UVCS/SOHO ABSTRACTS
Other MEETINGS (up to 2002)

Magnetic Helicity and CMEs

Raymond, J. C.

 INVITED PAPER: Abstract not available

Outflow speed of protons and O VI ions in a coronal hole

Zangrilli, L., Poletto, G., Nicolosi, P.

Memorie della Società Astronomica Italiana 72, pp.600-603

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 1031.9 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.

A solar wind coronal origin study from SOHO/UVCS and ACE/SWICS joint analysis

Ko, Y.-K.; Zurbuchen, T.; Strachan, L.; Riley, P.; Raymond, J.C.

AIP Conf. Proc. 598 pp. 133-8

The solar wind ionic charge composition is a powerful tool to distinguish between the slow wind and the coronal-hole associated fast wind. The solar wind heavy ions are believed to be 'frozen-in' within 5 solar radii of the Sun which falls right in the range of SOHO/UVCS coronal observations. We present a joint analysis from SOHO/UVCS and ACE/SWICS which attempts to establish observational evidence of the coronal origin of the solar wind. To connect the solar wind with its coronal origin, we adopt a 3D MHD model as a guide to link the solar wind at 1 AU to structures in the inner corona. We relate in-situ measured properties of the solar wind (elemental abundances and charge state distributions) with remotely sensed signatures in the corona, namely outflow velocity, electron temperature and elemental abundance

Coronal and Solar Wind Elemental Abundances

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.

AIP Conf. Proc. 598, pp.49-57

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.

Oxygen abundance in the extended corona at solar minimum

E. Antonucci and S. Giordano

AIP Conf. Proc. 598 pp.77-81

We present a study on the abundance of oxygen relative to hydrogen in the solar minimum corona and for the first time we measure this quantity in polar coronal holes. The results are derived from the observations of the extended corona obtained with the Ultraviolet Coronagraph Spectrometer (UVCS) on SOHO. The diagnostic method used to obtain the oxygen abundance is based on the resonant components of the O VI 1032 A and H I 1216 A emission lines. This method fully accounts for the effects of the outflow velocity of the solar wind, which can be determined through Doppler dimming, and of the width of the absorbing profiles of the coronal ions or neutral atoms involved in resonant scattering. The oxygen abundance is higher in the polar coronal hole regions, where the fast wind is accelerated, than in the streamer belt. In the polar regions the observed oxygen abundance is consistent with the photospheric value and with the composition results obtained with Ulysses for the fast wind. The oxygen abundance values derived with UVCS suggest that the plasma remains substantially contained in quiescent streamers, that therefore do not contribute significantly to the solar wind.

Comparison of Outflow Velocity Determinations with UVCS and LASCO for the Coronal Mass Ejection of 13--14 Aug 1997

L. Strachan, J.C. Raymond, S. Fineschi, R. O'Neal, J.L. Kohl, A. Modigliani, G. Noci, M.D. Andrews, J.S. Morril, and R.A. Howard

 The Ultraviolet Coronagraph Spectrometer (UVCS) on SOHO was used to observe a Coronal Mass Ejection (CME) on 13-14 August 1997. The event was observed simultaneously with the LASCO white light coronagraph. This paper describes the first results from a comparison of outflow velocities determined from UVCS Doppler dimming studies with the velocities determined by examining the proper motions of the CME as measured by LASCO. Strengths and weaknesses of the various outflow determinations will be discussed.

LASCO and UVCS Observations and Characterization of a Streamer CME on 13--14 Aug 97

M.D. Andrews, L. Strachan, J.C. Raymond, S. Fineschi, R. O'Neal, J.L. Kohl, J.S. Morril, R.A. Howard, A. Modigliani, G. Noci, D. A. Biesecker, R. Schwenn, and P. L. Lamy

 The Large Angle Spectroscopic Coronagraph (LASCO) instruments observed a low-velocity streamer blow-out type Coronal Mass Ejection (CME) on 13-14Aug97. At the same time, the Ultraviolet Coronagraph Spectrometer (UVCS) instrument was conducting streamer studies and observed the CME from 1.5 to 8 solar radii. Data from the two instruments have been combined to examine the 3-dimensional structure and velocity of this CME. The UVCS data show no evidence of cool material in this event. Both the LASCO and UVCS data suggest that all of the material in the CME came from a pre-existing streamer. LASCO and UVCS are instruments on the Solar and Heliospheric Observatory which is a mission of international cooperation between ESA and NASA.

