UVCS/SOHO ABSTRACTS
AGU MEETINGS

SOHO/UVCS Observations of the He I Focusing Cone Near the Sun

Raymond, J. C.; Lallement, R.; Bertaux, J.; Gardner, L.

The UVCS spectrometer has observed He I 584 emission scattered by the helium focusing cone. The cone has been observed both upwind and downwind of the Sun along with sightlines crossing the cone between about 0.15 and 0.75 solar radii. Observations since December 1996 show that the brightness has declined by a factor of 4. The fading indicates an increased rate of collisional ionization as solar activity increased.

Empirically Determined Anisotropic Velocity Distributions and Outflows of O⁵⁺ ions in a Coronal Streamer at Solar Minimum

Frazin, R. A.; Cranmer, S. R.; Kohl, J. L.

Empirical constraints on the O⁵⁺ velocity distributions and outflow speeds in a solar minimum equatorial streamer between 2.6 and 5.1 R_sun are determined using a spectral synthesis code that includes O VI Doppler dimming. These constraints follow directly from UV spectra taken on 12 October 1996 with the Ultraviolet Coronagraph Spectrometer (UVCS) on the SOHO satellite and 3D electron densities derived from tomography applied to a time series of polarized white-light images taken with the Large Angle Spectrometric Coronagraph Experiment (LASCO) on SOHO. Four conclusions result from this work: 1) Our analysis shows O⁵⁺ anisotropy in the streamer legs and stalk. The microscopic velocity distribution (which excludes wave motions that equally affect all charged particles) is also found to be anisotropic, where the most probable speed perpendicular to the magnetic field direction exceeds that in the parallel direction. 2) There is no evidence of such anisotropy in the streamer core. 3) There is preferential heating of the O⁵⁺ ions over the protons in the streamer stalk and legs, but not in the core. 4) The outflow velocity of the O⁵⁺ ions is determined at heights above 4.6 Rsun. This work is supported by NASA under grant NAG5-10093 to the Smithsonian Astrophysical Observatory.

    The Advanced Spectroscopic and Coronagraphic Explorer Mission

Kohl, J. L.; Howard, R.; Davila, J.; Noci, G.; Esser, R.; Ciaravella, A.; Cranmer, S.; Fineschi, S.; Gardner, L.;Raymond, J.; Romoli, M.; Smith, P.; Socker, D.; Strachan, L.; Van Ballegooijen, A.

SOHO has provided profound insights into the physics of solar wind acceleration and coronal mass ejections. Although significant progress has been made, most of the dominant physical processes controlling these phenomena are still not identified. The Advanced Spectroscopic and Coronagraphic Explorer Mission provides next generation spectroscopic and polarimetric instrumentation aimed at identifying these processes. The launch is planned for March 2007 with mission operations and data analysis continuing for 5 years. The data will be unrestricted and available to the community. The envisioned program includes a Guest Investigator Program with an average of 15 grants to be awarded in response to proposals submitted during the first year of the mission. Information about the proposed scientific goals and instrumentation will be presented.

    Modelling of a CME-driven Shock Detected by UVCS/SoHO on March 3, 2000

Mancuso, S.; Raymond, J. C.; Kohl, J. L.; Ko, Y.; Uzzo, M.; Wu, R.

We report the observation of a 1100 km/s CME-driven shock with the UltraViolet Coronagraph Spectrometer (UVCS) telescope operating on board SoHO on March 3, 2000. The CME was observed by the Large Angle Spectroscopic Coronagraph (LASCO), and the radio signature of the shock was detected by the Hiraiso and Culgoora radio spectrographs as an intense type II radio burst. We derived the density profile just before the passage of the shock from UVCS observations and obtained a reliable estimate of the shock speed from the type II radio burst drift rate. The spectral profiles of both the O VI and Lyman alpha lines were Doppler dimmed at the passage of the shock and showed broad wings caused by the emission from shocked material along the line of sight. By estimating a compression ratio of 1.8 from the observed splitting of the radio emission bands in the spectrographs and assuming perpendicular propagation of the shock we derive a magnetic field strength of 1 Gauss at 1.8 solar radii and an Alfvenic Mach number of 1.7. The observed line broadening for both the protons and the Oxygen ions was modeled by adopting a mechanism in which the heating is due to the nondeflection of the ions at the shock ramp.

