poletto

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Author name code: poletto
ADS astronomy entries on 2022-09-14
author:"Poletto, Giannina"

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Title: Evolution of active region outflows throughout an active
region lifetime
Authors: Zangrilli, L.; Poletto, G.
2016A&A...594A..40Z Altcode: 2016arXiv160807408Z
Context. We have shown previously that SOHO/UVCS data allow us to
detect active region (AR) outflows at coronal altitudes higher than
those reached by other instrumentation. These outflows are thought to
be a component of the slow solar wind. Aims: Our purpose is to
study the evolution of the outflows in the intermediate corona from
AR 8100, from the time the AR first forms until it dissolves, after
several transits at the solar limb. Methods: Data acquired by
SOHO/UVCS at the time of the AR limb transits, at medium latitudes
and at altitudes ranging from 1.5 to 2.3 R⊙, were used
to infer the physical properties of the outflows through the AR
evolution. To this end, we applied the Doppler dimming technique to
UVCS spectra. These spectra include the H I Lyα line and the O vi
doublet lines at 1031.9 and 1037.6 Å. Results: Plasma speeds
and electron densities of the outflows were inferred over several
rotations of the Sun. AR outflows are present in the newly born AR and
persist throughout the entire AR life. Moreover, we found two types of
outflows at different latitudes, both possibly originating in the same
negative polarity area of the AR. We also analyzed the behavior of the
Si xii 520 Å line along the UVCS slit in an attempt to reveal changes
in the Si abundance when different regions are traversed. Although we
found some evidence for a Si enrichment in the AR outflows, alternative
interpretations are also plausible. Conclusions: Our results
demonstrate that outflows from ARs are detectable in the intermediate
corona throughout the whole AR lifetime. This confirms that outflows
contribute to the slow wind.

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Title: Solar Coronal Plumes
Authors: Poletto, Giannina
2015LRSP...12....7P Altcode:
Polar plumes are thin long ray-like structures that project beyond the
limb of the Sun polar regions, maintaining their identity over distances
of several solar radii. Plumes have been first observed in white-light
(WL) images of the Sun, but, with the advent of the space era, they have
been identified also in X-ray and UV wavelengths (XUV) and, possibly,
even in in situ data. This review traces the history of plumes, from the
time they have been first imaged, to the complex means by which nowadays
we attempt to reconstruct their 3-D structure. Spectroscopic techniques
allowed us also to infer the physical parameters of plumes and estimate
their electron and kinetic temperatures and their densities. However,
perhaps the most interesting problem we need to solve is the role they
cover in the solar wind origin and acceleration: Does the solar wind
emanate from plumes or from the ambient coronal hole wherein they are
embedded? Do plumes have a role in solar wind acceleration and mass
loading? Answers to these questions are still somewhat ambiguous and
theoretical modeling does not provide definite answers either. Recent
data, with an unprecedented high spatial and temporal resolution,
provide new information on the fine structure of plumes, their temporal
evolution and relationship with other transient phenomena that may
shed further light on these elusive features.

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Title: Birth, Life, and Death of a Solar Coronal Plume
Authors: Pucci, Stefano; Poletto, Giannina; Sterling, Alphonse C.;
Romoli, Marco
2014ApJ...793...86P Altcode:
We analyze a solar polar-coronal-hole (CH) plume over its entire
≈40 hr lifetime, using high-resolution Solar Dynamic Observatory
Atmospheric Imaging Assembly (AIA) data. We examine (1) the plume's
relationship to a bright point (BP) that persists at its base, (2)
plume outflows and their possible contribution to the solar wind
mass supply, and (3) the physical properties of the plume. We find
that the plume started ≈2 hr after the BP first appeared and became
undetectable ≈1 hr after the BP disappeared. We detected radially
moving radiance variations from both the plume and from interplume
regions, corresponding to apparent outflow speeds ranging over
≈(30-300) km s-1 with outflow velocities being higher
in the "cooler" AIA 171 Å channel than in the "hotter" 193 Å and
211 Å channels, which is inconsistent with wave motions; therefore,
we conclude that the observed radiance variations represent material
outflows. If they persist into the heliosphere and plumes cover ≈10%
of a typical CH area, these flows could account for ≈50% of the
solar wind mass. From a differential emission measure analysis of the
AIA images, we find that the average electron temperature of the plume
remained approximately constant over its lifetime, at T e
≈ 8.5 × 105 K. Its density, however, decreased with the
age of the plume, being about a factor of three lower when the plume
faded compared to when it was born. We conclude that the plume died
due to a density reduction rather than to a temperature decrease.

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Title: The contribution of X-ray polar blowout jets to the solar
wind mass and energy
Authors: Poletto, Giannina; Sterling, Alphonse C.; Pucci, Stefano;
Romoli, Marco
2014IAUS..300..239P Altcode:
Blowout jets constitute about 50% of the total number of X-ray jets
observed in polar coronal holes. In these events, the base magnetic
loop is supposed to blow open in what is a scaled-down representation
of two-ribbon flares that accompany major coronal mass ejections
(CMEs): indeed, miniature CMEs resulting from blowout jets have been
observed. This raises the question of the possible contribution of
this class of events to the solar wind mass and energy flux. Here we
make a first crude evaluation of the mass contributed to the wind and
of the energy budget of the jets and related miniature CMEs, under
the assumption that small-scale events behave as their large-scale
analogs. This hypothesis allows us to adopt the same relationship
between jets and miniature-CME parameters that have been shown to hold
in the larger-scale events, thus inferring the values of the mass and
kinetic energy of the miniature CMEs, currently not available from
observations. We conclude our work estimating the mass flux and the
energy budget of a blowout jet, and giving a crude evaluation of the
role possibly played by these events in supplying the mass and energy
that feeds the solar wind.

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Title: Physical Parameters of Standard and Blowout Jets
Authors: Pucci, Stefano; Poletto, Giannina; Sterling, Alphonse C.;
Romoli, Marco
2013ApJ...776...16P Altcode:
The X-ray Telescope on board the Hinode mission revealed the
occurrence, in polar coronal holes, of much more numerous jets than
previously indicated by the Yohkoh/Soft X-ray Telescope. These plasma
ejections can be of two types, depending on whether they fit the
standard reconnection scenario for coronal jets or if they include a
blowout-like eruption. In this work, we analyze two jets, one standard
and one blowout, that have been observed by the Hinode and STEREO
experiments. We aim to infer differences in the physical parameters
that correspond to the different morphologies of the events. To this
end, we adopt spectroscopic techniques and determine the profiles of
the plasma temperature, density, and outflow speed versus time and
position along the jets. The blowout jet has a higher outflow speed,
a marginally higher temperature, and is rooted in a stronger magnetic
field region than the standard event. Our data provide evidence for
recursively occurring reconnection episodes within both the standard
and the blowout jet, pointing either to bursty reconnection or to
reconnection occurring at different locations over the jet lifetimes. We
make a crude estimate of the energy budget of the two jets and show
how energy is partitioned among different forms. Also, we show that
the magnetic energy that feeds the blowout jet is a factor of 10 higher
than the magnetic energy that fuels the standard event.

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Title: An upper limit to the solar wind mass loading by X-ray
polar jets
Authors: Pucci, Stefano; Poletto, Giannina; Sterling, Alphonse C.;
Romoli, Marco
2013AIPC.1539...62P Altcode:
Hinode observations of polar coronal holes revealed a larger population
of X-ray jets than previously reported. Some of these comply with
the standard reconnection model suggested by Shibata et al. (1992),
others, likely analogous to CME eruptions and referred to as blow-out
jets (e.g. Moore et al., 2010), show a more structured morphology. We
present here two events, representative of the two jet categories, that
have been observed by HINODE and STEREO in polar coronal holes. Their
outward speed has been evaluated from high resolution images; also,
because the jets have been observed in multiple filters, we have been
able to derive, via spectroscopic techniques, their temperature and
density evolution, both along the jets and in time. Knowledge of these
parameters allows us to estimate the mass flux that jets of the two
types transport to the solar wind and, assuming a given frequency of
events, to infer a value for the wind mass loading contributed by polar
jets. Because there are insufficient data to establish the percentage
of ejections which eventually fall back to the Sun and because the
jets we analyzed are probably among the more energetic within their
respective class of events, the estimate we give is an upper limit to
the jet wind mass loading.

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Title: Sources of solar wind over the solar activity cycle
Authors: Poletto, Giannina
2013JAdR....4..215P Altcode:
Fast solar wind has been recognized, about 40 years ago, to originate in
polar coronal holes (CHs), that, since then, have been identified with
sources of recurrent high speed wind streams. As of today, however,
there is no general consensus about whether there are, within CHs,
preferential locations where the solar wind is accelerated. Knowledge
of slow wind sources is far from complete as well. Slow wind
observed in situ can be traced back to its solar source by backward
extrapolation of magnetic fields whose field lines are streamlines
of the outflowing plasma. However, this technique often has not the
necessary precision for an indisputable identification of the region
where wind originates. As the Sun progresses through its activity
cycle, different wind sources prevail and contribute to filling
the heliosphere. Our present knowledge of different wind sources
is here summarized. Also, a Section addresses the problem of wind
acceleration in the low corona, as inferred from an analysis of UV
data, and illustrates changes between fast and slow wind profiles and
possible signatures of changes along the solar cycle. A brief reference
to recent work about the deep roots of solar wind and their changes
over different solar cycles concludes the review.

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Title: A SOHO/UVCS study of coronal outflows at the edge of an active
region complex
Authors: Zangrilli, L.; Poletto, G.
2012A&A...545A...8Z Altcode:
Context. In the past, active regions (ARs) have been suggested as
a possible source of the slow solar wind. Their role as solar wind
contributors has recently been supported by HINODE observations at
low coronal levels. Aims: Our purpose is to determine whether
outflows at the edges of ARs can be detected in higher layers of
the corona, supporting the low-corona evidence for the occurrence of
wind streams from ARs. Methods: Data acquired by SOHO/UVCS on
January 2, 1998, at altitudes ranging from 1.5 to 2.3 solar radii at mid
latitudes, were used to infer the physical properties of an AR complex
at the time of its limb passage. To this end, the Doppler dimming
technique was applied to UVCS observations of the H i Lyα and O vi
doublet lines at 1031.9 and 1037.6 Å. Results: Outflow speeds
(and electron densities) were inferred: outflows, at speeds increasing
with height, turn out to be confined within a narrow channel at the
edge of closed loop systems within the AR. Our results are compared
with those obtained by other authors with different techniques. 
Conclusions: Our results support the assumption that ARs are sources of
slow wind. To our knowledge these are the first direct measurements of
AR flows in the intermediate corona. Tentative profiles of the speed
vs. heliocentric altitudes at heliocentric distances between ≈ 1.5
and ≈ 2.3 solar radii show that AR flows are faster than streams
from equatorial coronal holes.

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Title: Observational Evidence for Interaction Between X-ray Jets
and Multiple Bright Points
Authors: Pucci, S.; Poletto, G.; Sterling, A.; Romoli, M.
2012ASPC..456..217P Altcode:
The Hinode X-ray telescope (XRT) observed in November 2007 the Northen
polar Coronal Hole (CH) over extended time periods. Among these we
selected two 20 hours long time intervals and carried out a photometric
analysis of several X-ray Bright Points (BPs), within a selected area,
aiming at ascertaining whether there is any correlation between the
BPs intensity fluctuations and the occurrence of jets originating
within this area. Our results indicate that jets result from magnetic
connectivity changes that also produced BP variability: the interaction
between BPs and jets may be interpreted as the small scale version of
the Active Regions phenomena where flares and eruptions are initiated
by interacting bipoles.

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Title: Physical Parameters of a Blowout Jet Observed by HINODE
and STEREO/EUVI
Authors: Pucci, S.; Poletto, G.; Sterling, A.; Romoli, M.
2012ASPC..456..219P Altcode:
The present work aims at identifying a typical blowout jet and
inferring its physical parameters. To this end, we present a preliminary
multi-instrument analysis of the bright X-ray jet that occurred in the
north polar coronal hole on Nov. 3, 2007, at 11:50 UT. The jet shows
the typical characteristics of “blowout jets” (Moore et al. 2010),
and was observed by Hinode/X-Ray Telescope (XRT) and by Stereo/Extreme
UltraViolett Imager (EUVI) and COR1. Temperatures and Emission Measures
(EMs) of the jet have been derived from the EUVI A data via the filter
ratio technique in the pre-event, near maximum and in the post-maximum
phases. Temperatures and EMs inferred from EUVI data are then used to
calculate the predicted XRT Al-poly intensity: predicted values are
compared with observed values and found to be consistent.

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Title: Solar Polar X-Ray Jets and Multiple Bright Points: Evidence
for Sympathetic Activity
Authors: Pucci, Stefano; Poletto, Giannina; Sterling, Alphonse C.;
Romoli, Marco
2012ApJ...745L..31P Altcode:
We present an analysis of X-ray bright points (BPs) and X-ray jets
observed by Hinode/X-Ray Telescope on 2007 November 2-4, within the
solar northern polar coronal hole. After selecting small subregions
that include several BPs, we followed their brightness evolution over
a time interval of a few hours, when several jets were observed. We
find that most of the jets occurred in close temporal association
with brightness maxima in multiple BPs: more precisely, most jets
are closely correlated with the brightening of at least two BPs. We
suggest that the jets result from magnetic connectivity changes that
also induce the BP variability. We surmise that the jets and implied
magnetic connectivity we describe are small-scale versions of the
active-region-scale phenomenon, whereby flares and eruptions are
triggered by interacting bipoles.

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Title: Morphology, dynamics and plasma parameters of plumes and
inter-plume regions in solar coronal holes
Authors: Wilhelm, K.; Abbo, L.; Auchère, F.; Barbey, N.; Feng, L.;
Gabriel, A. H.; Giordano, S.; Imada, S.; Llebaria, A.; Matthaeus,
W. H.; Poletto, G.; Raouafi, N. -E.; Suess, S. T.; Teriaca, L.; Wang,
Y. -M.
2011A&ARv..19...35W Altcode: 2011arXiv1103.4481W
Coronal plumes, which extend from solar coronal holes (CH) into the high
corona and—possibly—into the solar wind (SW), can now continuously
be studied with modern telescopes and spectrometers on spacecraft,
in addition to investigations from the ground, in particular, during
total eclipses. Despite the large amount of data available on these
prominent features and related phenomena, many questions remained
unanswered as to their generation and relative contributions to
the high-speed streams emanating from CHs. An understanding of the
processes of plume formation and evolution requires a better knowledge
of the physical conditions at the base of CHs, in plumes and in the
surrounding inter-plume regions. More specifically, information is
needed on the magnetic field configuration, the electron densities
and temperatures, effective ion temperatures, non-thermal motions,
plume cross sections relative to the size of a CH, the plasma bulk
speeds, as well as any plume signatures in the SW. In spring 2007, the
authors proposed a study on `Structure and dynamics of coronal plumes
and inter-plume regions in solar coronal holes' to the International
Space Science Institute (ISSI) in Bern to clarify some of these aspects
by considering relevant observations and the extensive literature. This
review summarizes the results and conclusions of the study. Stereoscopic
observations allowed us to include three-dimensional reconstructions
of plumes. Multi-instrument investigations carried out during several
campaigns led to progress in some areas, such as plasma densities,
temperatures, plume structure and the relation to other solar phenomena,
but not all questions could be answered concerning the details of
plume generation process(es) and interaction with the SW.

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Title: Astrophysical jets: what can we learn from solar ejections?.
Authors: Massi, M.; Poletto, G.
2011MmSAI..82..145M Altcode: 2010arXiv1011.1128M
Ejections from the Sun can be observed with a higher resolution than in
any other astrophysical object: can we build up on solar results and
apply them to astrophysical objects? Aim of this work is to establish
whether there is any analogy between solar ejections and ejections in
microquasars and AGNs. Briefly reviewing jets properties from these
objects and from the Sun, we point out some characteristics they share
and indicate research areas where cross-breeeding between astrophysical
and solar research is likely to be productive. Preliminary results of
this study suggest, for instance, that there may be an analogy between
blobs created by tearing instability in current sheets (CSs) associated
with solar coronal mass ejections (CMEs) and quasi periodic ejections
of plasma associated with large radio outbursts in microquasars.

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Title: Current Sheets in the Solar Atmosphere
Authors: Poletto, Giannina
2011sswh.book..157P Altcode:
No abstract at ADS

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Title: SOHO/ACE observations of two consecutive CMEs from the same
source region
Authors: Schettino, G.; Dasso, S.; Mandrini, C. H.; Poletto, G.;
Romoli, M.
2010AIPC.1216..420S Altcode:
On June 2, 2003, SOHO/LASCO coronagraph observed two CMEs at the West
limb of the Sun, at 00.30 and 08:54 UT, respectively, which appeared
to originate from the same source region. Both CMEs show the typical
three-part structure. These events have been also observed by SOHO/UVCS,
allowing us to infer their physical parameters. We also looked for
interplanetary signatures of the CMEs in ACE `in situ' observations but
we did not find evidence of the ejected flux rope; however, the solar
wind appeared significantly distorted, probably as a consequence of
the influence of both CMEs on their surrounding interplanetary plasma.

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Title: Associating flare-and CME current sheets by radio and SOHO
(UVCS, LASCO, MDI) data
Authors: Aurass, Henry; Poletto, Giannina; Landini, Federico
2010cosp...38.1953A Altcode: 2010cosp.meet.1953A
We aim at establishing the relationship between the current sheet
(CS) associated with a limb flare and CSs associated with a CME
that apparently develops after the flare. We use a unique data set,
acquired on May 17, 2002. Spectral radio diagnostics, UV spectroscopic
techniques, white light coronograph imaging, and (partly) radio imaging
are used to illustrate the relation between the CSs and to infer the
physical parameters of the radially aligned features that develop
in the aftermath of the CME. Several phenomena are interpreted as
evidence of flare CSs in the low corona. These are drifting pulsating
structures in dynamic radio spectra, an erupting filament, expanding
coronal loops morphologically recalling the later white light CME,
and associated with hard X-ray source sites. In the aftermath of the
CME, UV spectra allowed us to estimate the CS temperature and density,
over the 1.5-2.1 Rs interval. The UV detected CS, however, appears to
be only one of many current sheets that exist underneath the erupting
flux rope. A type II burst following the CME radio continuum in time
at lower frequencies is considered as the radio signature of a coronal
shock excited at the flank of the CME. The results show that we can
build an overall scenario where the CME is interpreted in terms of an
erupting arcade crossing the limb of the Sun and connected to underlying
structures via multiple CSs. Eventually, the observed limb flare seems
to be a consequence of the ongoing CME.

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Title: CMEs from AR 10365: Morphology and Physical Parameters of
the Ejections and of the Associated Current Sheet
Authors: Schettino, G.; Poletto, G.; Romoli, M.
2010ApJ...708.1135S Altcode:
We study the evolution and physical parameters of three consecutive
coronal mass ejections (CMEs) that occurred at the west limb of the
Sun on 2003 June 2 at 00:30, 08:54, 16:08 UT, respectively. The Large
Angle and Spectrometric Coronagraph Experiment (LASCO) CME catalog
shows that the CMEs entered the C2 field of view with position angles
within a 5° interval. This suggests a common origin for the ejections,
to be identified with the magnetic system associated with the active
region that lies below the CMEs. The close proximity in time and source
location of the events prompted us to analyze LASCO white light data
and Ultraviolet Coronagraph Spectrometer (UVCS) spectra with the aim
of identifying similarities and differences among the three CMEs. It
turns out that two of them display the typical three-part structure,
while no conclusion can be drawn about the morphology of the third
ejection. The CMEs plasma is "cool," i.e., electron temperatures
in the CMEs front are of the order of 2 × 105 K, with
no significant variation between different events. However, ejection
speeds vary by a factor of ~1.5 between consecutive events and electron
densities (more precisely emission measures) by a factor of ~6 between
the first CME and the second and third CMEs. In the aftermath of all
events, we found evidence of current sheets (CSs) both in LASCO and
UVCS. We give here the CS physical parameters (electron temperature,
density, and kinetic temperature) and follow, in one of the events,
their temporal evolution over a 6 hr time interval. A discussion of
our results, in the framework of previous findings, concludes the paper.

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Title: Large and small scale structures as sources of solar wind.
Authors: Poletto, Giannina
2010cosp...38.2842P Altcode: 2010cosp.meet.2842P
In the past century, recurrent magnetic activity observed at Earth
used to be ascribed to "streams" of particles flowing from unknown
solar sources, that, after Bartels' suggestion (1932), were dubbed
"M-regions". Through successive steps the search for these elusive
sources eventu-ally ended up, about 40 years later, with the
identification of M-regions as Coronal Holes (CHs): large-scale
magnetically open areas, covering about 15However, it did not take
long to realize that these regions, assumed to be unipolar, hosted also
mized polarity areas and smaller struc-tures such as bright points and
plumes, with typical sizes on the order of 1 arcmin., whose role had to
be ascertained: does solar wind emanate from the ambient large-scale
CH or from the small-scale features within it? While this debate is
still going on, HINODE observations with unprecedented high spatial
and temporal resolution,revealed even smaller CH substructures. X-ray
jets, with a size as small as 1/10th of the above mentioned small-scale
features, turned out to be ubiquitous in CHs and much more numerous
than anticipated. Jets are definitely correlated to plumes, possibly
preceding their formation, and once more we face the problem of
understanding whether these tiny events have a role in the wind
acceleration and mass loading. This talk describes the subsequently
smaller features identified in CHs and illustrates how they contributed
to our understanding of the solar wind origin and maintenance. "In situ"
data, possibly related to coronal structures, are also shortly reviewed.

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Title: An Erupting Filament and Associated CME Observed by Hinode,
STEREO and SOHO
Authors: Bemporad, A.; Del Zanna, G.; Andretta, V.; Magrí, M.;
Poletto, G.; Ko, Y. -K.
2009ASPC..415..385B Altcode:
A multi-spacecraft campaign was set up in May 2007 to observe the
off-limb corona with Hinode, STEREO and SOHO instruments (Hinode
HOP 7). During this campaign, a filament eruption and a coronal
mass ejection (CME) occurred on May 9 from NOAA 10953 at the West
limb. The filament eruption starts around 13:40 UT and results in a
CME at 4°SW latitude. Remarkably, the event was observed by STEREO
(EUVI and COR1) and by the Hinode/EIS and SOHO/UVCS spectrometers. We
present results from all these instruments. High-cadence data from
Stereo/EUVI A and B in the He II λ304 line were used to study the
3-D expansion of the filament. A slow rising phase, during which the
filament moved southward, was followed by an impulsive phase during
which the filament appeared to change direction and then contribute
to the westward-expanding CME as seen in STEREO/COR 1. Hinode/EIS was
scanning with the 2” slit the region where the filament erupted. The
EIS spectra show remarkable non-thermal broadening in lines emitted at
different temperatures at the location of the filament eruption. The
CME was also observed by the SOHO/UVCS instrument: the spectrograph
slit was centered at 1.7 solar radii, at a latitude of 5°SW and
recorded a sudden increase in the O VI λλ 1032-1037 and Si XI λ520
spectral line intensities. We discuss the overall morphology of this
interesting eruptive event, and provide a preliminary assessment of
its temperature and density structure.

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Title: Multi-Instrument Campaigns to Observe the Off-Limb Corona
Authors: Del Zanna, G.; Andretta, V.; Poletto, G.; Teriaca, L.; Ko,
Y. -K.; Mason, H. E.; Vourdilas, A.; Bemporad, A.; Magri, M.
2009ASPC..415..315D Altcode:
We briefly describe two multi-instrument campaigns we coordinated to
observe the off-limb corona in 2007, with some preliminary results. The
first one (Hinode HOP 7) was a SOHO/Hinode/TRACE/STEREO/Ulysses
week-long campaign during the SOHO-Ulysses quadrature in 2007 May. We
could not achieve all of our goals, however we were very fortunate in
that the “Del Zanna” active region appeared on the Sun at the right
longitude, and that a filament eruption and a CME were observed. Of
particular significance is the finding of large (100 km s-1)
non-thermal broadenings in all coronal lines observed by Hinode/EIS
in the region where the filament was erupting. The second campaign
(Hinode HOP 44) involved SOHO (CDS, SUMER, UVCS), Hinode, and TRACE to
measure the physical parameters of plume/interplume regions in the polar
coronal holes from the low corona to 1.7 solar radii, on 30/10-4/11. We
obtained a good set of observations, however various instrumental
constraints and the lack of fully developed plumes limited our goals.

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Title: Coronal current sheet signatures during the 17 May 2002
CME-flare
Authors: Aurass, H.; Landini, F.; Poletto, G.
2009A&A...506..901A Altcode:
Context: The relation between current sheets (CSs) associated with
flares, revealed by characteristic radio signatures, and current
sheets associated with coronal mass ejections (CMEs), detected in
coronal ultraviolet (UV) and white light data, has not been analyzed,
yet. Aims: We aim at establishing the relationship between
CSs associated with a limb flare and CSs associated with the CME
that apparently develops after the flare. We use a unique data set,
acquired on May 17, 2002, which includes radio and extreme ultraviolet
(XUV) observations. Methods: Spectral radio diagnostics, UV
spectroscopic techniques, white light coronograph imaging, and (partly)
radio imaging are used to illustrate the relation between the CSs and
to infer the physical parameters of the radially aligned features that
develop in the aftermath of the CME. Results: During the flare,
several phenomena are interpreted in accordance with earlier work and
with reference to the common eruptive flare scenario as evidence of
flare CSs in the low corona. These are drifting pulsating structures in
dynamic radio spectra, an erupting filament, expanding coronal loops
morphologically recalling the later white light CME, and associated
with earlier reported hard X-ray source sites. In the aftermath of the
CME, UV spectra allowed us to estimate the CS temperature and density,
over the 1.5-2.1 R_⊙ interval of heliocentric altitudes. The UV
detected CS, however, appears to be only one of many current sheets
that exist underneath the erupting flux rope. A type II burst following
the CME radio continuum in time at lower frequencies is considered
as the radio signature of a coronal shock excited at the flank of the
CME. Conclusions: The results show that we can build an overall
scenario where the CME is interpreted in terms of an erupting arcade
crossing the limb of the Sun and connected to underlying structures
via multiple CSs. Eventually, the observed limb flare seems to be a
consequence of the ongoing CME.