Comparison of Outflow Velocity Determinations with UVCS and LASCO for the Coronal Mass Ejection of 13-14 August 1997

L. Strachan, A. Ciaravella, J. C. Raymond, S. Fineschi, R. ONeal, J. L. Kohl, A. Modigliani, G. Noci, and M. D. Andrews

The Ultraviolet Coronagraph Spectrometer UVCS on SOHO observeda Coronal Mass Ejection CME on 13-14 August 1997. The event was observed simultaneously with the LASCO white light coronagraphs.This paper describes the results from a comparison of outflow velocities determined from UVCS Doppler dimming studies with the velocities determined by examining the proper motions of the CME as measured by LASCO. In addition, estimates of expansion velocities and line of sight motions are discussed. This work is supported in part by NASA under grant NAG-3192to the Smithsonian Astrophysical Observatory, by the Italian Space Agency and by Swiss funding agencies.

The Impact of Ion-Cyclotron Wave Dissipation on Heating and Accelerating the Fast Solar Wind

S. R. Cranmer, G. B. Field, and J. L. Kohl

We present theoretical models of the acceleration and heating of major and minor ions in the fast solar wind. We examine the compatibility between these models and spectroscopic determinations of velocity distribution functions from the SOHO Ultraviolet Coronagraph Spectrometer (UVCS/SOHO). It has become clear that to understand the dominant physical mechanisms in the nearly collisionless solar corona, each particle species must be treated individually, with its own anisotropic velocity distribution. Even minor ions which do not affect the overall energy and momentum budget of the plasma are important to measure as constraints on different theories. The primary momentum and energy deposition mechanism we investigate is the dissipation of high-frequency (ion-cyclotron resonant) Alfven waves, which can accelerate and heat ions differently depending on their charge and mass. Because the origin of these still-unobserved (kilohertz frequency) waves has not yet been determined, we model the waves as either propagating up from the coronal base or generated in the wind via turbulent cascade; we discuss methods of distinguishing between these two scenarios using the spectroscopic data. The models which best reproduce the SOHO and in-situ measurements can strongly constrain the physical processes behind the acceleration and heating of the solar wind. Also, they are useful as predictors of many qualitative features of the power spectrum of waves in the corona. Indeed, the more ionic species that are observed spectroscopically, the greater the extent in frequency space the wave spectrum can be
inferred.

This work is supported by the National Aeronautics and Space Administration under grant NAG5-3192 to the Smithsonian Astrophysical
Observatory, by Agenzia Spaziale Italiana, and by Swiss funding agencies.

UVCS Observations of Streamers and CMEs

J.C. Raymond, J.L. Kohl, G. Noci, M. Huber, E. Antonucci, G. Tondello, A. Ciaravella, J. Li, C. Benna, S. Fineschi, R. Frazin, L. Gardner, S. Giordano, J. Michels, A. Modigliani, G. Naletto, P. Nicolosi, M. Romoli, P.L. Smith, L. Strachan, and R. Suleiman 

The Ultraviolet Coronagraph Spectrometer has obtained spectra of coronal streamers and coronal mass ejections. We summarize the inferred physical parameters; density, ion and electron temperature, outflow and transverse speeds, elemental abundances. We discuss the implications for the origin of the slow solar wind and plasma heating in CMEs.

Geometry, Physical Properties and Outflow Velocities from the Polar and Equatorial Coronal Holes -- UVCS/SOHO Observations

