height, the EUI campfires could stand as a new element of the fine
structure of the transition region-low corona, that is, as apexes
of small-scale loops that undergo internal heating all the way up to
coronal temperatures. 3D MHD simulations with the MURaM code revealed
brightenings that are in many ways similar to the campfires by EUI. The
brightenings in the simulations suggest that campfires are triggered by
component reconnection inside flux bundles rather than flux emergence
or cancellation. Nevertheless, some of the observed campfires can
be clearly linked to flux cancellation events and, intriguingly,
are preceded by an erupting cool plasma structure. Analysis of the
dynamics of campfires revealed that some have the appearance of coronal
microjets, the smallest coronal jets observed in the quiet Sun. The
HRIEUV images also reveal transient jets on a somewhat bigger scale
with repeated outflows on the order of 100 km s1. In this paper we
will provide an overview of the campfire related phenomena that EUI
has observed and discuss the possible relevance for coronal heating.

---------------------------------------------------------
Title: Propagating brightenings in small loop-like structures in
the quiet-Sun corona: Observations from Solar Orbiter/EUI
Authors: Mandal, Sudip; Peter, Hardi; Chitta, Lakshmi Pradeep;
Solanki, Sami K.; Aznar Cuadrado, Regina; Teriaca, Luca; Schühle,
Udo; Berghmans, David; Auchère, Frédéric
2021A&A...656L..16M Altcode: 2021arXiv211108106M
Brightenings observed in solar extreme-ultraviolet images are generally
interpreted as signatures of micro- or nanoflares occurring in the
transition region or at coronal temperatures. Recent observations
with the Extreme Ultraviolet Imager (EUI) on board Solar Orbiter have
revealed the smallest of such brightenings (called campfires) in the
quiet-Sun corona. Analyzing EUI 174 Å data obtained at a resolution
of about 400 km on the Sun with a cadence of 5 s on 30 May 2020,
we report here a number of cases in which these campfires exhibit
propagating signatures along their apparently small (3-5 Mm) loop-like
structures. The measured propagation speeds are generally between 25
km s−1 and 60 km s−1. If the loop plasma is
assumed to be at a million Kelvin, these apparent motions would be
slower than the local sound speed. Furthermore, these brightenings
exhibit nontrivial propagation characteristics such as bifurcation,
merging, reflection, and repeated plasma ejections. We suggest that
these features are manifestations of the internal dynamics of these
small-scale magnetic structures and could provide important insights
into the dynamic response (∼40 s) of the loop plasma to the heating
events and also into the locations of the heating events themselves. Movies associated to Figs 2-5, A.1, and B.1 are available at <A
href="https://www.aanda.org/10.1051/0004-6361/202142041/olm">https://www.aanda.org</A>

---------------------------------------------------------
Title: The first coronal mass ejection observed in both visible-light
and UV H I Ly-α channels of the Metis coronagraph on board Solar
Orbiter
Authors: Andretta, V.; Bemporad, A.; De Leo, Y.; Jerse, G.; Landini,
F.; Mierla, M.; Naletto, G.; Romoli, M.; Sasso, C.; Slemer, A.;
Spadaro, D.; Susino, R.; Talpeanu, D. -C.; Telloni, D.; Teriaca, L.;
Uslenghi, M.; Antonucci, E.; Auchère, F.; Berghmans, D.; Berlicki,
A.; Capobianco, G.; Capuano, G. E.; Casini, C.; Casti, M.; Chioetto,
P.; Da Deppo, V.; Fabi, M.; Fineschi, S.; Frassati, F.; Frassetto,
F.; Giordano, S.; Grimani, C.; Heinzel, P.; Liberatore, A.; Magli, E.;
Massone, G.; Messerotti, M.; Moses, D.; Nicolini, G.; Pancrazzi, M.;
Pelizzo, M. -G.; Romano, P.; Schühle, U.; Stangalini, M.; Straus,
Th.; Volpicelli, C. A.; Zangrilli, L.; Zuppella, P.; Abbo, L.; Aznar
Cuadrado, R.; Bruno, R.; Ciaravella, A.; D'Amicis, R.; Lamy, P.;
Lanzafame, A.; Malvezzi, A. M.; Nicolosi, P.; Nisticò, G.; Peter,
H.; Plainaki, C.; Poletto, L.; Reale, F.; Solanki, S. K.; Strachan,
L.; Tondello, G.; Tsinganos, K.; Velli, M.; Ventura, R.; Vial, J. -C.;
Woch, J.; Zimbardo, G.
2021A&A...656L..14A Altcode:
Context. The Metis coronagraph on board Solar Orbiter offers a new
view of coronal mass ejections (CMEs), observing them for the first
time with simultaneous images acquired with a broad-band filter in
the visible-light interval and with a narrow-band filter around the
H I Ly-α line at 121.567 nm, the so-called Metis UV channel. 
Aims: We show the first Metis observations of a CME, obtained on 16
and 17 January 2021. The event was also observed by the EUI/FSI imager
on board Solar Orbiter, as well as by other space-based coronagraphs,
such as STEREO-A/COR2 and SOHO/LASCO/C2, whose images are combined here
with Metis data. Methods: Different images are analysed here
to reconstruct the 3D orientation of the expanding CME flux rope using
the graduated cylindrical shell model. This also allows us to identify
the possible location of the source region. Measurements of the CME
kinematics allow us to quantify the expected Doppler dimming in the
Ly-α channel. Results: Observations show that most CME features
seen in the visible-light images are also seen in the Ly-α images,
although some features in the latter channel appear more structured
than their visible-light counterparts. We estimated the expansion
velocity of this event to be below 140 km s−1. Hence,
these observations can be understood by assuming that Doppler dimming
effects do not strongly reduce the Ly-α emission from the CME. These
velocities are comparable with or smaller than the radial velocities
inferred from the same data in a similar coronal structure on the
east side of the Sun. Conclusions: The first observations by
Metis of a CME demonstrate the capability of the instrument to provide
valuable and novel information on the structure and dynamics of these
coronal events. Considering also its diagnostics capabilities regarding
the conditions of the ambient corona, Metis promises to significantly
advance our knowledge of such phenomena. Movies are available at <A
href="https://www.aanda.org/10.1051/0004-6361/202142407/olm">https://www.aanda.org</A>

---------------------------------------------------------
Title: Capturing transient plasma flows and jets in the solar corona
Authors: Chitta, L. P.; Solanki, S. K.; Peter, H.; Aznar Cuadrado,
R.; Teriaca, L.; Schühle, U.; Auchère, F.; Berghmans, D.; Kraaikamp,
E.; Gissot, S.; Verbeeck, C.
2021A&A...656L..13C Altcode: 2021arXiv210915106C
Intensity bursts in ultraviolet (UV) to X-ray wavelengths and plasma
jets are typical signatures of magnetic reconnection and the associated
impulsive heating of the solar atmospheric plasma. To gain new insights
into the process, high-cadence observations are required to capture
the rapid response of plasma to magnetic reconnection as well as the
highly dynamic evolution of jets. Here, we report the first 2 s cadence
extreme-UV observations recorded by the 174 Å High Resolution Imager of
the Extreme Ultraviolet Imager on board the Solar Orbiter mission. These
observations, covering a quiet-Sun coronal region, reveal the onset
signatures of magnetic reconnection as localized heating events. These
localized sources then exhibit repeated plasma eruptions or jet
activity. Our observations show that this spatial morphological change
from localized sources to jet activity could occur rapidly on timescales
of about 20 s. The jets themselves are intermittent and are produced
from the source region on timescales of about 20 s. In the initial
phases of these events, plasma jets are observed to exhibit speeds,
as inferred from propagating intensity disturbances, in the range of
100 km s−1 to 150 km s−1. These jets then
propagate to lengths of about 5 Mm. We discuss examples of bidirectional
and unidirectional jet activity observed to have been initiated from
the initially localized bursts in the corona. The transient nature
of coronal bursts and the associated plasma flows or jets along with
their dynamics could provide a benchmark for magnetic reconnection
models of coronal bursts and jets. Movies are available at <A
href="https://www.aanda.org/10.1051/0004-6361/202141683/olm">https://www.aanda.org</A>

---------------------------------------------------------
Title: First observations from the SPICE EUV spectrometer on Solar
Orbiter
Authors: Fludra, A.; Caldwell, M.; Giunta, A.; Grundy, T.; Guest,
S.; Leeks, S.; Sidher, S.; Auchère, F.; Carlsson, M.; Hassler, D.;
Peter, H.; Aznar Cuadrado, R.; Buchlin, É.; Caminade, S.; DeForest,
C.; Fredvik, T.; Haberreiter, M.; Harra, L.; Janvier, M.; Kucera, T.;
Müller, D.; Parenti, S.; Schmutz, W.; Schühle, U.; Solanki, S. K.;
Teriaca, L.; Thompson, W. T.; Tustain, S.; Williams, D.; Young, P. R.;
Chitta, L. P.
2021A&A...656A..38F Altcode: 2021arXiv211011252F
 Aims: We present first science observations taken during the
commissioning activities of the Spectral Imaging of the Coronal
Environment (SPICE) instrument on the ESA/NASA Solar Orbiter
mission. SPICE is a high-resolution imaging spectrometer operating at
extreme ultraviolet (EUV) wavelengths. In this paper we illustrate
the possible types of observations to give prospective users a
better understanding of the science capabilities of SPICE. 
Methods: We have reviewed the data obtained by SPICE between April
and June 2020 and selected representative results obtained with
different slits and a range of exposure times between 5 s and 180
s. Standard instrumental corrections have been applied to the raw
data. Results: The paper discusses the first observations
of the Sun on different targets and presents an example of the full
spectra from the quiet Sun, identifying over 40 spectral lines from
neutral hydrogen and ions of carbon, oxygen, nitrogen, neon, sulphur,
magnesium, and iron. These lines cover the temperature range between
20 000 K and 1 million K (10 MK in flares), providing slices of the
Sun's atmosphere in narrow temperature intervals. We provide a list
of count rates for the 23 brightest spectral lines. We show examples
of raster images of the quiet Sun in several strong transition region
lines, where we have found unusually bright, compact structures in the
quiet Sun network, with extreme intensities up to 25 times greater
than the average intensity across the image. The lifetimes of these
structures can exceed 2.5 hours. We identify them as a transition
region signature of coronal bright points and compare their areas and
intensity enhancements. We also show the first above-limb measurements
with SPICE above the polar limb in C III, O VI, and Ne VIII lines, and
far off limb measurements in the equatorial plane in Mg IX, Ne VIII,
and O VI lines. We discuss the potential to use abundance diagnostics
methods to study the variability of the elemental composition that can
be compared with in situ measurements to help confirm the magnetic
connection between the spacecraft location and the Sun's surface,
and locate the sources of the solar wind. Conclusions: The
SPICE instrument successfully performs measurements of EUV spectra
and raster images that will make vital contributions to the scientific
success of the Solar Orbiter mission.

---------------------------------------------------------
Title: First light observations of the solar wind in the outer corona
with the Metis coronagraph
Authors: Romoli, M.; Antonucci, E.; Andretta, V.; Capuano, G. E.; Da
Deppo, V.; De Leo, Y.; Downs, C.; Fineschi, S.; Heinzel, P.; Landini,
F.; Liberatore, A.; Naletto, G.; Nicolini, G.; Pancrazzi, M.; Sasso,
C.; Spadaro, D.; Susino, R.; Telloni, D.; Teriaca, L.; Uslenghi,
M.; Wang, Y. -M.; Bemporad, A.; Capobianco, G.; Casti, M.; Fabi, M.;
Frassati, F.; Frassetto, F.; Giordano, S.; Grimani, C.; Jerse, G.;
Magli, E.; Massone, G.; Messerotti, M.; Moses, D.; Pelizzo, M. -G.;
Romano, P.; Schühle, U.; Slemer, A.; Stangalini, M.; Straus, T.;
Volpicelli, C. A.; Zangrilli, L.; Zuppella, P.; Abbo, L.; Auchère,
F.; Aznar Cuadrado, R.; Berlicki, A.; Bruno, R.; Ciaravella, A.;
D'Amicis, R.; Lamy, P.; Lanzafame, A.; Malvezzi, A. M.; Nicolosi,
P.; Nisticò, G.; Peter, H.; Plainaki, C.; Poletto, L.; Reale, F.;
Solanki, S. K.; Strachan, L.; Tondello, G.; Tsinganos, K.; Velli,
M.; Ventura, R.; Vial, J. -C.; Woch, J.; Zimbardo, G.
2021A&A...656A..32R Altcode: 2021arXiv210613344R
In this work, we present an investigation of the wind in the solar
corona that has been initiated by observations of the resonantly
scattered ultraviolet emission of the coronal plasma obtained with
UVCS-SOHO, designed to measure the wind outflow speed by applying
Doppler dimming diagnostics. Metis on Solar Orbiter complements the
UVCS spectroscopic observations that were performed during solar
activity cycle 23 by simultaneously imaging the polarized visible
light and the H I Lyman-α corona in order to obtain high spatial and
temporal resolution maps of the outward velocity of the continuously
expanding solar atmosphere. The Metis observations, taken on May 15,
2020, provide the first H I Lyman-α images of the extended corona
and the first instantaneous map of the speed of the coronal plasma
outflows during the minimum of solar activity and allow us to identify
the layer where the slow wind flow is observed. The polarized visible
light (580-640 nm) and the ultraviolet H I Lyα (121.6 nm) coronal
emissions, obtained with the two Metis channels, were combined in
order to measure the dimming of the UV emission relative to a static
corona. This effect is caused by the outward motion of the coronal
plasma along the direction of incidence of the chromospheric photons
on the coronal neutral hydrogen. The plasma outflow velocity was then
derived as a function of the measured Doppler dimming. The static
corona UV emission was simulated on the basis of the plasma electron
density inferred from the polarized visible light. This study leads
to the identification, in the velocity maps of the solar corona, of
the high-density layer about ±10° wide, centered on the extension
of a quiet equatorial streamer present at the east limb - the coronal
origin of the heliospheric current sheet - where the slowest wind
flows at about 160 ± 18 km s−1 from 4 R⊙
to 6 R⊙. Beyond the boundaries of the high-density layer,
the wind velocity rapidly increases, marking the transition between
slow and fast wind in the corona.

---------------------------------------------------------
Title: Revisiting the formation mechanism for coronal rain from
previous studies
Authors: Li, Le-Ping; Peter, Hardi; Chitta, Lakshmi Pradeep; Song,
Hong-Qiang
2021RAA....21..255L Altcode: 2021arXiv210701339L
Solar coronal rain is classified generally into two categories:
flare-driven and quiescent coronal rain. Th latter is observed to form
along both closed and open magnetic field structures. Recently, we
proposed that some of the quiescent coronal rain events, detected in the
transition region and chromospheric diagnostics, along loop-like paths
could be explained by the formation mechanism for quiescent coronal
rain facilitated by interchange magnetic reconnection between open and
closed field lines. In this study, we revisited 38 coronal rain reports
from the literature. From theseearlier works, we picked 15 quiescent
coronal rain events out of the solar limb, mostly suggested to occur in
active region closed loops due to thermal nonequilibrium, to scrutinize
their formation mechanism. Employing the extreme ultraviolet images
and line-of-sight magnetograms, the evolution of the quiescent coronal
rain events and their magnetic fields and context coronal structures
is examined. We find that six, comprising 40%, of the 15 quiescent
coronal rain events could be totally or partially interpreted by the
formation mechanism for quiescent coronal rain along open structures
facilitated by interchange reconnection. The results suggest that the
quiescent coronal rain facilitated by interchange reconnection between
open and closed field lines deserves more attention.

---------------------------------------------------------
Title: Formation of a Solar Filament by Magnetic Reconnection and
Coronal Condensation
Authors: Li, Leping; Peter, Hardi; Chitta, Lakshmi Pradeep; Song,
Hongqiang
2021ApJ...919L..21L Altcode: 2021arXiv210905669L
In solar filament formation mechanisms, magnetic reconnection
between two sets of sheared arcades forms helical structures of the
filament with numerous magnetic dips, and cooling and condensation
of plasma trapped inside the helical structures supply mass to
the filament. Although each of these processes, namely, magnetic
reconnection and coronal condensation have been separately reported,
observations that show the whole process of filament formation are
rare. In this Letter, we present the formation of a sigmoid via
reconnection between two sets of coronal loops, and the subsequent
formation of a filament through cooling and condensation of plasma
inside the newly formed sigmoid. On 2014 August 27, a set of loops
in the active region 12151 reconnected with another set of loops
that are located to the east. A longer twisted sigmoidal structure
and a set of shorter lower-lying loops then formed. The observations
coincide well with the tether-cutting model. The newly formed sigmoid
remains stable and does not erupt as a coronal mass ejection. From the
eastern endpoint, signatures of injection of material into the sigmoid
(as brightenings) are detected, which closely outline the features of
increasing emission measure at these locations. This may indicate the
chromospheric evaporation caused by reconnection, supplying heated
plasma into the sigmoid. In the sigmoid, thermal instability occurs,
and rapid cooling and condensation of plasma take place, forming a
filament. The condensations then flow bidirectionally to the filament
endpoints. Our results provide a clear observational evidence of the
filament formation via magnetic reconnection and coronal condensation.

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Title: Flare-induced decay-less transverse oscillations in solar
coronal loops
Authors: Mandal, Sudip; Tian, Hui; Peter, Hardi
2021A&A...652L...3M Altcode: 2021arXiv210702247M
Evidence of flare-induced, large-amplitude, decay-less transverse
oscillations is presented. A system of multithermal coronal loops,
as observed with the Atmospheric Imaging Assembly (AIA), exhibit
decay-less transverse oscillations after a flare erupts nearby one
of the loop footpoints. Measured oscillation periods lie between 4.2
min and 6.9 min wherein the displacement amplitudes range from 0.17
Mm to 1.16 Mm. A motion-magnification technique has been employed
to detect the preflare decay-less oscillations. These oscillations
have similar periods (between 3.7 min and 5.0 min) similar to the
previous ones, but their amplitudes (0.04 Mm to 0.12 Mm) are found
to be significantly smaller. No phase difference is found among
oscillating threads of a loop when observed through a particular AIA
channel or when their multichannel signatures are compared. These
features suggest that the occurrence of a flare in this case neither
changed the nature of these oscillations (decaying versus decay-less),
nor the oscillation periods. The only effect the flare has is to
increase the oscillation amplitudes. Movie is available at <A
href="https://www.aanda.org/10.1051/0004-6361/202141542/olm">https://www.aanda.org</A>

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Title: Stellar X-rays and magnetic activity in 3D MHD coronal models
Authors: Zhuleku, J.; Warnecke, J.; Peter, H.
2021A&A...652A..32Z Altcode: 2021arXiv210200982Z
Context. Observations suggest a power-law relation between the
coronal emission in X-rays, LX, and the total (unsigned)
magnetic flux at the stellar surface, Φ. The physics basis for this
relation is poorly understood. Aims: We use three-dimensional
(3D) magnetohydrodynamics (MHD) numerical models of the coronae above
active regions, that is, strong concentrations of magnetic field, to
investigate the LX versus Φ relation and illustrate this
relation with an analytical model based on simple well-established
scaling relations. Methods: In the 3D MHD model horizontal
(convective) motions near the surface induce currents in the
coronal magnetic field that are dissipated and heat the plasma. This
self-consistently creates a corona with a temperature of 1 MK. We
run a series of models that differ in terms of the (unsigned)
magnetic flux at the surface by changing the (peak) magnetic field
strength while keeping all other parameters fixed. Results:
In the 3D MHD models we find that the energy input into the corona,
characterized by either the Poynting flux or the total volumetric
heating, scales roughly quadratically with the unsigned surface flux
Φ. This is expected from heating through field-line braiding. Our
central result is the nonlinear scaling of the X-ray emission as
LX ∝ Φ3.44. This scaling is slightly steeper
than found in recent observations that give power-law indices of
up to only 2 or 3. Assuming that on a real star, not only the peak
magnetic field strength in the active regions changes but also their
number (or surface filling factor), our results are consistent with
observations. Conclusions: Our model provides indications of
what causes the steep increase in X-ray luminosity by four orders of
magnitude from solar-type activity to fast rotating active stars.

---------------------------------------------------------
Title: Magnetic imaging of the outer solar atmosphere (MImOSA)
Authors: Peter, H.; Ballester, E. Alsina; Andretta, V.; Auchère, F.;
Belluzzi, L.; Bemporad, A.; Berghmans, D.; Buchlin, E.; Calcines, A.;
Chitta, L. P.; Dalmasse, K.; Alemán, T. del Pino; Feller, A.; Froment,
C.; Harrison, R.; Janvier, M.; Matthews, S.; Parenti, S.; Przybylski,
D.; Solanki, S. K.; Štěpán, J.; Teriaca, L.; Bueno, J. Trujillo
2021ExA...tmp...95P Altcode:
The magnetic activity of the Sun directly impacts the Earth and human
life. Likewise, other stars will have an impact on the habitability of
planets orbiting these host stars. Although the magnetic field at the
surface of the Sun is reasonably well characterised by observations,
the information on the magnetic field in the higher atmospheric layers
is mainly indirect. This lack of information hampers our progress in
understanding solar magnetic activity. Overcoming this limitation would
allow us to address four paramount long-standing questions: (1) How
does the magnetic field couple the different layers of the atmosphere,
and how does it transport energy? (2) How does the magnetic field
structure, drive and interact with the plasma in the chromosphere and
upper atmosphere? (3) How does the magnetic field destabilise the outer
solar atmosphere and thus affect the interplanetary environment? (4)
How do magnetic processes accelerate particles to high energies? New
ground-breaking observations are needed to address these science
questions. We suggest a suite of three instruments that far exceed
current capabilities in terms of spatial resolution, light-gathering
power, and polarimetric performance: (a) A large-aperture UV-to-IR
telescope of the 1-3 m class aimed mainly to measure the magnetic
field in the chromosphere by combining high spatial resolution
and high sensitivity. (b) An extreme-UV-to-IR coronagraph that is
designed to measure the large-scale magnetic field in the corona with
an aperture of about 40 cm. (c) An extreme-UV imaging polarimeter
based on a 30 cm telescope that combines high throughput in the
extreme UV with polarimetry to connect the magnetic measurements
of the other two instruments. Placed in a near-Earth orbit, the data
downlink would be maximised, while a location at L4 or L5 would provide
stereoscopic observations of the Sun in combination with Earth-based
observatories. This mission to measure the magnetic field will finally
unlock the driver of the dynamics in the outer solar atmosphere and
thereby will greatly advance our understanding of the Sun and the
heliosphere.

---------------------------------------------------------
Title: Coronal loops in a box: 3D models of their internal structure,
dynamics and heating
Authors: Breu, C. A.; Peter, H.; Cameron, R.; Solanki, S.; Przybylski,
D.; Chitta, L.
2021AAS...23810606B Altcode:
The corona of the Sun, and probably also of other stars, is built
up by loops defined through the magnetic field. They vividly appear
in solar observations in the extreme UV and X-rays. High-resolution
observations show individual strands with diameters down to a few 100
km, and so far it remains open what defines these strands, in particular
their width, and where the energy to heat them is generated. The
aim of our study is to understand how the magnetic field couples the
different layers of the solar atmosphere, how the energy generated
by magnetoconvection is transported into the upper atmosphere and
dissipated, and how this process determines the scales of observed
bright strands in the loop. To this end, we conduct 3D resistive
MHD simulations with the MURaM code. We include the effects of heat
conduction, radiative transfer and optically thin radiative losses.We
study an isolated coronal loop that is rooted with both footpoints
in a shallow convection zone layer. To properly resolve the internal
structure of the loop while limiting the size of the computational box,
the coronal loop is modelled as a straightened magnetic flux tube. By
including part of the convection zone, we drive the evolution of
the corona self-consistently by magnetoconvection. We find that
the energy injected into the loop is generated by internal coherent
motions within strong magnetic elements. The resulting Poynting
flux is channelled into the loop in vortex tubes forming a magnetic
connection between the photosphere and corona, where it is dissipated
and heats the upper atmosphere. The coronal emission as it would
be observed in solar extreme UV or X-ray observations, e.g. with AIA
or XRT, shows transient bright strands.The widths of these strands are
consistent with observations. From our model we find that the width
of the strands is governed by the size of the individual photospheric
magnetic field concentrations where the field line through these strands
are rooted. Essentially, each coronal strand is rooted in a single
magnetic patch in the photosphere, and the energy to heat the strand is
generated by internal motions within this magnetic concentration. With this model we can build a coherent picture of how energy and
matter are transported into the upper solar atmosphere and how these
processes structure the interior of coronal loops.

---------------------------------------------------------
Title: Small-scale Dynamo in Cool Main-Sequence Stars: Effect on
Stratification, Convection and Bolometric Intensity
Authors: Bhatia, T.; Cameron, R.; Solanki, S.; Peter, H.; Przybylski,
D.; Witzke, V.; Shapiro, A.
2021AAS...23830404B Altcode:
In cool main-sequence stars, the near-surface convection has an
impact on the center-to-limb variation of photospheric emission, with
implications for stellar lightcurves during planetary transits. In
the Sun, there is strong evidence for a small-scale dynamo (SSD)
maintaining the small-scale magnetic flux. This field could affect the
near-surface convection in other cool main-sequence stars. An SSD
could conceivably generate equipartition magnetic fields, which could
lead to non-negligible changes not only in convection and intensity
characteristics, but also in stratification. We aim to investigate these
changes for F, G, K and M stars. 3D MHD models of the four stellar types
covering the subsurface region to lower atmosphere in a small cartesian
box are studied using the MURaM rMHD simulation code. The MHD runs are
compared against a reference hydrodynamic (HD) run. The deviations
in stratification for the deeper convective layers is negligible,
except for the F-star, where reduction in turbulent pressure due to
magnetic fields is substantial. Convective velocities are reduced
by a similar percentage for all the cases due to inhibitory effect
of strong magnetic fields near the bottom boundary. All four cases
show small-scale brightenings in intergranular lanes, corresponding
to magnetic field concentrations, but overall effects on the r.m.s
contrast and spatial powerspectra are varied.

---------------------------------------------------------
Title: On-disk Solar Coronal Condensations Facilitated by Magnetic
Reconnection between Open and Closed Magnetic Structures
Authors: Li, Leping; Peter, Hardi; Chitta, Lakshmi Pradeep; Song,
Hongqiang
2021ApJ...910...82L Altcode: 2021arXiv210204605L
Coronal condensation and rain are a crucial part of the mass cycle
between the corona and chromosphere. In some cases, condensation and
subsequent rain originate in the magnetic dips formed during magnetic
reconnection. This provides a new and alternative formation mechanism
for coronal rain. Until now, only off-limb, rather than on-disk,
condensation events during reconnection have been reported. In
this paper, employing extreme-ultraviolet (EUV) images of the
Solar Terrestrial Relations Observatory (STEREO) and Solar Dynamics
Observatory (SDO), we investigate the condensations facilitated by
reconnection from 2011 July 14-15, when STEREO was in quadrature with
respect to the Sun-Earth line. Above the limb, in STEREO/EUV Imager
(EUVI) 171 Å images, higher-lying open structures move downward,
reconnect with the lower-lying closed loops, and form dips. Two
sets of newly reconnected structures then form. In the dips, bright
condensations occur in the EUVI 304 Å images repeatedly, which
then flow downward to the surface. In the on-disk observations by
SDO/Atmospheric Imaging Assembly (AIA) in the 171 Å channel, these
magnetic structures are difficult to identify. Dark condensations
appear in the AIA 304 Å images, and then move to the surface as
on-disk coronal rain. The cooling and condensation of coronal plasma
is revealed by the EUV light curves. If only the on-disk observations
were be available, the relation between the condensations and
reconnection, shown clearly by the off-limb observations, could not
be identified. Thus, we suggest that some on-disk condensation events
seen in transition region and chromospheric lines may be facilitated
by reconnection.

---------------------------------------------------------
Title: Transient small-scale brightenings in the quiet Sun corona:
a model for "campfires" observed with Solar Orbiter
Authors: Chen, Yajie; Przybylski, Damien; Peter, Hardi; Tian, Hui
2021EGUGA..23.5061C Altcode:
Recent observations by the Extreme Ultraviolet Imager (EUI)
onboard Solar Orbiter have revealed prevalent small-scale transient
brightenings in the quiet solar corona termed campfires. To understand
the generation mechanism of these coronal brightenings, we constructed
a self- consistent and time-dependent quiet-Sun model extending from
the upper convection zone to the lower corona using a realistic 3D
radiation MHD simulation. From the model we have synthesized the coronal
emission in the EUI 174 Å passband. We identified several transient
coronal brightenings similar to those in EUI observations. The size
and lifetime of these coronal brightenings are 2-4 Mm and ∼2 min,
respectively. These brightenings are located at a height of 2-4 Mm
above the photosphere, and the surrounding plasma is often heated
above 1 MK. These findings are consistent with the observational
characterisation of the campfires. Through a comparison of the magnetic
field structures before and after the occurrence of brightenings, we
conclude that these coronal brightenings are generated by component
magnetic reconnection between interacting bundles of field lines or
the relaxation of highly twisted flux ropes. Occurring in the coronal
part of the atmosphere, these events show no measurable signature
in the photosphere. These transient coronal brightenings may play an
important role in heating of the local coronal plasma.

---------------------------------------------------------
Title: First data for abundance diagnostics with SPICE, the EUV
spectrometer on-board Solar Orbiter
Authors: Zambrana Prado, Natalia; Buchlin, Éric; Peter, Hardi
2021EGUGA..2315555Z Altcode:
Linking solar activity on the surface and in the corona to the
heliosphere is one of Solar Orbiter"s main goals. Its EUV spectrometer
SPICE (SPectral Imaging of the Coronal Environment) will provide
relative abundance measurements which will be key in this quest,
as different structures on the Sun have different abundances as a
consequence of the FIP (First Ionization Potential) effect. From
the 16th to the 22nd of November 2020, the Solar Orbiter remote
sensing checkout window STP-122 was carried out. During this period
of observations, SPICE was lucky to catch a small AR in its field
of view. We carried out abundance specific observations in order
to provide relative FIP bias measurements with SPICE. Furthermore,
data from other types of observations carried out during that same
week allow us to identify the spectral lines that could be used for
abundance diagnostics. We take the SPICE instrument characteristics
into account to give recommendations regarding the types of studies
to carry out to obtain such abundance measurements.

---------------------------------------------------------
Title: Small-scale dynamo in an F-star: effects on near-surface
stratification, convection and intensity
Authors: Bhatia, Tanayveer; Cameron, Robert; Solanki, Sami; Peter,
Hardi; Przybylski, Damien; Witzke, Veronika; Shapiro, Alexander
2021csss.confE..75B Altcode:
The emission from the photosphere of stars shows a systematic
center-to-limb variation. In cool main-sequence stars, the near-surface
convection has an impact on this variation, with implications for
lightcurves of stars during planetary transits. In the Sun, there
is strong evidence for a small-scale dynamo (SSD) maintaining the
small-scale magnetic flux. We aim to investigate what additional
effects such a field would play for other cool main-sequence
stars. In our work we first concentrate on F-stars. This is because
they have sonic velocities near the surface, implying a rough
equipartition between internal and kinetic energies. In addition,
an SSD might create a significant magnetic energy density to impact
the results. We investigate the interplay between internal, kinetic
and magnetic energies in 3D cartesian box MHD models of a F3V-star in
the near-surface convection, using the MURaM radiative-MHD simulation
code. Along with a reference hydrodynamic run, two MHD models with
self-consistently generated magnetic fields with two different lower
boundary conditions are considered. We find that the SSD process
creates a magnetic field with energy within an order of magnitude of the
internal and the kinetic energy. Compared to the hydrodynamic run, we
find slight (~1-3%) but significant deviations in density, gas pressure
and temperature stratification. At the surface, this corresponds to a
temperature difference of ~130 K. As expected, there is a significant
reduction in kinetic energy flux once the SSD is operational. The
changes in intensity are more subtle, both in total intensity and
granulation pattern. From this we conclude that the presence of an
SSD will have a significant impact on the atmospheric structure and
intensity characteristics seen at the surface. This makes it clear
that it would be important to consider the spatially and temporally
averaged effects of the SSD also for global stellar models.

---------------------------------------------------------
Title: Extreme-ultraviolet bursts and nanoflares in the quiet-Sun
transition region and corona
Authors: Chitta, L. P.; Peter, H.; Young, P. R.
2021A&A...647A.159C Altcode: 2021arXiv210200730C
The quiet solar corona consists of myriads of loop-like features, with
magnetic fields originating from network and internetwork regions on
the solar surface. The continuous interaction between these different
magnetic patches leads to transient brightenings or bursts that might
contribute to the heating of the solar atmosphere. The literature
on a variety of such burst phenomena in the solar atmosphere is
rich. However, it remains unclear whether such transients, which are
mostly observed in the extreme ultraviolet (EUV), play a significant
role in atmospheric heating. We revisit the open question of these
bursts as a prelude to the new high-resolution EUV imagery expected
from the recently launched Solar Orbiter. We use EUV image sequences
recorded by the Atmospheric Imaging Assembly (AIA) on board the Solar
Dynamics Observatory (SDO) to investigate statistical properties of
the bursts. We detect the bursts in the 171 Å filter images of AIA in
an automated way through a pixel-wise analysis by imposing different
intensity thresholds. By exploiting the high cadence (12 s) of the
AIA observations, we find that the distribution of lifetimes of these
events peaks at about 120 s. However, a significant number of events
also have lifetimes shorter than 60 s. The sizes of the detected bursts
are limited by the spatial resolution, which indicates that a larger
number of events might be hidden in the AIA data. We estimate that about
100 new bursts appear per second on the whole Sun. The detected bursts
have nanoflare-like energies of 1024 erg per event. Based
on this, we estimate that at least 100 times more events of a similar
nature would be required to account for the energy that is required
to heat the corona. When AIA observations are considered alone, the
EUV bursts discussed here therefore play no significant role in the
coronal heating of the quiet Sun. If the coronal heating of the quiet
Sun is mainly bursty, then the high-resolution EUV observations from
Solar Orbiter may be able to reduce the deficit in the number of EUV
bursts seen with SDO/AIA at least partly by detecting more such events.

---------------------------------------------------------
Title: A magnetic reconnection model for hot explosions in the cool
atmosphere of the Sun
Authors: Ni, Lei; Chen, Yajie; Peter, Hardi; Tian, Hui; Lin, Jun
2021A&A...646A..88N Altcode: 2020arXiv201107692N
Context. Ultraviolet (UV) bursts and Ellerman bombs (EBs) are
transient brightenings observed in the low solar atmospheres of
emerging flux regions. Magnetic reconnection is believed to be the
main mechanism leading to formation of the two activities, which are
usually formed far apart from each other. However, observations also
led to the discovery of co-spatial and co-temporal EBs and UV bursts,
and their formation mechanisms are still not clear. The multi-thermal
components in these events, which span a large temperature range,
challenge our understanding of magnetic reconnection and heating
mechanisms in the partially ionized lower solar atmosphere. 
Aims: We studied magnetic reconnection between the emerging magnetic
flux and back ground magnetic fields in the partially ionized and
highly stratificated low solar atmosphere. We aim to explain the
multi-thermal characteristics of UV bursts, and to find out whether
EBs and UV bursts can be generated in the same reconnection process
and how they are related with each other. We also aim to unearth the
important small-scale physics in these events. Methods: We used
the single-fluid magnetohydrodynamic (MHD) code NIRVANA to perform
simulations. The background magnetic fields and emerging fields at the
solar surface are reasonably strong. The initial plasma parameters are
based on the C7 atmosphere model. We simulated cases with different
resolutions, and included the effects of ambipolar diffusion, radiative
cooling, and heat conduction. We analyzed the current density, plasma
density, temperature, and velocity distributions in the main current
sheet region, and synthesized the Si IV emission spectrum. 
Results: After the current sheet with dense photosphere plasma emerges
and reaches 0.5 Mm above the solar surface, plasmoid instability
appears. The plasmoids collide and coalesce with each other, which
causes the plasmas with different densities and temperatures to be mixed
up in the turbulent reconnection region. Therefore, the hot plasmas
corresponding to the UV emissions and colder plasmas corresponding to
the emissions from other wavelengths can move together and occur at
about the same height. In the meantime, the hot turbulent structures
concentrate above 0.4 Mm, whereas the cool plasmas extend to much
lower heights to the bottom of the current sheet. These phenomena
are consistent with published observations in which UV bursts have a
tendency to be located at greater heights close to corresponding EBs
and all the EBs have partial overlap with corresponding UV bursts
in space. The synthesized Si IV line profiles are similar to that
observed in UV bursts; the enhanced wing of the line profiles can
extend to about 100 km s-1. The differences are significant
among the numerical results with different resolutions, indicating
that the realistic magnetic diffusivity is crucial to revealing the
fine structures and realistic plasmas heating in these reconnection
events. Our results also show that the reconnection heating contributed
by ambipolar diffusion in the low chromosphere around the temperature
minimum region is not efficient.

---------------------------------------------------------
Title: Magnetic Reconnection between Loops Accelerated By a Nearby
Filament Eruption
Authors: Li, Leping; Peter, Hardi; Chitta, Lakshmi Pradeep; Song,
Hongqiang; Ji, Kaifan; Xiang, YongYuan
2021ApJ...908..213L Altcode: 2020arXiv201208710L
Magnetic reconnection modulated by nonlocal disturbances in the
solar atmosphere has been investigated theoretically, but rarely
observed. In this study, employing Hα and extreme ultraviolet (EUV)
images and line-of-sight magnetograms, we report the acceleration of
reconnection by an adjacent filament eruption. In Hα images, four
groups of chromospheric fibrils are observed to form a saddle-like
structure. Among them, two groups of fibrils converge and reconnect. Two
newly reconnected fibrils then form and retract away from the
reconnection region. In EUV images, similar structures and evolution
of coronal loops are identified. The current sheet forms repeatedly
at the interface of reconnecting loops, with a width and length of
1-2 and 5.3-7.2 Mm and a reconnection rate of 0.18-0.3. It appears
in the EUV low-temperature channels, with an average differential
emission measure (DEM) weighed temperature and EM of 2 MK and 2.5
× 1027 cm-5. Plasmoids appear in the current
sheet and propagate along it, and then further along the reconnection
loops. The filament, located to the southeast of the reconnection
region, erupts and pushes away the loops covering the reconnection
region. Thereafter, the current sheet has a width and length of 2
and 3.5 Mm and a reconnection rate of 0.57. It becomes much brighter
and appears in the EUV high-temperature channels, with an average
DEM-weighed temperature and EM of 5.5 MK and 1.7 × 1028
cm-5. In the current sheet, more hotter plasmoids form. More
thermal and kinetic energy is hence converted. These results suggest
that the reconnection is significantly accelerated by the propagating
disturbance caused by the nearby filament eruption.

---------------------------------------------------------
Title: New observational support for the role of magnetic field line
braiding in solar coronal heating
Authors: Pontin, David; Peter, Hardi; Yeates, Anthony; Pradeep Chitta,
L.; Candelaresi, Simon; Hornig, Gunnar; Bushby, Paul
2021cosp...43E1796P Altcode:
We present here new work that links models of magnetic field line
braiding in coronal loops to observations of the photosphere and
corona. We describe analysis of photospheric flows that quantifies the
rate at which coronal magnetic field lines are braided. The results
suggest that the photospheric motions induce complex tangling of the
coronal field on a timescale of minutes to hours. New data from DKIST
promises to further improve such estimates. Theoretical models show that
this persistent tangling inevitably leads to the onset of reconnection
and a turbulent heating of the plasma in the corona. We go on to
describe synthetic emissions in a 3D magnetohydrodynamic model of the
turbulent decay of an initially-braided magnetic field. We discuss how
previously unexplained key features of observed emission line profiles
in coronal loops - such as non-thermal widths and non-Gaussian profiles
- are reproduced in the synthesised spectra.

---------------------------------------------------------
Title: Magnetic Imaging of the Outer Solar Atmosphere (MImOSA):
Unlocking the driver of the dynamics in the upper solar atmosphere
Authors: Peter, H.; Alsina Ballester, E.; Andretta, V.; Auchere, F.;
Belluzzi, L.; Bemporad, A.; Berghmans, D.; Buchlin, E.; Calcines, A.;
Chitta, L. P.; Dalmasse, K.; del Pino Aleman, T.; Feller, A.; Froment,
C.; Harrison, R.; Janvier, M.; Matthews, S.; Parenti, S.; Przybylski,
D.; Solanki, S. K.; Stepan, J.; Teriaca, L.; Trujillo Bueno, J.
2021arXiv210101566P Altcode:
The magnetic activity of the Sun directly impacts the Earth and human
life. Likewise, other stars will have an impact on the habitability
of planets orbiting these host stars. The lack of information on the
magnetic field in the higher atmospheric layers hampers our progress in
understanding solar magnetic activity. Overcoming this limitation would
allow us to address four paramount long-standing questions: (1) How
does the magnetic field couple the different layers of the atmosphere,
and how does it transport energy? (2) How does the magnetic field
structure, drive and interact with the plasma in the chromosphere and
upper atmosphere? (3) How does the magnetic field destabilise the outer
solar atmosphere and thus affect the interplanetary environment? (4)
How do magnetic processes accelerate particles to high energies? New
ground-breaking observations are needed to address these science
questions. We suggest a suite of three instruments that far exceed
current capabilities in terms of spatial resolution, light-gathering
power, and polarimetric performance: (a) A large-aperture UV-to-IR
telescope of the 1-3 m class aimed mainly to measure the magnetic
field in the chromosphere by combining high spatial resolution and high
sensitivity. (b) An extreme-UV-to-IR coronagraph that is designed to
measure the large-scale magnetic field in the corona with an aperture
of about 40 cm. (c) An extreme-UV imaging polarimeter based on a 30
cm telescope that combines high throughput in the extreme UV with
polarimetry to connect the magnetic measurements of the other two
instruments. This mission to measure the magnetic field will unlock
the driver of the dynamics in the outer solar atmosphere and thereby
greatly advance our understanding of the Sun and the heliosphere.

---------------------------------------------------------
Title: Relative coronal abundance diagnostics with Solar Orbiter/SPICE
Authors: Zambrana Prado, N.; Buchlin, E.; Peter, H.; Young, P. R.;
Auchere, F.; Carlsson, M.; Fludra, A.; Hassler, D.; Aznar Cuadrado,
R.; Caminade, S.; Caldwell, M.; DeForest, C.; Fredvik, T.; Harra,
L.; Janvier, M.; Kucera, T. A.; Giunta, A. S.; Grundy, T.; Müller,
D.; Parenti, S.; Schmutz, W. K.; Schühle, U.; Sidher, S.; Teriaca,
L.; Thompson, W. T.; Williams, D.
2020AGUFMSH038..09Z Altcode:
Linking solar activity on the surface and in the corona to the inner
heliosphere is one of Solar Orbiter's main goals. Its UV spectrometer
SPICE (SPectral Imaging of the Coronal Environment) will provide
relative abundance measurements which will be key in this quest
as different structures on the Sun have different abundances as a
consequence of the FIP (First Ionization Potential) effect. Solar
Orbiter's unique combination of remote sensing and in-situ instruments
coupled with observation from other missions such as Parker Solar
Probe will allow us to compare in-situ and remote sensing composition
data. With the addition of modeling, these new results will allow us
to trace back the source of heliospheric plasma. As high telemetry
will not always be available with SPICE, we have developed a method
for measuring relative abundances that is both telemetry efficient
and reliable. Unlike methods based on Differential Emission Measure
(DEM) inversion, the Linear Combination Ratio (LCR) method does not
require a large number of spectral lines. This new method is based
on linear combinations of UV spectral lines. The coefficients of
the combinations are optimized such that the ratio of two linear
combinations of radiances would yield the relative abundance of two
elements. We present some abundance diagnostics tested on different
combinations of spectral lines observable by SPICE.

---------------------------------------------------------
Title: Dynamics and thermal structure in the quiet Sun seen by SPICE
Authors: Peter, H.; Aznar Cuadrado, R.; Schühle, U.; Teriaca, L.;
Auchere, F.; Carlsson, M.; Fludra, A.; Hassler, D.; Buchlin, E.;
Caminade, S.; Caldwell, M.; DeForest, C.; Fredvik, T.; Harra, L. K.;
Janvier, M.; Kucera, T. A.; Giunta, A. S.; Grundy, T.; Müller, D.;
Parenti, S.; Schmutz, W. K.; Sidher, S.; Thompson, W. T.; Williams,
D.; Young, P. R.
2020AGUFMSH038..03P Altcode:
We will present some of the early data of the Spectral Imaging of the
Coronal Environment (SPICE) instrument on Solar Orbiter. One of the
unique features of SPICE is its capability to record a wide range of
wavelengths in the extreme UV with the possibility to record spectral
lines giving access to a continuous plasma temperature range from 10.000
K to well above 1 MK. The data taken so far were for commissioning
purposes and they can be used for a preliminary evaluation of the
science performance of the instrument. Here we will concentrate on
sample spectra covering the whole wavelength region and on the early
raster maps acquired in bright lines in the quiet Sun close to disk
center. Looking at different quiet Sun features we investigate the
thermal structure of the atmosphere and flow structures. For this
we apply fits to the spectral profiles and check the performance in
terms of Doppler shifts and line widths to retrieve the structure of
the network in terms of dynamics. While the amount of data available
so far is limited, we will have a first look on how quiet Sun plasma
responds to heating events. For this, we will compare spectral lines
forming at different temperatures recorded at strictly the same time.

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Title: Spectroscopic Observations of the Eruption of an Filament
and Associated Magnetic Reconnection
Authors: Hu, H.; Liu, Y. D.; Peter, H.; Chitta, L. P.; Wang, R.
2020AGUFMSH0010013H Altcode:
We analyze the spectroscopic data from Interface Region Imaging
Spectrograph (IRIS) and images from Solar Dynamics Observatory (SDO)
to investigate the eruption and associated magnetic reconnection of
a filament structure in an active region (AR). Doppler maps derived
from Si IV 1394 Å based on single Gaussian fitting indicate that the
filament structure ascended rapidly after the birth of the situated
AR. The ascent apparently ceased ~2 days after the rapid ascent. The
filament structure gradually ascended again ~1 day before the
eruption. Blue and red shifts of ~30 km/s are observed in a narrow flare
region between two filament threads ~2 hours before the eruption, which
are probably the signatures of the outflows of magnetic reconnection
between the two filament threads. Eventually the upper filament thread
erupted and the lower filament thread remained. Downward motion with a
red shift of ~30 km/s and density enhancement are also observed in the
regions of flare ribbons during the eruption. This work pictures the
evolution of a filament structure before an eruption and the associated
magnetic reconnection between two filament threads.