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Title: Multispacecraft observations of a prominence eruption
Authors: Bemporad, A.; Del Zanna, G.; Andretta, V.; Poletto, G.;
Magrí, M.
2009AnGeo..27.3841B Altcode:
On 9 May 2007 a prominence eruption occurred at the West
limb. Remarkably, the event was observed by the STEREO/EUVI telescopes
and by the HINODE/EIS and SOHO/UVCS spectrometers. We present results
from all these instruments. High-cadence (~37 s) data from STEREO/EUVI
A and B in the He II λ304 line were used to study the 3-D shape and
expansion of the prominence. The high spatial resolution EUVI images
(~1.5"/pixel) have been used to infer via triangulation the 3-D shape
and orientation of the prominence 12 min after the eruption onset. At
this time the prominence has mainly the shape of a "hook" highly
inclined southward, has an average thickness of 0.068 R⊙,
a length of 0.43 R⊙ and lies, in first approximation,
on a plane. Hence, the prominence is mainly a 2-D structure and there
is no evidence for a twisted flux rope configuration. HINODE/EIS was
scanning with the 2" slit the region where the filament erupted. The
EIS spectra show during the eruption remarkable non-thermal broadening
(up to ~100 km s-1) in the region crossed by the filament
in spectral lines emitted at different temperatures, possibly with
differences among lines from higher Fe ionization stages. The CME was
also observed by the SOHO/UVCS instrument: the spectrograph slit was
centered at 1.7 R⊙, at a latitude of 5° SW and recorded
a sudden increase in the O VI λλ1032-1037 and Si XII λ520 spectral
line intensities, representative of the CME front transit.

---------------------------------------------------------
Title: Reconnection in Flares and CMEs
Authors: Poletto, G.
2009aogs...14...67P Altcode:
Magnetic reconnection is used nowadays to describe a wide
variety of phenomena that occur throughout the universe, from the
Earth's magnetosphere, to the Sun, to accretion disks around black
holes. However, we need to go back to the late fifties to find the first
suggestions about reconnection being at the origin of solar flares. At
those times the observational evidence for such an interpretation was
real scanty, with respect to the wealth of XUV, radio, and particles
data now available. This chapter reviews the observational evidence
of reconnection in flares and Coronal Mass Ejections (CMEs) provided
over the years by data mostly acquired by experiments onboard space
missions. Starting from the birth of ideas about the nature of the
physical processes that might fuel explosive transient events, first
attempts will be briefly illustrated together with basic concepts
developed by Sweet-Parker and Petschek. On this basis, a list of what
we can expect to observe if reconnection is working in transient events
will be drawn, and we will show how observations met expectations. The
most recent advances will be described and future possibilities will
be discussed at the end of the chapter.

---------------------------------------------------------
Title: Morphology and density structure of post-CME current sheets
Authors: Vršnak, B.; Poletto, G.; Vujić, E.; Vourlidas, A.; Ko,
Y. -K.; Raymond, J. C.; Ciaravella, A.; Žic, T.; Webb, D. F.;
Bemporad, A.; Landini, F.; Schettino, G.; Jacobs, C.; Suess, S. T.
2009A&A...499..905V Altcode: 2009arXiv0902.3705V
Context: Eruption of a coronal mass ejection (CME) drags and “opens”
the coronal magnetic field, presumably leading to the formation
of a large-scale current sheet and field relaxation by magnetic
reconnection. Aims: We analyze the physical characteristics
of ray-like coronal features formed in the aftermath of CMEs, to
confirm whether interpreting this phenomenon in terms of a reconnecting
current sheet is consistent with observations. Methods: The study
focuses on measurements of the ray width, density excess, and coronal
velocity field as a function of the radial distance. Results: The
morphology of the rays implies that they are produced by Petschek-like
reconnection in the large-scale current sheet formed in the wake of
CME. The hypothesis is supported by the flow pattern, often showing
outflows along the ray, and sometimes also inflows into the ray. The
inferred inflow velocities range from 3 to 30 km s-1, and
are consistent with the narrow opening-angle of rays, which add up to a
few degrees. The density of rays is an order of magnitude higher than
in the ambient corona. The density-excess measurements are compared
with the results of the analytical model in which the Petschek-like
reconnection geometry is applied to the vertical current sheet, taking
into account the decrease in the external coronal density and magnetic
field with height. Conclusions: The model results are consistent
with the observations, revealing that the main cause of the density
excess in rays is a transport of the dense plasma from lower to higher
heights by the reconnection outflow.

---------------------------------------------------------
Title: UV Transient Brightenings Associated with a Coronal Mass
Ejection
Authors: Schettino, G.; Poletto, G.; Romoli, M.
2009ApJ...697L..72S Altcode:
In this paper, we analyze transient UV brightenings in spectra acquired
by SOHO/UltraViolet Coronagraph Spectrometer (UVCS) on 2003 June 2 in
association with a coronal mass ejection (CME) that occurred at the West
limb of the Sun at 08:54 UT. Brightenings have been observed in lines
from cool (C III, O VI), intermediate (Si VIII, Si XII), and high ([Fe
XVIII]) temperature ions over about 7 hr from the CME. Brightenings in
cool lines are interpreted in terms of mini-ejections that appear at
the time of, and after, the passage of the CME front through the UVCS
slit. We give here their temperature and density and we point out that,
assuming a spherical shape, a few of these mini-CMEs can provide a
mass comparable to that quoted for typical CMEs. Hot lines, like the
[Fe XVIII] line at 974.9 Å which shows up in the CME associated
current sheet (CS), undergo transient brightness as well, but hot
lines brightenings are more difficult to interpret. We propose here
a scenario where they are signatures of the passage through the UVCS
slit of plasmoids similar to those observed in the filamentary CS
of the magnetotail that form as a consequence of the tearing-mode
instability or of a time-dependent Petschek-type reconnection.

---------------------------------------------------------
Title: Reconnection in a slow Coronal Mass Ejection
Authors: Poletto, G.; Bemporad, A.; Landini, F.; Romoli, M.
2008AnGeo..26.3067P Altcode:
This paper aims at studying reconnection occurring in the aftermath
of the 28 May 2004, CME, first imaged by the LASCO (Large Angle and
Spectrometric Coronagraph) C2 at 11:06 UT. The CME was observed in
White Light and UV radiation: images acquired by the LASCO C2 and C3
coronagraphs and spectra acquired by UVCS (Ultraviolet Coronagraph
Spectrometer) allowed us to identify the level at which field lines,
stretched outwards by the CME ejection, reconnect below the CME
bubble. As the CME propagates outwards, reconnection occurs at
increasingly higher levels. The process goes on at a low pace for
several hours: here we give the profile of the reconnection rate
vs. heliocentric distance over a time interval of ≍14 h after the CME
onset, extending estimates of the reconnection rate to larger distances
than previously inferred by other authors. The reconnection rate appears
to decrease with time/altitude. We also calculate upper and lower limits
to the density in the diffusion region between 4 and 7 R⊙
and conclude by comparing estimates of the classical and anomalous
resistivity in the diffusion region with the value inferred from the
data. The latter turns out to be ≥5 order of magnitudes larger than
predicted by classical or anomalous theories, pointing to the need of
identifying the process responsible for the observed value.

---------------------------------------------------------
Title: Magnetic reconnection processes induced by a CME expansion
Authors: Bemporad, A.; Poletto, G.; Landini, F.; Romoli, M.
2008AnGeo..26.3017B Altcode:
On 10 11 December 2005 a slow CME occurred in the Western Hemisphere
in between two coronal streamers. SOHO/MDI magnetograms show a
multipolar magnetic configuration at the photosphere: a complex of
active regions located at the CME source and two bipoles at the base of
the lateral coronal streamers. White light observations reveal that the
CME expansion affects both of them and induces the release of plasma
within or close to the nearby streamers. These transient phenomena are
possibly due to magnetic reconnections induced by the CME expansion and
occurring inside the streamer current sheet or between the CME flanks
and the streamer. These events have been observed by the SOHO/UVCS
with the spectrometer slit centered at 1.8 R⊙ over about
a full day. In this work we focus on the interaction between the CME
and the streamer: the UVCS spectral interval included UV lines from
ions at different temperatures of maximum formation such as O VI,
Si XIII and Al Xi. These data gave us the opportunity to infer the
evolution of plasma temperature and density at the reconnection site
and adjacent regions. These are relevant to characterize secondary
reconnection processes occurring during a CME development.

---------------------------------------------------------
Title: Low-Frequency Lyα Power Spectra Observed by UVCS in a Polar
Coronal Hole
Authors: Bemporad, A.; Matthaeus, W. H.; Poletto, G.
2008ApJ...677L.137B Altcode:
The occurrence of f-1 noise in interplanetary magnetic fields
(in the 1 × 10-5 to 1 × 10-4 Hz band) and other
plasma parameters has now been known for about 20 years and has been
recently identified also in the photospheric magnetic fields. However,
the relationship between interplanetary and solar fluctuation spectra
and the identification of their sources at the Sun are problems
that still need to be addressed. Moreover, interplanetary density
and magnetic field power spectra show a f-2 interval at
frequencies smaller that ~6 × 10-4 Hz whose source on the
Sun is at present not fully understood. In this work we report on the
first study of low-frequency density fluctuations in the solar corona
at 2.1 R⊙. In 2006 June the Ultraviolet Coronagraph
Spectrometer (SOHO UVCS) observed over a period of about 9.2 days
H Lyα intensity fluctuations at 2.1 R⊙ over a polar
coronal hole. The Lyα intensity power spectra S(f) (related mainly to
density fluctuations) showed a S(f) propto f-2 frequency
interval between 2.6 × 10-6 and 3.0 × 10-5
Hz and a S(f) propto f-1 frequency interval between 3.0
× 10-5 and 1.3 × 10-4 Hz. The detection of a
f-2 interval, in agreement with interplanetary density and
magnetic field power spectra, has been also predicted in solar wind
models as a consequence of phase-mixing mechanisms of waves propagating
in coronal holes. High-latitude power spectra show a f-1
band approximately in the same frequency interval where f-1
noise has been detected in interplanetary densities, and interplanetary
and photospheric magnetic fields, providing a connection between
photospheric, coronal, and interplanetary f-1 noises.

---------------------------------------------------------
Title: A study of Lyman-alpha power spectra observed by UVCS over
a polar coronal hole
Authors: Bemporad, Alessandro; Matthaeus, W. H.; Poletto, G.
2008cosp...37..239B Altcode: 2008cosp.meet..239B
First results from the Hinode/SOT instrument demonstrated that
the upper chromosphere is permeated by Alfvén waves that, despite
reflections occurring in the transition region, propagate e into
the corona. However, it is at present not fully understood how this
propagation occurs and if these waves are eventually suppressed or
enhanced in the solar wind before their detection in the interplanetary
medium. In this work we start addressing some of these questions by
carrying out a power spectral analysis of the Hydrogen Lyman-α line
intensity fluctuations observed by the SOHO/UVCS instrument over a polar
coronal hole. Data were acquired at 2.1 R over a period of about 9.2
days with a time resolution of 300 s between latitudes of 54° S and
90° S. Lyman-α power spectra, in first approximation representative
of density fluctuations, show two spectral bands: a lower frequency
f -2 band and a higher frequency f -1 band. In particular, the f -1
band is present approximately in the same frequency interval where f -1
noise has been detected in interplanetary densities, and interplanetary
and photospheric magnetic fields; this provides for the first time a
strong connection between photospheric, coronal and interplanetary f
-1 noises. Future developments of this work are also outlined.

---------------------------------------------------------
Title: Inferences on Reconnection from Observations of CMEs
Authors: Poletto, Giannina
2008cosp...37.2472P Altcode: 2008cosp.meet.2472P
Models of Coronal Mass Ejections (CMEs) invoke reconnection as a process
crucial to account for the major magnetic field reconfiguration that
accompanies these phenomena. Over the past few years a number of data
have been acquired in support of this prediction: these provided further
information on the properties of reconnection-related features. In
this talk I will review the observational signatures of reconnection
and the reconnection parameters that have been inferred from these. In
particular, I will address the problem of the Current Sheet that is
often detected in the aftermath of CMEs, illustrating what we know at
present about its physical conditions and its temporal evolution. Also,
recent results about the observed reconnection rate and its implications
will be discussed. A review of open issues will conclude the talk.

---------------------------------------------------------
Title: A review of SOHO/UVCS observations of sungrazing comets
Authors: Bemporad, A.; Poletto, G.; Raymond, J.; Giordano, S.
2007P&SS...55.1021B Altcode:
In the last 10 years more than 1000 sungrazing comets have been
discovered by the LASCO coronagraphs aboard SOHO the spacecraft; from
this huge amount of data it has been possible to study the common origin
of these comets and to explain some of the main peculiarities observed
in their lightcurves. Moreover, the UV Coronagraph Spectrometer (UVCS)
aboard SOHO allowed EUV spectroscopy of sungrazers in the final stage
of their trajectory (i.e. between 1.4 and 10 solar radii), but a few
sungrazers have been observed with this instrument. In this paper
we review the main results from the UVCS observation of sungrazers
C/1996 Y1, C/2000 C6 and C/2001 C2, discussing also the first possible
detection of two fragments and the determination of the pyroxene dust
grain number density in the latter one. Preliminary results on the
UVCS data interpretation of a sungrazer observed in 2002 (C/2002 S2)
are also presented here.

---------------------------------------------------------
Title: Cool-Plasma Jets that Escape into the Outer Corona
Authors: Corti, Gianni; Poletto, Giannina; Suess, Steve T.; Moore,
Ronald L.; Sterling, Alphonse C.
2007ApJ...659.1702C Altcode:
We report on observations acquired in 2003 May during a SOHO-Ulysses
quadrature campaign. The UVCS slit was set normal to the radial of
the Sun along the direction to Ulysses at 1.7 Rsolar, at
a northern latitude of 14.5°. From May 25 to May 28, UVCS acquired
spectra of several short-lived ejections that represent the extension
at higher altitudes of recursive EIT jets, imaged in He II λ304. The
jets were visible also in LASCO images and seem to propagate along
the radial to Ulysses. UVCS spectra showed an unusually high emission
in cool lines, lasting for about 10-25 minutes, with no evidence of
hot plasma. Analysis of the cool line emission allowed us to infer
the physical parameters (temperature, density, and outward velocity)
of jet plasma and the evolution of these quantities as the jet crossed
the UVCS slit. From these quantities, we estimated the energy needed
to produce the jet. We also looked for any evidence of the events in
the in situ data. We conclude by comparing our results with those of
previous works on similar events and propose a scenario that accounts
for the observed magnetic setting of the source of the jets and allows
the jets to be magnetically driven.

---------------------------------------------------------
Title: Density and Magnetic Field Signatures of Interplanetary
1/f Noise
Authors: Matthaeus, W. H.; Breech, B.; Dmitruk, P.; Bemporad, A.;
Poletto, G.; Velli, M.; Romoli, M.
2007ApJ...657L.121M Altcode:
We investigate the occurrence of 1/f noise in the interplanetary
density and the magnetic field at varying heliocentric latitudes. The
characteristic spectral amplitudes can be found in Ulysses density
and magnetic data in the expected frequency ranges at all available
latitudes, ranging from the ecliptic plane to more than 80°. Average
spectra indicate a latitudinal variation, with a 1/f density signal
becoming more pronounced in higher latitude bands. Azimuthal spectral
analysis of solar magnetogram data using the SOHO Michelson Doppler
Interferometer also shows 1/f noise in the photospheric magnetic field,
most clearly at high latitude. Accordingly, we discuss possibilities
that the 1/f signal arises at varying altitudes, possibly surviving
coronal dynamics. This raises questions that may be addressed in future
studies using spectroscopic, white light, and radio scintillation data.

---------------------------------------------------------
Title: Commission 10: Solar Activity
Authors: Melrose, Donald B.; Klimchuk, James A.; Benz, A. O.; Craig,
I. J. D.; Gopalswamy, N.; Harrison, R. A.; Kozlovsky, B. Z.; Poletto,
G.; Schrijver, K. J.; van Driel-Gesztelyi, L.; Wang, J. -X.
2007IAUTA..26...75M Altcode:
Commission 10 aims at the study of various forms of solar activity,
including networks, plages, pores, spots, fibrils, surges, jets,
filaments/prominences, coronal loops, flares, coronal mass ejections
(CMEs), solar cycle, microflares, nanoflares, coronal heating etc.,
which are all manifestation of the interplay of magnetic fields and
solar plasma. Increasingly important is the study of solar activities
as sources of various disturbances in the interplanetary space
and near-Earth "space weather".Over the past three years a major
component of research on the active Sun has involved data from the
RHESSI spacecraft. This review starts with an update on current and
planned solar observations from spacecraft. The discussion of solar
flares gives emphasis to new results from RHESSI, along with updates on
other aspects of flares. Recent progress on two theoretical concepts,
magnetic reconnection and magnetic helicity is then summarized, followed
by discussions of coronal loops and heating, the magnetic carpet
and filaments. The final topic discussed is coronal mass ejections
and space weather.The discussions on each topic is relatively brief,
and intended as an outline to put the extensive list of references
in context.The review was prepared jointly by the members of the
Organizing Committee, and the names of the primary contributors to
the various sections are indicated in parentheses.

---------------------------------------------------------
Title: A Comprehensive Study of the Initiation and Early Evolution
of a Coronal Mass Ejection from Ultraviolet and White-Light Data
Authors: Bemporad, A.; Raymond, J.; Poletto, G.; Romoli, M.
2007ApJ...655..576B Altcode:
In this work we analyze simultaneous UV and white-light (WL)
observations of a slow CME that occurred on 2000 January 31. Unlike
most CMEs studied in the UV so far, this event was not associated
with a flare or filament eruption. Based on vector magnetograph
data and magnetic field models, we find that field disruption in an
active region (AR) was driven by flux emergence and shearing motions,
leading to the CME and to post-CME arcades seen in the EUV. WL images,
acquired by the Mark IV coronagraph at the Mauna Loa Observatory,
allowed us to identify the CME front, bubble, and core shortly
(about 1 hr) after the CME ejection. From polarized brightness (pB)
Mauna Loa data we estimated the mass and electron densities of the
CME. The CME mass increases with time, indicating that about 2/3 of
the mass originates above 1.6 Rsolar. Analysis of the UV
spectra, acquired by the Solar and Heliospheric Observatory Ultraviolet
Coronagraph Spectrometer (SOHO UVCS) at 1.6 and 1.9 Rsolar,
allowed us to derive the electron temperature distribution across the
CME. The temperature maximizes at the CME core and increases between
1.6 and 1.9 Rsolar. This event was unusual, in that the
leading edge and the CME core were hotter than the ambient corona. We
discuss magnetic heating and adiabatic compression as explanations
for the high temperatures in the core and leading edge, respectively.

---------------------------------------------------------
Title: Wide and Narrow CMEs and their Source Explosions Observed at
the Spring 2003 SOHO-Sun-Ulysses Quadrature
Authors: Suess, S. T.; Corti, G.; Poletto, G.; Sterling, A.; Moore, R.
2006ESASP.617E.147S Altcode: 2006soho...17E.147S
No abstract at ADS

---------------------------------------------------------
Title: SOHO UVCS and Mauna Loa Mark IV Observations of a Slow CME
below 2 Solar Radii
Authors: Bemporad, A.; Poletto, G.; Raymond, J. C.
2006ESASP.617E..24B Altcode: 2006soho...17E..24B
No abstract at ADS

---------------------------------------------------------
Title: Past and Future SOHO-Ulysses Quadratures
Authors: Suess, S. T.; Poletto, G.
2006ESASP.617E.161S Altcode: 2006soho...17E.161S
No abstract at ADS

---------------------------------------------------------
Title: Diagnostics and Modelling of the Solar Wind Source Regions
Authors: Poletto, G.
2006ESASP.617E..14P Altcode: 2006soho...17E..14P
No abstract at ADS

---------------------------------------------------------
Title: Current Sheet Evolution in the Aftermath of a CME Event
Authors: Bemporad, A.; Poletto, G.; Suess, S. T.; Ko, Y. -K.;
Schwadron, N. A.; Elliott, H. A.; Raymond, J. C.
2006ApJ...638.1110B Altcode:
We report on SOHO UVCS observations of the coronal restructuring
following a coronal mass ejection (CME) on 2002 November 26, at the
time of a SOHO-Ulysses quadrature campaign. Starting about 1.5 hr
after a CME in the northwest quadrant, UVCS began taking spectra
at 1.7 Rsolar, covering emission from both cool and hot
plasma. Observations continued, with occasional gaps, for more than
2 days. Emission in the 974.8 Å line of [Fe XVIII], indicating
temperatures above 6×106 K, was observed throughout the
campaign in a spatially limited location. Comparison with EIT images
shows the [Fe XVIII] emission to overlie a growing post-flare loop
system formed in the aftermath of the CME. The emission most likely
originates in a current sheet overlying the arcade. Analysis of the [Fe
XVIII] emission allows us to infer the evolution of physical parameters
in the current sheet over the entire span of our observations: in
particular, we give the temperature versus time in the current sheet
and estimate its density. At the time of the quadrature, Ulysses was
directly above the location of the CME and intercepted the ejecta. High
ionization state Fe was detected by the Ulysses SWICS throughout the
magnetic cloud associated with the CME, although its rapid temporal
variation suggests bursty, rather than smooth, reconnection in the
coronal current sheet. The SOHO-Ulysses data set provided us with the
unique opportunity of analyzing a current sheet structure from its
lowest coronal levels out to its in situ properties. Both the remote
and in situ observations are compared with predictions of theoretical
CME models.

---------------------------------------------------------
Title: Lyman-α Observations of Sungrazing Comets with the SOHO/UVCS
Instrument
Authors: Bemporad, A.; Poletto, G.; Raymond, J.; Giordano, S.
2006aogs....3..171B Altcode:
The Large angle and spectrometric coronagraphs aboard the Solar
and helio-spheric observatory (SOHO) spacecraft observed a large
(more than 1000) number of sungrazers. This led to many studies which
tried to explain their origin and the peculiar shape of the observed
cometary lightcurves. However, in the last years a few sungrazers
have been observed also in the hydrogen Lyman-α spectral line by
the UV coronagraph spectrometer on SOHO. This instrument allowed to
perform UV spectroscopical observations of sungrazing comets on their
final stage of life at projected heliocentric distances between 1.4
and 10 solar radii. Ultra violet coronagraph spectrometer (UVCS)
detected in the sungrazer UV spectra mainly the Lyman-α spectral
line. Typically, emission in this line originates in the hydrogen cloud
produced by the water photodis-sociation, but, at these low heights,
it is necessary to take into account also strong interaction processes
(e.g., mass-loading and charge exchange) between the solar wind and
the outgassed materials. From these observations, it has been possible
to estimate cometary parameters such as the outgassing rates and the
nucleus sizes, as well as parameters of the coronal plasma encountered
by the comet. In this work we review the main results derived from the
UVCS observations of sungrazing comets: the detection of a “hidden”
mass below ∼6R⊙, the indirect and direct evidences for
the occurrence of fragmentation processes and a tentative estimate
for the pyroxene dust grain number density. Moreover, we present here
preliminary results on the UVCS data interpretation of a sungrazer
observed in 2002.

---------------------------------------------------------
Title: Coordinated Investigation Program defining a Reference
Heliosphere
Authors: Moebius, E.; Poletto, G.; Suess, S.
2006cosp...36.2152M Altcode: 2006cosp.meet.2152M
During the International Heliophysical Year 2007 8 the Sun-Solar
System Great Observatory will assemble in several constellations
that contain an ideal complement of spacecraft to allow coordinated
observations of the Sun and the heliosphere They will provide the
baseline for a reference heliosphere at solar minimum While Voyager
1 is already in the heliosheath and Voyager 2 is approaching the
termination shock Ulysses and the Earth with ACE Wind SOHO STEREO and
the full complement of ground-based observatories align in quadrature
configurations relative to the Sun over two extended periods December
2006 to May 2007 Q1 and December 2007 to May 2008 Q2 The Interstellar
Boundary Explorer IBEX will begin taking global neutral atom images
in the second half of 2008 just in time to capture the echo of the
solar input that was observed during Q1 1 5-2 years before with a
second opportunity 1 5-2 years after Q2 The near Earth spacecraft
and STEREO will provide the ecliptic plane input over 6-7 full solar
rotations while the combination of in-situ observations between the
Sun s poles with optical UV observations of the corona in the plane
perpendicular to the Earth-Sun line will provide the solar wind
structure in latitude Ulysses sweeps the latitude of the Voyagers
in 2006 7 providing benchmark observations of the solar wind in the
inner heliosphere that relate to the Voyager observations close to the
termination shock Complemented by IBEX with the capability to directly
observe the interstellar O flow which is strongly affected by the

---------------------------------------------------------
Title: Evidence for pyroxene dust grains in C/2001 C2 sungrazing comet
Authors: Bemporad, A.; Poletto, G.; Raymond, J. C.
2006AdSpR..38.1972B Altcode:
In this paper we analyze SOHO/UVCS data of the sungrazing comet C/2001
C2, a member of the Kreutz family, that was observed on February 7,
2001, at the heliocentric distances of 4.98 and 3.60 solar radii. This
comet splits in a main nucleus and a fragment which have been
identified in UV data. A study of the cometary Hydrogen Lyα emission
from these two objects revealed that the Lyα signal from the fragment
decays exponentially with time, while the signal from the main object
consists of an exponentially decaying term superposed onto a constant
background. The latter emission has been ascribed to the sublimation of
pyroxene dust grains, whose end products neutralize coronal protons via
charge exchange processes. This interpretation allowed us to estimate,
for the first time, the number density of pyroxene dust grains in a
sungrazing comet.

---------------------------------------------------------
Title: Recursive Narrowcmes Within a Coronal Streamer
Authors: Bemporad, A.; Sterling, A. C.; Moore, R. L.; Poletto, G.
2005ESASP.600E.153B Altcode: 2005ESPM...11..153B; 2005dysu.confE.153B
No abstract at ADS

---------------------------------------------------------
Title: A New Variety of Coronal Mass Ejection: Streamer Puffs from
Compact Ejective Flares
Authors: Bemporad, A.; Sterling, Alphonse C.; Moore, Ronald L.;
Poletto, G.
2005ApJ...635L.189B Altcode:
We report on SOHO UVCS, LASCO, EIT, and MDI observations of a
series of narrow ejections that occurred at the solar limb. These
ejections originated from homologous compact flares whose source
was an island of included polarity located just inside the base of
a coronal streamer. Some of these ejections result in narrow CMEs
(“streamer puffs”) that move out along the streamer. These streamer
puffs differ from “streamer blowout” CMEs in that (1) while the
streamer is transiently inflated by the puff, it is not disrupted, and
(2) each puff comes from a compact explosion in the outskirts of the
streamer arcade, not from an extensive eruption along the main neutral
line of the streamer arcade. From the observations, we infer that
each streamer puff is produced by means of the inflation or blowing
open of an outer loop of the arcade by ejecta from the compact-flare
explosion in the foot of the loop. So, in terms of their production,
our streamer puffs are a new variety of CME.