 D. Dobrzycka, A. Panasyuk, L. Strachan, and J. L. Kohl

Coronal holes formed over the north and south heliographic poles are relatively stable structures observed to exist permanently for several years around solar minimum. They presumably contain open magnetic field lines and are known sources of the fast solar wind. However, contribution to the solar wind from the equatorial coronal holes is still unclear. We present our analysis of the UVCS/SOHO data acquired during the period of the Whole Sun Month campaign (August 10 -- September 08, 1996) when the Sun was near the minimum of solar activity. At that time the north and south polar coronal holes were large, clearly seen structures and at the end of August 1996 a large trans-equatorial coronal hole appeared on the east limb. UVCS/SOHO obtained H~I $Ly\alpha$ and O~VI ($\lambda\lambda1032,1037$) observations of the polar coronal holes and the equatorial coronal hole as it was crossing the east solar limb in late August 1996 and then, the west limb in September 1996. We compare the H~I $Ly\alpha$ and O~VI ($\lambda\lambda1032,1037$) intensities, line--of--sight velocity distributions, and kinetic temperatures for hydrogen and O$^{5+}$ ions in both types of coronal holes. Detailed analysis of the emission lines intensity, as well as the line width distribution allowed us to put constraints on the geometry of the boundaries of the coronal holes. We found evidence for superradially diverging geometry for both polar and equatorial coronal holes. Measurements of the O~VI (1032\AA) to O~VI (1037\AA) line ratio indicate that the equatorial coronal hole may have O$^{5+}$ outflow velocities that are lower than those from polar coronal holes.

UVCS Observations of Polar Regions

Poletto, G., Corti, G., Romoli, M., Kohl, J.L., Noci, G.

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 semi-qualitative 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 $R_{sun}$ 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.

ESA-SP 421, 1998, in press

Models of Plumes: Their Flow, Their Geometric Spreading, and Their Mixing With Interplume Flows

Steven T. Suess
NASA Marshall Space Flight Center/ES82, Huntsville, AL 35812, USA

 Evidence is leading to the consensus that fine filamentary structures permeate coronal holes. Plumes are the mose easily studied of these structures and, therefore, the most often modeled. There are two types of plume flow models: (i) 1D models using ad hoc spreading functions, $f(r)$. (ii) MHD models. 1D models can be multifluid, time dependent, and incorporate very general descriptions of the energetics. They confirm empirical results that plume flow is slow relative to requirements for high speed wind. But, no published 1D model incorporates the rapid local spreading at the base ($f_l(r)$) which has an important effect on mass flux. The one published MHD model is isothermal, but confirms that if $\beta=8\pi p/B^2<<1$ then the field is nearly potential below $\sim70,000$ km. Building on the MHD result, we apply a two scale approximation to calculate $f_l(r)$. We also compute the global spreading ($f_g(r)$) out to 5.0 $R_\odot$ imposed by coronal hole geometry. Modern global MHD models provide a potent method of calculating $f_g(r)$. Unambiguous plume signatures have not yet been found in the solar wind. This is probably due to strong mixing of plume and interplume flows near the Sun. We describe a physical source for strong mixing due to the observed flows being unstable to shear instabilities that lead to rapid disruption.

Comparison of SPARTAN and UVCS/SOHO Observations

D. Dobrzycka, L. Strachan, M. P. Miralles, J. L. Kohl, L. D. Gardner, P. L. Smith, S. R. Cranmer, M. Guhathakurta, & R. Fisher

We present a comparison of the HI Lyman alpha Spartan Ultraviolet Coronal Spectrometer observations of the north and south polar coronal holes in 1993-1995 with SOHO Ultraviolet Coronograph Spectrometer data obtained near solar minimum. These data span several years of the declining phase of the current solar cycle. Detailed analysis of the data revealed that the average HI Lyman alpha intensities at similar heights decreased towards solar minimum in both polar coronal hole regions. In 1993 we observed a 15% - 40% scatter in the intensities measured at the same height but different position angles within the same coronal hole. Towards solar minimum the scatter was clearly reduced. Also the shape of the Lyman alpha profile changed over the last four years. The narrow component present in 1993 data being attributed to the contribution from streamers along the line-of-sight disappeared in 1996/97. We interpret these effects as mainly due to a decrease in the number of high latitude streamers. At solar minimum streamers occupy mostly the equatorial region and do not contribute to the line-of-sight intensity as much as in 1993.