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Title: First Results From SPICE EUV Spectrometer on Solar Orbiter
Authors: Fludra, A.; Caldwell, M.; Giunta, A. S.; Grundy, T.; Guest,
S.; Sidher, S.; Auchere, F.; Carlsson, M.; Hassler, D.; Peter, H.;
Aznar Cuadrado, R.; Buchlin, E.; Caminade, S.; DeForest, C.; Fredvik,
T.; Harra, L. K.; Janvier, M.; Kucera, T. A.; Leeks, S.; Mueller,
D.; Parenti, S.; Schmutz, W. K.; Schühle, U.; Teriaca, L.; Thompson,
W. T.; Tustain, S.; Williams, D.; Young, P. R.
2020AGUFMSH038..02F Altcode:
SPICE (Spectral Imaging of Coronal Environment) is one of the remote
sensing instruments onboard Solar Orbiter. It is an EUV imaging
spectrometer observing the Sun in two wavelength bands: 69.6-79.4 nm
and 96.6-105.1 nm. SPICE is capable of recording full spectra in these
bands with exposures as short as 1s. SPICE is the only Solar Orbiter
instrument that can measure EUV spectra from the disk and low corona
of the Sun and record all spectral lines simultaneously. SPICE uses
one of three narrow slits, 2"x11', 4”x11', 6”x11', or a wide slit
30”x14'. The primary mirror can be scanned in a direction perpendicular
to the slit, allowing raster images of up to 16' in size. We
present an overview of the first SPICE data taken on several days
during the instrument commissioning carried out by the RAL Space team
between 2020 April 21 and 2020 June 14. We also include results from
SPICE observations at the first Solar Orbiter perihelion at 0.52AU,
taken between June 16-21st. We give examples of full spectra
from the quiet Sun near disk centre and provide a list of key spectral
lines emitted in a range of temperatures between 10,000 K and over 1
million K, from neutral hydrogen and ions of carbon, oxygen, nitrogen,
neon, sulphur and magnesium. We show examples of first raster images
in several strong lines, obtained with different slits and a range
of exposure times between 5s and 180s. We describe the temperature
coverage and density diagnostics, determination of plasma flows, and
discuss possible applications to studies of the elemental abundances
in the corona. We also show the first off-limb measurements with SPICE,
as obtained when the spacecraft pointed at the limb.

---------------------------------------------------------
Title: Relation of Coronal Rain Originating from Coronal Condensations
to Interchange Magnetic Reconnection
Authors: Li, Leping; Peter, Hardi; Chitta, Lakshmi Pradeep; Song,
Hongqiang
2020ApJ...905...26L Altcode: 2020arXiv201100709L
Using extreme-ultraviolet images, we recently proposed a new and
alternative formation mechanism for coronal rain along magnetically
open field lines due to interchange magnetic reconnection. In this
paper we report coronal rain at chromospheric and transition region
temperatures originating from the coronal condensations facilitated
by reconnection between open and closed coronal loops. For this,
we employ the Interface Region Imaging Spectrograph (IRIS) and
the Atmospheric Imaging Assembly (AIA) of the Solar Dynamics
Observatory. Around 2013 October 19, a coronal rain along curved
paths was recorded by IRIS over the southeastern solar limb. Related
to this, we found reconnection between a system of higher-lying open
features and lower-lying closed loops that occurs repeatedly in AIA
images. In this process, the higher-lying features form magnetic
dips. In response, two sets of newly reconnected loops appear and
retract away from the reconnection region. In the dips, seven events
of cooling and condensation of coronal plasma repeatedly occur due
to thermal instability over several days, from October 18 to 20. The
condensations flow downward to the surface as coronal rain, with a
mean interval between condensations of ∼6.6 hr. In the cases where
IRIS data were available we found the condensations to cool all the
way down to chromospheric temperatures. Based on our observations we
suggest that some of the coronal rain events observed at chromospheric
temperatures could be explained by the new and alternative scenario for
the formation of coronal rain, where the condensation is facilitated
by interchange reconnection.

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Title: Calibrating optical distortions in the Solar Orbiter SPICE
spectrograph
Authors: Thompson, W. T.; Schühle, U.; Young, P. R.; Auchere, F.;
Carlsson, M.; Fludra, A.; Hassler, D.; Peter, H.; Aznar Cuadrado, R.;
Buchlin, E.; Caldwell, M.; DeForest, C.; Fredvik, T.; Harra, L. K.;
Janvier, M.; Kucera, T. A.; Giunta, A. S.; Grundy, T.; Müller, D.;
Parenti, S.; Caminade, S.; Schmutz, W. K.; Teriaca, L.; Williams,
D.; Sidher, S.
2020AGUFMSH0360029T Altcode:
The Spectral Imaging of the Coronal Environment (SPICE) instrument on
Solar Orbiter is a high-resolution imaging spectrometer operating
at extreme ultraviolet (EUV) wavelengths from 70.4-79.0 nm and
97.3-104.9 nm. A single-mirror off-axis paraboloid focuses the solar
image onto the entrance slit of the spectrometer section. A Toroidal
Variable Line Space (TVLS) grating images the entrance slit onto a
pair of MCP-intensified APS detectors. Ray-tracing analysis prior
to launch showed that the instrument was subject to a number of
small image distortions which need to be corrected in the final data
product. We compare the ray tracing results with measurements made in
flight. Co-alignment with other telescopes on Solar Orbiter will also
be examined.

---------------------------------------------------------
Title: First results from the EUI and SPICE observations of Alpha
Leo near Solar Orbiter first perihelion
Authors: Buchlin, E.; Teriaca, L.; Giunta, A. S.; Grundy, T.; Andretta,
V.; Auchere, F.; Peter, H.; Berghmans, D.; Carlsson, M.; Fludra, A.;
Harra, L.; Hassler, D.; Long, D.; Rochus, P. L.; Schühle, U.; Aznar
Cuadrado, R.; Caldwell, M.; Caminade, S.; DeForest, C.; Fredvik, T.;
Gissot, S.; Heerlein, K.; Janvier, M.; Kraaikamp, E.; Kucera, T. A.;
Müller, D.; Parenti, S.; Schmutz, W. K.; Sidher, S.; Smith, P.;
Stegen, K.; Thompson, W. T.; Verbeeck, C.; Williams, D.; Young, P. R.
2020AGUFMSH0360024B Altcode:
On June 16th 2020 Solar Orbiter made a dedicated observing campaign
where the spacecraft pointed to the solar limb to allow some of the
high resolution instruments to observe the ingress (at the east limb)
and later the egress (west limb) of the occultation of the star Alpha
Leonis by the solar disk. The star was chosen because its luminosity and
early spectral type ensure high and stable flux at wavelengths between
100 and 122 nanometers, a range observed by the High Resolution EUI
Lyman alpha telescope (HRI-LYA) and by the long wavelength channel
of the SPICE spectrograph. Star observations, when feasible, allow
to gather a great deal of information on the instrument performances,
such as the radiometric performance and the instrument optical point
spread function (PSF). We report here the first results from the
above campaign for the two instruments.

---------------------------------------------------------
Title: Solar Orbiter: connecting remote sensing and in situ
measurements
Authors: Horbury, T. S.; Auchere, F.; Antonucci, E.; Berghmans, D.;
Bruno, R.; Carlsson, M.; del Toro Iniesta, J. C.; Fludra, A.; Harra,
L.; Hassler, D.; Heinzel, P.; Howard, R. A.; Krucker, S.; Livi, S. A.;
Long, D.; Louarn, P.; Maksimovic, M.; Mueller, D.; Owen, C. J.; Peter,
H.; Rochus, P. L.; Rodriguez-Pacheco, J.; Romoli, M.; Schühle, U.;
Solanki, S. K.; Teriaca, L.; Wimmer-Schweingruber, R. F.; Zouganelis,
Y.; Laker, R.
2020AGUFMSH038..10H Altcode:
A key science goal of the Solar Orbiter mission is to make connections
between phenomena on the Sun and their manifestations in interplanetary
space. To that end, the spacecraft carries a carefully tailored
payload of six remote sensing instruments and four making in situ
measurements. During June 2020, while the spacecraft was around 0.5
AU from the Sun, the remote sensing instruments operated for several
days. While this was primarily an engineering activity, the resulting
observations provided outstanding measurements and represent the ideal
first opportunity to investigate the potential for making connections
between the remote sensing and in situ payloads on Solar Orbiter. We present a preliminary analysis of the available remote sensing and
in situ observations, showing how connections can be made, and discuss
the potential for further, more precise mapping to be performed as
the mission progresses.

---------------------------------------------------------
Title: First results from combined EUI and SPICE observations of
Lyman lines of Hydrogen and He II
Authors: Teriaca, L.; Aznar Cuadrado, R.; Giunta, A. S.; Grundy, T.;
Parenti, S.; Auchere, F.; Vial, J. C.; Fludra, A.; Berghmans, D.;
Carlsson, M.; Harra, L.; Hassler, D.; Long, D.; Peter, H.; Rochus,
P. L.; Schühle, U.; Buchlin, E.; Caldwell, M.; Caminade, S.; DeForest,
C.; Fredvik, T.; Gissot, S.; Heerlein, K.; Janvier, M.; Kraaikamp,
E.; Kucera, T. A.; Mueller, D.; Schmutz, W. K.; Sidher, S.; Smith, P.;
Stegen, K.; Thompson, W. T.; Verbeeck, C.; Williams, D.; Young, P. R.
2020AGUFMSH0360003T Altcode:
The Solar Orbiter spacecraft carries a powerful set of remote
sensing instruments that allow studying the solar atmosphere with
unprecedented diagnostic capabilities. Many such diagnostics require
the simultaneous usage of more than one instrument. One example of that
is the capability, for the first time, to obtain (near) simultaneous
spatially resolved observations of the emission from the first three
lines of the Lyman series of hydrogen and of He II Lyman alpha. In fact,
the SPectral Imaging of the Coronal Environment (SPICE) spectrometer
can observe the Lyman beta and gamma lines in its long wavelength
(SPICE-LW) channel, the High Resolution Lyman Alpha (HRI-LYA) telescope
of the Extreme Ultraviolet Imager (EUI) acquires narrow band images in
the Lyman alpha line while the Full Disk Imager (FSI) of EUI can take
images dominated by the Lyman alpha line of ionized Helium at 30.4 nm
(FSI-304). Being hydrogen and helium the main components of our star,
these very bright transitions play an important role in the energy
budget of the outer atmosphere via radiative losses and the measurement
of their profiles and radiance ratios is a fundamental constraint to
any comprehensive modelization effort of the upper solar chromosphere
and transition region. Additionally, monitoring their average ratios
can serve as a check out for the relative radiometric performance of
the two instruments throughout the mission. Although the engineering
data acquired so far are far from ideal in terms of time simultaneity
(often only within about 1 h) and line coverage (often only Lyman beta
was acquired by SPICE and not always near simultaneous images from all
three telescopes are available) the analysis we present here still
offers a great opportunity to have a first look at the potential of
this diagnostic from the two instruments. In fact, we have identified
a series of datasets obtained at disk center and at various positions
at the solar limb that allow studying the Lyman alpha to beta radiance
ratio and their relation to He II 30.4 as a function of the position
on the Sun (disk center versus limb and quiet Sun versus coronal holes).

---------------------------------------------------------
Title: Impulsive coronal heating during the interaction of surface
magnetic fields in the lower solar atmosphere
Authors: Chitta, L. P.; Peter, H.; Priest, E. R.; Solanki, S. K.
2020A&A...644A.130C Altcode: 2020arXiv201012560C
Coronal plasma in the cores of solar active regions is impulsively
heated to more than 5 MK. The nature and location of the magnetic
energy source responsible for such impulsive heating is poorly
understood. Using observations of seven active regions from the Solar
Dynamics Observatory, we found that a majority of coronal loops hosting
hot plasma have at least one footpoint rooted in regions of interacting
mixed magnetic polarity at the solar surface. In cases when co-temporal
observations from the Interface Region Imaging Spectrograph space
mission are available, we found spectroscopic evidence for magnetic
reconnection at the base of the hot coronal loops. Our analysis suggests
that interactions of magnetic patches of opposite polarity at the
solar surface and the associated energy release during reconnection
are key to impulsive coronal heating. Movies are available at <A
href="https://www.aanda.org/10.1051/0004-6361/202039099/olm">https://www.aanda.org</A>

---------------------------------------------------------
Title: JuliaData/DataFrames.jl: v0.22.1
Authors: Myles White, John; Kamiński, Bogumił; Powerdistribution;
Bouchet-Valat, Milan; Garborg, Sean; Quinn, Jacob; Kornblith, Simon;
Cjprybol; Stukalov, Alexey; Bates, Douglas; Short, Tom; DuBois, Chris;
Harris, Harlan; Squire, Kevin; Arslan, Alex; Pdeffebach; Anthoff,
David; Kleinschmidt, Dave; Noack, Andreas; Shah, Viral B.; Mellnik,
Alex; Arakaki, Takafumi; Mohapatra, Tanmay; Peter; Karpinski, Stefan;
Lin, Dahua; Timema; ExpandingMan; Oswald, Florian; White, Lyndon
2020zndo...4282946M Altcode:
DataFrames v0.22.1 Diff since v0.22.0 Closed issues: eltype width taken
into accounet in display even if it is not shown (#2540) Final ellipsis
appears on next row (#2544) clarify the interface for crossjoin when
makeunique=true (#2545) Two small typos in docs (#2550) Merged pull
requests: Fix size of float columns without eltypes (#2542) (@ronisbr)
Spaces after commas (#2546) (@kescobo) Optional args style (#2547)
(@kescobo) Zero after decimal (#2548) (@kescobo) issue #2550 fix two
small typos in docs (#2551) (@roualdes) Switch from travis to GitHub
Actions for CI testing (#2552) (@quinnj) error when using one dimension
for indexing (#2553) (@bkamins) Add link to CI status badge (#2555)
(@nalimilan)

---------------------------------------------------------
Title: Coordination within the remote sensing payload on the Solar
Orbiter mission
Authors: Auchère, F.; Andretta, V.; Antonucci, E.; Bach, N.;
Battaglia, M.; Bemporad, A.; Berghmans, D.; Buchlin, E.; Caminade,
S.; Carlsson, M.; Carlyle, J.; Cerullo, J. J.; Chamberlin, P. C.;
Colaninno, R. C.; Davila, J. M.; De Groof, A.; Etesi, L.; Fahmy,
S.; Fineschi, S.; Fludra, A.; Gilbert, H. R.; Giunta, A.; Grundy,
T.; Haberreiter, M.; Harra, L. K.; Hassler, D. M.; Hirzberger, J.;
Howard, R. A.; Hurford, G.; Kleint, L.; Kolleck, M.; Krucker, S.;
Lagg, A.; Landini, F.; Long, D. M.; Lefort, J.; Lodiot, S.; Mampaey,
B.; Maloney, S.; Marliani, F.; Martinez-Pillet, V.; McMullin, D. R.;
Müller, D.; Nicolini, G.; Orozco Suarez, D.; Pacros, A.; Pancrazzi,
M.; Parenti, S.; Peter, H.; Philippon, A.; Plunkett, S.; Rich, N.;
Rochus, P.; Rouillard, A.; Romoli, M.; Sanchez, L.; Schühle, U.;
Sidher, S.; Solanki, S. K.; Spadaro, D.; St Cyr, O. C.; Straus, T.;
Tanco, I.; Teriaca, L.; Thompson, W. T.; del Toro Iniesta, J. C.;
Verbeeck, C.; Vourlidas, A.; Watson, C.; Wiegelmann, T.; Williams,
D.; Woch, J.; Zhukov, A. N.; Zouganelis, I.
2020A&A...642A...6A Altcode:
Context. To meet the scientific objectives of the mission, the Solar
Orbiter spacecraft carries a suite of in-situ (IS) and remote sensing
(RS) instruments designed for joint operations with inter-instrument
communication capabilities. Indeed, previous missions have shown that
the Sun (imaged by the RS instruments) and the heliosphere (mainly
sampled by the IS instruments) should be considered as an integrated
system rather than separate entities. Many of the advances expected
from Solar Orbiter rely on this synergistic approach between IS and
RS measurements. Aims: Many aspects of hardware development,
integration, testing, and operations are common to two or more
RS instruments. In this paper, we describe the coordination effort
initiated from the early mission phases by the Remote Sensing Working
Group. We review the scientific goals and challenges, and give an
overview of the technical solutions devised to successfully operate
these instruments together. Methods: A major constraint for the
RS instruments is the limited telemetry (TM) bandwidth of the Solar
Orbiter deep-space mission compared to missions in Earth orbit. Hence,
many of the strategies developed to maximise the scientific return from
these instruments revolve around the optimisation of TM usage, relying
for example on onboard autonomy for data processing, compression,
and selection for downlink. The planning process itself has been
optimised to alleviate the dynamic nature of the targets, and an
inter-instrument communication scheme has been implemented which can
be used to autonomously alter the observing modes. We also outline the
plans for in-flight cross-calibration, which will be essential to the
joint data reduction and analysis. Results: The RS instrument
package on Solar Orbiter will carry out comprehensive measurements
from the solar interior to the inner heliosphere. Thanks to the close
coordination between the instrument teams and the European Space
Agency, several challenges specific to the RS suite were identified
and addressed in a timely manner.

---------------------------------------------------------
Title: Evidence for and Analysis of Multiple Hidden Coronal Strands
in Cross-sectional Emission Profiles: Further Results from NASA's
High-resolution Solar Coronal Imager
Authors: Williams, Thomas; Walsh, Robert W.; Peter, Hardi; Winebarger,
Amy R.
2020ApJ...902...90W Altcode: 2020arXiv200902210W
Previous work utilizing NASA's High-resolution Coronal Imager (Hi-C
2.1) 172 Å observations revealed that, even at the increased spatial
scales available in the dataset, there may be evidence for coronal
structures that are still not fully resolved. In this follow-up study,
cross-section slices of coronal strands are taken across the Hi-C 2.1
field of view. Following previous loop-width studies, the background
emission is removed to isolate the coronal strands. The resulting
intensity variations are reproduced by simultaneously fitting multiple
Gaussian profiles using a nonlinear least-squares curve-fitting
method. In total, 183 Gaussian profiles are examined for possible
structures that are hinted at in the data. The full width at half
maximum is determined for each Gaussian, which are then collated and
analyzed. The most frequent structural widths are ≍450-575 km with
47% of the strand widths beneath NASA's Solar Dynamics Observatory
Atmospheric Imaging Assembly (AIA) resolving scale (600-1000 km). Only
17% reside beneath an AIA pixel width (435 km) with just 6% of the
strands at the Hi-C 2.1 resolving scale (≍220-340 km). These results
suggest that non-Gaussian shaped cross-sectional emission profiles
observed by Hi-C 2.1 are the result of multiple strands along the
integrated line of sight that can be resolved, rather than being the
result of even finer sub-resolution elements.

---------------------------------------------------------
Title: Observations and Modeling of the Onset of Fast Reconnection
in the Solar Transition Region
Authors: Guo, L. -J.; De Pontieu, Bart; Huang, Y. -M.; Peter, H.;
Bhattacharjee, A.
2020ApJ...901..148G Altcode: 2020arXiv200911475G
Magnetic reconnection is a fundamental plasma process that plays a
critical role not only in energy release in the solar atmosphere, but
also in fusion, astrophysics, and other space plasma environments. One
of the challenges in explaining solar observations in which reconnection
is thought to play a critical role is to account for the transition of
the dynamics from a slow quasi-continuous phase to a fast and impulsive
energetic burst of much shorter duration. Despite the theoretical
progress in identifying mechanisms that might lead to rapid onset,
a lack of observations of this transition has left models poorly
constrained. High-resolution spectroscopic observations from NASA's
Interface Region Imaging Spectrograph now reveal tell-tale signatures
of the abrupt transition of reconnection from a slow phase to a fast,
impulsive phase during UV bursts or explosive events in the Sun's
atmosphere. Our observations are consistent with numerical simulations
of the plasmoid instability, and provide evidence for the onset of
fast reconnection mediated by plasmoids and new opportunities for
remote-sensing diagnostics of reconnection mechanisms on the Sun.

---------------------------------------------------------
Title: Models and data analysis tools for the Solar Orbiter mission
Authors: Rouillard, A. P.; Pinto, R. F.; Vourlidas, A.; De Groof, A.;
Thompson, W. T.; Bemporad, A.; Dolei, S.; Indurain, M.; Buchlin, E.;
Sasso, C.; Spadaro, D.; Dalmasse, K.; Hirzberger, J.; Zouganelis, I.;
Strugarek, A.; Brun, A. S.; Alexandre, M.; Berghmans, D.; Raouafi,
N. E.; Wiegelmann, T.; Pagano, P.; Arge, C. N.; Nieves-Chinchilla,
T.; Lavarra, M.; Poirier, N.; Amari, T.; Aran, A.; Andretta, V.;
Antonucci, E.; Anastasiadis, A.; Auchère, F.; Bellot Rubio, L.;
Nicula, B.; Bonnin, X.; Bouchemit, M.; Budnik, E.; Caminade, S.;
Cecconi, B.; Carlyle, J.; Cernuda, I.; Davila, J. M.; Etesi, L.;
Espinosa Lara, F.; Fedorov, A.; Fineschi, S.; Fludra, A.; Génot,
V.; Georgoulis, M. K.; Gilbert, H. R.; Giunta, A.; Gomez-Herrero, R.;
Guest, S.; Haberreiter, M.; Hassler, D.; Henney, C. J.; Howard, R. A.;
Horbury, T. S.; Janvier, M.; Jones, S. I.; Kozarev, K.; Kraaikamp,
E.; Kouloumvakos, A.; Krucker, S.; Lagg, A.; Linker, J.; Lavraud,
B.; Louarn, P.; Maksimovic, M.; Maloney, S.; Mann, G.; Masson, A.;
Müller, D.; Önel, H.; Osuna, P.; Orozco Suarez, D.; Owen, C. J.;
Papaioannou, A.; Pérez-Suárez, D.; Rodriguez-Pacheco, J.; Parenti,
S.; Pariat, E.; Peter, H.; Plunkett, S.; Pomoell, J.; Raines, J. M.;
Riethmüller, T. L.; Rich, N.; Rodriguez, L.; Romoli, M.; Sanchez,
L.; Solanki, S. K.; St Cyr, O. C.; Straus, T.; Susino, R.; Teriaca,
L.; del Toro Iniesta, J. C.; Ventura, R.; Verbeeck, C.; Vilmer, N.;
Warmuth, A.; Walsh, A. P.; Watson, C.; Williams, D.; Wu, Y.; Zhukov,
A. N.
2020A&A...642A...2R Altcode:
Context. The Solar Orbiter spacecraft will be equipped with a wide
range of remote-sensing (RS) and in situ (IS) instruments to record
novel and unprecedented measurements of the solar atmosphere and
the inner heliosphere. To take full advantage of these new datasets,
tools and techniques must be developed to ease multi-instrument and
multi-spacecraft studies. In particular the currently inaccessible
low solar corona below two solar radii can only be observed
remotely. Furthermore techniques must be used to retrieve coronal
plasma properties in time and in three dimensional (3D) space. Solar
Orbiter will run complex observation campaigns that provide interesting
opportunities to maximise the likelihood of linking IS data to their
source region near the Sun. Several RS instruments can be directed
to specific targets situated on the solar disk just days before
data acquisition. To compare IS and RS, data we must improve our
understanding of how heliospheric probes magnetically connect to the
solar disk. Aims: The aim of the present paper is to briefly
review how the current modelling of the Sun and its atmosphere
can support Solar Orbiter science. We describe the results of a
community-led effort by European Space Agency's Modelling and Data
Analysis Working Group (MADAWG) to develop different models, tools,
and techniques deemed necessary to test different theories for the
physical processes that may occur in the solar plasma. The focus here
is on the large scales and little is described with regards to kinetic
processes. To exploit future IS and RS data fully, many techniques have
been adapted to model the evolving 3D solar magneto-plasma from the
solar interior to the solar wind. A particular focus in the paper is
placed on techniques that can estimate how Solar Orbiter will connect
magnetically through the complex coronal magnetic fields to various
photospheric and coronal features in support of spacecraft operations
and future scientific studies. Methods: Recent missions such as
STEREO, provided great opportunities for RS, IS, and multi-spacecraft
studies. We summarise the achievements and highlight the challenges
faced during these investigations, many of which motivated the Solar
Orbiter mission. We present the new tools and techniques developed
by the MADAWG to support the science operations and the analysis of
the data from the many instruments on Solar Orbiter. Results:
This article reviews current modelling and tool developments that ease
the comparison of model results with RS and IS data made available
by current and upcoming missions. It also describes the modelling
strategy to support the science operations and subsequent exploitation
of Solar Orbiter data in order to maximise the scientific output
of the mission. Conclusions: The on-going community effort
presented in this paper has provided new models and tools necessary
to support mission operations as well as the science exploitation of
the Solar Orbiter data. The tools and techniques will no doubt evolve
significantly as we refine our procedure and methodology during the
first year of operations of this highly promising mission.

---------------------------------------------------------
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 SPICE instrument. An extreme UV imaging
spectrometer
Authors: SPICE Consortium; Anderson, M.; Appourchaux, T.; Auchère, F.;
Aznar Cuadrado, R.; Barbay, J.; Baudin, F.; Beardsley, S.; Bocchialini,
K.; Borgo, B.; Bruzzi, D.; Buchlin, E.; Burton, G.; Büchel, V.;
Caldwell, M.; Caminade, S.; Carlsson, M.; Curdt, W.; Davenne, J.;
Davila, J.; Deforest, C. E.; Del Zanna, G.; Drummond, D.; Dubau,
J.; Dumesnil, C.; Dunn, G.; Eccleston, P.; Fludra, A.; Fredvik, T.;
Gabriel, A.; Giunta, A.; Gottwald, A.; Griffin, D.; Grundy, T.; Guest,
S.; Gyo, M.; Haberreiter, M.; Hansteen, V.; Harrison, R.; Hassler,
D. M.; Haugan, S. V. H.; Howe, C.; Janvier, M.; Klein, R.; Koller,
S.; Kucera, T. A.; Kouliche, D.; Marsch, E.; Marshall, A.; Marshall,
G.; Matthews, S. A.; McQuirk, C.; Meining, S.; Mercier, C.; Morris,
N.; Morse, T.; Munro, G.; Parenti, S.; Pastor-Santos, C.; Peter, H.;
Pfiffner, D.; Phelan, P.; Philippon, A.; Richards, A.; Rogers, K.;
Sawyer, C.; Schlatter, P.; Schmutz, W.; Schühle, U.; Shaughnessy,
B.; Sidher, S.; Solanki, S. K.; Speight, R.; Spescha, M.; Szwec, N.;
Tamiatto, C.; Teriaca, L.; Thompson, W.; Tosh, I.; Tustain, S.; Vial,
J. -C.; Walls, B.; Waltham, N.; Wimmer-Schweingruber, R.; Woodward,
S.; Young, P.; de Groof, A.; Pacros, A.; Williams, D.; Müller, D.
2020A&A...642A..14S Altcode: 2019arXiv190901183A; 2019arXiv190901183S
 Aims: The Spectral Imaging of the Coronal Environment (SPICE)
instrument is a high-resolution imaging spectrometer operating at
extreme ultraviolet wavelengths. In this paper, we present the concept,
design, and pre-launch performance of this facility instrument on the
ESA/NASA Solar Orbiter mission. Methods: The goal of this paper
is to give prospective users a better understanding of the possible
types of observations, the data acquisition, and the sources that
contribute to the instrument's signal. Results: The paper
discusses the science objectives, with a focus on the SPICE-specific
aspects, before presenting the instrument's design, including optical,
mechanical, thermal, and electronics aspects. This is followed by a
characterisation and calibration of the instrument's performance. The
paper concludes with descriptions of the operations concept and data
processing. Conclusions: The performance measurements of the
various instrument parameters meet the requirements derived from the
mission's science objectives. The SPICE instrument is ready to perform
measurements that will provide vital contributions to the scientific
success of the Solar Orbiter mission.

---------------------------------------------------------
Title: The Solar Orbiter mission. Science overview
Authors: Müller, D.; St. Cyr, O. C.; Zouganelis, I.; Gilbert, H. R.;
Marsden, R.; Nieves-Chinchilla, T.; Antonucci, E.; Auchère, F.;
Berghmans, D.; Horbury, T. S.; Howard, R. A.; Krucker, S.; Maksimovic,
M.; Owen, C. J.; Rochus, P.; Rodriguez-Pacheco, J.; Romoli, M.;
Solanki, S. K.; Bruno, R.; Carlsson, M.; Fludra, A.; Harra, L.;
Hassler, D. M.; Livi, S.; Louarn, P.; Peter, H.; Schühle, U.;
Teriaca, L.; del Toro Iniesta, J. C.; Wimmer-Schweingruber, R. F.;
Marsch, E.; Velli, M.; De Groof, A.; Walsh, A.; Williams, D.
2020A&A...642A...1M Altcode: 2020arXiv200900861M
 Aims: Solar Orbiter, the first mission of ESA's Cosmic Vision
2015-2025 programme and a mission of international collaboration between
ESA and NASA, will explore the Sun and heliosphere from close up and
out of the ecliptic plane. It was launched on 10 February 2020 04:03
UTC from Cape Canaveral and aims to address key questions of solar and
heliospheric physics pertaining to how the Sun creates and controls
the Heliosphere, and why solar activity changes with time. To answer
these, the mission carries six remote-sensing instruments to observe
the Sun and the solar corona, and four in-situ instruments to measure
the solar wind, energetic particles, and electromagnetic fields. In
this paper, we describe the science objectives of the mission, and how
these will be addressed by the joint observations of the instruments
onboard. Methods: The paper first summarises the mission-level
science objectives, followed by an overview of the spacecraft and
payload. We report the observables and performance figures of each
instrument, as well as the trajectory design. This is followed by a
summary of the science operations concept. The paper concludes with a
more detailed description of the science objectives. Results:
Solar Orbiter will combine in-situ measurements in the heliosphere
with high-resolution remote-sensing observations of the Sun to address
fundamental questions of solar and heliospheric physics. The performance
of the Solar Orbiter payload meets the requirements derived from the
mission's science objectives. Its science return will be augmented
further by coordinated observations with other space missions and
ground-based observatories. ARRAY(0x207ce98)

---------------------------------------------------------
Title: The Solar Orbiter EUI instrument: The Extreme Ultraviolet
Imager
Authors: Rochus, P.; Auchère, F.; Berghmans, D.; Harra, L.; Schmutz,
W.; Schühle, U.; Addison, P.; Appourchaux, T.; Aznar Cuadrado,
R.; Baker, D.; Barbay, J.; Bates, D.; BenMoussa, A.; Bergmann, M.;
Beurthe, C.; Borgo, B.; Bonte, K.; Bouzit, M.; Bradley, L.; Büchel,
V.; Buchlin, E.; Büchner, J.; Cabé, F.; Cadiergues, L.; Chaigneau,
M.; Chares, B.; Choque Cortez, C.; Coker, P.; Condamin, M.; Coumar,
S.; Curdt, W.; Cutler, J.; Davies, D.; Davison, G.; Defise, J. -M.;
Del Zanna, G.; Delmotte, F.; Delouille, V.; Dolla, L.; Dumesnil, C.;
Dürig, F.; Enge, R.; François, S.; Fourmond, J. -J.; Gillis, J. -M.;
Giordanengo, B.; Gissot, S.; Green, L. M.; Guerreiro, N.; Guilbaud,
A.; Gyo, M.; Haberreiter, M.; Hafiz, A.; Hailey, M.; Halain, J. -P.;
Hansotte, J.; Hecquet, C.; Heerlein, K.; Hellin, M. -L.; Hemsley, S.;
Hermans, A.; Hervier, V.; Hochedez, J. -F.; Houbrechts, Y.; Ihsan,
K.; Jacques, L.; Jérôme, A.; Jones, J.; Kahle, M.; Kennedy, T.;
Klaproth, M.; Kolleck, M.; Koller, S.; Kotsialos, E.; Kraaikamp, E.;
Langer, P.; Lawrenson, A.; Le Clech', J. -C.; Lenaerts, C.; Liebecq,
S.; Linder, D.; Long, D. M.; Mampaey, B.; Markiewicz-Innes, D.;
Marquet, B.; Marsch, E.; Matthews, S.; Mazy, E.; Mazzoli, A.; Meining,
S.; Meltchakov, E.; Mercier, R.; Meyer, S.; Monecke, M.; Monfort,
F.; Morinaud, G.; Moron, F.; Mountney, L.; Müller, R.; Nicula, B.;
Parenti, S.; Peter, H.; Pfiffner, D.; Philippon, A.; Phillips, I.;
Plesseria, J. -Y.; Pylyser, E.; Rabecki, F.; Ravet-Krill, M. -F.;
Rebellato, J.; Renotte, E.; Rodriguez, L.; Roose, S.; Rosin, J.;
Rossi, L.; Roth, P.; Rouesnel, F.; Roulliay, M.; Rousseau, A.; Ruane,
K.; Scanlan, J.; Schlatter, P.; Seaton, D. B.; Silliman, K.; Smit,
S.; Smith, P. J.; Solanki, S. K.; Spescha, M.; Spencer, A.; Stegen,
K.; Stockman, Y.; Szwec, N.; Tamiatto, C.; Tandy, J.; Teriaca, L.;
Theobald, C.; Tychon, I.; van Driel-Gesztelyi, L.; Verbeeck, C.;
Vial, J. -C.; Werner, S.; West, M. J.; Westwood, D.; Wiegelmann, T.;
Willis, G.; Winter, B.; Zerr, A.; Zhang, X.; Zhukov, A. N.
2020A&A...642A...8R Altcode:
Context. The Extreme Ultraviolet Imager (EUI) is part of the remote
sensing instrument package of the ESA/NASA Solar Orbiter mission
that will explore the inner heliosphere and observe the Sun from
vantage points close to the Sun and out of the ecliptic. Solar Orbiter
will advance the "connection science" between solar activity and the
heliosphere. Aims: With EUI we aim to improve our understanding
of the structure and dynamics of the solar atmosphere, globally as well
as at high resolution, and from high solar latitude perspectives. 
Methods: The EUI consists of three telescopes, the Full Sun Imager and
two High Resolution Imagers, which are optimised to image in Lyman-α
and EUV (17.4 nm, 30.4 nm) to provide a coverage from chromosphere
up to corona. The EUI is designed to cope with the strong constraints
imposed by the Solar Orbiter mission characteristics. Limited telemetry
availability is compensated by state-of-the-art image compression,
onboard image processing, and event selection. The imposed power
limitations and potentially harsh radiation environment necessitate
the use of novel CMOS sensors. As the unobstructed field of view of
the telescopes needs to protrude through the spacecraft's heat shield,
the apertures have been kept as small as possible, without compromising
optical performance. This led to a systematic effort to optimise the
throughput of every optical element and the reduction of noise levels
in the sensor. Results: In this paper we review the design
of the two elements of the EUI instrument: the Optical Bench System
and the Common Electronic Box. Particular attention is also given to
the onboard software, the intended operations, the ground software,
and the foreseen data products. Conclusions: The EUI will
bring unique science opportunities thanks to its specific design,
its viewpoint, and to the planned synergies with the other Solar
Orbiter instruments. In particular, we highlight science opportunities
brought by the out-of-ecliptic vantage point of the solar poles,
the high-resolution imaging of the high chromosphere and corona,
and the connection to the outer corona as observed by coronagraphs.

---------------------------------------------------------
Title: Metis: the Solar Orbiter visible light and ultraviolet
coronal imager
Authors: Antonucci, Ester; Romoli, Marco; Andretta, Vincenzo; Fineschi,
Silvano; Heinzel, Petr; Moses, J. Daniel; Naletto, Giampiero; Nicolini,
Gianalfredo; Spadaro, Daniele; Teriaca, Luca; Berlicki, Arkadiusz;
Capobianco, Gerardo; Crescenzio, Giuseppe; Da Deppo, Vania; Focardi,
Mauro; Frassetto, Fabio; Heerlein, Klaus; Landini, Federico; Magli,
Enrico; Marco Malvezzi, Andrea; Massone, Giuseppe; Melich, Radek;
Nicolosi, Piergiorgio; Noci, Giancarlo; Pancrazzi, Maurizio; Pelizzo,
Maria G.; Poletto, Luca; Sasso, Clementina; Schühle, Udo; Solanki,
Sami K.; Strachan, Leonard; Susino, Roberto; Tondello, Giuseppe;
Uslenghi, Michela; Woch, Joachim; Abbo, Lucia; Bemporad, Alessandro;
Casti, Marta; Dolei, Sergio; Grimani, Catia; Messerotti, Mauro;
Ricci, Marco; Straus, Thomas; Telloni, Daniele; Zuppella, Paola;
Auchère, Frederic; Bruno, Roberto; Ciaravella, Angela; Corso,
Alain J.; Alvarez Copano, Miguel; Aznar Cuadrado, Regina; D'Amicis,
Raffaella; Enge, Reiner; Gravina, Alessio; Jejčič, Sonja; Lamy,
Philippe; Lanzafame, Alessandro; Meierdierks, Thimo; Papagiannaki,
Ioanna; Peter, Hardi; Fernandez Rico, German; Giday Sertsu, Mewael;
Staub, Jan; Tsinganos, Kanaris; Velli, Marco; Ventura, Rita; Verroi,
Enrico; Vial, Jean-Claude; Vives, Sebastien; Volpicelli, Antonio;
Werner, Stephan; Zerr, Andreas; Negri, Barbara; Castronuovo, Marco;
Gabrielli, Alessandro; Bertacin, Roberto; Carpentiero, Rita; Natalucci,
Silvia; Marliani, Filippo; Cesa, Marco; Laget, Philippe; Morea, Danilo;
Pieraccini, Stefano; Radaelli, Paolo; Sandri, Paolo; Sarra, Paolo;
Cesare, Stefano; Del Forno, Felice; Massa, Ernesto; Montabone, Mauro;
Mottini, Sergio; Quattropani, Daniele; Schillaci, Tiziano; Boccardo,
Roberto; Brando, Rosario; Pandi, Arianna; Baietto, Cristian; Bertone,
Riccardo; Alvarez-Herrero, Alberto; García Parejo, Pilar; Cebollero,
María; Amoruso, Mauro; Centonze, Vito
2020A&A...642A..10A Altcode: 2019arXiv191108462A
 Aims: Metis is the first solar coronagraph designed for a
space mission and is capable of performing simultaneous imaging of the
off-limb solar corona in both visible and UV light. The observations
obtained with Metis aboard the Solar Orbiter ESA-NASA observatory
will enable us to diagnose, with unprecedented temporal coverage and
spatial resolution, the structures and dynamics of the full corona
in a square field of view (FoV) of ±2.9° in width, with an inner
circular FoV at 1.6°, thus spanning the solar atmosphere from 1.7
R⊙ to about 9 R⊙, owing to the eccentricity
of the spacecraft orbit. Due to the uniqueness of the Solar Orbiter
mission profile, Metis will be able to observe the solar corona
from a close (0.28 AU, at the closest perihelion) vantage point,
achieving increasing out-of-ecliptic views with the increase of the
orbit inclination over time. Moreover, observations near perihelion,
during the phase of lower rotational velocity of the solar surface
relative to the spacecraft, allow longer-term studies of the off-limb
coronal features, thus finally disentangling their intrinsic evolution
from effects due to solar rotation. Methods: Thanks to a novel
occultation design and a combination of a UV interference coating of
the mirrors and a spectral bandpass filter, Metis images the solar
corona simultaneously in the visible light band, between 580 and 640
nm, and in the UV H I Lyman-α line at 121.6 nm. The visible light
channel also includes a broadband polarimeter able to observe the
linearly polarised component of the K corona. The coronal images in
both the UV H I Lyman-α and polarised visible light are obtained at
high spatial resolution with a spatial scale down to about 2000 km
and 15 000 km at perihelion, in the cases of the visible and UV light,
respectively. A temporal resolution down to 1 s can be achieved when
observing coronal fluctuations in visible light. Results: The
Metis measurements, obtained from different latitudes, will allow for
complete characterisation of the main physical parameters and dynamics
of the electron and neutral hydrogen/proton plasma components of the
corona in the region where the solar wind undergoes the acceleration
process and where the onset and initial propagation of coronal mass
ejections (CMEs) take place. The near-Sun multi-wavelength coronal
imaging performed with Metis, combined with the unique opportunities
offered by the Solar Orbiter mission, can effectively address crucial
issues of solar physics such as: the origin and heating/acceleration
of the fast and slow solar wind streams; the origin, acceleration,
and transport of the solar energetic particles; and the transient
ejection of coronal mass and its evolution in the inner heliosphere,
thus significantly improving our understanding of the region connecting
the Sun to the heliosphere and of the processes generating and driving
the solar wind and coronal mass ejections. Conclusions: This
paper presents the scientific objectives and requirements, the overall
optical design of the Metis instrument, the thermo-mechanical design,
and the processing and power unit; reports on the results of the
campaigns dedicated to integration, alignment, and tests, and to
the characterisation of the instrument performance; describes the
operation concept, data handling, and software tools; and, finally,
the diagnostic techniques to be applied to the data, as well as a brief
description of the expected scientific products. The performance of the
instrument measured during calibrations ensures that the scientific
objectives of Metis can be pursued with success. Metis website:
<A href="http://metis.oato.inaf.it">http://metis.oato.inaf.it</A>

---------------------------------------------------------
Title: A Coronal Loop in a Box: Energy Generation, Heating and
Dynamics
Authors: Breu, C.; Peter, H.; Cameron, R.; Solanki, S.; Chitta, P.;
Przybylski, D.
2020SPD....5121008B Altcode:
In our study we aim at an understanding how the energy to heat the
upper atmosphere is generated by the photospheric magneto-convection,
transported into the upper atmosphere, and how its dissipation governs
the formation of the internal structure of a coronal magnetic loop. In
a 3D MHD model we study a coronal loop that is rooted with both
footpoints in a shallow convection zone layer. Therefore the driving
at the coronal base arises self-consistently from magneto-convection
in plage-type areas. To fit into a cartesian box, we straighten the
coronal loop. This allows a high spatial resolution within the loop
that cannot be achieved in a model of a whole active region. To
conduct the numerical experiments we employ the MURaM code that
includes heat conduction, radiative transfer and optically thin
radiative losses. We find that the Poynting flux into the loop is
generated by small-scale photospheric motions within strong magnetic
flux concentrations. Turbulent behaviour develops in the upper layers
of the atmosphere as a response to the footpoint motions. Vortex flows
are found at various heights within the loop. These are organised in
swirls that form coherent structures with a magnetic connection from
the intergranular lanes in the photosphere through the chromosphere
up to several megameters into the corona. In the coronal part of
the loop plasma motions perpendicular to the magnetic axis of the
swirl are associated with an increased heating rate and thus enhanced
temperatures. At any given time, only part of the loop is filled with
swirls which leads to a substructure of the loop in terms of temperature
and density. Consequently the emission as it would be observed by AIA
or XRT reveals transient bright strands that form in response to the
heating events related to the swirls. With this model we can build a
coherent picture of how the energy flux to heat the upper atmosphere
is generated near the solar surface and how this process drives and
governs the heating and dynamics of a coronal loop

---------------------------------------------------------
Title: Effects of inclusion of small-scale dynamo in near-surface
structure of F-stars
Authors: Bhatia, T. S.; Cameron, R.; Solanki, S.; Peter, H.; Przbylski,
D.; Witzke, V.
2020SPD....5120704B Altcode:
The presence of (unresolved) small-scale mixed polarity regions in
the quiet Sun photosphere plays an important role in determining
the basal magnetic flux. Observationally, the magnitude of the
vertical component of this field is estimated to be ~50-100 G on the
Sun. This field is important for determining the energy balance in
the chromosphere and may also subtly affect the radiative properties
of the photosphere. These fields are believed to be the result of a
small-scale dynamo (SSD) operating near the surface. While significant
progress has been made in investigating the role of the SSD in the Sun,
it is unclear what effects SSDs have on other stars. In particular,
for F-stars, the photosheric kinetic and internal energies seem to be
of the same order of magnitude. Since there is a rough equipartition
in energies for a saturated SSD, deviations from a pure hydrodynamic
(HD) stratification are expected. We aim to characterize these
deviations. Box simulations of the upper convection zone and the
photosphere are carried out using the radiative MHD code MURaM. To
obtain SSD simulations, we use initial HD simulations and seed a
magnetic field of negligible strength and zero net flux, which we
then run till the magnetic field reaches saturation. We consider two
different lower boundary conditions (BCs) for the magnetic field to
characterize BC-effects: a) only vertical magnetic field is allowed, b)
both vertical and horizontal magnetic field is allowed. Both boundary
conditions exhibit SSD action. We observe slight increase (fraction
of a percent) in the horizontally-averaged temperature profile for
both the cases. Other thermodynamic quantities exhibit deviations (~
a percent) depending on the boundary condition considered. In addition,
the spatial power spectra of the bolometric intensity shows deviations
from the corresponding HD (without magnetic field) run, implying
larger power at smaller spatial scales for SSD case. The presence of
a SSD results in a significant amount of "quiet"-star magnetic flux
with associated changes in the stratification of the atmosphere and
spatial distribution of the bolometric intensity.

---------------------------------------------------------
Title: Stellar coronal X-ray emission and surface magnetic flux
Authors: Zhuleku, J.; Warnecke, J.; Peter, H.
2020A&A...640A.119Z Altcode: 2020arXiv200613978Z
Context. Observations show that the coronal X-ray emission of the
Sun and other stars depends on the surface magnetic field. 
Aims: Using power-law scaling relations between different physical
parameters, we aim to build an analytical model to connect the
observed X-ray emission to the surface magnetic flux. Methods:
The basis for our model are the scaling laws of Rosner, Tucker &amp;
Vaiana (RTV) that connect the temperature and pressure of a coronal
loop to its length and energy input. To estimate the energy flux into
the upper atmosphere, we used scalings derived for different heating
mechanisms, such as field-line braiding or Alfvén wave heating. We
supplemented this with observed relations between active region size
and magnetic flux and derived scalings of how X-ray emissivity depends
on temperature. Results: Based on our analytical model, we find
a power-law dependence of the X-ray emission on the magnetic flux,
LX ∝ Φm, with a power-law index m being
in the range from about one to two. This finding is consistent with
a wide range of observations, from individual features on the Sun,
such as bright points or active regions, to stars of different types
and varying levels of activity. The power-law index m depends on the
choice of the heating mechanism, and our results slightly favor the
braiding and nanoflare scenarios over Alfvén wave heating. In addition,
the choice of instrument will have an impact on the power-law index
m because of the sensitivity of the observed wavelength region to
the temperature of the coronal plasma. Conclusions: Overall,
our simple analytical model based on the RTV scaling laws gives a good
representation of the observed X-ray emission. Therefore we might be
able to understand stellar coronal activity though a collection of
basic building blocks, like loops, which we can study in spatially
resolved detail on the Sun.

---------------------------------------------------------
Title: peterpeterp/atlantic_ace_seasonal_forecast: v2
Authors: Peter
2020zndo...3925816P Altcode:
No description provided.

