UVCS/SOHO ABSTRACTS
SOHO MEETINGS

Abstract is available here

Invited Review: Theoretical Aspects of Wave Acceleration in Open Magnetic Structures

L. Ofman

Abstract is available here

Acceleration of the Solar Wind through Minor Ions

Xing Li

Abstract is available here

Ion heating across the magnetic field in the solar corona

Y. Voitenko and M. Goossens

Abstract is available here

Observational constraints on ion acceleration by waves in coronal holes

I. D. Xia and E. Marach

Abstract is available here

ESA SP-508, pp.351-359

UVCS/SOHO has been used to measure the plasma properties of several types of coronal holes from 1996 to early 2002 at heights from 1.5 to 3.5 R_sun. UVCS observations show a variation in ion properties between coronal holes from solar minimum to solar maximum. Different coronal holes seem to exhibit different heating and acceleration rates. Polar coronal holes at solar minimum exhibited the most extreme ion properties with O^5+ perpendicular temperatures in excess of 2x10^8 K, O^5+ outflow speeds of at least 400 km/s by 3 R_sun, and the lowest densities. Equatorial coronal holes at solar maximum exhibited the least extreme ion plasma properties with O^5+ perpendicular temperatures less than 8x10^7 K, O^5+ outflow speeds of only 100 km/s by 3 R_sun, and the largest densities. However, large polar and equatorial coronal holes produce interplanetary wind streams with similar speeds (v~700 km/s). Thus, most of the solar wind acceleration in large equatorial coronal holes must occur above 3 R_sun. The first high-latitude coronal hole of the new negative magnetic polarity observed at the north in 2001 exhibited extreme properties similar to those of the 1996--1997 polar coronal holes, even though it was 6 years prior to the next minimum. During 2001--2002, we have observed mid-latitude coronal holes, with properties in between large polar and equatorial coronal holes.

Spectroscopic diagnostics of CME material

J.C. Raymond

ESA SP-508, pp.421-430

SUMER, CDS and UVCS provide unique spectroscopic diagnostics of CME material both in the Doppler shifts and the line intensities. The Doppler shift information complements imaging data from LASCO and EIT, providing a probe of the structure of the expanding plasma along the line-of-sight. The line intensities provide unique information about the density, temperature and ionization state of the expanding plasma. Both very high and very low ions have been detected, H I to [Fe XIX]. The combination of temperature, density and temperature constrains the thermal history of the CME plasma.

Solar Wind Acceleration in Coronal Holes

Steven R. Cranmer

ESA SP-508, pp.361-366

This paper reviews the current state of our understanding of high-speed solar wind acceleration in coronal holes. Observations by SOHO, coupled with interplanetary particle measurements going back several decades, have put strong constraints on possible explanations for how the protons, electrons, and minor ions receive their extreme kinetic properties. The asymptotic plasma conditions of the wind depend on energy and momentum deposition both at the coronal base (where, e.g., the mass flux is determined) and in the extended acceleration region between 2 and 10 solar radii (where the plasma becomes collisionless and individual particle species begin to exhibit non-Maxwellian velocity distributions with different moments). The dissipation of magnetohydrodynamic fluctuations (i.e., waves, turbulence, and shocks) is believed to dominate the heating in the extended corona, and spectroscopic observations from the UVCS instrument on SOHO have helped to narrow the field of possibilities for the precise modes, generation mechanisms, and damping channels. We will survey recent theoretical and observational results that have contributed to new insights, and we will also show how next-generation instruments can be designed to identify and characterize the dominant physical processes to an unprecedented degree.

Contributed Papers

Page numbers are given for papers when available in conference proceedings:
ESA SP-508 (SOHO-11: From Solar Minimum to Solar Maximum - Half a Solar Cycle with SOHO).
Full text of papers available; click here or or search under [Papers & Abstracts] --> [PAPERS [2002]] on the UVCS home page.

THE RADIOMETRIC CALIBRATION AND INTERCALIBRATION OF SOHO

M.C.E. Huber, A. Pauluhn and R. von Steiger

ESA SP-508, pp.213-214

The radiometric calibration of spectrometric telescopes assures that the observed spectral radiance (or irradiance) is measured on a scale that is defined by the radiometric standards realized and used in terrestrial laboratories. All SOHO instruments therefore have been calibrated by use of source and detector standards that are traceable to the primary radiometric standards. In two workshops held at the International Space Science Institute in Bern the individual instrument calibrations were discussed and reconciled. The outcome of the workshops, to which all instrument groups contributed, is summarized in a book that is presented here before it goes to press.

CURRENT SHEETS AND STREAMER STRUCTURE IN THE CORONA THROUGH THE SOLAR CYCLE

E. Gavryuseva, G. Noci, and E. A. Gavryuseva

We analyzed the UVCS and LASCO data taken in 1996-2001 from minimum up to maximum of solar activity, and later, after the change of the polarity to reveal the structure of the streamers. The distribution of the coronal brightness in H I, O, and white light was compared with the photospheric magnetic field observations in WSO and with the calculations of the current sheet position. The recurrent predictions for the coronal magnetic field structure are suggested.

SOLAR CYCLE VARIATION OF UV SPECTRAL LINES IN THE EXTENDED SOLAR CORONA

S. Giordano, M. Romoli, and C. Benna

The UVCS instrument onboard SOHO has measured UV spectral lines intensities and profiles, and broadband visible light polarized brightness (pB) in the extended solar corona from 1996 to present. For the first time, there is a large set of data with fine temporal coverage, able to describe the physical condition of the extended corona, spanning the solar cycle from minimum to maximum of the solar activity. The daily synoptic observations of H I Lyman alpha and O VI 103.2 and 103.7 nm lines prO VIde line intensities and velocity distributions along the line–of–sight for hydrogen atoms, whereas the special observations with high spectral resolution have been used to derive the velocity distributions for oxygen ions. In addition, simultaneous observations of pB performed with the UVCS/WLC allow us to determine to electron density distribution and its effect on the observed UV line intensities. The variation of measured parameters has been studied at different latitudes (equatorial, polar, mid) and at different heliocentric distances in order to obtain the global change of the extended solar corona throughout the transition between minimum and maximum of the solar activity. In particular, the variation with solar cycle of H I Ly-alpha intensity and O VI line ratio, through the Doppler dimming technique, give a signature of the different origin and regimes of slow and fast solar wind from minimum to maximum of solar activity.