The Impact of UVCS/SOHO Observations on Models of Ion-Cyclotron Resonance Heating of the Solar Corona

S. R. Cranmer, G. B. Field, and J. L. Kohl

We examine the compatibility between theoretical models and observations of the temperatures and anisotropic velocity distributions of hydrogen and minor ions in the solar corona. The UVCS instrument on board SOHO has measured hydrogen kinetic temperatures along lines of sight in coronal holes in excess of 3 million K, and ionized oxygen kinetic temperatures of at least 200 million K. In addition, the velocity distributions in the radial direction (mainly perpendicular to the line of sight) are smaller, possibly implying temperature anisotropies of order T(perpendicular) / T(parallel) = 6 for the oxygen ions.

These properties can only be understood in terms of a mechanism which heats and/or accelerates heavier ions more than lighter ones (possibly proportionally to m_ion^q, where q > 1), and preferentially in directions perpendicular to the magnetic field. We examine various features of plasma heating by the dissipation of high-frequency ion-cyclotron resonance Alfven waves, which may be the most natural physical mechanism to produce such plasma conditions. We show that a quantitative model should predict the spectrum of waves required to reproduce the observations.

Ultraviolet Spectroscopy of Coronal Mass Ejections

A. Ciaravella, R. Raymond, S. Fineschi, M. Romoli, C. Benna, L. Gardner, S. Giordano, R. O'Neal, J. Michels, E. Antonucci, G. Noci & J. L. Kohl

Synoptic Observations of the Solar Corona with UVCS/SOHO

 L. Strachan, A. V. Panasyuk, S. Fineschi, L. D. Gardner, J. L. Kohl, E. Antonucci, S. Giordano & M. Romoli

Absolute Elemental Abundances in the Solar Corona from UVCS

J. Raymond, J. L. Kohl, G. Noci, E. Antonucci, G. Tondello, M. Huber, L. D. Gardner, S. Fineschi, M. Romoli, C. Benna, A. Ciaravella, S. Giordano, A. V. Panasyuk & R. Suleiman

National Radio Science Meeting, Boulder, CO Jan 2000

 SOHO Observations of Coronal Mass Ejections

J. C. Raymond

By combining observations made with different instruments aboard SOHO, one can derive a great deal of information about the speed, morphology, density and temperature structure of the plasma. This talk concentrates two CMEs studied by EIT, LASCO and UVCS. EIT shows the initial ejection, LASCO shows the evolving morphology and the speed, and UVCS provides doppler shifts, line widths and line intensities from which we derive the ionization state and electron and ion temperatures.

The first CME was a slow prominence eruption, and we describe the helical structure, the temperature structure and the heating requirements. For likely initial conditions, we find that the plasma did not start at coronal temperatures and that gradual heating was needed, amounting to an energy comparable to the gravitational potential energy.

The second event was a 1200 km/s CME that produced Type II radio bursts. By enormous good fortune, the radio bursts coincided with the time that the compressed gas crossed the UVCS slit. The Ly$\alpha$ intensity decreased by 10\% due to the high velocity and increasing ionization level. The O VI lines brightened by 25\% and the high temperature Si XII line doubled in brightness. We compare the densities derived from the Type II bursts with the pre-CME density estimated from the O VI doublet ratio observed by UVCS. We also discuss electron-ion and ion-ion equilibration in the collisionless shock. The very large widths of the O VI lines (900 km/s FWHM) suggests that the bulk velocities of the particles are randomized independently by the shock, and that little sharing of thermal energy among species occurs during the observation period.

Physics of Space: Growth Points and Problems (Meudon, France, January 10-14, 2000)

 Kinetic Coronal Heating

S. R. Cranmer

This talk will review the kinetic origins of several physical processes that are thought to heat the solar corona and accelerate solar wind particles. Classical dissipative phenomena (viscosity, heat conductivity, electrical resistivity) depend mainly on the strength of Coulomb collisions in the corona, but many collisionless channels for, e.g., wave or current dissipation have been proposed. Specifically, the damping of high frequency (10 to 10,000 Hz) ion cyclotron resonant Alfven waves has been proposed as a leading candidate for ion energization in the high-speed solar wind. The spectroscopic and in situ observations that have led to this conclusion will be reviewed. The ion cyclotron resonance produces a non-standard type of pitch-angle scattering in velocity space which can be expressed as a nonlinear diffusion equation. Test solutions of this equation showing the natural development of large perpendicular kinetic temperatures will be presented. Because ions with very low abundances can damp the waves, it is necessary to take a large number of ion species into account, and the summed effect of more than 2000 minor ions will be discussed. The surprisingly effective damping ability of minor ions can be understood in simple terms by applying the Sobolev approximation from the theory of hot-star winds. The mean state of the coronal and heliospheric plasma is intimately coupled with kinetic fluctuations about that mean, and theories of turbulence, wave dissipation, and instabilities must continue to be developed along with steady state solar wind models.