---------------------------------------------------------
Title: Non-thermal line broadening due to braiding-induced turbulence
in solar coronal loops
Authors: Pontin, D. I.; Peter, H.; Chitta, L. P.
2020A&A...639A..21P Altcode: 2020arXiv200811915P
 Aims: Emission line profiles from solar coronal loops exhibit
properties that are unexplained by current models. We investigate
the non-thermal broadening associated with plasma heating in coronal
loops that is induced by magnetic field line braiding. Methods:
We describe the coronal loop by a 3D magnetohydrodynamic model of
the turbulent decay of an initially-braided magnetic field. From
this, we synthesised the Fe XII line at 193 Å that forms around
1.5 MK. Results: The key features of current observations of
extreme ultraviolet (UV) lines from the corona are reproduced in the
synthesised spectra: (i) Typical non-thermal widths range from 15 to
20 km s-1. (ii) The widths are approximately independent
of the size of the field of view. (iii) There is a correlation between
the line intensity and non-thermal broadening. (iv) Spectra are found
to be non-Gaussian, with enhanced power in the wings of the order
of 10-20%. Conclusions: Our model provides an explanation
that self-consistently connects the heating process to the observed
non-thermal line broadening. The non-Gaussian nature of the spectra
is a consequence of the non-Gaussian nature of the underlying velocity
fluctuations, which is interpreted as a signature of intermittency in
the turbulence.

---------------------------------------------------------
Title: Observation and Modeling of High-temperature Solar Active
Region Emission during the High-resolution Coronal Imager Flight of
2018 May 29
Authors: Warren, Harry P.; Reep, Jeffrey W.; Crump, Nicholas A.;
Ugarte-Urra, Ignacio; Brooks, David H.; Winebarger, Amy R.; Savage,
Sabrina; De Pontieu, Bart; Peter, Hardi; Cirtain, Jonathan W.; Golub,
Leon; Kobayashi, Ken; McKenzie, David; Morton, Richard; Rachmeler,
Laurel; Testa, Paola; Tiwari, Sanjiv; Walsh, Robert
2020ApJ...896...51W Altcode:
Excellent coordinated observations of NOAA active region 12712 were
obtained during the flight of the High-resolution Coronal Imager (Hi-C)
sounding rocket on 2018 May 29. This region displayed a typical active
region core structure with relatively short, high-temperature loops
crossing the polarity inversion line and bright "moss" located at the
footpoints of these loops. The differential emission measure (DEM) in
the active region core is very sharply peaked at about 4 MK. Further,
there is little evidence for impulsive heating events in the moss, even
at the high spatial resolution and cadence of Hi-C. This suggests that
active region core heating is occurring at a high frequency and keeping
the loops close to equilibrium. To create a time-dependent simulation of
the active region core, we combine nonlinear force-free extrapolations
of the measured magnetic field with a heating rate that is dependent
on the field strength and loop length and has a Poisson waiting time
distribution. We use the approximate solutions to the hydrodynamic
loop equations to simulate the full ensemble of active region core
loops for a range of heating parameters. In all cases, we find that
high-frequency heating provides the best match to the observed DEM. For
selected field lines, we solve the full hydrodynamic loop equations,
including radiative transfer in the chromosphere, to simulate transition
region and chromospheric emission. We find that for heating scenarios
consistent with the DEM, classical signatures of energy release,
such as transition region brightenings and chromospheric evaporation,
are weak, suggesting that they would be difficult to detect.

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Title: The Drivers of Active Region Outflows into the Slow Solar Wind
Authors: Brooks, David H.; Winebarger, Amy R.; Savage, Sabrina; Warren,
Harry P.; De Pontieu, Bart; Peter, Hardi; Cirtain, Jonathan W.; Golub,
Leon; Kobayashi, Ken; McIntosh, Scott W.; McKenzie, David; Morton,
Richard; Rachmeler, Laurel; Testa, Paola; Tiwari, Sanjiv; Walsh, Robert
2020ApJ...894..144B Altcode: 2020arXiv200407461B
Plasma outflows from the edges of active regions have been suggested as
a possible source of the slow solar wind. Spectroscopic measurements
show that these outflows have an enhanced elemental composition,
which is a distinct signature of the slow wind. Current spectroscopic
observations, however, do not have sufficient spatial resolution to
distinguish what structures are being measured or determine the driver
of the outflows. The High-resolution Coronal Imager (Hi-C) flew on a
sounding rocket in 2018 May and observed areas of active region outflow
at the highest spatial resolution ever achieved (250 km). Here we use
the Hi-C data to disentangle the outflow composition signatures observed
with the Hinode satellite during the flight. We show that there are
two components to the outflow emission: a substantial contribution
from expanded plasma that appears to have been expelled from closed
loops in the active region core and a second contribution from dynamic
activity in active region plage, with a composition signature that
reflects solar photospheric abundances. The two competing drivers of the
outflows may explain the variable composition of the slow solar wind.

---------------------------------------------------------
Title: Relative abundance diagnostics with SPICE, the EUV spectrometer
on-board Solar Orbiter
Authors: Zambrana Prado, Natalia; Buchlin, Eric; Peter, Hardi
2020EGUGA..2220154Z Altcode:
With the launches of Parker Solar Probe and Solar Orbiter, we are
closer than ever to linking solar activity on the surface and in the
corona to the inner heliosphere. In this quest, relative abundance
measurements will be key as different structures on the Sun have
different abundances as a consequence of the FIP (First Ionization
Potential) effect.Comparing in-situ and remote sensing composition
data, coupled with modeling, will allow us to trace back the source of
heliospheric plasma. Solar Orbiter has a unique combination of in-situ
and remote sensing instruments that will hopefully allow us to make
such comparisons.High telemetry will not always be available with SPICE
(SPectral Imaging of the Coronal Environment), the EUV spectrometer
on board Solar Orbiter. We have therefore developed a method for
measuring relative abundances that is both telemetry efficient and
reliable. Unlike methods based on Differential Emission Measure (DEM)
inversion, the Linear Combination Ratio (LCR) method does not require a
large number of spectral lines. This new method is based on optimized
linear combinations of only a few UV spectral lines. We present some
abundance diagnostics applied to synthesized radiances of spectral
lines observable by SPICE.

---------------------------------------------------------
Title: Is the High-Resolution Coronal Imager Resolving Coronal
Strands? Results from AR 12712
Authors: Williams, Thomas; Walsh, Robert W.; Winebarger, Amy R.;
Brooks, David H.; Cirtain, Jonathan W.; De Pontieu, Bart; Golub,
Leon; Kobayashi, Ken; McKenzie, David E.; Morton, Richard J.; Peter,
Hardi; Rachmeler, Laurel A.; Savage, Sabrina L.; Testa, Paola; Tiwari,
Sanjiv K.; Warren, Harry P.; Watkinson, Benjamin J.
2020ApJ...892..134W Altcode: 2020arXiv200111254W
Following the success of the first mission, the High-Resolution
Coronal Imager (Hi-C) was launched for a third time (Hi-C 2.1)
on 2018 May 29 from the White Sands Missile Range, NM, USA. On this
occasion, 329 s of 17.2 nm data of target active region AR 12712 were
captured with a cadence of ≈4 s, and a plate scale of 0.129 arcsec
pixel-1. Using data captured by Hi-C 2.1 and co-aligned
observations from SDO/AIA 17.1 nm, we investigate the widths of 49
coronal strands. We search for evidence of substructure within the
strands that is not detected by AIA, and further consider whether these
strands are fully resolved by Hi-C 2.1. With the aid of multi-scale
Gaussian normalization, strands from a region of low emission that can
only be visualized against the contrast of the darker, underlying moss
are studied. A comparison is made between these low-emission strands
and those from regions of higher emission within the target active
region. It is found that Hi-C 2.1 can resolve individual strands as
small as ≈202 km, though the more typical strand widths seen are
≈513 km. For coronal strands within the region of low emission, the
most likely width is significantly narrower than the high-emission
strands at ≈388 km. This places the low-emission coronal strands
beneath the resolving capabilities of SDO/AIA, highlighting the need
for a permanent solar observatory with the resolving power of Hi-C.

---------------------------------------------------------
Title: Observations and modeling of the onset of fast reconnection
in the solar transition region
Authors: Bhattacharjee, Amitava; Guo, Lijia; de Pontieu, Bart; Huang,
Yi-Min; Peter, Hardi
2020APS..DPPP10005B Altcode:
Magnetic reconnection is a fundamental plasma process that plays a
critical role not only in energy release in the solar atmosphere, but
also in fusion, astrophysical, and other space plasma environments. One
of the challenges in explaining solar observations in which reconnection
is thought to play a critical role is to account for the transition
of the dynamics from a slow quasi-continuous phase to a fast and
impulsive energetic burst of much shorter duration. Despite the
theoretical progress in identifying mechanisms that might lead
to rapid onset, a lack of observations of this transition has left
models poorly constrained. High-resolution spectroscopic observations
from NASA's Interface Region Imaging Spectrograph (IRIS) now reveal
tell-tale signatures of the abrupt transition of reconnection from
a slow phase to a fast, impulsive phase during explosive events in
the Sun's atmosphere. Our observations are consistent with numerical
simulations of the plasmoid instability, and provide evidence for the
onset of fast reconnection mediated by plasmoids and new opportunities
for remote-sensing diagnostics of reconnection mechanisms on the Sun.

---------------------------------------------------------
Title: Hi-C 2.1 Observations of Jetlet-like Events at Edges of Solar
Magnetic Network Lanes
Authors: Panesar, Navdeep K.; Sterling, Alphonse C.; Moore, Ronald L.;
Winebarger, Amy R.; Tiwari, Sanjiv K.; Savage, Sabrina L.; Golub, Leon
E.; Rachmeler, Laurel A.; Kobayashi, Ken; Brooks, David H.; Cirtain,
Jonathan W.; De Pontieu, Bart; McKenzie, David E.; Morton, Richard J.;
Peter, Hardi; Testa, Paola; Walsh, Robert W.; Warren, Harry P.
2019ApJ...887L...8P Altcode: 2019arXiv191102331P
We present high-resolution, high-cadence observations of six,
fine-scale, on-disk jet-like events observed by the High-resolution
Coronal Imager 2.1 (Hi-C 2.1) during its sounding-rocket flight. We
combine the Hi-C 2.1 images with images from the Solar Dynamics
Observatory (SDO)/Atmospheric Imaging Assembly (AIA) and the Interface
Region Imaging Spectrograph (IRIS), and investigate each event’s
magnetic setting with co-aligned line-of-sight magnetograms from the
SDO/Helioseismic and Magnetic Imager (HMI). We find that (i) all six
events are jetlet-like (having apparent properties of jetlets), (ii)
all six are rooted at edges of magnetic network lanes, (iii) four of
the jetlet-like events stem from sites of flux cancelation between
majority-polarity network flux and merging minority-polarity flux, and
(iv) four of the jetlet-like events show brightenings at their bases
reminiscent of the base brightenings in coronal jets. The average
spire length of the six jetlet-like events (9000 ± 3000 km) is three
times shorter than that for IRIS jetlets (27,000 ± 8000 km). While
not ruling out other generation mechanisms, the observations suggest
that at least four of these events may be miniature versions of both
larger-scale coronal jets that are driven by minifilament eruptions
and still-larger-scale solar eruptions that are driven by filament
eruptions. Therefore, we propose that our Hi-C events are driven by
the eruption of a tiny sheared-field flux rope, and that the flux rope
field is built and triggered to erupt by flux cancelation.

---------------------------------------------------------
Title: The SPICE (Spectral Imaging of the Coronal Environment)
Ultraviolet Imaging Spectrograph Investigation
Authors: Hassler, D.; Auchere, F.; Carlsson, M.; Fludra, A.; Giunta,
A. S.; Mueller, D.; Peter, H.; Parenti, S.; Teriaca, L.; Fredvik, T.
2019AGUFMSH24A..02H Altcode:
One of the primary objectives of the Solar Orbiter mission is to link
remote sensing observations of the solar surface structures with in-situ
observations of solar wind streams. The SPICE (Spectral Imaging of the
Coronal Environment) instrument will characterize the plasma properties
of regions near the Sun to directly compare with in-situ measurements
from both Solar Orbiter &amp; Parker Solar Probe. Specifically, SPICE
will map outflow velocities of surface features to solar wind structures
with similar composition (FIP, M/q) measured in-situ by the SWA/HIS
instrument on Solar Orbiter. These observations will help discriminate
models of solar wind origin by matching composition signatures in
solar wind streams to surface feature composition, and discriminate
physical processes that inject material from closed structures into
solar wind streams. This presentation will provide an overview of
the SPICE investigation, including science &amp; measurement objective,
instrument design, capabilities and performance as measured during
calibration prior to delivery to the Solar Orbiter spacecraft. The
presentation will also provide a description of the operations concept
and data processing during the mission.

---------------------------------------------------------
Title: Fine-scale Explosive Energy Release at Sites of Prospective
Magnetic Flux Cancellation in the Core of the Solar Active Region
Observed by Hi-C 2.1, IRIS, and SDO
Authors: Tiwari, Sanjiv K.; Panesar, Navdeep K.; Moore, Ronald L.;
De Pontieu, Bart; Winebarger, Amy R.; Golub, Leon; Savage, Sabrina L.;
Rachmeler, Laurel A.; Kobayashi, Ken; Testa, Paola; Warren, Harry P.;
Brooks, David H.; Cirtain, Jonathan W.; McKenzie, David E.; Morton,
Richard J.; Peter, Hardi; Walsh, Robert W.
2019ApJ...887...56T Altcode: 2019arXiv191101424T
The second Hi-C flight (Hi-C 2.1) provided unprecedentedly high spatial
and temporal resolution (∼250 km, 4.4 s) coronal EUV images of Fe IX/X
emission at 172 Å of AR 12712 on 2018 May 29, during 18:56:21-19:01:56
UT. Three morphologically different types (I: dot-like; II: loop-like;
III: surge/jet-like) of fine-scale sudden-brightening events (tiny
microflares) are seen within and at the ends of an arch filament system
in the core of the AR. Although type Is (not reported before) resemble
IRIS bombs (in size, and brightness with respect to surroundings),
our dot-like events are apparently much hotter and shorter in span
(70 s). We complement the 5 minute duration Hi-C 2.1 data with SDO/HMI
magnetograms, SDO/AIA EUV images, and IRIS UV spectra and slit-jaw
images to examine, at the sites of these events, brightenings and
flows in the transition region and corona and evolution of magnetic
flux in the photosphere. Most, if not all, of the events are seated
at sites of opposite-polarity magnetic flux convergence (sometimes
driven by adjacent flux emergence), implying likely flux cancellation
at the microflare’s polarity inversion line. In the IRIS spectra
and images, we find confirming evidence of field-aligned outflow from
brightenings at the ends of loops of the arch filament system. In types
I and II the explosion is confined, while in type III the explosion
is ejective and drives jet-like outflow. The light curves from Hi-C,
AIA, and IRIS peak nearly simultaneously for many of these events,
and none of the events display a systematic cooling sequence as seen in
typical coronal flares, suggesting that these tiny brightening events
have chromospheric/transition region origin.

---------------------------------------------------------
Title: The High-Resolution Coronal Imager, Flight 2.1
Authors: Rachmeler, Laurel A.; Winebarger, Amy R.; Savage, Sabrina L.;
Golub, Leon; Kobayashi, Ken; Vigil, Genevieve D.; Brooks, David H.;
Cirtain, Jonathan W.; De Pontieu, Bart; McKenzie, David E.; Morton,
Richard J.; Peter, Hardi; Testa, Paola; Tiwari, Sanjiv K.; Walsh,
Robert W.; Warren, Harry P.; Alexander, Caroline; Ansell, Darren;
Beabout, Brent L.; Beabout, Dyana L.; Bethge, Christian W.; Champey,
Patrick R.; Cheimets, Peter N.; Cooper, Mark A.; Creel, Helen K.;
Gates, Richard; Gomez, Carlos; Guillory, Anthony; Haight, Harlan;
Hogue, William D.; Holloway, Todd; Hyde, David W.; Kenyon, Richard;
Marshall, Joseph N.; McCracken, Jeff E.; McCracken, Kenneth; Mitchell,
Karen O.; Ordway, Mark; Owen, Tim; Ranganathan, Jagan; Robertson,
Bryan A.; Payne, M. Janie; Podgorski, William; Pryor, Jonathan; Samra,
Jenna; Sloan, Mark D.; Soohoo, Howard A.; Steele, D. Brandon; Thompson,
Furman V.; Thornton, Gary S.; Watkinson, Benjamin; Windt, David
2019SoPh..294..174R Altcode: 2019arXiv190905942R
The third flight of the High-Resolution Coronal Imager (Hi-C 2.1)
occurred on May 29, 2018; the Sounding Rocket was launched from White
Sands Missile Range in New Mexico. The instrument has been modified
from its original configuration (Hi-C 1) to observe the solar corona
in a passband that peaks near 172 Å, and uses a new, custom-built
low-noise camera. The instrument targeted Active Region 12712, and
captured 78 images at a cadence of 4.4 s (18:56:22 - 19:01:57 UT; 5
min and 35 s observing time). The image spatial resolution varies due
to quasi-periodic motion blur from the rocket; sharp images contain
resolved features of at least 0.47 arcsec. There are coordinated
observations from multiple ground- and space-based telescopes providing
an unprecedented opportunity to observe the mass and energy coupling
between the chromosphere and the corona. Details of the instrument
and the data set are presented in this paper.

---------------------------------------------------------
Title: Generation of solar spicules and subsequent atmospheric heating
Authors: Samanta, Tanmoy; Tian, Hui; Yurchyshyn, Vasyl; Peter, Hardi;
Cao, Wenda; Sterling, Alphonse; Erdélyi, Robertus; Ahn, Kwangsu;
Feng, Song; Utz, Dominik; Banerjee, Dipankar; Chen, Yajie
2019Sci...366..890S Altcode: 2020arXiv200602571S
Spicules are rapidly evolving fine-scale jets of magnetized plasma in
the solar chromosphere. It remains unclear how these prevalent jets
originate from the solar surface and what role they play in heating
the solar atmosphere. Using the Goode Solar Telescope at the Big Bear
Solar Observatory, we observed spicules emerging within minutes of the
appearance of opposite-polarity magnetic flux around dominant-polarity
magnetic field concentrations. Data from the Solar Dynamics Observatory
showed subsequent heating of the adjacent corona. The dynamic
interaction of magnetic fields (likely due to magnetic reconnection)
in the partially ionized lower solar atmosphere appears to generate
these spicules and heat the upper solar atmosphere.

---------------------------------------------------------
Title: Repeated Coronal Condensations Caused by Magnetic Reconnection
between Solar Coronal Loops
Authors: Li, Leping; Peter, Hardi; Chitta, Lakshmi Pradeep; Zhang,
Jun; Su, Jiangtao; Song, Hongqiang; Hou, Yijun; Xia, Chun
2019ApJ...884...34L Altcode:
We recently presented coronal condensations, caused by magnetic
reconnection (MR) between coronal loops from extreme ultraviolet
observations, over the course of one day, on 2012 January 19. In
this paper, by investigating the loops over an extended period of
time from January 16 to 20, we present a case for repeated coronal
condensations caused by repeated MR between them. In these five days,
MR between higher-lying open loops and lower-lying closed loops occurs
repeatedly, forming magnetic dips in the higher-lying open loops. During
the MR process, cooling and condensation of coronal plasma occur
repeatedly. Early on January 16, cooling, but not condensation, of
coronal plasma happens. Later, condensation appears at the edge of the
dips and falls down along the loops as coronal rains. On January 17,
a similar condensation happens at the edge of the higher-lying dips
and falls down along the loops. However, another condensation appears
in the lower-lying dips and rains down across them. From January 18
to 19, multiple condensations mostly occur at the edge of the dips
and fall down both along the loops and across the dips. On January
20, five condensations sequentially appear and rain down across the
dips. Overall, 15 condensation events occur in five days, lasting from
0.5 to 15.6 hr. We suggest that the formation of coronal condensations
by MR between loops is common in the solar corona. The repeated MR
between loops thus plays an essential role in the mass cycle of coronal
plasma by initiating repeated catastrophic cooling and condensation.

---------------------------------------------------------
Title: On the influence of magnetic helicity on X-rays emission of
solar and stellar coronae
Authors: Warnecke, Jörn; Peter, Hardi
2019arXiv191006896W Altcode:
Observation of solar-like stars show a clear relation between X-ray
emission and their rotation. Higher stellar rotation can lead to a
larger magnetic helicity production in stars. We aim to understand
the relation between magnetic helicity on the surface of a star to
their coronal X-ray emission. We use 3D MHD simulations to model the
corona of the solar-like stars. We take an observed magnetogram as in
photospheric activity input, and inject different values of magnetic
helicity. We use synthesis emission to calculate the X-ray emission
flux of each simulation and investigate how this scales with injected
magnetic helicity. We find that for larger injected magnetic helicities
an increase in temperature and an increase in X-ray emission. The
X-ray emission scaled cubicly with the injected helicity. We can
related this to increase of horizontal magnetic field and therefore
higher Poynting flux at the coronal base. Using typical scaling of
magnetic helicity production with stellar rotation, we can explain
the increase of X-ray emission with rotation only by an increase of
magnetic helicity at the surface of a star.

---------------------------------------------------------
Title: Plasmoid-mediated reconnection in solar UV bursts
Authors: Peter, H.; Huang, Y. -M.; Chitta, L. P.; Young, P. R.
2019A&A...628A...8P Altcode: 2019arXiv190704335P
Context. Ultraviolet bursts are transients in the solar atmosphere with
an increased impulsive emission in the extreme UV lasting for one to
several tens of minutes. They often show spectral profiles indicative
of a bi-directional outflow in response to magnetic reconnection. Aims: To understand UV bursts, we study how motions of magnetic
elements at the surface can drive the self-consistent formation
of a current sheet resulting in plasmoid-mediated reconnection. In
particular, we want to study the role of the height of the reconnection
in the atmosphere. Methods: We conducted numerical experiments
solving the 2D magnetohydrodynamic equations from the solar surface
to the upper atmosphere. Motivated by observations, we drove a small
magnetic patch embedded in a larger system of magnetic field of opposite
polarity. This type of configuration creates an X-type neutral point
in the initial potential field. The models are characterized by the
(average) plasma-β at the height of this X point. Results:
The driving at the surface stretches the X-point into a thin current
sheet, where plasmoids appear, accelerating the reconnection, and a
bi-directional jet forms. This is consistent with what is expected
for UV bursts or explosive events, and we provide a self-consistent
model of the formation of the reconnection region in such events. The
gravitational stratification gives a natural explanation for why
explosive events are restricted to a temperature range around a few
0.1 MK, and the presence of plasmoids in the reconnection process
provides an understanding of the observed variability during the
transient events on a timescale of minutes. Conclusions: Our
numerical experiments provide a comprehensive understanding of UV bursts
and explosive events, in particular of how the atmospheric response
changes if the reconnection happens at different plasma-β, that is,
at different heights in the atmosphere. This analysis also gives
new insight into how UV bursts might be related to the photospheric
Ellerman bombs. Movie attached to Fig. 2 is available at <A
href="https://www.aanda.org/10.1051/0004-6361/201935820/olm">https://www.aanda.org</A>

---------------------------------------------------------
Title: Hot prominence spicules launched from turbulent cool solar
prominences
Authors: Chitta, L. P.; Peter, H.; Li, L.
2019A&A...627L...5C Altcode: 2019arXiv190609125C
A solar filament is a dense cool condensation that is supported and
thermally insulated by magnetic fields in the rarefied hot corona. Its
evolution and stability, leading to either an eruption or disappearance,
depend on its coupling with the surrounding hot corona through a
thin transition region, where the temperature steeply rises. However,
the heating and dynamics of this transition region remain elusive. We
report extreme-ultraviolet observations of quiescent filaments from the
Solar Dynamics Observatory that reveal prominence spicules propagating
through the transition region of the filament-corona system. These thin
needle-like jet features are generated and heated to at least 0.7 MK
by turbulent motions of the material in the filament. We suggest that
the prominence spicules continuously channel the heated mass into the
corona and aid in the filament evaporation and decay. Our results shed
light on the turbulence-driven heating in magnetized condensations
that are commonly observed on the Sun and in the interstellar
medium. The movie associated to Fig. 1 is available at <A
href="https://www.aanda.org/10.1051/0004-6361/201936027/olm">https://www.aanda.org</A>.

---------------------------------------------------------
Title: Effects of Coronal Density and Magnetic Field Distributions
on a Global Solar EUV Wave
Authors: Hu, Huidong; Liu, Ying D.; Zhu, Bei; Peter, Hardi; He, Wen;
Wang, Rui; Yang, Zhongwei
2019ApJ...878..106H Altcode: 2019arXiv190501211H
We investigate a global extreme-ultraviolet (EUV) wave associated
with a coronal mass ejection (CME)-driven shock on 2017 September
10. The EUV wave is transmitted by north- and south-polar coronal
holes (CHs), which is observed by the Solar Dynamics Observatory
(SDO) and Solar Terrestrial Relations Observatory A (STEREO-A) from
opposite sides of the Sun. We obtain key findings on how the EUV wave
interacts with multiple coronal structures, and its connection with the
CME-driven shock: (1) the transmitted EUV wave is still connected with
the shock that is incurvated to the Sun, after the shock has reached
the opposite side of the eruption; (2) the south CH transmitted EUV
wave is accelerated inside an on-disk, low-density region with closed
magnetic fields, which implies that an EUV wave can be accelerated in
both open and closed magnetic field regions; (3) part of the primary
EUV wavefront turns around a bright point (BP) with a bipolar magnetic
structure when it approaches a dim, low-density filament channel near
the BP; (4) the primary EUV wave is diffused and apparently halted
near the boundaries of remote active regions (ARs) that are far from
the eruption, and no obvious AR related secondary waves are detected;
(5) the EUV wave extends to an unprecedented scale of ∼360° in
latitudes, which is attributed to the polar CH transmission. These
results provide insights into the effects of coronal density and
magnetic field distributions on the evolution of an EUV wave, and into
the connection between the EUV wave and the associated CME-driven shock.

---------------------------------------------------------
Title: Plasma injection into a solar coronal loop
Authors: Li, L. P.; Peter, H.
2019A&A...626A..98L Altcode: 2019arXiv190507800L
Context. The details of the spectral profiles of extreme UV
emission lines from solar active regions contain key information for
investigating the structure, dynamics, and energetics of the solar
upper atmosphere. Aims: We characterize the line profiles not
only through the Doppler shift and intensity of the bulk part of
the profile. More importantly, we investigate the excess emission
and asymmetries in the line wings to study twisting motions and
helicity. Methods: We used a raster scan of the Interface Region
Imaging Spectrograph (IRIS) in an active region. We concentrated on the
Si IV line at 1394 Å, which forms just below 0.1 MK, and followed the
plasma that moves in a cool loop from one footpoint to the other. We
applied single-Gaussian fits to the line core, determined the excess
emission in the red and blue wings, and derived the asymmetry of the red
and blue wings. Results: The blue wing excess at one footpoint
shows injection of plasma into the loop that then flows to the other
side. At the same footpoint, redshifts in the line core indicate
that energy is deposited at around 0.1 MK. The enhanced pressure
would then push the cool plasma down and inject some plasma into the
loop. In the middle part of the loop, the spectral tilts of the line
profiles indicate that the magnetic field has a helical structure,
and the line wings are symmetrically enhanced. This is an indication
that the loop is driven through the injection of helicity at the loop
feet. Conclusions: If the loop is driven to be helical, then the
magnetic field can be expected to be in a turbulent state, as has been
shown by existing magnetohydrodynamics models. The turbulent motions
might explain the (symmetric) line wing enhancements that have also
been seen in loops at coronal temperatures, but are not understood
so far. The movie associated to Fig. 7 is available at <A
href="https://www.aanda.org/10.1051/0004-6361/201935165/olm">https://www.aanda.org</A>

---------------------------------------------------------
Title: Data-driven model of the solar corona above an active region
Authors: Warnecke, J.; Peter, H.
2019A&A...624L..12W Altcode: 2019arXiv190300455W
 Aims: We aim to reproduce the structure of the corona above a
solar active region as seen in the extreme ultraviolet (EUV) using a
three-dimensional magnetohydrodynamic (3D MHD) model. Methods:
The 3D MHD data-driven model solves the induction equation and the mass,
momentum, and energy balance. To drive the system, we feed the observed
evolution of the magnetic field in the photosphere of the active region
AR 12139 into the bottom boundary. This creates a hot corona above the
cool photosphere in a self-consistent way. We synthesize the coronal EUV
emission from the densities and temperatures in the model and compare
this to the actual coronal observations. Results: We are able
to reproduce the overall appearance and key features of the corona in
this active region on a qualitative level. The model shows long loops,
fan loops, compact loops, and diffuse emission forming at the same
locations and at similar times as in the observation. Furthermore,
the low-intensity contrast of the model loops in EUV matches the
observations. Conclusions: In our model the energy input into the
corona is similar as in the scenarios of fieldline-braiding or flux-tube
tectonics, that is, energy is transported to the corona through the
driving of the vertical magnetic field by horizontal photospheric
motions. The success of our model shows the central role that this
process plays for the structure, dynamics, and heating of the corona.

---------------------------------------------------------
Title: Flame-like Ellerman Bombs and Their Connection to Solar
Ultraviolet Bursts
Authors: Chen, Yajie; Tian, Hui; Peter, Hardi; Samanta, Tanmoy;
Yurchyshyn, Vasyl; Wang, Haimin; Cao, Wenda; Wang, Linghua; He, Jiansen
2019ApJ...875L..30C Altcode: 2019arXiv190301981C
Ellerman bombs (EBs) are small-scale intense brightenings in Hα
wing images, which are generally believed to be signatures of
magnetic reconnection around the temperature minimum region of the
solar atmosphere. They have a flame-like morphology when observed
near the solar limb. Recent observations from the Interface Region
Imaging Spectrograph (IRIS) reveal another type of small-scale
reconnection event called an ultraviolet (UV) burst, in the lower solar
atmosphere. Though previous observations have shown a clear coincidence
between the occurrence of some UV bursts and EBs, the exact relationship
between these two phenomena is still debated. We investigate the spatial
and temporal relationship between flame-like EBs and UV bursts using
joint near-limb observations between the 1.6 m Goode Solar Telescope
(GST) and IRIS. In total, 161 EBs have been identified from the GST
observations, and ∼20 of them reveal signatures of UV bursts in
the IRIS images. Interestingly, we find that these UV bursts have a
tendency to appear at the upper parts of their associated flame-like
EBs. The intensity variations of most EB-related UV bursts and their
corresponding EBs match well. Our results suggest that some of these
UV bursts and EBs likely form at different heights during a common
reconnection process.

---------------------------------------------------------
Title: Energetics of magnetic transients in a solar active region
plage
Authors: Chitta, L. P.; Sukarmadji, A. R. C.; Rouppe van der Voort,
L.; Peter, H.
2019A&A...623A.176C Altcode: 2019arXiv190201650C
Context. Densely packed coronal loops are rooted in photospheric
plages in the vicinity of active regions on the Sun. The photospheric
magnetic features underlying these plage areas are patches of mostly
unidirectional magnetic field extending several arcsec on the solar
surface. Aims: We aim to explore the transient nature of
the magnetic field, its mixed-polarity characteristics, and the
associated energetics in the active region plage using high spatial
resolution observations and numerical simulations. Methods:
We used photospheric Fe I 6173 Å spectropolarimetric observations of
a decaying active region obtained from the Swedish 1-m Solar Telescope
(SST). These data were inverted to retrieve the photospheric magnetic
field underlying the plage as identified in the extreme-ultraviolet
emission maps obtained from the Atmospheric Imaging Assembly (AIA)
on board the Solar Dynamics Observatory (SDO). To obtain better
insight into the evolution of extended unidirectional magnetic field
patches on the Sun, we performed 3D radiation magnetohydrodynamic
simulations of magnetoconvection using the MURaM code. 
Results: The observations show transient magnetic flux emergence
and cancellation events within the extended predominantly unipolar
patch on timescales of a few 100 s and on spatial scales comparable
to granules. These transient events occur at the footpoints of active
region plage loops. In one case the coronal response at the footpoints
of these loops is clearly associated with the underlying transient. The
numerical simulations also reveal similar magnetic flux emergence and
cancellation events that extend to even smaller spatial and temporal
scales. Individual simulated transient events transfer an energy
flux in excess of 1 MW m-2 through the photosphere. Conclusions: We suggest that the magnetic transients could play
an important role in the energetics of active region plage. Both in
observations and simulations, the opposite-polarity magnetic field
brought up by transient flux emergence cancels with the surrounding
plage field. Magnetic reconnection associated with such transient events
likely conduits magnetic energy to power the overlying chromosphere
and coronal loops.

---------------------------------------------------------
Title: Investigating the Transition Region Explosive Events and
Their Relationship to Network Jets
Authors: Chen, Yajie; Tian, Hui; Huang, Zhenghua; Peter, Hardi;
Samanta, Tanmoy
2019ApJ...873...79C Altcode: 2019arXiv190111215C
Recent imaging observations with the Interface Region Imaging
Spectrograph (IRIS) have revealed prevalent intermittent jets with
apparent speeds of 80-250 km s-1 from the network lanes
in the solar transition region (TR). Additionally, spectroscopic
observations of the TR lines have revealed the frequent presence of
highly non-Gaussian line profiles with enhanced emission at the line
wings, often referred to as explosive events (EEs). Using simultaneous
imaging and spectroscopic observations from IRIS, we investigate
the relationship between EEs and network jets. We first identify
EEs from the Si IV 1393.755 Å line profiles in our observations,
then examine related features in the 1330 Å slit-jaw images. Our
analysis suggests that EEs with double peaks or enhancements in both
wings appear to be located at either the footpoints of network jets or
transient compact brightenings. These EEs are most likely produced by
magnetic reconnection. We also find that EEs with enhancements only
at the blue wing are mainly located on network jets, away from the
footpoints. These EEs clearly result from the superposition of the
high-speed network jets on the TR background. In addition, EEs showing
enhancement only at the red wing of the line are often located around
the jet footpoints, which is possibly caused by the superposition of
reconnection downflows on the background emission. Moreover, we find
some network jets that are not associated with any detectable EEs. Our
analysis suggests that some EEs are related to the birth or propagation
of network jets, and that others are not connected to network jets.

---------------------------------------------------------
Title: Chapter 3 - The Sun's Atmospher
Authors: Shapiro, Alexander I.; Peter, Hardi; Solanki, Sami K.
2019sgsp.book...59S Altcode:
The solar atmosphere covers a broad range of temperatures and densities
from the solar surface, via the chromosphere and transition region, and
to the corona. Although one-dimensional (1D) models of the atmospheric
structure have reached a high level of maturity, high-spatial
resolution observations have cast some doubt on their validity. Thus,
such observations have revealed a richness of highly variable spatial
structure, often reaching down to the current resolution limit
of 0.1 arcsec, or roughly 70 km on the Sun, in the photosphere and
chromosphere. These observational advances have led to a new generation
of models that describe the solar atmosphere self-consistently using 3D
magnetohydrodynamic approximation simulations, including 3D radiative
energy transport for those that cover the lower atmosphere, while
simplistically taking into account the complex magnetic structure and
energy dissipation processes in the upper atmosphere. These models have
achieved considerable success in explaining the best observations,
although there are still a number of open questions. Nonetheless,
thanks to modern advances, the solar atmosphere now provides an
excellent setting to test models of stellar atmospheres critically.

---------------------------------------------------------
Title: Quasi-periodic Fast Propagating Magnetoacoustic Waves during
the Magnetic Reconnection Between Solar Coronal Loops
Authors: Li, Leping; Zhang, Jun; Peter, Hardi; Chitta, Lakshmi Pradeep;
Su, Jiangtao; Song, Hongqiang; Xia, Chun; Hou, Yijun
2018ApJ...868L..33L Altcode: 2018arXiv181108553L
Employing Solar Dynamics Observatory/Atmospheric Imaging Assembly
(AIA) multi-wavelength images, we have presented coronal condensations
caused by magnetic reconnection between a system of open and closed
solar coronal loops. In this Letter, we report the quasi-periodic fast
magnetoacoustic waves propagating away from the reconnection region
upward across the higher-lying open loops during the reconnection
process. On 2012 January 19, reconnection between the higher-lying
open loops and lower-lying closed loops took place, and two sets of
newly reconnected loops formed. Thereafter, cooling and condensations
of coronal plasma occurred in the magnetic dip region of higher-lying
open loops. During the reconnection process, disturbances originating
from the reconnection region propagate upward across the magnetic
dip region of higher-lying loops with the mean speed and mean speed
amplitude of 200 and 30 km s-1, respectively. The mean speed
of the propagating disturbances decreases from ∼230 km s-1
to ∼150 km s-1 during the coronal condensation process,
and then increases to ∼220 km s-1. This temporal evolution
of the mean speed anti-correlates with the light curves of the AIA 131
and 304 Å channels that show the cooling and condensation process
of coronal plasma. Furthermore, the propagating disturbances appear
quasi-periodically with a peak period of 4 minutes. Our results suggest
that the disturbances represent the quasi-periodic fast propagating
magnetoacoustic (QFPM) waves originating from the magnetic reconnection
between coronal loops.

---------------------------------------------------------
Title: Solar Ultraviolet Bursts
Authors: Young, Peter R.; Tian, Hui; Peter, Hardi; Rutten, Robert J.;
Nelson, Chris J.; Huang, Zhenghua; Schmieder, Brigitte; Vissers, Gregal
J. M.; Toriumi, Shin; Rouppe van der Voort, Luc H. M.; Madjarska, Maria
S.; Danilovic, Sanja; Berlicki, Arkadiusz; Chitta, L. P.; Cheung, Mark
C. M.; Madsen, Chad; Reardon, Kevin P.; Katsukawa, Yukio; Heinzel, Petr
2018SSRv..214..120Y Altcode: 2018arXiv180505850Y
The term "ultraviolet (UV) burst" is introduced to describe small,
intense, transient brightenings in ultraviolet images of solar active
regions. We inventorize their properties and provide a definition
based on image sequences in transition-region lines. Coronal signatures
are rare, and most bursts are associated with small-scale, canceling
opposite-polarity fields in the photosphere that occur in emerging flux
regions, moving magnetic features in sunspot moats, and sunspot light
bridges. We also compare UV bursts with similar transition-region
phenomena found previously in solar ultraviolet spectrometry and
with similar phenomena at optical wavelengths, in particular Ellerman
bombs. Akin to the latter, UV bursts are probably small-scale magnetic
reconnection events occurring in the low atmosphere, at photospheric
and/or chromospheric heights. Their intense emission in lines with
optically thin formation gives unique diagnostic opportunities
for studying the physics of magnetic reconnection in the low solar
atmosphere. This paper is a review report from an International Space
Science Institute team that met in 2016-2017.

---------------------------------------------------------
Title: Emission of solar chromospheric and transition region features
related to the underlying magnetic field
Authors: Barczynski, K.; Peter, H.; Chitta, L. P.; Solanki, S. K.
2018A&A...619A...5B Altcode: 2018arXiv180702372B
Context. The emission of the upper atmosphere of the Sun is closely
related to magnetic field concentrations at the solar surface. 
Aims: It is well established that this relation between chromospheric
emission and magnetic field is nonlinear. Here we investigate
systematically how this relation, characterised by the exponent
of a power-law fit, changes through the atmosphere, from the upper
photosphere through the temperature minimum region and chromosphere
to the transition region. Methods: We used spectral maps from
the Interface Region Imaging Spectrograph (IRIS) covering Mg II and
its wings, C II, and Si IV together with magnetograms and UV continuum
images from the Solar Dynamics Observatory. After a careful alignment
of the data we performed a power-law fit for the relation between each
pair of observables and determine the power-law index (or exponent) for
these. This was done for different spatial resolutions and different
features on the Sun. Results: While the correlation between
emission and magnetic field drops monotonically with temperature,
the power-law index shows a hockey-stick-type variation: from the
upper photosphere to the temperature-minimum it drops sharply and then
increases through the chromosphere into the transition region. This
is even seen through the features of the Mg II line, this is,
from k1 to k2 and k3. It is irrespective of spatial resolution or
whether we investigate active regions, plage areas, quiet Sun, or
coronal holes. Conclusions: In accordance with the general
picture of flux-flux relations from the chromosphere to the corona,
above the temperature minimum the sensitivity of the emission to the
plasma heating increases with temperature. Below the temperature
minimum a different mechanism has to govern the opposite trend of
the power-law index with temperature. We suggest four possibilities,
in other words, a geometric effect of expanding flux tubes filling the
available chromospheric volume, the height of formation of the emitted
radiation, the dependence on wavelength of the intensity-temperature
relationship, and the dependence of the heating of flux tubes on the
magnetic flux density.

---------------------------------------------------------
Title: Quiet-Sun and Coronal Hole in Mg II k Line as Observed by IRIS
Authors: Kayshap, Pradeep; Tripathi, Durgesh; Solanki, Sami K.;
Peter, Hardi
2018ApJ...864...21K Altcode: 2018arXiv180703494K
Coronal hole (CH) regions are dark in comparison to the quiet Sun (QS)
at coronal temperatures. However, at chromospheric and transition
region temperatures, the QS and CHs are hardly distinguishable. In
this study, we have used the Mg II 2796.35 Å spectral line recorded
by the Interface Region Imaging Spectrometer (IRIS) to understand
the similarities and differences in the QS and CH at chromospheric
levels. Our analysis reveals that the emission from Mg II k3 and k2v
that originates in the chromosphere is significantly lower in CH than
in QS for the regions with similar magnetic field strength. The wing
emissions of Mg II k that originates from the photospheric layer,
however, do not show any difference between QS and CH. The difference
in Mg II k3 intensities between QS and CH increases with increasing
magnetic field strength. We further studied the effects of spectral
resolution on these differences and found that the difference in
the intensities decreases with decreasing spectral resolution. For
a resolution of 11 Å, the difference completely disappears. These
findings are not only important for mass and energy supply from the
chromosphere to the corona but also provides essential ingredients for
the modeling of the solar spectral irradiance for the understanding
of the Sun-climate relationships.

---------------------------------------------------------
Title: Coronal Condensations Caused by Magnetic Reconnection between
Solar Coronal Loops
Authors: Li, Leping; Zhang, Jun; Peter, Hardi; Chitta, Lakshmi Pradeep;
Su, Jiangtao; Xia, Chun; Song, Hongqiang; Hou, Yijun
2018ApJ...864L...4L Altcode: 2018arXiv180809626L
Employing Solar Dynamics Observatory/Atmospheric Imaging Assembly
(AIA) multi-wavelength images, we report the coronal condensation
during the magnetic reconnection (MR) between a system of open and
closed coronal loops. Higher-lying magnetically open structures,
observed in AIA 171 Å images above the solar limb, move downward and
interact with the lower-lying closed loops, resulting in the formation
of dips in the former. An X-type structure forms at the interface. The
interacting loops reconnect and disappear. Two sets of newly reconnected
loops then form and recede from the MR region. During the MR process,
bright emission appears sequentially in the AIA 131 and 304 Å channels
repeatedly in the dips of higher-lying open structures. This indicates
the cooling and condensation process of hotter plasma from ∼0.9
MK down to ∼0.6 MK, and then to ∼0.05 MK, also supported by the
light curves of the AIA 171, 131, and 304 Å channels. The part of
higher-lying open structures supporting the condensation participate
in the successive MR. Without support from underlying loops, the
condensation then rains back to the solar surface along the newly
reconnected loops. Our results suggest that the MR between coronal loops
leads to the condensation of hotter coronal plasma and its downflows. MR
thus plays an active role in the mass cycle of coronal plasma because it
can initiate the catastrophic cooling and condensation. This underlines
that the magnetic and thermal evolution has to be treated together
and cannot be separated, even in the case of catastrophic cooling.

---------------------------------------------------------
Title: Dark Structures in Sunspot Light Bridges
Authors: Zhang, Jingwen; Tian, Hui; Solanki, Sami K.; Wang, Haimin;
Peter, Hardi; Ahn, Kwangsu; Xu, Yan; Zhu, Yingjie; Cao, Wenda; He,
Jiansen; Wang, Linghua
2018ApJ...865...29Z Altcode: 2018arXiv180900146Z
We present unprecedented high-resolution TiO images and Fe I 1565
nm spectropolarimetric data of two light bridges taken by the 1.6
m Goode Solar Telescope at Big Bear Solar Observatory. In the first
light bridge (LB1), we find striking knot-like dark structures within
the central dark lane. Many dark knots show migration away from the
penumbra along the light bridge. The sizes, intensity depressions,
and apparent speeds of their proper motion along the light bridges of
33 dark knots identified from the TiO images are mainly in the ranges
of 80 ∼ 200 km, 30% ∼ 50%, and 0.3 ∼ 1.2 km s-1,
respectively. In the second light bridge (LB2), a faint central dark
lane and striking transverse intergranular lanes were observed. These
intergranular lanes have sizes and intensity depressions comparable
to those of the dark knots in LB1 and also migrate away from the
penumbra at similar speeds. Our observations reveal that LB2 is made
up of a chain of evolving convection cells, as indicated by patches of
blueshift surrounded by narrow lanes of redshift. The central dark lane
generally corresponds to blueshifts, supporting the previous suggestion
of central dark lanes being the top parts of convection upflows. In
contrast, the intergranular lanes are associated with redshifts and
located at two sides of each convection cell. The magnetic fields are
stronger in intergranular lanes than in the central dark lane. These
results suggest that these intergranular lanes are manifestations of
convergent convective downflows in the light bridge. We also provide
evidence that the dark knots observed in LB1 may have a similar origin.

