Author name code: poletto ADS astronomy entries on 2022-09-14 author:"Poletto, Giannina" ------------------------------------------------------------------------ Title: Evolution of active region outflows throughout an active region lifetime Authors: Zangrilli, L.; Poletto, G. Bibcode: 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. Title: Solar Coronal Plumes Authors: Poletto, Giannina Bibcode: 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. Title: Birth, Life, and Death of a Solar Coronal Plume Authors: Pucci, Stefano; Poletto, Giannina; Sterling, Alphonse C.; Romoli, Marco Bibcode: 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. 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 Bibcode: 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. Title: Physical Parameters of Standard and Blowout Jets Authors: Pucci, Stefano; Poletto, Giannina; Sterling, Alphonse C.; Romoli, Marco Bibcode: 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. 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 Bibcode: 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. Title: Sources of solar wind over the solar activity cycle Authors: Poletto, Giannina Bibcode: 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. Title: A SOHO/UVCS study of coronal outflows at the edge of an active region complex Authors: Zangrilli, L.; Poletto, G. Bibcode: 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. Title: Observational Evidence for Interaction Between X-ray Jets and Multiple Bright Points Authors: Pucci, S.; Poletto, G.; Sterling, A.; Romoli, M. Bibcode: 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. Title: Physical Parameters of a Blowout Jet Observed by HINODE and STEREO/EUVI Authors: Pucci, S.; Poletto, G.; Sterling, A.; Romoli, M. Bibcode: 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. Title: Solar Polar X-Ray Jets and Multiple Bright Points: Evidence for Sympathetic Activity Authors: Pucci, Stefano; Poletto, Giannina; Sterling, Alphonse C.; Romoli, Marco Bibcode: 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. 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. Bibcode: 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. Title: Astrophysical jets: what can we learn from solar ejections?. Authors: Massi, M.; Poletto, G. Bibcode: 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. Title: Current Sheets in the Solar Atmosphere Authors: Poletto, Giannina Bibcode: 2011sswh.book..157P Altcode: No abstract at ADS 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. Bibcode: 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. Title: Associating flare-and CME current sheets by radio and SOHO (UVCS, LASCO, MDI) data Authors: Aurass, Henry; Poletto, Giannina; Landini, Federico Bibcode: 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. 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. Bibcode: 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. Title: Large and small scale structures as sources of solar wind. Authors: Poletto, Giannina Bibcode: 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. 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. Bibcode: 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. 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. Bibcode: 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. Title: Coronal current sheet signatures during the 17 May 2002 CME-flare Authors: Aurass, H.; Landini, F.; Poletto, G. Bibcode: 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. Title: Multispacecraft observations of a prominence eruption Authors: Bemporad, A.; Del Zanna, G.; Andretta, V.; Poletto, G.; Magrí, M. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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 Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 2006ESASP.617E..24B Altcode: 2006soho...17E..24B No abstract at ADS Title: Past and Future SOHO-Ulysses Quadratures Authors: Suess, S. T.; Poletto, G. Bibcode: 2006ESASP.617E.161S Altcode: 2006soho...17E.161S No abstract at ADS Title: Diagnostics and Modelling of the Solar Wind Source Regions Authors: Poletto, G. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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., & Fineschi, S. 2002, Astrophys. J., 575, 1116 Ko, Y.-K., Raymond, J. C., Li, J., Ciaravella, A., Michels, J., Fineschi, S., & Wu, R. 2002, Astrophys. J., 578, 979 Lepri, S. T., & Zurbuchen, T. H. 2004, J. Geophys. Res., 109(A1), A01112 Raymond, J. C., Ciaravella, A., Dobrzycka, D., Strachan, L., Ko, Y.-K., & Uzzo, M. 2003, Astrophys. J., 597, 1106 Title: The Sun and the Heliosphere as an Integrated System Authors: Poletto, G.; Suess, S. T. Bibcode: 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: http://www.springeronline.com/sgw/cda/frontpage/0,11855,5-40109-22-35889411-0,00.html