    UVCS Observations of Post-CME Heating and Streamer Relaxation by Current Sheets

Ciaravella, A.; Raymond, J. C.; Ko, K.; Lin, J

Many flux rope models for Coronal Mass Ejections predict that a current sheet forms in the wake of the CME. This current sheet may heat both the post-CME X-ray arcade and the CME plasma, and it may be a play an important part in the relaxation of the post-CME corona to a structure similar to the pre-CME streamer. We present UVCS observations of events on March 23 1998, March 18 1999 and August 7 2001. Two show very high temperatures as indicated by [Fe XVIII] emission, and one shows only relatively normal coronal temperatures. We consider densities, pressures, outflow speed and the overall energy budget.

    Two Recent Electron-Rich Energetic Particle Events and Their Associated CMEs

St.Cyr, O. C.; Cane, H. V.; Nitta, N. V.; Ciaravella, A.; Raymond, J. C.; Howard, R. A.

Electron-rich energetic particle events were defined by Evenson et al. (1984) as a class that correlated with solar flares that produced gamma-rays. Cane et al. (1986) demonstrated that these events are associated with impulsive (i.e. compact) flares. We have identified two electron-rich energetic particle events in the IMP 8 data in cycle 23. The dates of the two events are 01-May-2000 and 10-March-2001. The March 2001 event was well-observed by Yohkoh and showed a small hard X-ray source at the flare site. The soft/hard X-ray flux ratio was low. We have also examined SOHO LASCO and EIT images to investigate other forms of solar activity. Both events appear to be associated with coronal mass ejections (CMEs) that possess somewhat unusual morphology (bright, structured material, with little evidence of leading coronal material). Moreover, the two CME events appear similar to each other, at least so far as morphology in the LASCO observations. Additionally, observations of the March 2001 CME were obtained by the ultraviolet spectrometer (UVCS) on SOHO. UVCS observed the narrow ejecta following the leading feature at several heights (from 1.7 up to 3.1 solar radii). The CME material appeared bright in cool lines of OVI (1032,1037 A doublet), CIII (977 A), Lyman-beta and Lyman-alpha. The Doppler shift suggests a very small speed along the line of sight, consistent with the CME being near the plane of the sky. We present the SOHO observations and the Yohkoh SXT images (for the 10-March-2001 impulsive flare), and we describe our results.

    UVCS/SOHO Observations of Coronal Holes from Solar Minimum to Solar Maximum

Miralles, M. P.; Cranmer, S. R.; Esser, R.; Kohl, J. L.

Coronal holes are open field, low-density source regions of the solar wind. At solar minimum, large coronal holes are present at the poles and are the dominant source of the solar wind flow for this part of the solar cycle. At solar maximum, coronal holes of varying sizes and shapes appear at all latitudes and last for several rotations. During this stage of the cycle, the dominant component is mainly slow wind, but fast wind streams are generated by large coronal holes. UVCS/SOHO has been used to measure the plasma properties in several types of coronal holes from 1996 to 2001. Spectroscopic diagnostics of O⁵⁺ velocity distributions and outflow velocities are derived from measurements of intensities and line widths for O~VI 103.2 and 103.7 nm as a function of height. We compare the plasma properties of coronal holes from solar minimum to solar maximum and discuss the evolution of coronal holes during the solar cycle. We also study the compatibility between the growing database of coronal hole plasma properties and theoretical models of extended coronal heating via ion cyclotron resonance. This work is supported by NASA under Grant NAG5-10093 to the Smithsonian Astrophysical Observatory, by the Italian Space Agency and by PRODEX (Swiss contribution).

    Multifluid and Hybrid Modeling of Waves in Coronal Holes: Implications for Heating Theories

Ofman, L.; Davila, J. M.

Recent SOHO Ultraviolet Coronagraph Spectrometer (UVCS) observations show that protons and minor ions are hot (T_p>10⁶ K, T_i>10⁷ K) and anisotropic in coronal holes. A possible cause of the large perpendicular motions is unresolved Alfvénic fluctuations in the solar wind. Using the three-fluid 2.5D MHD model we have shown that the unresolved Alfvénic fluctuations lead to apparent proton temperature and anisotropy consistent with UVCS observations. However, \Alfven waves with realistic amplitudes can not reproduce the O⁵⁺ perpendicular temperature and anisotropy deduced from UVCS observations. We use the hybrid model to investigate constrains on the anisotropy of the minor ions. Our results suggests that the minor ions are heated and accelerated by high-frequency waves ( ^~10³ Hz), while proton heating occurs by low frequency waves ( ^~10^-3 Hz).