---------------------------------------------------------
Title: Amueller/Word_Cloud: Wordcloud 1.5.0
Authors: Mueller, Andreas; Fillion-Robin, Jean-Christophe; Boidol,
Raphael; Tian, Font; Nechifor, Paul; yoonsubKim; Peter; Rampin,
Remi; Corvellec, Marianne; Medina, Juan; Dai, Yuchao; Petrushev,
Baze; Langner, Karol M.; Hong; Alessio; Ozsvald, Ian; vkolmakov;
Jones, Terry; Bailey, Eric; Rho, Valentina; IgorAPM; Roy, Divakar;
May, Chandler; foobuzz; Piyush; Kian Seong, Low; Van Goey, Jeroen;
Seden Smith, James; Gus; Mai, Feng
2018zndo....594952M Altcode:
A little word cloud generator in Python

---------------------------------------------------------
Title: Nature of the energy source powering solar coronal loops
driven by nanoflares
Authors: Chitta, L. P.; Peter, H.; Solanki, S. K.
2018A&A...615L...9C Altcode: 2018arXiv180611045C
Context. Magnetic energy is required to heat the corona, the outer
atmosphere of the Sun, to millions of degrees. Aims: We study the
nature of the magnetic energy source that is probably responsible for
the brightening of coronal loops driven by nanoflares in the cores of
solar active regions. Methods: We consider observations of two
active regions (ARs), 11890 and 12234, in which nanoflares have been
detected. To this end, we use ultraviolet (UV) and extreme ultraviolet
(EUV) images from the Atmospheric Imaging Assembly (AIA) onboard the
Solar Dynamics Observatory (SDO) for coronal loop diagnostics. These
images are combined with the co-temporal line-of-sight magnetic
field maps from the Helioseismic and Magnetic Imager (HMI) onboard
SDO to investigate the connection between coronal loops and their
magnetic roots in the photosphere. Results: The core of
these ARs exhibit loop brightening in multiple EUV channels of AIA,
particularly in its 9.4 nm filter. The HMI magnetic field maps reveal
the presence of a complex mixed polarity magnetic field distribution
at the base of these loops. We detect the cancellation of photospheric
magnetic flux at these locations at a rate of about 1015
Mx s-1. The associated compact coronal brightenings directly
above the cancelling magnetic features are indicative of plasma heating
due to chromospheric magnetic reconnection. Conclusions:
We suggest that the complex magnetic topology and the evolution of
magnetic field, such as flux cancellation in the photosphere and
the resulting chromospheric reconnection, can play an important role
in energizing active region coronal loops driven by nanoflares. Our
estimate of magnetic energy release during flux cancellation in the
quiet Sun suggests that chromospheric reconnection can also power the
quiet corona. The movie associated to Fig. 1 is available at <A
href="https://www.aanda.org/10.1051/0004-6361/201833404/olm">https://www.aanda.org</A>

---------------------------------------------------------
Title: Kinetic Simulation of Slow Magnetosonic Waves and
Quasi-Periodic Upflows in the Solar Corona
Authors: He, Jiansen; Peter, Hardi; Vocks, Christian; Marsch, Eckart;
Wang, Linghua; Zhang, Lei; Ruan, Wenzhi
2018cosp...42E1405H Altcode:
Quasi-periodic disturbances of emission-line parameters are frequently
observed in the corona. These disturbances propagate upward along
the magnetic field with speeds of _100 km/s. This phenomenon has been
interpreted as evidence of the propagation of slow magnetosonic waves or
has been argued to be a signature of intermittent outflows superposed on
the background plasmas. Here we aim to present a new "wave + flow" model
to interpret these observations. In our scenario, the oscillatory motion
is a slow-mode wave, and the flow is associated with a beam created by
the wave-particle interaction owing to Landau resonance. With the help
of a kinetic model, we simulate the propagation of slow-mode waves and
the generation of beam flows. We find that weak periodic beam flows
can be generated by to Landau resonance in the solar corona, and the
phase with the strongest blueward asymmetry is ahead of that with the
strongest blueshift by about 1/4 period. We also find that the slow wave
dampsto the level of 1/e after the transit time of two wave periods,
owing to Landau damping and Coulomb collisions in our simulation. This
damping timescale is similar to that resulting from thermal conduction
in the MHD regime.The beam flow is weakened/attenuated with increasing
wave period and decreasing wave amplitude since Coulomb collisions
become more and more dominant over the wave action. We suggest that
this "wave + flow"kinetic model provides an alternative explanation
for the observed quasi-periodic propagating perturbations in various
parameters in the solar corona.

---------------------------------------------------------
Title: Two Solar Tornadoes Observed with the Interface Region
Imaging Spectrograph
Authors: Yang, Zihao; Peter, Hardi; Su, Yang; Samanta, Tanmoy; Zhang,
Jingwen; Tian, Hui; Chen, Yajie
2018cosp...42E3746Y Altcode:
The barbs or legs of some prominences show an apparent motion of
rotation, which are often termed solar tornadoes. It is under debate
whether the apparent motion is a real rotating motion, or caused by
oscillations or counter-streaming flows. We present analysis results
from spectroscopic observations of two tornadoes by the Interface
Region Imaging Spectrograph. Each tornado was observed for more than 2.5
hours. Doppler velocities are derived through a single Gaussian fit to
the Mg II k 2796Å and Si IV 1393Å line profiles. We find coherent and
stable red and blue shifts adjacent to each other across the tornado
axes, which appears to favor the interpretation of these tornadoes
as rotating cool plasmas with temperatures of 10^4 K-10^5 K. This
interpretation is further supported by simultaneous observations of the
Atmospheric Imaging Assembly on board the Solar Dynamics Observatory,
which reveal periodic motions of dark structures in the tornadoes. Our
results demonstrate that spectroscopic observations can provide key
information to disentangle different physical processes in solar
prominences.

---------------------------------------------------------
Title: Concurrence of Cool and Warm Jets by Magnetic Flux Emerging
from below the Solar Chromosphere to the Transition Region
Authors: He, Jiansen; Tu, Chuanyi; Peter, Hardi; Wang, Linghua; Yang,
Liping; Zhang, Lei; Yan, Limei
2018cosp...42E1402H Altcode:
In the solar atmosphere, jets are ubiquitous at various spatial-temporal
scales. They are important for understanding the energy and mass
transports in the solar atmosphere. According to recent observational
studies, the high-speed network jets are likely to be intermittent but
continual sources of mass and energy for the solar wind. Here, weconduct
a magnetohydrodynamics simulation to investigate the mechanism of these
network jets. A combination of magnetic flux emergence and horizontal
advection is used to drive the magnetic reconnection in the transition
region between a strong magnetic loop and a background open flux. The
simulation results show that not only a fast warm jet, much similar
to the network jets, is found, but also an adjacent slow cool jet,
mostly like classical spicules, is launched. Differing from the fast
warm jet as driven by magnetic reconnection, the slow cool jet is mainly
accelerated by gradients of both thermal pressure and magnetic pressure
near the outer border of the mass-concentrated region compressed
by the emerging loop. These results provide a new perspective on our
understanding of the formation of both the slow cool jets from the solar
chromosphere and the fast warm jets from the solar transition region.

---------------------------------------------------------
Title: A Si IV/O IV Electron Density Diagnostic for the Analysis of
IRIS Solar Spectra
Authors: Young, P. R.; Keenan, F. P.; Milligan, R. O.; Peter, H.
2018ApJ...857....5Y Altcode: 2018arXiv180301721Y
Solar spectra of ultraviolet bursts and flare ribbons from the Interface
Region Imaging Spectrograph (IRIS) have suggested high electron
densities of &gt; {10}12 cm-3 at transition
region temperatures of 0.1 MK, based on large intensity ratios of Si
IV λ1402.77 to O IV λ1401.16. In this work, a rare observation of
the weak O IV λ1343.51 line is reported from an X-class flare that
peaked at 21:41 UT on 2014 October 24. This line is used to develop
a theoretical prediction of the Si IV λ1402.77 to O IV λ1401.16
ratio as a function of density that is recommended to be used in the
high-density regime. The method makes use of new pressure-dependent
ionization fractions that take account of the suppression of
dielectronic recombination at high densities. It is applied to two
sequences of flare kernel observations from the October 24 flare. The
first shows densities that vary between 3× {10}12 and
3× {10}13 cm-3 over a seven-minute period,
while the second location shows stable density values of around 2×
{10}12 cm-3 over a three-minute period.

---------------------------------------------------------
Title: Mass and energy supply of a cool coronal loop near its apex
Authors: Yan, Limei; Peter, Hardi; He, Jiansen; Xia, Lidong; Wang,
Linghua
2018A&A...611A..49Y Altcode:
Context. Different models for the heating of solar corona assume or
predict different locations of the energy input: concentrated at the
footpoints, at the apex, or uniformly distributed. The brightening of
a loop could be due to the increase in electron density ne,
the temperature T, or a mixture of both. Aim. We investigate possible
reasons for the brightening of a cool loop at transition region
temperatures through imaging and spectral observation. Methods:
We observed a loop with the Interface Region Imaging Spectrograph
(IRIS) and used the slit-jaw images together with spectra taken at
a fixed slit position to study the evolution of plasma properties in
and below the loop. We used spectra of Si IV, which forms at around 80
000 K in equilibrium, to identify plasma motions and derive electron
densities from the ratio of inter-combination lines of O IV. Additional
observations from the Solar Dynamics Observatory (SDO) were employed
to study the response at coronal temperatures (Atmospheric Imaging
Assembly, AIA) and to investigate the surface magnetic field below
the loop (Helioseismic and Magnetic Imager, HMI). Results:
The loop first appears at transition region temperatures and later
also at coronal temperatures, indicating a heating of the plasma
in the loop. The appearance of hot plasma in the loop coincides
with a possible accelerating upflow seen in Si IV, with the Doppler
velocity shifting continuously from -70 km s-1 to -265 km
s-1. The 3D magnetic field lines extrapolated from the HMI
magnetogram indicate possible magnetic reconnection between small-scale
magnetic flux tubes below or near the loop apex. At the same time, an
additional intensity enhancement near the loop apex is visible in the
IRIS slit-jaw images at 1400 Å. These observations suggest that the
loop is probably heated by the interaction between the loop and the
upflows, which are accelerated by the magnetic reconnection between
small-scale magnetic flux tubes at lower altitudes. Before and after
the possible heating phase, the intensity changes in the optically
thin (Si IV) and optical thick line (C II) are mainly contributed by
the density variation without significant heating. Conclusions:
We therefore provide evidence for the heating of an envelope loop that
is affected by accelerating upflows, which are probably launched by
magnetic reconnection between small-scale magnetic flux tubes underneath
the envelope loop. This study emphasizes that in the complex upper
atmosphere of the Sun, the dynamics of the 3D coupled magnetic field
and flow field plays a key role in thermalizing 1D structures such as
coronal loops. An animation associated to Fig. 1 is available at <A
href="https://www.aanda.org/10.1051/0004-6361/201628436/olm">https://www.aanda.org</A>

---------------------------------------------------------
Title: Frequently Occurring Reconnection Jets from Sunspot Light
Bridges
Authors: Tian, Hui; Yurchyshyn, Vasyl; Peter, Hardi; Solanki, Sami
K.; Young, Peter R.; Ni, Lei; Cao, Wenda; Ji, Kaifan; Zhu, Yingjie;
Zhang, Jingwen; Samanta, Tanmoy; Song, Yongliang; He, Jiansen; Wang,
Linghua; Chen, Yajie
2018ApJ...854...92T Altcode: 2018arXiv180106802T
Solid evidence of magnetic reconnection is rarely reported within
sunspots, the darkest regions with the strongest magnetic fields
and lowest temperatures in the solar atmosphere. Using the world’s
largest solar telescope, the 1.6 m Goode Solar Telescope, we detect
prevalent reconnection through frequently occurring fine-scale jets
in the Hα line wings at light bridges, the bright lanes that may
divide the dark sunspot core into multiple parts. Many jets have an
inverted Y-shape, shown by models to be typical of reconnection in a
unipolar field environment. Simultaneous spectral imaging data from
the Interface Region Imaging Spectrograph show that the reconnection
drives bidirectional flows up to 200 km s-1, and that the
weakly ionized plasma is heated by at least an order of magnitude up
to ∼80,000 K. Such highly dynamic reconnection jets and efficient
heating should be properly accounted for in future modeling efforts
of sunspots. Our observations also reveal that the surge-like activity
previously reported above light bridges in some chromospheric passbands
such as the Hα core has two components: the ever-present short surges
likely to be related to the upward leakage of magnetoacoustic waves
from the photosphere, and the occasionally occurring long and fast
surges that are obviously caused by the intermittent reconnection jets.

---------------------------------------------------------
Title: Magnetic Reconnection at the Earliest Stage of Solar Flux
Emergence
Authors: Tian, Hui; Zhu, Xiaoshuai; Peter, Hardi; Zhao, Jie; Samanta,
Tanmoy; Chen, Yajie
2018ApJ...854..174T Altcode: 2018arXiv180106785T
On 2016 September 20, the Interface Region Imaging Spectrograph observed
an active region during its earliest emerging phase for almost 7 hr. The
Helioseismic and Magnetic Imager on board the Solar Dynamics Observatory
observed continuous emergence of small-scale magnetic bipoles with
a rate of ∼1016 Mx s-1. The emergence of
magnetic fluxes and interactions between different polarities lead to
the frequent occurrence of ultraviolet (UV) bursts, which exhibit as
intense transient brightenings in the 1400 Å images. In the meantime,
discrete small patches with the same magnetic polarity tend to move
together and merge, leading to the enhancement of the magnetic fields
and thus the formation of pores (small sunspots) at some locations. The
spectra of these UV bursts are characterized by the superposition of
several chromospheric absorption lines on the greatly broadened profiles
of some emission lines formed at typical transition region temperatures,
suggesting heating of the local materials to a few tens of thousands of
kelvin in the lower atmosphere by magnetic reconnection. Some bursts
reveal blue- and redshifts of ∼100 km s-1 at neighboring
pixels, indicating the spatially resolved bidirectional reconnection
outflows. Many such bursts appear to be associated with the cancellation
of magnetic fluxes with a rate of the order of ∼1015 Mx
s-1. We also investigate the three-dimensional magnetic
field topology through a magnetohydrostatic model and find that a
small fraction of the bursts are associated with bald patches (magnetic
dips). Finally, we find that almost all bursts are located in regions
of large squashing factor at the height of ∼1 Mm, reinforcing our
conclusion that these bursts are produced through reconnection in the
lower atmosphere.

---------------------------------------------------------
Title: Two Solar Tornadoes Observed with the Interface Region
Imaging Spectrograph
Authors: Yang, Zihao; Tian, Hui; Peter, Hardi; Su, Yang; Samanta,
Tanmoy; Zhang, Jingwen; Chen, Yajie
2018ApJ...852...79Y Altcode: 2017arXiv171108968Y
The barbs or legs of some prominences show an apparent motion of
rotation, which are often termed solar tornadoes. It is under debate
whether the apparent motion is a real rotating motion, or caused by
oscillations or counter-streaming flows. We present analysis results
from spectroscopic observations of two tornadoes by the Interface
Region Imaging Spectrograph. Each tornado was observed for more than
2.5 hr. Doppler velocities are derived through a single Gaussian fit to
the Mg II k 2796 Å and Si IV 1393 Å line profiles. We find coherent
and stable redshifts and blueshifts adjacent to each other across
the tornado axes, which appears to favor the interpretation of these
tornadoes as rotating cool plasmas with temperatures of 104
K-105 K. This interpretation is further supported by
simultaneous observations of the Atmospheric Imaging Assembly on
board the Solar Dynamics Observatory, which reveal periodic motions
of dark structures in the tornadoes. Our results demonstrate that
spectroscopic observations can provide key information to disentangle
different physical processes in solar prominences.

---------------------------------------------------------
Title: Formation of Cool and Warm Jets by Magnetic Flux Emerging
from the Solar Chromosphere to Transition Region
Authors: Yang, Liping; Peter, Hardi; He, Jiansen; Tu, Chuanyi; Wang,
Linghua; Zhang, Lei; Yan, Limei
2018ApJ...852...16Y Altcode:
In the solar atmosphere, jets are ubiquitous at various spatial-temporal
scales. They are important for understanding the energy and mass
transports in the solar atmosphere. According to recent observational
studies, the high-speed network jets are likely to be intermittent
but continual sources of mass and energy for the solar wind. Here,
we conduct a 2D magnetohydrodynamics simulation to investigate the
mechanism of these network jets. A combination of magnetic flux
emergence and horizontal advection is used to drive the magnetic
reconnection in the transition region between a strong magnetic loop
and a background open flux. The simulation results show that not
only a fast warm jet, much similar to the network jets, is found,
but also an adjacent slow cool jet, mostly like classical spicules,
is launched. Differing from the fast warm jet driven by magnetic
reconnection, the slow cool jet is mainly accelerated by gradients of
both thermal pressure and magnetic pressure near the outer border of
the mass-concentrated region compressed by the emerging loop. These
results provide a different perspective on our understanding of the
formation of both the slow cool jets from the solar chromosphere and
the fast warm jets from the solar transition region.

---------------------------------------------------------
Title: The temporal evolution of explosive events and its implication
on reconnection dynamics
Authors: Guo, L.; Liu, W.; De Pontieu, B.; Huang, Y. M.; Peter, H.;
Bhattacharjee, A.
2017AGUFMSH43A2803G Altcode:
Transition-region explosive events and other bursts seen in extreme UV
light are characterized by broad spectral line profiles, and the more
violent ones show a strong enhancement of emission. They are thought
to be driven by magnetic reconnection, because of their characteristic
spectral profiles often indicating strong Alfvénic flows, and because
of the fact that they typically occur where magnetic flux concentrations
of opposite polarity intersect. In this presentation, we will focus
on the temporal evolution of transition-region explosive events. In
particular, we will investigate fast onsets of these events and the
rapid oscillations of intensity during these event. The fast onset
refers to the beginning of an explosive event, where the intensities
and the widths of its line profiles increase dramatically (often within
less than 10 seconds) and the rapid oscillations of intensity refer
to blinks of emission that usually last less than 10 seconds during
the event. In order to interpret and understand underlying mechanisms
of these observations, we conduct numerical simulation of an explosive
event and calculate its spectra. We observe a similar temporal evolution
in the synthetic Si IV spectra when the explosive event is driven by
time-dependent reconnection—plasmoid instability. The qualitative
agreement between observations and simulations suggests that the
temporal evolution of Si IV spectra of explosive events are closely
related to reconnection dynamics.

---------------------------------------------------------
Title: Current systems of coronal loops in 3D MHD simulations
Authors: Warnecke, J.; Chen, F.; Bingert, S.; Peter, H.
2017A&A...607A..53W Altcode: 2016arXiv161106170W
 Aims: We study the magnetic field and current structure
associated with a coronal loop. Through this we investigate to
what extent the assumptions of a force-free magnetic field break
down and where they might be justified. Methods: We analyze
a three-dimensional (3D) magnetohydrodynamic (MHD) model of the
solar corona in an emerging active region with the focus on the
structure of the forming coronal loops. The lower boundary of this
simulation is taken from a model of an emerging active region. As a
consequence of the emerging magnetic flux and the horizontal motions
at the surface a coronal loop forms self-consistently. We investigate
the current density along magnetic field lines inside (and outside)
this loop and study the magnetic and plasma properties in and around
this loop. The loop is defined as the bundle of field lines that
coincides with enhanced emission in extreme UV. Results:
We find that the total current along the emerging loop changes its
sign from being antiparallel to parallel to the magnetic field. This
is caused by the inclination of the loop together with the footpoint
motion. Around the loop, the currents form a complex non-force-free
helical structure. This is directly related to a bipolar current
structure at the loop footpoints at the base of the corona and a local
reduction of the background magnetic field (I.e., outside the loop)
caused by the plasma flow into and along the loop. Furthermore, the
locally reduced magnetic pressure in the loop allows the loop to sustain
a higher density, which is crucial for the emission in extreme UV. The
action of the flow on the magnetic field hosting the loop turns out
to also be responsible for the observed squashing of the loop. 
Conclusions: The complex magnetic field and current system surrounding
it can only be modeled in 3D MHD models where the magnetic field has
to balance the plasma pressure. A one-dimensional coronal loop model
or a force-free extrapolation cannot capture the current system and
the complex interaction of the plasma and the magnetic field in the
coronal loop, despite the fact that the loop is under low-β conditions.

---------------------------------------------------------
Title: Compact solar UV burst triggered in a magnetic field with a
fan-spine topology
Authors: Chitta, L. P.; Peter, H.; Young, P. R.; Huang, Y. -M.
2017A&A...605A..49C Altcode: 2017arXiv170608059C
Context. Solar ultraviolet (UV) bursts are small-scale features
that exhibit intermittent brightenings that are thought to be due to
magnetic reconnection. They are observed abundantly in the chromosphere
and transition region, in particular in active regions. Aims:
We investigate in detail a UV burst related to a magnetic feature that
is advected by the moat flow from a sunspot towards a pore. The moving
feature is parasitic in that its magnetic polarity is opposite to that
of the spot and the pore. This comparably simple photospheric magnetic
field distribution allows for an unambiguous interpretation of the
magnetic geometry leading to the onset of the observed UV burst. 
Methods: We used UV spectroscopic and slit-jaw observations from the
Interface Region Imaging Spectrograph (IRIS) to identify and study
chromospheric and transition region spectral signatures of said UV
burst. To investigate the magnetic topology surrounding the UV burst,
we used a two-hour-long time sequence of simultaneous line-of-sight
magnetograms from the Helioseismic and Magnetic Imager (HMI) and
performed data-driven 3D magnetic field extrapolations by means of
a magnetofrictional relaxation technique. We can connect UV burst
signatures to the overlying extreme UV (EUV) coronal loops observed
by the Atmospheric Imaging Assembly (AIA). Results: The UV
burst shows a variety of extremely broad line profiles indicating
plasma flows in excess of ±200 km s-1 at times. The whole
structure is divided into two spatially distinct zones of predominantly
up- and downflows. The magnetic field extrapolations show a persistent
fan-spine magnetic topology at the UV burst. The associated 3D magnetic
null point exists at a height of about 500 km above the photosphere
and evolves co-spatially with the observed UV burst. The EUV emission
at the footpoints of coronal loops is correlated with the evolution of
the underlying UV burst. Conclusions: The magnetic field around
the null point is sheared by photospheric motions, triggering magnetic
reconnection that ultimately powers the observed UV burst and energises
the overlying coronal loops. The location of the null point suggests
that the burst is triggered low in the solar chromosphere. Movies associated to Figs. 2 and 4 are available at <A
href="http://www.aanda.org/10.1051/0004-6361/201730830/olm">http://www.aanda.org</A>

---------------------------------------------------------
Title: Sentinel-1A - First precise orbit determination results
Authors: Peter, H.; Jäggi, A.; Fernández, J.; Escobar, D.; Ayuga,
F.; Arnold, D.; Wermuth, M.; Hackel, S.; Otten, M.; Simons, W.;
Visser, P.; Hugentobler, U.; Féménias, P.
2017AdSpR..60..879P Altcode:
Sentinel-1A is the first satellite of the European Copernicus
programme. Equipped with a Synthetic Aperture Radar (SAR) instrument
the satellite was launched on April 3, 2014. Operational since October
2014 the satellite delivers valuable data for more than two years. The
orbit accuracy requirements are given as 5 cm in 3D. In order to
fulfill this stringent requirement the precise orbit determination
(POD) is based on the dual-frequency GPS observations delivered
by an eight-channel GPS receiver. The Copernicus POD (CPOD)
Service is in charge of providing the orbital and auxiliary products
required by the PDGS (Payload Data Ground Segment). External orbit
validation is regularly performed by comparing the CPOD Service orbits
to orbit solutions provided by POD expert members of the Copernicus POD
Quality Working Group (QWG). The orbit comparisons revealed systematic
orbit offsets mainly in radial direction (approx. 3 cm). Although
no independent observation technique (e.g. DORIS, SLR) is available
to validate the GPS-derived orbit solutions, comparisons between the
different antenna phase center variations and different reduced-dynamic
orbit determination approaches used in the various software packages
helped to detect the cause of the systematic offset. An error in the
given geometry information about the satellite has been found. After
correction of the geometry the orbit validation shows a significant
reduction of the radial offset to below 5 mm. The 5 cm orbit accuracy
requirement in 3D is fulfilled according to the results of the orbit
comparisons between the different orbit solutions from the QWG.

---------------------------------------------------------
Title: Association of solar coronal loops to photospheric magnetic
field
Authors: Pradeep Chitta, Lakshmi; Peter, Hardi; Solanki, Sami
2017SPD....4810630P Altcode:
Magnetic connectivity and its evolution from the solar photosphere
to the corona will play a crucial role in the energetics of the
solar atmosphere. To explore this connectivity, we use high spatial
resolution magnetic field observations of an active region from the
balloon-borne SUNRISE telescope, in combination with the observations
of coronal loops imaged in extreme ultraviolet by SDO/AIA. We show
that photospheric magnetic field at the base of coronal loops is
rapidly evolving through small-scale flux emergence and cancellation
events with rates on the order of 10^15 Mx/s. When observed at high
spatial resolution better than 0.5 arcsec, we find that basically
all coronal loops considered so far are rooted in the photosphere
above small-scale opposite polarity magnetic field patches. In the
photosphere, the magnetic field threading coronal loops is interacting
with opposite polarity parasitic magnetic concentrations leading to
dynamic signatures in the upper atmosphere. Chromospheric small-scale
jets aligned to coronal loops are observed at these locations. We
will present preliminary results from 3D MHD simulations of coronal
loops driven by realistic magneto-convection and discuss what role
the magnetic interactions at coronal loop footpoints could play in
the evolution of coronal loops and their heating.

---------------------------------------------------------
Title: The Width Distribution of Loops and Strands in the Solar
Corona—Are We Hitting Rock Bottom?
Authors: Aschwanden, Markus J.; Peter, Hardi
2017ApJ...840....4A Altcode: 2017arXiv170101177A
In this study, we analyze Atmospheric Imaging Assembly (AIA) and Hi-C
images in order to investigate absolute limits for the finest loop
strands. We develop a model of the occurrence-size distribution function
of coronal loop widths, characterized by the lower limit of widths w
min, the peak (or most frequent) width w p , the
peak occurrence number n p , and a power-law slope a. Our
data analysis includes automated tracing of curvilinear features with
the OCCULT-2 code, automated sampling of the cross-sectional widths of
coronal loops, and fitting of the theoretical size distribution to the
observed distribution. With Monte Carlo simulations and variable pixel
sizes {{Δ }}x, we derive a first diagnostic criterion to discriminate
whether the loop widths are unresolved ({w}p/{{Δ }}x≈
2.5+/- 0.2) or fully resolved (if {w}p/{{Δ }}x≳ 2.7). For
images with resolved loop widths, we can apply a second diagnostic
criterion that predicts the lower limit of loop widths as a function
of the spatial resolution. We find that the loop widths are marginally
resolved in AIA images but are fully resolved in Hi-C images, where
our model predicts a most frequent (peak) value at {w}p≈
550 {km}, in agreement with recent results of Brooks et al. This result
agrees with the statistics of photospheric granulation sizes and thus
supports coronal heating mechanisms operating on the macroscopic scale
of photospheric magneto-convection, rather than nanoflare braiding
models on unresolved microscopic scales.

---------------------------------------------------------
Title: Solar Coronal Loops Associated with Small-scale Mixed Polarity
Surface Magnetic Fields
Authors: Chitta, L. P.; Peter, H.; Solanki, S. K.; Barthol, P.;
Gandorfer, A.; Gizon, L.; Hirzberger, J.; Riethmüller, T. L.; van
Noort, M.; Blanco Rodríguez, J.; Del Toro Iniesta, J. C.; Orozco
Suárez, D.; Schmidt, W.; Martínez Pillet, V.; Knölker, M.
2017ApJS..229....4C Altcode: 2016arXiv161007484C
How and where are coronal loops rooted in the solar lower
atmosphere? The details of the magnetic environment and its evolution
at the footpoints of coronal loops are crucial to understanding the
processes of mass and energy supply to the solar corona. To address
the above question, we use high-resolution line-of-sight magnetic
field data from the Imaging Magnetograph eXperiment instrument on the
Sunrise balloon-borne observatory and coronal observations from the
Atmospheric Imaging Assembly onboard the Solar Dynamics Observatory
of an emerging active region. We find that the coronal loops are
often rooted at the locations with minor small-scale but persistent
opposite-polarity magnetic elements very close to the larger dominant
polarity. These opposite-polarity small-scale elements continually
interact with the dominant polarity underlying the coronal loop through
flux cancellation. At these locations we detect small inverse Y-shaped
jets in chromospheric Ca II H images obtained from the Sunrise Filter
Imager during the flux cancellation. Our results indicate that magnetic
flux cancellation and reconnection at the base of coronal loops due
to mixed polarity fields might be a crucial feature for the supply of
mass and energy into the corona.

---------------------------------------------------------
Title: Miniature loops in the solar corona
Authors: Barczynski, K.; Peter, H.; Savage, S. L.
2017A&A...599A.137B Altcode: 2016arXiv161108513B
Context. Magnetic loops filled with hot plasma are the main building
blocks of the solar corona. Usually they have lengths of the order
of the barometric scale height in the corona that is 50 Mm. 
Aims: Previously it has been suggested that miniature versions of hot
loops exist. These would have lengths of only 1 Mm barely protruding
from the chromosphere and spanning across just one granule in the
photosphere. Such short loops are well established at transition
region temperatures (0.1 MK), and we investigate if such miniature
loops also exist at coronal temperatures (&gt;1 MK). Methods:
We used extreme UV (EUV) imaging observations from the High-resolution
Coronal Imager (Hi-C) at an unprecedented spatial resolution of 0.3”
to 0.4”. Together with EUV imaging and magnetogram data from the Solar
Dynamics Observatory (SDO) and X-Ray Telescope (XRT) data from Hinode
we investigated the spatial, temporal and thermal evolution of small
loop-like structures in the solar corona above a plage region close to
an active region and compared this to a moss area within the active
region. Results: We find that the size, motion and temporal
evolution of the loop-like features are consistent with photospheric
motions, suggesting a close connection to the photospheric magnetic
field. Aligned magnetograms show that one of their endpoints is rooted
at a magnetic concentration. Their thermal structure, as revealed
together with the X-ray observations, shows significant differences
to moss-like features. Conclusions: Considering different
scenarios, these features are most probably miniature versions of hot
loops rooted at magnetic concentrations at opposite sides of a granule
in small emerging magnetic loops (or flux tubes).

---------------------------------------------------------
Title: A Form of Nascent Solar Wind Outflow: Beam flow Generated by
Slow-Mode Waves Through Landau Resonance in the Weakly Collisional
Solar Atmosphere
Authors: He, J.; Ruan, W.; Zhang, L.; Vocks, C.; Marsch, E.; Tu, C.;
Peter, H.; Wang, L.
2016AGUFMSH51B2589H Altcode:
Quasi-periodic disturbances of emission-line parameters are frequently
observed in the corona. These disturbances propagate upward along
the magnetic field with speeds 100 km s-1. This phenomenon has been
interpreted as an evidence of the propagation of slow magnetosonic waves
or argued to be a signature of the intermittent outflows superposed
on the background plasmas. Here we aim to present a new "wave + flow"
model to interpret these observations. In our scenario, the oscillatory
motion is a slow mode wave, and the flow is associated with a beam
created by the wave-particle interaction owing to Landau resonance. With
the help of a kinetic model, we simulate the propagation of slow mode
waves and the generation of beam flows. We find that weak periodic beam
flows can be generated owing to Landau resonance in the solar corona,
and the phase with strongest blueward asymmetry is ahead of that with
strongest blueshift by about 1/4 period. We also find that the slow wave
damps to the level of 1/e after the transit time of two wave periods,
owing to Landau damping and Coulomb collisions in our simulation. This
damping time scale is similar to that resulting from thermal-conduction
in the MHD regime. The beam flow is weakened/attenuated with increasing
wave period and decreasing wave amplitude since Coulomb collision
becomes more and more dominant over the wave action. We suggest that
this "wave + flow" kinetic model provides an alternative explanation
for the observed quasi-periodic propagating perturbations in various
parameters in the solar corona. Therefore, the compressible slow-mode
waves, which can be driven and launched by magnetic reconnection,
vertical piston oscillation, or periodic horizontal squeezing, is
believed to play an important role in accelerating the plasmas into
a form of the solar wind nascent outflows.

---------------------------------------------------------
Title: The importance of high-resolution observations of the solar
corona
Authors: Winebarger, A. R.; Cirtain, J. W.; Golub, L.; Walsh, R. W.;
De Pontieu, B.; Savage, S. L.; Rachmeler, L.; Kobayashi, K.; Testa,
P.; Brooks, D.; Warren, H.; Mcintosh, S. W.; Peter, H.; Morton, R. J.;
Alexander, C. E.; Tiwari, S. K.
2016AGUFMSH31B2577W Altcode:
The spatial and temporal resolutions of the available coronal
observatories are inadequate to resolve the signatures of coronal
heating. High-resolution and high-cadence observations available with
the Interface Region Imaging Spectrograph (IRIS) and the High-resolution
Coronal Imager (Hi-C) instrument hint that 0.3 arcsec resolution images
and &lt; 10 s cadence provide the necessary resolution to detect
heating events. Hi-C was launched from White Sands Missile Range on
July 11, 2012 (before the launch with IRIS) and obtained images of
a solar active region in the 19.3 nm passband. In this presentation,
I will discuss the potential of combining a flight in Hi-C with a 17.1
nm passband, in conjunction with IRIS. This combination will provide,
for the first time, a definitive method of tracing the energy flow
between the chromosphere and corona and vice versa.

---------------------------------------------------------
Title: Fine flow structures in the transition region small-scale loops
Authors: Yan, L.; Peter, H.; He, J.; Wei, Y.
2016AGUFMSH31B2569Y Altcode:
The observation and model have suggested that the transition region EUV
emission from the quiet sun region is contributed by very small scale
loops which have not been resolved. Recently, the observation from
IRIS has revealed that this kind of small scale loops. Based on the
high resolution spectral and imaging observation from IRIS, much more
detail work needs to be done to reveal the fine flow features in this
kind of loop to help us understand the loop heating. Here, we present
a detail statistical study of the spatial and temporal evolution of Si
IV line profiles of small scale loops and report the spectral features:
there is a transition from blue (red) wing enhancement dominant to red
(blue) wing enhancement dominant along the cross-section of the loop,
which is independent of time. This feature appears as the loop appear
and disappear as the loop un-visible. This is probably the signature of
helical flow along the loop. The result suggests that the brightening
of this kind of loop is probably due to the current dissipation heating
in the twisted magnetic field flux tube.

---------------------------------------------------------
Title: GREGOR first results
Authors: Peter, Hardi; Forveille, Thierry; Alves, Joao
2016A&A...596E...1P Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Magnetic reconnection between a solar filament and nearby
coronal loops
Authors: Li, Leping; Zhang, Jun; Peter, Hardi; Priest, Eric; Chen,
Huadong; Guo, Lijia; Chen, Feng; Mackay, Duncan
2016NatPh..12..847L Altcode: 2016arXiv160503320L
Magnetic reconnection is difficult to observe directly but coronal
structures on the Sun often betray the magnetic field geometry and
its evolution. Here we report the observation of magnetic reconnection
between an erupting filament and its nearby coronal loops, resulting
in changes in the filament connection. X-type structures form when the
erupting filament encounters the loops. The filament becomes straight,
and bright current sheets form at the interfaces. Plasmoids appear
in these current sheets and propagate bi-directionally. The filament
disconnects from the current sheets, which gradually disperse and
disappear, then reconnects to the loops. This evolution suggests
successive magnetic reconnection events predicted by theory but rarely
detected with such clarity in observations. Our results confirm the
three-dimensional magnetic reconnection theory and have implications
for the evolution of dissipation regions and the release of magnetic
energy for reconnection in many magnetized plasma systems.

---------------------------------------------------------
Title: The SPICE Spectral Imager on Solar Orbiter: Linking the Sun
to the Heliosphere
Authors: Fludra, Andrzej; Haberreiter, Margit; Peter, Hardi; Vial,
Jean-Claude; Harrison, Richard; Parenti, Susanna; Innes, Davina;
Schmutz, Werner; Buchlin, Eric; Chamberlin, Phillip; Thompson,
William; Gabriel, Alan; Morris, Nigel; Caldwell, Martin; Auchere,
Frederic; Curdt, Werner; Teriaca, Luca; Hassler, Donald M.; DeForest,
Craig; Hansteen, Viggo; Carlsson, Mats; Philippon, Anne; Janvier, Miho;
Wimmer-Schweingruber, Robert; Griffin, Douglas; Davila, Joseph; Giunta,
Alessandra; Waltham, Nick; Eccleston, Paul; Gottwald, Alexander;
Klein, Roman; Hanley, John; Walls, Buddy; Howe, Chris; Schuehle, Udo
2016cosp...41E.607F Altcode:
The SPICE (Spectral Imaging of the Coronal Environment) instrument is
one of the key remote sensing instruments onboard the upcoming Solar
Orbiter Mission. SPICE has been designed to contribute to the science
goals of the mission by investigating the source regions of outflows
and ejection processes which link the solar surface and corona to the
heliosphere. In particular, SPICE will provide quantitative information
on the physical state and composition of the solar atmosphere
plasma. For example, SPICE will access relative abundances of ions to
study the origin and the spatial/temporal variations of the 'First
Ionization Potential effect', which are key signatures to trace the
solar wind and plasma ejections paths within the heliosphere. Here we
will present the instrument and its performance capability to attain the
scientific requirements. We will also discuss how different observation
modes can be chosen to obtain the best science results during the
different orbits of the mission. To maximize the scientific return of
the instrument, the SPICE team is working to optimize the instrument
operations, and to facilitate the data access and their exploitation.

---------------------------------------------------------
Title: Solar abundances with the SPICE spectral imager on Solar
Orbiter
Authors: Giunta, Alessandra; Haberreiter, Margit; Peter, Hardi;
Vial, Jean-Claude; Harrison, Richard; Parenti, Susanna; Innes, Davina;
Schmutz, Werner; Buchlin, Eric; Chamberlin, Phillip; Thompson, William;
Bocchialini, Karine; Gabriel, Alan; Morris, Nigel; Caldwell, Martin;
Auchere, Frederic; Curdt, Werner; Teriaca, Luca; Hassler, Donald M.;
DeForest, Craig; Hansteen, Viggo; Carlsson, Mats; Philippon, Anne;
Janvier, Miho; Wimmer-Schweingruber, Robert; Griffin, Douglas; Baudin,
Frederic; Davila, Joseph; Fludra, Andrzej; Waltham, Nick; Eccleston,
Paul; Gottwald, Alexander; Klein, Roman; Hanley, John; Walls, Buddy;
Howe, Chris; Schuehle, Udo; Gyo, Manfred; Pfiffner, Dany
2016cosp...41E.681G Altcode:
Elemental composition of the solar atmosphere and in particular
abundance bias of low and high First Ionization Potential (FIP)
elements are a key tracer of the source regions of the solar wind. These
abundances and their spatio-temporal variations, as well as the other
plasma parameters , will be derived by the SPICE (Spectral Imaging
of the Coronal Environment) EUV spectral imager on the upcoming
Solar Orbiter mission. SPICE is designed to provide spectroheliograms
(spectral images) using a core set of emission lines arising from ions
of both low-FIP and high-FIP elements. These lines are formed over
a wide range of temperatures, enabling the analysis of the different
layers of the solar atmosphere. SPICE will use these spectroheliograms
to produce dynamic composition maps of the solar atmosphere to be
compared to in-situ measurements of the solar wind composition of
the same elements (i.e. O, Ne, Mg, Fe). This will provide a tool to
study the connectivity between the spacecraft (the Heliosphere) and
the Sun. We will discuss the SPICE capabilities for such composition
measurements.

---------------------------------------------------------
Title: Kinetic Simulation of Slow Magnetosonic Waves and
Quasi-Periodic Upflows in the Solar Corona
Authors: Ruan, Wenzhi; He, Jiansen; Zhang, Lei; Vocks, Christian;
Marsch, Eckart; Tu, Chuanyi; Peter, Hardi; Wang, Linghua
2016ApJ...825...58R Altcode: 2016arXiv160101823R
Quasi-periodic disturbances of emission-line parameters are frequently
observed in the corona. These disturbances propagate upward along
the magnetic field with speeds of ∼100 km s-1. This
phenomenon has been interpreted as evidence of the propagation of slow
magnetosonic waves or has been argued to be a signature of intermittent
outflows superposed on the background plasmas. Here we aim to present
a new “wave + flow” model to interpret these observations. In our
scenario, the oscillatory motion is a slow-mode wave, and the flow is
associated with a beam created by the wave-particle interaction owing
to Landau resonance. With the help of a kinetic model, we simulate the
propagation of slow-mode waves and the generation of beam flows. We find
that weak periodic beam flows can be generated by to Landau resonance in
the solar corona, and the phase with the strongest blueward asymmetry
is ahead of that with the strongest blueshift by about 1/4 period. We
also find that the slow wave damps to the level of 1/e after the
transit time of two wave periods, owing to Landau damping and Coulomb
collisions in our simulation. This damping timescale is similar to that
resulting from thermal conduction in the MHD regime. The beam flow is
weakened/attenuated with increasing wave period and decreasing wave
amplitude since Coulomb collisions become more and more dominant over
the wave action. We suggest that this “wave + flow” kinetic model
provides an alternative explanation for the observed quasi-periodic
propagating perturbations in various parameters in the solar corona.

---------------------------------------------------------
Title: Scaling laws of coronal loops compared to a 3D MHD model of
an active region
Authors: Bourdin, Ph. -A.; Bingert, S.; Peter, H.
2016A&A...589A..86B Altcode: 2016arXiv160305276B
Context. The structure and heating of coronal loops have been
investigated for decades. Established scaling laws relate fundamental
quantities like the loop apex temperature, pressure, length, and
coronal heating. Aims: We test these scaling laws against a
large-scale 3D magneto-hydrodynamics (MHD) model of the solar corona,
which became feasible with current high-performance computing. Methods: We drove an active region simulation with photospheric
observations and find strong similarities to the observed coronal loops
in X-rays and extreme-ultraviolet (EUV) wavelength. A 3D reconstruction
of stereoscopic observations shows that our model loops have a realistic
spatial structure. We compared scaling laws to our model data extracted
along an ensemble of field lines. Finally, we fit a new scaling law
that represents hot loops and also cooler structures, which was not
possible before based only on observations. Results: Our model
data gives some support for scaling laws that were established for
hot and EUV-emissive coronal loops. For the Rosner-Tucker-Vaiana (RTV)
scaling law we find an offset to our model data, which can be explained
by 1D considerations of a static loop with a constant heat input and
conduction. With a fit to our model data we set up a new scaling law for
the coronal heat input along magnetic field lines. Conclusions:
RTV-like scaling laws were fitted to hot loops and therefore do not
predict well the coronal heat input for cooler structures that are
barely observable. The basic differences between 1D and self-consistent
3D modeling account for deviations between earlier scaling laws and
ours. We also conclude that a heating mechanism by MHD-turbulent
dissipation within a braided flux tube would heat the corona stronger
than is consistent with our model corona.

---------------------------------------------------------
Title: A closer look at a coronal loop rooted in a sunspot umbra
Authors: Chitta, L. P.; Peter, H.; Young, P. R.
2016A&A...587A..20C Altcode: 2015arXiv151203831C
Context. Extreme UV (EUV) and X-ray loops in the solar corona connect
regions of enhanced magnetic activity, but they are not usually rooted
in the dark umbrae of sunspots because the strong magnetic field
found there suppresses convection. This means that the Poynting flux
of magnetic energy into the upper atmosphere is not significant within
the umbra as long as there are no light bridges or umbral dots. 
Aims: Here we report a rare observation of a coronal loop rooted in the
dark umbra of a sunspot without any traces of light bridges or umbral
dots. This allows us to investigate the loop without much confusion
from background or line-of-sight integration effects. Methods:
We used the slit-jaw images and spectroscopic data from the Interface
Region Imaging Spectrograph (IRIS) and concentrate on the line profiles
of O iv and Si iv that show persistent strong redshifted components in
the loop rooted in the umbra. Using the ratios of O iv, we can estimate
the density and thus investigate the mass flux. The coronal context
and temperature diagnostics of these observations is provided through
the EUV channels of the Atmospheric Imaging Assembly (AIA). 
Results: The coronal loop, embedded within cooler downflows, hosts
supersonic downflows. The speed of more than 100 km s-1 is
on the same order of magnitude in the transition region lines of O iv
and Si iv, and is even seen at comparable speed in the chromospheric
Mg II lines. At a projected distance of within 1” of the footpoint,
we see a shock transition to smaller downflow speeds of about 15
km s-1 being consistent with mass conservation across a
stationary isothermal shock. Conclusions: We see no direct
evidence for energy input into the loop because the loop is rooted
in the dark uniform part of the umbra with no light bridges or umbral
dots near by. Thus one might conclude that we are seeing a siphon flow
driven from the footpoint at the other end of the loop. However, for a
final result data of similar quality at the other footpoint are needed,
but this is too far away to be covered by the IRIS field of view.

---------------------------------------------------------
Title: A Numerical Investigation of the Recurrent High-speed Jets
as a Possibility of Solar Wind Origin
Authors: Yang, Liping; He, Jiansen; Peter, Hardi; Tu, Chuanyi; Zhang,
Lei; Marsch, Eckart; Wang, Linghua; Feng, Xueshang
2015arXiv151201868Y Altcode:
In the solar atmosphere, jets are prevalent and they are significant for
the mass and energy transport. Here we conduct numerical simulations to
investigate the mass and energy contributions of the recently observed
high-speed jets to the solar wind. With a one-dimensional hydrodynamic
solar wind model, the time-dependent pulses are imposed at the bottom
to simulate the jets. The simulation results show that without other
energy source, the injected plasmas are accelerated effectively to be
a transonic wind with a substantial mass flux. The rapid acceleration
occurs close to the Sun, and the resulting asymptotic speed, number
density at 0.3 AU, as well as mass flux normalized to 1 AU are
compatible with in situ observations. As a result of the high speed,
the imposed pulses generate a train of shocks traveling upward. By
tracing the motions of the injected plasma, it is found that these
shocks heat and accelerate the injected plasmas successively step by
step to push them upward and eventually allow them to escape. The
parametric studies show that increasing the speed of the imposed
pulses or their temperature gives a considerably faster, and hotter
solar wind, while increasing their number density or decreasing their
recurring period only bring a denser solar wind. These studies provide
a possibility that the ubiquitous high-speed jets are a substantial
mass and energy contributions to the solar wind.

---------------------------------------------------------
Title: Limitations of force-free magnetic field extrapolations:
Revisiting basic assumptions
Authors: Peter, H.; Warnecke, J.; Chitta, L. P.; Cameron, R. H.
2015A&A...584A..68P Altcode: 2015arXiv151004642P
Context. Force-free extrapolations are widely used to study the magnetic
field in the solar corona based on surface measurements. Aims:
The extrapolations assume that the ratio of internal energy of the
plasma to magnetic energy, the plasma β, is negligible. Despite the
widespread use of this assumption observations, models, and theoretical
considerations show that β is of the order of a few percent to more
than 10%, and thus not small. We investigate what consequences this
has for the reliability of extrapolation results. Methods: We
use basic concepts starting with force and energy balance to infer
relations between plasma β and free magnetic energy to study the
direction of currents in the corona with respect to the magnetic
field, and to estimate the errors in the free magnetic energy by
neglecting effects of the plasma (β ≪ 1). A comparison with a 3D
magneto-hydrodynamics (MHD) model supports our basic considerations. Results: If plasma β is of the order of the relative free energy
(the ratio of the free magnetic energy to the total magnetic energy)
then the pressure gradient can balance the Lorentz force. This is the
case in solar corona, and therefore the currents are not properly
described. In particular, the error in terms of magnetic energy by
neglecting the plasma is of the order of the free magnetic energy, so
that the latter cannot be reliably determined by an extrapolation. Conclusions: While a force-free extrapolation might capture the
magnetic structure and connectivity of the coronal magnetic field,
the derived currents and free magnetic energy are not reliable. Thus
quantitative results of extrapolations on the location and amount of
heating in the corona (through current dissipation) and on the energy
storage of the magnetic field (e.g. for eruptive events) are limited.