---------------------------------------------------------
Title: Opening Address
Authors: Poletto, G.
2005ESASP.600E...1P Altcode: 2005ESPM...11....1P; 2005dysu.confE...1P
No abstract at ADS

---------------------------------------------------------
Title: Early Evolution of a CME from White Light and UV Observations
Authors: Bemporad, A.; Poletto, G.; Raymond, J. C.
2005ESASP.592..711B Altcode: 2005ESASP.592E.143B; 2005soho...16E.143B
No abstract at ADS

---------------------------------------------------------
Title: Current Sheet Evolution in the Aftermath of a CME
Authors: Bemporad, A.; Poletto, G.; Suess, S. T.; Ko, Y. -K.;
Schwadron, N. A.; Elliott, H. A.; Raymond, J. C.
2005ESASP.592..715B Altcode: 2005soho...16E.144B; 2005ESASP.592E.144B
No abstract at ADS

---------------------------------------------------------
Title: UVCS Observation of Sungrazer C/2001 C2: Possible Comet
Fragmentation and Plasma-Dust Interactions
Authors: Bemporad, A.; Poletto, G.; Raymond, J. C.; Biesecker, D. A.;
Marsden, B.; Lamy, P.; Ko, Y. -K.; Uzzo, M.
2005ApJ...620..523B Altcode:
In this paper we analyze SOHO Ultraviolet Coronagraph Spectrometer
(UVCS) observations of the sungrazing comet C/2001 C2, a member of the
Kreutz family, observed on 2001 February 7 at heliocentric distances
of 4.98 and 3.60 Rsolar. This comet apparently went through
sequential fragmentation events along its path: further indication of
fragmentation processes is provided by UVCS observations, which show
the presence of two separate tails in the 4.98 Rsolar data
set, which we interpret as two fragments unresolved by LASCO images,
one of which sublimates before reaching 3.60 Rsolar. The
cometary hydrogen Lyα signal, decaying exponentially with time,
has been interpreted in terms of the H2O outgassing rate
and the interactions of coronal protons with atoms created by the
photodissociation of water. However, one of the fragments shows an
additional Lyα contribution, constant with time, which adds to the
temporally decaying signal. This contribution has been ascribed to
the sublimation of pyroxene dust grains, whose end products neutralize
coronal protons via charge exchange processes. Hence, the two fragments
have different composition; differences throughout the comet body may
have been the primary cause for the comet fragmentation.

---------------------------------------------------------
Title: JD 7: The Sun and the Heliosphere as an Integrated System
Authors: Poletto, Giannina; Suess, Steven T.
2005HiA....13..213P Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Post-CME events: cool jets and current sheet evolution
Authors: Bemporad, A.; Poletto, G.; Suess, S. T.
2005IAUS..226...77B Altcode:
In this work we focus on UVCS data acquired during the November 2002
SOHO-Ulysses quadrature, at an altitude of 1.7 R⊙ over a
range of latitudes centered around 27 °N in the western quadrant. A
couple of hours before our observations started, a CME event (November
26, 15:30 UT) originating at about 27 °N, disrupted the coronal
configuration of the region. In the ∼ 2.3 days following the event
UVCS detected emission in the neutral H Ly β and Ly γ lines as well
as in lines from both high and low ionization ions such as C iii, O vi,
Si viii, ix and xii, Fe x and xviii. Enhanced emission from the hot
Fe xviii ion (log Tmax = 6.7), lasting nearly to the end of
our observations and originating in a region between 10 °N and 30 °N,
has been identified with a post-CME current sheet. Our interpretation
is supported by EIT Fe xii images which show a system of loops at
increasingly higher altitudes after the event. Northward of the CME,
UVCS observed repeated, sudden and short lived emission peaks in the
"cool" Ly β, Ly γ, C iii and O vi lines. These events seem to be
the extension at higher altitudes of the chromospheric plasma jets
observed in the EIT He ii images. Electron temperatures of both the
hot and cool region will be presented here and their time evolution
will also be illustrated.

---------------------------------------------------------
Title: A Detection of the Same Hot Plasma in the Corona - During a
CME - and Later at Ulysses
Authors: Suess, S. T.; Poletto, G.; Bemporad, A.
2004AGUFMSH21B0402S Altcode:
We show direct evidence for the same very hot plasma being detected
remotely from SOHO in the corona and subsequently, in situ, at Ulysses
in the solar wind. This is, to our knowledge, the first time that
such an unambiguous identification has been made in the case of hot
plasma. This detection complements studies correlating other plasma
and field properties observed in situ to the properties measured
at the source in the corona. This observation takes advantage
of a SOHO-Sun-Ulysses quadrature, during which the Sun-Ulysses
included angle is 90o and it is possible to observe in
situ with Ulysses instruments the same plasma that has previously
been remotely observed with SOHO instruments in the corona on the
limb of the Sun. The identification builds on an existing base of
separate SOHO and interplanetary detections of hot plasma. SOHO/UVCS
has found evidence for very hot coronal plasma in current sheets
in the aftermath of CMEs (Ciaravella et al., 2002; Raymond et al.,
2003; Ko et al., 2002) in the [Fe XVIII] λ 974 Å line, implying a
temperature on the order of 6 × 106 K. This temperature
is unusually high even for active regions, but is compatible with the
high temperature predicted in current sheets. In the solar wind, ACE
data from early 1998 to middle 2000 revealed high frozen-in Fe charge
state (Fe16+)in many cases to be present in interplanetary
plasma (Lepri et al., 2004). These identifications were associated with
ICMEs. Ciaravella, A., Raymond, J. C., Li, J., Reiser, P., Gardner,
L. D., Ko, Y.-K., &amp; Fineschi, S. 2002, Astrophys. J., 575, 1116 Ko,
Y.-K., Raymond, J. C., Li, J., Ciaravella, A., Michels, J., Fineschi,
S., &amp; Wu, R. 2002, Astrophys. J., 578, 979 Lepri, S. T., &amp;
Zurbuchen, T. H. 2004, J. Geophys. Res., 109(A1), A01112 Raymond,
J. C., Ciaravella, A., Dobrzycka, D., Strachan, L., Ko, Y.-K., &amp;
Uzzo, M. 2003, Astrophys. J., 597, 1106

---------------------------------------------------------
Title: The Sun and the Heliosphere as an Integrated System
Authors: Poletto, G.; Suess, S. T.
2004ASSL..317.....P Altcode: 2004shis.conf.....P
This book, for the first time, ties together physical processes across
the full scale of the heliosphere. It is about the natural connections
that exist between the various parts of the system. Therefore, it
is mainly cast in terms of those mechanisms and phenomena rather
than individual missions in space. However, to give credit, this has
only been possible because of the existence of a fleet of deep space
missions such as Ulysses, SOHO, and the Voyagers. It is only with
them working in concert that a real understanding of the physics
can be, and has been achieved. There are fourteen chapters in the
book written by top scientists from around the world. The level of
presentation is very high but the authors were given enough space
to present understandable introductions, physical discussions, and
extensive bibliographies. The audience for this book consists of
graduate students and researchers in astronomy as well as specialists
in solar physics and interplanetary plasma physics. Link: <A
href="http://www.springeronline.com/sgw/cda/frontpage/0,11855,5-40109-22-35889411-0,00.html">
http://www.springeronline.com/sgw/cda/frontpage/0,11855,5-40109-22-35889411-0,00.html</A>
<A
href="http://www.springeronline.com/sgw/cda/frontpage/0,11855,5-40109-22-35889362-0,00.html">http://www.springeronline.com/sgw/cda/frontpage/0,11855,5-40109-22-35889362-0,00.html</A>

---------------------------------------------------------
Title: Evidence for the Same Hot Plasma after Coronal Mass Ejection
Events, in Both Remote and In Situ Observations
Authors: Poletto, G.; Suess, Steven T.; Bemporad, Alessandro;
Schwadron, Nathan A.; Elliott, Heather A.; Zurbuchen, Thomas H.; Ko,
Y. -K.
2004ApJ...613L.173P Altcode:
We present here evidence for highly ionized Fe observed both in the
corona, in the aftermath of a coronal mass ejection, and, after
propagation, in situ. The apparent source temperature is greater
than 6 MK. To our knowledge, this is the first time that such an
unambiguous identification has been made. This detection complements
studies correlating other properties of plasma observed in situ to the
same properties of the same plasma remotely observed at its source in
the corona.

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Title: A slow streamer blowout at the Sun and Ulysses
Authors: Suess, S. T.; Bemporad, A.; Poletto, G.
2004GeoRL..31.5801S Altcode: 2004GeoRL..3105801S
On 10 June 2000 a streamer on the southeast limb slowly disappeared from
LASCO/C2 over ~10 hours. A small CME was reported in C2. A substantial
interplanetary CME (ICME) was later detected at Ulysses, which was at
quadrature with the Sun and SOHO at the time. This detection illustrates
the properties of an ICME for a known solar source and demonstrates
that the identification can be done even beyond 3 AU. Slow streamer
blowouts such as this have long been known but are little studied.

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Title: SUMER, UVCS and LASCO Observations of Small-Scale Ejecta
Authors: Teriaca, L.; Curdt, W.; Poletto, G.
2004ESASP.547..291T Altcode: 2004soho...13..291T
During the fall 2002 SOHO-Sun-Ulysses quadrature, coordinated SUMER/UVCS
observations were carried out off the west limb. Data were acquired
over six consecutive days in several lines formed in the 2 104 - 106
K temperature range. The center of the SUMER slit was placed around
1.13 R and oriented in the north south direction, while the UVCS slit
was set tangent to the solar limb at altitudes ranging between 1.6 and
2.1 R. On 19 and 20 November SUMER observed repeated transient events
characterized by a strong increase of the intensity of transition region
and Hydrogen Lyman and lines with large line broadenings and line of
sight velocities, while little if any variation is seen in lines formed
around 106 K. The duration of these events varies between 10-15 minutes
up to 1 hour. The SUMER events are associated to streamer-like outflows
seen in LASCO images and, in the case of the larger 19 November event,
with a small jet travelling at ~400 km/s across the LASCO C2 fiel
of view.

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Title: Evidence for pyroxene dust grains in C/2001 C2 sungrazing comet
Authors: Bemporad, A.; Poletto, G.; Raymond, J.
2004cosp...35.3526B Altcode: 2004cosp.meet.3526B
In this paper we analyze SOHO/UVCS data of the sungrazing comet C/2001
C2, a member of the Kreutz family, observed on February 7, 2001, at
the heliocentric distances of 4.94 and 3.44 solar radii. As confirmed
also by LASCO/C3 images, this comet splits in a main nucleus and a
fragment which have been identified also in our UV data. A study of
the cometary Hydrogen Lyα emission from these two objects showed
a different behaviour: the Lyα signal from the fragment decays
exponentially with time, as expected in terms of the H_2O outgassing
rate and of the charge transfer between the coronal protons and atoms
created by the photodissociation of water. On the contrary the signal
from the main object consists of an exponentially decaying term plus
a constant background. This secondary component has been ascribed to
the sublimation of pyroxene dust grains, whose end products neutralize
coronal protons via charge exchange processes. Hence, the two fragments
have a different composition; differences throughout the comet body
may have been the primary cause for the comet fragmentation.

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Title: Origin and Acceleration of the Fast and Slow Solar Wind
Authors: Poletto, G.
2004IAUS..219..563P Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Preliminary analysis of a CME observed by SOHO and Ulysses
experiments
Authors: Bemporad, A.; Poletto, G.; Romoli, M.; Suess, S. T.
2003ESASP.535..567B Altcode: 2003iscs.symp..567B
Over the last week of November 2002 SOHO/LASCO observed several Coronal
Mass Ejections, most of which occurring in the NW quadrant. At that
time SOHO/UVCS was involved in a SOHO-Sun-Ulysses quadrature campaign,
making observations off the west limb of the Sun, at a northern latitude
of 27°. Here we focus on data taken at 1.7 solar radii, over a time
interval of ≍7 hours, on 26/27 November, 2002, when a large streamer
disruption was imaged by LASCO C2 and C3 coronagraphs. UVCS spectra
revealed the presence of lines from both high and low ionization ions,
such as C III, O VI, Si VIII, IX and XII, Fe X and XVIII, which brighten
at different times, with a different time scale and at different
positions and are apparently related to different phenomena. In
particular, the intensity increase and fast disappearance of the C
III 977 Å line represents the passage through the UVCS slit of cold
material released in a jet imaged by EIT in the He II 304 Å line. The
persistent presence of the Fe XVIII 974 Å line is not easily related
to any special feature crossing the UVCS slit. We suggest to interpret
this behavior in terms of the reconnection events which lead to the
formation of loops observed in the EIT He II 304 Å line.

---------------------------------------------------------
Title: Solar Wind Characteristics from Soho-Sun-Ulysses Quadrature
Observations
Authors: Poletto, G.; Suess, S. T.
2003AIPC..679..102P Altcode:
Coronal and solar wind observations of the same plasma, first observed
remotely in the corona and later, in situ, provide the best way to
determine the evolution of plasma as it is being accelerated from the
corona out to interplanetary distances. We have used this technique to
derive solar wind characteristics from the analysis of data acquired
by SOHO and Ulysses when the SOHO-Sun-Ulysses included angle is 90
degrees: that is, when SOHO, the Sun and Ulysses are in quadrature. We
summarize here the results obtained from the study of the December
1998 quadrature, when we focussed on the behavior of slow wind from
low-latitude regions, and anticipate some results from the June 2000
quadrature, which focussed on establishing a relationship between
coronal and wind abundances of different elements and whose analysis
is in progress. We conclude by illustrating briefly the objectives of
future quadrature studies.

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Title: Solar wind acceleration in low density regions
Authors: Teriaca, L.; Poletto, G.; Romoli, M.; Biesecker, D.
2003AIPC..679..327T Altcode:
High speed solar wind is known to originate in polar coronal holes
which, however, are made up of two components: bright, high density
regions known as plumes, and dark, weakly emitting low density regions
known as interplumes. Recent space observations have shown that the
width of UV lines is larger in interplume regions [see e.g. 1, 2]
while observations of the ratio of the O VI doublet lines at 1032 and
1037 Å, at the altitude of 1.7 solar radii, suggest higher outflows in
interplume regions than in plumes [3]. These results seem to locate the
source of the fast solar wind in the interplume regions. The present
work aims at identifying the outflow speed vs. altitude profile of
the O VI ions, at heights up to 2 solar radii, both in plumes and
interplume regions. To this end, we examined SUMER and UVCS data taken
in the North polar coronal hole on June 3, 1996 over the altitude
range between 1 and 2 solar radii. A Doppler dimming analysis applied
to our data allows us to determine the outflow speed in interplume
regions throughout the range covered by the observations. Our results
favor interplumes as sources of fast wind. However, models mimicking
observations in plume regions will also be discussed.

---------------------------------------------------------
Title: Temporal Evolution of a Streamer Complex: Coronal and in Situ
Plasma Parameters
Authors: Bemporad, A.; Poletto, G.; Suess, S. T.; Ko, Y. K.; Parenti,
S.; Riley, P.; Romoli, M.; Zurbuchen, T. Z.
2003ApJ...593.1146B Altcode:
We report on observations acquired by the Ultraviolet Coronagraph
Spectrometer (UVCS) aboard the Solar and Heliospheric Observatory
(SOHO), from 2000 June 10 to June 17 at the time of a SOHO-Sun-Ulysses
quadrature. UVCS took data at 1.6 and 1.9 Rsolar with a slit
normal to the solar radius and centered along the radial to Ulysses. A
streamer complex was sampled by UVCS throughout the quadrature
campaign, giving us the opportunity to derive plasma parameters
in different streamers and to compare them with plasma properties
measured in situ. Large Angle Spectroscopic Coronagraph images above 2
Rsolar helped us understand the temporal evolution of the
streamer complex. We derive densities, temperatures, and elemental
abundances in two streamers, which have different temperatures and
element abundances. In spite of these differences, both structures
have the same first ionization potential (FIP) bias. The Fe/O ratio,
which may be considered a proxy for the FIP effect, was measured in
situ by the Solar Wind Ion Composition Spectrometer aboard the Ulysses
spacecraft. Values of Fe/O measured in the corona at the sites where
in situ plasma originated agree with in situ Fe/O values.

---------------------------------------------------------
Title: The Nascent Solar Wind: Origin and Acceleration
Authors: Teriaca, Luca; Poletto, Giannina; Romoli, Marco; Biesecker,
Doug A.
2003ApJ...588..566T Altcode:
High-speed solar wind is known to originate in polar coronal holes,
which, however, are made up of two components: bright, high-density
regions known as “plumes” and dark, weakly emitting low-density
regions known as “interplumes.” Recent space observations have
shown that the width of UV lines is larger in interplume regions, while
observations of the ratio of the O VI doublet lines at 1032 and 1037 Å,
at 1.7 solar radii, suggest higher outflows in interplume regions than
in plumes at that altitude. These results favor interplume regions as
sources of the fast solar wind. The present work aims at investigating
the outflow speed versus altitude properties of the O VI and H I
ions, at heights below 2 solar radii, in both plumes and interplume
regions. To this end, we examined Solar Ultraviolet Measurement of
Emitted Radiation (SUMER) and Ultraviolet Coronagraph Spectrometer
(UVCS) observations of a north polar coronal hole taken on 1996 June
3, over the altitude range between 1 and 2 solar radii, and through
a Doppler dimming analysis of our data, we show that interplume
areas may be really identified as sources of fast wind streams. The
behavior of plumes, on the contrary, can be interpreted in terms of
static structures embedded in the interplume ambient. We conclude by
comparing our results with the predictions of theoretical models of
the solar wind and giving an empirical estimate of the heating rate,
per particle, for H I and O VI ions in interplume regions at 1.75 and
2.0 solar radii.

---------------------------------------------------------
Title: Interplume as source of the fast solar wind
Authors: Teriaca, L.; Poletto, G.; Romoli, M.; Biesecker, D. A.
2003MmSAI..74..713T Altcode:
High speed solar wind is known to originate in polar coronal holes
which, however, are made up of two components: bright, high density
regions known as plumes and dark, weakly emitting low density
regions known as interplumes. Recent space observations have shown
that the width of UV lines is larger in interplume regions. Moreover,
observations of the ratio of the O VI doublet lines at 1032 and 1037 Å,
at 1.7 Rsun, suggest higher outflows in interplume regions
than in plumes at that altitude. In this work we examine SUMER and
UVCS observations of a north polar coronal hole taken on 1996 June 3,
over the altitude range between 1 and 2 Rsun and, through
a Doppler dimming analysis of our data, we show that interplume areas
may be really identified as sources of fast wind streams. The behavior
of plumes, on the contrary, can be interpreted in terms of static
structures embedded in the interplume ambient. We conclude comparing our
results with the predictions of theoretical models of the solar wind.

---------------------------------------------------------
Title: Physical parameters of coronal streamers near the maximum
phase of solar cycle
Authors: Bemporad, A.; Poletto, G.; Romoli, M.
2003MmSAI..74..721B Altcode:
During june 10-17, 2000 the Ultraviolet Coronograph Spectrometer
(UVCS) aboard the Solar and Heliospheric Observatory observed a
streamer complex. Data were acquired at the time of a SOHO-Sun-Ulysses
quadrature. We identify two streamers for which we derive electron
densities, temperatures and elemental abundances and we point out
differences and analogies between the two structures. We also derive
the coronal Fe/O, which we consider a proxy for the FIP effect and we
compare it with Fe/O values measured in situ by SWICS.

---------------------------------------------------------
Title: Giancarlo Noci: his science and personality. A tribute for
his 70th birthday.
Authors: Poletto, G.
2003MmSAI..74..550P Altcode:
The scientific achievements of Giancarlo Noci are here summarized
starting from his first steps as a student and young scientist in
Arcetri and going on to his more recent success in space science
investigation. His scientific life and personality is highlighted
through the words of friends and colleagues who recollect different
episodes of their relationship with him.

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Title: Spatial and temporal behavior of the oxygen abundance in a
streamer complex
Authors: Bemporad, A.; Poletto, G.; Romoli, M.
2002ESASP.506..545B Altcode: 2002svco.conf..545B; 2002ESPM...10..545B
The determination of the abundance of trace elements in different solar
structures and in the solar wind may be crucial for the identification
of the solar wind sources. In the last few years, SOHO data allowed
an evaluation of the oxygen abundance at previously unattainable
coronal levels (Zangrilli et al., 2001). Analyses of streamer
data taken at the minimum of the solar activity cycle raised the
question of whether streamers' legs might be the site where slow wind
originates, because the oxygen abundance in the lateral branches of the
streamer, at coronal levels, turned out to be similar to the slow wind
abundance. In this work we analyse UVCS streamers observations, taken
at 1.6Rsolar, near the maximum phase of the activity cycle,
to check whether the behavior found at minimum is shared by streamers at
maximum. We derive also the abundance of oxygen in different streamers
and, within a streamer, across its axis, to get more information on
the spatial variability of the oxygen abundance. Our results show
that the oxygen abundance in different streamers may be significantly
different, implying that a more thorough analysis is needed before
drawing conclusions about the site where slow wind originates.

---------------------------------------------------------
Title: Low-latitude solar wind during the Fall 1998 SOHO-Ulysses
quadrature
Authors: Poletto, G.; Suess, S. T.; Biesecker, D. A.; Esser, R.;
Gloeckler, G.; Ko, Y. -K.; Zurbuchen, T. H.
2002JGRA..107.1300P Altcode:
The Fall 1998 Solar and Heliospheric Observatory (SOHO)-Ulysses
quadrature occurred when Ulysses was at 5.2 AU, 17.4°S of the
equator, and off the west limb of the Sun. SOHO coronal observations,
at heliocentric distances of a few solar radii, showed that the line
through the solar center and Ulysses crossed, over the first days of
observations, a dark, weakly emitting area and through the northern
edge of a streamer complex during the second half of the quadrature
campaign. Ulysses in situ observations showed this transition to
correspond to a decrease from higher-speed wind typical of coronal hole
flow to low-speed wind. Physical parameters of the low-latitude coronal
plasma sampled over the campaign are determined using constraints
from what is the same plasma measured later in situ and simulating the
intensities of the hydrogen Lyman-α and OVI 1032 and 1037 Å lines,
measured by the Ultraviolet Coronagraph Spectrometer on SOHO. It
appears that low-latitude wind from small coronal holes and polar
wind have different characteristics in the corona, differences well
known at interplanetary distances through in situ experiments. Small,
low-latitude coronal holes have a higher expansion factor than typical
polar holes, and their plasma moves at a lower speed than plasma from
polar holes, reaching, at 3.5 Rsun, only about one-fifth
of the terminal speed. Wind emanating from bright regions, above
streamer complexes, is, at the altitudes we analyzed (i.e., 3.5 and 4.5
Rsun), about a factor 3 slower than the low-latitude coronal
hole wind, implying a shift to even higher altitudes of the region
where plasma gets accelerated. We surmise that open field regions,
interspersed amidst closed coronal loops/streamers, may be at least
partially responsible for the well-known slow wind speed variability. As
in polar fast wind, OVI ions move faster than protons, over the range
of altitudes we sampled, and are frozen-in at temperatures of ≈1.3-1.5
106 K, depending on the site where the outflow originates. An
oxygen abundance variation from a value of 8.55, in low-latitude holes,
to 8.73 in bright areas, has also been inferred.

---------------------------------------------------------
Title: Two-dimensional Structure of a Polar Coronal Hole at Solar
Minimum: New Semiempirical Methodology for Deriving Plasma Parameters
Authors: Zangrilli, L.; Poletto, G.; Nicolosi, P.; Noci, G.; Romoli, M.
2002ApJ...574..477Z Altcode:
We develop a new technique to determine the plasma parameters in a
polar coronal hole. This method makes use of the line intensities of
the H I Lyα λ1215.6 line and of the O VI λλ1031.9, 1037.6 doublet,
measured with the Ultraviolet Coronagraph Spectrometer (UVCS) on board
the ESA-NASA solar spacecraft Solar and Heliospheric Observatory (SOHO)
during 1996 August. The observed intensities are self-consistently
reproduced with a two-dimensional semiempirical coronal hole model,
for heliocentric distances between 1.4 and 2.6 Rsolar
and latitudes between 90° (north pole) and 40°. Electron densities
are derived by separating the O VI doublet collisional components from
those due to resonant scattering. The calculated electron density radial
profiles are consistent with typical polar coronal hole data and show
only a moderate increase with latitude decreasing, in regions close to
the equatorial streamer. The outflow speeds of protons and O VI ions are
determined by means of the Doppler dimming technique. In the Doppler
dimming analysis we use kinetic temperatures Tk derived
from UVCS observations of the line profiles, whenever available, or we
keep Tk as a free parameter if not provided by data. Mass
flux conservation along the magnetic field lines is studied adopting a
simple analytical model for the geometry of the magnetic flux tubes. Our
model shows that protons and O VI ions accelerate outward, but their
outflow speed turns out to decrease slowly as latitude decreases. The
O VI speed, initially comparable to the speed of protons, exceeds the
proton speed beyond ~1.7 Rsolar. Anisotropic O VI kinetic
temperatures, T∥ and T⊥, turn out to be
necessary to ensure the consistency of the model parameters with mass
flux conservation, while the H kinetic temperature distribution is
kept isotropic. Results from our model are compared with those from
other two-dimensional models recently developed.

---------------------------------------------------------
Title: Energy input to O VI ions and protons in the fast solar wind
Authors: Zangrilli, L.; Poletto, G.; Nicolosi, P.; Noci, G.; Romoli, M.
2002ESASP.508..493Z Altcode: 2002soho...11..493Z
Observations with UVCS of a polar coronal hole, acquired during August
1996, have been analysed with the purpose of deriving the radial and
latitudinal outflow speed profiles of O VI ions and protons in the
altitude range between 1.4 and 2.6 Rsolar, and latitudes
between 40° and 90°. We used the results obtained along the direction
of the North pole to estimate the energy input to O VI and protons
in the extended solar corona. The O VI and proton outflow speeds
have been derived from a Doppler dimming analysis of the λλ1031.9,
1037.6 O VI doublet and H I Lyα λ1215.6 lines. The coronal hole
morphology has been modelled with a simple magnetic field geometry, in
order to derive the expansion factor of the magnetic field lines. The
O VI and H I Lyα line intensities and the mass flux at 1 A.U. have
been used as constraints for identifying the physical conditions of
the plasma where lines originate. The free parameters that allowed
us to comply with the requirement of a constant mass flux throughout
the region we examine, are the magnetic field geometry, and the O VI
parallel kinetic temperature, for which we have no direct information
from observations. It turns out that the temperature anisotropy
increases with altitude, indicating an increasing asymmetry of the ion
distribution about the magnetic field lines, possibly related to the
heavy ions heating mechanism. Our results show that the oxygen ions flow
at speed of ~350 km s-1, at the highest level we consider,
2.6 Rsolar, in polar regions. However, as the latitude
decreases, the outflow speed tends to decrease, and, for latitudes
lower than 60° and altitudes greater than 2 Rsolar, keeps
below ~300 km s-1. From the analysis of polar data we found
that the O VI heating rate is larger than the proton heating rate,
and it increases with distance.