TRANSITION FROMFAST TO SLOWSOLAR WIND AT SOLAR MAXIMUMIN THE INNER CORONA

S. Rifai Habbal and R. Woo

Probing the physical conditions of different ion species in the inner corona out to 10 R_sun has been made possible for the first time with the Ultraviolet Coronagraph Spectrometer (UVCS) on SOHO. One of the intriguing and unresolved problems is how does the transition from the fast to the slow solar wind occur, and where do the sources at the Sun of these two types of wind reside. These issues are particularly puzzling at solar maximum when polar coronal holes are significantly reduced in size. Using UVCS observations made at high latitudes in May 2000, close to solar maximum, we prO VIde some answers to these questions. We also show how these results compare with solar minimum conditions.

COMPARISON OF OUTFLOW PROPERTIES OF EQUATORIAL AND POLAR CORONAL HOLES OBSERVED WITH SOHO/SUMER

D. M. Hassler, E. Buchlin, and H. Jones

SUMER observations have prO VIded new insight into the source region of the solar wind, and its relationship to the chromospheric magnetic network. Specifically, velocity maps in Ne VIII, formed at the base of the corona, show a relationship between outflow velocity and the underlying network structure (Hassler et al., SCIENCE, 1999). We present observations from a campaign performed in November 1999 involving several of the instruments on SOHO (SUMER, CDS, EIT, UVCS, MDI), TRACE, and Kitt Peak. Extensive, coordinated observations were made of a large equatorial coronal hole which rotated from the East limb to the MDI high-resolution field-of-view at central meridian. Intensity, line-of sight velocity, and line width maps were produced for emission lines formed at several heights in the solar atmosphere as the coronal hole rotated across the disk. We compare the outflow properties observed in this equatorial coronal hole with previous observations of a polar coronal hole. Preliminary results suggest that outflow velocities are lower in this equatorial coronal hole than in previous observations of a polar coronal hole. These different observed velocities may be related to the different degrees of expansion of the solar wind flux tubes in equatorial and polar regions.

OBSERVATIONS OF TWO CORONAL MASS EJECTIONS BY UVCS-SOHO

R. Ventura and D. Spadaro

UVCS - SOHO spectroscopic observations of two coronal mass ejections have been analyzed in order to get information on the distributions of ionic densities and flow velocities in the solar coronal plasma ejected during these transient events. Intensity and profile of the O VI resonant doublet lines (103.2 and 103.7 nm) and H I Ly-alpha line, together with the intensity of some other minor ions have been computed. LASCO and EIT simultaneous observations of both CMEs helped the authors in better defining the morphology of the bright regions involved in the transients.

CORONAL HOLE-STREAMER INTERFACE AND THE SOURCE OF THE SLOWWIND

L. Abbo and E. Antonucci

ESA SP-508, pp.477-480

We present preliminary results of an investigation concerning the source of the variable slow solar wind that emerges from the corona adjacent to the fast streams, originating in coronal holes, and that dominates the low latitude heliosphere during the minimum of solar activity. In order to investigate the sources of the slow solar wind, it is important to determine the physical conditions, such as kinetic temperature of ions, electron density, outflow velocity of the wind, across the boundary of streamers. The present study is based on data obtained with the Ultraviolet Coronagraph Spectrometer onboard SOHO, relative to streamers observed at mid-low latitudes, in the years 1996, 1997 and 1998. The analysis is based on the ad hoc diagnostics techniques developed to obtain the solar wind velocity, the density and the abundance of the coronal plasma based on the O VI 103.2 and 103.7 nm and the H I 121.6 nm lines.

TEMPORAL PROFILE OF POLAR WIND FROM SOHO-SUN-ULYSSES QUADRATURE DATA: PRELIMINARY RESULTS

R. Aznar Cuadrado, G. Poletto, L. Teriaca and S. T. Suess

ESA SP-508, pp.481-484

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 degrees 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 degrees, 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 radii, 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 H I Lyman-alpha and in the 103.2 and 103.7 nm O VI doublet lines have been made at 1.6 and 2 R_sun. 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 interpretation of the data is outlined.

LATITUDINAL PROFILE OF HEAVY IONS OUTFLOWS IN A POLAR CORONAL HOLE AT MINIMUM ACTIVITY

L. Zangrilli, G. Poletto, P. Nicolosi, G. Noci and M. Romoli

ESA SP-508, pp.493-496

UVCS observations of a polar coronal hole, acquired in August 1996, have been analysed with the purpose of deriving the latitudinal profile of the outflow speed of heavy ions in the altitude range between 1.4 and 2.6 R_sun and latitudes between 40 and 90 degrees. To this end, electron densities and O VI outflow speeds have been derived from a Doppler dimming analysis of the 103.2 and 103 7 nm O VI doublet lines. The coronal hole morphology has been modeled with a simple magnetic field geometry; the O VI line intensities and the oxygen mass flux at 1 A.U. have been used as constraints for identifying the physical conditions of the plasma where lines originate. The free parameter that allowed us to reproduce the O VI line intensities and ratios, as well as to comply with the requirement of a constant mass flux throughout the region we examine, is the O VI ion parallel kinetic temperature, for which we have no direct information from observations. It turns out that the temperature anisotropy T(parallel)/T(perpendicular) (where T(perpendicular) has been derived from the line widths) 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 a speed of ~350 km/s, at the highest level we consider, 2.6 R_sun, in polar regions. However, as the latitude decreases, the outflow speed tends to decrease, and, for latitudes lower than 60 degrees, and altitudes greater than 2 R_sun, keeps below 300 km/s. Results from this study are compared with those from similar analysis as well as with predictions from theoretical works.