---------------------------------------------------------
Title: Mass and Energy Transfer Between the Solar Photosphere
and Corona
Authors: Peter, H.
2015AGUFMSH23D..03P Altcode:
The problem of chromospheric and coronal heating is also a
problem of mass supply to the corona. On average we see redshifts
at transition region temperatures of the order of 10 km/s. If
interpreted as downflows, this would quickly empty the corona,
and fresh material has to be transported into the corona. Several
models have been proposed to understand this mass cycle between
the different atmospheric layers. However, as of yet all these
proposals have serious shortcomings. On the observational side open
questions remain, too. With the new IRIS mission we can observe the
transition region at unprecedented spatial and spectral resolution,
but the observational results are still puzzling. In particular the
finding that the spatial distribution of line widths and Doppler
shifts do not change with increasing resolution is against physical
intuition. This shows that even with IRIS we still have significant
velocity gradients along the line-of-sight, indicating that shocks
might play a significant role. Likewise the temporal evolution might
be a key for our understanding of the mass cycle. It might well be
that the filling and draining of hot plasma occurs on significantly
different time scales, which might be part of the difficulty to arrive
at a conclusive observational picture. Considering the progress made
for the quiet Sun, it seems clear that the processes responsible for
the mass exchange are not resolved (yet). Therefore one might wonder
to what extent one could use larger and resolved individual events
in more active parts of the Sun to understand the details of the mass
transport. In particular a common understanding of reconnection events
such as Ellerman bombs in the photosphere, explosive events in the
transition region and the recently discovered IRIS bombs in-between
might provide the key to better understand the mass cycle throughout
the atmospheric layers from the photosphere to the corona.

---------------------------------------------------------
Title: Origin of the High-speed Jets Fom Magnetic Flux Emergence
in the Solar Transition Region as well as Their Mass and Energy
Contribuctions to the Solar Wind
Authors: Liping, Y.; He, J.; Peter, H.; Tu, C. Y.; Feng, X. S.
2015AGUFMSH31B2406L Altcode:
In the solar atmosphere, the jets are ubiquitous and found to be at
various spatia-temporal scales. They are significant to understand
energy and mass transport in the solar atmosphere. Recently,
the high-speed transition region jets are reported from the
observation. Here we conduct a numerical simulation to investigate
the mechanism in their formation, as well as their mass and energy
contributions to the solar wind. Driven by the supergranular convection
motion, the magnetic reconnection between the magnetic loop and the
background open flux occurring in the transition region is simulated
with a two-dimensional MHD model. The simulation results show that not
only a fast hot jet, much resemble the found transition region jets,
but also a adjacent slow cool jet, mostly like classical spicules, is
launched. The force analysis shows that the fast hot jet is continually
driven by the Lorentz force around the reconnection region, while the
slow cool jet is induced by an initial kick through the Lorentz force
associated with the emerging magnetic flux. Also, the features of
the driven jets change with the amount of the emerging magnetic flux,
giving the varieties of both jets.With the developed one-dimensional
hydrodynamic solar wind model, the time-dependent pulses are imposed at
the bottom to simulate the jet behaviors. The simulation results show
that without other energy source, the injected plasmas are accelerated
effectively to be a transonic wind with a substantial mass flux. The
rapid acceleration occurs close to the Sun, and the resulting asymptotic
speeds, number density at 0.3 AU, as well as mass flux normalized to
1 AU are compatible with in site observations. As a result of the high
speed, the imposed pulses lead to a train of shocks traveling upward. By
tracing the motions of the injected plasma, it is found that these
shocks heat and accelerate the injected plasma to make part of them
propagate upward and eventually escape. The parametric study shows
that as the speed and temperature of the imposed pulses increase, we
get an increase of the speed and temperature of the driven solar wind,
which do not be influenced by the increase of the number density of
the imposed pulses. When the recurring period of the imposed pulses
decreases, the obtained solar wind becomes slower and cooler.

---------------------------------------------------------
Title: Origin of Both the Fast Hot Jet and the Slow Cool Jet from
Magnetic Flux Emergence and Advection in the Solar Transition Region
Authors: Yang, Liping; Peter, Hardi; He, Jiansen; Tu, Chuanyi; Wang,
Linghua; Zhang, Lei; Feng, Xueshang
2015arXiv151201869Y Altcode:
In the solar atmosphere, the jets are ubiquitous and found to be at
various spatia-temporal scales. They are significant to understand
energy and mass transport in the solar atmosphere. Recently,
the high-speed transition region jets are reported from the
observation. Here we conduct a numerical simulation to investigate the
mechanism in their formation. Driven by the supergranular convection
motion, the magnetic reconnection between the magnetic loop and the
background open flux occurring in the transition region is simulated
with a two-dimensional magnetohydrodynamics model. The simulation
results show that not only a fast hot jet, much resemble the found
transition region jets, but also a adjacent slow cool jet, mostly
like classical spicules, is launched. The force analysis shows that
the fast hot jet is continually driven by the Lorentz force around
the reconnection region, while the slow cool jet is induced by an
initial kick through the Lorentz force associated with the emerging
magnetic flux. Also, the features of the driven jets change with the
amount of the emerging magnetic flux, giving the varieties of both
jets. These results will inspire our understanding of the formation
of the prevalence of both the fast hot jet and slow cool jet from the
solar transition region and chromosphere.

---------------------------------------------------------
Title: Heating and cooling of coronal loops observed by SDO
Authors: Li, L. P.; Peter, H.; Chen, F.; Zhang, J.
2015A&A...583A.109L Altcode: 2015arXiv150904510L
Context. One of the most prominent processes to have been suggested
as heating the corona to well above 106 K builds on
nanoflares, which are short bursts of energy dissipation. Aims:
We compare observations to model predictions to test the validity
of the nanoflare process. Methods: Using extreme UV data
from AIA/SDO and HMI/SDO line-of-sight magnetograms, we study the
spatial and temporal evolution of a set of loops in active region
AR 11850. Results: We find a transient brightening of loops
in emission from Fe xviii forming at about 7.2 MK, while at the same
time these loops dim in emission from lower temperatures. This points
to a fast heating of the loop that goes along with evaporation of
material that we observe as apparent upward motions in the image
sequence. After this initial phase lasting some 10 min, the loops
brighten in a sequence of AIA channels that show progressively cooler
plasma, indicating that this cooling of the loops lasts about one
hour. A comparison to the predictions from a 1D loop model shows
that this observation supports the nanoflare process in (almost) all
aspects. In addition, our observations show that the loops get broader
while getting brighter, which cannot be understood in a 1D model. Movie associated to Fig. 1 is available in electronic form at <A
href="http://www.aanda.org/10.1051/0004-6361/201526912/olm">http://www.aanda.org</A>

---------------------------------------------------------
Title: Self-Absorption in the Solar Transition Region
Authors: Yan, Limei; Peter, Hardi; He, Jiansen; Tian, Hui; Xia,
Lidong; Wang, Linghua; Tu, Chuanyi; Zhang, Lei; Chen, Feng; Barczynski,
Krzysztof
2015ApJ...811...48Y Altcode: 2015arXiv150105706Y
Transient brightenings in the transition region of the Sun have
been studied for decades and are usually related to magnetic
reconnection. Recently, absorption features due to chromospheric
lines have been identified in transition region emission lines raising
the question of the thermal stratification during such reconnection
events. We analyze data from the Interface Region Imaging Spectrograph
in an emerging active region. Here the spectral profiles show clear
self-absorption features in the transition region lines of Si iv. While
some indications existed that opacity effects might play some role
in strong transition region lines, self-absorption has not been
observed before. We show why previous instruments could not observe
such self-absorption features, and discuss some implications of this
observation for the corresponding structure of reconnection events in
the atmosphere. Based on this we speculate that a range of phenomena,
such as explosive events, blinkers or Ellerman bombs, are just different
aspects of the same reconnection event occurring at different heights
in the atmosphere.

---------------------------------------------------------
Title: Using coronal seismology to estimate the magnetic field
strength in a realistic coronal model
Authors: Chen, F.; Peter, H.
2015A&A...581A.137C Altcode: 2015arXiv150800593C
 Aims: Coronal seismology is used extensively to estimate
properties of the corona, e.g. the coronal magnetic field strength
is derived from oscillations observed in coronal loops. We present a
three-dimensional coronal simulation, including a realistic energy
balance in which we observe oscillations of a loop in synthesised
coronal emission. We use these results to test the inversions based on
coronal seismology. Methods: From the simulation of the corona
above an active region, we synthesise extreme ultraviolet emission
from the model corona. From this, we derive maps of line intensity and
Doppler shift providing synthetic data in the same format as obtained
from observations. We fit the (Doppler) oscillation of the loop in the
same fashion as done for observations to derive the oscillation period
and damping time. Results: The loop oscillation seen in our model
is similar to imaging and spectroscopic observations of the Sun. The
velocity disturbance of the kink oscillation shows an oscillation period
of 52.5 s and a damping time of 125 s, which are both consistent with
the ranges of periods and damping times found in observations. Using
standard coronal seismology techniques, we find an average magnetic
field strength of Bkink = 79 G for our loop in the
simulation, while in the loop the field strength drops from roughly
300 G at the coronal base to 50 G at the apex. Using the data from
our simulation, we can infer what the average magnetic field derived
from coronal seismology actually means. It is close to the magnetic
field strength in a constant cross-section flux tube, which would give
the same wave travel time through the loop. Conclusions: Our
model produced a realistic looking loop-dominated corona, and provides
realistic information on the oscillation properties that can be used to
calibrate and better understand the result from coronal seismology. A movie associated with Fig. 1 is available in electronic form at <A
href="http://www.aanda.org/10.1051/0004-6361/201526237/olm">http://www.aanda.org</A>

---------------------------------------------------------
Title: Coronal energy input and dissipation in a solar active region
3D MHD model
Authors: Bourdin, Ph. -A.; Bingert, S.; Peter, H.
2015A&A...580A..72B Altcode: 2015arXiv150703573B
Context. We have conducted a 3D MHD simulation of the solar corona
above an active region (AR) in full scale and high resolution,
which shows coronal loops, and plasma flows within them, similar to
observations. Aims: We want to find the connection between the
photospheric energy input by field-line braiding with the coronal
energy conversion by Ohmic dissipation of induced currents. Methods: To this end we compare the coronal energy input and
dissipation within our simulation domain above different fields of
view, e.g. for a small loops system in the AR core. We also choose
an ensemble of field lines to compare, e.g., the magnetic energy
input to the heating per particle along these field lines. 
Results: We find an enhanced Ohmic dissipation of currents in the
corona above areas that also have enhanced upwards-directed Poynting
flux. These regions coincide with the regions where hot coronal loops
within the AR core are observed. The coronal density plays a role in
estimating the coronal temperature due to the generated heat input. A
minimum flux density of about 200 Gauss is needed in the photosphere
to heat a field line to coronal temperatures of about 1 MK. 
Conclusions: This suggests that the field-line braiding mechanism
provides the coronal energy input and that the Ohmic dissipation of
induced currents dominates the coronal heating mechanism.

---------------------------------------------------------
Title: Division II: Commission 10: Solar Activity
Authors: van Driel-Gesztelyi, Lidia; Scrijver, Karel J.; Klimchuk,
James A.; Charbonneau, Paul; Fletcher, Lyndsay; Hasan, S. Sirajul;
Hudson, Hugh S.; Kusano, Kanya; Mandrini, Cristina H.; Peter, Hardi;
Vršnak, Bojan; Yan, Yihua
2015IAUTB..28..106V Altcode:
The Business Meeting of Commission 10 was held as part of the Business
Meeting of Division II (Sun and Heliosphere), chaired by Valentin
Martínez-Pillet, the President of the Division. The President of
Commission 10 (C10; Solar activity), Lidia van Driel-Gesztelyi, took
the chair for the business meeting of C10. She summarised the activities
of C10 over the triennium and the election of the incoming OC.

---------------------------------------------------------
Title: Thermal Diagnostics with the Atmospheric Imaging Assembly
on board the Solar Dynamics Observatory: A Validated Method for
Differential Emission Measure Inversions
Authors: Cheung, Mark C. M.; Boerner, P.; Schrijver, C. J.; Testa,
P.; Chen, F.; Peter, H.; Malanushenko, A.
2015ApJ...807..143C Altcode: 2015arXiv150403258C
We present a new method for performing differential emission measure
(DEM) inversions on narrow-band EUV images from the Atmospheric
Imaging Assembly (AIA) on board the Solar Dynamics Observatory. The
method yields positive definite DEM solutions by solving a linear
program. This method has been validated against a diverse set of
thermal models of varying complexity and realism. These include
(1) idealized Gaussian DEM distributions, (2) 3D models of NOAA
Active Region 11158 comprising quasi-steady loop atmospheres in a
nonlinear force-free field, and (3) thermodynamic models from a fully
compressible, 3D MHD simulation of active region (AR) corona formation
following magnetic flux emergence. We then present results from the
application of the method to AIA observations of Active Region 11158,
comparing the region's thermal structure on two successive solar
rotations. Additionally, we show how the DEM inversion method can be
adapted to simultaneously invert AIA and Hinode X-ray Telescope data,
and how supplementing AIA data with the latter improves the inversion
result. The speed of the method allows for routine production of DEM
maps, thus facilitating science studies that require tracking of the
thermal structure of the solar corona in time and space.

---------------------------------------------------------
Title: Magnetic jam in the corona of the Sun
Authors: Chen, F.; Peter, H.; Bingert, S.; Cheung, M. C. M.
2015NatPh..11..492C Altcode: 2015arXiv150501174C
The outer solar atmosphere, the corona, contains plasma at temperatures
of more than a million kelvin--more than 100 times hotter than
the solar surface. How this gas is heated is a fundamental question
tightly interwoven with the structure of the magnetic field. Together
this governs the evolution of coronal loops, the basic building block
prominently seen in X-rays and extreme ultraviolet (EUV) images. Here
we present numerical experiments accounting for both the evolving
three-dimensional structure of the magnetic field and its complex
interaction with the plasma. Although the magnetic field continuously
expands as new magnetic flux emerges through the solar surface, plasma
on successive field lines is heated in succession, giving the illusion
that an EUV loop remains roughly at the same place. For each snapshot
the EUV images outline the magnetic field. However, in contrast to
the traditional view, the temporal evolution of the magnetic field
and the EUV loops can be quite different. This indicates that the
thermal and the magnetic evolution in the outer atmosphere of a cool
star should be treated together, and should not be simply separated
as predominantly done so far.

---------------------------------------------------------
Title: What can large-scale magnetohydrodynamic numerical experiments
tell us about coronal heating?
Authors: Peter, H.
2015RSPTA.37350055P Altcode:
The upper atmosphere of the Sun is governed by the complex structure
of the magnetic field. This controls the heating of the coronal
plasma to over a million kelvin. Numerical experiments in the form
of three-dimensional magnetohydrodynamic simulations are used to
investigate the intimate interaction between magnetic field and
plasma. These models allow one to synthesize the coronal emission just
as it would be observed by real solar instrumentation. Large-scale
models encompassing a whole active region form evolving coronal loops
with properties similar to those seen in extreme ultraviolet light from
the Sun, and reproduce a number of average observed quantities. This
suggests that the spatial and temporal distributions of the heating as
well as the energy distribution of individual heat deposition events
in the model are a good representation of the real Sun. This provides
evidence that the braiding of fieldlines through magneto-convective
motions in the photosphere is a good concept to heat the upper
atmosphere of the Sun.

---------------------------------------------------------
Title: Coronal Heating By the Interaction between Emerging Active
Regions and the Quiet Sun Observed By the Solar Dynamics Observatory
Authors: Zhang, Jun; Zhang, Bin; Li, Ting; Yang, Shuhong; Zhang,
Yuzong; Li, Leping; Chen, Feng; Peter, Hardi
2015ApJ...799L..27Z Altcode:
The question of what heats the solar corona remains one of the most
important puzzles in solar physics and astrophysics. Here we report
Solar Dynamics Observatory Atmospheric Imaging Assembly observations
of coronal heating by the interaction between emerging active regions
(EARs) and the surrounding quiet Sun (QS). The EARs continuously
interact with the surrounding QS, resulting in dark ribbons which appear
at the boundary of the EARs and the QS. The dark ribbons visible in
extreme-ultraviolet wavelengths propagate away from the EARs with speeds
of a few km s-1. The regions swept by the dark ribbons are
brightening afterward, with the mean temperature increasing by one
quarter. The observational findings demonstrate that uninterrupted
magnetic reconnection between EARs and the QS occurs. When the EARs
develop, the reconnection continues. The dark ribbons may be the
track of the interface between the reconnected magnetic fields and the
undisturbed QS’s fields. The propagating speed of the dark ribbons
reflects the reconnection rate and is consistent with our numerical
simulation. A long-term coronal heating which occurs in turn from
nearby the EARs to far away from the EARs is proposed.

---------------------------------------------------------
Title: Numerical Simulation of Fast-mode Magnetosonic Waves Excited
by Plasmoid Ejections in the Solar Corona
Authors: Yang, Liping; Zhang, Lei; He, Jiansen; Peter, Hardi; Tu,
Chuanyi; Wang, Linghua; Zhang, Shaohua; Feng, Xueshang
2015ApJ...800..111Y Altcode:
The Atmospheric Imaging Assembly instrument on board the Solar Dynamics
Observatory has directly imaged the fast-propagating magnetosonic
waves (FMWs) successively propagating outward along coronal magnetic
funnels. In this study we perform a numerical investigation of
the excitation of FMWs in the interchange reconnection scenario,
with footpoint shearing flow being used to energize the system and
drive the reconnection. The modeling results show that as a result of
magnetic reconnection, the plasma in the current sheet is heated up by
Joule dissipation to ~10 MK and is ejected rapidly, developing the hot
outflows. Meanwhile, the current sheet is torn into plasmoids, which
are shot quickly both upward and downward. When the plasmoids reach the
outflow regions, they impact and collide with the ambient magnetic field
there, which consecutively launches FMWs. The FMWs propagate outward
divergently away from the impact regions, with a phase speed of the
Alfvén speed of ~1000 km s-1. In the k - ω diagram of the
Fourier wave power, the FMWs display a broad frequency distribution with
a straight ridge that represents the dispersion relation. With the WKB
approximation, at the distance of 15 Mm from the wave source region,
we estimate the energy flux of FMWs to be E ~ 7.0 × 106
erg cm-2 s-1, which is ~50 times smaller than the
energy flux related to the tube-channeled reconnection outflow. These
simulation results indicate that energetically and dynamically the
outflow is far more important than the waves.

---------------------------------------------------------
Title: Why is Non-Thermal Line Broadening of Spectral Lines in the
Lower Transition Region of the Sun Independent of Spatial Resolution?
Authors: De Pontieu, B.; McIntosh, S.; Martinez-Sykora, J.; Peter,
H.; Pereira, T. M. D.
2015ApJ...799L..12D Altcode: 2017arXiv171006807D
Spectral observations of the solar transition region (TR) and
corona show broadening of spectral lines beyond what is expected
from thermal and instrumental broadening. The remaining non-thermal
broadening is significant (5-30 km s-1) and correlated with
intensity. Here we study spectra of the TR Si iv 1403 Å line obtained
at high resolution with the Interface Region Imaging Spectrograph
(IRIS). We find that the large improvement in spatial resolution
(0.″33) of IRIS compared to previous spectrographs (2″) does
not resolve the non-thermal line broadening which, in most regions,
remains at pre-IRIS levels of about 20 km s-1. This
invariance to spatial resolution indicates that the processes behind
the broadening occur along the line-of-sight (LOS) and/or on spatial
scales (perpendicular to the LOS) smaller than 250 km. Both effects
appear to play a role. Comparison with IRIS chromospheric observations
shows that, in regions where the LOS is more parallel to the field,
magneto-acoustic shocks driven from below impact the TR and can lead
to significant non-thermal line broadening. This scenario is supported
by MHD simulations. While these do not show enough non-thermal line
broadening, they do reproduce the long-known puzzling correlation
between non-thermal line broadening and intensity. This correlation
is caused by the shocks, but only if non-equilibrium ionization is
taken into account. In regions where the LOS is more perpendicular
to the field, the prevalence of small-scale twist is likely to play
a significant role in explaining the invariance and correlation with
intensity.

---------------------------------------------------------
Title: Coronal loops above an active region: Observation versus model
Authors: Bourdin, Philippe-A.; Bingert, Sven; Peter, Hardi
2014PASJ...66S...7B Altcode: 2014PASJ..tmp..113B; 2014arXiv1410.1216B
We conducted a high-resolution numerical simulation of the solar corona
above a stable active region. The aim is to test the field line braiding
mechanism for a sufficient coronal energy input. We also check the
applicability of scaling laws for coronal loop properties like the
temperature and density. Our 3D MHD model is driven from below by
Hinode observations of the photosphere, in particular a high-cadence
time series of line-of-sight magnetograms and horizontal velocities
derived from the magnetograms. This driving applies stress to the
magnetic field and thereby delivers magnetic energy into the corona,
where currents are induced that heat the coronal plasma by Ohmic
dissipation. We compute synthetic coronal emission that we directly
compare to coronal observations of the same active region taken by
Hinode. In the model, coronal loops form at the same places as they
are found in coronal observations. Even the shapes of the synthetic
loops in 3D space match those found from a stereoscopic reconstruction
based on STEREO spacecraft data. Some loops turn out to be slightly
over-dense in the model, as expected from observations. This shows that
the spatial and temporal distribution of the Ohmic heating produces
the structure and dynamics of a coronal loops system close to what is
found in observations.

---------------------------------------------------------
Title: Why Is Non-thermal Line Broadening of Lower Transition Region
Lines Independent of Spatial Resolution?
Authors: De Pontieu, B.; Mcintosh, S. W.; Martínez-Sykora, J.; Peter,
H.; Pereira, T. M. D.
2014AGUFMSH51C4175D Altcode:
Spectral observations of the solar transition region (TR) and
corona typically show broadening of the spectral lines beyond what
is expected from thermal and instrumental broadening. The remaining
non-thermal broadening is significant (10-30 km/s), correlated with
the intensity, and has been attributed to waves, macro and micro
turbulence, nanoflares, etc... Here we study spectra of the low
TR Si IV 1403 Angstrom line obtained at high spatial and spectral
resolution with the Interface Region Imaging Spectrograph (IRIS). We
find that the large improvement in spatial resolution (0.33 arcsec)
of IRIS compared to previous spectrographs (2 arcsec) does not resolve
the non-thermal line broadening which remains at pre-IRIS levels of
20 km/s. This surprising invariance to spatial resolution indicates
that the physical processes behind the non-thermal line broadening
either occur along the line-of-sight (LOS) and/or on spatial scales
(perpendicular to the LOS) smaller than 250 km. Both effects appear
to play a role. Comparison with IRIS chromospheric observations
shows that, in regions where the LOS is more parallel to the field,
magneto-acoustic shocks driven from below impact the low TR leading to
strong non-thermal line broadening from line-of-sight integration across
the shock at the time of impact. This scenario is confirmed by advanced
MHD simulations. In regions where the LOS is perpendicular to the field,
the prevalence of small-scale twist is likely to play a significant
role in explaining the invariance and the correlation with intensity.

---------------------------------------------------------
Title: Planck 2013 results
Authors: Alves, Joao; Bertout, Claude; Combes, Françoise; Ferrara,
Andrea; Forveille, Thierry; Guillot, Tristan; Napiwotzki, Ralf; Peter,
Hardi; Shore, Steve; Tolstoy, Eline; Walmsley, Malcolm
2014A&A...571E...1A Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Hot explosions in the cool atmosphere of the Sun
Authors: Peter, H.; Tian, H.; Curdt, W.; Schmit, D.; Innes, D.;
De Pontieu, B.; Lemen, J.; Title, A.; Boerner, P.; Hurlburt, N.;
Tarbell, T. D.; Wuelser, J. P.; Martínez-Sykora, Juan; Kleint,
L.; Golub, L.; McKillop, S.; Reeves, K. K.; Saar, S.; Testa, P.;
Kankelborg, C.; Jaeggli, S.; Carlsson, M.; Hansteen, V.
2014Sci...346C.315P Altcode: 2014arXiv1410.5842P
The solar atmosphere was traditionally represented with a simple
one-dimensional model. Over the past few decades, this paradigm shifted
for the chromosphere and corona that constitute the outer atmosphere,
which is now considered a dynamic structured envelope. Recent
observations by the Interface Region Imaging Spectrograph (IRIS) reveal
that it is difficult to determine what is up and down, even in the cool
6000-kelvin photosphere just above the solar surface: This region hosts
pockets of hot plasma transiently heated to almost 100,000 kelvin. The
energy to heat and accelerate the plasma requires a considerable
fraction of the energy from flares, the largest solar disruptions. These
IRIS observations not only confirm that the photosphere is more complex
than conventionally thought, but also provide insight into the energy
conversion in the process of magnetic reconnection.

---------------------------------------------------------
Title: Conversion from mutual helicity to self-helicity observed
with IRIS
Authors: Li, L. P.; Peter, H.; Chen, F.; Zhang, J.
2014A&A...570A..93L Altcode: 2014arXiv1410.5597L
Context. In the upper atmosphere of the Sun observations show
convincing evidence for crossing and twisted structures, which are
interpreted as mutual helicity and self-helicity. Aims: We
use observations with the new Interface Region Imaging Spectrograph
(IRIS) to show the conversion of mutual helicity into self-helicity
in coronal structures on the Sun. Methods: Using far UV spectra
and slit-jaw images from IRIS and coronal images and magnetograms from
SDO, we investigated the evolution of two crossing loops in an active
region, in particular, the properties of the Si IV line profile in
cool loops. Results: In the early stage two cool loops cross
each other and accordingly have mutual helicity. The Doppler shifts in
the loops indicate that they wind around each other. As a consequence,
near the crossing point of the loops (interchange) reconnection sets
in, which heats the plasma. This is consistent with the observed
increase of the line width and of the appearance of the loops at
higher temperatures. After this interaction, the two new loops run in
parallel, and in one of them shows a clear spectral tilt of the Si
IV line profile. This is indicative of a helical (twisting) motion,
which is the same as to say that the loop has self-helicity. 
Conclusions: The high spatial and spectral resolution of IRIS allowed
us to see the conversion of mutual helicity to self-helicity in
the (interchange) reconnection of two loops. This is observational
evidence for earlier theoretical speculations. Movie associated
with Fig. 1 and Appendix A are available in electronic form at <A
href="http://www.aanda.org/10.1051/0004-6361/201424377/olm">http://www.aanda.org</A>

---------------------------------------------------------
Title: Prevalence of small-scale jets from the networks of the solar
transition region and chromosphere
Authors: Tian, H.; DeLuca, E. E.; Cranmer, S. R.; De Pontieu, B.;
Peter, H.; Martínez-Sykora, J.; Golub, L.; McKillop, S.; Reeves,
K. K.; Miralles, M. P.; McCauley, P.; Saar, S.; Testa, P.; Weber,
M.; Murphy, N.; Lemen, J.; Title, A.; Boerner, P.; Hurlburt, N.;
Tarbell, T. D.; Wuelser, J. P.; Kleint, L.; Kankelborg, C.; Jaeggli,
S.; Carlsson, M.; Hansteen, V.; McIntosh, S. W.
2014Sci...346A.315T Altcode: 2014arXiv1410.6143T
As the interface between the Sun’s photosphere and corona, the
chromosphere and transition region play a key role in the formation and
acceleration of the solar wind. Observations from the Interface Region
Imaging Spectrograph reveal the prevalence of intermittent small-scale
jets with speeds of 80 to 250 kilometers per second from the narrow
bright network lanes of this interface region. These jets have lifetimes
of 20 to 80 seconds and widths of ≤300 kilometers. They originate from
small-scale bright regions, often preceded by footpoint brightenings
and accompanied by transverse waves with amplitudes of ~20 kilometers
per second. Many jets reach temperatures of at least ~105
kelvin and constitute an important element of the transition region
structures. They are likely an intermittent but persistent source of
mass and energy for the solar wind.

---------------------------------------------------------
Title: Molecular absorption in transition region spectral lines
Authors: Schmit, D. J.; Innes, D.; Ayres, T.; Peter, H.; Curdt, W.;
Jaeggli, S.
2014A&A...569L...7S Altcode: 2014arXiv1409.1702S
 Aims: We present observations from the Interface Region Imaging
Spectrograph (IRIS) of absorption features from a multitude of cool
atomic and molecular lines within the profiles of Si IV transition
region lines. Many of these spectral lines have not previously
been detected in solar spectra. Methods: We examined spectra
taken from deep exposures of plage on 12 October 2013. We observed
unique absorption spectra over a magnetic element which is bright in
transition region line emission and the ultraviolet continuum. We
compared the absorption spectra with emission spectra that is
likely related to fluorescence. Results: The absorption
features require a population of sub-5000 K plasma to exist above
the transition region. This peculiar stratification is an extreme
deviation from the canonical structure of the chromosphere-corona
boundary. The cool material is not associated with a filament or
discernible coronal rain. This suggests that molecules may form in
the upper solar atmosphere on small spatial scales and introduces a
new complexity into our understanding of solar thermal structure. It
lends credence to previous numerical studies that found evidence
for elevated pockets of cool gas in the chromosphere. Movies
associated to Figs. 1 and 2 are available in electronic form at <A
href="http://www.aanda.org/10.1051/0004-6361/201424432/olm">http://www.aanda.org</A>

---------------------------------------------------------
Title: Observations of Subarcsecond Bright Dots in the Transition
Region above Sunspots with the Interface Region Imaging Spectrograph
Authors: Tian, H.; Kleint, L.; Peter, H.; Weber, M.; Testa, P.;
DeLuca, E.; Golub, L.; Schanche, N.
2014ApJ...790L..29T Altcode: 2014arXiv1407.1060T
Observations with the Interface Region Imaging Spectrograph (IRIS)
have revealed numerous sub-arcsecond bright dots in the transition
region above sunspots. These bright dots are seen in the 1400 Å and
1330 Å slit-jaw images. They are clearly present in all sunspots we
investigated, mostly in the penumbrae, but also occasionally in some
umbrae and light bridges. The bright dots in the penumbrae typically
appear slightly elongated, with the two dimensions being 300-600 km and
250-450 km, respectively. The long sides of these dots are often nearly
parallel to the bright filamentary structures in the penumbrae but
sometimes clearly deviate from the radial direction. Their lifetimes
are mostly less than one minute, although some dots last for a few
minutes or even longer. Their intensities are often a few times stronger
than the intensities of the surrounding environment in the slit-jaw
images. About half of the bright dots show apparent movement with
speeds of ~10-40 km s-1 in the radial direction. Spectra of
a few bright dots were obtained and the Si IV 1402.77 Å line profiles
in these dots are significantly broadened. The line intensity can be
enhanced by one to two orders of magnitude. Some relatively bright
and long-lasting dots are also observed in several passbands of the
Atmospheric Imaging Assembly onboard the Solar Dynamics Observatory,
and they appear to be located at the bases of loop-like structures. Many
of these bright dots are likely associated with small-scale energy
release events at the transition region footpoints of magnetic loops.

---------------------------------------------------------
Title: Discovery of the Sun's million-degree hot corona
Authors: Peter, Hardi; Dwivedi, Bhola N.
2014FrASS...1....2P Altcode: 2014FrASS...1....2H
As time goes by, discoveries become common knowledge, and often the
person who first changed a paradigm gets forgotten. One such case is the
discovery that the Sun's corona is a million degrees hot - much hotter
than its surface. While we still work on solving how the Sun heats the
corona, the name of the discoverer seems to be forgotten. Instead,
other people get the credit who contributed important pieces to the
puzzle, but the person who solved this puzzle was someone else. In this
historical note we show that this credit should go to Hannes Alfvén.

---------------------------------------------------------
Title: Exploring the Components of IRIS Spectra: More Shift, Twist,
and Sway Than Shake, Rattle, and Roll
Authors: McIntosh, Scott W.; De Pontieu, Bart; Peter, Hardi
2014AAS...22431304M Altcode:
The beautifully rich spectra of the IRIS spacecraft offer an
unparalleled avenue to explore the mass and energy transport processes
which sustain the Sun's outer atmosphere. In this presentation we will
look in detail at the various components of the spectrographic data
and place them in context with Slit-Jaw imaging and EUV imaging from
SDO/AIA. We will show that the line profiles display many intriguing
features including the clear signatures of strong line-of-sight flows
(in all magnetized regions) that are almost always accompanied by
transverse and torsional motions at the finest resolvable scales. We
will demonstrate that many interesting relationships develop when
studying the spectra statistically. These relationships indicate IRIS's
ability to spectrally and temporally resolve the energetic processes
affecting the outer solar atmosphere.

---------------------------------------------------------
Title: A model for the formation of the active region corona driven
by magnetic flux emergence
Authors: Chen, F.; Peter, H.; Bingert, S.; Cheung, M. C. M.
2014A&A...564A..12C Altcode: 2014arXiv1402.5343C
 Aims: We present the first model that couples the formation of
the corona of a solar active region to a model of the emergence of
a sunspot pair. This allows us to study when, where, and why active
region loops form, and how they evolve. Methods: We use a 3D
radiation magnetohydrodynamics (MHD) simulation of the emergence of an
active region through the upper convection zone and the photosphere as
a lower boundary for a 3D MHD coronal model. The coronal model accounts
for the braiding of the magnetic fieldlines, which induces currents in
the corona to heat up the plasma. We synthesize the coronal emission
for a direct comparison to observations. Starting with a basically
field-free atmosphere we follow the filling of the corona with magnetic
field and plasma. Results: Numerous individually identifiable
hot coronal loops form, and reach temperatures well above 1 MK with
densities comparable to observations. The footpoints of these loops
are found where small patches of magnetic flux concentrations move
into the sunspots. The loop formation is triggered by an increase in
upward-directed Poynting flux at their footpoints in the photosphere. In
the synthesized extreme ultraviolet (EUV) emission these loops develop
within a few minutes. The first EUV loop appears as a thin tube, then
rises and expands significantly in the horizontal direction. Later,
the spatially inhomogeneous heat input leads to a fragmented system
of multiple loops or strands in a growing envelope. Animation
associated with Fig. 2 is available in electronic form at <A
href="http://www.aanda.org/10.1051/0004-6361/201322859/olm">http://www.aanda.org</A>

---------------------------------------------------------
Title: MASC: Magnetic Activity of the Solar Corona
Authors: Auchere, Frederic; Fineschi, Silvano; Gan, Weiqun; Peter,
Hardi; Vial, Jean-Claude; Zhukov, Andrei; Parenti, Susanna; Li, Hui;
Romoli, Marco
2014cosp...40E.149A Altcode:
We present MASC, an innovative payload designed to explore the magnetic
activity of the solar corona. It is composed of three complementary
instruments: a Hard-X-ray spectrometer, a UV / EUV imager, and a Visible
Light / UV polarimetric coronagraph able to measure the coronal magnetic
field. The solar corona is structured in magnetically closed and
open structures from which slow and fast solar winds are respectively
released. In spite of much progress brought by two decades of almost
uninterrupted observations from several space missions, the sources and
acceleration mechanisms of both types are still not understood. This
continuous expansion of the solar atmosphere is disturbed by sporadic
but frequent and violent events. Coronal mass ejections (CMEs) are
large-scale massive eruptions of magnetic structures out of the corona,
while solar flares trace the sudden heating of coronal plasma and the
acceleration of electrons and ions to high, sometimes relativistic,
energies. Both phenomena are most probably driven by instabilities
of the magnetic field in the corona. The relations between flares
and CMEs are still not understood in terms of initiation and energy
partition between large-scale motions, small-scale heating and
particle acceleration. The initiation is probably related to magnetic
reconnection which itself results magnetic topological changes due to
e.g. flux emergence, footpoints motions, etc. Acceleration and heating
are also strongly coupled since the atmospheric heating is thought to
result from the impact of accelerated particles. The measurement of
both physical processes and their outputs is consequently of major
importance. However, despite its fundamental importance as a driver
for the physics of the Sun and of the heliosphere, the magnetic field
of our star’s outer atmosphere remains poorly understood. This
is due in large part to the fact that the magnetic field is a very
difficult quantity to measure. Our knowledge of its strength and
orientation is primarily based on extrapolations from photospheric
observations, not from direct measurements. These extrapolations
require strong assumptions on critical but unobserved quantities and
thus fail to accurately reproduce the complex topologies inferred
from remote-sensing observations of coronal structures in white
light, EUV, and X-rays. Direct measurements of the coronal magnetic
field are also clearly identified by the international heliophysics
community as a key element susceptible to lead to major breakthroughs
in the understanding of our star. MASC is thus designed to answer
the following top-level scientific questions: 1. What is the global
magnetic field configuration in the corona? 2. What is the role of
the magnetic field in the triggering of flares and CMEs? 3. What is
the role of the magnetic field in the acceleration mechanisms of the
solar winds? 4. What is the energy spectrum and in particular what are
the highest energies to which charged particles can be accelerated in
the solar corona? MASC will address these fundamental questions with
a suite of instruments composed of an X-ray spectrometer, a UV / EUV
imager, and a coronagraph working in the visible and at Lyman alpha. The
spectrometer will provide information on the energetics of solar flares,
in particular at very high energies of accelerated particles. The
UV / EUV imager will provide constraints on the temperature of the
flaring and non-flaring corona. The coronagraph will provide the number
density of free electrons in the corona, maps of the outflow velocity
of neutral hydrogen, and measurements of the coronal magnetic field,
via the Hanle effect. These measurements will be performed at all
steps of the flare-CME processes, thus providing a detailed picture
of the solar coronal dynamics in the quiet and eruptive periods.

---------------------------------------------------------
Title: Magnetic Field Diagnostics and Spatio-Temporal Variability
of the Solar Transition Region
Authors: Peter, H.
2013SoPh..288..531P Altcode: 2013arXiv1303.1825P
Magnetic field diagnostics of the transition region from the
chromosphere to the corona faces us with the problem that one has to
apply extreme-ultraviolet (EUV) spectro-polarimetry. While for the
coronal diagnostics techniques already exist in the form of infrared
coronagraphy above the limb and radio observations on the disk, one
has to investigate EUV observations for the transition region. However,
so far the success of such observations has been limited, but various
current projects aim to obtain spectro-polarimetric data in the
extreme UV in the near future. Therefore it is timely to study the
polarimetric signals we can expect from these observations through
realistic forward modeling.

---------------------------------------------------------
Title: Numerical Simulations of Chromospheric Anemone Jets Associated
with Moving Magnetic Features
Authors: Yang, Liping; He, Jiansen; Peter, Hardi; Tu, Chuanyi; Zhang,
Lei; Feng, Xueshang; Zhang, Shaohua
2013ApJ...777...16Y Altcode:
Observations with the space-based solar observatory Hinode show
that small-scale magnetic structures in the photosphere are found
to be associated with a particular class of jets of plasma in the
chromosphere called anemone jets. The goal of our study is to conduct
a numerical experiment of such chromospheric anemone jets related to
the moving magnetic features (MMFs). We construct a 2.5 dimensional
numerical MHD model to describe the process of magnetic reconnection
between the MMFs and the pre-existing ambient magnetic field, which
is driven by the horizontal motion of the magnetic structure in the
photosphere. We include thermal conduction parallel to the magnetic
field and optically thin radiative losses in the corona to account
for a self-consistent description of the evaporation process during
the heating of the plasma due to the reconnection process. The motion
of the MMFs leads to the expected jet and our numerical results can
reproduce many observed characteristics of chromospheric anemone
jets, topologically and quantitatively. As a result of the tearing
instability, plasmoids are generated in the reconnection process that
are consistent with the observed bright moving blobs in the anemone
jets. An increase in the thermal pressure at the base of the jet is
also driven by the reconnection, which induces a train of slow-mode
shocks propagating upward. These shocks are a secondary effect, and
only modulate the outflow of the anemone jet. The jet itself is driven
by the energy input due to the reconnection of the MMFs and the ambient
magnetic field.

---------------------------------------------------------
Title: Temperature dependence of ultraviolet line parameters in
network and internetwork regions of the quiet Sun and coronal holes
Authors: Wang, X.; McIntosh, S. W.; Curdt, W.; Tian, H.; Peter, H.;
Xia, L. -D.
2013A&A...557A.126W Altcode:
 Aims: We study the temperature dependence of the average Doppler
shift and the non-thermal line width in network and internetwork
regions for both the quiet Sun (QS) and the coronal hole (CH), by
using observations of the Solar Ultraviolet Measurements of Emitted
Radiation instrument onboard the Solar and Heliospheric Observatory
spacecraft. Methods: We obtain the average Doppler shift and
non-thermal line width in the network regions of QS, internetwork
regions of QS, network regions of CH, and internetwork regions of CH by
applying a single-Gaussian fit to the line profiles averaged in each
of the four regions. The formation temperatures of the lines we use
cover the range from 104 to 1.2 × 106 K. Two
simple scenarios are proposed to explain the temperature dependence of
the line parameters in the network regions. In one of the scenarios,
the spectral line consists of three components: a rapid, weak upflow
generated in the lower atmosphere, a nearly static background, and
a slow cooling downflow. In the other scenario, there are just two
components, which include a bright core component and a faint wide tail
one. Results: An enhancement of the Doppler shift magnitude
and the non-thermal line width in network regions compared to the
internetwork regions is reported. We also report that most transition
region lines are less redshifted (by 0-8 km s-1) and broader
(by 0-5 km s-1) in CH compared to the counterparts of QS. In
internetwork regions, the difference in the Doppler shifts between the
coronal hole and the QS is slightly smaller, especially for the lines
with formation temperatures lower than 2 × 105 K. And the
two simple scenarios can reproduce the variation in the line parameters
with the temperature very well. Conclusions: Our results suggest
that the physical processes in network and internetwork regions are
different and that one needs to separate network and internetwork when
discussing dynamics and physical properties of the solar atmosphere. The
agreement between the results of the observation and our scenarios
suggests that the temperature dependence of Doppler shifts and line
widths might be caused by the different relative contributions of the
three components at different temperatures. The results may shed new
light on our understanding of the complex chromosphere-corona mass
cycle. However, the existing observational results do not allow us to
distinguish between the two scenarios. At this stage, a high-resolution
instrument Interface Region Imaging Spectrograph is highly desirable.

---------------------------------------------------------
Title: Structure of solar coronal loops: from miniature to large-scale
Authors: Peter, H.; Bingert, S.; Klimchuk, J. A.; de Forest, C.;
Cirtain, J. W.; Golub, L.; Winebarger, A. R.; Kobayashi, K.; Korreck,
K. E.
2013A&A...556A.104P Altcode: 2013arXiv1306.4685P
 Aims: We use new data from the High-resolution Coronal Imager
(Hi-C) with its unprecedented spatial resolution of the solar corona
to investigate the structure of coronal loops down to 0.2”. 
Methods: During a rocket flight, Hi-C provided images of the solar
corona in a wavelength band around 193 Å that is dominated by emission
from Fe xii showing plasma at temperatures around 1.5 MK. We analyze
part of the Hi-C field-of-view to study the smallest coronal loops
observed so far and search for the possible substructuring of larger
loops. Results: We find tiny 1.5 MK loop-like structures that
we interpret as miniature coronal loops. Their coronal segments above
the chromosphere have a length of only about 1 Mm and a thickness of
less than 200 km. They could be interpreted as the coronal signature
of small flux tubes breaking through the photosphere with a footpoint
distance corresponding to the diameter of a cell of granulation. We
find that loops that are longer than 50 Mm have diameters of about 2”
or 1.5 Mm, which is consistent with previous observations. However, Hi-C
really resolves these loops with some 20 pixels across the loop. Even
at this greatly improved spatial resolution, the large loops seem to
have no visible substructure. Instead they show a smooth variation in
cross-section. Conclusions: That the large coronal loops do not
show a substructure on the spatial scale of 0.1” per pixel implies that
either the densities and temperatures are smoothly varying across these
loops or it places an upper limit on the diameter of the strands the
loops might be composed of. We estimate that strands that compose the
2” thick loop would have to be thinner than 15 km. The miniature loops
we find for the first time pose a challenge to be properly understood
through modeling. Appendices are available in electronic form at
<A href="http://www.aanda.org">http://www.aanda.org</A>

---------------------------------------------------------
Title: VizieR Online Data Catalog: 3D-MHD model of a solar active
region corona (Bourdin+, 2013)
Authors: Bourdin, P. -A.; Bingert, S.; Peter, H.
2013yCat..35550123B Altcode: 2013yCat..35559123B
Parameter and setup files used for a 3D-MHD simulation with the
Pencil Code. The parameters are needed to reproduce the simulation,
while the setup files show which modules of the Pencil Code were
used to conduct the simulation. The parameters file are in the
state as used at the end of the simulation, when the analysis was
performed. With the logfile, one can reconstruct the state at any
time during the simulation run (this applies to "run.in"). The
code revision logfile indicates which code revision was used when,
where only changes in the configuration are listed together with the
full initial and final configuration. All *.in files are in
Fortran Namelist format. The *.in and *.local files are all ready
to be used with Pencil Code. The Pencil Code can be obtained at:
http://pencil-code.nordita.org/ (7 data files).