http://www.springeronline.com/sgw/cda/frontpage/0,11855,5-40109-22-35889362-0,00.html 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. Bibcode: 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. Title: A slow streamer blowout at the Sun and Ulysses Authors: Suess, S. T.; Bemporad, A.; Poletto, G. Bibcode: 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. Title: SUMER, UVCS and LASCO Observations of Small-Scale Ejecta Authors: Teriaca, L.; Curdt, W.; Poletto, G. Bibcode: 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. Title: Evidence for pyroxene dust grains in C/2001 C2 sungrazing comet Authors: Bemporad, A.; Poletto, G.; Raymond, J. Bibcode: 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. Title: Origin and Acceleration of the Fast and Slow Solar Wind Authors: Poletto, G. Bibcode: 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. Bibcode: 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. Bibcode: 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. Title: Solar wind acceleration in low density regions Authors: Teriaca, L.; Poletto, G.; Romoli, M.; Biesecker, D. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Title: Spatial and temporal behavior of the oxygen abundance in a streamer complex Authors: Bemporad, A.; Poletto, G.; Romoli, M. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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 >=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. Bibcode: 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<=2.2Rsolar. In this paper we analyze UVCS observations of two streamers, observed during solar minimum at altitudes h>=2.4Rsolar to derive the oxygen abundance, relative to hydrogen, and its latitude dependence within streamers, in the range 2.4<=h<=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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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 Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 2000IAUTA..24...67A Altcode: No abstract at ADS Title: Plasma Flows In Coronal Hole Regions Authors: Landi, E.; Mullan, D.; Poletto, G.; Wilhelm, K. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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 Bibcode: 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 Bibcode: 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 & Mullan but has not previously been applied in modeling efforts. After extending the Khabibrakhmanov & 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 1999ApJ...511..481C Altcode: We present a comprehensive and self-consistent empirical model for several plasma parameters in the extended solar corona above a polar coronal hole. The model is derived from observations with the SOHO Ultraviolet Coronagraph Spectrometer (UVCS/SOHO) during the period between 1996 November and 1997 April. We compare observations of H I Lyα and O VI λλ1032, 1037 emission lines with detailed three-dimensional models of the plasma parameters and iterate for optimal consistency between measured and synthesized observable quantities. Empirical constraints are obtained for the radial and latitudinal distribution of density for electrons, H0, and O5+, as well as the outflow velocity and unresolved anisotropic most probable speeds for H0 and O5+. The electron density measured by UVCS/SOHO is consistent with previous solar minimum determinations of the white-light coronal structure; we also perform a statistical analysis of the distribution of polar plumes using a long time series. From the emission lines we find that the unexpectedly large line widths of H0 atoms and O5+ ions at most heights are the result of anisotropic velocity distributions. These distributions are not consistent with purely thermal motions or the expected motions from a combination of thermal and transverse wave velocities. Above 2 Rsolar, the observed transverse most probable speeds for O5+ are significantly larger than the corresponding motions for H0, and the outflow velocities of O5+ are also significantly larger than the corresponding velocities of H0. Also, the latitudinal dependence of intensity constrains the geometry of the wind velocity vectors, and superradial expansion is more consistent with observations than radial flow. We discuss the constraints and implications on various theoretical models of coronal heating and acceleration. Title: Ulysses-UVCS Coordinated Observations Authors: Suess, S. T.; Poletto, G.; Corti, G.; Simnett, G.; Noci, G.; Romoli, M.; Kohl, J.; Goldstein, B. Bibcode: 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. Bibcode: 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 Title: On the Lyman α and O VI Line Profiles in Streamers and Coronal Holes Authors: Zangrilli, L.; Nicolosi, P.; Poletto, G.; Noci, G. Bibcode: 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. Title: Coronal Heating: a Comparison of Ion-cyclotron and Gravity Damping Models Authors: Cuseri, I.; Mullan, D.; Poletto, G. Bibcode: 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. 