1999

ESA SP-446, pp. 317-320 (1999)

In the extended corona, the state of linear polarization of ultraviolet (UV) line emission, is affected by the presence of magnetic fields. 
This provides a useful diagnostics of the coronal magnetic field, that, to date, is still largely unknown. The interpretation through the {\it Hanle effect} of the strength and direction of the polarization vector of the H~I~Lyman series lines (i.e., Ly--$\alpha$, 1216~\AA, Ly--$\beta$, 1025~\AA, Ly--$\gamma$, 972~\AA) yields information on the vector magnetic field in corona. The polarization direction of the O~VI, 1032~\AA, line is  affected by non-radial outflow velocities of the solar wind. This may be used to obtain information on the coronal field topology. The parameter study presented here shows that the H~I~Lyman series lines have sensitivities to the field stregths larger than 1~gauss, at heliocentric heights comprised between 1.2 to 2~solar radii. The {\it Advanced Solar Coronal Explorer} mission, briefly described here, is designed to carry out spectro-polarimetric measurements of these UV  coronal lines.

Resonant heating of protons and ions in coronal holes: two-proton closure

J. V. Hollweg

in Proc. 8th SOHO Workshop, ESA SP-446, pp. 357-362.

The ion-cyclotron mode does not extend above the proton cyclotron frequency. Thus only roughly half of the protons can be in resonance. We calculate the trajectories of individual protons in the electric, magnetic, and gravitational fields in a coronal hole, and we include the resonant heating and acceleration for an average resonant particle. To provide closure we consider two protons, which are proxies for the resonant and non-resonant halves of the distribution. For dispersive waves, k_res becomes large. If the dissipation is determined by a turbulent cascade, k_res controls the relative importance of resonant acceleration and resonant heating. Such models yield good agreement with what is known about the behavior of protons in coronal holes. We also consider, in a cruder model, the behavior of minor ions such as O+5. We show qualitatively how such ions can be more than mass-proportionally heated, and that dispersion is important. We also show that the observed radial profile of T_perp for O+5 requires a steep power spectrum. It is concluded that the cyclotron resonance can account for many observed features of protons and heavy minor ions in coronal holes. However, the source of the resonant waves remains uncertain. 

A Short Tutorial on Kinetic Aspects of Cyclotron Resonances in Coronal Holes

J. V. Hollweg

ESA SP-446, 53, in Proc. 8th SOHO Workshop

Coronal hole boundaries and interactions with adjacent regions: Summary of working group 3

R. Esser

Summarized below are the discussions of working group 3 on ``Coronal hole boundaries and interactions with adjacent regions'' which took place at the 7th SOHO workshop in Northeast Harbor, Maine, USA, 28 September to 1 October 1998. A number of recent observational and theoretical results were presented during the discussions to shed light on different aspects of coronal hole boundaries. The working group also included presentations on streamers and coronal holes to emphasis the difference between the plasma properties in these regions, and to serve as guidelines for the definition of the boundaries. Observations, particularly white light observations, show that multiple streamers are present close to the solar limb at all times. At some distance from the sun, typically below 2 $R_S$, these streamers merge into a relatively narrow sheet as seen in for example LASCO and UVCS images. The presence of multiple current sheets in interplanetary space was also briefly addressed. Coronal hole boundaries were defined as the abrupt transition from the bright appearing plasma sheet to the dark coronal hole regions. Observations in the inner corona seem to indicate a transition of typically10 to 20 deg,  whereas observations in interplanetary space  carried out from Ulysses, show on one hand,an even faster transition of less than 2 deg which is in agreement with earlier HELIOS results. On the other hand, these observations also show that the transition happens on different scales, some of which are significantly larger.  The slow solar wind is connected to thestreamer belt/plasma sheet, even though, the discussions were still not conclusive on the point where exactly the slow solar wind originates. Considered the high variability of plasma characteristics in slow wind streams, it seems most likely that several types of coronal regions produce slow solar wind, such as streamer stalks, streamer legs and open field regions between active regions, and maybe even regions just inside of the coronal holes. Observational and theoretical studies presented during the discussions show evidence  that each of these regions may indeed contribute to the solar slow wind.

Constraints on Coronal Outflow Velocities Derived from UVCS Doppler Dimming Measurements and In-Situ Charge State data

L. Strachan, Y.-K. Ko, A. V. Panasyuk, D. Dobrzycka, J.L. Kohl, M. Romoli, and G. Noci

We constrain coronal outflow velocity solutions, resolved along the line-of-sight, by using Doppler dimming models of HI Lyman alpha and O VI 1032/1037 Angstrom emissivities obtained with data from the Ultraviolet Coronagraph Spectrometer UVCS on SOHO. The local emissivities, from heliocentric heights of 1.5 to 3.0 radii, were determined from 3-D reconstructions of line-of-sight intensities obtained during the first Whole Sun Month Campaign 10 Aug.to 8 Sept. 1996. The models use electron densities derived from polarized brightness measurements made with the visible light coronagraphs on UVCS and LASCO, supplemented with data from Mark III at NCAR/MLSO. Electron temperature profiles are derived from freezing-in temperatures obtained from an analysis of charge state data from SWICS/Ulysses. The work concentrates on neutral hydrogen outflow velocities which depend on modeling the absolute coronal HI Ly alpha emissivities. We use an iterative method todetermine the neutral hydrogen outflow velocity with consistent values for the electron temperatures derived from a freezing-in model.

Spectroscopic Constraints on Models of Ion-Cyclotron Resonance Heating in the Polar Solar Corona

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

Using empirical velocity distributions derived from UVCS and SUMER ultraviolet spectroscopy, we construct theoretical models of anisotropic ion temperatures in the polar solar corona. The primary energy deposition mechanism we investigate is the dissipation of high frequency (10--10000 Hz) ion-cyclotron resonant Alfven waves which can heat and accelerate ions differently depending on their charge and mass. We find that it is possible to explain the observed high perpendicular temperatures and strong anisotropies with relatively small amplitudes for the resonant waves. There is suggestive evidence for steepening of the Alfven wave spectrum between the coronal base and the largest heights observed spectroscopically. Because the ion-cyclotron wave dissipation is rapid, even for minor ions like O^{5+}, the observed extended heating seems to demand a constantly replenished population of waves over several solar radii. This indicates that the waves are generated gradually throughout the wind rather than propagated up from the base of the corona.