---------------------------------------------------------
Title: Observationally driven 3D magnetohydrodynamics model of the
solar corona above an active region
Authors: Bourdin, Ph. -A.; Bingert, S.; Peter, H.
2013A&A...555A.123B Altcode: 2013arXiv1305.5693B
Context. Aims: The goal is to employ a 3D magnetohydrodynamics
(MHD) model including spectral synthesis to model the corona in an
observed solar active region. This will allow us to judge the merits
of the coronal heating mechanism built into the 3D model. 
Methods: Photospheric observations of the magnetic field and horizontal
velocities in an active region are used to drive our coronal simulation
from the bottom. The currents induced by this heat the corona through
Ohmic dissipation. Heat conduction redistributes the energy that is
lost in the end through optically thin radiation. Based on the MHD
model, we synthesized profiles of coronal emission lines which can
be directly compared to actual coronal observations of the very same
active region. Results: In the synthesized model data we find
hot coronal loops which host siphon flows or which expand and lose mass
through draining. These synthesized loops are at the same location as
and show similar dynamics in terms of Doppler shifts to the observed
structures. This match is shown through a comparison with Hinode data as
well as with 3D stereoscopic reconstructions of data from STEREO. 
Conclusions: The considerable match to the actual observations shows
that the field-line braiding mechanism leading to the energy input
in our corona provides the proper distribution of heat input in space
and time. From this we conclude that in an active region the field-line
braiding is the dominant heating process, at least at the spatial scales
available to current observations. Parameters and simulation
log-files are only available at the CDS via anonymous ftp to <A
href="http://cdsarc.u-strasbg.fr">http://cdsarc.u-strasbg.fr</A>
(ftp://130.79.128.5) or via <A
href="http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/555/A123">http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/555/A123</A>

---------------------------------------------------------
Title: Injection of Plasma into the Nascent Solar Wind via
Reconnection Driven by Supergranular Advection
Authors: Yang, Liping; He, Jiansen; Peter, Hardi; Tu, Chuanyi; Chen,
Wenlei; Zhang, Lei; Marsch, Eckart; Wang, Linghua; Feng, Xueshang;
Yan, Limei
2013ApJ...770....6Y Altcode:
To understand the origin of the solar wind is one of the key research
topics in modern solar and heliospheric physics. Previous solar wind
models assumed that plasma flows outward along a steady magnetic
flux tube that reaches continuously from the photosphere through the
chromosphere into the corona. Inspired by more recent comprehensive
observations, Tu et al. suggested a new scenario for the origin
of the solar wind, in which it flows out in a magnetically open
coronal funnel and mass is provided to the funnel by small-scale side
loops. Thus mass is supplied by means of magnetic reconnection that
is driven by supergranular convection. To validate this scenario and
simulate the processes involved, a 2.5 dimensional (2.5D) numerical
MHD model is established in the present paper. In our simulation a
closed loop moves toward an open funnel, which has opposite polarity
and is located at the edge of a supergranulation cell, and magnetic
reconnection is triggered and continues while gradually opening up
one half of the closed loop. Its other half connects with the root
of the open funnel and forms a new closed loop which is submerged by
a reconnection plasma stream flowing downward. Thus we find that the
outflowing plasma in the newly reconnected funnel originates not only
from the upward reconnection flow but also from the high-pressure leg
of the originally closed loop. This implies an efficient supply of mass
from the dense loop to the dilute funnel. The mass flux of the outflow
released from the funnel considered in our study is calculated to be
appropriate for providing the mass flux at the coronal base of the
solar wind, though additional heating and acceleration mechanisms are
necessary to keep the velocity at the higher location. Our numerical
model demonstrates that in the funnel the mass for the solar wind may
be supplied from adjacent closed loops via magnetic reconnection as
well as directly from the footpoints of open funnels.

---------------------------------------------------------
Title: Parameterisation of coronal heating: spatial distribution
and observable consequences
Authors: van Wettum, T.; Bingert, S.; Peter, H.
2013A&A...554A..39V Altcode: 2013arXiv1303.1371V
 Aims: We investigate the difference in the spatial distribution
of the energy input for parameterisations of different mechanisms
to heat the corona of the Sun and possible impacts on the coronal
emission. Methods: We use a 3D magneto-hydrodynamic (MHD) model
of a solar active region as a reference and compare the Ohmic-type
heating in this model to parameterisations for alternating current (AC)
and direct current (DC) heating models; in particular, we use Alfvén
wave and MHD turbulence heating. We extract the quantities needed for
these two parameterisations from the reference model and investigate the
spatial distribution of the heat input in all three cases, globally and
along individual field lines. To study differences in the resulting
coronal emission, we employ 1D loop models with a prescribed heat
input based on the heating rate we extracted along a bundle of field
lines. Results: On average, all heating implementations show
a rough drop of the heating rate with height. This also holds for
individual field lines. While all mechanisms show a concentration of
the energy input towards the low parts of the atmosphere, for individual
field lines the concentration towards the foot points is much stronger
for the DC mechanisms than for the Alfvén wave AC case. In contrast,
the AC model gives a stronger concentration of the emission towards the
foot points. This is because the more homogeneous distribution of the
energy input leads to higher coronal temperatures and a more extended
transition region. Conclusions: The significant difference
in the concentration of the heat input towards the foot points for
the AC and DC mechanisms and the pointed difference in the spatial
distribution of the coronal emission for these cases show that the two
mechanisms should be discriminable by observations. Before drawing
final conclusions, these parameterisations should be implemented in
new 3D models in a more self-consistent way.

---------------------------------------------------------
Title: Evolution of the Fine Structure of Magnetic Fields in the
Quiet Sun: Observations from Sunrise/IMaX and Extrapolations
Authors: Wiegelmann, Thomas; Solanki, Sami; Borrero, Juan; Peter,
Hardi; Sunrise Team
2013EGUGA..15.5251W Altcode:
Observations with the balloon-borne Sunrise/ Imaging Magnetograph
eXperiment (IMaX) provide high spatial resolution (roughly 100 km at
disk center) measurements of the magnetic field in the photosphere of
the quiet Sun. To investigate the magnetic structure of the chromosphere
and corona, we extrapolate these photospheric measurements into
the upper solar atmosphere and analyse a 22-minute long time series
with a cadence of 33 seconds. Using the extrapolated magnetic-field
lines as tracer, we investigate temporal evolution of the magnetic
connectivity in the quiet Sun's atmosphere. The majority of magnetic
loops are asymmetric in the sense that the photospheric field strength
at the loop footpoints is very different. We find that the magnetic
connectivity of the loops changes rapidly with a typical connection
recycling time of about 3 ± 1 minutes in the upper solar atmosphere and
12 ± 4 minutes in the photosphere. This is considerably shorter than
previously found. Nonetheless, our estimate of the energy released by
the associated magnetic-reconnection processes is not likely to be the
sole source for heating the chromosphere and corona in the quiet Sun.

---------------------------------------------------------
Title: Evolution of the Fine Structure of Magnetic Fields in the
Quiet Sun: Observations from Sunrise/IMaX and Extrapolations
Authors: Wiegelmann, T.; Solanki, S. K.; Borrero, J. M.; Peter,
H.; Barthol, P.; Gandorfer, A.; Martínez Pillet, V.; Schmidt, W.;
Knölker, M.
2013SoPh..283..253W Altcode:
Observations with the balloon-borne Sunrise/Imaging Magnetograph
eXperiment (IMaX) provide high spatial resolution (roughly 100 km at
disk center) measurements of the magnetic field in the photosphere of
the quiet Sun. To investigate the magnetic structure of the chromosphere
and corona, we extrapolate these photospheric measurements into
the upper solar atmosphere and analyze a 22-minute long time series
with a cadence of 33 seconds. Using the extrapolated magnetic-field
lines as tracer, we investigate temporal evolution of the magnetic
connectivity in the quiet Sun's atmosphere. The majority of magnetic
loops are asymmetric in the sense that the photospheric field strength
at the loop foot points is very different. We find that the magnetic
connectivity of the loops changes rapidly with a typical connection
recycling time of about 3±1 minutes in the upper solar atmosphere and
12±4 minutes in the photosphere. This is considerably shorter than
previously found. Nonetheless, our estimate of the energy released by
the associated magnetic-reconnection processes is not likely to be the
sole source for heating the chromosphere and corona in the quiet Sun.

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Title: Coronal structure and dynamics above an active region -
MHD model versus observation
Authors: Bourdin, Philippe-A.; Bingert, Sven; Peter, Hardi
2013enss.confE..56B Altcode:
We present a one-to-one comparison between an observed active region
and a 3D MHD model including spectral synthesis. We set up the 3D MHD
model from the photosphere to the corona and use the actually observed
photospheric magnetograms and horizontal motions as a lower boundary
condition to drive the 3D coronal model. Following Parker's model for
field-line braiding this induces currents that are dissipated and heat
the corona. From the 3D MHD model we synthesize emission spectra in
EUV and X-rays that can be compared directly to the Hinode/EIS and XRT
observation of the active region we model. We find that the hot coronal
loops that form in the model occur at just the same places as they are
found in the actual observations. Moreover, their spatial structure
and the flows along the loops as seen in the synthesized intensity
and Doppler maps compare well to the actual observations. By this we
present the first coronal model driven by photospheric observations
that provides a one-to-one match to the coronal structure and dynamics
observed for that same active region. This shows that the distribution
of the energy input in time and space through the field-line braiding
is close to the real solar coronal energy deposition.

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Title: "Nanoflare heating in the solar corona - Parker was right"
Authors: Bingert, Sven; Peter, Hardi
2013enss.confE..48B Altcode:
We investigate the energy distribution of the heat input in a 3D
MHD model of a solar active region. We find that the energy is
deposited mostly in quantities around 10^17 J, which is very close
to the nanoflare energy derived by Parker. For our study we employ
a 3D MHD model of the solar corona to investigate the spatial and
temporal evolution of the heat input based on Ohmic dissipation. The
model is driven by horizontal motions shuffling around the magnetic
field in the photosphere. This induces currents and their dissipation
heats the coronal plasma, very similar to the field-line braiding
mechanism proposed by Parker. We find a power-law behavior of the
energy input due to Ohmic dissipation indicating that the system
is scale invariant. However considering the coronal part of the
computational box alone, we find a knee in the energy distribution
and a preferred energy for the heat deposition. This energy coincides
with the nanoflare energy proposed by Parker. While Parker considered
a quite idealized setup, we model a realistic corona, accounting for
gravity, heat conduction and radiative losses, and account for the full
interaction of plasma and magnetic field. Our results are remarkable,
because even in the complex and dynamic setup we find a result that
basically supports Parker's original proposal. By synthesizing coronal
emission from our model we can go one step further, though, and show
that the resulting model corona really resembles the observed corona
in structure and dynamics.

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Title: Studies of the dynamics and energetics of cool plasma ejections
into the corona
Authors: Zacharias, Pia; Bingert, Sven; Peter, Hardi
2013enss.confE.142Z Altcode:
The corona is highly dynamic and shows transient events on various
scales in space and time. Most of these features are related to
changes in the magnetic field structure or impulsive heating caused
by the conversion of magnetic to thermal energy. We are applying
three-dimensional magnetohydrodynamic models in order to investigate
the structure and dynamics in the upper solar atmosphere above a small
active region. Emission line spectra are synthesized from the model
and compared to spectra and images observed by current space-based
instruments, such as the EUV Imaging Spectrometer (EIS) onboard the
Hinode satellite and the Atmospheric Imaging Assembly (AIA) onboard the
Solar Dynamics Observatory. We investigate mass and energy flows between
the solar chromosphere and corona and discuss possible scenarios for a
mass cycle between the lower and upper solar atmosphere. In particular,
we have studied the processes that lead to the formation and ejection
of a confined plasma ejection into the solar corona. A description of
the nature of this particular feature will be presented which is found
to be a hydrodynamic phenomenon triggered by a heating event above the
chromosphere. A detailed analysis of 1D coronal loop models has been
performed to understand how the plasma responds to a heating pulse. The
results confirm the formation mechanism of the blob observed in the 3D
model. This raises the question if other small-scale ejection features
seen on the Sun could also be based on hydrodynamic processes instead
of being plasmoid-type phenomena as it is usually assumed.

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Title: Coupled model for the formation of an active region corona
Authors: Chen, Feng; Bingert, Sven; Peter, Hardi; Cameron, Robert;
Schüssler; , Manfred; Cheung, Mark C. M.
2013enss.confE..21C Altcode:
We will present the first model that couples the formation of an active
region corona to a model of the emergence. This allows us to study
when, where, and why active region loops form, and how they evolve. For
this we use an existing 3D radiation MHD model of the emergence of an
active region through the upper convection zone and the photosphere
as a lower boundary for a coronal model. Our 3D MHD coronal model
accounts for the braiding of the magnetic field lines that induces
currents in the corona that is getting filled with the emerging magnetic
field. Starting with a basically field-free atmosphere we follow the
flux emergence until numerous individually identifiable hot coronal
loops have been formed. The temperatures in the coronal loops of well
above 1 MK are reached at densities corresponding to actually observed
active region loops. The loops develop over a very short time period
of the order of several minutes through the evaporation of material
from the chromosphere. Because we have full access to the heating
rate as a function of time and space in our computational domain we
can determine the conditions under which these loops form.

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Title: Nanoflare statistics in an active region 3D MHD coronal model
Authors: Bingert, S.; Peter, H.
2013A&A...550A..30B Altcode: 2012arXiv1211.6417B
 Aims: We investigate the statistics for the spatial and temporal
distribution of the energy input into the corona in a three-dimensional
magneto-hydrodynamical (3D MHD) model. The model describes the temporal
evolution of the corona above an observed active region. The model
is driven by photospheric granular motions that braid the magnetic
field lines. This induces currents that are dissipated, thereby
leading to transient heating of the coronal plasma. We evaluate
the transient heating as subsequent heating events and analyze their
statistics. The results are then interpreted in the context of observed
flare statistics and coronal heating mechanisms. Observed solar flares
and other smaller transients cover a wide range of energies. The
frequency distribution of energies follow a power law, the lower
end of the distribution given by the detection limit of current
instrumentation. One particular heating mechanism is based on the
occurrence of so-called nanoflares, i.e. very low-energy deposition
events. Methods: To conduct the numerical experiment we use a
high-order finite-difference code that solves the partial differential
equations for the conservation of mass, the momentum and energy balance,
and the induction equation. The energy balance includes Spitzer heat
conduction and optically thin radiative losses in the corona. 
Results: The temporal and spatial distribution of the Ohmic heating in
the 3D MHD model follows a power law and can therefore be understood as
a system in a self-organized critical state. The slopes of the power
law are similar to the results based on observations of flares and
smaller transients. We find that the coronal heating is dominated by
events similar to the so-called nanoflares with energies on the order
of 1017 J or 1024 erg.

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Title: Constant cross section of loops in the solar corona
Authors: Peter, H.; Bingert, S.
2012A&A...548A...1P Altcode: 2012arXiv1209.0789P
Context. The corona of the Sun is dominated by emission from loop-like
structures. When observed in X-ray or extreme ultraviolet emission,
these million K hot coronal loops show a more or less constant
cross section. Aims: In this study we show how the interplay
of heating, radiative cooling, and heat conduction in an expanding
magnetic structure can explain the observed constant cross section. Methods: We employ a three-dimensional magnetohydrodynamics (3D MHD)
model of the corona. The heating of the coronal plasma is the result
of braiding of the magnetic field lines through footpoint motions
and subsequent dissipation of the induced currents. From the model
we synthesize the coronal emission, which is directly comparable
to observations from, e.g., the Atmospheric Imaging Assembly on the
Solar Dynamics Observatory (AIA/SDO). Results: We find that the
synthesized observation of a coronal loop seen in the 3D data cube does
match actually observed loops in count rate and that the cross section
is roughly constant, as observed. The magnetic field in the loop is
expanding and the plasma density is concentrated in this expanding loop;
however, the temperature is not constant perpendicular to the plasma
loop. The higher temperature in the upper outer parts of the loop is so
high that this part of the loop is outside the contribution function
of the respective emission line(s). In effect, the upper part of the
plasma loop is not bright and thus the loop actually seen in coronal
emission appears to have a constant width. Conclusions: From
this we can conclude that the underlying field-line-braiding heating
mechanism provides the proper spatial and temporal distribution of the
energy input into the corona - at least on the observable scales. Movies associated to Figs. 1 and 2 are available in electronic form
at <A href="http://www.aanda.org">http://www.aanda.org</A>

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Title: Mass flows between the chromosphere and corona - comparison
of 1D and 3D coronal loop models
Authors: Zacharias, P.; Bingert, S.; Peter, H.
2012AGUFMSH33B2239Z Altcode:
The ejection and return of cool transition region plasma into the
corona will be discussed in the context of our three-dimensional
magnetohydrodynamic (3D MHD) model of the solar corona. The dynamics
of the ejection are investigated in more detail in a 1D loop model
and are compared to observations from Hinode/EIS and SDO/AIA. Results
from the 3D model analysis serve as input for the 1D loop model. In the
3D case, a heating pulse is the main driver of the ejection. To mimic
the situation in 1D, a heating pulse is injected at different heights
along the loop with varying amplitude and width. As a consequence,
the heating rate is strongly increased in a localized area and leads
to enhanced evaporation that causes the material to rise. We present
results that show the successful reproduction of the ejection in a 1D
loop model following the injection of a heating pulse. In contrast to
earlier studies, where similar heating events lead to both redshifts
in transition region emission lines and blueshifts in coronal emission
lines, preliminary results of our parameter study show exclusively
upflows along the loop and almost no downflows during the heating
phase. We will discuss these findings in terms of the mass cycle
between the chromosphere and corona.

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Title: Active region coronal loops in a large scale self consistent
3D MHD model
Authors: Bingert, S.; Peter, H.
2012AGUFMSH33B2238B Altcode:
Observations of the solar corona in EUV show a dominance of loops above
active regions. These loops show an almost constant cross-section which
is in contradiction to the expanding magnetic field. To understand
their appearance the detailed knowledge of the distribution of the
coronal heating and heat transport is needed. We investigate the
building process of these structures in a large-scale three dimensional
magneto-hydrodynamic (MHD) model of the solar corona above an active
region. The model expands from the photosphere up to a height of 80 Mm
and spans over 100x100 Mm^2 in the horizontal directions. The dynamics
of the model is driven by photopsheric granular motions driving
the magnetic field in an active region as observed by HMI/SDO. The
model solves the set of MHD equations, i.e. the induction equation
along with the conservation of mass, momentum and energy. The energy
equation includes radiative losses for the optically thin corona
and anisotropic Spitzer heat conduction. It is essential to treat
this term properly to get the correct coronal pressure, and for the
synthesis of coronal emission lines. Heat conduction is the dominant
process in the hot corona and therefore limits the progress of of
the numerical experiment. To improve the performance of the model
we extend the standard set of the MHD equations to include the time
evolution of the heat flux vector.; Synthetic MgX emission aligned
with the magnetic field lines connecting the main polarities of the
active region. Isocontur show a roughly constant cross-section of the
emission structure.

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Title: Persistent Doppler Shift Oscillations Observed with Hinode/EIS
in the Solar Corona: Spectroscopic Signatures of Alfvénic Waves
and Recurring Upflows
Authors: Tian, Hui; McIntosh, Scott W.; Wang, Tongjiang; Ofman, Leon;
De Pontieu, Bart; Innes, Davina E.; Peter, Hardi
2012ApJ...759..144T Altcode: 2012arXiv1209.5286T
Using data obtained by the EUV Imaging Spectrometer on board Hinode,
we have performed a survey of obvious and persistent (without
significant damping) Doppler shift oscillations in the corona. We
have found mainly two types of oscillations from February to April
in 2007. One type is found at loop footpoint regions, with a dominant
period around 10 minutes. They are characterized by coherent behavior
of all line parameters (line intensity, Doppler shift, line width,
and profile asymmetry), and apparent blueshift and blueward asymmetry
throughout almost the entire duration. Such oscillations are likely to
be signatures of quasi-periodic upflows (small-scale jets, or coronal
counterpart of type-II spicules), which may play an important role
in the supply of mass and energy to the hot corona. The other type of
oscillation is usually associated with the upper part of loops. They are
most clearly seen in the Doppler shift of coronal lines with formation
temperatures between one and two million degrees. The global wavelets
of these oscillations usually peak sharply around a period in the range
of three to six minutes. No obvious profile asymmetry is found and
the variation of the line width is typically very small. The intensity
variation is often less than 2%. These oscillations are more likely to
be signatures of kink/Alfvén waves rather than flows. In a few cases,
there seems to be a π/2 phase shift between the intensity and Doppler
shift oscillations, which may suggest the presence of slow-mode standing
waves according to wave theories. However, we demonstrate that such a
phase shift could also be produced by loops moving into and out of a
spatial pixel as a result of Alfvénic oscillations. In this scenario,
the intensity oscillations associated with Alfvénic waves are caused by
loop displacement rather than density change. These coronal waves may be
used to investigate properties of the coronal plasma and magnetic field.

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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 - 1 or
better. LEMUR has been proposed to ESA as the European contribution
to the Solar C mission.

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Title: Commission 10: Solar Activity
Authors: van Driel-Gesztelyi, Lidia; Schrijver, Carolus J.; Klimchuk,
James A.; Charbonneau, Paul; Fletcher, Lyndsay; Hasan, S. Sirajul;
Hudson, Hugh S.; Kusano, Kanya; Mandrini, Cristina H.; Peter, Hardi;
Vršnak, Bojan; Yan, Yihua
2012IAUTA..28...69V Altcode:
Commission 10 of the International Astronomical Union has more than
650 members who study a wide range of activity phenomena produced by
our nearest star, the Sun. Solar activity is intrinsically related
to solar magnetic fields and encompasses events from the smallest
energy releases (nano- or even picoflares) to the largest eruptions
in the Solar System, coronal mass ejections (CMEs), which propagate
into the Heliosphere reaching the Earth and beyond. Solar activity is
manifested in the appearance of sunspot groups or active regions, which
are the principal sources of activity phenomena from the emergence of
their magnetic flux through their dispersion and decay. The period
2008-2009 saw an unanticipated extended solar cycle minimum and
unprecedentedly weak polar-cap and heliospheric field. Associated with
that was the 2009 historical maximum in galactic cosmic rays flux since
measurements begun in the middle of the 20th Century. Since then Cycle
24 has re-started solar activity producing some spectacular eruptions
observed with a fleet of spacecraft and ground-based facilities. In
the last triennium major advances in our knowledge and understanding
of solar activity were due to continuing success of space missions as
SOHO, Hinode, RHESSI and the twin STEREO spacecraft, further enriched
by the breathtaking images of the solar atmosphere produced by the
Solar Dynamic Observatory (SDO) launched on 11 February 2010 in the
framework of NASA's Living with a Star program. In August 2012, at the
time of the IAU General Assembly in Beijing when the mandate of this
Commission ends, we will be in the unique position to have for the
first time a full 3-D view of the Sun and solar activity phenomena
provided by the twin STEREO missions about 120 degrees behind and
ahead of Earth and other spacecraft around the Earth and ground-based
observatories. These new observational insights are continuously
posing new questions, inspiring and advancing theoretical analysis
and modelling, improving our understanding of the physics underlying
magnetic activity phenomena. Commission 10 reports on a vigorously
evolving field of research produced by a large community. The number
of refereed publications containing `Sun', `heliosphere', or a synonym
in their abstracts continued the steady growth seen over the preceding
decades, reaching about 2000 in the years 2008-2010, with a total of
close to 4000 unique authors. This report, however, has its limitations
and it is inherently incomplete, as it was prepared jointly by the
members of the Organising Committee of Commission 10 (see the names
of the primary contributors to the sections indicated in parentheses)
reflecting their fields of expertise and interest. Nevertheless, we
believe that it is a representative sample of significant new results
obtained during the last triennium in the field of solar activity.

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Title: Solar magnetism eXplorer (SolmeX). Exploring the magnetic
field in the upper atmosphere of our closest star
Authors: Peter, Hardi; Abbo, L.; Andretta, V.; Auchère, F.; Bemporad,
A.; Berrilli, F.; Bommier, V.; Braukhane, A.; Casini, R.; Curdt,
W.; Davila, J.; Dittus, H.; Fineschi, S.; Fludra, A.; Gandorfer, A.;
Griffin, D.; Inhester, B.; Lagg, A.; Landi Degl'Innocenti, E.; Maiwald,
V.; Sainz, R. Manso; Martínez Pillet, V; Matthews, S.; Moses, D.;
Parenti, S.; Pietarila, A.; Quantius, D.; Raouafi, N. -E.; Raymond, J.;
Rochus, P.; Romberg, O.; Schlotterer, M.; Schühle, U.; Solanki, S.;
Spadaro, D.; Teriaca, L.; Tomczyk, S.; Trujillo Bueno, J.; Vial, J. -C.
2012ExA....33..271P Altcode: 2011arXiv1108.5304P; 2011ExA...tmp..134P
The magnetic field plays a pivotal role in many fields of
Astrophysics. This is especially true for the physics of the solar
atmosphere. Measuring the magnetic field in the upper solar atmosphere
is crucial to understand the nature of the underlying physical
processes that drive the violent dynamics of the solar corona—that
can also affect life on Earth. SolmeX, a fully equipped solar space
observatory for remote-sensing observations, will provide the first
comprehensive measurements of the strength and direction of the
magnetic field in the upper solar atmosphere. The mission consists
of two spacecraft, one carrying the instruments, and another one in
formation flight at a distance of about 200 m carrying the occulter to
provide an artificial total solar eclipse. This will ensure high-quality
coronagraphic observations above the solar limb. SolmeX integrates two
spectro-polarimetric coronagraphs for off-limb observations, one in
the EUV and one in the IR, and three instruments for observations on
the disk. The latter comprises one imaging polarimeter in the EUV for
coronal studies, a spectro-polarimeter in the EUV to investigate the low
corona, and an imaging spectro-polarimeter in the UV for chromospheric
studies. SOHO and other existing missions have investigated the emission
of the upper atmosphere in detail (not considering polarization),
and as this will be the case also for missions planned for the near
future. Therefore it is timely that SolmeX provides the final piece of
the observational quest by measuring the magnetic field in the upper
atmosphere through polarimetric observations.

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Title: Large scale MHD model of the solar corona above time dependent
HMI/SDO magnetograms
Authors: Bingert, S.; Peter, H.
2012decs.confE...3B Altcode:
The SDO spacecraft provides a unique tool to observe the solar
atmosphere simultaneously in the photosphere and the corona. The
magnetic field and the energy transport couples the whole system,
which requires a model that describes the atmosphere all the way from
the photosphere into the corona. We present the results of a large
scale three dimensional magneto-hydrodynamic model of the solar corona,
that is driven by the (time variable) magnetic field in the photosphere
as observed by HMI/SDO. The results of the 3D MHD model are then used
to synthesize the coronal emission and is directly compared to AIA/SDO
observations. The domain of the numerical model spans over 100x100 Mm^2
in horizontal directions and reaches a height of 80 Mm, thus containing
the full (small) active region. The spatial resolution is sufficient
to resolve thin loops and fine structure in the transition region and
corona. This large scale model includes all needed physics, such as
anisotropic heat conduction and radiative loss to account for a proper
coronal pressure. Based on the data we also derive basic parameters,
e.g. the energy flux through the domain or the structure and energy
content of the coronal magnetic field.

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Title: Coronal loops with constant cross-section reproduced in 3D
MHD models
Authors: Peter, Hardi; Bingert, Sven
2012decs.confE..59P Altcode:
EUV and X-ray images of the solar corona show loops with a more or
less constant cross-section. Because the magnetic field is expanding
with height, one would expect the coronal loops to expand with
height. Suggestions on special magnetic structures have been made to
understand the constant cross section of the loops, e.g. introducing
helicity. However no convincing picture could be presented yet. We
present results from a 3D MHD box model of a solar active region,
which is heated through braiding of magnetic field lines and subsequent
Ohmic dissipation. From the MHD model we synthesize emission as it
would be observed with AIA/SDO. These synthetic images clearly show EUV
loops with constant cross-section and thus can reproduce the observed
structures. The analysis of the densities and temperatures in relation
to the magnetic structure in the 3D model box shows that the constant
cross section is a result of the temperature and density variation in
the loop structure perpendicular to the magnetic field. These results
underline that one has to account for the three-dimensional nature
of the corona even when investigating a seemingly one-dimensional
structure such as a coronal loop.

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Title: Ejection of cool plasma into the corona - comparison of
results from a 3D MHD model with results from AIA/SDO, EIS/Hinode
and a 1D loop model
Authors: Zacharias, Pia; Bingert, Sven; Peter, Hardi
2012decs.confE..48Z Altcode:
The formation and subsequent ejection of cool plasma into the
corona will be discussed, as observed in our three-dimensional
magnetohydrodynamic (3D MHD) model of the solar atmosphere extending
from the photosphere into the corona. The model accounts properly
for the energy balance, especially for heat conduction and radiative
losses, allowing us to reliably synthesize the profiles of optically
thin extreme ultraviolet emission lines and compare them to existing
observations. A detailed description of the nature of this particular
phenomenon will be provided. The analysis of the various forces
acting upon the plasma in the 3D model shows that the pressure
gradient which is driving the ejection is due to Ohmic dissipation of
currents resulting from the braiding of the magnetic field lines by
photospheric plasma motions. Preliminary results of a parameter study
on the reproduction of the phenomenon in a one-dimensional loop model
support the scenario of a heating event that leads to the ejection
of cool plasma into the corona in both, the 1D loop model and the 3D
model. In addition, results of the numerical model will be compared to
observations from the Extreme Ultraviolet Imaging Spectrometer (EIS)
onboard Hinode and the Atmospheric Imaging Assembly (AIA) onboard SDO,
where we have also found evidence of cool plasma ejecta that are moving
along magnetic field lines.

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Title: Siphon flow in a cool magnetic loop
Authors: Bethge, C.; Beck, C.; Peter, H.; Lagg, A.
2012A&A...537A.130B Altcode: 2011arXiv1111.5564B
Context. Siphon flows that are driven by a gas pressure difference
between two photospheric footpoints of different magnetic field strength
connected by magnetic field lines are a well-studied phenomenon in
theory, but observational evidence is scarce. Aims. We investigate the
properties of a structure in the solar chromosphere in an active region
to find out whether the feature is consistent with a siphon flow in
a magnetic loop filled with chromospheric material. Methods. We
derived the line-of-sight (LOS) velocity of several photospheric
spectral lines and two chromospheric spectral lines, Ca II H 3968.5
*Aring; and He I 10830 Å, in spectropolarimetric observations of
NOAA 10978 done with the Tenerife Infrared Polarimeter (TIP-II) and
the POlarimetric LIttrow Spectrograph (POLIS). The structure can be
clearly traced in the LOS velocity maps and the absorption depth of
He I. The magnetic field configuration in the photosphere is inferred
directly from the observed Stokes parameters and from inversions with
the HELIX+ code. Data from the full-disk Chromospheric
Telescope (ChroTel) in He I in intensity and LOS velocity are used for
tracking the temporal evolution of the flow, along with TRACE Fe IX/X
171 Å data for additional information about coronal regions related to
the structure under investigation. Results. The inner end of the
structure is located in the penumbra of a sunspot. It shows downflows
whose strength decreases with decreasing height in the atmosphere. The
flow velocity in He I falls abruptly from above 40 km s-1
to about zero further into the penumbra. A slight increase of emission
is seen in the Ca II H spectra at the endpoint. At the outer end of the
structure, the photospheric lines that form higher up in the atmosphere
show upflows that accelerate with height. The polarization signal near
the outer end shows a polarity opposite to that of the sunspot, the
magnetic field strength of 580 G is roughly half as large as at the
inner end. The structure exists for about 90 min. Its appearance is
preceeded by a brightening in its middle in the coronal TRACE data. Conclusions. The observed flows match theoretical predictions of
chromospheric and coronal siphon flows, with accelerating upflowing
plasma at one footpoint with low field strength and decelerating
downflowing plasma at the other end. A tube shock at the inner end is
probable, but the evidence is not conclusive. The TRACE data suggest
that the structure forms because of a reorganization of field lines
after a reconnection event.

---------------------------------------------------------
Title: Catastrophic cooling and cessation of heating in the solar
corona
Authors: Peter, H.; Bingert, S.; Kamio, S.
2012A&A...537A.152P Altcode: 2011arXiv1112.3667P
Context. Condensations in the more than 106 K hot
corona of the Sun are commonly observed in the extreme ultraviolet
(EUV). While their contribution to the total solar EUV radiation is
still a matter of debate, these condensations certainly provide a
valuable tool for studying the dynamic response of the corona to the
heating processes. Aims: We investigate different distributions
of energy input in time and space to investigate which process is
most relevant for understanding these coronal condensations. 
Methods: For a comparison to observations we synthesize EUV emission
from a time-dependent, one-dimensional model for coronal loops, where
we employ two heating scenarios: simply shutting down the heating and
a model where the heating is very concentrated at the loop footpoints,
while keeping the total heat input constant. Results: The heating
off/on model does not lead to significant EUV count rates that one
observes with SDO/AIA. In contrast, the concentration of the heating
near the footpoints leads to thermal non-equilibrium near the loop
top resulting in the well-known catastrophic cooling. This process
gives a good match to observations of coronal condensations. Conclusions: This shows that the corona needs a steady supply
of energy to support the coronal plasma, even during coronal
condensations. Otherwise the corona would drain very fast, too fast
to even form a condensation. Movies are available in electronic
form at <A href="http://www.aanda.org">http://www.aanda.org</A>

---------------------------------------------------------
Title: The Chromospheric Telescope
Authors: Bethge, C.; Peter, H.; Kentischer, T. J.; Halbgewachs, C.;
Elmore, D. F.; Beck, C.
2011A&A...534A.105B Altcode: 2011arXiv1108.4880B
 Aims: We introduce the Chromospheric Telescope (ChroTel) at the
Observatorio del Teide in Izaña on Tenerife as a new multi-wavelength
imaging telescope for full-disk synoptic observations of the solar
chromosphere. We describe the design of the instrument and summarize
its performance during the first one and a half years of operation. We
present a method to derive line-of-sight velocity maps of the full
solar disk from filtergrams taken in and near the He i infrared line
at 10 830 Å. Methods: ChroTel observations are conducted
using Lyot-type filters for the chromospheric lines of Ca ii K,
Hα, and He i 10 830 Å. The instrument operates autonomically and
gathers imaging data in all three channels with a cadence of down to
one minute. The use of a tunable filter for the He i line allows us
to determine line-shifts by calibrating the line-of-sight velocity
maps derived from the filtergram intensities with spectrographic data
from the Tenerife Infrared Polarimeter at high spatial and spectral
resolution. Results: The robotic operation and automated data
reduction have proven to operate reliably in the first one and and
half years. The achieved spatial resolution of the data is close to
the theoretical limit of 2 arcsec in Hα and Ca ii K and 3 arcsec in He
i. Line-of-sight velocities in He i can be determined with a precision
of better than 3-4 km s-1 when co-temporal spectrographic
maps are available for calibration. Conclusions: ChroTel offers a
unique combination of imaging in the most important chromospheric lines,
along with the possibility to determine line-of-sight velocities in
one of the lines. This is of interest for scientific investigations
of large-scale structures in the solar chromosphere, as well as for
context imaging of high-resolution solar observations.

---------------------------------------------------------
Title: Continuous upflows and sporadic downflows observed in active
regions
Authors: Kamio, S.; Peter, H.; Curdt, W.; Solanki, S. K.
2011A&A...532A..96K Altcode: 2011arXiv1107.1993K
 Aims: We present a study of the temporal evolution of coronal
loops in active regions and its implications for the dynamics in coronal
loops. Methods: We analyzed images of the Atmospheric Imaging
Assembly (AIA) on the Solar Dynamics Observatory (SDO) at multiple
temperatures to detect apparent motions in the coronal loops. 
Results: Quasi-periodic brightness fluctuations propagate upwards from
the loop footpoint in hot emission at 1 MK, while sporadic downflows
are seen in cool emission below 1 MK. The upward motion in hot
emission increases just after the cool downflows. Conclusions:
The apparent propagating pattern suggests a hot upflow from the
loop footpoints, and is considered to supply hot plasma into the
coronal loop, but a wavelike phenomenon cannot be ruled out. Coronal
condensation occasionally happens in the coronal loop, and the cool
material flows down to the footpoint. Emission from cool plasma could
have a significant contribution to hot AIA channels in the event of
coronal condensation.

---------------------------------------------------------
Title: Ejection of cool plasma into the hot corona
Authors: Zacharias, P.; Peter, H.; Bingert, S.
2011A&A...532A.112Z Altcode: 2011arXiv1106.5972Z
Context. The corona is highly dynamic and shows transient events
on various scales in space and time. Most of these features are
related to changes in the magnetic field structure or impulsive
heating caused by the conversion of magnetic to thermal energy. Aims: We investigate the processes that lead to the formation,
ejection and fall of a confined plasma ejection that was observed in
a numerical experiment of the solar corona. By quantifying physical
parameters such as mass, velocity, and orientation of the plasma
ejection relative to the magnetic field, we provide a description of
the nature of this particular plasma ejection. Methods: The
time-dependent three-dimensional magnetohydrodynamic (3D MHD) equations
are solved in a box extending from the chromosphere, which serves as
a reservoir for mass and energy, to the lower corona. The plasma is
heated by currents that are induced through field line braiding as
a consequence of photospheric motions included in the model. Spectra
of optically thin emission lines in the extreme ultraviolet range are
synthesized, and magnetic field lines are traced over time. We determine
the trajectory of the plasma ejection and identify anomalies in the
profiles of the plasma parameters. Results: Following strong
heating just above the chromosphere, the pressure rapidly increases,
leading to a hydrodynamic explosion above the upper chromosphere in the
low transition region. The explosion drives the plasma, which needs
to follow the magnetic field lines. The ejection is then moving more
or less ballistically along the loop-like field lines and eventually
drops down onto the surface of the Sun. The speed of the ejection is in
the range of the sound speed, well below the Alfvén velocity. 
Conclusions: The plasma ejection observed in a numerical experiment
of the solar corona is basically a hydrodynamic phenomenon, whereas
the rise of the heating rate is of magnetic nature. The granular
motions in the photosphere lead (by chance) to a strong braiding of
the magnetic field lines at the location of the explosion that in
turn is causing strong currents which are dissipated. Future studies
need to determine if this process is a ubiquitous phenomenon on the
Sun on small scales. Data from the Atmospheric Imaging Assembly on
the Solar Dynamics Observatory (AIA/SDO) might provide the relevant
information. Appendix and movie are available in electronic form
at <A href="http://www.aanda.org">http://www.aanda.org</A>

---------------------------------------------------------
Title: Investigation of mass flows in the transition region and
corona in a three-dimensional numerical model approach
Authors: Zacharias, P.; Peter, H.; Bingert, S.
2011A&A...531A..97Z Altcode: 2011arXiv1105.5491Z
Context. The origin of solar transition region redshifts is not
completely understood. Current research is addressing this issue
by investigating three-dimensional magneto-hydrodynamic models
that extend from the photosphere to the corona. Aims: By
studying the average properties of emission line profiles synthesized
from the simulation runs and comparing them to observations with
present-day instrumentation, we investigate the origin of mass
flows in the solar transition region and corona. Methods:
Doppler shifts were determined from the emission line profiles of
various extreme-ultraviolet emission lines formed in the range of T =
104-106 K. Plasma velocities and mass flows
were investigated for their contribution to the observed Doppler
shifts in the model. In particular, the temporal evolution of plasma
flows along the magnetic field lines was analyzed. Results:
Comparing observed vs. modeled Doppler shifts shows a good correlation
in the temperature range log (T/[K]) = 4.5-5.7, which is the basis of
our search for the origin of the line shifts. The vertical velocity
obtained when weighting the velocity by the density squared is shown
to be almost identical to the corresponding Doppler shift. Therefore,
a direct comparison between Doppler shifts and the model parameters
is allowed. A simple interpretation of Doppler shifts in terms of
mass flux leads to overestimating the mass flux. Upflows in the model
appear in the form of cool pockets of gas that heat up slowly as they
rise. Their low temperature means that these pockets are not observed
as blueshifts in the transition region and coronal lines. For a set of
magnetic field lines, two different flow phases could be identified. The
coronal part of the field line is intermittently connected to subjacent
layers of either strong or weak heating, leading either to mass flows
into the loop (observed as a blueshift) or to the draining of the loop
(observed as a redshift).

---------------------------------------------------------
Title: Intermittent heating in the solar corona employing a 3D
MHD model
Authors: Bingert, S.; Peter, H.
2011A&A...530A.112B Altcode: 2011arXiv1103.6042B
 Aims: We investigate the spatial and temporal evolution
of the heating of the corona of a cool star such as our Sun in a
three-dimensional magneto-hydrodynamic (3D MHD) model. Methods:
We solve the 3D MHD problem numerically in a box representing part of
the (solar) corona. The energy balance includes Spitzer heat conduction
along the magnetic field and optically thin radiative losses. The
self-consistent heating mechanism is based on the braiding of magnetic
field lines rooted in the convective photosphere. Magnetic stress
induced by photospheric motions leads to currents in the atmosphere that
heat the corona through Ohmic dissipation. Results: While the
horizontally averaged quantities, such as heating rate, temperature,
or density, are relatively constant in time, the simulated corona is
highly variable and dynamic, on average reaching the temperatures and
densities found in observations. The strongest heating per particle is
found in the transition region from the chromosphere to the corona. The
heating is concentrated in current sheets roughly aligned with the
magnetic field and is transient in time and space. This supports the
idea that numerous small heating events heat the corona, often referred
to as nanoflares.

---------------------------------------------------------
Title: Asymmetries of solar coronal extreme ultraviolet emission lines
Authors: Peter, H.
2010A&A...521A..51P Altcode: 2010arXiv1004.5403P
Context. The profiles of emission lines formed in the corona contain
information on the dynamics and the heating of the hot plasma. Only
recently has data with sufficiently high spectral resolution become
available for investigating the details of the profiles of emission
lines formed well above 106 K. These show enhanced emission
in the line wings, which has not been understood yet. Aims: We
study the underlying processes leading to asymmetric line profiles, in
particular the responsible plasma flows and line broadening mechanisms
in a highly filamentary and dynamic atmosphere. Methods: Line
profiles of Fe XV formed at 2.5 MK acquired by the Extreme ultraviolet
Imaging Spectrometer (EIS) onboard the Hinode solar space observatory
are studied using multi Gaussian fits, with emphasis on the resulting
line widths and Doppler shifts. Results: In the major part
of the active region, the spectra are best fit by a narrow line core
and a broad minor component. The latter contributes some 10% to 20%
to the total emission, is about a factor of 2 broader than the core,
and shows strong blueshifts of up to 50 km s-1, especially in
the footpoint regions of the loops. On average, the line width increases
from the footpoints to the loop top for both components. A component
with high upflow speeds can be found also in small restricted areas. Conclusions: The coronal structures consist of at least two classes
that are not resolved spatially but only spectroscopically and that
are associated with the line core and the minor component. Because
of their huge line width and strong upflows, it is proposed that
the major part of the heating and the mass supply to the corona is
actually located in source regions of the minor component. It might
be that these are identical to type II spicules. The siphon flows and
draining loops seen in the line core component are consistent with
structures found in a three-dimensional magneto-hydrodynamic (3D MHD)
coronal model. Despite the quite different appearance of the large
active region corona and small network elements seen in transition
region lines, both show similar line profile characteristics. This
indicates that the same processes govern the heating and dynamics of
the transition region and the corona.

---------------------------------------------------------
Title: Dynamics of Active Regions: Observations and 3D MHD Modeling
Authors: Peter, Hardi; Bingert, S.
2010AAS...21630005P Altcode:
We present data from Hinode/EIS, compare these to 3D MHD coronal models
and outline forward models using SDO data. EUV lines originating in
an active region show asymmetric line profiles that are interpreted
using multi-Gaussian line fitting. Depending of the structure, a minor
component can show high upflow speeds of above 100 km/S or it can
be subject to strong heating resulting in a very strong broadening in
combination with upflows of some 50 km/s. The latter ones are found near
loop footpoints and might be associated with type II spicules feeding
mass into coronal structures. The bulk part of the active region
emission shows loops with either siphon-type loops, associated with
asymmetric heating, or with downflows on both legs, associated with a
lack of heating, i.e. cooling. We find these typical structures also
in 3D MHD models where we can directly investigate the dynamics in the
computational box. The properties of the observed coronal spectral
profiles is surprisingly similar to those in the transition region
suggesting common mechanisms driving the heating and dynamics from the
cool transition region to the hot corona. This is also supported by
the 3D MHD models which treat the chromosphere - transition region -
corona system as one single system. Based on this work we will
present the concept to use HMI/SDO magnetic field data as input at the
lower boundary of our 3D coronal models. The coronal model will then
be used to synthesize the emission that would be observed by AIA/SDO,
which then can be directly compared to the actual AIA observations. As
the numerical simulations are computationally time-consuming, we will
not be able to show final results based on HMI data, but will present
first results and results from older data sets.

---------------------------------------------------------
Title: On the nature of coronal loops above the quiet sun network
Authors: Bingert, S.; Zacharias, P.; Peter, H.; Gudiksen, B. V.
2010AdSpR..45..310B Altcode:
The structure and dynamics of a box in a stellar corona can be
modeled employing a 3D MHD model for different levels of magnetic
activity. Depending on the magnetic flux through the surface the
nature of the resulting coronal structures can be quite different. We
investigate a model of an active region for two sunspots surrounded by
magnetic field patches comparable in magnetic flux to the sunspots. The
model results in emission from the model corona being concentrated in
loop structures. In Gudiksen and Nordlund (2005) the loops seen in EUV
and X-ray emission outline the magnetic field, following the general
paradigm. However, in our model, where the magnetic field is far from
a force-free state, the loops seen in X-ray emission do not follow
the magnetic field lines. This result is of interest especially for
loops as found in areas where the magnetic field emerging from active
regions interacts with the surrounding network.

---------------------------------------------------------
Title: Spectral analysis of 3D MHD models of coronal structures
Authors: Zacharias, Pia; Bingert, Sven; Peter, Hardi
2009AdSpR..43.1451Z Altcode: 2009arXiv0904.2312Z
We study extreme-ultraviolet emission line spectra derived from
three-dimensional magnetohydrodynamic models of structures in the
corona. In order to investigate the effects of increased magnetic
activity at photospheric levels in a numerical experiment, a much
higher magnetic flux density is applied at the photosphere as compared
to the Sun. Thus, we can expect our results to highlight the differences
between the Sun and more active, but still solar-like stars. We discuss
signatures seen in extreme-ultraviolet emission lines synthesized from
these models and compare them to observed signatures in the spatial
distribution and temporal evolution of Doppler shifts in lines formed
in the transition region and corona. This is of major interest to test
the quality of the underlying magnetohydrodynamic model to heat the
corona, i.e. currents in the corona driven by photospheric motions
(flux braiding).

---------------------------------------------------------
Title: Commission 10: Solar Activity
Authors: Klimchuk, James A.; van Driel-Gesztelyi, Lidia; Schrijver,
Carolus J.; Melrose, Donald B.; Fletcher, Lyndsay; Gopalswamy,
Natchimuthuk; Harrison, Richard A.; Mandrini, Cristina H.; Peter,
Hardi; Tsuneta, Saku; Vršnak, Bojan; Wang, Jing-Xiu
2009IAUTA..27...79K Altcode: 2008arXiv0809.1444K
Commission 10 deals with solar activity in all of its forms,
ranging from the smallest nanoflares to the largest coronal mass
ejections. This report reviews scientific progress over the roughly
two-year period ending in the middle of 2008. This has been an exciting
time in solar physics, highlighted by the launches of the Hinode and
STEREO missions late in 2006. The report is reasonably comprehensive,
though it is far from exhaustive. Limited space prevents the inclusion
of many significant results. The report is divided into the following
sections: Photosphere and chromosphere; Transition region; Corona and
coronal heating; Coronal jets; flares; Coronal mass ejection initiation;
Global coronal waves and shocks; Coronal dimming; The link between low
coronal CME signatures and magnetic clouds; Coronal mass ejections in
the heliosphere; and Coronal mass ejections and space weather. Primary
authorship is indicated at the beginning of each section.