XLIV Congresso Nazionale S.A.It. 2000

 Risultati recenti di UVCS

E. Antonucci, S. Giordano

TRACE Meeting: Physics of the Solar Corona and Transition Region (August 24-27, 1999)

 Acceleration of the High-Speed Solar Wind

S. R. Cranmer

 This talk will review the current state of understanding about how the steady-state, high-speed solar wind is accelerated from the base of the corona to its terminal speed of 600-800 km/s. Spectroscopic observations of the extended corona (in the primary acceleration region of 1-10 solar radii) from, e.g., SOHO and Spartan 201, continue to complement in situ spacecraft measurements (at distances greater than 0.3 AU). These observations present theorists with a large number of firm constraints that must be reproduced by models. Because the majority of the fast solar wind is a collisionless plasma, it is becoming evident that the energy and momentum of electrons, protons, and minor ions should be modeled independently. Also, since departures from isotropic Maxwellian velocity distributions are observed ubiquitously, simple fluid treatments of the solar wind need to be re-examined and compared with more complete kinetic models. A large number of physical mechanisms have been postulated to provide the outward acceleration of the solar wind, and this talk will attempt to classify and re-examine these processes in the light of the most current observations. Many acceleration mechanisms rely solely on coronal heating to generate a plasma pressure able to counteract gravity, but there are also several plausible sources of direct momentum deposition. In any case, it is clear that the dynamical state of the solar wind is intimately linked with the still-unknown mechanisms that transport subphotospheric convective energy above the transition region.

European Solar Physics Meeting, Florence

STREAMER H~I Ly-alpha LINE PROFILES DURING THE  SPARTAN 2O1-05/SOHO COORDINATED OBSERVATIONS

M. P. Miralles, L. Strachan, L. D. Gardner,  D. Dobryzcka, Y.-K. Ko, J. Michels, A. Panasyuk, R. Suleiman, J. L. Kohl

ESA SP-448, p.1193-1197 (1999) European Solar Physics Meeting, Florence

We present H~I Ly-alpha observations of coronal streamers obtained by UVCS/SOHO during the coordinated observations with UVCS/Spartan on 1-3 November 1998. Two different streamer regions were observed, one relatively stable above the Northeast limb, and a post-CME streamer complex above the  Southwest limb. H~I Ly-alpha profiles and intensities were measured at 1.5 and 2~R_sun in the NE streamer and its boundary regions, and also at heights ranging from 1.5 to 2.5 R_sun in the SW streamer complex. We analyze integrated intensities and line widths in each streamer structure.

Electron Density Measurements in a Polar Coronal Hole Using HI Ly alpha and Ly beta Line

V. Krishnakumar, E. Antonucci, S. Giordano

UVCS Science Meeting 1999

Empirical Modelling of Streamers

G. Noci and L. Maccari

 UVCS Science Meeting (Marispica, Italy, 13 - 18 June 1999)

Understanding the physical properties of the solar corona by incorporating UVCS data with the solar wind in-situ measurements

Y.-K. Ko

UVCS Science Meeting (Marispica, Italy, 13 - 18 June 1999)

TRACE Meeting: Physics of the Solar Corona and Transition Region (August 24-27, 1999)

Coordinated UVCS/SOHO-TRACE observations of the solar corona

C.-R. Wu, Y.-K. Ko, S. Fineschi, A. Panasyuk, L. Strachan, J. Kohl, T. Tarbell, R. Shine, B. Handy

We present the first results of joint observations of the solar corona in HI Lyman-alpha (1215.7 A) obtained with the SOHO Ultraviolet Coronagraph Spectrometer (UVCS/SOHO) and the Transition Region and Coronal Explorer (TRACE). Together UVCS/SOHO and TRACE provide near-continuous coverage of the corona extending from the solar limb to 3.0 solar radii. Images of the extended corona (i.e. 1.5-3.0 Ro) are constructed from UVCS/SOHO synoptic data of the Lyman-alpha line. They are combined with composite images of the limb obtained at nearly the same time with the TRACE Lyman-alpha filter during their Full Disk Mosaic program. In addition, we also compare and discuss cospatial and cotemporal observations made by UVCS and TRACE at 1.5 Ro.