Composition and Elemental Abundance Variations in the Solar Corona Solar Atmosphere and Solar Wind

John C. Raymond

Order of magnitude variations in the relative abundances are observed in the solar corona and solar wind. The instruments aboard SOHO make it possible to explore these variations in detail to determine whether they arise near the solar surface or higher in the corona. First Ionization Potential (FIP) effect is clearly seen, and that must arise in the chromosphere, whilefrom gravitational settling is observed at larger heighers in quiescent streamers.

COMPOSITION VARIATIONS IN THE SOLAR CORONA AND SOLAR WIND

Raymond, J.C.

Order of magnitude variations in relative elemental abundances are observed in the solar corona and solar wind. The instruments aboard SOHO make it possible to explore these variations in detail to determine whether they arise near the solar surface or higher in the corona. A substantial enhancement of low First Ionization Potential (FIP) elements relative to high FIP elements is often seen in both the corona and the solar wind, and that must arise in the chromosphere. Several theoretical models have been put forward to account for the FIP effect, but as yet even the basic physical mechanism responsible remains an open question. Evidence for gravitational settling is also found at larger heights in quiescent streamers. The question is why the heavier elements don't settle out completely.

Variation of Polar Coronal Hole properties with Solar Cycle,

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

I Lyman alpha observations of polar coronal holes were obtained from three SPARTAN-201 flights (in 1993, 1994, and 1995) and the more recent UVCS/SOHO mission. These data span several years of the declining phase, the minimum, and currently rising phase of a solar cycle. We apply the latest laboratory calibration to the UVCS/SPARTAN data and analyze them using various diagnostic techniques. We obtain constraints on the changes of the HI Lyman alpha intensity, profile, hydrogen line-of-sight velocity distribution and outflow velocities. We compare UVCS/SPARTAN HI Lyman alpha observations with UVCS/SOHO to characterize variation of the plasma parameters in the polar coronal holes over a five year period.

Comparison of Polar and Equatorial Coronal Holes observed by UVCS/SOHO - Geometry and Physical Properties

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

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, stable structures and at the end of August 1996 a large trans-equatorial coronal hole appeared on the east limb. UVCS/SOHO obtained HI Lyman alpha and OVI (103.2,103.7 nm) 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 HI Lyman alpha and OVI (103.2,103.7 nm) intensities, line-of-sight velocity distributions, and kinetic temperatures for hydrogen and O5+ ions in both types of coronal holes. Detailed analysis of the emission line intensities, as well as the line width distribution allowed us to put constraints on the geometry of the boundaries of the coronal holes. We modeled the boundaries with flow tubes that expand radially or super-radially and found evidence for superradially diverging geometry for both polar and equatorial coronal holes. Measurements of the OVI (103.2 nm) to OVI (103.7 nm) line ratio indicate that the equatorial coronal hole may have O5+ outflow velocities that are lower than those from polar coronal holes.

Invited Talk: Instrument Highlight

J. L. Kohl, G. Noci, E. Antonucci, T. Tondello, M. C. E. Huber, L. D. Gardner, P. Nicolosi, L. Strachan, A. Ciaravella, S. R. Cranmer, S. Fineschi, A. Panasyuk, G. Poletto, J. C. Raymond & M. Romoli

A brief review of the UVCS/SOHO results from the first year of science operations will be presented. A highlight is the observation of spectral line profiles demonstrating that the widths of velocity distributions perpendicular to the apparent magnetic field in polar coronal holes depend on the mass of the particles and can be very large, for example, the velocity at 1/e for O^5+ at a heliocentric height of 3 Rsubsun is typically 500 km/s while the value for protons is about 200 km/s. An upper limit for the same quantity along the apparent magnetic field is a factor of 6 smaller. The most natural explanation of this result is that ion cyclotron resonance is playing a role in the velocity distributions of at least the O^5+. Observations of equatorial streamers reveal a similar behavior, but at larger heights. Posters providing more details of the UVCS results will be introduced.

This work was supported by NASA Grant NAG5-3192 to the Smithsonian Astrophysical Observatory, the Italian Space Agency and Swiss funding sources.

Invited Talk on a Meeting Theme

G. Noci, J. L. Kohl, L. Maccari, M. Romoli, J. C. Raymond, D. Spadero, L. D. Gardner & P. Nicolosi

KOPP, R. A.

Conceptually, coronal streamers can form (and disappear) by either of two distinct processes: (1) plasma 'filling' and outward distention of a preexisting closed magnetic structure; and (2) magnetic reconnection, for whatever reason, of an open bipolar field configuration. We argue that the majority of stable-appearing streamers on the Sun at any time are in fact of the latter category - namely, open-field structures undergoing gradual reconnection. Quasi-steady (i.e., 'convectively relaxed') reconnection models may be required to explain the narrow high-density cores exhibited by most streamers out to distances of many solar radii. Some of the observational signatures of reconnection within streamers, which the instrumentation aboard SOHO may be capable of detecting are discussed.

Signature of open and closed field lines in the extended corona

E. Antonucci¹, S. Giordano², C. Benna², J.L. Kohl³, G. Noci⁴

¹ Observatory of Torino, Torino, Italy 
² University of Torino, Torino, Italy 
³ Harvard-Smithsonian Center for Astrophysics, Cambridge, US 
⁴ Università di Firenze, Firenze, Italy

The Ultraviolet Coronagraph Spectrometer (UVCS) on SOHO has observed the full corona at high spectral resolution (0.2 Å) in several coronal UV lines within 1.5 and 4 solar radii. The full corona was covered in 12 days of observations during August-September 1996. The high spectral resolution observations were aimed to characterize thermal and non-thermal velocity fields. The major result obtained is that open field line regions, where we expect the high-speed solar wind flow, are characterized by O VI 1032 and HI Ly  1216 lines which are broader than in equatorial and mid-latitude streamers.