---------------------------------------------------------
Title: The fall 2001 polar SOHO-Ulysses quadrature campaign:
preliminary results
Authors: Aznar Cuadrado, R.; Poletto, G.; Teriaca, L.; Suess, S. T.
2002ESASP.508..481A Altcode: 2002soho...11..481A
We present here UVCS observations of a polar coronal hole,
acquired during the October/November 2001 SOHO-Sun-Ulysses
quadrature. SOHO-Ulysses quadratures occur when the SOHO-Sun-Ulysses
included angle is 90° and offer the unique opportunity of comparing
the properties of plasma parcels, observed by SOHO in the corona,
with properties of the same parcels, measured in situ, in due time,
by Ulysses. The October/November 2001 quadrature occurred at a time
when Ulysses was at ≍2.2 A.U., at a northern heliographic latitude
of ≍80°, off the West limb of the Sun. Observations were taken from
October 29 to November 12, 2001, with a ≍3 days data gap, after the
eruption of CMEs and the emission of highly energetic particles, on 3-4
November. The UVCS slit was set normal to the solar radius, with the
radial to Ulysses going through its zero position. At the time of the
campaign, the radial to Ulysses crossed a polar coronal hole. Although
its shape was changing, Ulysses was permanently located in a high speed
region where CMEs signature can be recognized. Observations in hydrogen
Lyman-α and in the 1032 and 1037 Å O VI doublet lines have been made
at 1.6 and 2 Rsolar. Line intensities are compared with
intensities typically found, at the same altitudes, in polar coronal
holes at minimum solar activity and in equatorial holes. The temporal
profile of the O VI doublet line ratio and of the O VI line widths,
at the position where the radial to Ulysses traverses the solar corona,
are shown and a tentative interpreation of the data is outlined.

---------------------------------------------------------
Title: Lyman α intensities in a polar coronal hole from a 2D model
Authors: Zangrilli, L.; Poletto, G.; Nicolosi, P.; Noci, G.
2002AdSpR..30..523Z Altcode:
We simulate the coronal H I Lyman α intensity for heliocentric
distances between 1.5 and 2.5 R⊙, and latitudes between
90° (North pole) and 30°, making use of a 2D semiempirical coronal
hole model. Observations are made with the UltraViolet Coronagraph
Spectrometer (UVCS) on board the ESA-NASA solar satellite SOHO (SOlar
and Heliospheric Observatory). Model electron densities are derived from
the collisional part of the O VI λ1037.6 Å line and the proton outflow
speed is calculated from mass flux conservation along the magnetic
field lines. The expansion factor and the direction of the magnetic
flux tubes have been derived by adopting a simple analytical magnetic
field configuration. The intensities of the Ly α line predicted by
the model are compared with the observed intensities.

---------------------------------------------------------
Title: Oxygen abundance in polar coronal holes
Authors: Teriaca, L.; Poletto, G.; Falchi, A.; Doyle, J. G.
2001AIPC..598...65T Altcode: 2001sgc..conf...65T
Fast solar wind is known to emanate from polar coronal holes. However,
only recently attention has been given to the problem of where,
within coronal holes, fast wind originates. Information on whether the
fast solar wind originates from plumes or interplume regions may be
obtained by comparing the elemental abundances in these regions with
those characterizing the fast wind. Here we present a first attempt
to determine the oxygen abundance in the interplume regions by using
spectra taken at times of minimum in the solar cycle (when it is
easier to identify these structures) by the SUMER spectrograph aboard
SoHO. To this end, we analyze spectra taken in 1996 in polar regions,
at altitudes ranging between 1.05 and 1.3 Rsolar, finding a
value &gt;=8.5 for the oxygen abundance in the interplume regions. From
the analysis of the O VI 1032 to 1037 line intensity ratio we also find
no evidence of outflow velocities below 1.2 solar radii in interplume
regions, while there are indications that outflow motions start to be
significant above 1.5 solar radii. The method used and the assumptions
made are discussed in light of the derived values. Our values are
compared with previous determinations in the corona and solar wind. .

---------------------------------------------------------
Title: Oxygen abundance in streamers above 2 solar radii
Authors: Zangrilli, L.; Poletto, G.; Biesecker, D.; Raymond, J. C.
2001AIPC..598...71Z Altcode: 2001sgc..conf...71Z
The oxygen abundance in streamers has been evaluated by several
authors [see e.g. 1, 2, 3] who found, in the core of streamers,
an oxygen abundance lower by a factor 3-4 than in the lateral
branches (legs). All estimates were made at heliocentric distances
h&lt;=2.2Rsolar. In this paper we analyze UVCS
observations of two streamers, observed during solar minimum at
altitudes h&gt;=2.4Rsolar to derive the oxygen abundance,
relative to hydrogen, and its latitude dependence within streamers,
in the range 2.4&lt;=h&lt;=4Rsolar. To this end, electron
densities have been derived from LASCO data, taken at the time of the
UVCS observations, and the radial temperature profile has been taken
from literature. These parameters allow us, after the collisional
contribution to the O VI 1032, 1037 Å line intensities has been
identified, to determine the oxygen abundance that reproduces the
observed collisional components. Our results are compared with previous
abundance determinations and the relationship between coronal and in
situ abundances is also discussed. .

---------------------------------------------------------
Title: Preliminary results from coordinated SOHO-Ulysses observations
Authors: Parenti, S.; Poletto, G.; Bromage, B. J. I.; Suess, S. T.;
Raymond, J. C.; Noci, G.; Bromage, G. E.
2001AIPC..598...83P Altcode: 2001sgc..conf...83P
SOHO-Ulysses quadratures occur at times when the SOHO-Sun-Ulysses angle
is 90° and offer a unique possibility to compare properties of plasma
parcels observed in the low corona with properties of the same parcels
measured, in due time, in situ. The June 2000 quadrature occurred
at a time Ulysses was at 3.35 AU and at a latitude of 58.2 degrees
in the south-east quadrant. Here we focus on the UVCS observations
made on June 11, 12, 13, 16. UVCS data were acquired at heliocentric
altitudes ranging from 1.6 to 2.2 solar radii, using different grating
positions, in order to get a wide wavelength range. The radial direction
to Ulysses, throughout the 4 days of observation, traversed a region
where high latitude streamers were present. Analysis of the spectra
taken by UVCS along this direction shows a variation of the element
abundances in the streamers over our observing interval: however,
because the radial to Ulysses crosses through different parts of
streamers in different days, the variation could be ascribed either
to a temporal or to a spatial effect. The oxygen abundance, however,
seems to increase at the edge of streamers, as indicated by previous
analyses. This suggests the variation may be a function of position
within the streamer, rather than a temporal effect. Physical conditions
in streamers, as derived from UVCS observations, are also discussed. .

---------------------------------------------------------
Title: Coronal and solar wind elemental abundances
Authors: Raymond, J. C.; Mazur, J. E.; Allegrini, F.; Antonucci, E.;
Del Zanna, G.; Giordano, S.; Ho, G.; Ko, Y. -K.; Landi, E.; Lazarus,
A.; Parenti, S.; Poletto, G.; Reinard, A.; Rodriguez-Pacheco, J.;
Teriaca, L.; Wurz, P.; Zangrilli, L.
2001AIPC..598...49R Altcode: 2001sgc..conf...49R
Coronal elemental abundances, as compared with abundances in the solar
wind and solar energetic particles, provide the means for connecting
solar wind gas with its coronal source. Comparison of coronal abundances
with photospheric values shows fractionation with the ionization
potential of the atom, providing important, though not yet fully
understood, information about the exchange of material between corona
and chromosphere. Fractionation due to gravitational settling provides
clues about flows within the corona. In this paper, we discuss the
uncertainties of abundance determinations with spectroscopic techniques
and in situ measurements, we survey the ranges of abundance variations
in both the corona and solar wind, and we discuss the progress in
correlating solar wind features with their coronal sources. .

---------------------------------------------------------
Title: The Fall 2000 and Fall 2001 SOHO-Ulysses Quadratures
Authors: Suess, S.; Poletto, G.
2001SSRv...97...59S Altcode:
SOHO-Ulysses quadrature occurs when their included angle with the
Sun is 90°. At these times the same plasma leaving the Sun in the
direction of Ulysses can first be remotely analyzed with SOHO and then
later be sampled in situ at Ulysses. Quadratures in Fall 2000/2001
are of special interest because Ulysses will be near the south and
north heliographic poles, respectively, and it will be near sunspot
maximum. But, the quadrature geometry is complex - Ulysses is not in a
true polar orbit and the orbital speed of Ulysses and SOHO about the
Sun will be comparable. In neither case is true quadrature achieved,
but this works to the observer's advantage. Here we show plots of the
relative positions of SOHO and Ulysses throughout the two quadrature
intervals.

---------------------------------------------------------
Title: Properties of Different Coronal Stremers
Authors: Parenti, S.; Bromage, B. J. I.; Poletto, G.; Noci, G.;
Reymond, J. C.; Bromage, G. E.
2001IAUS..203..413P Altcode:
Element abundance in equatorial and mid-latitude streamers have been
derived from data taken by SOHO/CDS and UVCS experiments. Observations
were made at 1.1, 1.5,1.6 Rodot, to allow us to check
a possible variation of elemental composition with altitude. Part
of the CDS data were taken at the border of the south Corona Hole,
so that the variation of coronal composition at the streamer edge is
investigated. UVCS spectra have been acquired using three different
grating positions to cover lines from low and high First Ionization
Potential. Absolute abundance of Oxygen and Iron have been determined
via the evaluation of the radiat ive and collisional components
of the H-Lyman β and O VI (1032 Å) lines and of th e intensities
of lines from Fe X-XIII-XV-XVIII. Abundance of Fe, Si, Al, Mg were
estimated using the Differential Emission Measure technique. This
method gives us information also on the plasma electron temperature
(Te), which is compared with temperatures estimates from line
ratio technique. The variability of (Te) and of abundances
in the observed streamers are discussed and compared with estimates
from the literature.

---------------------------------------------------------
Title: The SOHO-Sun-Ulysses quadratures campaigns
Authors: Poletto, Giannina; Suess, Steve
2001MmSAI..72..628P Altcode:
A SOHO-Sun-Ulysses quadrature occurs when the SOHO-Sun-Ulysses angle
is 90°. This configuration occurs twice per year and offers the
unique opportunity to compare properties of plasma parcels observed
in the corona with plasma properties of the same parcel measured, in
due time, in situ. Here we summarize objectives and results from past
observational quadrature campaigns and briefly describe future programs.

---------------------------------------------------------
Title: Element abundances in streamers from SOHO/UVCS CDS observations
Authors: Parenti, S.; Poletto, G.; Bromage, B. J. I.; Raymond, J. C.;
Noci, G.
2001MmSAI..72..604P Altcode:
The variation of the element abundances in coronal streamers with
solar distance and latitude has been studied. The data were acquired
in an equatorial and mid-latitude streamer by SOHO/UVCS and CDS,
during a coordinated observing campaign held on March, 8 1998. CDS
data refer to 1.1 solar radii, UVCS data to 1.6 solar radii. A
further mid-latitude streamer was observed by UVCS at 1.6 solar
radii, on May 24 of the same year. Element abundances, relative to
photospheric iron, were derived from CDS data using the Differential
Emission Measure (DEM) technique. Absolute element abundances were
derived from UVCS data using a) the O VI doublet lines for oxygen,
b) the line ratio between Fe lines and Lyman-beta for iron and, c)
the DEM technique for the other elements. Our results show a depletion
of the abundances from their photospheric values in the high corona,
while almost photospheric values of the abundances relative to iron
have been found in the low corona. Spectra do not show any clear
indication for a latitude dependence of elemental abundances.

---------------------------------------------------------
Title: Outflow speed of protons and O VI ions in a coronal hole
Authors: Zangrilli, L.; Poletto, G.; Nicolosi, P.
2001MmSAI..72..600Z Altcode:
In this work we estimate the outflow speed of protons and O VI ions
as a function of latitude and heliocentric distance within a coronal
hole. The outflow speed of protons is obtained from the mass flux
conservation along the coronal magnetic field lines, while that of O
VI ions is derived by applying the Doppler dimming technique to the
intensity ratio of the O VI doublet lines at λλ1031.9 Å and 1037.6
Å, observed by the UVCS experiment. To this end we develop a 2D
semiempirical coronal hole model, also based on UVCS data. We obtain
that the outflow speed of these ions increases with the heliocentric
distance, and with latitude from regions close to the equatorial
streamer to the pole.

---------------------------------------------------------
Title: Characteristics of solar coronal streamers. Element
abundance, temperature and density from coordinated CDS and UVCS
SOHO observations
Authors: Parenti, S.; Bromage, B. J. I.; Poletto, G.; Noci, G.;
Raymond, J. C.; Bromage, G. E.
2000A&A...363..800P Altcode:
This paper presents the results from coordinated observations of
streamers acquired by the SOHO Coronal Diagnostic Spectrometer (CDS)
and UltraViolet Coronograph Spectrometer (UVCS) experiments. Data
from different altitudes within the solar corona were taken, with
the purpose of determining their physical parameters - densities,
electron temperatures and element abundances - and their changes
over the altitude range between 1.02 and 1.6 R_sun. Further UVCS
streamer data, taken about two months later are used for comparison
with the behaviour seen in two different streamers. Whenever possible,
alternative methods have been adopted to determine the same physical
parameter, as a cross check. In particular, the DEM technique has
been applied to UVCS data, in order to compare abundance values
derived in this way, with those obtained using the method of Raymond
et al. (\cite{ray97}). We conclude that abundances in the low corona
covered by CDS data do not show evidence for abundance variation, with
respect to photospheric values, while, at UVCS altitudes, a depletion
of all element abundances is clearly evident. No clear evidence of
a FIP effect in streamers was found; we get contrasting results from
the only two high FIP elements present in our spectra.

---------------------------------------------------------
Title: The May 1997 SOHO-Ulysses quadrature
Authors: Suess, S. T.; Poletto, G.; Romoli, M.; Neugebauer, M.;
Goldstein, B. E.; Simnett, G.
2000JGR...10525033S Altcode:
We present results from the May 1997 SOHO-Ulysses quadrature
(SOHO-Sun-Ulysses angle=90°), near sunspot minimum. Ulysses was at
5.1 AU, 10° north of the solar equator, and off the east limb. It was
also at the very northern edge of the streamer belt. Nevertheless,
the Solar Wind Observations Over the Poles of the Sun instrument
(SWOOPS) detected only slow, unusually smooth wind and there was no
direct evidence of fast wind from the northern polar coronal hole or of
mixing with fast wind. The Large-Angle and Spectrometric Coronagraph
(LASCO) images show that the streamer belt at 10°N was narrow and
sharp at the beginning and end of the 2 week observation interval,
but broadened in the middle. A related change in density, but not flow
speed, occurred at Ulysses. Under these conditions it was possible
to show that densities derived from the Ultraviolet Coronagraph
Spectrometer (UVCS) in the lower corona are closely related to those
in the solar wind, both over quiet intervals and in transient events
on the limb. Density and velocity in one small transient observed by
both LASCO and UVCS are analyzed in detail.

---------------------------------------------------------
Title: UVCS WLC Observations of Compressional Waves in the South
Polar Coronal Hole
Authors: Ofman, L.; Romoli, M.; Poletto, G.; Noci, G.; Kohl, J. L.
2000ApJ...529..592O Altcode:
Recent SOHO Ultraviolet Coronagraph Spectrometer (UVCS) white light
channel (WLC) observations of the south polar coronal hole plumes and
interplume regions produce signatures of quasi-periodic variations in
the polarized brightness (pB) at a heliocentric distance of 1.9 solar
radii (Rsolar). The Fourier power spectrum of the pB time
series shows significant peaks at about 1.6-2.5 mHz and additional
smaller peaks at longer and shorter timescales. Wavelet analysis of
the pB time series shows that the coherence time of the fluctuations
is about 30 minutes. The new observations strongly suggest that the
fluctuations are compressional wave packets propagating in the coronal
hole high above the limb. The presence of compressional waves may have
important implications that help to explain the heating of coronal
holes and the fast solar wind acceleration.

---------------------------------------------------------
Title: Commission 10: Solar Activity: (Activite Solaire)
Authors: Ai, G.; Benz, A.; Dere, K. P.; Engvold, O.; Gopalswamy, N.;
Hammer, R.; Hood, A.; Jackson, B. V.; Kim, I.; Marten, P. C.; Poletto,
G.; Rozelot, J. P.; Sanchez, A. J.; Shibata, K.; van Driel-Geztelyi, L.
2000IAUTA..24...67A Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Plasma Flows In Coronal Hole Regions
Authors: Landi, E.; Mullan, D.; Poletto, G.; Wilhelm, K.
1999ESASP.446..417L Altcode: 1999soho....8..417L
More than two decades after coronal holes (CH) had been recognized
to be the source regions of solar wind, we still do not know which
structures, within CH, most contribute to the solar wind mass flux. In
a recent work, Hassler et al. (1999) obtained velocity maps of a
coronal hole region, in the Ne VIII 770 Angstrom line, which suggest
that localized areas within the network might be sources of the solar
wind. On the opposite, an earlier work of Dupree et al. (1996), from
an analysis of the He I 10830 Angstrom line, suggested cell regions
as sources of the solar wind. In the present work, we reinvestigate
this issue analysing SUMER data taken in an equatorial and in a polar
coronal hole, observed respectively on 29 August 1996 and 21 September
1996. We study the behavior of Si II, C IV, O V, N V, Ne VIII, Mg X and
Fe XII ions, whose temperatures of formation range from chromospheric
(around 2x104 K) to coronal values (around 1.5x105
K). In particular, we analysed intensity and velocity distributions
of these lines, and illustrate changes in the plasma velocity pattern
as a function of the temperature regime where lines form.

---------------------------------------------------------
Title: Latitudinal Dependence Of The Outflow Speed Of the Solar Wind
From Uvcs Observations
Authors: Zangrilli, L.; Poletto, G.; Nicolosi, P.; Corti, G.; Noci, G.
1999ESASP.446..721Z Altcode: 1999soho....8..721Z
Observations of the OVI doublet lines at 1032 and 1037 Angstrom have
been acquired by UVCS, in August 1996, in the range of heliocentric
distances between 1.5 and 2 solar radii, and over a range of latitudes
including a 90 degree sector, spanning from equatorial to coronal
hole regions. OVI and Lyman alpha line profiles have been discussed
in a previous paper (Zangrilli et al., 1999), which focussed on the
latitudinal behavior of Hydrogen and Oxygen kinetic temperatures,
as a diagnostics of coronal heating processes. In the present paper,
emphasis is shifted to the latitudinal behavior of plasma acceleration
processes. Information on this issue can be derived via the analysis
of the ratio between the intensity of the OVI doublet lines, whose
value depends on the outflow speed of Oxygen ions. In order to derive
accurate values of the OVI line intensities, we carefully considered
the effects of different choices of the background continuum, which
turn out to lead to radically different results. The effect of the
stray light correction on the intensity ratio of the OVI doublet lines
has also been analysed. We discuss our results addressing two issues in
particular: i) is there a level, within the range covered by our data,
where the wind plasma gets most of its acceleration? ii) does coronal
plasma change from a stationary state in streamers to a constant high
speed in coronal holes, or is there a well defined latitude where the
wind plasma attains a speed maximum? In order to answer these questions
we need also to know other coronal parameters, such as densities and
expansion factors of the flux tubes. Densities have been derived on the
basis of a technique which uses the collisional components of Oxygen
lines - easily derived from total intensities - under the assumption
that the electron density dependence on altitude can be expressed in
terms of a power law. The expansion factor of coronal flux tubes is
not well known; hence, we kept this as a free parameter, and different
flux tube geometries have been considered. Results from this work are
compared with the latitudinal behavior of the wind speed obtained from
other experiments (SWAN, Ulysses).

---------------------------------------------------------
Title: Working Group 6: Activity on all Scales
Authors: Clette, F.; Poletto, G.; Ŝvestka, Z.
1999ESASP.446..103C Altcode: 1999soho....8..103C
No abstract at ADS

---------------------------------------------------------
Title: Physical Parameters in Streamer From CDS and UVCS Observations
Authors: Parenti, S.; Poletto, G.; Raymond, J.; Bromage, B. J. I.
1999ESASP.446..531P Altcode: 1999soho....8..531P
UVCS and CDS observations of a streamer in the southern hemisphere,
at a latitude of 40 Degrees, have been acquired on March 8, 1998. UVCS
data have been taken at an heliocentric altitude of 1.6 solar radii and
cover the spectral range from 950 to 1250 Angstrom; CDS data have been
taken at an altitude of 1.1 solar radii and cover the range from 308 to
381, and 513 to 633, Angstrom. These data have been used to determine
the physical conditions of a streamer structure: in particular, we give
an estimate of the electron temperature, electron density and element
abundance in the structure. The electron temperature has been evaluated
from lines of different ions from the same elements, crude values of
densities have been derived from an analysis of the OVI doublet lines
at 1032 and 1037 Angstrom and element abundances have been estimated
both from a DEM (Differential Emission Measure) analysis and from other
techniques. Because UVCS spectra have been taken at different times,
during the day, we have been looking also at temporal variations in
the physical parameters of the streamer. Changes across the streamer
have been analyzed as well. Coordinated CDS and UVCS observations
allow us also to compare results from the two experiments and look for
variations, with solar distance, of the streamer physical parameters.

---------------------------------------------------------
Title: Bernard Fleck and Zdenek Švestka (eds.), The First Results
from SOHO
Authors: Poletto, Giannina
1999SSRv...88..606P Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Heating and Acceleration of the Solar Wind via Gravity Damping
of Alfvén Waves
Authors: Cuseri, Iolanda; Mullan, Dermott; Noci, Giancarlo; Poletto,
Giannina
1999ApJ...514..989C Altcode:
In this paper we present a two-fluid model for the heating of the solar
corona and acceleration of the solar wind, based on the dissipation
of Alfvén waves by gravity damping. This mechanism was proposed by
Khabibrakhmanov &amp; Mullan but has not previously been applied in
modeling efforts. After extending the Khabibrakhmanov &amp; Mullan
theory to give an expression for the evolution of the Alfvén wave
amplitude as a function of the local parameters of the atmosphere,
we show how gravity damping compares with other mechanisms that have
been proposed for the dissipation of Alfvén waves. Then we introduce
the system of equations that we use for the wind model: this includes,
in the energy equation, a gravity dissipation term and, in the momentum
equation, a different wave acceleration term from that which is usually
adopted. Initial conditions for the integration of the equations
are compatible with recent Ulysses measurements, and the integration
proceeds from 1 AU toward the base of the solar corona and into the
transition region [where T=(1-2)×105 K]. Our results show
that the gravity damping of Alfvén waves heats protons in the solar
plasma to several million degrees and accelerates the solar wind
to 600-700 km s-1. Model predictions at low heliocentric
distances compare favorably with recently acquired data. One prediction
of our model is that the damping process is most effective in regions
where the Alfvén speed is low. Another prediction is that although
the energy is deposited mainly into protons, the deposition occurs
close enough to the Sun that collisional coupling also leads to
effective heating of the electrons (to Te~106
K). We compare and contrast the present model with models based on
ion-cyclotron resonant processes.

---------------------------------------------------------
Title: A two-fluid, MHD coronal model
Authors: Suess, S. T.; Wang, A. -H.; Wu, S. T.; Poletto, G.; McComas,
D. J.
1999JGR...104.4697S Altcode:
We describe first results from a numerical two-fluid MHD model of
the global structure of the solar corona. The model is two-fluid in
the sense that it accounts for the collisional energy exchange between
protons and electrons. As in our single-fluid model, volumetric heat and
momentum sources are required to produce high speed wind from coronal
holes, low speed wind above streamers, and mass fluxes similar to
the empirical solar wind. By specifying different proton and electron
heating functions we obtain a high proton temperature in the coronal
hole and a relatively low proton temperature above the streamer
(in comparison with the electron temperature). This is consistent
with inferences from SOHO/UltraViolet Coronagraph Spectrometer
instrument (UVCS) [Kohl et al., 1997], and with the Ulysses/Solar Wind
Observations Over the Poles of the Sun instrument (SWOOPS) proton and
electron temperature measurements which we show from the fast latitude
scan. The density in the coronal hole between 2 and 5 solar radii (2 and
5RS) is similar to the density reported from SPARTAN 201-01
measurements by Fisher and Guhathakurta [1994]. The proton mass flux
scaled to 1 AU is 2.4×108cm-2s-1,
which is consistent with Ulysses observations [Phillips et al.,
1995]. Inside the closed field region, the density is sufficiently high
so that the simulation gives equal proton and electron temperatures due
to the high collision rate. In open field regions (in the coronal hole
and above the streamer) the proton and electron temperatures differ
by varying amounts. In the streamer the temperature and density are
similar to those reported empirically by Li et al. [1998], and the
plasma β is larger than unity everywhere above ~1.5RS, as
it is in all other MHD coronal streamer models [e.g., Steinolfson et
al., 1982; also G. A. Gary and D. Alexander, Constructing the coronal
magnetic field, submitted to Solar Physics, 1998].

---------------------------------------------------------
Title: Latitudinal properties of the Lyman alpha and O VI profiles
in the extended solar corona
Authors: Zangrilli, L.; Nicolosi, P.; Poletto, G.; Noci, G.; Romoli,
M.; Kohl, J. L.
1999A&A...342..592Z Altcode:
We have analysed the latitudinal properties of the profiles of the H I
Lyman alpha line at 1215.6 protect Angstroms and of the O VI doublet at
1031.9 protect Angstroms and 1037.6 protect Angstroms in the extended
solar corona, between 1.5 R_sun and 2.0 R_sun. Observations have
been performed with the UltraViolet Coronagraph Spectrometer (UVCS)
on board the ESA-NASA solar satellite SOHO (SOlar and Heliospheric
Observatory). The results show that these lines have quite a different
behaviour with latitude: the Ly alpha line has larger full width at
half maximum (FWHM) values in the streamer region and narrower ones
towards polar latitudes, while the O VI lines have a minimum FWHM at
the center of the streamer, which almost steadily increases towards
polar regions. The observations have been analysed looking also
for an interpretation in terms of selective heating mechanisms. The
implications of our results for coronal heating theories are also
examined. In particular we discuss the possibility for the presence
of the ion-cyclotron coronal heating mechanism. Moreover, we point out
an interesting correlation between the intensity of the coronal lines
and their widths, which may be relevant to the open question of the
different morphological features visible in the Ly alpha and O VI lines.