---------------------------------------------------------
Title: Doppler shifts in the transition region and corona. Mass
cycle between the chromosphere and the corona
Authors: Zacharias, P.; Bingert, S.; Peter, H.
2009MmSAI..80..654Z Altcode:
Emission lines in the transition region and corona show persistent
line shifts. It is a major challenge to understand the dynamics in
the upper atmosphere and thus these line shifts, which are a signature
of the mass cycle between the chromosphere and the corona. We examine
EUV emission line profiles synthesized from a 3D MHD coronal model of
a solar-like corona, in particular of an active region surrounded by
strong chromospheric network. This allows us to investigate the physical
processes leading to the line Doppler shifts, since we have access to
both, the synthetic spectra and the physical parameters, i.e. magnetic
field, temperature and density in the simulation box. By analyzing the
evolution of the flows along field lines together with the changing
magnetic structure we can investigate the mass cycle. We find evidence
that loops are loaded with mass during a reconnection process, leading
to upflows. After the loops disconnect from the reconnection site,
they cool and drain which leads to the observed redshifts. Previous 1D
loop models (neglecting the 3D nature) assumed that heating leads to
evaporation and upflows followed by a cooling phase after the heating
stops. The scenario modeled here is quite different, as it shows
that the continuously changing three-dimensional magnetic structure
is of pivotal importance to understand the mass balance between the
chromosphere and the corona.

---------------------------------------------------------
Title: Spectral Analysis of 3D MHD Models of Quiet Sun and Active
Region Structures
Authors: Zacharias, P.; Bingert, S.; Peter, H.
2008ESPM...12.3.39Z Altcode:
We study EUV emission line spectra derived from 3D MHD models
of structures in the corona, in particular of an active region
surrounded by a strong chromospheric network. The 3D MHD models account
properly for the energy balance, especially for heat conduction and
radiative losses. This allows us to reliably synthesize the profiles
of EUV emission lines observable with current EUV spectrometers,
e.g. SUMER/SOHO and EIS/Hinode. We investigate the temporal evolution
and spatial distribution of the Doppler shifts of the EUV emission
lines synthesized from these models. This is of major interest
for the underlying mechanism of the heating of the solar corona,
i.e. dissipation of currents in the corona driven by photospheric
motions (flux braiding). Based on the 3D MHD models we can also derive
intensity maps as they will be observed through the coronal channels
of the AIA-instrument onboard SDO and we can analyze how to process the
AIA maps in order to derive physical quantities such as temperatures and
densities. Since we have access not only to the synthetic spectra, but
also to the magnetic field in the box we can explore how the magnetic
field relates to the emission in various coronal lines. In the present
paper we will show results on the evolution of spectral properties
such as line shifts or widths in different modeled coronal structures
and compare these to results from SUMER/SOHO as well as EIS/Hinode data.

---------------------------------------------------------
Title: On the Nature of Coronal Loops
Authors: Bingert, S.; Zacharias, P.; Peter, H.; Gudiksen, B.
2008ESPM...12.3.29B Altcode:
The structure and dynamics of a box in a stellar corona can be
modeled employing a 3D MHD model for different levels of magnetic
activity. Depending on the magnetic flux through the surface the
nature of the resulting coronal structures can be quite different. We will compare two different models of an active region, one for
two basically isolated sunspots, and another one for two sunspots
surrounded by magnetic field patches similar to the chromospheric
network. The current paradigm is that these loops follow magnetic
field lines as pearls on a string, and thus the majority of present
corona models describe structures following the field lines. Our
study challenges this paradigm by showing through a three-dimensional
model that coronal structures in complex magnetic field geometries might
appear loop-like while they are not aligned with the magnetic field. Using a forward model approach, both models result in emission from
the corona being concentrated in loop structures. In the first case
the loops seen in EUV and X-ray emission are following the magnetic
field. However, in the second case, where the magnetic field is
far from a force-free state, the loops seen in X-ray emission do not
follow the magnetic field, but are more related to the current sheets
formed in response to the footpoint motions of the magnetic field. This result is of interest especially for loops as found in areas
where the magnetic field emerging from active regions interacts with
the surrounding network or in the complex magnetic structures within
chromospheric network patches.

---------------------------------------------------------
Title: 12th European Solar Physics Meeting
Authors: Peter, H.
2008ESPM...12.....P Altcode:
The meeting will cover all aspects of solar physics and is the
ideal place for European and international solar researchers to
come together. It begins with a session, where we ask experienced
researchers to give a broad view on what the real key questions in
our field are. This will give a stimulating start for the discussions
during the meeting. The main part of the meeting will be session 2 and
3, where the problems and results in solar physics will be discussed
from the observationally as well as from the theory side. This does not
mean that observations and theory will be split. In the contrary, twice
we will look at the same problems from two sides: what new observations
drive us to run new models and how do new models motivate new concepts
of observational approaches. In a way, we do the journey from the core
of the Sun to the outer edge of the heliosphere twice. Following these
major sessions of the meeting we will have room to discuss how solar
work relates to other stars, and vice versa, and how to understand the
Sun-Earth system. The final session will deal with plans for future
research in our field, including the European Solar Telescope (EST),
the status of the Solar Orbiter or activities in theory and modeling.

---------------------------------------------------------
Title: The control and data concept for the robotic solar telescope
ChroTel
Authors: Halbgewachs, C.; Bethge, Ch.; Caligari, P.; Elmore, D.;
Kentischer, T. J.; Peter, H.; Sigwarth, M.; Schmidt, W.
2008SPIE.7019E..2TH Altcode: 2008SPIE.7019E..93H
The solar telescope ChroTel is designed as a robotic telescope so
that no user interaction is necessary for observation. The telescope
will start tracking in the morning as soon as weather conditions are
appropriate and will process a user defined observation routine until
sunset. Weather conditions and system status are continuously monitored
to close the telescope shutter in case of bad weather or to drive to
the stow position in case of an error. The ChroTel control software
was programmed in LabVIEW.

---------------------------------------------------------
Title: ChroTel: a robotic telescope to observe the chromosphere of
the Sun
Authors: Kentischer, T. J.; Bethge, Ch.; Elmore, D. F.; Friedlein,
R.; Halbgewachs, C.; Knölker, M.; Peter, H.; Schmidt, W.; Sigwarth,
M.; Streander, K.
2008SPIE.7014E..13K Altcode: 2008SPIE.7014E..36K
The Chromospheric Telescope (ChroTel) is a 10 cm robotic telescope
to observe the full solar disk with a 2k × 2k CCD at high temporal
cadence. It is located at the Observatorio del Teide, Tenerife, Spain,
next to the 70 cm German Vacuum Tower Telescope (VTT). ChroTel contains
a turret system that relays a stabilized image of the solar disk into
a laboratory within the VTT building. The control design allows a fully
robotic operation. Observations are carried out in three chromospheric
wavelengths (CaK: 393 nm, Ha: 652 nm, HeI 1083 nm).

---------------------------------------------------------
Title: On the nature of coronal loops
Authors: Peter, H.; Bingert, S.; Gudiksen, B. V.
2008AGUSMSP41C..05P Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Editorial
Authors: Walmsley, M.; Peter, H.
2008A&A...481E..17W Altcode:
In September 2006 the solar space observatory Hinode (Japanese for
sunrise) was launched. The project is led by the Japan Aerospace
Exploration Agency (JAXA) together with the National Astronomical
Observatory of Japan (NAOJ) and contributions from the United States
and the United Kingdom. The European Space Agency (ESA) is providing
ground station coverage through the Svalbard Satellite Station in
Norway. The Hinode satellite carries a solar optical telescope
(SOT), a X-ray telescope (XRT), and an EUV imaging spectrometer
(EIS). Together, these permit an investigation of the interior of the
Sun, and all atmospheric regions, from the photosphere and chromosphere
to the corona, addressing the origin of the Sun's magnetic field,
the driving force behind solar eruptive events, and the nature of the
hot corona. As a recognition of the impact provided by the new solar
observations using HINODE, we publish a “special feature” in this
issue. It consists of 18 letters which document these new results.

---------------------------------------------------------
Title: On the nature of coronal loops
Authors: Bingert, Sven; Zacharias, Pia; Peter, Hardi
2008cosp...37..302B Altcode: 2008cosp.meet..302B
The structure and dynamics of a box in a stellar corona can be
modeled employing a 3D MHD model for different levels of magnetic
activity. In these models we account for the mass, momentum and energy
balance including heat conduction and radiative losses. The heating
is through current dissipation in the corona driven by photospheric
motions (flux braiding). Depending on the magnetic flux through
the surface the nature of the resulting coronal structures can be
quite different. We will compare two different models of an active
region, one for two basically isolated sunspots, and another one for
two sunspots surrounded by strong magnetic field patches mimicking a
strong chromospheric network. Both models result in emission from the
model corona being concentrated in loop structures. In the first case
the loops seen in EUV and X-ray emission are aligned with the magnetic
field, following the general paradigm. However, in the second case,
where the magnetic field is far from a force-free state, the loops seen
in X-ray emission do not follow the magnetic field, but are related to
the current sheets formed in response to the footpoint motions of the
magnetic field. For the Sun this result is of interest especially for
loops as found in areas where the magnetic field emerging from active
regions interacts with the surrounding network. These models are now
ready to face detailed comparisons with EUV spectroscopic observations
from Hinode and imaging from SDO/AIA.

---------------------------------------------------------
Title: 3D MHD models compared to EUV observations of quiet Sun and
active region structures
Authors: Zacharias, Pia; Bingert, Sven; Peter, Hardi
2008cosp...37.3579Z Altcode: 2008cosp.meet.3579Z
We study EUV emission line spectra derived from 3D MHD models of
structures in the corona, in particular of an active region surrounded
by a strong chromospheric network. The 3D MHD models account properly
for the energy balance, especially for heat conduction and radiative
losses, which allows us to reliably synthesize the profiles of
EUV emission lines observable with current EUV spectrometers,
i.e. SUMER/SOHO and EIS/Hinode. Thus we can directly compare these
synthesized spectra to real observations with these instruments. We
will discuss differences of models with different levels of magnetic
activity in terms of signatures seen in EUV lines synthesized from
these models and compare them to signatures found, e.g., in the spatial
distribution and temporal evolution of Doppler shifts of lines formed
in the transition region and corona. This is of major interest to test
the quality of the underlying model to heat the corona, i.e. currents
in the corona driven by photospheric motions (flux braiding). Based
on the 3D MHD model we can also derive intensity maps as they will
be observed through the coronal channels of the AIA-instrument on
SDO. Through this we can provide some guidance on how to process the
AIA maps in order to derive physical quantities such as temperature
and density through a combination of filters.

---------------------------------------------------------
Title: The Coronal Heating Paradox
Authors: Aschwanden, Markus J.; Winebarger, Amy; Tsiklauri, David;
Peter, Hardi
2007ApJ...659.1673A Altcode:
The “coronal heating problem” has been with us over 60 years, and
hundreds of theoretical models have been proposed without an obvious
solution in sight. In this paper we point out that observations show no
evidence for local heating in the solar corona, but rather for heating
below the corona in the transition region and upper chromosphere,
with subsequent chromospheric evaporation as known in flares. New
observational evidence for this scenario comes from (1) the temperature
evolution of coronal loops, (2) the overdensity of hot coronal loops,
(3) upflows in coronal loops, (4) the Doppler shift in coronal loops,
(5) upward propagating waves, (6) the energy balance in coronal loops,
(7) the magnetic complexity in the transition region, (8) the altitude
of nanoflares and microflares, (9) the cross section of elementary
loops, as well as (10) 3D MHD simulations of coronal heating. The phrase
“coronal heating problem” is therefore a paradoxical misnomer for
what should rather be addressed as the “chromospheric heating problem”
and “coronal loop filling process.” This paradigm shift substantially
reduces the number of relevant theoretical models for coronal heating
in active regions and the quiet Sun, but our arguments do not apply
to coronal holes and the extended heliospheric corona.

---------------------------------------------------------
Title: Das Heliophysikalische Jahr 2007 in Deutschland
Authors: Heber, Bernd; Fichtner, Horst; Scherer, Klaus; Büchner,
Jörg; Peter, Hardi
2007S&W....46d..18H Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Modeling the (upper) solar atmosphere including the magnetic
field
Authors: Peter, H.
2007AdSpR..39.1814P Altcode: 2007astro.ph..3575P
The atmosphere of the Sun is highly structured and dynamic in
nature. From the photosphere and chromosphere into the transition region
and the corona plasma- β changes from above to below one, i.e., while
in the lower atmosphere the energy density of the plasma dominates,
in the upper atmosphere the magnetic field plays the governing role -
one might speak of a "magnetic transition". Therefore the dynamics
of the overshooting convection in the photosphere, the granulation,
is shuffling the magnetic field around in the photosphere. This leads
not only to a (re-)structuring of the magnetic field in the upper
atmosphere, but induces also the dynamic reaction of the coronal plasma,
e.g., due to reconnection events. Therefore the (complex) structure and
the interaction of various magnetic patches is crucial to understand
the structure, dynamics and heating of coronal plasma as well as its
acceleration into the solar wind. The present article will emphasize
the need for three-dimensional modeling accounting for the complexity
of the solar atmosphere to understand these processes. Some advances
on 3D modeling of the upper solar atmosphere in magnetically closed as
well as open regions will be presented together with diagnostic tools to
compare these models to observations. This highlights the recent success
of these models which in many respects closely match the observations.

---------------------------------------------------------
Title: S ynergies With Other Missions Concerning Ultraviolet Imaging
And Spectroscopy
Authors: Peter, H.
2007ESASP.641E..18P Altcode:
The Solar Orbiter will provide a number of unique opportunities
to observe the Sun from close-by, at co-rotation and from high
latitudes not accessible for observatories in Earth orbit or at
L1. Nevertheless other missions providing information in the VUV using
imaging and spectroscopic instruments can provide valuable complementary
information. In phases when the Orbiter observes parts of the Sun also
accessible from other space observatories, the latter ones can provide
data with a higher rate than the orbiter and through this allow a
larger field of view and/or a faster time cadence. Also imagers could
cover more wavelength bands and spectrometers might provide a larger
spectral coverage and higher spectral resolution than possible on the
Orbiter. The different profiles of the instrumentation on-board the
Orbiter and other space observatories will answer different aspects
on the physical problems tackled by future models and by this supply
complementary information to better understand our Sun. Instrumentation
complementing Solar Orbiter, especially concerning fast raster maps
with full spectral coverage and VUV spectro-polarimetry to investigate
coronal magnetic fields, are highly desirable. In order to answer
questions to be posed by elaborate future coronal models the solar
community should be really ambitious and aim at a combination of such
instruments in near Earth orbit for coordinated observations with the
Solar Orbiter

---------------------------------------------------------
Title: Link between the chromospheric network and magnetic structures
of the corona
Authors: Jendersie, S.; Peter, H.
2006A&A...460..901J Altcode: 2006astro.ph..9280J
Context: . Recent work suggested that the traditional picture of the
corona above the quiet Sun being rooted in the magnetic concentrations
of the chromospheric network alone is strongly questionable. 
Aims: . Building on that previous study we explore the impact of
magnetic configurations in the photosphere and the low corona on the
magnetic connectivity from the network to the corona. Observational
studies of this connectivity are often utilizing magnetic field
extrapolations. However, it is open to which extent such extrapolations
really represent the connectivity found on the Sun, as observations are
not able to resolve all fine scale magnetic structures. The present
numerical experiments aim at contributing to this question. 
Methods: . We investigated random salt-and-pepper-type distributions
of kilo-Gauss internetwork flux elements carrying some 1015
to 1017 Mx, which are hardly distinguishable by current
observational techniques. These photospheric distributions are then
extrapolated into the corona using different sets of boundary conditions
at the bottom and the top. This allows us to investigate the fraction
of network flux which is connected to the corona, as well as the
locations of those coronal regions which are connected to the network
patches. Results: . We find that with current instrumentation
one cannot really determine from observations, which regions on the
quiet Sun surface, i.e. in the network and internetwork, are connected
to which parts of the corona through extrapolation techniques. Future
spectro-polarimetric instruments, such as with Solar B or Gregor, will
provide a higher sensitivity, and studies like the present one could
help to estimate to which extent one can then pinpoint the connection
from the chromosphere to the corona. Conclusions: .

---------------------------------------------------------
Title: First VUV Sun-As-A-Star Spectrum Compared to Other Cool Stars
Authors: Peter, H.
2006ESASP.617E..10P Altcode: 2006soho...17E..10P
No abstract at ADS

---------------------------------------------------------
Title: First high spectral resolution VUV full-Sun spectrum compared
to cool stars
Authors: Peter, Hardi
2006A&A...449..759P Altcode:
This paper reports the first full-Sun vacuum ultraviolet (VUV)
emission line profile originating from the transition region from
the chromosphere to the corona. It is based on a raster scan of
the whole solar disk using SUMER/SOHO. The full-Sun spectrum has a
spectral resolution which allows an investigation of details in the
line profile as well as a thorough comparison to stellar spectra
as obtained, e.g. with FUSE or STIS/HST. The full-Sun spectrum
shows enhanced emission in the wings, and is well described by a
double Gaussian fit with a narrow and a broad component. It is shown
that the broad component is due to structures on the solar surface,
especially those related to the magnetic chromospheric network. Thus
it is proposed that the broad components of other solar-like stars
are also a consequence of the mixture of surface structures, and
not necessarily a signature of small-scale heating processes like
explosive events, as it is commonly argued. A comparison to spectra
of luminous cool stars shows that the line asymmetries of these stars
might also be a surface structure effect and not or only partly due
to opacity effects in their cool dense winds. These comparisons show
the potential of high quality full-Sun VUV spectra and their value
for the study of solar-stellar connections. As an example, this study
proposes that αCen A has a considerably higher amount of magnetic
flux concentrated in the chromospheric magnetic network than the Sun.

---------------------------------------------------------
Title: Forward Modeling of the Corona of the Sun and Solar-like Stars:
From a Three-dimensional Magnetohydrodynamic Model to Synthetic
Extreme-Ultraviolet Spectra
Authors: Peter, Hardi; Gudiksen, Boris V.; Nordlund, Åke
2006ApJ...638.1086P Altcode: 2005astro.ph..3342P
A forward model is described in which we synthesize spectra from an ab
initio three-dimensional MHD simulation of an outer stellar atmosphere,
where the coronal heating is based on braiding of magnetic flux due to
photospheric footpoint motions. We discuss the validity of assumptions
such as ionization equilibrium and investigate the applicability of
diagnostics like the differential emission measure inversion. We find
that the general appearance of the synthesized corona is similar to
the solar corona and that, on a statistical basis, integral quantities
such as average Doppler shifts or differential emission measures are
reproduced remarkably well. The persistent redshifts in the transition
region, which have puzzled theorists since their discovery, are
explained by this model as caused by the flows induced by the heating
through braiding of magnetic flux. While the model corona is only
slowly evolving in intensity, as is observed, the amount of structure
and variability in Doppler shift is very large. This emphasizes the need
for fast coronal spectroscopic observations, as the dynamical response
of the corona to the heating process manifests itself in a comparably
slow evolving coronal intensity but rapid changes in Doppler shift.

---------------------------------------------------------
Title: High resolution solar telescope GREGOR
Authors: Peter, H.; von der Luehe, O.
2006cosp...36.3628P Altcode: 2006cosp.meet.3628P
GREGOR is a new 1 5 m solar telescope assembled on Tenerife Spain by a
German consortium together with international partners It is designed
for high-precision measurements of the magnetic field and the gas motion
in the solar photosphere and chromosphere with a resolution of 70 km on
the Sun and for high resolution stellar spectroscopy The telescope has a
Gregorian configuration mounted in an open structure with a retractable
dome for thermal control and features a multi-conjugate adaptive optics
system GREGOR will be equipped with several post-focus instruments
including polarimetric longslit spectrographs for the visible and
infrared and a high resolution Fabry-Perot filter spectrometer for 3D
spectroscopy Apart from a report on the present status of the instrument
the talk will focus on a selection of science goals of GREGOR Among
these are the emergence evolution and disappearance of small-scale
magnetic flux the energy budget of sunspots and the structure of their
penumbrae as well as the dynamics of the chromosphere In this context
an attempt will be made to put future observations with GREGOR in the
context of modeling of the photosphere chromosphere and corona

---------------------------------------------------------
Title: Evidence for coronal plasma oscillations over supergranular
cells
Authors: Gontikakis, C.; Peter, H.; Dara, H. C.
2006IAUS..233..189G Altcode:
Evidence of coronal oscillations over the interior of supergranular
cells was found through SUMER observations. The observations are
rasters of quiet Sun regions and the oscillations were detected,
in the Ne VIII 770 Å Doppler maps, as a characteristic pattern. It
should be noted that the Ne VIII ion has coronal formation temperature
(650 000 K) and that reports of oscillations in the quiet Sun corona
are scarce. Magnetic extrapolation from MDI magnetogram showed that at
the location where the oscillation was detected, the gas and magnetic
pressures get equalized (β=1) higher in the atmosphere, compared
to the surrounding, non oscillating quiet Sun. This could indicate a
non-compressible wave propagating inside the gas dominated medium of
the cell causing the detected oscillation.

---------------------------------------------------------
Title: Modelling the solar atmosphere including the magnetic field
Authors: Peter, H.
2006cosp...36.2989P Altcode: 2006cosp.meet.2989P
The lower corona and transition region of the Sun are highly structured
through the magnetic field and are very dynamic To account for both
the structure and the dynamics of the solar atmosphere a 3D MHD model
has to be employed The paper will present recent 3D MHD coronal models
and will discuss them with special emphasis on a possible comparison
to observations Results will be presented for spectra derived from the
complex coronal models which can be treated as synthetic observations
The agreement of these to actual average observations of the solar
outer atmosphere is very good especially with respect to Doppler shifts
and the emission measure The results from the 3D MHD models will also
be compared to modeling stellar atmospheres through a superposition
of a large number of individual loops as derived from potential field
extrapolations This will show the limitations as well as the potential
of such multi-loop models Finally the results of modern models of the
solar corona will be put into the context of stellar observations and
possible future directions in coronal modeling will be discussed

---------------------------------------------------------
Title: Forward modeling of coronal funnels
Authors: Aiouaz, T.; Peter, H.; Keppens, R.
2005A&A...442L..35A Altcode:
We propose a forward modeling approach of coronal funnels to investigate
the outer layers of the solar atmosphere with respect to their
thermodynamical properties and resulting emission line spectra. We
investigate the plasma flow out of funnels with a new 2D MHD time
dependent model including the solar atmosphere all the way from
the chromosphere to the corona. The plasma in the funnel is treated
in the single-fluid MHD approximation including radiative losses,
anisotropic thermal conduction, and two different parameterized heating
functions. We obtain plasma properties (e.g. density, temperature
and flow speed) within the funnel for each heating function. From
the results of the MHD calculation we derive spectral profiles of a
low corona emission line (Ne VIII, 770 Å). This allows us e.g. to
study the Doppler shifts across the funnel. These results indicate a
systematic variation of the Doppler shifts in lines formed in the low
corona depending on the heating function used. The line shift above
the magnetic field concentration in the network is stronger than in the
inter-network in both cases. However, for one of the heating functions,
the maximum blue-shift (outflow) is not to be found in the very center
of the funnel but in the vicinity of the center. This is not the case
of the second heating function where the maximum is well aligned with
the centre of the funnel. This model directly relates for the first
time the form of the heating function to the thermodynamic and spectral
properties of the plasma in a funnel.

---------------------------------------------------------
Title: Coronal Heating Through Braiding of Magnetic Field Lines
Synthesized Coronal EUV Emission and Magnetic Structure
Authors: Peter, H.; Gudiksen, B. V.; Nordlund, A.
2005ESASP.596E..14P Altcode: 2005ccmf.confE..14P
No abstract at ADS

---------------------------------------------------------
Title: Coronal oscillation above a supergranular cell of the quiet
Sun chromospheric network?
Authors: Gontikakis, C.; Peter, H.; Dara, H. C.
2005A&A...441.1191G Altcode:
We have detected an oscillation in the low corona, using a raster of
the SUMER EUV spectrograph in the Ne viii, 770 Å line formed at about
700 000 K. The oscillation was found in the Ne viii Doppler map above
the interior of a supergranular cell of the chromospheric network in
the quiet Sun, while it is absent in line radiance. The photospheric
magnetic field, extrapolated to coronal levels, was used to relate
this phenomenon to the magnetic structure. This oscillation phenomenon,
reported here for the first time, seems to occur only above the darkest
cells of the chromospheric network. We interpret our findings as a
collective non-compressible oscillation of the corona above the whole
cell interior. This oscillation may originate at the chromosphere and
the driving wave may undergo a mode conversion at the top chromosphere,
where the magnetic pressure equals the gas pressure. Our interpretation
cannot be definitive and should be verified with more data.

---------------------------------------------------------
Title: First VUV full-Sun spectrum of the transition region with
high spectral resolution compared to cool stars
Authors: Peter, Hardi
2005astro.ph.10319P Altcode:
This paper reports the first full-Sun vacuum ultraviolet (VUV)
emission line profile originating from the transition region from
the chromosphere to the corona. It is based on a raster scan of
the whole solar disk using SUMER/SOHO. The full-Sun spectrum has a
spectral resolution which allows an investigation of details in the
line profile as well as a thorough comparison to stellar spectra
as obtained, e.g. with FUSE or STIS/HST. The full-Sun spectrum
shows enhanced emission in the wings, and is well described by a
double Gaussian fit with a narrow and a broad component. It is shown
that the broad component is due to structures on the solar surface,
especially those related to the magnetic chromospheric network. Thus
it is proposed that the broad components of other solar-like stars
are also a consequence of the mixture of surface structures, and
not necessarily a signature of small-scale heating processes like
explosive events, as it is commonly argued. A comparison to spectra
of luminous cool stars shows that the line asymmetries of these stars
might also be a surface structure effect and not or only partly due
to opacity effects in their cool dense winds. These comparisons show
the potential of high quality full-Sun VUV spectra and their value
for the study of solar-stellar connections. As an example, this study
proposes that alpha Cen A has a considerably higher amount of magnetic
flux concentrated in the chromospheric magnetic network than the Sun.

---------------------------------------------------------
Title: EUV Emission from a 3D MHD Coronal Model: Temporal Variability
in a Synthesized Corona
Authors: Peter, H.; Gudiksen, B. V.; Nordlund, Å.
2005ESASP.592..527P Altcode: 2005soho...16E..98P; 2005ESASP.592E..98P
No abstract at ADS

---------------------------------------------------------
Title: The Structure of the Base of the Corona
Authors: Bingert, S.; Peter, H.; Gudiksen, B.; Nordlund, Ake
2005ESASP.592..471B Altcode: 2005ESASP.592E..84B; 2005soho...16E..84B
No abstract at ADS

---------------------------------------------------------
Title: Relation of the Chromospheric Network to Coronal Funnels and
the Solar Wind
Authors: Aiouaz, T.; Peter, H.; Keppens, R.
2005ESASP.592..135A Altcode: 2005ESASP.592E..20A; 2005soho...16E..20A
No abstract at ADS

---------------------------------------------------------
Title: High-speed coronal rain
Authors: Müller, D. A. N.; De Groof, A.; Hansteen, V. H.; Peter, H.
2005A&A...436.1067M Altcode:
At high spatial and temporal resolution, coronal loops are observed to
have a highly dynamic nature. Recent observations with SOHO and TRACE
frequently show localized brightenings "raining" down towards the solar
surface. What is the origin of these features? Here we present for
the first time a comparison of observed intensity enhancements from an
EIT shutterless campaign with non-equilibrium ionization simulations
of coronal loops in order to reveal the physical processes governing
fast flows and localized brightenings. We show that catastrophic cooling
around the loop apex as a consequence of footpoint-concentrated heating
offers a simple explanation for these observations. An advantage of
this model is that no external driving mechanism is necessary as the
dynamics result entirely from the non-linear character of the problem.

---------------------------------------------------------
Title: The correlation between coronal Doppler shifts and the
supergranular network
Authors: Aiouaz, T.; Peter, H.; Lemaire, P.
2005A&A...435..713A Altcode:
We examine properties of line profiles as found with large raster
scans of the solar corona acquired by the UV spectrometer SUMER on
board SOHO. The observed regions include an equatorial coronal hole,
a polar coronal hole, as well as surrounding quiet Sun areas. In
order to reveal the network and remove strong local brightenings,
a filter is applied to a continuum image. The filtered continuum
image, the intensity image and the dopplergram are used to produce
“scatter diagrams” (dispersion plots). We find correlations
between the chromospheric network, the Ne VIII (770 Å) intensity
and the Ne VIII (770 Å) Doppler shift in quiet Sun areas and in
coronal holes. We establish that the maximum outflow (blue-shift) at
low corona temperatures does not appear in the centre of the network
but rather near network boundaries. Furthermore the maximum blue-shift
seems to appear in the dark regions in Ne VIII line intensity, which
is in agreement with Wilhelm (2000). The opposite correlation appears
for very low intensities (less than half of the average intensity),
revealing in these regions a lack of energy to either accelerate the
solar wind or produce any detectable radiation. The absence of magnetic
field concentration in these regions in a reconstructed magnetogram
from a MDI/SOHO series seems to confirm the lack of energy.

---------------------------------------------------------
Title: Tackling the coronal heating problem using 3D MHD coronal
simulations with spectral synthesis
Authors: Peter, H.; Gudiksen, B. V.; Nordlund, A.
2005ESASP.560...59P Altcode: 2005csss...13...59P
No abstract at ADS

---------------------------------------------------------
Title: On the Outflow at Solar Corona Heights
Authors: Aiouaz, T.; Peter, H.; Lemaire, P.
2004ESASP.575..331A Altcode: 2004soho...15..331A
No abstract at ADS

---------------------------------------------------------
Title: Forward Modelling of Coronal Funnels
Authors: Aiouaz, T.; Peter, H.; Keppens, R.
2004ESASP.575..337A Altcode: 2004soho...15..337A
No abstract at ADS

---------------------------------------------------------
Title: Oscillations Over a Supergranular Cell Observed with SUMER
Authors: Gontikakis, C.; Peter, H.; Dara, H. C.
2004ESASP.575..131G Altcode: 2004soho...15..131G
No abstract at ADS

---------------------------------------------------------
Title: Statistical Comparison of Blinkers and Explosive Events
Authors: Brkovic, A.; Peter, H.
2004ESASP.575..471B Altcode: 2004soho...15..471B
No abstract at ADS

---------------------------------------------------------
Title: Analysis of Synthetic EUV Spectra from 3d Models of the Corona
Authors: Bingert, S.; Peter, H.; Gudiksen, B.; Nordlund, A.; Dobler, W.
2004ESASP.575..348B Altcode: 2004soho...15..348B
No abstract at ADS

---------------------------------------------------------
Title: Synthetic EUV Spectra from 3D MHD Coronal Simulations:
Coronal Heating Through Magnetic Braiding
Authors: Peter, H.; Gudiksen, B. V.; Nordlund, Å.
2004ESASP.575...50P Altcode: 2004soho...15...50P
No abstract at ADS

---------------------------------------------------------
Title: Coronal Heating through Braiding of Magnetic Field Lines
Authors: Peter, Hardi; Gudiksen, Boris V.; Nordlund, Åke
2004ApJ...617L..85P Altcode: 2004astro.ph..9504P
Cool stars such as our Sun are surrounded by a million degree hot outer
atmosphere, the corona. For more than 60 years, the physical nature
of the processes heating the corona to temperatures well in excess of
those on the stellar surface have remained puzzling. Recent progress in
observational techniques and numerical modeling now opens a new window
to approach this problem. We present the first coronal emission-line
spectra synthesized from three-dimensional numerical models describing
the evolution of the dynamics and energetics as well as of the magnetic
field in the corona. In these models the corona is heated through
motions on the stellar surface that lead to a braiding of magnetic
field lines inducing currents that are finally dissipated. These
forward models enable us to synthesize observed properties such as
(average) emission-line Doppler shifts or emission measures in the outer
atmosphere, which until now have not been understood theoretically,
even though many suggestions have been made in the past. As our model
passes these observational tests, we conclude that the flux braiding
mechanism is a prime candidate for being the dominant heating process
of the magnetically closed corona of the Sun and solar-like stars.

---------------------------------------------------------
Title: Thermal Instability as the Origin of High Speed Coronal Rain
Authors: Müller, D. A. N.; de Groof, A.; Hansteen, V. H.; Peter, H.
2004ESASP.575..291M Altcode: 2004soho...15..291M
No abstract at ADS

---------------------------------------------------------
Title: Dynamics of solar coronal loops. II. Catastrophic cooling
and high-speed downflows
Authors: Müller, D. A. N.; Peter, H.; Hansteen, V. H.
2004A&A...424..289M Altcode: 2004astro.ph..5538M
This work addresses the problem of plasma condensation and
“catastrophic cooling” in solar coronal loops. We have carried out
numerical calculations of coronal loops and find several classes of
time-dependent solutions (static, periodic, irregular), depending on
the spatial distribution of a temporally constant energy deposition
in the loop. Dynamic loops exhibit recurrent plasma condensations,
accompanied by high-speed downflows and transient brightenings of
transition region lines, in good agreement with features observed with
TRACE. Furthermore, these results also offer an explanation for the
recent EIT observations of \cite{DeGroof+al2004AA} of moving bright
blobs in large coronal loops. In contrast to earlier models, we suggest
that the process of catastrophic cooling is not initiated by a drastic
decrease of the total loop heating but rather results from a loss
of equilibrium at the loop apex as a natural consequence of heating
concentrated at the footpoints of the loop, but constant in time.

---------------------------------------------------------
Title: Statistical comparison of transition region blinkers and
explosive events
Authors: Brković, A.; Peter, H.
2004A&A...422..709B Altcode:
Explosive events and blinkers are two observational classes
of transients seen on the quiet Sun and an investigation of the
significance of and relationship between such events may be critical
for understanding basic processes at work in the solar atmosphere. We
analysed five time-series spectra of the quiet Sun of transition region
O XV 629 Å, O XVI 1032 Å and O XVI 1038 Å lines. We investigated how
often explosive events occurred during the course of a blinker at the
same location and found that slightly more than a half of all explosive
events happened during about one third of all blinkers. In some cases
during a blinker more than one explosive event was registered. The
largest average maximum relative intensity enhancement was for blinkers
with explosive events, followed by the blinkers without explosive
events, with the least being for the explosive events which did not
happen during the course of a blinker. Due to these differences among
the maximum enhancements between these events we suppose that blinkers
and explosive events are two independent phenomena. Intensity light
curves of blinkers show that events can be separated into two classes,
specifically: 1) simple blinkers with smooth increase in intensity
having only one significant peak, and 2) complex blinkers characterised
by multiple (2-4) significant peaks. These two classes were equally
represented when frequencies of their occurrences were averaged over
five analysed data-sets. The analysis of the line profile parameters
and their correlations for these two classes did not give any result
which could further distinguish between them. During blinkers the
intensity peaks mostly at the middle of their durations, while the line
width peaks somewhat earlier than the intensity. This was a general
character for both simple and complex blinkers, as well as for all
explosive events.

---------------------------------------------------------
Title: Transition region blinkers versus explosive events
Authors: Brkovic, A.; Peter, H.
2004IAUS..223..449B Altcode: 2005IAUS..223..449B
Explosive events and blinkers are two observational classes
of transients seen on the quiet Sun and an investigation of the
significance of and relationship between such events may be critical
for understanding basic processes at work in the solar atmosphere. Our
analysis showed that blinkers and explosive events are independent
phenomena which have to be explained separately.

---------------------------------------------------------
Title: Analysis of Intensities, Line Widths and Line Shifts during
Blinkers
Authors: Brkovic, A.; Peter, H.
2004ESASP.547..251B Altcode: 2004soho...13..251B
Explosive events and blinkers are two major observational classes of
transients seen on the quiet Sun. We analysed five time-series spectra
of transition region lines O V 629 Å, O VI 1032 Å and O VI 1038 Å
and detected 209 blinkers and 55 explosive events. In 44 cases both
events were present at the same pixel simultaneously. This means that
about 21% of blinkers coincided with explosive events and that 80%
of explosive events had intensity enhancements typical for blinkers
on the time scale longer than an hour. In more than a half of the
eleven remaining explosive events we found that intensity enhancements
relative to the pre-event level were on average on the 100% level
on the time scale somewhat longer than duration of explosive event,
i.e., shorter than ten minutes. The blinkers without an explosive
event signature could be separated into two observational classes:
1) Simple blinkers with smooth increase in intensity having only one
significant peak and 2) Complex or oscillating blinkers characterised
by multiple (2-4) significant peaks. By percentage the class 1) was
represented with about 45% and the class 2) with about 34%.

---------------------------------------------------------
Title: Thermal non-equilibrium in coronal loops: A road to complex
evolution
Authors: Müller, Daniel; de Groof, A.; Hansteen, V. H.; Peter, H.
2004IAUS..223..289M Altcode: 2005IAUS..223..289M
At high spatial and temporal resolution, coronal loops are observed to
have a highly dynamic nature. Recent observations with SOHO and TRACE
frequently show localized brightening "raining" down towards the solar
surface. What is the origin of these features? Here we present for
the first time a comparison of observed intensity enhancements from an
EIT shutterless campaign with non-equilibrium ionization simulations
of coronal loops in order to reveal the physical processes governing
fast flows and localized brightening. We show that catastrophic cooling
around the loop apex as a consequence of footpoint-concentrated heating
offers a simple explanation for these observations. An advantage of
this model is that no external driving mechanism is necessary as the
dynamics result entirely from the non-linear character of the system.

---------------------------------------------------------
Title: Catastrophic Cooling and High-Speed Downflows in Solar
Coronal Loops
Authors: Müller, D.; Peter, H.; Hansteen, V.
2004IAUS..219..765M Altcode: 2003IAUS..219E..48M
We report numerical simulations of the condensation of plasma in
short solar coronal loops which has several interesting physical
consequences. Firstly we propose a connection between small cool loops
which presumably constitute the solar transition region and prominences
in the sense that the same physical mechanism governs their dynamics
namely the onset of instability and runaway cooling due to strong
radiative losses. Secondly we show that the temporal evolution of
these loop models exhibit a cyclic pattern of chromospheric evaporation
condensation formation motion of the condensation region to either side
of the loop and finally loop reheating with a period of 4000 - 6000
s for a loop of 10 Mm length. Thirdly we have synthesized transition
region lines from these simulations which show strong periodic intensity
variations making condensation processes in loops a candidate to
account for the observed temporal variability of these lines.

---------------------------------------------------------
Title: Plasma Condensation in Solar Coronal Loops: II. "Catastrophic
Cooling" and High-Speed Downflows
Authors: Müller, D. A. N.; Peter, H.; Hansteen, V. H.
2004ESASP.547..199M Altcode: 2004soho...13..199M
The second part of this work focuses on the application of the
concept of plasma condensation to large coronal loops. In contrast
to the short loops analyzed in Müller et al. (2003a), these models
can more easily be compared to SOHO and TRACE observations. From our
numerical calculations of coronal loops we find several classes of
time-dependent solutions (static, periodic, irregular), depending on
the spatial dependence of a temporally constant energy deposition
in the loop. One of these classes is in remarkably close agreement
with the features observed with TRACE, described by Schrijver (2001):
Emission in C IV (154.8 nm), developing initially near the loop tops,
cool plasma sliding down on both sides of the loop, downflow velocities
of up to 100 km/s, and a downward acceleration which is substantially
reduced with respect to the solar surface gravity. Furthermore, these
results also offer an explanation for the observations of De Groof
et al. (2003a,b). In contrast to earlier models, we suggest that the
process of catastrophic cooling does not have to be initiated by a
drastic decrease of the loop heating. It can also result from a loss
of equilibrium at the loop apex which is a natural consequence if the
loop is heated predominantly at the footpoints, but constant in time.

---------------------------------------------------------
Title: SOHO/SUMER Results: Mass Flows
Authors: Peter, H.
2004IAUS..219..575P Altcode: 2003IAUS..219E.195P
Hardly any part of the chromosphere and the low corona of the Sun is
in a static state. Spectrographs reveal line shifts and non-thermal
broadening indicating mass supply to the corona draining of coronal
material siphon flows wave propagation and more. Imaging instruments
show apparent motions of bright or dark structures indicating the
presence of flows and waves too. This paper will review recent
observations of mass and wave motions in the low corona focusing
on spectroscopic investigations and will discuss their relevance to
the understanding of the dynamics and energetics of the corona. Special emphasis will be devoted to the question what these solar
observations might teach us with respect to stellar coronae and how
we could use observations and models of stellar coronae to improve
our knowledge of the Sun.

---------------------------------------------------------
Title: Structure and Dynamics of the Low Corona of the Sun (With
13 Figures)
Authors: Peter, Hardi
2004RvMA...17...87P Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Dynamics and Properties of Coronal Funnels
Authors: Aiouaz, T.; Peter, H.; Lemaire, P.; Keppens, R.
2004ESASP.547..375A Altcode: 2004soho...13..375A
Coronal funnels are open magnetic structures connecting the chromosphere
with the solar corona [5, 3]. We investigate the stationary plasma
flow out of funnels with a 2D- MHD model. The funnel area function is
derived from a magnetic field model and the funnel is approximately 10
Mm high and 20 Mm wide. The energy balance includes radiative losses,
thermal conduction, and a parametrized heating function. We adjust the
parameters to the quantities measured in the lower solar corona. We
obtained 2D plasma properties (e.g. density, temperature, flow speed,
etc.) within the funnel. From the results of the MHD calculation we
synthesize emision profiles of various lines formed in the transition
region from the chromosphere to the corona. This allows us to study
e.g. the Doppler shifts at various temperatures across the funnel
and thus enables a detailed comparison of the model results with
observations. For this we investigate SUMER data and study Doppler
shifts perpendicular to the chromospheric network for different emission
lines, where a tessalation technique is used to derive the outlines of
the chromospheric network. In this paper typical results are presented
for the Ne VIII(770.4 Å) line. Preliminary results show that these
model caclulations compare well to the observations.

---------------------------------------------------------
Title: Plasma Condensation in Solar Coronal Loops -- I. Basic
Processes
Authors: Müller, D. A. N.; Hansteen, V. H.; Peter, H.
2004ESASP.547..285M Altcode: 2004soho...13..285M
In the first part of this work, we report numerical calculations
of the condensation of plasma in short coronal loops, which has
several interesting physical consequences. We propose a connection
between small, cool loops, which presumably constitute the solar
transition region, and prominences in the sense that the same physical
mechanism governs their dynamics, namely the onset of instability
and runaway cooling due to strong radiative losses. We show that the
temporal evolution of these loop models exhibits a cyclic pattern of
chromospheric evaporation, condensation, motion of the condensation
region to either side of the loop, and finally loop reheating with
a period of 4000 - 8000 s for a loop of 10 Mm length. Furthermore,
we have synthesized transition region lines from these calculations
which show strong periodic intensity variations, making condensation
in loops a candidate to account for observed transient brightenings of
solar transition region lines. Remarkably, all these dynamic processes
take place for a heating function which is constant in time and has a
simple exponential height dependence. In the second part of this work
(Müller et al., 2003b), we apply this concept to large coronal loops.

---------------------------------------------------------
Title: Heating the magnetically open ambient background corona of
the Sun by Alfvén waves
Authors: Peter, H.; Vocks, C.
2003A&A...411L.481P Altcode:
Observations of UVCS/SOHO of very high emission line widths in the
outer corona suggest that the open field regions there are heated by
ion-cyclotron resonance absorption of Alfvén waves resulting in the
ions being much hotter than the electrons. In the lower corona it is
usually assumed that the effective Coulomb-interactions ensure equal
temperatures of ions and electrons. However, recent models have shown
that in regions of strong magnetic field gradients the ion-cyclotron
absorption can be so efficient that the ion temperature overcomes the
electron temperature. In this paper we will present new observational
results from SUMER/SOHO showing that the lines of O 5 and S 6 have very
large line widths just above the limb. The peak line width occurs at
about 10 arcsec above the limb and corresponds to ion temperatures of
more than 3x 106 K. We compare these observational results to
new models in which plasma in coronal funnels is heated and accelerated
by means of ion-cyclotron absorption of high-frequency waves. As our
model is in good qualitative agreement with the observations we come
to the conclusion that the open corona in coronal funnels could well
be heated by an ion-cyclotron absorption mechanism, even close to the
Sun in the low corona.

---------------------------------------------------------
Title: Dynamics of solar coronal loops. I. Condensation in cool
loops and its effect on transition region lines
Authors: Müller, D. A. N.; Hansteen, V. H.; Peter, H.
2003A&A...411..605M Altcode:
We report numerical calculations of the condensation of plasma
in short coronal loops, which have several interesting physical
consequences. Firstly, we propose a connection between small, cool
loops (T &lt; 106 K), which constitute one of the basic
components of the solar transition region, and prominences, in the
sense that the same physical mechanism governs their dynamics: Namely
the onset of instability and runaway cooling due to strong radiative
losses. Secondly, we show that the temporal evolution of these
loop models exhibits a cyclic pattern of chromospheric evaporation,
condensation, motion of the condensation region to either side of the
loop, and finally loop reheating with a period of 4000-8000 s for a loop
of 10 Mm length. Thirdly, we have synthesized transition region lines
from these calculations which show strong periodic intensity variations,
making condensation in loops a candidate to account for observed
transient brightenings of solar transition region lines. Remarkably,
all these dynamic processes take place for a heating function which
is constant in time and has a simple exponential height dependence.

---------------------------------------------------------
Title: Sizes of quiet Sun transition region structures
Authors: Gontikakis, C.; Peter, H.; Dara, H. C.
2003A&A...408..743G Altcode:
We studied the morphology of the transition region of the quiet Sun,
with data obtained by the Solar Ultraviolet Measurements of Emitted
Radiation spectrometer (SUMER) and the Extreme-Ultraviolet Imaging
Telescope (EIT), in September 1996. We analyzed lines emitted in the
chromosphere, the low transition region and the low corona. We computed
the mean autocorrelation function for the radiance images in order
to estimate the characteristic size of the features present in the
transition region. Moreover different estimate McCly-mont. Moreover,
we calculated autocorrelation functions for the dopplergrams and
line width images deduced from the SUMER data. In addition to the
line core of the C IV line, we investigated a broader tail component,
whose origin is still unclear. We found that the size of the bright
radiance features is always larger than the size of the structures
of the dopplergrams and Doppler widths, at any altitude. The network
features seem to diminish at a temperature around 105 K,
due to the thermodynamic properties of the transition region. The mean
size of the structures of the tail component radiance is smaller than
the one of the core radiance.

---------------------------------------------------------
Title: Relation of transition region blinkers to the low chromosphere
Authors: Brković, A.; Peter, H.
2003A&A...406..363B Altcode:
We investigated the coupling between the low chromosphere, lower and
upper transition region through the study of blinkers. Blinkers are
extreme ultraviolet (EUV) small-scale transient brightenings best
detected in transition region lines showing an intensity enhancement
on the 60-100% level on average. We analysed time-series spectra of
the \cii 1037 Å (2-4x 104 K, lower transition region) and
\oxvi 1038 Å (3x 105 K, upper transition region) lines, as
well as the \ci continuum at 1042 Å formed about 1 Mm above the solar
surface, obtained with the Solar Ultraviolet Measurement of Emitted
Radiation (SUMER) spectrometer on SOHO. Blinkers detected in \cii and
\oxvi have similar enhancement levels. We found a modest space-time
overlap between blinkers in the two lines and a small correlation
between \cii or \oxvi blinkers and the corresponding light curve in
the chromospheric continuum. This suggests a relation of EUV blinkers
to the chromosphere, which could support the idea that blinkers are
the consequence of granular collisions. The average duration of \oxvi
blinkers amounts to 10.0 min and of \cii blinkers to 6.7 min.