The effect is much more pronounced in the O VI line. The broadening enhancement in open field line regions is increasing with distance from the Sun. These observations have allowed us to reconstruct global solar corona maps of the line-of-sight velocity fields giving origin to line broadening.

Working Group: 6.

C. Benna¹, E. Antonucci², J.L. Kohl³, G. Noci⁴, S. Fineschi,³, S. Giordano¹, D. Spadaro⁵

¹ University of Torino, Torino, Italy 
² Observatory of Torino, Torino, Italy 
³ Harvard-Smithsonian Center for Astrophysics, Cambridge, US 
⁴ Università di Firenze, Firenze, Italy 
⁵ Osservatorio Astrofisico di Catania, Catania, Italy

The ultraviolet corona was observed with UVCS in the HI Ly  1216, HI Ly  1025, O VI 1032-1037, Si XII 520-499, Fe XII 1242, N V 1239, S X 1196 at high spectral resolution (0.2 Å) and a spatial resolution of 20 arcsec within 1.25 and 3.5 solar radii in April-May 1997. Here we present the results obtained from these observations on the topology of the global corona in the different lines. The relevance of this observation is that coronal features and in particular streamers are mapped from 1.25 to 1.5 solar radii, where they are seldom observed with the Ultraviolet Coronagraph Spectrometer (UVCS). Mid-latitude and equatorial streamers in HI Ly  and O VI appear very often to have different configurations outside of 1.5 solar radii, that is, a bifurcation in oxygen not observed in the Ly  line (Noci et al. 1997, Kohl et al. 1997). Here we show that such a bifurcation can also occur in the inner corona.

Working Group: 6.

A. Ciaravella¹, J. Raymond², S.Fineschi²,M. Romoli³,C. Benna⁴,L. Gardner²,S. Giordano⁴,R. O'Neal²,J. Michels²,E.Antonucci⁵,G. Noci³,J. Kohl²

¹ European Space Agency Smithsonian Astrophysical Observatory 
² Harvard-Smithsonian Center for Astrophysics 
³ University of Florence, Italy 
⁴ University of Turin, Italy 
⁵ Astronomical Observatory of Turin, Italy 

The Ultraviolet Coronagraph Spectrometer (UVCS) aboard SOHO observed a coronal mass ejection (CME) at ultraviolet wavelengths providing unprecedentedly very detailed diagnostics of physical and dynamical parameters of ejected plasmas. We present the CME observed on December 23 1996 for 1h and 50min at heliocentric height of 1.5 R. The Lyman lines of hydrogen are very bright and show excursions of more than two orders of magnitude during the CME evolution, as well as the C III line at 977.02 Å. Low temperature lines, like N III (989.79 Å, 991.58 Å), N II (1084.56 Å), N V (1242.80 Å), have also been detected. During the rise phase of the CME, absorption is seen in the hot coronal line of Si XII (499 Å). Lines widths show non-thermal line broadening due to an expansion of plasma with velocity larger than 50 km/s. The Ly line shift inside the CME region shows red and blue shifts, up to 0.2 Å ( 50km/s) and 0.8 Å( 200 km/s) respectively.

Working Group: 5.

Gianni Corti¹, Giannina Poletto², Marco Romoli¹, Joe Michels³, John Kohl³ and Giancarlo Noci¹

¹ Università di Firenze, Firenze, Italy 
² Osservatorio di Arcetri, Firenze, Italy 
³ Harvard Smithsonian Center for Astrophysics, Cambridge, MA 02138, USA 

UVCS data acquired in coronal holes between 1.5 and 2.3  have been analyzed with the aim of deriving some information about the physical parameters of the plume and interplume plasma at these heights. To this end, we used intensity and profiles of Hydrogen Lyman- and of OVI 1032 and 1037 Å lines to infer the profiles of electron density, kinetic temperature and flow speed vs. height. The density profile is in good agreement with previous estimates obtained from white light observations and represents the first determination of densities from UV lines in this range of altitudes; OVI kinetic temperatures are much higher than H kinetic temperatures, and both increase with heliocentric distance, as indicated by prior analyses of UVCS observations. Plasma flow speeds range between  50 km/s at 1.5  and  150 km/s at altitudes > 2  and there are indications for a super-radial flow expansion. These estimates are based on several assumptions which are here thoroughly discussed. Implications of our results are also illustrated. 

Working Group: 3.

S. R. Cranmer¹, J. L. Kohl¹, G. Noci², L. Strachan¹, A. V. Panasyuk¹, M. Romoli², S. Fineschi¹, D. Dobrzycka¹, J. C. Raymond¹, R. M. Suleiman¹, and R. H. O'Neal¹

¹ Smithsonian Astrophysical Observatory, Cambridge, MA 02138, USA 
² Università di Firenze, I-50125 Firenze, Italy

We develop a self-consistent empirical model for the major plasma parameters in a solar-minimum coronal hole using UVCS/SOHO. The model describes the radial and latitudinal distribution of density, velocity, and kinetic temperature for electrons, neutral hydrogen, and ionized oxygen, during the period between November 1996 and April 1997. This model is intended to provide experimental values which can be used to constrain theoretical models of the fast solar wind. We present models of the 3D electron density structure of coronal holes between 1.5 and 4 solar radii, including a statistical analysis of the distribution of polar plumes. We then compare observations of Lyman alpha and O VI 1032, 1037 emission lines with Doppler-dimming models, and iterate for optimal consistency in all derived velocities. The large line widths of H I atoms and O VI ions at most radii (corresponding to line-of-sight velocities around 250 and 500 km/s, respectively) are incompatible with either thermal equilibrium or common small-scale motions. The inferred kinetic temperatures are proportional to the ion mass to a higher power than unity. 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 implications on various theoretical models of coronal heating and acceleration. 