    Analysis and Modeling of the UV Spectra of the Feb. 12, 2000 Flux Rope CME.

Ciaravella, A.; Raymond, J.; van ballegooijen, A.

UltraViolet spectra of a typical flux rope CME have been taken with the UltraViolet Coronagraph Spectrometer aboard SOHO above the NW limb at heliocentric distance of 2.3 Rsun. The high temporal and spectral resolutions of the spectra provide a detailed monitoring of the dynamical and physical properties of the CME. Beside the cool lines of H I (1216 and 1025 A) and the intermediate lines of O VI (1032, 1037 A) usually observed in CME this event shows emission in the hot lines of SI XII (520 A) and Mg X (610 A). Doppler shift of the observed spectral lines give the line of sight velocity of the bright front and the prominence core plasma. The latter showing evidence for helical motion. A model of the Doppler shift evolution in both front and core of the CME is presented.

    Stucture of CMEs in 3D as Inferred From Doppler Shifts

Raymond, J. C.; Ciaravella, A.

Some models of CMEs are characterized by simple homologous expansion. With a combination of coronagraph images and long slit spectra to provide Doppler shifts, or with long slit spectra at several heights, it is possible to reconstruct the CME structure in 3D and follow its evolution. An earlier event was interpreted in terms of an untwisting helix. Here we consider two events (May 10 1999 and October 21 2000) that can almost, but not quite, be matched by expansion from an point explosion with a smooth range of expansion speeds.

Coronal hole boundaries from the Sun to the Heliosphere: Constraints on the sources and structure of the solar wind

Zurbuchen, T. H.; Von Steiger, R.; Riley, P.; Raymond, J.; Geiss, J.;Antonucci, E.; Abbo, L.

Coronal holes are known to be a source of fast, relatively homogenous solar wind. A more variable slow solar wind emerges from the corona adjacent to these fast streams and dominates the low latitude heliosphere. The relation between these two qualitatively different solar wind types is best studied by investigating in detail the structure and evolution of the coronal hole boundaries from the low atmosphere of the Sun, through the corona and into the deep heliosphere. We present a comprehensive data-study combining data from He I 10830A, EIT, UVCS and in situ plasma and composition measurements from SWICS on Ulysses and ACE. First, the location and structure of the coronal hole boundary is determined in each of the remote data-sets. We then project the in situ plasma and composition measurements to 30 Rs using a sophisticated 2D MHD tracing technique. This technique then allows a direct comparison of solar and in situ coronal hole boundaries. We particularly concentrate on UVCS and SWICS data of heavy ions in the solar wind that allow the most rigorous comparisons of solar and in situ data, using the same measurement in the corona as in the solar wind. We will then discuss these data in the context of models and theories of the structure of the three-dimensional structure of the corona and the solar wind. We will also compare the observations with an 3D MHD calculation that predicts super-radial expansion of the fast solar wind associated with coronal holes. This paper is a report of an ISSI International Team on coronal hole boundaries.

Observations of a High-latitude Coronal Hole at Solar Maximum

Miralles, M.; Cranmer, S. R.; Kohl, J. L.

A large coronal hole at a latitude of about 60 degrees was observed above the north pole with the Ultraviolet Coronagraph Spectrometer (UVCS) aboard SOHO during 10--19 February 2001. These observations are part of an ongoing campaign to characterize equatorial and mid-latitude coronal holes during the active phase of the current solar cycle. Observations in H~I Lyα and O~VI 103.2 and 103.7 nm provided spectroscopic diagnostics of proton and O5+ velocity distributions. The O~VI line profiles show a narrow core and broad wings. The narrow core is attributed to the foreground and background streamers. The broad wings are attributed to the coronal hole. We compare the observed line intensities and widths of this high-latitude hole with those of other solar maximum (lower latitude) holes and solar minimum polar coronal holes. The comparison of the line widths shows that the O~VI line widths of this solar maximum hole are similar to those observed in polar coronal holes at solar minimum. The observation of extremely high ion kinetic temperatures at the north pole occurs simultaneously with the polarity change of the Sun's magnetic field, as seen in recent magnetogram data. This coronal hole may represent the first manifestation of the stable polar coronal holes that will dominate the Sun's open magnetic flux tubes at the next solar minimum. The re-appearance of broad O~VI profiles at a time when not all of the ``new polarity'' magnetic flux has migrated to the poles is an interesting development that may provide a crucial constraint on models of extended coronal heating. This work is supported by NASA under Grant NAG5-10093 to the Smithsonian Astrophysical Observatory, by the Italian Space Agency and by PRODEX (Swiss contribution).