---------------------------------------------------------
Title: Latitudinal Properties of the Solar Wind Outflow Speed Derived
from UVCS Observations
Authors: Zangrilli, L.; Nicolosi, P.; Poletto, G.; Noci, G.
1999RoAJ....9S.111Z Altcode:
In this paper we investigate the latitudinal dependence of the outflow
speed of the solar wind from SOHO/UVCS observations. To this end,
we measure the intensity of the O VI doublet lines at 1031.9 Å and
1037.6 Å, and consider the ratio R = I1032/I1037 as a diagnostic for
wind speed. At distances larger than 1.6 R?, a local minimum in the
ratio R at mid latitudes is observed, that might be attributed to a
local increase of the wind speed. To check whether this interpretation
is plausible, we derived the velocity field of the solar wind from
mass flux conservation, after mapping electron densities from synoptic
observations and adopting a simple magnetic field configuration. It
turns out that the outflow plasma speed shows a local peak at mid
latitudes between 1.5 and 2.5 R?, as inferred from UVCS observations.

---------------------------------------------------------
Title: An Empirical Model of a Polar Coronal Hole at Solar Minimum
Authors: Cranmer, S. R.; Kohl, J. L.; Noci, G.; Antonucci, E.;
Tondello, G.; Huber, M. C. E.; Strachan, L.; Panasyuk, A. V.;
Gardner, L. D.; Romoli, M.; Fineschi, S.; Dobrzycka, D.; Raymond,
J. C.; Nicolosi, P.; Siegmund, O. H. W.; Spadaro, D.; Benna, C.;
Ciaravella, A.; Giordano, S.; Habbal, S. R.; Karovska, M.; Li, X.;
Martin, R.; Michels, J. G.; Modigliani, A.; Naletto, G.; O'Neal,
R. H.; Pernechele, C.; Poletto, G.; Smith, P. L.; Suleiman, R. M.
1999ApJ...511..481C Altcode:
We present a comprehensive and self-consistent empirical model
for several plasma parameters in the extended solar corona above
a polar coronal hole. The model is derived from observations
with the SOHO Ultraviolet Coronagraph Spectrometer (UVCS/SOHO)
during the period between 1996 November and 1997 April. We compare
observations of H I Lyα and O VI λλ1032, 1037 emission lines
with detailed three-dimensional models of the plasma parameters and
iterate for optimal consistency between measured and synthesized
observable quantities. Empirical constraints are obtained for
the radial and latitudinal distribution of density for electrons,
H0, and O5+, as well as the outflow velocity
and unresolved anisotropic most probable speeds for H0 and
O5+. The electron density measured by UVCS/SOHO is consistent
with previous solar minimum determinations of the white-light coronal
structure; we also perform a statistical analysis of the distribution
of polar plumes using a long time series. From the emission lines we
find that the unexpectedly large line widths of H0 atoms
and O5+ ions at most heights are the result of anisotropic
velocity distributions. These distributions are not consistent with
purely thermal motions or the expected motions from a combination of
thermal and transverse wave velocities. Above 2 Rsolar,
the observed transverse most probable speeds for O5+ are
significantly larger than the corresponding motions for H0,
and the outflow velocities of O5+ are also significantly
larger than the corresponding velocities of H0. Also, the
latitudinal dependence of intensity constrains the geometry of the
wind velocity vectors, and superradial expansion is more consistent
with observations than radial flow. We discuss the constraints and
implications on various theoretical models of coronal heating and
acceleration.

---------------------------------------------------------
Title: Ulysses-UVCS Coordinated Observations
Authors: Suess, S. T.; Poletto, G.; Corti, G.; Simnett, G.; Noci,
G.; Romoli, M.; Kohl, J.; Goldstein, B.
1999SSRv...87..319S Altcode:
We present results from SOHO/UVCS measurements of the density and
flow speed of plasma at the Sun and again of the same plasma by
Ulysses/SWOOPS in the solar wind. UVCS made measurements at 3.5 and
4.5 solar radii and Ulysses was at 5.1 AU. Data were taken for nearly
2 weeks in May June 1997 at 9 10 degrees north of the equator in the
streamer belt on the east limb. Density and flow speed were compared
to see if near Sun characteristics are preserved in the interplanetary
medium. By chance, Ulysses was at the very northern edge of the streamer
belt. Nevertheless, no evidence was found of fast wind or mixing of slow
wind with fast wind coming from the northern polar coronal hole. The
morphology of the streamer belt was similar at the beginning and end
of the observing period, but was markedly different during the middle
of the period. A corresponding change in density (but not flow speed)
was noted at Ulysses.

---------------------------------------------------------
Title: The Gradual Phase of Flares
Authors: Svestka, Z. F.; Poletto, G.; Fontenla, J.; Hick, P.; Kopp,
R. A.; Sylwester, B.; Sylwester, J.
1999mfs..conf..409S Altcode:
Heating and Cooling in the Gradual Phase Emission Measure-Temperature
Diagrams Flaring Arches Gradual Phase of Eruptive Flares Postflare
Giant Arches Giant Arches: Modeling and Interpretation

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Title: On the Lyman α and O VI Line Profiles in Streamers and
Coronal Holes
Authors: Zangrilli, L.; Nicolosi, P.; Poletto, G.; Noci, G.
1999SSRv...87..349Z Altcode:
The profiles of the Lyα line at 1215.6 Å and of the O VI doublet at
1031.9 Å and 1037.6 Å in the extended solar corona have been analyzed
vs. latitude and radial direction, performing observations with the
Ultraviolet Coronagraph Spectrometer (UVCS) on board the ESA-NASA
solar satellite SOHO (Solar and Heliospheric Observatory). The results
show that these lines behave differently with latitude: the H I Ly
α line has larger full width at half maximum (FWHM) values in the
streamer region and narrower values towards the pole, while the FWHM
of O VI lines has a minimum at the center of the streamer and slightly
increases towards the polar regions. We briefly discuss the impact of
the results on coronal heating theories.

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Title: Coronal Heating: a Comparison of Ion-cyclotron and Gravity
Damping Models
Authors: Cuseri, I.; Mullan, D.; Poletto, G.
1999SSRv...87..153C Altcode:
SOHO/UVCS data indicate that minor ions in the corona are heated more
than hydrogen, and that coronal heating results in T⊥
larger than T‖. Analogous behavior has been known from
in situ measurements in solar wind for many years. Here we compare
and contrast two mechanisms which have been proposed to account for
the above behavior: ion-cyclotron resonance and gravity damping.

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Title: SOHO Observations of Density Fluctuations in Coronal Holes
Authors: Ofman, L.; Romoli, M.; Noci, G.; Poletto, G.; Kohl, J. L.;
Howard, R. A.; Cyr, C. St.; Deforest, C. E.
1999SSRv...87..287O Altcode:
In recent UVCS/SOHO White Light Channel (WLC) observations we found
quasi-periodic variations in the polarized brightness (pB) in the
polar coronal holes at heliocentric distances of 1.9 to 2.45 solar
radii. The motivation for the observation is the 2.5D MHD model of
solar wind acceleration by nonlinear waves, that predicts compressive
fluctuations in coronal holes. In February 1998 we performed new
observations using the UVCS/WLC in the coronal hole and obtained
additional data. The new data corroborate our earlier findings with
higher statistical significance. The new longer observations show that
the power spectrum peaks in the 10 12 minute range. These timescales
agree with EIT observations of brightness fluctuations in polar
plumes. We performed preliminary LASCO/C2 observations in an effort
to further establish the coronal origin of the fluctuations.

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Title: Ultraviolet Coronagraph Spectrometer Observations of Density
Fluctuations in the Solar Wind
Authors: Ofman, L.; Romoli, M.; Poletto, G.; Noci, G.; Kohl, J. L.
1998ApJ...507L.189O Altcode:
In the Letter “Ultraviolet Coronagraph Spectrometer
Observations of Density Fluctuations in the Solar Wind” by
L. Ofman, M. Romoli, G. Poletto, G. Noci, and J. L. Kohl (<A
href="/abs/1997ApJ...491L.111">ApJ, 491, L111 [1997]</A>), there was
an error in the data reduction of the polarized brightness (pB). It
was assumed that the cadence of the data and the exposure time are
equal. However, the correct cadence is30 s longer than the exposure
time because of the time it takes the polarizer to change orientation
between exposures. This error does not affect the main result of the
Letter, i.e., the detection of quasi-periodic density fluctuations in
the solar wind. However, the correct cadences of the data in Table 1
are 30 s longer. This correction can be taken into account in Figure
1 by multiplying the times by 1.5 and dividing the frequencies by
the same factor. Thus, the highest peak in the power spectrum is at
1.8+/-0.07 mHz (the corresponding period is 9.3+/-0.4 minutes). The
correction factor is 1.1 in Figure 2 because of the longer exposure
time in this observation.

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Title: UVCS/SOHO Empirical Determinations of Anisotropic Velocity
Distributions in the Solar Corona
Authors: Kohl, J. L.; Noci, G.; Antonucci, E.; Tondello, G.; Huber,
M. C. E.; Cranmer, S. R.; Strachan, L.; Panasyuk, A. V.; Gardner,
L. D.; Romoli, M.; Fineschi, S.; Dobrzycka, D.; Raymond, J. C.;
Nicolosi, P.; Siegmund, O. H. W.; Spadaro, D.; Benna, C.; Ciaravella,
A.; Giordano, S.; Habbal, S. R.; Karovska, M.; Li, X.; Martin, R.;
Michels, J. G.; Modigliani, A.; Naletto, G.; O'Neal, R. H.; Pernechele,
C.; Poletto, G.; Smith, P. L.; Suleiman, R. M.
1998ApJ...501L.127K Altcode:
We present a self-consistent empirical model for several plasma
parameters of a polar coronal hole near solar minimum, derived from
observations with the Solar and Heliospheric Observatory Ultraviolet
Coronagraph Spectrometer. The model describes the radial distribution of
density for electrons, H0, and O5+ and the outflow
velocity and unresolved most probable velocities for H0
and O5+ during the period between 1996 November and 1997
April. In this Letter, we compare observations of H I Lyα and O
VI λλ1032, 1037 emission lines with spatial models of the plasma
parameters, and we iterate for optimal consistency between measured and
synthesized observable quantities. The unexpectedly large line widths
of H0 atoms and O5+ ions at most radii are the
result of anisotropic velocity distributions, which are not consistent
with purely thermal motions or the expected motions from a combination
of thermal and transverse wave velocities. Above 2 Rsolar,
the observed transverse, most probable speeds for O5+ are
significantly larger than the corresponding motions for H0,
and the outflow velocities of O5+ are also significantly
larger than the corresponding velocities of H0. We discuss
the constraints and implications on various theoretical models of
coronal heating and acceleration.

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Title: The Geometric Spreading of Coronal Plumes and Coronal Holes
Authors: Suess, S. T.; Poletto, G.; Wang, A. -H.; Wu, S. T.; Cuseri, I.
1998SoPh..180..231S Altcode:
The geometric spreading in plumes and in the interplume region in
coronal holes is calculated, using analytic and numerical theoretical
models, between 1.0 and 5.0 R⊙. We apply a two-scale
approximation that permits the rapid local spreading at the base of
plumes (fl) to be evaluated separately from the global
spreading (fg) imposed by coronal hole geometry. We show
that fl can be computed from a potential-field model
and fg can be computed from global magnetohydrodynamic
simulations of coronal structure. The approximations are valid when the
plasma beta is small with respect to unity and for a plume separation
small with respect to a solar radius.

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Title: Global model of the corona with heat and momentum addition
Authors: Wang, A. H.; Wu, S. T.; Suess, S. T.; Poletto, G.
1998JGR...103.1913W Altcode:
We have been developing a series of global coronal models directed at a
better simulation of empirical coronal hole and streamer properties. In
a previous study, a volumetric heat source was used to produce a
thin current sheet above streamers and high solar wind speed in the
coronal hole. This improved the preexisting coronal structure for
coronal mass ejection simulations even when not using a polytropic
energy equation. Here we report on the addition of a momentum source
to the model with volumetric heating and thermal conduction. Most
theoretical acceleration models in coronal holes are driven either
by thermal pressure or waves (magnetosonic, Alfvén, and sonic
waves). In the thermal pressure driven models an artificially high
effective temperature is assumed. In the wave driven models the force
is generally not big enough to accelerate the solar wind as quickly as
observed. In the present model, in comparison to earlier calculations
[Suess et al., 1996], we reduce the heat source and add momentum. These
changes appear to further improve the numerical simulation results
in comparison to empirical properties. We have high solar wind speed
in the hole without using unrealistic high plasma temperature. We also
demonstrates that the deposition height of the momentum addition affects
the mass flux. The model still predicts a slow-speed solar wind source
in the streamer and high plasma β at the top of the streamer.

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Title: UVCS observations of polar regions
Authors: Poletto, G.; Corti, G.; Romoli, M.; Kohl, J. L.; Noci, G.
1998ESASP.421...69P Altcode: 1998sjcp.conf...69P
In order to facilitate the interpretation of UVCS data, the first
section of this paper gives a short summary of the mechanisms of line
formation in the extended corona and of the diagnostic techniques
adopted to analyze UVCS observations. This allows us to interpret, in
a semiqualitative way, the morphology of polar regions, as revealed
by UVCS, which are next illustrated. Results of data analysis,
i.e. densities, kinetic temperatures and flow speeds at heliocentric
distances between 1.5 and 3.5 Rsun are then discussed. The
ensuing scenario has a strong impact on the theories of heating
and acceleration of the solar wind plasma: we briefly outline the
theoretical implications emerging from UVCS results and the theories
which may comply with the observational requirements.

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Title: A new heating and acceleration mechanism for the fast
solar wind
Authors: Cuseri, I.; Mullan, D. J.; Noci, G.; Poletto, G.
1998MmSAI..69..745C Altcode:
No abstract at ADS

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Title: Coronal Plumes and the Solar Wind: Observations and Theories
(invited)
Authors: Poletto, G.; Corti, G.; Romoli, M.
1998asct.conf..235P Altcode:
No abstract at ADS

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Title: Ultraviolet Coronagraph Spectrometer Observations of Density
Fluctuations in the Solar Wind
Authors: Ofman, L.; Romoli, M.; Poletto, G.; Noci, G.; Kohl, J. L.
1997ApJ...491L.111O Altcode:
Recent Ultraviolet Coronagraph Spectrometer (UVCS) white-light
channel (WLC) observations on board the Solar and Heliospheric
Observatory (SOHO) indicate quasi-periodic variations in the
polarized brightness (pB) in the polar coronal holes. This is
the first observation of possible signatures of compressional
waves high above the limb (at heliocentric distances in the range
1.9-2.45 Rsolar). The Fourier power spectrum of the
pB time series at 1.9 Rsolar shows significant peak
at about 6 minutes and possible fluctuations on longer timescales
(20-50 minutes). The observation at 1.9 Rsolar is the only
currently available WLC data set with sufficient cadence to resolve
the 6 minute period. These preliminary observations may result from
density fluctuations caused by compressional waves propagating in
polar coronal holes. We stress that our results are preliminary, and
we plan future high-cadence observations in both plume and interplume
regions of coronal holes. Recently, Ofman &amp; Davila used a 2.5 D
MHD model and found that Alfvén waves with an amplitude of 20-70 km
s-1 at the base of the coronal hole can generate nonlinear,
high-amplitude compressional waves that can contribute significantly to
the acceleration of the fast solar wind. The nonlinear solitary-like
waves appear as fluctuations in the density and the radial outflow
velocity and contribute significantly to solar wind acceleration
in open magnetic field structures. The motivation for the reported
observations is the MHD model prediction.

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Title: Composition of Coronal Streamers from the SOHO Ultraviolet
Coronagraph Spectrometer
Authors: Raymond, J. C.; Kohl, J. L.; Noci, G.; Antonucci, E.;
Tondello, G.; Huber, M. C. E.; Gardner, L. D.; Nicolosi, P.; Fineschi,
S.; Romoli, M.; Spadaro, D.; Siegmund, O. H. W.; Benna, C.; Ciaravella,
A.; Cranmer, S.; Giordano, S.; Karovska, M.; Martin, R.; Michels, J.;
Modigliani, A.; Naletto, G.; Panasyuk, A.; Pernechele, C.; Poletto,
G.; Smith, Peter L.; Suleiman, R. M.; Strachan, L.
1997SoPh..175..645R Altcode:
The Ultraviolet Coronagraph Spectrometer on the SOHO satellite covers
the 940-1350 Å range as well as the 470-630 Å range in second
order. It has detected coronal emission lines of H, N, O, Mg, Al, Si,
S, Ar, Ca, Fe, and Ni, particularly in coronal streamers. Resonance
scattering of emission lines from the solar disk dominates the
intensities of a few lines, but electron collisional excitation produces
most of the lines observed. Resonance, intercombination and forbidden
lines are seen, and their relative line intensities are diagnostics
for the ionization state and elemental abundances of the coronal gas.

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Title: First Results from the SOHO Ultraviolet Coronagraph
Spectrometer
Authors: Kohl, J. L.; Noci, G.; Antonucci, E.; Tondello, G.; Huber,
M. C. E.; Gardner, L. D.; Nicolosi, P.; Strachan, L.; Fineschi, S.;
Raymond, J. C.; Romoli, M.; Spadaro, D.; Panasyuk, A.; Siegmund,
O. H. W.; Benna, C.; Ciaravella, A.; Cranmer, S. R.; Giordano, S.;
Karovska, M.; Martin, R.; Michels, J.; Modigliani, A.; Naletto, G.;
Pernechele, C.; Poletto, G.; Smith, P. L.
1997SoPh..175..613K Altcode:
The SOHO Ultraviolet Coronagraph Spectrometer (UVCS/SOHO) is being
used to observe the extended solar corona from 1.25 to 10 R⊙ from
Sun center. Initial observations of polar coronal holes and equatorial
streamers are described. The observations include measurements of
spectral line profiles for HI Lα and Lβ, Ovi 1032 Å and 1037 Å,
Mgx 625 Å, Fexii 1242 Å and several others. Intensities for Mgx
610 Å, Sixii 499 Å, and 520 Å, Sx 1196 Å, and 22 others have been
observed. Preliminary results for derived H0, O5+,
Mg9+, and Fe11+ velocity distributions and initial
indications of outflow velocities for O5+ are described. In
streamers, the H0 velocity distribution along the line of
sight (specified by the value at e-1, along the line of
sight) decreases from a maximum value of about 180 km s-1
at 2 R⊙ to about 140 km s-1 at 8 R⊙. The value for
O5+ increases with height reaching a value of 150 km
s-1 at 4.7 R⊙. In polar coronal holes, the O5+
velocity at e-1 is about equal to that of H0
at 1.7 R⊙ and significantly larger at 2.1 R⊙. The O5+
in both streamers and coronal holes were found to have anisotropic
velocity distributions with the smaller values in the radial direction.

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Title: Inferences on Coronal Magnetic Fields from SOHO UVCS
Observations
Authors: Poletto, G.; Romoli, M.; Suess, S. T.; Wang, A. H.; Wu, S. T.
1997SoPh..174...53P Altcode:
The characteristics of the magnetic field ubiquitously permeating the
coronal plasma are still largely unknown. In this paper we analyze
some aspects of coronal physics, related to the magnetic field
behavior, which forthcoming SOHO UVCS observations can help better
understand. To this end, three coronal structures will be examined:
streamers, coronal mass ejections (CMEs), and coronal holes.

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Title: Magnetic Flux Tubes at 3 Au?
Authors: Parenti, S.; Velli, M.; Poletto, G.; Suess, S. T.; McComas,
D. J.
1997SoPh..174..329P Altcode:
We present an analysis of plasma and magnetic field data acquired by
the Ulysses spacecraft on May 1994. Our study is motivated by the
result of Poletto et al. (1996) who found some evidence for a peak
in the power spectrum of magnetic pressure at a frequency ν ≈
2 × 10−5 Hz, during that period. A re-evaluation of
the plasma pressure power spectrum, on the basis of better data than
used in the previous work, gives only marginal evidence for a peak at
that frequency. If both spectra had excess power in the same spectral
range, one might hypothesize that the Pressure Balanced Structures
(PBS) detected in the data trace periodically distributed coronal
structures which maintain their identity up to large distances. A
careful data analysis, however, shows that this interpretation is
hardly tenable. Hence, we consider the alternative hypotheses that
the observed PBS are either a bundle of magnetic flux tubes, with no
characteristic periodicity, in pressure equilibrium with the ambient,
or the manifestation, at large distances, of waves generated close to
the Sun. To prove the latter case, we made a test simulation of the
evolution with heliocentric distance of an ensemble of Alfvén and
slow mode waves, generated close to the Sun, and show that structures
similar to those we analyzed may form in the interplanetary medium. Our
simulations also seem to show that together with PBS, magnetic holes,
frequently observed in the Ulysses data, could also originate from the
nonlinear evolution of large amplitude slow waves in quasi-perpendicular
propagation. We conclude that the observed PBS most likely arise via
an in situ generation mechanism, rather than being remnants of solar
structures.

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Title: Expansion Factors in Coronal Holes and Plume/Interplume
UVCS Observations
Authors: Poletto, G.; Corti, G.; Noci, G.; Kohl, J.; Suess, S.
1997SPD....28.0108P Altcode: 1997BAAS...29..880P
We show that expansion factors in plumes and coronal hole areas devoid
of plumes are nearly equal because the plasma beta is &lt;&lt;1. Hence,
the overall coronal hole expansion factor is equal to the expansion
factors of its densest structures. UVCS plume and interplume
observations of coronal holes are illustrated, with the purpose of
showing the data capabilities. Integration along the line of sight,
through a medium containing high and low pressure regions, and the
rapid decrease with heliocentric distance of plume intensity, presently
hinder an observational determination of the expansion factors between
1.5 and 2 solar radii.

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Title: Possible Signatures of Nonlinear MHD Waves in the Solar Wind:
UVCS Observatio ns and Models
Authors: Ofman, L.; Romoli, M.; Davila, J. M.; Poletto, G.; Kohl,
J.; Noci, G.
1997ESASP.404..571O Altcode: 1997cswn.conf..571O
No abstract at ADS

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Title: Measurements of H I and O VI velocity distributions in the
extended solar corona with UVCS/SOHO and UVCS/Spartan 201
Authors: Kohl, J. H.; Noci, G.; Antonucci, E.; Tondello, G.; Huber,
M. C. E.; Gardner, L. D.; Nicolosi, P.; Fineschi, S.; Raymond, J. C.;
Romoli, M.; Spadaro, D.; Siegmund, O. H. W.; Benna, C.; Ciaravella,
A.; Cranmer, S. R.; Giordano, S.; Karovska, M.; Martin, R.; Michels,
J.; Modigliani, A.; Naletto, G.; Panasyuk, A.; Pernechele, C.; Poletto,
G.; Smith, P. L.; Strachan, L.
1997AdSpR..20....3K Altcode:
The Ultraviolet Coronagraph Spectrometer on the Solar and Heliospheric
Observatory, UVCS/SOHO, and the Ultraviolet Coronal Spectrometer on
the Spartan 201 satellite, UVCS/Spartan, have been used to measure
H I 1215.67 A˚ line profiles in polar coronal holes of the Sun at
projected heliocentric heights between 1.5 and 3.0 R_solar. UVCS/SOHO
also measured line profiles for H I 1025.72 A˚, O VI 1032/1037 A˚,
and Mg X 625 A˚. The reported UVCS/SOHO observations were made between
5 April and 21 June 1996 and the UVCS/Spartan observations were made
between 11 and 12 April 1993. Both sets of measurements indicate that a
significant fraction of the protons along the line of sight in coronal
holes have velocities larger than those for a Maxwellian velocity
distribution at the expected electron temperature. Most probable
speeds for O^5+ velocity distributions along the lines of sight are
smaller than those of H^0 at 1.5 R_solar, are comparable at about 1.7
R_solar and become significantly larger than the H^0 velocities above
2 R_solar. There is a tendency for the O^5+ line of sight velocity
distribution in concentrations of polar plumes to be more narrow than
those in regions away from such concentrations. UVCS/SOHO has identified
31 spectral lines in the extended solar corona.

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Title: First results from UVCS/SOHO
Authors: Noci, G.; Kohl, J. L.; Antonucci, E.; Tondello, G.; Huber,
M. C. E.; Fineschi, S.; Gardner, L. D.; Naletto, G.; Nicolosi, P.;
Raymond, J. C.; Romoli, M.; Spadaro, D.; Siegmund, O. H. W.; Benna, C.;
Ciaravella, A.; Giordano, S.; Michels, J.; Modigliani, A.; Panasyuk,
A.; Pernechele, C.; Poletto, G.; Smith, P. L.; Strachan, L.
1997AdSpR..20.2219N Altcode:
We present here the first results obtained by the Ultraviolet
Coronagraph Spectrometer (UVCS) operating on board the SOHO
satellite. The UVCS started to observe the extended corona at the end
of January 1996; it routinely obtains coronal spectra in the 1145 A˚ -
1287 A˚, 984 A˚ - 1080 A˚ ranges, and intensity data in the visible
continuum. Through the composition of slit images it also produces
monocromatic images of the extended corona. The performance of the
instrument is excellent and the data obtained up to now are of great
interest. We briefly describe preliminary results concerning polar
coronal holes, streamers and a coronal mass ejection, in particular: the
very large r.m.s. velocities of ions in polar holes (hundreds km/sec
for OVI and MgX); the puzzling difference between the HI Ly-alpha
image and that in the OVI resonance doublet, for most streamers; the
different signatures of the core and external layers of the streamers
in the width of the ion lines and in the OVI doublet ratio, indicating
larger line-of-sight (l.o.s.) and outflow velocities in the latter.

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Title: Physical Parameters in Plume and Interplume Regions from
UVCS Observations
Authors: Corti, G.; Poletto, G.; Romoli, M.; Michels, J.; Kohl, J.;
Noci, G.
1997ESASP.404..289C Altcode: 1997cswn.conf..289C
No abstract at ADS

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Title: The quiescent corona and slow solar wind
Authors: Noci, G.; Kohl, J. L.; Antonucci, E.; Tondello, G.; Huber,
M. C. E.; Fineschi, S.; Gardner, L. D.; Korendyke, C. M.; Nicolosi,
P.; Romoli, M.; Spadaro, D.; Maccari, L.; Raymond, J. C.; Siegmund,
O. H. W.; Benna, C.; Ciaravella, A.; Giordano, S.; Michels, J.;
Modigliani, A.; Naletto, G.; Panasyuk, A.; Pernechele, C.; Poletto,
G.; Smith, P. L.; Strachan, L.
1997ESASP.404...75N Altcode: 1997cswn.conf...75N; 1997soho....5...75N
No abstract at ADS

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Title: Observations of Plume and Interplume Regions with SOHO UVCS
Authors: Poletto, G.
1997IAUJD..19E...8P Altcode:
Observations of plumes and interplume regions acquired with
SoHO-UVCS at heliocentric heights between 1.5 and 2 solar radii are
presented. Analysis of these data allow us to derive information on
the behavior of plasma in the structured and unstructured corona. We
present here some examples of the intensity vs. height profile in
Ly alpha and O VI lines, which possibly may be ascribed to Doppler
dimming effects, and thus provide an estimate of coronal densities
and flow speeds both in plumes and interplumes. We also compare our
results with simulations from available models.