Working Group: 3.

R. Esser¹, R. Edgar¹ , N.Brickhouse¹

¹ Harvard-Smithsonian Center for Astrophysics, Cambridge MA, USA 

Flow speedsw derived from recent chromospheric/transition region and coronal observations indicate that the solar wind acceleration process takes place at heights in the solar atmosphere much lower than previously imagined (Dupree et al. 1996). Doppler dimming observations of the O VI 1032/1037 Å spectral lines show that this is not only true for the background electron-proton solar wind but also for minor ions (Kohl et al. 1997). The limits that these observations place on the flow speed of the O⁺⁵ ions are at least a factor of 3 to 4 higher than expected from earlier minor ion studies. We investigate what these high outflow speeds imply for the interpretation of in situ charge state measurements. Under non-equilibrium conditions the interpretation of these observations is only possible in the context of models since the ion ratios are extremely sensitive functions of the electron density, electron temperature and minor ion outflow speeds. Using the newest available atomic data together with most recent observational constraints on electron temperatures, electron densities and flow speeds, we show that high minor ion outflow speeds of the order of the O⁺⁵ outflow speed (about 130 to 230 km s^-1 below 3 R_S) are in agreement with charge state observations. We then discuss how minor ion charge state observations can be used in future observational and theoretical studies to place limits on solar wind acceleration and heating mechanisms.

Working Group: 3. 

S. Fineschi¹, J.L. Kohl¹, L. Strachan¹, L.D. Gardner¹, M. Romoli², M.C. Huber³ and G. Noci²

¹ Harvard-Smithsonian Center for Astrophysics, Cambridge, MA, USA 
² Università di Firenze, Firenze, Italy 
³ Space Science Dept., ESA/ESTEC, Noordwijk, The Netherlands 

Spectroscopic measurements are presented of the electron scattered HI Lyman- observed with the Ultraviolet Coronagraph Spectrometer (UVCS) in an equatorial streamer, on April 28, 1997. The different contributions to the instrument background (i.e., grating scattering, Fraunhofer diffraction, and detector background) have been carefully characterized, and the analysis of each contribution is presented.
The line intensity of the Thomson scattered HI Lyman- is proportional to the coronal electron density. The measured intensity is consistent with the polarized brightness (pB) of the visible K-corona measured with UVCS.
From the line profile, a preliminary value of the electron temperature of the observed coronal region has been derived. 

Working Group: 4.

S. Fineschi¹, M. Romoli², A. Renzi², A. Ciaravella^1,3 J.L. Kohl¹, G. Noci² and D. Biesecker⁴

¹ Harvard-Smithsonian Center for Astrophysics, Cambridge, MA, USA 
² Università di Firenze, Firenze, Italy
³ European Space Agency 
⁴ Birmingham University, Birminghan, UK 

The Ultraviolet Coronagraph Spectrometer (UVCS) of the SOHO mission has observed, in the solar corona and on the disk, the Lyman-, -, and - lines of the HI-Lyman series. The observations in these spectral lines, presented here, include absolute intensities, profiles, and images of coronal streamers, polar holes, and mass ejections (CMEs).
From the simultaneous observation in corona of several lines of the HI-Lyman series, the relative contribution to the total line intensity of the radiative and collisional components can be derived. The collisional component is proportional to the square of the electron density, N_e², averaged along the line of sight (los). The radiative component, on the other hand, is proportional to N_e, averaged along the los. The comparison between these two components, together with LASCO measurements of the K-corona polarized brightness, is used as a diagnostics of the coronal electron density inhomogeneity (i.e., filling factor).

The potential use is also discussed of polarimetric observations of HI-Lyman series lines for coronal magnetic field diagnostics (Hanle effect). The Hanle effect of coronal H-Lyman series lines is expected to be sensitive to magnetic field strengths as small as a few gauss. 

Working Group: 6.

Lyndsay Fletcher¹ and Martin C.E.Huber¹

¹ ESA Space Science Department, ESTEC, P.O.Box 299, 2200 AG Noordwijk, The Netherlands 

Indications from the UVCS instrument are that O⁵⁺ ions in the fast solar wind are accelerated by a selective (resonant) process (eg., Kohl 1996, in ESA Information note 23-96). We address the problem of O⁵⁺ wave-particle acceleration and present the results of preliminary simulations of O⁵⁺ resonance with shear Alfvén waves in open field structures in the solar wind. Such waves are generated by low energy ( 5keV) non-thermal electrons beams, which in turn could be generated by small reconnection events, such as bright-point activity lower in the corona. With this in mind, we look for observational evidence of variations in the O⁵⁺ velocity diagnostic in and out of polar plumes, which are possibly rooted in small magnetic features in the coronal hole.

Working Group: 3.

S. Giordano¹, E. Antonucci², C. Benna¹, M. Romoli³, G. Noci³, J.L. Kohl⁴

¹ University of Torino, Torino, Italy 
² Observatory of Torino, Torino, Italy 
³ Università di Firenze, Firenze, Italy 
⁴ Harvard-Smithsonian Center for Astrophysics, Cambridge, US 

The first spectroscopic observations obtained with the Ultraviolet Coronagraph Spectrometer (UVCS) on SOHO in the O VI 1032 line have revealed differences in the physical characteristics of the plume and interplume regions in polar coronal holes (Kohl et al. 1997, Antonucci et al. 1997). In particular O VI lines are much broader within plumes and the effect is increasing with distance from the Sun. In this paper we present an analysis of O VI 1032 and H Ly  1216 line broadenings and O VI 1032-1037 doublet intensity ratio obtained in several observations of polar regions during subsequent runs of the Joint Observing Programs (JOP2) aimed to characterise the temperature structure and outflow velocity in polar regions.

Working Group: 3. Category 2nd choice: 2. 