---------------------------------------------------------
Title: Dynamics of Coronal loops: "Catastrophic Cooling" and
High-speed Downflows
Authors: Müller, D. A. N.; Hansteen, V. H.; Peter, H.
2003ANS...324...13M Altcode: 2003ANS...324..B09M
No abstract at ADS

---------------------------------------------------------
Title: Dynamics and Properties of Coronal Funnels
Authors: Aiouaz, T.; Peter, H.; Lemaire, Philippe; Keppens, Rony
2003ANS...324....7A Altcode: 2003ANS...324..B01A
No abstract at ADS

---------------------------------------------------------
Title: Condensation in Cool Coronal Loops and its Effect on Transition
Region Lines
Authors: Müller, D. A. N.; Hansteen, V. H.; Peter, H.
2003ANS...324..108M Altcode: 2003ANS...324..P14M
No abstract at ADS

---------------------------------------------------------
Title: Ion-cyclotron Heating in the Low Corona
Authors: Peter, Hardi; Vocks, Christian
2003ANS...324R..16P Altcode: 2003ANS...324..B13P
No abstract at ADS

---------------------------------------------------------
Title: Relation of Transition Region Blinkers to the Low Chromosphere
Authors: Brković, Alen; Peter, Hardi
2003ANS...324..107B Altcode: 2003ANS...324..P13B
No abstract at ADS

---------------------------------------------------------
Title: Variability of EUV-spectra from the quiet upper solar
atmosphere: Intensity and Doppler shift
Authors: Brković, A.; Peter, H.; Solanki, S. K.
2003A&A...403..725B Altcode:
We have studied SUMER and CDS time series of spectra and images of
quiet-Sun regions at the solar disc centre. The data contain ultraviolet
emission lines sampling temperatures of the chromosphere, transition
region and corona. We find a high correlation between average net
Doppler shifts and relative brightness variabilities of the studied
lines (correlation coefficient of 0.92), suggesting a connection between
the two quantities. The anti-correlation between differential emission
measures and relative brightness variabilities is weaker (correlation
coefficient of -0.78). We discuss the observed relationships on the
basis of differential emission measures and linear wave calculations.

---------------------------------------------------------
Title: Explosive events and transition region blinkers: Time
variability of non-Gaussian quiet Sun EUV spectra
Authors: Peter, H.; Brković, A.
2003A&A...403..287P Altcode:
The transition region (TR) from the chromosphere to the corona of
the Sun and solar type stars is a very dynamic regime. On the Sun
at least two major observational classes of transients can be seen:
explosive events and blinkers. Besides these transients there is
also a more steady spectral component in transition region lines
that accounts for the deviation of the line profile from a (single)
Gaussian shape, i.e. for enhanced wings that are well described by a
second broad Gaussian, a tail component. The present paper discusses
the spectral properties of these features in order to learn more
about a possible connection between blinkers, explosive events and
tail components. This paper will show that explosive events are most
probably not related to the tail components or to transition region
blinkers. During a blinker not only the intensity rises, as described
by many CDS studies, but also the line width and shift are changing,
as we show with SUMER spectra. The variation in line shift and width
is closely related to the intensity variation. The line width drops
to very small values at the midst of a blinker, almost reaching the
thermal line width, while at the same time the Doppler shifts reach a
maximum value. From this we may conclude that blinkers are driven by
events in the chromosphere heating a loop asymmetrically and powering
a strong laminar flow through the loop.

---------------------------------------------------------
Title: Two-component structure of the solar transition region
Authors: Gontikakis, C.; Peter, H.; Dara, H. C.
2002ESASP.506..625G Altcode: 2002svco.conf..625G; 2002ESPM...10..625G
We studied the morphology of the quiet Sun in the Transition Region,
using observations of the SUMER spectrograph in three emission lines (Si
II, 1533 Å, C IV, 1548 Å and Ne VIII, 770 Å), emitted respectively
in the chromosphere, the low transition region and the low corona, as
well as EIT images in the four passbands of the instrument. We computed
the mean autocorrelation function for the intensity images in order
to estimate the characteristic size of the features present in the
Transition Region. Moreover, we deduced autocorrelation functions for
the Dopplergrams and line width images. Specifically, using images of
the C IV emission lines tail component, as this is estimated by a double
Gaussian fit, we studied the morphology of the coronal funnels, as they
appear at 105K (formation temperature of the C IV line). We
found that the size of the intensity bright features is always larger
than the size of the structures of the dopplergrams and dopplerwidths,
at all altitudes. The mean size of the structures of the tail component
intensity is smaller than the one of the core intensity component.

---------------------------------------------------------
Title: Multi-component transition region structure of the Sun
and stars
Authors: Peter, H.
2002ASPC..277..291P Altcode: 2002sccx.conf..291P
No abstract at ADS

---------------------------------------------------------
Title: Open and closed magnetic structures in the transition region
Authors: Peter, Hardi
2002ESASP.505..525P Altcode: 2002solm.conf..525P; 2002IAUCo.188..525P
To trace back the origin of the solar wind to the transition region and
chromosphere it is of importance to distinguish between magnetically
open and closed regions. As it is not yet possible to measure
coronal fields with the required accuracy, one has to fall back on
interpreting the observed spectra. If heated by the same energy flux
a magnetically closed region should be significantly denser than an
open region. This is because the solar wind carries away up to 90%
of the energy input. Therefore the emission is dominated by closed
structures almost everywhere on the Sun. The noticeable difference
in density of open and closed regions allows to distinguish open
and closed regions by means of spectroscopy. As the non-thermal
broadening, e.g. due to waves, is larger in a less dense plasma, one
expects two-component spectral profiles in areas where open and closed
regions are not resolved spatially: a narrow intense line core from the
dense low coronal loops and a broad weaker tail component from coronal
funnels. The latter ones might be either feet of large less dense loops
or the base of the solar wind. This paper will present results on the
spectroscopic deconvolution of magnetically open and closed regions,
e.g., wave transport of energy in the coronal funnels. The results
will also be related to stellar transition region observations.

---------------------------------------------------------
Title: Hierarchy of chromospheric structures and their relation to
the magnetic field
Authors: Peter, Hardi
2002ESASP.505..155P Altcode: 2002IAUCo.188..155P; 2002solm.conf..155P
While the plasma is dominating the magnetic field in the
photosphere, the roles are exchanged in the corona. In a "traditional"
one-dimensional picture the change from plasma to magnetically dominated
(at plasma β = 1) takes place somewhere in the chromosphere. Therefore
the magnetic structure of the chromosphere is one of the keys to
understand the relevant processes in the solar atmosphere. The
most prominent structure of the chromosphere is the network with
strong magnetic fields. The interior of the super-granulation cells
are non-magnetic and dominated by shocks producing the well known
grains. The oscillations can be heavily influenced by the magnetic
structure: e.g. in case of a low canopy the usually prominent
3 minute intensity fluctuations might vanish. The structure of
the network, however, is far more complicated. A large number of
phenomena, spicules being the most prominent one, are found in the
network. While the chromospheric structures in the visible and near UV
are now studied for more than 100 years, it was not until recently that
also the EUV emission lines and continua from the chromosphere can be
studied. Furthermore EUV images in lines formed at coronal temperatures
revealed new chromospheric phenomena, like the "moss", and their
relation to the "classical" chromosphere is still unclear. This paper
will try to review (some of) the important chromospheric structures
and discuss their relation to photospheric and coronal processes,
especially with respect to the magnetic field.

---------------------------------------------------------
Title: Time variability of coronal funnels
Authors: Brković, A.; Peter, H.
2002ESASP.505..215B Altcode: 2002IAUCo.188..215B; 2002solm.conf..215B
Transition region spectra from the network are commonly composed by two
components: a narrow one from smaller loops and a broad tail component
that can be interpreted as originating from coronal funnels. We present
a time series analysis of tail components for one network region. A
comparison of fitted spectra obtained by applying running means with
full time resolution spectra shows that typical explosive events are not
responsible for the observed tail components. The correlation between
core and tail intensities on time-scales of minutes is not significant.

---------------------------------------------------------
Title: Composition of the solar chromosphere and transition region
Authors: Peter, Hardi
2002AdSpR..30...13P Altcode:
The composition of the solar plasma is an important tool to study
several physical processes, e.g. to trace back the source region of
the solar wind. The most prominent effect is the change of elemental
abundances from the photosphere to the corona according to the first
ionisation potential, the FIP-effect. It is widely accepted that
this takes place in the chromosphere, where the particles turn from
neutral to ionised. Many models for the element fractionation have been
presented so far. Basically they all make use of the separation of ions
and neutrals, but still, there is no conclusion as to which of them is
the most important physical process leading to this separation. The
situation is a bit like with coronal heating: many suggestions, but
very limited ability to to prove them right or wrong. Of course, the
ideal way to test the models for the composition in the chromosphere
and the transition region would be to perform direct observations
of that region. But unlike in the corona a reliable inversion of the
spectral observations of chromospheric and transition region emission
lines is nearly impossible. But probably new thoughts on the structure
of the chromosphere and the transition region combined with advanced
forward modeling will finally lead to some new insights to this
puzzling question.

---------------------------------------------------------
Title: Relative brightness variability vs. averaged Doppler shift
in the quiet Sun
Authors: Brković, A.; Peter, H.; Solanki, S. K.
2002ESASP.508..281B Altcode: 2002soho...11..281B
We studied SUMER and CDS time series of spectra and images of quiet-Sun
regions at disc centre. Ultraviolet emission lines sampling temperatures
of the chromosphere, transition region and corona were recorded. We
found a high correlation between average net Doppler shifts and
relative brightness variabilities of the studied lines. We point to
some basic ideas which could eventually model the variability-Doppler
shift relationship.

---------------------------------------------------------
Title: The nature of the solar transition region
Authors: Peter, Hardi
2002ESASP.508..237P Altcode: 2002soho...11..237P
One of the keys to the understanding of coronal heating is the structure
of the thin transition region from the chromosphere to the corona. All
the energy that is ultimately heating the corona has to be transported
somehow from the photosphere through this thin layer. As the "natural"
time-scales are very small in the transition region the analysis of
the EUV emission formed between 104 to 106K
provides a suitable tool to study effects of the energy transport. As
we are far from spatially resolving the transition region, spectroscopy
can be used to deconvolve the emission from different structures. If
either the line width or the line shift or both signatures differ,
one can still study two regions even though they are not spatially
resolved. This is especially true if the different structures are on
top of each other ("vertically"). One example are large coronal funnels
arching over smaller transition region loops. These spectroscopic
techniques can also be used to interpret observations of stellar
transition regions. This paper will try to give an overview of the
various transition region structures and their physical nature, as
well as on the required observational techniques.

---------------------------------------------------------
Title: New views of the solar transition region
Authors: Peter, Hardi
2002AdSpR..30..501P Altcode:
Two decades ago it was discovered that emission lines from the solar
transition region from the chromosphere to the corona are composed by
two Gaussian components: a narrow core and a broad second component
contributing up to 25% to the total intensity. New observations with
SUMER/SOHO allow for the first time statistically significant results on
the widths and Doppler shifts of the broad second components. Evidence
will be presented that the two components of the line profile correspond
to two radically different physical regimes. Of course, the results
for the dominant line core fit into the well known properties of
transition region lines, e.g. the redshifts. In contrast, the second
broad components, which occur only in the bright network, show different
properties. Most striking is the fact that large parts of the network
show blueshifts in the second components, while the core is redshifted
at the same location. The results suggest that the second component is
formed in Gabriel-type coronal funnels and that these are heated in
the same manner as open field regions, i.e. the solar wind. However,
the analysis of the Doppler shifts shows that these funnels should
not be magnetically open, but rather the footpoint regions of large
coronal loops spanning across several network elements.

---------------------------------------------------------
Title: Multi-component structure of the solar transition region
Authors: Peter, Hardi
2001ESASP.493..327P Altcode: 2001sefs.work..327P
No abstract at ADS

---------------------------------------------------------
Title: On the nature of the transition region from the chromosphere
to the corona of the Sun
Authors: Peter, H.
2001A&A...374.1108P Altcode:
One of the keys to understand coronal heating is to understand the
(magnetic) structure of the atmosphere below the respective coronal
features. The EUV emission lines formed in the thin transition region
from the chromosphere to the corona present a sensitive tool to study
the structure and dynamics of the lowermost corona and its connection
to the chromosphere. Data from the SUMER spectrograph on SOHO show
for the first time that broad components are a common feature of
emission line profiles formed from some 40 000 K to 106
K. The contribution of that tail component to the total intensity of
the line exhibits a trend with line formation temperature that peaks
in the middle transition region with smaller contribution at high
and low temperatures. The line width of the tail component shows a
monotonic increase with temperature that is consistent with a passing
Alfvén wave, which is in contrast to the trend in width of the line
core. Together with previous observations this presents evidence that
the line core and the tail component are formed in radically different
physically regimes. It is proposed that these are small closed loops
and coronal funnels, respectively, with the latter being the footpoints
of large coronal loops. The new results on the structuring of the
transition region will improve understanding on heating the corona
and accelerating the solar wind.

---------------------------------------------------------
Title: An Observational Manifestation of Magnetoatmospheric Waves
in Internetwork Regions of the Chromosphere and Transition Region
Authors: McIntosh, S. W.; Bogdan, T. J.; Cally, P. S.; Carlsson, M.;
Hansteen, V. H.; Judge, P. G.; Lites, B. W.; Peter, H.; Rosenthal,
C. S.; Tarbell, T. D.
2001ApJ...548L.237M Altcode:
We discuss an observational signature of magnetoatmospheric waves in
the chromosphere and transition region away from network magnetic
fields. We demonstrate that when the observed quantity, line or
continuum emission, is formed under high-β conditions, where β is
the ratio of the plasma and magnetic pressures, we see fluctuations in
intensity and line-of-sight (LOS) Doppler velocity consistent with the
passage of the magnetoatmospheric waves. Conversely, if the observations
form under low-β conditions, the intensity fluctuation is suppressed,
but we retain the LOS Doppler velocity fluctuations. We speculate that
mode conversion in the β~1 region is responsible for this change in
the observational manifestation of the magnetoatmospheric waves.

---------------------------------------------------------
Title: Coronal Heating and Solar Wind Acceleration: Future Work
on Observations
Authors: Peter, Hardi
2001SSRv...95..107P Altcode:
The space-based observatories SOHO and TRACE have shown some very
interesting results on the structure and dynamics of the Sun and its
atmosphere, e.g., the extremely high ion temperatures or the enormous
variability in the corona. But one question is still open to debate:
how to use these data to distinguish between different types of physical
heating processes, as, e.g., absorption of high-frequency Alfvén-waves
or reconnection events? This paper will discuss some possibilities on
how to tackle this type of question. These include observations of ion
temperature anisotropies and electron temperatures in the corona as
well as measurements of coronal magnetic fields. Emphasis will be put
on simultaneous observations of the whole solar atmosphere from the
photosphere into the solar wind and on solar-stellar connections. In
the light of these ideas new proposed space missions as well as ground
based efforts will be discussed.

---------------------------------------------------------
Title: Erratum: Multi-component structure of solar and stellar
transition regions
Authors: Peter, H.
2000A&A...364..933P Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Multi-component structure of solar and stellar transition
regions
Authors: Peter, H.
2000A&A...360..761P Altcode:
Emission lines from the solar transition region between the chromosphere
and the corona often show a two Gaussian component profile with a
core and a broad second component contributing up to 25% to the total
intensity. For the first time a systematic study of the broadening and
Doppler shift of the second weaker components is performed using SUMER
on SOHO to explore the spatial structures of the second components. It
is found that the two component structure is basically restricted
to the bright chromospheric network. The narrow core component shows
the familiar transition region redshifts, with hardly any blueshifts
in the network. The broad second components are blueshifted compared
to the core, but are still predominantly redshifted. However, quite
large areas in the network (up to 20”× 20”) show concentrations
of blueshifts in the second component. In the inter-network the
line profile has a single Gaussian shape and shows small red- and
also some blueshifts. It is suggested that the two components in the
network correspond with two spatially unresolved physical regimes in
quiet Sun network: small scale loops and larger scale coronal loop
structures anchored in the network. The footpoint regions of the
latter are of a funnel-type and form a "canopy" above inter-network
regions of the chromosphere. Shocks propagating upward from the non-
magnetic chromosphere interact with this canopy, which leads to
the transition region inter-network emission. A further analysis,
especially of emission lines originating from higher temperatures, is
required to confirm this scenario. The distribution and correlations
of the line intensities, shifts and widths show that these physical
regimes are heated by different mechanisms. This sheds new light on the
interpretation of stellar observations in terms of coronal heating. A
comparison to existing studies of stellar transition regions shows the
need for more thorough theoretical investigations on the formation of
stellar transition region lines.

---------------------------------------------------------
Title: On the Doppler Shifts of Solar Ultraviolet Emission Lines
Authors: Peter, H.; Judge, P. G.
1999ApJ...522.1148P Altcode:
We examine emission-line profiles observed with the Solar Ultraviolet
Measurement of Emitted Radiation (SUMER) instrument during the roll
of the SOHO spacecraft on 1997 March 20. SUMER data were acquired in
selected wavelength bands including lines from the low chromosphere to
the corona. Our main aim is to determine the center-to-limb behavior
of emission lines formed in the chromosphere, transition region,
and corona, especially of the observed Doppler shifts, to try to
form a consistent picture of the basic kinematic properties of the
emitting plasmas. To achieve this we combine the roll data with data
from the full disk discussed elsewhere and fitted Gaussian profiles
to the cores of the line profiles. The Doppler-shift data at large
spatial scales (&gt;50") clearly reveal center-to-limb redshift
behavior consistent with a cosϑ variation in all transition region
lines. The three “coronal” lines in the data set (of Ne VIII and
Mg X) reveal center-to-limb behavior consistent with disk-center
blueshifts, in contradiction to some previous work. The redshift
to blueshift transition occurs at electron temperatures of about
5×105 K. Furthermore, we present evidence for an outflow
of the fast solar wind from the coronal holes throughout the whole
transition region. These results confirm and extend earlier work and
point toward a (re-) measurement of rest wavelengths of lines formed at
coronal temperatures in the laboratory. Together these results provide
a firmer observational foundation for the development of classes of
models to account for the well-known redshifts and point to the need
to develop models that can also account for the coronal-line blueshifts.

---------------------------------------------------------
Title: The Chromosphere in Coronal Holes and the Quiet-Sun Network:
an HE I (584 Å) Full-Disk Scan by SUMER/SOHO
Authors: Peter, H.
1999ApJ...522L..77P Altcode:
A raster scan by Solar Ultraviolet Measurements of Emitted
Radiation/Solar and Heliospheric Observatory (SOHO) of the full solar
disk containing over 2 million individual spectra of the He I line
at 584 Å provides the possibility to study small- and large-scale
variations of intensity, line shift, and line width. New striking
features are the enhanced line width and the blueshifts in the coronal
holes as well as the long-known reduced intensity there. The relation
of intensity versus line shift and the variation of the line shift
in the coronal holes indicate that the blueshifts in the holes are
not consistent with a uniform outflow. The observations suggest that
optical depth effects might be responsible for the observed blueshifts
and line widths. These results motivate new observations by SOHO and
ground-based facilities.

---------------------------------------------------------
Title: Doppler shifts of solar UV emission lines and the source
region of the (fast) solar wind
Authors: Peter, Hardi
1999AIPC..471..281P Altcode: 1999sowi.conf..281P
Full-disk observations with the UV spectrograph SUMER on board SOHO
offer the possibility to study emission line profiles on the whole solar
disk, beyond what was possible in previous UV studies, e.g. with HRTS
or on board Skylab. SUMER data acquired during a SOHO spacecraft roll
are complementary to the full-disk data as they cover a wider range
of emission lines. In both data sets the center-to-limb variation of
the Doppler shifts can be studied, allowing a precise determination
of the Doppler shift at disk center. The most interesting result
is the opposite center-to-limb variation of the lines formed below
and above 5.105 K and the blueshift of the hotter lines
found at disk center. This is of importance for the understanding of
physical models for the transition region from the chromosphere to the
corona. By comparing the quiet Sun and coronal hole regions the outflow
velocity of the fast solar wind and the variation of the cross-section
of the flow channels of the fast solar wind throughout the transition
region can be estimated. Finally by comparing different methods of
wavelength calibration one can re-evaluate the rest (or “laboratory”)
wavelengths, which are but poorly known for the hotter lines.

---------------------------------------------------------
Title: Analysis of Transition-Region Emission-Line Profiles from
Full-Disk Scans of the Sun Using the SUMER Instrument on SOHO
Authors: Peter, H.
1999ApJ...516..490P Altcode:
We examine statistical properties of line profiles seen in full-disk
observations with the UV spectrograph SUMER on board SOHO. In the
SUMER data archive, full-disk data with complete spectral information
are available only for wavelength regions including the He I (584 Å),
Ne VIII (770 Å), C III (977 Å) and C IV (1548 Å) emission lines. In
this paper we will concentrate on C IV and Ne VIII. Collectively these
data provide us with the unique opportunity to study the properties of
line profiles in the lower and upper solar transition-region beyond
what could be achieved with earlier instruments. In particular,
these data reveal the center-to-limb behavior of line shifts and line
widths for the first time in a statistically meaningful way. For
C IV these data show the well-known redshift of the transition-region
lines in the quiet Sun and a clear correlation of the Doppler shift
and the nonthermal broadening to the intensity as a characteristic of
the network structure. This correlation is not found in the coronal
holes. No indications for the network can be found in Ne VIII. For Ne
VIII we find a center-to-limb variation of the line shift opposite to
C IV, which leads to the conclusion that Ne VIII must be blueshifted
at disk center. This also shows the need for a remeasurement of the
wavelength of Ne VIII in the laboratory. The center-to-limb variation
of the line width leads to the conclusion that the nonresolved motions
are not isotropic with a preference for the vertical component. Both
lines show a clear signal for an outflow in the polar coronal holes. We
discuss the implications of these and other observations for models
of the transition-region and corona. The line shift behavior of Ne
VIII and other lines from the upper transition-region deserves deeper
investigation and probably has pivotal importance in our understanding
of the solar transition-region. We are pursuing such work.

---------------------------------------------------------
Title: The chromospheric network and the solar wind outflow
Authors: Peter, H.
1999AGAb...15...12P Altcode: 1999AGM....15..A15P
It is widely accepted that the quiet solar wind originates from the
magnetically dominated chromospheric network, but there is still
no definite proof of this concept of co-existing closed magnetic
structures (loops) and open funnels. The emission of typical transition
region EUV lines, like C IV (1548 Å), is redshifted in the network
elements by up to 10 km/s or more. Most models trying to explain
these redshifts assume that the emission is concentrated in closed
magnetic structures. Two recent studies of SUMER data show that the
emission of coronal lines, like Ne VIII (770 Å), is blueshifted in
the network. Simple considerations of the energy budget in open and
closed regions suggest that the inward heat flux, and by this the
density and the emissivity in closed field regions should be at least
a factor of 10 higher compared to open field regions. In conclusion
the emission in both, transition region and coronal lines, should be
dominated by closed field regions. Following these considerations, the
line profiles obtained from spectra with good signal-to-noise ratio
should show a core, originating from the closed loops, and a second
(10%) component that is due to emission from open field regions in the
network. This paper will present evidence for this scenario. Analyzing
the differences of network and inter-network regions with respect to
line shifts and widths of the core and the second component of the
emission lines will have impact on the understanding of the structure
of the network and the formation of the solar wind. A comparison to
spectra of stellar transition regions will shed new light on their
use to better understand the structure of stellar coronae.

---------------------------------------------------------
Title: Element fractionation in the solar chromosphere driven by
ionization-diffusion processes
Authors: Peter, Hardi
1998A&A...335..691P Altcode:
An ionization-diffusion mechanism is proposed to understand the
first ionization potential (FIP) fractionation as observed in the
solar corona and the solar wind. The enrichment of the low-FIP
elements (&lt;10 eV) compared to the high-FIP elements in a large
variety of phenomena, as e. slow and fast wind or polar plumes, is
explained. Also the special behaviour of the heavy noble gases becomes
perceptive and the absolute fractionation, i. in relation to hydrogen,
can be calculated and fits well to the measurements. Additionally the
theoretical velocity-dependence of the fractionation will be used to
determine the velocities of the solar wind in the chromosphere. The
main achievement of this paper is the explanation of a great variety
of fractionation-related phenomena on the basis of one single model.

---------------------------------------------------------
Title: Element Separation in the Chromosphere Ionization-Diffusion
Models for the FIP-Effect
Authors: Peter, Hardi
1998SSRv...85..253P Altcode:
Ionization-diffusion mechanisms to understand the first ionization
potential (FIP) fractionation as observed in the solar corona and the
solar wind are reviewed. The enrichment of the low-FIP elements (&lt;10
eV) compared to the high-FIP elements, seen in e.g. slow and fast wind
or polar plumes, is explained. The behaviour of the heavy noble gases
becomes understandable. The absolute fractionation, i.e. in relation
to hydrogen, can be calculated and fits well to the measurements. The
theoretical velocity-dependence of the fractionation will with used
to determine the velocities of the solar wind in the chromosphere.

---------------------------------------------------------
Title: Hydrogen and helium in the solar chromosphere: a background
model for fractionation
Authors: Peter, Hardi; Marsch, Eckart
1998A&A...333.1069P Altcode:
A multi-fluid model for a hydrogen-helium mixture in an
ionization-diffusion layer in the (solar) chromosphere is presented. The
purpose of this model is to serve as a background for fractionation
models calculating the abundance variations of minor species from the
photosphere to the solar wind. The emphasis will be on the determination
of the (mean) flow velocity in that ionization layer. The equations
of continuity and momentum of every component, neutral and (singly)
ionized for both elements, will be solved together with an energy
equation including heating and radiative losses. Special attention
will be paid to the ionization and the elastic collisions as well as
to resonant charge exchange. One of the main results is the connection
of the particle flux through the chromosphere with the ionization rate,
i. with the photon flux in the UV. Furthermore the abundance variations
of helium are discussed with the result, that the ion-neutral separation
processes leading to the fractionation of the minor elements cannot
explain the fractionation of helium as measured in the solar wind.

---------------------------------------------------------
Title: The Structure of the Chromosphere Properties Pertaining to
Element Fractionation
Authors: Judge, P. G.; Peter, H.
1998SSRv...85..187J Altcode:
We review the structure and dynamics of the solar chromosphere with
emphasis on the quiet Sun and properties that are relevant to element
fractionation mechanisms. Attention is given to the chromospheric
magnetic field, its connections to the photosphere, and to the dynamical
evolution of the chromosphere. While some profound advances have been
made in the “unmagnetized” chromosphere, our knowledge of the
magnetically controlled chromosphere, more relevant for the discussion
of element fractionation, is limited. Given the dynamic nature of the
chromosphere and the poorly understood magnetic linkage to the corona,
it is unlikely that we will soon know the detailed processes leading
to FIP fractionation.

---------------------------------------------------------
Title: Element Separation in the Chromosphere
Authors: Peter, H.
1998sce..conf..253P Altcode:
No abstract at ADS

---------------------------------------------------------
Title: The Structure of the Chromosphere
Authors: Judge, P. G.; Peter, H.
1998sce..conf..187J Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Mehrflüssigkeitsmodelle der unteren Sonnenatmosphäre und
Schlußfolgerungen für den Sonnenwind

---------------------------------------------------------
Title: Mehrflüssigkeitsmodelle
der unteren Sonnenatmosphäre und Schlußfolgerungen für den
Sonnenwind

---------------------------------------------------------
Title: Multi-fluid models of the lower solar atmosphere
and conclusions for the solar wind;
Authors: Peter, Hardi
1997PhDT.......272P Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Ionization Layer of Hydrogen in the Solar Chromosphere and
the Solar Wind Mass Flux
Authors: Peter, H.; Marsch, E.
1997ESASP.404..591P Altcode: 1997cswn.conf..591P
No abstract at ADS

---------------------------------------------------------
Title: Superpenumbral vortex structures.
Authors: Peter, H.
1996NAWG.1996..197P Altcode:
Spectroheliograms in Hα often show vortex structures in the
superpenumbral area of sunspots which covers a region from the outer
boundary of the spot to about five spot radii. It is possible to
find an analytical solution of the magnetohydrodynamic (MHD) basic
equations for a special (one dimensional) case of an axisymmetric
horizontal layer around a sunspot. Despite its simplicity, this
solution reproduces the main facts of the statistical observations
and quantitative measurements.

---------------------------------------------------------
Title: Velocity-dependent fractionation in the solar chromosphere.
Authors: Peter, H.
1996A&A...312L..37P Altcode:
An explanation of the observed patterns of the first ionisation
potential (FIP) fractionation of element abundances in the slow as
well as in the fast speed solar wind is proposed. In the former the
low-FIP (&lt;10eV) elements are enriched in relation to the high-FIP
elements by a factor of 4 compared to the photosphere. In the latter
this separation is weaker, or vanishes at all. This velocity dependence
can be understood by a simple analysis of atomic and plasma parameters
in the solar chromosphere. For this purpose an appropriate layer of
constant (hydrogen) density (10^16^m-3) and temperature (10^4^K)
is assumed. It is permeated by ionising photons and embedded in a
homogeneous vertical magnetic field. Only trace gases in a hydrogen
background are investigated. Instead of solving the equations only the
asymptotic behaviour is analysed. At the lower boundary a neutral gas
mixture and a constant velocity of the neutrals is assumed. Thus there
the differential equations for a trace gas are reduced to an algebraic
system. This results in the constant total particle flux of the
respective minor species. The obtained fractionation depends not only
on atomic parameters, i.e. ionisation times and collision frequencies,
but also on the plasma parameters, i.e. density, temperature and
velocity. Using typical values for the chromosphere a mass flow velocity
of about 200m/s leads to the observed fractionation in the slow wind,
while 1000m/s correspond to the patterns in the high speed solar wind.

---------------------------------------------------------
Title: Superpenumbral vortices
Authors: Peter, Hardi
1996MNRAS.278..821P Altcode:
Spectroheliograms, especially in Hα, often show vortex structures in
the superpenumbral area of a sunspot, which covers a region from the
outer boundary of the spot to about five spot radii. Attempts were made
at the beginning of this century to understand the physics of these
solar vortices, but pure hydrodynamical or electrodynamical theories
failed. The model presented in this paper is based on simplified
magnetohydrodynamic equations. The assumptions chosen render an
analytical solution practicable, and an obvious explanation for this
long-standing problem is obtained. Although this magnetohydrodynamic
theory is accomplished in a simple way, it is able to reproduce the main
facts of the statistical observations and quantitative measurements.

---------------------------------------------------------
Title: First Steps to a Multi-fluid Model of the Solar Transition
Region
Authors: Peter, H.; Marsch, E.
1996ApL&C..34...83P Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Superpenumbral Vortex Structures
Authors: Peter, H.
1996ApL&C..34...77P Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Superpenumbral vortex structures and Coriolis force
Authors: Peter, H.
1994smf..conf..222P Altcode:
No abstract at ADS

---------------------------------------------------------
Title: The yellow amplitude of RS Leporis.
Authors: Germann, R.; Kohl, M.; Locher, K.; Peter, H.
1986BBSAG..81....5G Altcode:
No abstract at ADS

---------------------------------------------------------
Title: 99th list of minima of eclipsing binaries.
Authors: Andrakakou, M.; Boninsegna, R.; Dequinze, R.; Elias,
D. P.; Germann, R.; Locher, K.; Louis, P.; Pampaloni, C.; Peter, H.;
Stoikidis, N.; Wils, P.
1983BBSAG..66....1A Altcode:
No abstract at ADS

---------------------------------------------------------
Title: 97th list of minima of eclipsing binaries.
Authors: Diethelm, R.; Elias, D. P.; Germann, R.; Kohl, M.; Locher,
K.; Mavrofridis, G.; Mourikis, D.; Nezry, E.; Nikolaou, I.; Pampaloni,
C.; Peter, H.; Schildknecht, T.; Stefanopoulos, G.; Stoikidis, N.
1983BBSAG..64....1D Altcode:
No abstract at ADS

---------------------------------------------------------
Title: 98th list of minima of eclipsing binaries.
Authors: Diethelm, R.; Elias, D. P.; Germann, R.; Keller, T.; Locher,
K.; Nezry, E.; Pampaloni, C.; Parris, A.; Peter, H.; Schildknecht,
T.; Stefanopoulos, G.; Stoikidis, N.; Wils, P.
1983BBSAG..65....1D Altcode:
No abstract at ADS

---------------------------------------------------------
Title: 94th - 96th list of minima of eclipsing binaries.
Authors: Boistel, G.; Diethelm, R.; Elias, D. P.; Germann, R.;
Locher, K.; Mavrofridis, G.; Mourikis, D.; Ralincourt, P.; Peter,
H.; Schildknecht, T.; Stefanopoulos, G.; Stoikidis, N.; Boninsegna,
R.; Kohl, M.; Le Borgne, J. -F.; Leyman, R.; Louis, P.; Andrakakou, M.
1982BBSAG..61....1B Altcode:
No abstract at ADS

---------------------------------------------------------
Title: 91st - 93rd list of minima of eclipsing binaries.
Authors: Amsler, S.; Andrakakou, M.; Boninsegna, R.; Cadalbert, R.;
Delhaye, D.; Dokic, P.; Elias, D. P.; Germann, R.; Grüebler, T.;
Häfliger, M.; Horowitz, L.; Kukan, J.; Le Borgne, J. -F.; Leyman,
D.; Leyman, R.; Locher, K.; Mammoliti, S.; Mavrofridis, G.; Mouillard,
C.; Mouillard, G.; Mourikis, D.; Nikolaou, I.; Peter, H.; Staub, B.;
Stucky, A.; Stefanopoulos, G.; Stoikidis, N.; Zwing, W.; Capol, L.;
Diethelm, R.; Häring, R.; Hunn, D.; Kägi, J.; Kocian, K.; Kohl,
M.; Maranta, C.; Biedermann, B.; Ferrand, S.; Hasler, N.; Kaiser,
A.; Liégeois, J. -P.; Louis, P.; Schildknecht, T.
1982BBSAG..58....1A Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Jost Bürgi und seine Himmelsgloben.
Authors: Peter, H.
1981Orion..39...40P Altcode:
No abstract at ADS

---------------------------------------------------------
Title: 89th - 90th list of minima of eclipsing binaries.
Authors: Andrakakou, M.; Boistel, G.; Boninsegna, R.; Diethelm,
R.; Elias, D. P.; Germann, R.; Leyman, R.; Locher, K.; Matagne, P.;
Mourikis, D.; Nezry, E.; Nikolaou, I.; Parris, A.; Peter, H.; Poretti,
E.; Ralincourt, P.; Vialle, J.; Capol, L.; Contopoulos, N.; Maranta,
C.; Mavrofridis, G.; Pampaloni, C.; Stoikidis, N.; Zwing, W.
1981BBSAG..56....1A Altcode:
No abstract at ADS

---------------------------------------------------------
Title: 85th - 88th list of minima of eclipsing binaries.
Authors: Boistel, G.; Boninsegna, R.; Diethelm, R.; Germann, R.;
Locher, K.; Mallama, A. D.; Mavrofridis, G.; Peter, H.; Stefanopoulos,
G.; Stoikidis, N.; Andrakakou, M.; Andreolo, L.; Elias, D. P.; Ficola,
L.; Franchini, M.; Mugnaini, P.; Pampaloni, C.; Parris, A.; Poretti,
E.; Mourikis, D.; Nikolaou, I.
1981BBSAG..52....1B Altcode:
No abstract at ADS

---------------------------------------------------------
Title: 79th - 81st list of minima of eclipsing binaries.
Authors: Agnesoni, C.; Andrakakou, M.; Boistel, G.; Buzzoni, A.;
Diethelm, R.; Germann, R.; Locher, K.; Mourikis, D.; Pampaloni, C.;
Peter, H.; Poretti, E.; Ralincourt, P.; Troispoux, G.; Chiantini,
L.; Ficola, L.; Mugnaini, P.; Antoniadou, T.; Boninsegna, R.; Elias, D.
1980BBSAG..46....1A Altcode:
No abstract at ADS

---------------------------------------------------------
Title: 82nd - 84th list of minima of eclipsing binaries.
Authors: Andrakakou, M.; Diethelm, R.; Elias, D. P.; Germann, R.;
Leyman, R.; Locher, K.; Mavrofridis, G.; Mourikis, D.; Parris, A.;
Peter, H.; Stoikidis, N.; Franchini, M.; Nikolaou, I.; Pampaloni,
C.; Boistel, G.; Buzzoni, A.; Leyman, D.; Nezry, E.; Ralincourt, P.;
Troispoux, G.
1980BBSAG..49....1A Altcode:
No abstract at ADS

---------------------------------------------------------
Title: 77th - 78th list of minima of eclipsing binaries.
Authors: Andrakakou, M.; Buzzoni, A.; Diethelm, R.; Germann, R.;
Locher, K.; Marot, A.; Mavrofridis, G.; Mourikis, D.; Del Parigi,
A.; Parris, A.; Peter, H.; Poretti, E.; Ralincourt, P.; Stoikidis,
N.; Troispoux, G.; Franchini, M.; Ferraro, F.; Le Borgne, J. -F.;
Leyman, R.; Mengoli, G.; Pampaloni, C.; Plasmati, C.; Remis, J.;
Stefanopoulos, G.
1979BBSAG..44....1A Altcode:
No abstract at ADS

---------------------------------------------------------
Title: 74th - 76th list of minima of eclipsing binaries.
Authors: Agnesoni, C.; Berquet, R.; Boninsegna, R.; Buzzoni, A.;
Clovin, J. -P.; Cutispoto, G.; Danthine, P.; Diethelm, R.; Germann, R.;
Leyman, R.; Locher, K.; van Loo, E.; Pampaloni, C.; Peter, H.; Poretti,
E.; Ralincourt, P.; Stefanopoulos, G.; Troispoux, G.; Zaccaria, N.;
Andrakakou, M.; Chiantini, L.; Dimou, G.; Mourikis, D.; Parris, A.;
Stoikidis, N.; Franchini, M.; Nezry, E.
1979BBSAG..41....1A Altcode:
No abstract at ADS

---------------------------------------------------------
Title: 71st - 73rd of minima of eclipsing binaries.
Authors: Boninsegna, R.; Buzzoni, A.; Carradori, T.; Clovin, J. -P.;
Diethelm, R.; Dore, R.; Germann, R.; Le Borgne, J. -F.; Locher, K.;
Lucentini, E.; Nezry, E.; Pampaloni, C.; Del Parigi, A.; Penna, M.;
Peter, H.; Poretti, E.; Ralincourt, P.; Troispoux, G.; Andrakakou,
M.; Ferraro, F.; Franchini, M.; Mourikis, D.; Plasmati, C.; Royer,
A.; Agnesoni, C.; Mavrofridis, G.; Stefanopoulos, G.; Zaccaria, N.
1978BBSAG..38....1B Altcode:
No abstract at ADS

---------------------------------------------------------
Title: V342 Aquilae: probable recent shallowing of the minimum I.
Authors: Diethelm, R.; Locher, K.; Peter, H.
1978BBSAG..38....7D Altcode:
No abstract at ADS

---------------------------------------------------------
Title: 69th and 70th list of minima of eclipsing binaries.
Authors: Agnesoni, C.; Albert, P.; Benucci, M.; Boninsegna, R.;
Bourgeois, J.; Buzzoni, A.; Carradori, T.; Clovin, J. -P.; Danthine,
P.; Diethelm, R.; Duquesne, J. -L.; Ferraro, F.; Franchini, M.;
Frangeul, M.; Frère, A.; Germann, R.; Hevesi, Z.; Leyman, R.; Locher,
K.; Lucentini, E.; Nezry, E.; Pampaloni, C.; Del Parigi, A.; Peter,
H.; Piazza, R.; Plasmati, C.; Poretti, E.; Ralincourt, P.; Remis, J.;
Royer, A.; Troispoux, G.; Vespe, F.; Zaccaria, N.; Livi, A.; Penna, M.
1978BBSAG..36....1A Altcode:
No abstract at ADS

---------------------------------------------------------
Title: 67th, 68th list of minima of eclipsing binaries.
Authors: Albert, P.; Boninsegna, R.; Bourgeois, J.; Clovin, J. -P.;
Danthine, P.; Diethelm, R.; Frangeul, M.; Germann, R.; Lardinois,
V.; Le Borgne, J. -F.; Le Strat, P.; Leydon, R.; Locher, K.; Marot,
A.; Mons, P.; Penna, M.; Royer, A.; Remis, J.; Troispoux, G.; Wabniz,
S.; Benucci, M.; Bouzin, B.; Buzzoni, A.; Duquesne, J. -L.; Ferrara,
F.; de Francesco, M.; Hevesi, Z.; Livi, A.; Le Jehan, S.; Leyman,
R.; Maniet, T.; Nezry, E.; Del Parigi, A.; Pampaloni, C.; Plasmati,
C.; Peter, H.; Poretti, E.; Ralincourt, P.; Travaglino, F.; Tuboly,
V.; Vespe, F.; Zaccaria, N.
1977BBSAG..34....1A Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Deceptive observations of UU Canis Maioris.
Authors: Locher, K.; Peter, H.
1977BBSAG..32....5L Altcode:
No abstract at ADS

---------------------------------------------------------
Title: 62nd - 66th list of minima of eclipsing binaries.
Authors: Boninsegna, R.; Clovin, J. -P.; Diethelm, R.; Doby, P.;
Frangeul, M.; Germann, R.; Hevesi, Z.; Locher, K.; Marot, A.; Peter,
H.; Poretti, E.; Remis, J.; Troispoux, G.; Behagle, M.; Le Borgne,
J. -F.; Ralincourt, P.; Royer, A.; Seretti, A.; Squelard, J.; Zaccaria,
N.; Travaglino, F.; Tuboly, V.; Berrilli, F.; Boninsegna, V.; Bouzin,
B.; Cayla, P.; Le Saout, M.; Leydon, R.; Wabniz, S.; Buzzoni, A.;
Kratochwill, R.; Lucentini, E.; Del Parigi, A.; Plasmati, C.
1976BBSAG..29....1B Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Lists of minima of eclipsing binaries.
Authors: Diethelm, R.; Figer, A.; Germann, R.; Locher, K.; Peter,
H.; Royer, A.; Tuboly, V.; Zajàcz, G.; Behagle, M.; Boninsegna, R.;
Bourgeois, J.; Carnevali, P.; Clovin, J. -P.; Doby, P.; Fenyvesi, A.;
Frangeul, M.; Le Borgne, J. -F.; Leydon, R.; Marot, A.; Poretti, E.;
Ralincourt, P.; Remis, J.; Seretti, A.; Wilmet, M.; Troispoux, G.;
Aresi, P.; Le Saout, M.
1976BBSAG..25....1D Altcode:
No abstract at ADS

---------------------------------------------------------
Title: The totality duration of TY Lib.
Authors: Peter, H.; Locher, K.
1975BBSAG..22....5P Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Lists of minima of eclipsing binaries.
Authors: Carnevali, P.; Diethelm, R.; Figer, A.; Germann, R.;
Le Borgne, J. -F.; Locher, K.; Mauron, N.; Marot, A.; Peter, H.;
Ralincourt, P.; Remis, J.; Sanchez, C.; Domec, C.; Hevesi, Z.; Rolland,
R.; Roudier, T.; Behagle, M.; Royer, A.; Dumarchi, G.
1975BBSAG..19....1C Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Lists of minima of eclipsing binaries.
Authors: Bonneville, T.; Chetanneau, A.; Desprez, F.; Diethelm, R.;
Dumarchi, G.; Fries, A.; Germann, R.; Le Borgne, J. -F.; Leydon, R.;
Locher, K.; Marot, A.; Mauron, N.; Peter, H.; Ralincourt, P.; Remis,
J.; Rolland, R.; Romoli, C.; Royer, A.; Sieber, W.; Steimer, P.;
Baumann, M.; Boninsegna, R.; Bourgeois, J.; Carnevali, P.; Clovin,
J. -P.; Kissling, M.; Maurin, L.; Troispoux, G.; Wüthrich, T.;
Zajàcz, G.
1975BBSAG..23....1B Altcode:
No abstract at ADS

---------------------------------------------------------
Title: 1. Südwestdeutsche Regionaltagung der VdS in Karlsruhe.
Authors: Peter, H.
1974Orion..32..232P Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Lists of minima of eclipsing binaries.
Authors: Diethelm, R.; Figer, A.; Germann, R.; Locher, K.; Peter,
H.; Remis, J.; Rolland, R.; Zajacz, G.; Carnevali, P.; Mauron, N.;
Ralincourt, P.; Romoli, C.; Hevesi, Z.
1974BBSAG..16....1D Altcode:
No abstract at ADS

---------------------------------------------------------
Title: List of minima of eclipsing binaries.
Authors: Diethelm, R.; Germann, R.; Locher, K.; Peter, H.; Wittwer,
H.; Forster, S.; Morger, P.
1974BBSAG..13....1D Altcode:
No abstract at ADS

---------------------------------------------------------
Title: The totality duration of TU Her.
Authors: Peter, H.; Locher, K.
1973BBSAG...9....3P Altcode:
No abstract at ADS

---------------------------------------------------------
Title: List of minima of eclipsing binaries.
Authors: Diethelm, R.; Germann, R.; Gliba, G.; Locher, K.; Mallama,
A.; Morger, P.; Peter, H.; Aeberli, R.; Boss, U.; Forbes, S.; Heer,
A.; Jucker, A.; Jucker, B.; Kobelt, V.; Senn, M.; Staub, J.
1973BBSAG..10....1D Altcode:
No abstract at ADS

---------------------------------------------------------
Title: The totality duration duration of TZ Eri.
Authors: Peter, H.; Locher, K.
1973BBSAG..11....6P Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Lists of minima of eclipsing binaries.
Authors: Diethelm, R.; Germann, R.; Locher, K.; Mallama, T.; Meier,
R.; Morger, P.; Peter, H.
1973BBSAG...7....1D Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Lists of minima of eclipsing binaries.
Authors: Diethelm, R.; Germann, R.; Giger, M.; Locher, K.; Peter,
H.; Schäpper, F.
1972BBSAG...5....1D Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Lists of minima of eclipsing binaries.
Authors: Diethelm, R.; Germann, R.; Locher, K.; Peter, H.
1972BBSAG...1....1D Altcode:
No abstract at ADS