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Title: Searching for coronal plumes in ULYSSES observations of the
far solar wind.
Authors: Poletto, G.; Parenti, S.; Noci, G.; Livi, S.; Suess, S. T.;
Balogh, A.; McComas, D. J.
1996A&A...316..374P Altcode:
In the past, from the analysis of data acquired by the Helios
spacecrafts within distances &lt;=1AU, some evidence has been found of
the presence of coronal plumes in the solar wind. Ulysses observations
offer a unique opportunity to search for plume remnants in the
polar wind at larger distances. Pressure balanced structures (PBS),
which might possibly be a signature of those features, have in fact
been recently identified in its data. On the basis of previous work,
which detected significant peaks (possibly related to plumes) in power
spectra of solar wind parameters, we present here the results from
a similar research. However, our analysis does not confirm previous
findings, because power spectra bear no evidence of significant
periodicities. This result allows for different interpretations,
but does not rule out the presence of a typical periodicity in the
data. By developing a simple 2-D model for structures traversed by
Ulysses, we show how easily, even if they were regularly distributed,
the original periodicity may become hardly identifiable in power
spectra analyses. We conclude that this is not a viable technique for
tracing plumes in the solar wind and we suggest alternative means for
an unambiguous identification of these features.

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Title: First Results from the SOHO Ultraviolet Coronagraph
Spectrometer
Authors: Kohl, J. L.; Noci, G.; Antonucci, E.; Tondello, G.; Huber,
M. C. E.; Benna, C.; Ciaravella, A.; Fineschi, S.; Gardner, L. D.;
Giordano, S.; Karovska, M.; Michels, J.; Naletto, G.; Nicolosi, P.;
Poletto, G.; Pernechele, C.; Raymond, J. C.; Romoli, M.; Siegmund,
O. H. W.; Spadaro, D.; Smith, P. L.; Strachan, L.
1996AAS...188.4906K Altcode: 1996BAAS...28R.897K
The SOHO Ultraviolet Coronagraph Spectrometer (UVCS/SOHO) is being used
to observe the extended solar corona from 1.25 to 10 R_⊙ from Sun
center. Initial observations of polar coronal holes, polar plumes,
equatorial streamers and the diffuse mid-latitude corona will be
presented. The observations include measurements of spectral line
profiles for HI Lyman alpha and beta, and O VI 103.2 and 103.7
nm. Line intensities for Mg X 61.0 nm, Si XII 49.9 and 52.0 nm,
S X 119.6 nm, Fe XII 124.2 nm and several other minor ions have been
observed. Observations with moderate time resolution (about 1 minute) at
one strip of the corona will also be presented. Preliminary results for
derived proton and O VI velocity distributions and initial indications
of outflow velocities for protons, and O VI will be discussed as
well as preliminary results for other spectroscopic diagnostics
techniques. This research is supported by NASA Contract NAS5-31250 to
the Smithsonian Astrophysical Observatory, by the Italian Space Agency
and by Switzerland.

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Title: Flare energy transport.
Authors: Poletto, G.
1996joso.proc..127P Altcode:
Transport of energy within loops comprises well known processes which
fit into an overall thoroughly described scenario. In a broad sense,
one can say that flares also transport energy in the corona, if one
assumes that the existence of coronal loops is a manifestation of a
myriad of heating episodes - nanoflares - which occur randomly in
time. This paper describes a diagnostic technique, based on power
spectra analysis of X-ray brightness fluctuations, which may lead to
confirm/reject the nanoflare hypothesis.

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Title: The Ultraviolet Coronagraph Spectrometer for the Solar and
Heliospheric Observatory
Authors: Kohl, J. L.; Esser, R.; Gardner, L. D.; Habbal, S.; Daigneau,
P. S.; Dennis, E. F.; Nystrom, G. U.; Panasyuk, A.; Raymond, J. C.;
Smith, P. L.; Strachan, L.; Van Ballegooijen, A. A.; Noci, G.;
Fineschi, S.; Romoli, M.; Ciaravella, A.; Modigliani, A.; Huber,
M. C. E.; Antonucci, E.; Benna, C.; Giordano, S.; Tondello, G.;
Nicolosi, P.; Naletto, G.; Pernechele, C.; Spadaro, D.; Poletto, G.;
Livi, S.; Von Der Lühe, O.; Geiss, J.; Timothy, J. G.; Gloeckler,
G.; Allegra, A.; Basile, G.; Brusa, R.; Wood, B.; Siegmund, O. H. W.;
Fowler, W.; Fisher, R.; Jhabvala, M.
1995SoPh..162..313K Altcode:
The SOHO Ultraviolet Coronagraph Spectrometer (UVCS/SOHO) is composed of
three reflecting telescopes with external and internal occultation and
a spectrometer assembly consisting of two toric grating spectrometers
and a visible light polarimeter. The purpose of the UVCS instrument is
to provide a body of data that can be used to address a broad range
of scientific questions regarding the nature of the solar corona and
the generation of the solar wind. The primary scientific goals are
the following: to locate and characterize the coronal source regions
of the solar wind, to identify and understand the dominant physical
processes that accelerate the solar wind, to understand how the coronal
plasma is heated in solar wind acceleration regions, and to increase the
knowledge of coronal phenomena that control the physical properties of
the solar wind as determined byin situ measurements. To progress toward
these goals, the UVCS will perform ultraviolet spectroscopy and visible
polarimetry to be combined with plasma diagnostic analysis techniques
to provide detailed empirical descriptions of the extended solar corona
from the coronal base to a heliocentric height of 12 solar radii.

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Title: Numerical Modeling of Coronal Mass Ejections Based on Various
Pre-Event Model Atmospheres
Authors: Wang, A. H.; Wu, S. T.; Suess, S. T.; Poletto, G.
1995SoPh..161..365W Altcode:
We examine how the initial state (pre-event corona) affects the
numerical MHD simulation for a coronal mass ejection (CME). Earlier
simulations based on a pre-event corona with a homogeneous density and
temperature distribution at the lower boundary (i.e., solar surface)
have been used to analyze the role of streamer properties in determining
the characteristics of loop-like transients. The present paper extends
these studies to show how a broader class of global coronal properties
leads not only to different types of CMEs, but also modifies the
adjacent quiet corona and/or coronal holes.

---------------------------------------------------------
Title: Ultraviolet Coronagraph Spectrometer for the Solar and
Heliospheric Observatory: instrument description and calibration
overview
Authors: Kohl, J. L.; Esser, R.; Gardner, Larry D.; Habbal, S.;
Daigneau, P. S.; Nystrom, George U.; Raymond, John C.; Strachan,
Leonard; van Ballegooijen, A. A.; Noci, G.; Fineschi, Silvano; Romoli,
Marco; Ciaravella, A.; Modigliani, A.; Huber, Martin C.; Antonucci, E.;
Benna, C.; Giordano, S.; von der Luehe, Oskar; Tondello, Giuseppe;
Nicolosi, Piergiorgio; Naletto, Giampiero; Pernechele, Claudio;
Geiss, J.; Gloeckler, G.; Poletto, G.; Spadaro, D.; Allegra, A.;
Basile, G.; Brusa, R.; Wood, B.; Siegmund, Oswald H.
1995SPIE.2517...40K Altcode:
The SOHO ultraviolet coronagraph spectrometer (UVCS/SOHO) is
composed of three reflecting telescopes with external and internal
occultation and a spectrometer assembly consisting of two toric grating
spectrometers and a visible light polarimeter. The UVCS will perform
ultraviolet spectroscopy and visible polarimetry to be combined with
plasma diagnostic analysis techniques to provide detailed empirical
descriptions of the extended solar corona from the coronal base to a
heliographic height of 12 R. In this paper, the salient features of
the design of the UVCS instrument are described. An overview of the
UVCS test and calibration activities is presented. The results from
the calibration activity have demonstrated that the UVCS can achieve
all its primary scientific observational goals.

---------------------------------------------------------
Title: Search for fine scale structures in high latitude solar wind
Authors: Livi, S.; Parenti, S.; Poletto, G.
1995sowi.conf...93L Altcode:
About 25 years ago, E. Parker suggested that, as a consequence of the
inhomogeneous structure of the corona, the solar wind might consist
of adjacent structures with different physical conditions. Since that
suggestion was made, the solar wind plasma characteristics have been
measured in situ through many experiments, but little has been done
to check whether the solar wind shows any evidence for fine scale
structures, and, in the affirmative, how far from the Sun these
structures persist. A previous work on this subject, by Thieme,
Marsch and Schwenn (1990), based on Helios data, lead these authors
to claim that the solar wind, between 0.3 and 1 AU, is inhomogeneous
on a scale consistent with the hypothesis that the plume-interplume
plasmas, at those distances, still retain their identity. In this work
we present preliminary results from an investigation of the solar wind
fine structure from Ulysses high latitude observations. To this end,
we have analyzed data over several months, during 1994, at times well
after Ulysses's last encounter with the Heliospheric Current Sheet,
when the spacecraft was at latitudes above 50 degrees. These data refer
to high speed wind coming from southern polar coronal holes and are
best suited for plume-interplume identification. We have performed a
power spectra analysis of typical plasma parameters, to test whether
the wind plasma consist of two distinct plasma populations. We also
examined data to check whether there is any evidence for an horizontal
pressure balance over the hypothesized distinct structures. Our results
are discussed and compared with previous findings.

---------------------------------------------------------
Title: Book Review: Solor Coronal Structures
Authors: Poletto, G.
1995SoPh..157..393P Altcode:
No abstract at ADS

---------------------------------------------------------
Title: L'osservatorio di Arcetri.
Authors: Poletto, G.
1995Ori....32...38P Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Quantitative numerical modeling of a coronal mass ejection
Authors: Wang, A. H.; Wu, S. T.; Suess, S. T.; Poletto, G.
1994ESASP.373...35W Altcode: 1994soho....3...35W
No abstract at ADS

---------------------------------------------------------
Title: X-ray bright points and high-speed wind streams: a preliminary
analysis from Yohkoh and Ulysses data
Authors: Poletto, G.; Suess, S. T.; Khan, J. I.; Uchida, Y.; Hiei,
E.; Neugebauer, M.; Goldstein, B. E.; Strong, K. T.; Harvey, K. L.
1994ESASP.373..143P Altcode: 1994soho....3..143P
No abstract at ADS

---------------------------------------------------------
Title: Foreword
Authors: Fleck, B.; Noci, G.; Poletto, G.
1994SSRv...70D..17F Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Mass Supply and Flows in the Solar Corona - Conference
Authors: Fleck, B.; Noci, G.; Poletto, G.
1994SSRv...70....1F Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Mass supply and flows in the solar corona. Proceedings. 2. SOHO
Workshop, Marciana Marina, Island of Elba (Italy), 27 Sep - 1
Oct 1993.
Authors: Fleck, B.; Noci, G.; Poletto, G.
1994SSRv...70.....F Altcode:
This workshop focused on the following topics: 1. Fine scale
structures. 2. Loops and prominences. 3. Coronal streamers. 4. Coronal
holes and solar wind. Each of these four topics was introduced by an
observational and a theoretical overview highlighting the most recent
advances in their area. A third review illustrated how SOHO might help
in solving open problems.

---------------------------------------------------------
Title: Understanding solar streamers: The role of SOHO
Authors: Poletto, Giannina
1994SSRv...70..241P Altcode:
Streamers have been observed since far back in time, but our knowledge
of their morphology and of their physical characteristics is still very
limited. As a consequence, the present streamer picture is largely
incomplete: because individual features are poorly known, their role
in more general phenomena (like the evolution of the global corona or
the solar wind mass and flow pattern) is also poorly known. In this
presentation, the more relevant open problems in the understanding of
streamers will be illustrated and it will be shown how new data acquired
by SOHO may help us to reach a better understanding of these structures.

---------------------------------------------------------
Title: Magnetohydrodynamic simulation of a streamer beside a realistic
coronal hole
Authors: Suess, S. T.; Wu, S. T.; Wang, A. -H.; Poletto, G.
1994SSRv...70..295S Altcode:
Existing models of coronal streamers establish their credibility and
act as the initial state for transients. The models have produced
satisfactory streamer simulations, but unsatisfactory coronal hole
simulations. This is a consequence of the character of the models and
the boundary conditions. The models all have higher densities in the
magnetically open regions than occur in coronal holes (Noci,et al.,
1993).

---------------------------------------------------------
Title: Observational Signatures of Nanoflare Heating
Authors: Poletto, G.; Kopp, R.
1994kofu.symp...71P Altcode:
During the past few years it has been suggested that the solar
corona results from the superposition of a large number of tiny
impulsive energy-release events, which have come to be known as
“nanoflares”. However, these events have not yet been observed;
moreover, it remains to be shown theoretically that the repetitive
occurrence of nanoflares can eventually build up a plasma at typical
coronal densities and temperatures. The purpose of this work is to
describe the temporal evolution of the plasma in a rigid, originally
cool and nearly empty coronal flux tube with footpoints rooted in
the chromosphere, when the flux tube is subject to the sporadic
release of typical nanoflare energies. To this end, by analytically
integrating the partial differential equations for mass, momentum,
and energy conservation over the loop's spatial coordinate, we have
developed a simple model involving only the spatial averages of the
plasma thermodynamic variables. The model allows us to show how the
repeated occurrence of low energy events in loops of different sizes
eventually builds up a higher density, high temperature plasma -
i.e., a nanoflare-heated corona. The observational consequences of
our modeling, as well as future work in this area, are also discussed.

---------------------------------------------------------
Title: A quasi-steady model of a microflare-heated corona
Authors: Poletto, G.; Kopp, R. A.
1994AdSpR..14d.149P Altcode: 1994AdSpR..14..149P
It has been recently proposed that the solar corona is heated via the
superposition of a large number of tiny energy-release events, the
so-called nanoflares. In this paper we develop a simple semi-analytical
model to describe the temporal evolution of the nanoflare plasma,
confined in rigid magnetic flux tubes and subject to typical nanoflare
energy releases. Assuming a power law for the nanoflare energy
distribution and hypothesizing the repeated occurrence of nanoflares
at random time intervals in an originally cool, low pressure loop, we
show how a high temperature, high pressure plasma eventually builds up,
leading to a nanoflare-heated corona. Even if the feasibility of the
nanoflare mechanism as a coronal heating agent is thus demonstrated,
we conclude by pointing out that present instrumentaiton cannot provide
a definitive observational test of this hypothesis.

---------------------------------------------------------
Title: Numerical modeling of coronal mass ejections based on various
pre-event model atmospheres
Authors: Suess, S. T.; Wang, A. H.; Wu, S. T.; Poletto, G.
1994alab.reptV....S Altcode:
We examine how the initial state (pre-event corona) affects the
numerical MHD simulation for a coronal mass ejection (CME). Earlier
simulations based on a pre-event corona with a homogeneous density and
temperature distribution at lower boundary (i.e. solar surface) have
been used to analyze the role of streamer properties in determining the
characteristics of loop-like transients. The present paper extends these
studies to show how a broader class of global coronal properties leads
not only to different types of CME's, but also modifies the adjacent
quiet corona and/or coronal holes. We consider four pre-event coronal
cases: (1) Constant boundary conditions and a polytropic gas with gamma
= 1.05; (2) Non-constant (latitude dependent) boundary conditions and
a polytropic gas with gamma = 1.05; (3) Constant boundary conditions
with a volumetric energy source and gamma = 1.67; (4) Non-constant
(latitude dependent) boundary conditions with a volumetric energy
source and gamma = 1.67. In all models, the pre-event magnetic fields
separate the corona into closed field regions (streamers) and open field
regions. The CME's initiation is simulated by introducing at the base
of the corona, within the streamer region, a standard pressure pulse and
velocity change. Boundary values are determined using MHD characteristic
theory. The simulations show how different CME's, including loop-like
transients, clouds, and bright rays, might occur. There are significant
new features in comparison to published results. We conclude that the
pre-event corona is a crucial factor in dictating CME's properties.

---------------------------------------------------------
Title: Coronal heating via nanoflares
Authors: Poletto, Giannina; Kopp, Roger
1994LNP...432..161P Altcode: 1994LNPM...11..161P
It has been recently proposed that the coronae of single late-type
main sequence stars represent the radiative output from a large number
of tiny energy release events, the so-called nanoflares. Although
this suggestion is attractive and order of magnitude estimates of
the physical parameters involved in the process are consistent with
available data, nanoflares have not yet been observed and theoretical
descriptions of these phenomena are still very crude. In this paper we
examine the temporal behavior of a magnetic flux tube subject to the
repeated occurrence of energy release events, randomly distributed in
time, and we show that an originally empty cool loop may, in fact,
reach typical coronal density and temperature values via nanoflare
heating. By choosing physical parameters appropriate to solar conditions
we also explore the possibilities for observationally detecting
nanoflares. Although the Sun is the only star where nanoflares might
be observed, present instrumentation appears to be inadequate for
this purpose.

---------------------------------------------------------
Title: Mass supply and flows in the solar corona
Authors: Fleck, B.; Noci, G.; Poletto, G.
1994msfs.conf.....F Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Coronal Heating by Nanoflares: Individual Events and Global
Energetics
Authors: Kopp, R. A.; Poletto, G.
1993ApJ...418..496K Altcode:
Various mechanisms have been proposed to heat the solar corona, but
none have been completely successful in accounting for its observed
characteristics. Recently a further candidate has been advanced; namely,
stochastic heating via a large number of tiny impulsive energy-release
events, the so-called nanoflares. In this paper we develop a simple
semianalytical model to describe the temporal evolution of the nanoflare
plasma and to determine the response of magnetic flux tubes of different
sizes to typical nanoflare energy releases. This allows us to show how
the repeated occurrence of low-energy events in an originally cool loop
may eventually build up a high-temperature plasma a nanoflare-heated
corona. We also calculate the average nanoflare rate of occurrence,
as a function of loop size, required to keep the plasma at coronal
temperatures. The collective effect of this minievent population
is shown to account for the observed coronal temperature and global
emission measure. The present estimates may be used as guidelines for
defining the requisites of future experiments aimed at observationally
testing the nanoflare heating hypothesis.

---------------------------------------------------------
Title: A Two-Dimensional Magnetohydrodynamic Global Coronal Model -
Steady-State Streamers
Authors: Wang, A. -H.; Wu, S. T.; Suess, S. T.; Poletto, G.
1993SoPh..147...55W Altcode:
We describe a two-dimensional time-dependent, numerical,
magnetohydrodynamic model for the determination of the physical
properties of coronal streamers from the top of the transition zone
(R⊙ = 1) to 15R⊙. Four examples are given: for dipole, quadrupole,
and hexapole initial field topologies. The computed parameters are
density, temperature, velocity, and magnetic field. In addition to
the properties of the solutions, their accuracy is discussed. We use
the model as the basis for a general discussion of the way boundary
conditions are specified in this and similar simulations.

---------------------------------------------------------
Title: Lα intensity in coronal streamers
Authors: Noci, G.; Poletto, G.; Suess, S. T.; Wang, A. -H.; Wu, S. T.
1993SoPh..147...73N Altcode:
White-light images are presently the primary source of information on
physical conditions in the solar corona at distances greater than a
few tenths of a solar radius above the limb. As a consequence, we still
only have an incomplete description of structures extending beyond the
solar limb. In particular, streamers, although observed for decades,
represent a poorly known phenomenon. SOHO, to be launched in 1995,
will be able to make long-term observations of these features up to
heights of a fewR⊙, both in white light and UV. In this paper we
present simulations of Lα intensity in coronal streamers, based on
the two-dimensional (2-D) model developed by Wanget al. (1992, 1993)
via a time-dependent numerical relaxation approach. Because the model
is 2-D, we make ana priori hypothesis about the extension of streamers
in the third dimension. Lα data, obtained from a rocket (Kohlet al.,
1983), allowed us to identify a shape which fits the observations. We
consider streamers with different magnetic field configurations and
at different position angles with respect to the plane of the sky to
illustrate how different regions along the line of sight contribute to
the emergent intensity. Our purpose is twofold: to provide guidelines
for UVCS observational operations and to explore the parameter space in
order to understand the role of geometric factors and of the physical
state of the corona in determining the overall streamer brightness. We
conclude by showing how the results guide the future development of
streamer models.

---------------------------------------------------------
Title: A Global Coronal Hole and Streamer Model
Authors: Wang, A. -H.; Wu, S. T.; Suess, S. T.; Poletto, G.
1993BAAS...25.1203W Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Interactive Flare Sites Within an Active Region Complex
Authors: Poletto, G.; Gary, G. A.; Machado, M. E.
1993SoPh..144..113P Altcode:
The problem of physical relationships between different active
regions has been dealt with only rarely and mainly in connection
with flares. How sympathetic activity can be triggered between
distant regions is therefore, so far, largely unknown. Soft X-ray
images of large-scale coronal structures connecting different active
regions were obtained by Skylab nearly 20 years ago, while SMM,
more recently, did not provide any clear evidence for this kind of
loop. As a consequence, we do not know how common these features are
nor how they form nor whether they represent the only means by which
distant active regions may be linked. In the latter case, however,
interconnecting loops should be detected by analyzing the interaction
between different active regions. We examine here a set of images of
an active region complex, acquired on June 24-25, 1980, by the Hard
X-ray Imaging Spectrometer on SMM, with the purpose of establishing
whether there was any interplay between the frequent activity observed
at different sites in the activity center and, in such a case, how the
interaction was established. By analyzing both quiet and active orbits
we show that, as a rule, activity originating in one region triggers the
other region's activity. However, we find little unambiguous evidence
for the presence of large-scale interconnecting loops. A comparison
of X-ray images with magnetic field observations suggested that we
interpret the active region behavior in terms of the interaction
between different loop systems, in a scenario quite analogous to the
interacting bipole representation of individual flares. We conclude
that active region interplay provides an easily observable case to
study the time-dependent topology and the mechanisms for the spreading
of activity in transient events over all energy scales.

---------------------------------------------------------
Title: LY-A-CO-PO (LY α coronograph/polarimeter): an instrument to
measure coronal magnetic fields
Authors: Fineschi, S.; Chiuderi, C.; Poletto, G.; Hoover, R. B.;
Walker, A. B. C., Jr.
1993MmSAI..64..441F Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Coronal heating via nanoflares
Authors: Poletto, G.; Kopp, R.
1993STIN...9426696P Altcode:
It has been recently proposed that the coronae of single late-type
main sequence stars represent the radiative output from a large number
of tiny energy release events, the so-called nanoflares. Although
this suggestion is attractive and order of magnitude estimates of
the physical parameters involved in the process are consistent with
available data, nanoflares have not yet been observed and theoretical
descriptions of these phenomena are still very crude. The temporal
behavior of a magnetic flux tube subject to the repeated occurrence
of energy release events, randomly distributed in time are examined,
and it was shown that an originally empty cool loop may, in fact, reach
typical coronal density and temperature values via nanoflare heating. By
choosing physical parameters appropriate to solar conditions, the
possibilities for observationally detecting nanoflares were also
examined. Although the Sun is the only star where nanoflares might
be observed, present instrumentation appears to be inadequate for
this purpose.

---------------------------------------------------------
Title: Book Review: Plasma loops in the solar corona / Cambridge U
Press, 1991
Authors: Poletto, G.; Poletto, G.
1992SoPh..142..217P Altcode: 1992SoPh..142..217B
No abstract at ADS

---------------------------------------------------------
Title: Predicting Ly-α intensities in coronal streamers.
Authors: Noci, Giancarlo; Poletto, Giannina; Suess, Steven T.; Wang,
A. -H.; Wu, S. T.
1992ESASP.348...93N Altcode: 1992cscl.work...93N
In the near future, SOHO UVCS will make long-term observations of
coronal streamers in UV lines, providing a new tool for the analysis
of structures which have been known for decades but are still far from
being adequately described. The purpose of this work is to evaluate
the Ly-α brightness of coronal streamers, adopting the streamer
models obtained, via a time-dependent numerical relaxation technique,
by Wang et al. This allows both to understand the role of geometric
vs. physical factors in determining the streamer Ly-α intensity and to
provide guidelines for UVCS observational operations. Future prospects
along this line of research are also briefly summarized.

---------------------------------------------------------
Title: The Ulysses space mission.
Authors: Monsignori Fossi, B. C.; Noci, G.; Poletto, G.
1992NCimC..15..493M Altcode:
The authors describe briefly the collaborative ESA-NASA Ulysses
mission which will provide, for the first time in the history of the
solar-system exploration, in situ observations of the heliosphere over
a broad range of heliographic latitudes. Launched on October 6, 1990,
Ulysses has been injected in a high-inclination orbit by means of a
gravity-assisted manoeuvre at the time of his encounter with Jupiter,
in February 1992. On-board instrumentation will obtain data on the
solar wind, the heliosphere magnetic field, radio, X- and γ-bursts,
plasma waves and interplanetary and interstellar gas and dust.

---------------------------------------------------------
Title: The heating mechanism and stability of the giant post flare
arch of May 21 - 22, 1980.
Authors: Tang, Yu-Hua; Poletto, G.
1992ChJSS..12..161T Altcode:
It is proposed that the fast tearing modes in cylindrical geometry is
an effective heating mechanism for the post-flare coronal arch of 21 -
22 May, 1980 which have remained visible for more than 10 hours after
the flare onset. The MHD equilibrium and stability of the arch are
discussed and the main conclusions are given.

---------------------------------------------------------
Title: Interacting Confined-Eruptive Flare Sites Within a Magnetic
Active Region Complex
Authors: Gary, G. A.; Poletto, G.; Mechado, M. E.
1992AAS...180.4106G Altcode: 1992BAAS...24Q.795G
No abstract at ADS

---------------------------------------------------------
Title: The Birth of Giant Post-Flare Arches
Authors: Poletto, G.; Svestka, Z.
1992SoPh..138..189P Altcode:
Using short accumulation times, we have succeeded in the detection
in HXIS images of the initial growth of the giant post-flare arch
of 6 November, 1980 at 14:44 UT and part of the initial growth of
the giant arch of 7 November, 1980 at 04:30 UT. These observations
are relevant to the problem of the origin of giant arches: the fact
that the arch of 6 November was imaged more than half an hour before
the first flare loops had been recorded in the associated flare,
proves that giant arches cannot: be interpreted as upper products of
the reconnection process that creates the growing systems of flare
loops (as the original interpretation by Švestka et al. (1982a)
suggested). However, also the alternative hypothesis by Poletto and Kopp
(1988) that these structures originate through a reconnection process
in a peripheral, large-scale configuration meets with difficulties:
after the initial rise, the maximum brightness in both arches seems
to descend, until a much slower rise was resumed about two hours later.