S. Giordano¹, E. Antonucci², G. Noci³, J.L. Kohl⁴, D. Spadaro ⁵, C. Benna¹

¹ University of Torino, Torino, Italy 
² Observatory of Torino, Torino, Italy 
³ Università di Firenze, Firenze, Italy 
⁴ Harvard-Smithsonian Center for Astrophysics, Cambridge, US 
⁵ Osservatorio Astrofisico di Catania, Catania, Italy

The coronal region behind the front of the coronal mass ejection detected by the LASCO coronagraph on June 6-7, 1996, was observed from 1.5 to 3  in several ultraviolet emission lines by the Ultraviolet Coronagraph Spectrometer (UVCS). In this region we have identified, in the O VI 1032 line, a bright feature which we presume is magnetically connected to the front of the coronal mass ejection. This structure is clearly characterized by a lower temperature (9 10⁵ K) than in the surroundings (1.5 10⁶ K) and by either circular or helical motions, which we suggest are evidence of untwisting magnetic fields in the erupted flux rope. The identified motions are characterized by line of sight velocities of the order of 30-50 km/sec, as derived by the Doppler shifts of the HI Ly  line.

Working Group: 5.

S. R. Habbal¹, R. Woo², S. Fineschi¹ and J. L. Kohl¹

¹ Harvard-Smithsonian Center for Astrophysics, 60 Garden St., Cambridge, MA 02138, USA 
² JPL, 4800 Oak Grove Rd., Pasadena, CA 91109, USA

Using observations made with the Ultraviolet Coronagraph Spectrometer (UVCS) on SOHO during the Galileo and NEAR spacecraft solar conjunctions in January and February 1997, as well as during a specially tailored observing sequence in April 1997, we show how the latitudinal transition from fast to slow solar wind occurs within  10?° of the axis of streamers by 5 solar radii. The UVCS observations also show that the slow solar wind is limited to a  10?° halo around the axes of streamers, with the slowest wind flowing along their axes. These results derive from the use of the Doppler dimming/pumping of the two oxygen 1032 and 1037 Å lines, and the changes in the ratio of their intensities. These UVCS observations offer the first direct confirmation of the recent suggestion by Woo and Habbal [GRL, 24, 1159, 1997], that the fast solar wind originates from the quiet sun as well as from polar coronal holes, flowing along the raylike structures that pervade the corona. Radio occultation measurements combined with white light images of the corona and ultraviolet observations of the solar disk, such as from Skylab, strongly suggest a picture where coronal holes and the quiet sun are filled with raylike structures having their footpoints in the boundaries of supergranular cells. These isolated flux tubes also exist within the radial extensions of the base of equatorial streamers, or their halos, as observed in eclipse images of the Sun, and radio occultation measurements. Such a picture of the magnetic structure of the corona is indeed confirmed by the UVCS synoptic images and LASCO white light images. The picture that emerges from these recent UVCS observations also suggests that plasma characteristics in the different contrast raylike structures that fill the corona are similar. This view of the corona lends a natural explanation for the predominance of the fast solar wind in interplanetary space down to latitudes as low as 20?° as detected by the pole to pole Ulysses observations.

Working Group: 4.

A J Lazarus¹, J T Steinberg¹, D A Biesecker², R J Forsyth³, A B Galvin⁴, F M Ipavich⁴, 
S E Gibson⁵, A Lecinski⁶, D M Hassler⁶, J T Hoeksema⁷, P Riley⁸, L Strachan, Jr.⁹, 
A Szabo⁵, R P Lepping⁵, K W Ogilvie⁵, B J Thompson⁵

¹ MIT, Cambridge, MA, USA, ² Univ. of Birmingham, Edgbaston, Birmingham, UK 
³ Imperial College, London, UK, ⁴ Univ. of Md., College Park, MD, USA 
⁵ NASA/GSFC, Greenbelt, MD, USA, ⁶ HAO/NCAR, Boulder, CO, USA 
⁷ HEPL, Stanford Univ., Stanford, CA, USA, ⁸ LANL, NM, USA, ⁹ Center for Astrophysics, Cambridge, MA, USA 

Several solar wind streams having speeds in excess of 500 km/s were observed from the Wind and SOHO spacecraft during the Whole Sun Month (WSM, August 10 to September 8, 1996). By assuming that the solar wind observed in the trailing edge of a high speed stream propagates radially outward from the Sun at constant speed, an apparent heliographic longitude for its source can be determined. We compare the sources determined in that manner with observations from instruments on the SOHO spacecraft. The highest speed stream is associated with the central meridian passage of a coronal hole (CH) that has a clear equatorial extension as viewed from the SOHO EUV Imaging Telescope (EIT). As of the time of preparation of this abstract, the other streams sources apparently show little association with coronal or photospheric features, though that relationship is currently under investigation. 

Working Group: 3.

Correspondence between the broadening of the Lyman- line and temperatures in the acceleration region of high speed solar wind

Espen Lyngdal Olsen¹

¹ Institute of Theoretical Astrophysics, University of Oslo, P.O. Box 1029, Blindern, 0315 Oslo, Norway

Spectroscopy of the Lyman- line from neutral hydrogen is used for obtaining information about the corona and the acceleration region of the solar wind There are two major factors making the attempt to obtain information about the corona by means of spectroscopy a difficult task: First, since the corona is optically thin all regions along the line of sight, with different physical properties, are contributing to the observed spectrum. The second problem is the one of relating the physical properties of the neutral hydrogen to the physical properties of the electron-proton solar wind. We here investigate the Lyman- line from neutral hydrogen in an eight-moment, two-fluid, high speed solar wind model. In this model the proton heat flux decreases rapidly in the solar wind acceleration region, and extended coronal heating of the proton gas leads to high coronal proton temperatures and large solar wind flow speeds. We show that the temperature maximum in the corona inferred from the observed Lyman- line may be more than 20% lower than the proton temperature maximum.

Working Group: 3.