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. Bibcode: 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. Title: Ultraviolet Coronagraph Spectrometer Observations of Density Fluctuations in the Solar Wind Authors: Ofman, L.; Romoli, M.; Poletto, G.; Noci, G.; Kohl, J. L. Bibcode: 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 (ApJ, 491, L111 [1997]), 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. Title: UVCS/SOHO Empirical Determinations of Anisotropic Velocity Distributions in the Solar Corona Authors: Kohl, J. L.; Noci, G.; Antonucci, E.; Tondello, G.; Huber, M. C. E.; Cranmer, S. R.; Strachan, L.; Panasyuk, A. V.; Gardner, L. D.; Romoli, M.; Fineschi, S.; Dobrzycka, D.; Raymond, J. C.; Nicolosi, P.; Siegmund, O. H. W.; Spadaro, D.; Benna, C.; Ciaravella, A.; Giordano, S.; Habbal, S. R.; Karovska, M.; Li, X.; Martin, R.; Michels, J. G.; Modigliani, A.; Naletto, G.; O'Neal, R. H.; Pernechele, C.; Poletto, G.; Smith, P. L.; Suleiman, R. M. Bibcode: 1998ApJ...501L.127K Altcode: We present a self-consistent empirical model for several plasma parameters of a polar coronal hole near solar minimum, derived from observations with the Solar and Heliospheric Observatory Ultraviolet Coronagraph Spectrometer. The model describes the radial distribution of density for electrons, H0, and O5+ and the outflow velocity and unresolved most probable velocities for H0 and O5+ during the period between 1996 November and 1997 April. In this Letter, we compare observations of H I Lyα and O VI λλ1032, 1037 emission lines with spatial models of the plasma parameters, and we iterate for optimal consistency between measured and synthesized observable quantities. The unexpectedly large line widths of H0 atoms and O5+ ions at most radii are the result of anisotropic velocity distributions, which are not consistent with purely thermal motions or the expected motions from a combination of thermal and transverse wave velocities. Above 2 Rsolar, the observed transverse, most probable speeds for O5+ are significantly larger than the corresponding motions for H0, and the outflow velocities of O5+ are also significantly larger than the corresponding velocities of H0. We discuss the constraints and implications on various theoretical models of coronal heating and acceleration. Title: The Geometric Spreading of Coronal Plumes and Coronal Holes Authors: Suess, S. T.; Poletto, G.; Wang, A. -H.; Wu, S. T.; Cuseri, I. Bibcode: 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. Title: Global model of the corona with heat and momentum addition Authors: Wang, A. H.; Wu, S. T.; Suess, S. T.; Poletto, G. Bibcode: 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. Title: UVCS observations of polar regions Authors: Poletto, G.; Corti, G.; Romoli, M.; Kohl, J. L.; Noci, G. Bibcode: 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. Title: A new heating and acceleration mechanism for the fast solar wind Authors: Cuseri, I.; Mullan, D. J.; Noci, G.; Poletto, G. Bibcode: 1998MmSAI..69..745C Altcode: No abstract at ADS Title: Coronal Plumes and the Solar Wind: Observations and Theories (invited) Authors: Poletto, G.; Corti, G.; Romoli, M. Bibcode: 1998asct.conf..235P Altcode: No abstract at ADS Title: Ultraviolet Coronagraph Spectrometer Observations of Density Fluctuations in the Solar Wind Authors: Ofman, L.; Romoli, M.; Poletto, G.; Noci, G.; Kohl, J. L. Bibcode: 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 & 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. 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. Bibcode: 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. 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. Bibcode: 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. Title: Inferences on Coronal Magnetic Fields from SOHO UVCS Observations Authors: Poletto, G.; Romoli, M.; Suess, S. T.; Wang, A. H.; Wu, S. T. Bibcode: 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. Title: Magnetic Flux Tubes at 3 Au? Authors: Parenti, S.; Velli, M.; Poletto, G.; Suess, S. T.; McComas, D. J. Bibcode: 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. Title: Expansion Factors in Coronal Holes and Plume/Interplume UVCS Observations Authors: Poletto, G.; Corti, G.; Noci, G.; Kohl, J.; Suess, S. Bibcode: 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 <<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. 