SOHO CELIAS 5th Post-Launch Workshop (Oct. 19-21, 1998)

The Ultraviolet Coronagraph Spectrometer (UVCS) on SOHO

Y.-K. Ko 

The Wave Driven Solar Wind

J.V. Hollweg 

International Workshop on Nonlinear Waves and Turbulence in Space Plasmas, Koeln, Germany, February 1997.

A Determination of Localized Coronal Outflow Velocities from UVCS Synoptic Data 

18th NSO/Sacramento Peak Summer Workshop, 1997
L. Strachan, A.V. Panasyuk, S. Fineschi, L.D. Gardner, J. Raymond, J.L. Kohl, E. Antonucci, S. Giordano, M. Romoli

 The Ultraviolet Coronagraph Spectrometer on SOHO has been used to determine estimates for line-of-sight averaged outflow velocities for hydrogen and O5+ in the extended solar corona. The outflow velocities are determined from an Doppler dimming analysis of the resonantly scattered intensities of H I Lyman alpha and O VI 1032/1037. These results are averages because the observed intensities contain contributions from the entire line-of-sight through the corona. While these averages may be appropriate for extended, uniform regions, e.g. coronal holes, they are not for localized structures like helmet streamers. We present here a method of producing outflow velocity maps of individual features along the line-of-sight based on 3D reconstructions from UVCS daily synoptic observations (see paper by Panasyuk, et al., this conference). It should be possible to determine outflow velocities out to 3 solar radii from Sun center using the present UVCS synoptic observations. The results from this work are important for connecting outflow velocity measurements made at the base of the corona with determinations of velocities made at higher heliocentric heights. The derived velocities can then be used to provide constraints for models of solar wind acceleration. This work is supported by NASA under Grant NAG5-3192 to the Smithsonian Astrophysical Observatory, by the Italian Space Agency, and by Swiss funding sources.

Tomographic Reconstructions of the Corona from UVCS/SOHO Synoptic Observations

18th NSO/Sacramento Peak Summer Workshop, 1997.
A.V. Panasyuk, L. Strachan, S. Fineschi, L.D. Gardner, J. Raymond, J.L. Kohl, E. Antonucci, S. Giordano, M. Romoli

 ynoptic observations from the Ultraviolet Coronagraph Spectrometer on SOHO are used to obtain spectral profiles and intensities (integrated along the line-of-sight) for a number of emission lines in the corona including H I Lyman alpha and the O VI 1032/1037 doublet. The UVCS synoptic program makes a complete scan around the Sun once per day, covering heights from 1.5 to 3 solar radii in the equatorial regions and heights from 1.5 to 2.5 solar radii in the polar and midlatitude regions. These data provide a direct measure of the line-of-sight velocities for the emitting atoms or ions. Further analysis can be used to derive densities, temperatures, and outflow velocities for hydrogen and O5+ ions in particular. Here we present the results from our efforts to resolve the line-of-sight distribution of intensities with the help of 3D reconstruction techniques. In theory, it is possible to resolve 3D spatial structures using these techniques but the analysis of the synoptic data can be complicated due to the fact that the corona is not stationary, but evolving over time. We will discuss these complications and some first results for the tomographic reconstructions. This work is supported by NASA under Grant NAG5-3192 to the Smithsonian Astrophysical Observatory, by the Italian Space Agency, and by Swiss funding sources.