L. Ofman¹, M. Romoli², J.M. Davila⁴, G. Poletto³, G. Noci², and J. Kohl⁵

¹ Hughes STX and NASA GSFC, Code 682.1, Greenbelt, MD 20771, USA 
² University of Florence, Largo Fermi 5, 50125 Florence, Italy 
³ Arcetri Observatory, I-50125 Florence, Italy 
⁴ NASA GSFC, Code 682.1, Greenbelt, MD 20771, USA
⁵ Harvard-Smithsonian Center for Astrophysics, Cambridge, MA, USA

Recent UVCS Visible Light Channel (VLC) observations indicate quasi-periodic variations in the polarized brightness (pB) in the polar coronal holes. Fourier power spectrum of the pB time series show significant peaks at 6.20.3, 211.2 and 517 minute periods. These preliminary observation indicate the possible presence of compressional waves, consistent with EIT observations of compressional waves in polar plumes (DeForest 1997). We stress that our results are preliminary and we plan future high cadence observations in both plume and interplume regions. We model the solar wind acceleration by solitary-like waves, by solving numerically the time-dependent, nonlinear, resistive 2.5-D MHD equations. We find that large amplitude nonlinear compressional waves are generated in coronal holes by Alfvén waves for a broad range of solar wind parameters when the Alfvén wave amplitude is 30-50 km/sec at the base of the corona. From the model we find that the solar wind speed and density fluctuate considerably on timescales of 20-40 min in agreement timescale of the long period fluctuations found with the VLC. The amplitude of the velocity fluctuations at  increases with the amplitude of the driving Alfvén waves at the base of the corona and the magnetic field strength, and decreases with the temperature. We find that low frequency Alfvén waves ( Hz) accelerate the solar wind velocity more effectively than higher frequency Alfvén waves.

Working Group: 3.

G. Peres¹, A. Ciaravella², S. Orlando1, R. Betta¹, F. Reale1, UVCS team

¹ Istituto ed Osservatorio Astronomico di Palermo 
² European Space Agency; Smithsonian Astrophysical Observatory

We report on the UVCS/SOHO extensive observations of the north polar wind and its source region made during a week-long observing campaign. We show images of the wind, in the  and O VI (1032 A and 1037 A) lines, line shapes and intensities at various heliocentric distances, as well as a first analysis and interpretation of the relevant data.

Working Group: 2.

M. Romoli¹, C. Benna², S. Cranmer³, S. Fineschi³, L.D. Gardner³, L. Strachan³, J.L. Kohl³, G. Noci¹

¹ Università di Firenze, Firenze, Italy 
² Università di Torino, Torino, Italy 
³ Harvard-Smithsonian Center for Astrophysics, Cambridge, MA, USA 

The White Light Channel (WLC) of the Ultraviolet Coronagraph Spectrometer (UVCS) on SOHO is a coronagraph polarimeter that measures the polarized brightness (pB) of the K-corona between 1.6 and 5 R in the 450-600 nm wavelength range. The WLC is co-registered with the UV spectrometers of UVCS, thus providing a measurement of the electron density (Van de Hulst, 1950), a key parameter for plasma diagnostics. 
After a description of the calibration of the WLC, we present the measured polarized brightness for streamers and coronal holes, and the corresponding electron densities computed using a spherical symmetrical model.
Comparisons with electron densities given in the literature and electron densities obtained with techniques that make use of coronal UV spectroscopy are also given.

Working Group: 6.

M. Romoli¹, D. Biesecker², C. Benna³, P.L. Lamy⁴, A. Llebaria⁴, J.L. Kohl⁵, G. Noci¹

¹ Università di Firenze, Firenze, Italy 
² University of Birmingham, Birmingham, UK 
³ Università di Torino, Torino, Italy 
⁴ Laboratoire d'Astronomie Spatiale, F-13376 Marseille Cedex 12, France 
⁵ Harvard-Smithsonian Center for Astrophysics, Cambridge, MA, USA 

The White Light Channel (WLC) of the Ultraviolet Coronagraph Spectrometer (UVCS) measures the polarized brightness (pB) of the K-corona between 1.6 and 5 R in the 450-600 nm wavelength range. The WLC is coregistered with the UV spectrometers of UVCS, thus providing a measurement of the electron density (Van de Hulst, 1950), a key parameter for plasma diagnostics. 
The coronagraph C2 of the Large Angle Spectroscopic Coronagraph (LASCO) provides images of polarized brightness of the full corona between 2 and 6 R in the 400-850 nm wavelength range.
In this paper we present a comparison between the pB measured by the two instruments for different coronal structures between 2 and 3.5 R using data obtained during the SOHO Campaign of the Whole Sun Month (August-September 1996).

Working Group: 4.

L. Strachan¹, J.C. Raymond¹, J.L. Kohl¹, A.V. Panasyuk¹, S. Fineschi¹, L.D. Gardner¹, E. Antonucci², S. Giordano² and M. Romoli³

¹ Harvard-Smithsonian Center for Astrophysics, Cambridge, MA, USA
² Università di Torino, Torino, Italy 
³ Università di Firenze, Firenze, Italy

The spatial distribution of plasma parameters in the extended corona are derived from UVCS/SOHO observations made during the Whole Sun Month Campaign (10 Aug. to 8 Sept. 1996). Daily coronal synoptic scans in H I Lyman  and O VI  1032 and 1037 Å were used to make synoptic maps of integrated intensities and line of sight velocities for all three lines. Maps of bulk outflow velocities of O⁵⁺ based on the Doppler dimming of the O VI lines are also presented. The maps show several interesting correlations of plasma characteristics with coronal structures. For example, low latitude streamers show clear depletions of O⁵⁺ in their cores (Raymond et al., 1997) while high latitude active region streamers do not. Also H⁰and O⁵⁺ LOS (Line of sight) velocity distribution widths appear to be anti-correlated with  for O⁵⁺ being larger in coronal holes than in streamers, while H⁰ shows the opposite effect. Possible physical explanations for the observed features are discussed.

This work is supported by NASA under Grant NAG5-3192 to the Smithsonian Astrophysical Observatory, by the Italian Space Agency, and by Swiss Funding Agencies.