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. Bibcode: 1997ESASP.404..571O Altcode: 1997cswn.conf..571O No abstract at ADS 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. Bibcode: 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. 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. Bibcode: 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. Title: Physical Parameters in Plume and Interplume Regions from UVCS Observations Authors: Corti, G.; Poletto, G.; Romoli, M.; Michels, J.; Kohl, J.; Noci, G. Bibcode: 1997ESASP.404..289C Altcode: 1997cswn.conf..289C No abstract at ADS 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. Bibcode: 1997ESASP.404...75N Altcode: 1997cswn.conf...75N; 1997soho....5...75N No abstract at ADS Title: Observations of Plume and Interplume Regions with SOHO UVCS Authors: Poletto, G. Bibcode: 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. 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. Bibcode: 1996A&A...316..374P Altcode: In the past, from the analysis of data acquired by the Helios spacecrafts within distances <=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. 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. Bibcode: 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. Title: Flare energy transport. Authors: Poletto, G. Bibcode: 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. Title: The Ultraviolet Coronagraph Spectrometer for the Solar and Heliospheric Observatory Authors: Kohl, J. L.; Esser, R.; Gardner, L. D.; Habbal, S.; Daigneau, P. S.; Dennis, E. F.; Nystrom, G. U.; Panasyuk, A.; Raymond, J. C.; Smith, P. L.; Strachan, L.; Van Ballegooijen, A. A.; Noci, G.; Fineschi, S.; Romoli, M.; Ciaravella, A.; Modigliani, A.; Huber, M. C. E.; Antonucci, E.; Benna, C.; Giordano, S.; Tondello, G.; Nicolosi, P.; Naletto, G.; Pernechele, C.; Spadaro, D.; Poletto, G.; Livi, S.; Von Der Lühe, O.; Geiss, J.; Timothy, J. G.; Gloeckler, G.; Allegra, A.; Basile, G.; Brusa, R.; Wood, B.; Siegmund, O. H. W.; Fowler, W.; Fisher, R.; Jhabvala, M. Bibcode: 1995SoPh..162..313K Altcode: The SOHO Ultraviolet Coronagraph Spectrometer (UVCS/SOHO) is composed of three reflecting telescopes with external and internal occultation and a spectrometer assembly consisting of two toric grating spectrometers and a visible light polarimeter. The purpose of the UVCS instrument is to provide a body of data that can be used to address a broad range of scientific questions regarding the nature of the solar corona and the generation of the solar wind. The primary scientific goals are the following: to locate and characterize the coronal source regions of the solar wind, to identify and understand the dominant physical processes that accelerate the solar wind, to understand how the coronal plasma is heated in solar wind acceleration regions, and to increase the knowledge of coronal phenomena that control the physical properties of the solar wind as determined byin situ measurements. To progress toward these goals, the UVCS will perform ultraviolet spectroscopy and visible polarimetry to be combined with plasma diagnostic analysis techniques to provide detailed empirical descriptions of the extended solar corona from the coronal base to a heliocentric height of 12 solar radii. Title: 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. Bibcode: 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. Bibcode: 1995SPIE.2517...40K Altcode: The SOHO ultraviolet coronagraph spectrometer (UVCS/SOHO) is composed of three reflecting telescopes with external and internal occultation and a spectrometer assembly consisting of two toric grating spectrometers and a visible light polarimeter. The UVCS will perform ultraviolet spectroscopy and visible polarimetry to be combined with plasma diagnostic analysis techniques to provide detailed empirical descriptions of the extended solar corona from the coronal base to a heliographic height of 12 R. In this paper, the salient features of the design of the UVCS instrument are described. An overview of the UVCS test and calibration activities is presented. The results from the calibration activity have demonstrated that the UVCS can achieve all its primary scientific observational goals. Title: Search for fine scale structures in high latitude solar wind Authors: Livi, S.; Parenti, S.; Poletto, G. Bibcode: 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. Bibcode: 1995SoPh..157..393P Altcode: No abstract at ADS Title: L'osservatorio di Arcetri. Authors: Poletto, G. Bibcode: 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. Bibcode: 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. Bibcode: 1994ESASP.373..143P Altcode: 1994soho....3..143P No abstract at ADS Title: Foreword Authors: Fleck, B.; Noci, G.; Poletto, G. Bibcode: 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. Bibcode: 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. Bibcode: 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 Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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 Bibcode: 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. Bibcode: 1994msfs.conf.....F Altcode: No abstract at ADS Title: Coronal Heating by Nanoflares: Individual Events and Global Energetics Authors: Kopp, R. A.; Poletto, G. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 1993MmSAI..64..441F Altcode: No abstract at ADS Title: Coronal heating via nanoflares Authors: Poletto, G.; Kopp, R. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 1992AAS...180.4106G Altcode: 1992BAAS...24Q.795G No abstract at ADS Title: The Birth of Giant Post-Flare Arches Authors: Poletto, G.; Svestka, Z. Bibcode: 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 Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 1992LNP...399..197K Altcode: 1992esf..coll..197K; 1992IAUCo.133..197K No abstract at ADS Title: Un antico incostante sole. I. Authors: Poletto, G. Bibcode: 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. Bibcode: 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 Bibcode: 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. Bibcode: 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. Bibcode: 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 Bibcode: 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 Bibcode: 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. Bibcode: 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. Bibcode: 1989SoPh..119..419P Altcode: 1989SoPh..119..419S No abstract at ADS Title: Long-Duration Solar and Stellar Flares Authors: Poletto, Giannina Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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 Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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 Bibcode: 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 (> 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. Bibcode: 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. Bibcode: 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. Bibcode: 1983BAAS...15..715S Altcode: No abstract at ADS Title: Active region coronal evolution Authors: Golub, L.; Noci, G.; Poletto, G.; Vaiana, G. S. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 1981BAAS...13..835B Altcode: No abstract at ADS Title: Hot downflows above supergranular boundaries Authors: Poletto, G. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 1979GAst....5...19P Altcode: No abstract at ADS Title: Possibilità di vita e civiltà in ambiente extraterrestri. Authors: Poletto, G. Bibcode: 1979Coel...47....1P Altcode: No abstract at ADS Title: Oscillazioni dell'emissione solare UV e radio dalla zona di transizione. Authors: Poletto, G. Bibcode: 1979RSAI...22..160P Altcode: No abstract at ADS Title: Is there anything new on the sun? Authors: Pallavicini, R.; Poletto, G. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 1974OMOAA.104..175P Altcode: No abstract at ADS Title: Solar radio brightness distribution from OSO IV UV spectroheliograms Authors: Chiuderi Drago, F.; Poletto, G. Bibcode: 1973MmSAI..44..171C Altcode: No abstract at ADS Title: Proceedings of the first European Astronomical Meeting Authors: Poletto, G. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 1972MmSAI..43..371C Altcode: No abstract at ADS Title: Astronomy and astrophysics abstracts (Recensione) Authors: Poletto, G. Bibcode: 1971MmSAI..42..652P Altcode: No abstract at ADS Title: La zona di transizione tra la cromosfera e la corona solare (Rassegna) Authors: Poletto, G. Bibcode: 1971MmSAI..42..585P Altcode: No abstract at ADS Title: Particles and fields in the magnetosphere (Recensione) Authors: Poletto, G. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 1969SoPh...10..494G Altcode: No abstract at ADS Title: An Outstanding Lyman-Alpha Event Authors: Monsignori Fossi, B. C.; Poletto, G.; Tagliaferri, G. L. Bibcode: 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. Bibcode: 1969MmSAI..40...95L Altcode: No abstract at ADS Title: La scuola estiva 1969 dell'ESRO (Congressi e Simposi) Authors: Barletti, R.; Poletto, G. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 1967MmSAI..38..241G Altcode: No abstract at ADS Title: On the height of solar prominences Authors: Cantù, A.; Godoli, G.; Poletto, G. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 1964ZA.....60..199P Altcode: No abstract at ADS