(invited) E.Antonucci 
XL Riunione della SAIt `Prospettive dell'Astrofisica alle Soglie del 2000' Roma, 7--12 Maggio 1996 

SOHO early new results

(invited) Ester Antonucci 
8th European Meeting on solar physics: `Solar and heliospheric plasma physics' 13-18 May 1996, Thessaloniki, Greece

Future Space Solar Instrumentation

(invited) Ester Antonucci 
8th European Meeting on solar physics: `Solar and heliospheric plasma physics' 13-18 May 1996, Thessaloniki, Greece 

A discussion on the future perspectives of space solar physics in Europe is timely following the SOHO success. The past efforts of the european solar physics community in conceiving a space mission dedicated to the study of the Sun and in developing space instrumentation have been rewarded with a successfull launch of the SOHO satellite on December 2, 1995, and the excellent performance of its scientific payload. Following a brief comment on the novelty and impact on science of the SOHO instrumentation, the discussion will mainly focus on the existing possibilities of development for space solar physics and on the present opportunities within the programs of the major space agencies. The solar space missions already approved or under study and definition will be presented. 

First Results from UVCS

E.Antonucci 
Advances in Solar Physics Euroconferences: Advances in the Physics of Sunspots 2--6 October, 1996, Tenerife, Spain

The Ultraviolet Coronagraph Spectrometer (UVCS) started to observe the Sun at the end of January 1996. The performance of the instrument is excellent and the data obtained up to now are of great interest. The UVCS obtains UV images and white light information on the solar extended corona up to 12 solar radii and measures profiles and intensities of the H I Ly alpha, OVI lines and several minor lines such as Mg X, Si XII, Fe XII, and S X. The first results obtained by the UVCS team are the following. Spectral line profiles in coronal holes, and, in general, open field line regions, have r.m.s. velocities larger than in closed field line regions. Polar plumes have narrower profiles than the interplume regions. The O VI ratio diagnostic indicates that in polar coronal holes the outflow velocity is progressively increasing with heliodistance and exceeds 100 km/sec near 2.5 solar radii. A Doppler dimming nalysis of H I Ly alpha indicates supersonic outflows of hydrogen within 2.5 solar radii in coronal holes. A CME observation has revealed line of sight plasma motions of 100 km/sec and a complex dynamics. The global structure of the extended corona has evolved in a few months from a mainly dipolar configuration to one that also shows a quadrupolar component. Over 40 spectral lines have been observed up to now in the two UV channels of the instrument, including the emission of highly ionized ions such as Fe XVIII. The UVCS is the result of a collaborative effort between NASA and the Agenzia Spaziale Italiana (ASI), with a Swiss participation. The Scientific program is led by the Principal Investigator Dr. J. Kohl of the Smithsonian Astrophysical Observatory, in collaboration with several Italian scientific institutions coordinated by Prof. G. Noci, University of Florence, Co-Principal Investigator.

Status and major results of UVCS

E.Antonucci 
SUMER/CDS Meeting 5-7 November 1996, Paris, France 

The Sun from space: first results from SOHO 

(invited) E. Antonucci 
Scientific Satellites Achievements and Prospects in Europe, AAAF/ESA 20-22 November 1996, Paris, France 

The Solar Heliospheric Observatory (SOHO), launched on December 2, 1995, is successfully operating since its insertion in a halo orbit around the Lagrangian point L1 in February 14, 1996. SOHO, the first european solar space mission, is the most comprehensive solar observatory ever flown in space. It was conceived to broaden and complement the investigations of the major most recent solar missions, the Solar Maximum Mission (NASA) and Yohkoh (ISAS), limited to the study of the high-energy solar phenomena, observable in the high energy part of the electromagnetic spectrum. The twelve instruments onboard SOHO, that are operating in optimum observing conditions and continuously viewing the Sun, are capable of providing information on the whole star from the deep interior to the solar wind. They examine the quiet sun processes leading to the heating of the corona and the acceleration of the solar wind with unprecedented resolution and in unexplored regions of the solar atmosphere, probe the solar interior with the techniques of helio- seismology, and monitor the response of the heliosphere to solar processes. 

Impact of These Results on Theories of Solar Wind Acceleration: What is Still Viable, What Not, and Why

J. V. Hollweg 
Solar Probe Scientific Definition Team Meeting, JPL, Pasadena, CA, July 1996. 

Coronal structure and the solar wind

Suess, S. T.
Gordon Research Conference on Solar Terrestrial Physics, Henniker, New Hampshire, June 1996. 

Solar coronal structure large and small

Suess, S. T.
Osservatorio Astrofisico di Arcetri, Firenze, Italy, September 1996.