---------------------------------------------------------
Title: The X-ray ultraviolet imager for the orbiting solar laboratory
Authors: Antonucci, Ester; Malvezzi, Marco; Ciminiera, Luigi; Angrilli,
Francesco; Bruner, Marilyn E.; Perona, Giovanni; Adele Dodero, Maria;
Evans, Brian L.; Golub, Leon; Landini, Massimo; Noci, Giancarlo;
McWhirter, Peter; Fossi, Brunella Monsignori; Poletto, Giannina;
Neidig, Donald F.; Schmidt, Wolfgang K. H.; Thomas, Roger J.;
Tondello, Giuseppe
1992AIPC..267..126A Altcode: 1992ecsa.work..126A
A normal incidence multimirror telescope, the X-ray Ultraviolet
Imager, for high resolution imaging of the solar atmosphere in the
soft X-ray/XUV region, is being developed as part of the scientific
payload of the NASA Orbiting Solar Laboratory. The X-ray Ultraviolet
Imager is formed by two units: a high resolution telescope (0.25
arcsec pixel size and 8×8 arcmin2 field of view) and a wide field one
(2.3 arcsec pixel size and 5×5 solar radii2 field of view). The two
systems complement each other and allow a full coverage of solar
features from the small scale (200 km on the sun) to the global
phenomena. Each system consists of 8 channels with multilayer mirrors,
imaging at different wavelengths. In each channel the mirror coating
is optimized to select a narrow spectroscopic window corresponding to
an intense line in the region 40-400 A˚. In order to provide imaging
and temperature diagnostics from the chromosphere to the upper corona,
8 wavelengths are chosen to cover the broad temperature range from 105
to 107 K. Four images, two high resolution and two full disk ones,
are simultaneously obtained by the X-ray Ultraviolet Imager, at a
cadence which in flares can be of 0.4-1 s.

---------------------------------------------------------
Title: A two-dimensional MHD global coronal model - Steady-state
streamers
Authors: Wang, A. -H.; Wu, S. T.; Suess, S. T.; Poletto, G.
1992sws..coll..311W Altcode:
A 2D, time-dependent, numerical, MHD model for the simulation of coronal
streamers from the solar surface to 15 solar is presented. Three
examples are given; for dipole, quadrupole and hexapole (Legendre
polynomials P1, P2, and P3) initial field topologies. The computed
properties are density, temperature, velocity, and magnetic field. The
calculation is set up as an initial-boundary value problem wherein a
relaxation in time produces the steady state solution. In addition to
the properties of the solutions, their accuracy is discussed. Besides
solutions for dipole, quadrupole, and hexapole geometries, the model
use of realistic values for the density and Alfven speed while still
meeting the requirement that the flow speed be super-Alfvenic at the
outer boundary by extending the outer boundary to 15 solar radii.

---------------------------------------------------------
Title: A Semi-analytical Model of Stellar Flares
Authors: Kopp, R. A.; Poletto, G.
1992LNP...397..295K Altcode: 1992sils.conf..295K
No abstract at ADS

---------------------------------------------------------
Title: Largescale Quasi-Stationary X-Ray Coronal Structures Associated
with Eruptive Solar Flares
Authors: Kopp, R. A.; Poletto, G.
1992LNP...399..197K Altcode: 1992esf..coll..197K; 1992IAUCo.133..197K
No abstract at ADS

---------------------------------------------------------
Title: Un antico incostante sole. I.
Authors: Poletto, G.
1991Ori....11...24P Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Coronal Heating by Nanoflares: Plasma Dynamics of Elementary
Events (With 2 Figures)
Authors: Kopp, R. A.; Poletto, G.
1991mcch.conf..634K Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Real-time simulation of a potential magnetic field in a
post-flare arch
Authors: Poletto, Giannina; Svestka, Zdenek
1990SoPh..129..363P Altcode:
We analyze the X-ray observations on 7-8 November of the last revival
of a giant coronal arch first observed in the morning hours of 6
November, 1980. We compare these data with observations of earlier
revivals of this arch, in order to determine whether the successive
brightenings repeat without any apparent modification, or whether they
show a varying behavior as they keep occurring. We also examine the
magnetic structure of the revived arches in order to ascertain whether
the subsequent phenomena involve the same magnetic configuration. The
information about the magnetic structure of the last revival is the
best we have, because the revival started close to the time of the
Kitt Peak magnetogram which has been used for the magnetic modelling
of the whole series of these giant arches.

---------------------------------------------------------
Title: The XUV imager for the OSL.
Authors: Landini, M.; Noci, G.; Antonucci, E.; Bruner, M. E.; Evans,
B. L.; Golub, L.; Malvezzi, M.; McWhirter, R. W.; Monsignori Fossi,
B. C.; Poletto, G.; Neidig, D.; Perona, G.; Thomas, R.; Tondello, G.
1990BAAS...22.1148L Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Formation and cooling of the giant HXIS arches of November
6 7, 1980
Authors: Kopp, R. A.; Poletto, G.
1990SoPh..127..267K Altcode:
Giant arches, first detected by the HXIS instrument aboard SMM, are
still a poorly understood component of the flare scenario. Their
origin remains uncertain and their behavior, quite different in
separate events, has not yet been satisfactorily explained. The
purpose of the present paper is to analyze the giant arches imaged
on November 6-7, 1980, which, in contrast to that observed on May
21, 1980, were not stationary and had shorter cooling times. In
particular, we use a procedure, already applied to the May 21 case,
to compute the three-dimensional topology of the magnetic field which
forms by reconnection over the active region containing the November
arches. This technique allows us to verify that the observed structures
are aligned with the computed field lines, lending support to the
hypothesis that they originate through a reconnection process which
occurs at progressively larger altitudes. Moreover, a calculation
of the magnetic energy liberated by reconnection shows that enough
energy may be thereby released to account for the observed thermal
energy enhancement of the HXIS arches. Finally, the lifetime of the
features is shown to be consistent with that predicted by cooling via
radiation and field-aligned conduction to the underlying chromosphere.

---------------------------------------------------------
Title: Coronal heating by nanoflares: Plasma dynamics of elementary
events
Authors: Kopp, Roger A.; Poletto, Giannina
1990STIN...9110830K Altcode:
It has been suggested by Parker Sturrock et al., and others that the
corona may be stochastically heated, on spatial scales at or below
current instrumental resolution limits, by a continuous succession of
many small flarelike events commonly referred to as nanoflares. In this
paper we extend a semi-analytical point model developed previously for
solar compact flares, to include gravitational plasma downfall during
the late decay phase. Applying the model to conditions representative of
nanoflares allows us to predict the temporal variation of average plasma
properties in such events and should ultimately facilitate a calculation
of the spectral characteristics of a nanoflare-heated corona.

---------------------------------------------------------
Title: A semi-analytical model of stellar flares
Authors: Kopp, Roger A.; Poletto, Giannina
1990STIN...9110817K Altcode:
We present a simplified 'point' model to describe the hydrodynamic
response of coronal loop plasma to the sudden release of energy
which occurs at the time of a flare. Our simplification allows the
full set of partial differential equations for energy, momentum, and
mass conservation to be replaced by a corresponding set of ordinary
differential equations for the plasma properties averaged over the
loop volume. The temporal profiles of plasma temperature, density,
and velocity are calculated over a time interval long enough to ensure
that pre-flare conditions are re-established. The model is used for
the interpretation of stellar flare data. In particular, we derive a
set of representative loop geometries and flare energy inputs which
allows us to reproduce the high emission measures typically inferred
from observations of stellar flares.

---------------------------------------------------------
Title: A Simple Model for the Stellar Analogy of Compact Solar Flares
Authors: Kopp, R. A.; Poletto, G.
1990ASPC....9..119K Altcode: 1990csss....6..119K
No abstract at ADS

---------------------------------------------------------
Title: Book Review: Solar and stellar physics. / Springer-Verlag, 1987
Authors: Poletto, Giannina; Dimitrov, D. L.; Švestka, Z.; Poletto, G.
1989SoPh..119..419P Altcode: 1989SoPh..119..419S
No abstract at ADS

---------------------------------------------------------
Title: Long-Duration Solar and Stellar Flares
Authors: Poletto, Giannina
1989SoPh..121..313P Altcode: 1989IAUCo.104..313P
According to one of the most popular classifications, solar flares may
be assigned either to the category of small short-lived events, or to
the category of large, long-duration two-ribbon (2-R) flares. Even
if such abroad division oversimplifies the flare phenomenon, our
knowledge of the characteristics of stellar flares is so poor, that
it is worthwhile to investigate the possibility of adopting this
classification scheme for stellar flares as well. In particular we
will analyze Einstein observations of a long duration flare on EQ Peg
to establish whether it might be considered as a stellar analogy of 2-R
solar events. To this end we apply to EQ Peg data a reconnection model,
developed originally for solar 2-R flares, and conclude that stellar
observations are consistent with model predictions, although additional
information is required to identify uniquely the physical parameters of
the flare region. Application of the model to integrated observations
of a 2-R solar flare, for which high spatial resolution data are
also available, shows, however, that future integrated observations
may allow us to solve the ambiguities of the model and use it as a
diagnostic tool for a better understanding of stellar flares.

---------------------------------------------------------
Title: Coronal mass ejections and coronal structures.
Authors: Hildner, E.; Bassi, J.; Bougeret, J. L.; Duncan, R. A.;
Gary, D. E.; Gergely, T. E.; Harrison, R. A.; Howard, R. A.; Illing,
R. M. E.; Jackson, B. V.; Kahler, S. W.; Kopp, K.; Low, B. C.; Lantos,
P.; Phillips, K. J. H.; Poletto, G.; Sheeley, N. R., Jr.; Stewart,
R. T.; Svestka, Z.; Waggett, P. W.; Wu, S. T.
1989epos.conf..493H Altcode:
The work of this team was concerned with modelling of post-flare arches,
the reconnection theory of flares, the slow variation of coronal
structure, and the coronal and interplanetary detection, evolution,
and consequences of mass ejections.

---------------------------------------------------------
Title: A simple model for the stellar analogy of compact solar flares
Authors: Kopp, R. A.; Poletto, G.
1989STIN...9015877K Altcode:
We have developed a simple point model to describe the average
thermodynamical properties of a compact flare loop as a function of time
during the flare decay phase. The model includes thermal conduction,
chromospheric evaporation, and radiative losses; moreover, it assumes
lateral (gas + magnetic) pressure balance with the background corona
at all times. For the case of a low-(beta) plasma (rigid flux tube),
detailed 1-D hydrodynamical simulations are available in the literature
for comparison; we show that the temporal variation of average loop
properties predicted by the point model are in good agreement with
these numerical simulations for a loop with the same energy input.

---------------------------------------------------------
Title: Modeling of coronal magnetic fields during solar flares
Authors: Kopp, R. A.; Poletto, G.
1989MmSAI..60...65K Altcode:
Conversion of magnetic energy into diverse forms of plasma energy
comprises the basic mechanism of flare phenomena. In this process
magnetic fields undergo major rearrangements which, at least during the
gradual phase of flares, may be described as a sequence of equilibrium
configurations. In this paper, the basic techniques used to model
flaring magnetic configurations are reviewed and results of comparisons
between predicted and observed topologies are briefly summarized.

---------------------------------------------------------
Title: Modeling of long-duration two-ribbon flares on M dwarf stars.
Authors: Poletto, G.; Pallavicini, R.; Kopp, R. A.
1988A&A...201...93P Altcode:
A time-dependent model of magnetic reconnection for the decay phase
of solar two-ribbon flares is applied to long-duration stellar flares
observed by the Einstein and Exosat observatories on the stars EQ Peg
and Prox Cen. It is shown that the model reproduces correctly the
energy release rate and temporal evolution during the decay phase
of the observed events. It is concluded that the observed behavior
is consistent with the interpretation of these flares as stellar
counterparts of solar two-ribbon flares. In addition, taking into
account recent measurements of stellar magnetic fields by Saar and
Linsky (1985), it is shown that the agreement between the data and the
analytical model results in a well-defined set of physical parameters
for the emitting region.

---------------------------------------------------------
Title: The magnetic geometry and structure of the giant post-flare
arch of 21 22 May, 1980
Authors: Poletto, G.; Kopp, R. A.
1988SoPh..116..163P Altcode:
On 21-22 May, 1980 the HXIS instrument aboard SMM imaged an enormous,
more-or-less stationary, X-ray arch structure near the position of
a large two-ribbon flare which immediately preceded it in time. As
described by Švestka et al. (1982), the arch remained visible for
up to 10 hours. Previous inferences of the height, orientation, and
physical parameters of this feature have been based largely on the
X-ray data and on radio observations of the associated stationary
Type I noise storm. In the present paper we use the observed
photospheric line-of-sight magnetic field distribution to compute,
in the current-free approximation, the three-dimensional topology of
the coronal field above the flare site. Comparing the HXIS intensity
contours of the arch to the projected shapes of the field lines suggests
that the arch is indeed aligned with certain coronal flux tubes and
allows an independent determination of the geometrical arch parameters
to be made. This procedure indicates that the true height of the arch
is about 70000 km, i.e., appreciably less than was suggested previously
(although it is still certainly to be classified as a `giant" feature
of the post-flare evolution).

---------------------------------------------------------
Title: The determination of coronal fieldline connectivity from
photospheric flare observations
Authors: Kopp, R. A.; Poletto, G.
1988AdSpR...8k.209K Altcode: 1988AdSpR...8..209K
According to current ideas, during the gradual phase of two-ribbon
flares magnetic reconnection causes the open field configuration created
at flare onset to relax back to a closed, lower energy state. The shapes
and orientations of the newly formed loops are indicative of whether
the reconnected field is potential or force-free and, in the latter
case, afford a direct evaluation of the amount of shear involved. In
the present paper we describe an empirical method for deriving the
footpoint connectivity of the reconnected field lines, based on the
point-by-point variation of the merging rate above the flare site;
the latter can in principle be derived from photospheric observations
alone. As an illustration we apply the method to a simplistic model
of reconnection above a non-uniform surface field. Future application
to specific solar events will also be discussed.

---------------------------------------------------------
Title: Modeling of long-decay stellar flares on EQ Peg and Prox Cen
Authors: Pallavicini, R.; Poletto, G.; Kopp, R. A.
1988ASSL..143..171P Altcode: 1988acse.conf..171P
A magnetic reconnection model of solar 2-ribbon flares is applied to
long-duration events observed by Einstein and Exosat on the stars
EQ Peg and Prox Cen. The authors show that the model is capable of
reproducing the energy release rate and temporal evolution of the decay
phase of the observed events, strongly supporting their identification
as stellar counterparts of solar 2-R flares. The model is also used
to put constraints on the physical parameters of the emitting region.

---------------------------------------------------------
Title: Magnetic modelling of giant HXIS arches
Authors: Kopp, R. A.; Poletto, G.
1988AdSpR...8k.203K Altcode: 1988AdSpR...8..203K
The HXIS instrument onboard SMM detected for the first time a new type
of flare-associated phenomenon - the so-called “giant coronal arch”
- which extends to high altitudes and whose nature has not yet been
clearly identified. Like post-flare loops, however, giant arches
apparently occur only after two-ribbon flares, thus suggesting that
both structures originate from a common mechanism. In order to test
this hypothesis we examine the possibility that the giant HXIS arches
observed on 6/7 November 1980 formed by magnetic reconnection high in
the corona. We conclude that the observed configuration of the HXIS
structures is indeed consistent with the geometry of magnetic field
lines reconnecting to a potential configuration.

---------------------------------------------------------
Title: Multi-thermal observations of newly formed loops in a
dynamic flare
Authors: Švestka, Zdeněk F.; Fontenla, Juan M.; Machado, Marcos E.;
Martin, Sara F.; Neidig, Donald F.; Poletto, Giannina
1987SoPh..108..237S Altcode:
The dynamic flare of 6 November, 1980 (max ≈ 15:26 UT) developed a
rich system of growing loops which could be followed in Hα for 1.5
hr. Throughout the flare, these loops, near the limb, were seen in
emission against the disk. Theoretical computations of deviations from
LTE populations for a hydrogen atom reveal that this requires electron
densities in the loops close to, or in excess of 1012
cm -3. From measured widths of higher Balmer lines the
density at the tops of the loops was found to be 4 x 1012
cm -3 if no non-thermal motions were present, or 5 ×
1011 cm -3 for a turbulent velocity of ~ 12 km
s -1.

---------------------------------------------------------
Title: Topology of Reconnected Magnetic Fields after Two-Ribbon Flares
Authors: Kopp, R. A.; Poletto, G.
1987sman.work..103K Altcode:
Magnetic reconnection is recognized to be responsible for a variety
of phenomena which occur during flare events. An outstanding example
of this process is given by the magnetic field restructuring during
the decay phase of two-ribbon flares. The authors briefly review a 2-D
analytical model developed by Kopp and Poletto (1984) which has been
shown to be capable of reproducing the major characteristics of these
post-flare effects and present an extension of this model to 3-D. For
this latter case they present, for a simple magnetic configuration
where the opposite polarities are skewed with respect to one another,
a set of field line maps which have been obtained under the hypothesis
that reconnection proceeded up to different heights.

---------------------------------------------------------
Title: On the origin of HXIS arches
Authors: Kopp, R. A.; Poletto, G.
1987PAICz..66..249K Altcode: 1987eram....1..249K
During SMM operation in 1980 the HXIS instrument detected a few giant
coronal arches, extending to high altitude (≡10 km) and with widely
separated footpoints, which always appeared after two-ribbon (2-R)
flares. In this paper the authors examine the possibility that HXIS
arches form as a results of magnetic reconnection occurring at high
levels.

---------------------------------------------------------
Title: Modelling Solar Magnetic Field Configurations
Authors: Poletto, G.
1987HvaOB..11...79P Altcode:
Measurements of solar magnetic fields provide information on their
behavior only in a thin layer. Thus the problem of deducing the vertical
structure of the magnetic field has to be solved theoretically. The
three most extensively used techniques to extrapolate magnetic fields
to high levels are described together with their shortcomings.

---------------------------------------------------------
Title: Interplanetary Effects of Coronal Mass Ejections
Authors: Hildner, E.; Bassi, J.; Bougeret, J. L.; Duncan, R. A.;
Gary, D. E.; Gergely, T. E.; Harrison, R. A.; Howard, R. A.; Illing,
R. M. E.; Jackson, B. V.; Kahler, S. W.; Kopp, K.; Low, B. C.; Lantos,
P.; Phillips, K. J. H.; Poletto, G.; Sheeley, N. R., Jr.; Steward,
R. T.; Svestka, Z.; Waggett, P. W.; Wu, S. T.
1986epos.conf.6.52H Altcode: 1986epos.confF..52H
No abstract at ADS

---------------------------------------------------------
Title: Initiations of Coronal Mass Ejections
Authors: Hildner, E.; Bassi, J.; Bougeret, J. L.; Duncan, R. A.;
Gary, D. E.; Gergely, T. E.; Harrison, R. A.; Howard, R. A.; Illing,
R. M. E.; Jackson, B. V.; Kahler, S. W.; Kopp, K.; Low, B. C.; Lantos,
P.; Phillips, K. J. H.; Poletto, G.; Sheeley, N. R., Jr.; Steward,
R. T.; Svestka, Z.; Waggett, P. W.; Wu, S. T.
1986epos.conf.6.27H Altcode: 1986epos.confF..27H
No abstract at ADS

---------------------------------------------------------
Title: Magnetic field re-arrangement after prominence eruption.
Authors: Kopp, R. A.; Poletto, G.
1986NASCP2442..235K Altcode: 1986copp.nasa..235K
It has long been known that magnetic reconnection plays a fundamental
role in a variety of solar events. Although mainly invoked in flare
problems, large scale loops interconnecting active regions, evolving
coronal hole boundaries, the solar magnetic cycle itself, provide
different evidence of phenomena which involve magnetic reconnection. A
further example might be given by the magnetic field rearrangement
which occurs after the eruption of a prominence. Since most often
a prominence reforms after its disappearance and may be observed at
about the same position it occupied before erupting, the magnetic field
has to undergo a temporary disruption of relax back, via reconnection,
to a configuration similar to the previous one. The above sequence of
events is best observable in the case of two ribbon (2-R) flares but
most probably is associated with all filament eruptions. Even if the
explanation of the magnetic field rearrangement after 2-R flares in
terms of reconnection is generally accepted, the lack of a 3-dimensional
model capable of describing the field reconfiguration, has prevented,
up to now, a thorough analysis of its topology as traced by H alpha/x
ray loops. A numerical technique is presented which enables oneto
predict and visualize the reconnected configuration, at any time, and
therefore allows one to make a significant comparison of observations
and model predictions throughout the whole process.

---------------------------------------------------------
Title: The Slowly Varying Corona Near Solar Activity Maximum
Authors: Hildner, E.; Bassi, J.; Bougeret, J. L.; Duncan, R. A.;
Gary, D. E.; Gergely, T. E.; Harrison, R. A.; Howard, R. A.; Illing,
R. M. E.; Jackson, B. V.; Kahler, S. W.; Kopp, K.; Low, B. C.; Lantos,
P.; Phillips, K. J. H.; Poletto, G.; Sheeley, N. R., Jr.; Steward,
R. T.; Svestka, Z.; Waggett, P. W.; Wu, S. T.
1986epos.conf.6.57H Altcode: 1986epos.confF..57H
No abstract at ADS

---------------------------------------------------------
Title: Modelling of Coronal Mass Ejections and POST Flare Arches
Authors: Hildner, E.; Bassi, J.; Bougeret, J. L.; Duncan, R. A.;
Gary, D. E.; Gergely, T. E.; Harrison, R. A.; Howard, R. A.; Illing,
R. M. E.; Jackson, B. V.; Kahler, S. W.; Kopp, K.; Low, B. C.; Lantos,
P.; Phillips, K. J. H.; Poletto, G.; Sheeley, N. R., Jr.; Steward,
R. T.; Svestka, Z.; Waggett, P. W.; Wu, S. T.
1986epos.conf6.366H Altcode: 1986epos.confF.366H
No abstract at ADS

---------------------------------------------------------
Title: Large-scale electric fields resulting from magnetic
reconnection in the corona.
Authors: Kopp, R. A.; Poletto, G.
1986NASCP2442..469K Altcode: 1986copp.nasa..469K
The authors have applied the method of Forbes and Priest to the
large two-ribbon flare of 29 July, 1973, for which both detailed Hα
observations and magnetic data are available. One sees from this
calculation that, as reconnection sets in at the beginning of the
decay phase, the electric field grows rapidly to reach a maximum value
of about 2 V/cm within just a few minutes. Thereafter E1
declines monotonically with time, as one would expect for any relaxation
process: as more and more of the magnetic flux disrupted by the flare
reconnects, the merging rate itself decreases.

---------------------------------------------------------
Title: Modeling of Long Duration Stellar Flares
Authors: Poletto, G.; Pallavicini, R.; Kopp, R. A.
1986BAAS...18Q.962P Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Coronal mass ejections and coronal structures.
Authors: Hildner, E.; Bassi, J.; Bougeret, J. L.; Duncan, R. A.;
Gary, D. E.; Gergely, T. E.; Harrison, R. A.; Howard, R. A.; Illing,
R. M. E.; Jackson, B. V.; Kahler, S. W.; Kopp, K.; Low, B. C.; Lantos,
P.; Phillips, K. J. H.; Poletto, G.; Sheeley, N. R., Jr.; Stewart,
R. T.; Svestka, Z.; Waggett, P. W.; Wu, S. T.
1986NASCP2439....6H Altcode:
Contents: 1. Introduction. 2. Observations. 3. Initiation of
coronal mass ejections - observations. 4. Modelling of coronal mass
ejections and post-flare arches. 5. Interplanetary effects of coronal
mass ejections. 6. The slowly varying corona near solar activity
maximum. 7. Summary.

---------------------------------------------------------
Title: Magnetic reconnection and energy release in a long-duration
stellar flare
Authors: Poletto, G.; Pallavicini, R.; Kopp, R. A.
1986AdSpR...6h.145P Altcode: 1986AdSpR...6..145P
A dynamical model of magnetic reconnection in solar two-ribbon flares
is applied to EXOSAT observations of a long-decay flare from the star
EQ Peg. We show that the model is able of reproducing correctly the
energy release rate and temporal evolution of the decay phase of the
observed flare. We conclude that the flare was the stellar counterpart
of solar two-ribbon flares and we derive the physical parameters of
the emitting region.

---------------------------------------------------------
Title: A dynamic flare with anomalously dense flare loops
Authors: Svestka, Z.; Fontenla, J. M.; Machado, M. E.; Martin, S. F.;
Neidig, D. F.; Poletto, G.
1986AdSpR...6f.253S Altcode: 1986AdSpR...6..253S
The dynamic flare of 6 November 1980 (max. ~ 15:26 UT) developed a
rich system of growing loops which could be followed in Hα for 1.5
hours. Throughout the flare, these loops, near the limb, were seen in
emission against the disk. Theoretical computations of b-values for
a hydrogen atom reveal that this requires electron densities in the
loops to be close to 1012 cm-3. From measured
widths of higher Balmer lines the density at the loops of the loops
was found to be 4 × 1012 cm-3 if no non-thermal
motions were present. It is now general knowledge that flare loops
are initially observed in X-rays and become visible in Hα only after
cooling. For such a high density a loop would cool through radiation
from 107 K to 104 K within a few minutes so that
the dense Hα loops should have heights very close to the heights of
the X-ray loops. This, however, contradicts the observations obtained by
the HXIS and FCS instruments on board SMM which show the X-ray loops at
much higher altitudes than the loops in Hα. Therefore, the density must
have been significantly smaller when the loops were formed and the flare
loops were apparently both shrinking and becoming denser while cooling.

---------------------------------------------------------
Title: Macroscopic electric fields during two-ribbon flares.
Authors: Poletto, G.; Kopp, R. A.
1986lasf.conf..453P Altcode: 1986lasf.symp..453P
Large-scale electric fields present during solar flares might provide a
mechanism for continuously accelerating particles to high energies. The
authors use the magnetic reconnection model of two-ribbon flares
(Kopp et al., 1976, 1984) to calculate the temporal variation of the
coronal electric field for the large flares of 29 July, 1973 and 21
May, 1980. This calculation shows that the electric field declines
monotonically during the decay phase. The authors conclude that the
actual reconnection rate after these two-ribbon flares is being governed
by the global dynamics of the perturbed coronal field-plasma system,
rather than by processes within the magnetic diffusion region itself.

---------------------------------------------------------
Title: Three-Dimensional Reconnection after a Prominence Eruption
Authors: Kopp, R. A.; Poletto, G.
1986ASSL..123...65K Altcode: 1986shtd.symp...65K
A currently widely held explanation of the diverse phenomena following
a prominence eruption is that these are the direct result of the ensuing
reconnection of open magnetic field lines created by the eruption. Kopp
and Pneuman (1976) and Kopp and Poletto (1984) developed a 2-D model
wherein an analytical time-dependent magnetic field geometry was used
to account quantitatively for the major characteristics of many of
these post-flare effects. In the present paper, after mentioning a
few situations for which a 2-D treatment would nevertheless clearly be
inadequate, the authors extend to three dimensions their earlier model.

---------------------------------------------------------
Title: Analysis of loop flows observed on 27 March, 1980 by the UVSP
instrument during the Solar Maximum Mission
Authors: Kopp, R. A.; Poletto, G.; Noci, G.; Bruner, M.
1985SoPh...98...91K Altcode:
In this paper we present the results of an analysis of a set of
observations in the C IV 1548 Å line obtained on 27 March, 1980 by
the Solar Maximum Mission Ultraviolet Spectrometer and Polarimeter
(UVSP). The observed region covers an area of 240 × 240 arc sec
and includes a system of bright loops at the limb. Simultaneous
spectroheliograms and dopplergrams of the loop region allowed us to
derive empirical velocity and emission-measure profiles on individual
loops. These have been compared with the theoretical profiles for:
(i) a steady-state loop model with siphon flow, (ii) a steady state
loop model with downflow in both legs maintained by continuous mass
addition near the loop summit, (iii) a non-steady loop model with
downflow, whereby the initial plasma density decays exponentially with
time (similarity solution). None of these simple models is capable of
simultaneously representing both the velocity and emission measure
profiles; thus we still lack a realistic description of cool loop
dynamics. New observations aimed at determining such parameters as
the loop lifetime are considered crucial for providing the necessary
constraints for future modeling efforts.

---------------------------------------------------------
Title: Hard X-ray images of possible reconnection in the flare of
21 May, 1980
Authors: Svestka, Z.; Poletto, G.
1985SoPh...97..113S Altcode:
An analysis of the growth of X-ray loops in the flare of 21 May, 1980,
observed by HXIS on board SMM spacecraft, has been carried out with
high time resolution in six energy channels from 3.5 to 30 keV. This
analysis has revealed that the tops of the loops stay for minutes at a
given altitude before, quite abruptly, other loop tops begin to appear
above them. One of the jumps in altitude, from ∼27 000 to ∼45
000 km if the loops extended radially, which occurred quite late in
the flare development, is studied in detail. The fact that the tops,
of higher loops were first seen in the 22-30 keV energy channel, and
only minutes later at lower energies, suggests a new release of energy
in a very small volume high in the corona. An initial temperature of
at least 50 × 106 K is indicated by the data, inside a
volume which may not exceed a few hundred km in diameter. A magnetic
reconnection of previously distended field lines appears to be a likely
candidate for the observed phenomenon.

---------------------------------------------------------
Title: Modeling of reconnection processes in ribbon flares
Authors: Kopp, R. A.; Poletto, G.
1985MmSAI..56..809K Altcode:
In a study of how flares are sustained by magnetic energy, the work
of Hirayama (1974) is extended. Hirayama identified reconnection of
the open field lines created by filament eruption as the source of
prolonged energy release observed during the decay phase of two-ribbon
flares. It is shown that the morphological properties of the decay phase
of two-ribbon flares may be interpreted in terms of reconnection. A
two-dimensional model (which can be extended to three dimensions)
capable of reproducing the large-scale behavior of the observed
scenario is presented. The capabilities of both models is discussed
in the context of ongoing research in this area.

---------------------------------------------------------
Title: Extension of the Reconnection Theory of Two-Ribbon Solar Flares
Authors: Kopp, R. A.; Poletto, G.
1984SoPh...93..351K Altcode:
The magnetic reconnection theory for two-ribbon flares and flare loops
hypothesizes that the gradual energy release during the decay phase
is a direct result of dissipative relaxation of the open coronal
magnetic configuration created by an eruptive prominence/coronal
transient precursor. This scenario is here developed quantitatively
to the point where a realistic comparison with observational data
can be attempted. Our major refinements are (i) to use an analytical
description of the reconnecting field geometry specifically chosen
to characterize the spatial scale of the active region where a flare
occurs, and (ii) to take account of the fact that the volume occupied
by X-ray-emitting plasma (hot loops) generally increases with time
during the flare.

---------------------------------------------------------
Title: Wave observations in the solar transition region with the
solar maximum mission
Authors: Bruner, M. E.; Poletto, G.
1984MmSAI..55..313B Altcode:
Observations of intensity and velocity oscillations in the solar
transition region obtained with the UVSP instrument on the Solar
Maximum Mission in the N V line at 1238 A have been analyzed in order
to ascertain their nature. It has been reported that in about 2/3 of
the experiments, the data were consistent with the behavior expected
from acoustic waves. It has been found that an estimate of the energy
flux carried by the waves still yields a value too low to provide for
coronal heating. There is evidence for the existence of an upward
directed flux, and there are indications that through observations
with improved spatial and temporal resolution a higher energy flux
level might be revealed. Methods used to confirm the nature of the
waves are presented, and the observations are described.

---------------------------------------------------------
Title: Magnetic reconnection in two-ribbon flares - Theory and
applications
Authors: Kopp, R. A.; Poletto, G.
1984MmSAI..55..737K Altcode:
The magnetic reconnection theory of two-ribbon flares and flare loops
is applied to flares observed both during the Solar Maximum Mission
and earlier. In order to compare it quantitatively with observational
data, the original theory is refined in two respects. First, an
analytical description of the reconnecting field geometry is used
which is specifically chosen to characterize the actual spatial scale
of the active region where a flare occurs. Second, the increase in
coronal volume occupied by the thermal flare plasma is taken into
account. Application of the modified theory to the large two-ribbon
flare of July 29, 1973 yields excellent agreement with observations
of the time variation of the flare plasma energy density, extending
to rather early times in the flare history. A similar analysis for
another flare allowed the reconnection process to be directly observed.

---------------------------------------------------------
Title: Imaging of reconnection processes in hard X-rays
Authors: Švestka, Zdenek; Poletto, Giannina
1984AdSpR...4g.287S Altcode: 1984AdSpR...4Q.287S
The Hard X-ray Spectrometer aboard the SMM detected several events of
energy release late in the development of two-ribbon flares. One such
event, at 21:12 UT on 21 May, 1980 (~ 20 min after the flare onset and
15 min after the peak of the impulsive phase) is studied in detail. The
site of new brightening first became visible in hard X-rays (&gt; 22
keV) and only afterwards showed up at lower energies. It was clearly
located high in the corona so that one can identify it with energy
release at the tops of newly formed post-flare loops. Thus, if the
Kopp and Pneuman model of the loop formation is adopted, we may have
imaged here a reconnection process in the solar corona. An attempt is
made to estimate physical parameters at the reconnection site.

---------------------------------------------------------
Title: Observational Evidence for Coronal Magnetic Reconnection
during the Two-Ribbon Flare of 21 may 1980
Authors: Kopp, R. A.; Poletto, G.
1984uxsa.coll...17K Altcode: 1984IAUCo..86...17K; 1984uxsa.conf...17K
No abstract at ADS

---------------------------------------------------------
Title: Analysis of active region loop flows as observed from SMM
Authors: Poletto, G.; Kopp, R. A.
1984MmSAI..55..773P Altcode:
The physical properties of plasma motions within solar loop structures
are studied by analyzing and interpreting space observations of
flows in active regions outside flare conditions. The indirect
evidence for the presence of plasma motions in loops that derives
either from observational data or from theoretical arguments is first
discussed. Direct observations of plasma flows, mostly acquired by
the SMM USVP experiment, are then reviewed. Finally, the results of
one recent attempt to compare theory and observations are presented
and discussed.

---------------------------------------------------------
Title: SMM Observations of Coronal Arcade at the Onset of a Flare
Authors: Strong, K. T.; Bruner, M. E.; Poletto, G.; Kopp, R.
1983BAAS...15..715S Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Active region coronal evolution
Authors: Golub, L.; Noci, G.; Poletto, G.; Vaiana, G. S.
1982ApJ...259..359G Altcode:
Scaling relations between coronal base pressure and longitudinal
photospheric magnetic field strength are tested for the case of a
single active region observed for five solar rotations from Skylab. The
evolution of measureable quantities, such as coronal thermal energy
content, total longitudinal photospheric magnetic flux, region scale
size, and peak energy density, is traced throughout the five rotations
observed. The theoretically derived scaling law of Golub et al. (1980)
is found to provide an acceptable fit to the data throughout the entire
evolutionary history of the region from an age of about 3 days to
the fully evolved state in which the mature active region merges into
the general large-scale structure of the quiet corona. An alternative
scaling law obtained by including the results of Galeev et al. (1981),
however, is found to provide a somewhat better fit to the data. The
study is seen as providing additional justification for the belief
that magnetic field-related heating is the operative mechanism in the
solar corona.

---------------------------------------------------------
Title: Observations of solar flare transition zone plasmas from the
Solar Maximum Mission
Authors: Cheng, C. -C.; Bruner, E. C.; Tandberg-Hanssen, E.; Woodgate,
B. E.; Shine, R. A.; Kenny, P. J.; Henze, W.; Poletto, G.
1982ApJ...253..353C Altcode:
The spatial and temporal evolution of the Si IV and O IV intensity,
density and mass motions in preflare and flare transition zone plasmas
are studied for the case of the April 8, 1980 flare. It is found that:
(1) the UV flare observed in the Si IV and O IV lines is unambiguously
identified as occurring in a low-lying, preexisting transition zone loop
which spanned the magnetic neutral line separating a larger leader spot
and a newly emerged, isolated spot of opposite polarity; (2) at the
onset of the flare, the easternmost footpoint, which was anchored in
an isolated spot region of high longitudinal magnetic field gradient,
showed sudden, impulsive brightening with large intensity increases;
and (3) the release flare energy was transported by way of large-scale
connecting field lines to other parts of the active region, producing
the hot plasma and H-alpha kernels observed near the trailing spot.

---------------------------------------------------------
Title: Preliminary Results from an Analysis of SMM Observations of
Loop Flows.
Authors: Bruner, M.; Kopp, R. A.; Noci, G.; Poletto, G.
1982uxsa.coll....2B Altcode: 1982IAUCo..73....2B
No abstract at ADS

---------------------------------------------------------
Title: Wave motions and wave heating in the upper solar atmosphere
Authors: Poletto, G.
1982MmSAI..53..411P Altcode:
The experimental and theoretical evidence favoring the wave heating
mechanism in the low chromosphere is briefly reviewed, and the
possibility of maintaining this mechanism, with proper modifications,
in the higher layer is studied. Wave mode candidates for heating at high
levels are analyzed, including gravity waves and Alfven waves. Waves
in the upper chromosphere and the transition region are considered,
showing power spectra of oscillations in lines forming at increasing
heights in the solar atmosphere, fluctuations in UV line intensity,
the predicted relationship between velocity and intensity modulation for
acoustic waves, and sample results from UV spectrometer and polarimeter
observations. It is concluded that in the upper chromosphere and
transition regions, observations fail to reveal an acoustic flux
adequate to compensate for the energy losses in these layers. Alfven
waves, observed in the solar wind, could supply the required energy
flux, but their presence cannot either be confirmed or ruled out.

---------------------------------------------------------
Title: Mass Motions in the Transition Region
Authors: Poletto, G.
1981SoPh...73..233P Altcode:
Following previous order of magnitude estimates (Poletto, 1980), the
possibility that hot downflowing motions in the solar transition region
could be ascribed to spicular matter returning to the chromosphere
after being heated by compression, is more thoroughly investigated. The
equations describing the one-dimensional non stationary motion of the
spicular plasma during the heating process are analytically solved,
and the temporal profiles of temperature, density and velocity are
given for a set of representative situations. The results are finally
compared with available data.

---------------------------------------------------------
Title: Accustic Energy Flux in the Solar Transition Zone
Authors: Bruner, M. E.; Poletto, G.
1981BAAS...13..835B Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Hot downflows above supergranular boundaries
Authors: Poletto, G.
1980ApJ...240L..69P Altcode:
In recent years, several UV observations have detected, above
supergranular boundaries, hot downflows, which have been interpreted
as cool spicular matter falling back after being heated to coronal
temperatures. An examination of possible heating mechanisms leads us
to discard the process of conductive or radiative heating from the hot
corona. An alternative process which involves the compressive heating
of the cool spicular material is proposed and shown to be able to
reproduce the required temperature rise over the correct time scale.

---------------------------------------------------------
Title: Common Origin for Ultraviolet and Radio Fluctuations
Authors: Poletto, G.
1980SoPh...66..323P Altcode:
Brightness temperature fluctuations induced by a shock wave transit
through the solar transition region are computed at several decimetric
wavelengths. A simplified method previously used to reproduce the
observed UV line intensity fluctuations is shown to give oscillation
amplitudes which are consistent with experimental results. The
detectability of shock-induced radio fluctuations is briefly discussed,
to check the possibility of a common origin for the observed UV and
radio phenomena.

---------------------------------------------------------
Title: UV emitting spicules
Authors: Poletto, G.
1980IAUS...91..199P Altcode:
EUV observations of spicules in the solar chromospheric network are
discussed. Spectroheliograms each produced at seven wavelengths were
acquired by the EUV Harvard spectrometer on board Skylab. Analysis of
the frequency vs. intensity distribution of chromospheric and transition
region lines of ions formed in different temperature regions indicates
a network area percentage on the order of 40%, with approximately 1500
spicules in each spectroheliogram. If it is assumed that the network
consists of evenly spaced spicules along the supergranular boundaries,
then the average intensities derived from the frequency vs. intensity
distribution would be representative of spicule emission and could be
used to give an upper limit to the values of the differential emission
measure. If, on the other hand, the spicules are assumed to be clumped
together, the average intensities of the spicules could be derived
from those of the brightest network elements and would provide a lower
limit to the differential emission measure. Data is consistent with
the UV spicules being H alpha spicules falling back after heating,
and leads to an estimate of 2 x 10 to the 10th/cu cm for the average
density of the spicules.

---------------------------------------------------------
Title: Shock wave transit through the transition region and related
radio fluctuations
Authors: Poletto, G.
1980IAUS...86...57P Altcode:
The effects of the passage of a shock wave through the solar transition
region on the brightness temperature of the region at decimetric
wavelengths are evaluated. A simplified method is used to solve the
partial differential equations describing the fluid motion behind
the shock front, resulting in models of the temperature and density
perturbations caused by the passage of the shock. Shock-perturbed
brightness temperatures are then calculated for wavelengths of 60,
80 and 100 cm at various times after shock passage, and a measured
temperature fluctuation amounting to 1% is obtained. Results are noted
to be in agreement with observed fluctuations, thus supporting the
wave hypothesis for the origin of the phenomenon for times less than
the radiative and conductive cooling times.

---------------------------------------------------------
Title: Brightness fluctuations of solar ultraviolet line intensities
during a shock-wave passage.
Authors: Poletto, G.
1979SoPh...61..389P Altcode:
A simplified method is developed to derive the modifications
induced at successive times by the passage of a shock wave in a
standard unperturbed transition region atmosphere. Time dependent
`shocked' models allow the evaluation of the effects of the vertically
propagating shock wave upon the intensity of ultraviolet lines. Out
of equilibrium effects are taken into account to evaluate time varying
ion abundances. The behavior of the modified UV intensities is compared
with the experimental results of Vernazza et al. (1975).

---------------------------------------------------------
Title: Risultati recenti e problemi aperti in fisica solare.
Authors: Pallavicini, R.; Poletto, G.
1979GAst....5...19P Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Possibilità di vita e civiltà in ambiente extraterrestri.
Authors: Poletto, G.
1979Coel...47....1P Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Oscillazioni dell'emissione solare UV e radio dalla zona
di transizione.
Authors: Poletto, G.
1979RSAI...22..160P Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Is there anything new on the sun?
Authors: Pallavicini, R.; Poletto, G.
1978Mercu...7...23P Altcode:
The current state of knowledge regarding the sun and the processes
taking place in it is examined. It is found that in addition to the
neutrino problem there are many other intriguing problems. Recent
observations represent a challenge with respect to basic theoretical
interpretations of solar phenomena. Elementary facts about the sun
are considered, taking into account the significance of the presence
of sunspots with their very strong magnetic fields, flares, auroras,
faculae, and the differential rotation of the sun. A description is
presented of a theory which explains the high temperatures of the
chromosphere and the corona. Investigations based on observations
of radio waves, infrared and ultraviolet radiation, and X-rays are
considered. Attention is also given to holes in the solar corona,
quiescent periods in solar activity, and problems related to an
occurrence of 'Maunder minima'.

---------------------------------------------------------
Title: Osservazioni radio di buchi coronali.
Authors: Chiuderi-Drago, F.; Poletto, G.
1977MmSAI..48..762C Altcode:
No abstract at ADS

---------------------------------------------------------
Title: A dynamical model of coronal holes based on radio observations
Authors: Chiuderi Drago, F.; Poletto, G.
1977A&A....60..227C Altcode:
A dynamical homogeneous model of coronal holes, taking into account a
more than radial divergence of magnetic-field lines, is derived under
the assumptions of a constant temperature at coronal levels and of a
constant ratio (p-squared/Fc) of the square of the pressure to the
conductive flux in the transition region. Available observations
of brightness temperatures at several radio frequencies allow the
determination of p-squared/Fe as well as the temperature and density at
the base of the corona compatible with radio observations. The model so
obtained gives the correct values of the EUV line intensities arising
from the transition region, since they depend only on p-squared/Fc,
while the Mg X coronal-line intensity at 625 A turns out to be lower
than observed by about one order of magnitude. This indicates that the
discrepancy previously found in the interpretation of EUV and radio
data assuming a hydrostatic atmosphere still persists.

---------------------------------------------------------
Title: Magnetic and microwave structure in solar active regions.
Authors: Felli, M.; Poletto, G.; Tofani, G.
1977SoPh...51...65F Altcode:
The structure of six active regions observed at 2.8 cm with the Stanford
interferometer is compared with the configuration of the underlying
photospheric magnetic fields, as given by the Kitt Peak magnetograph.

---------------------------------------------------------
Title: Dynamical Effects in the EUV Chromospheric Network.
Authors: Chiuderi-Drago, F. G.; Poletto, G.
1977uxsa.coll...10C Altcode: 1977IAUCo..43...10C
No abstract at ADS

---------------------------------------------------------
Title: A Comparison of Coronal X-Ray Structures of Active Regions
with Magnetic Fields Computed from Photospheric Observations
Authors: Poletto, G.; Vaiana, G. S.; Zombeck, M. V.; Krieger, A. S.;
Timothy, A. F.
1975SoPh...44...83P Altcode:
The appearances of several X-ray active regions observed on March 7,
1970 and June 15, 1973 are compared with the corresponding coronal
magnetic field topology. Coronal fields have been computed from
measurements of the longitudinal component of the underlying magnetic
fields, under the current-free hypothesis. An overall correspondence
between X-ray structures and calculated field lines is established,
and the magnetic counterpart of different X-ray features is also
examined. A correspondence between enhanced X-ray emission and the
location of compact closed field lines is suggested by this study.

---------------------------------------------------------
Title: Coronal X-ray structures and coronal magnetic fields
Authors: Poletto, G.; Timothy, A. F.; Krieger, A. S.; Vaiana, G. S.
1975xtcg.work..175P Altcode:
Coronal X-ray structures are compared with corresponding current-free
coronal magnetic fields, particularly with regard to compact structures
where potential fields are expected to be strong enough to correspond
to energy densities well above the plasma densities. The comparison
is conducted using X-ray images of several active regions obtained
by five different days and ground-based magnetograms for the same
days. Images of the active regions are superposed on extrapolated
potential field lines, and qualitative agreement is found between
the two configurations. It is noted that this agreement is limited
to compact structures and is especially apparent in the absence of
flare activity or large structural changes. Since the extrapolated
potential fields seem to represent well the general topology outlined
by the X-ray structures, it is concluded that current fields make a
minor contribution to the total coronal field.

---------------------------------------------------------
Title: Coronal X-ray structures and coronal magnetic fields.
Authors: Poletto, G.; Timothy, A. F.; Krieger, A. S.; Vaiana, G. S.
1975MmArc.104..175P Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Extrapolation of Photospheric Magnetic Fields into the Corona
Authors: Poletto, G.; Krieger, A.; Silk, J. K.; Timothy, A.; Vaiana, G.
1974BAAS....6..292P Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Coronal X-ray Structures and Coronal Magnetic Fields
Authors: Poletto, G.; Timothy, A. F.; Krieger, A. S.; Vaiana, G. S.
1974OMOAA.104..175P Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Solar radio brightness distribution from OSO IV UV
spectroheliograms
Authors: Chiuderi Drago, F.; Poletto, G.
1973MmSAI..44..171C Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Proceedings of the first European Astronomical Meeting
Authors: Poletto, G.
1973MmSAI..44..711P Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Models of Active Regions in the Transition Zone from UV
Observations
Authors: Cantú, A. M.; Poletto, G.; Tagliaferri, G. L.
1972SSRv...13..638C Altcode: 1972IAUCo..14..638C
No abstract at ADS

---------------------------------------------------------
Title: Solar XUV fluxes of SOLRAD 10 satellite from July to December
1971 (Lettera alla Direzione)
Authors: Landini, M.; Monsignori Fossi, B. C.; Poletto, G.;
Tagliaferri, G. L.
1972MmSAI..43..383L Altcode:
No abstract at ADS

---------------------------------------------------------
Title: On the structure of the solar transition zone in active regions
Authors: Cantù, A. M.; Poletto, G.; Tagliaferri, G. L.
1972MmSAI..43..371C Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Astronomy and astrophysics abstracts (Recensione)
Authors: Poletto, G.
1971MmSAI..42..652P Altcode:
No abstract at ADS

---------------------------------------------------------
Title: La zona di transizione tra la cromosfera e la corona solare
(Rassegna)
Authors: Poletto, G.
1971MmSAI..42..585P Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Particles and fields in the magnetosphere (Recensione)
Authors: Poletto, G.
1971MmSAI..42..113P Altcode:
No abstract at ADS

---------------------------------------------------------
Title: On the Connection between N-S and E-W Solar Asymmetries
Authors: Cantú, A. M.; Godoli, G.; Poletto, G.
1970SoPh...15..356C Altcode:
No abstract at ADS

---------------------------------------------------------
Title: X-Ray Fluxes from Solrad 9 Satellite
Authors: Landini, M.; Monsignori Fossi, B. C.; Poletto, G.; Russo,
D.; Tagliaferri, G. L.
1970SoPh...13..226L Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Il simposio internazionale sulle relazioni sole-terra.
Authors: Fossi, B. C.; Poletto, G.; Tagliaferri, G. L.
1970MmSAI..41..255F Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Il simposio internazionale sulle relazioni Sole-Terra
(Congressi e Simposi)
Authors: Monsignori Fossi, B. C.; Poletto, G.; Tagliaferri, G. L.
1970MmSAI..41..255M Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Measurements of solar UV by the Solrad 8 satellite.
Authors: Fossi, B. C.; Poletto, G.; Tagliaferri, G. L.
1970spre.conf..903F Altcode:
No abstract at ADS

---------------------------------------------------------
Title: A Possible Connection between N-S and E-W Solar Asymmetries
Authors: Godoli, G.; Poletto, G.
1969SoPh...10..494G Altcode:
No abstract at ADS

---------------------------------------------------------
Title: An Outstanding Lyman-Alpha Event
Authors: Monsignori Fossi, B. C.; Poletto, G.; Tagliaferri, G. L.
1969SoPh...10..196M Altcode: 1969SoPh...10..196F
No abstract at ADS

---------------------------------------------------------
Title: X-ray fluxes from the Solrad 9 satellite (1968-17A) from
March 1968 to December 1968 (Lettera alla Direzione)
Authors: Landini, M.; Monsignori Fossi, B.; Poletto, G.; Russo, D.;
Tagliaferri, G. L.
1969MmSAI..40...95L Altcode:
No abstract at ADS

---------------------------------------------------------
Title: La scuola estiva 1969 dell'ESRO (Congressi e Simposi)
Authors: Barletti, R.; Poletto, G.
1969MmSAI..40..361B Altcode:
No abstract at ADS

---------------------------------------------------------
Title: The 44 60 Å flux during the ascending period of the solar
cycle no. 20 (1964 67)
Authors: Landini, M.; Fossi, B. C. Monsignori; Poletto, G.;
Tagliaferri, G. L.
1968SoPh....5..546L Altcode:
An attempt is made to separate the `true' 44-60 Å flux from the
`nominal' one measured by the Solrad 8 satellite during 1966.

---------------------------------------------------------
Title: On the activity of solar prominences
Authors: Cantù, A. M.; Godoli, G.; Poletto, G.
1968MmSAI..39..507C Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Solar Lyman-alpha variations in March and May, 1966
Authors: Monsignori Fossi, B.; Poletto, G.; Tagliaferri, G. L.
1968MmSAI..39..201M Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Variation of the Calibration Curve from Laboratory to Flight
Conditions in the SOLRAD Lyman-Alpha Ion Chamber
Authors: Barletti, R.; Fossi, B. M.; Poletto, G.; Tagliaferri, G. L.
1968cmux.conf..213B Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Variation of the calibration curve from laboratory to flight
conditions in the Solrad Lyman-alpha ion chamber.
Authors: Barletti, R.; Fossi, B.; Poletto, G.; Tagliaferri, G. L.
1968cmux..200..213B Altcode:
No abstract at ADS

---------------------------------------------------------
Title: On the evaluation of solar activity at different heliographic
latitudes (Lettera alla Direzione)
Authors: Godoli, G.; Poletto, G.
1967MmSAI..38..241G Altcode:
No abstract at ADS

---------------------------------------------------------
Title: On the height of solar prominences
Authors: Cantù, A.; Godoli, G.; Poletto, G.
1967MmSAI..38..367C Altcode:
No abstract at ADS

---------------------------------------------------------
Title: The spectra of some quiescent prominences observed during
the total solar eclipse of 1952, February 25 - Nota I
Authors: Poletto, G.; Rigutti, M.
1967MmSAI..38..479P Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Erratum to the paper "Solar Excitation Temperature from two
CN Bands. ƒ-value for the CN Electronic Transition X2
Σ - A2Π”.Z.f. Astrophysik 60, 199-206 (1964)
Authors: Poletto, G.; Rigutti, M.
1965ZA.....61..285P Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Erratum to the paper "Solar Excitation Temperature
from Two CN Bands. ƒ-value for the CN Electronic Transition
X2Σ-A2Π" Z. f. Astrophysik Bd. 60, S. 199-206
(1964)
Authors: Poletto, G.; Rigutti, M.
1965ZA.....60..289P Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Solar Excitation Temperature from Two CN Bands. ƒ-value for
the CN Electronic Transition X2Σ - A2Π. With
2 Figures in the Text
Authors: Poletto, G.; Rigutti, M.
1964ZA.....60..199P Altcode:
No abstract at ADS