Observed Variations of O5+ Velocity Distributions with Electron Density

Kohl, J. L.; Cranmer, S. R.; Frazin, R. A.; Miralles, M.; Strachan, L.

The Ultraviolet Coronagraph Spectrometer (UVCS) on the SOHO satellite has been used to measure the line profiles of O~VI 103.2 and 103.7 nm versus heliographic height in a variety of coronal holes and streamers during the period from 1996 to 2001. Those observations have been used to derive velocity distributions in the line-of-sight direction, which is typically perpendicular to the apparent magnetic field direction. In the case of polar coronal holes at solar minimum, the electron density is the smallest observed and the most-probable speed is the largest observed reaching values as high as 500 km/s at the largest heights. The O5+ most-probable speed is much larger than the hydrogen speed in those structures. The ratio of O5+ to hydrogen most-probable speeds increases with height. In contrast, the O5+ values are much smaller than those of hydrogen at the base of high-latitude streamers and never reach the hydrogen values at any observed height. The electron density in those structures is much greater than in the solar minimum coronal holes. Other structures have intermediate values of the electron density and O5+ most-probable speeds. In general, the O5+ most-probable speed and its ratio to the hydrogen value seem to decrease with increasing density. This apparent observational correlation may be related to thermalization from higher collision rates or it might be related to the physical process that causes the extreme O5+ perpendicular heating. This work is supported by NASA under Grant NAG5-10093 to the Smithsonian Astrophysical Observatory, by the Italian Space Agency, and by PRODEX (Swiss Contribution).

New Applications of Ultraviolet Spectroscopy to the Identification of Coronal Heating and Solar Wind Acceleration Processes

Cranmer, S. R.

The Ultraviolet Coronagraph Spectrometer (UVCS) aboard SOHO has revealed surprisingly extreme plasma conditions in the extended solar corona. This presentation reviews several new ways that UVCS and future spectroscopic instruments can be used to identify the physical processes responsible for producing the various components of the solar wind. The most promising mechanism for heating and accelerating heavy ions remains the dissipation of ion cyclotron waves, but the origin of these waves---as well as the dominant direction of propagation relative to the background magnetic field---is not yet known. Ultraviolet spectroscopy of a sufficient number of ions would be able to pinpoint the precise magnetohydrodynamic modes and the relative amounts of damping, turbulent cascade, and local plasma instability in the corona. (A simple graphical comparison of line-width ratios will be presented as a first step in this direction.) Spectroscopic observations with sufficient sensitivity can also detect departures from Gaussian line shapes that are unique identifiers of non-Maxwellian velocity distributions arising from cyclotron (or other) processes. Even without these next-generation diagnostics, UVCS data are continuing to put constraints on how the heating and acceleration mechanisms respond to changes in the ``background'' properties of coronal holes and streamers; i.e., geometry, latitude, and density. These provide crucial scaling relations in the acceleration region of the fast and slow solar wind that must be reproduced by any candidate theory. This work is supported by the National Aeronautics and Space Administration under grant NAG5-10093 to the Smithsonian Astrophysical Observatory, by Agenzia Spaziale Italiana, and by the Swiss contribution to the ESA PRODEX program.

Coordinated UVCS/LASCO/EIT Observations of a High Latitude CME

Karovska, M.; Esser, R.; Dobrzycka, D.; Kohl, J.

We present here the results of our coordinated UVCS/LASCO/EIT observations of a CME on 2000 March 5. The northern polar region of the Sun at a position angle 270 degrees was monitored with UVCS at 2 solar radii for about 8 hours. During that time interval a spectacular CME developed in the northern hemisphere. This event was also detected and monitored with LASCO C2 and C3 and the EIT for several hours. We compare the edge-enhanced LASCO and EIT images of this event with the increased intensities of the H I Lyman-alpha spectral line and the line pair O VI 1031.91 A and 1037.61 A seen in the UVCS observations. LASCO and EIT images are essential in providing the larger scale context for this event and for correlating the small-scale sub-structure observed in white light with the the plasma morphology as observed with the UVCS.

Multifluid and Hybrid Modeling of Waves in Coronal Holes: Implications for Heating Theories

Ofman, L.; Davila, J. M.

Recent SOHO Ultraviolet Coronagraph Spectrometer (UVCS) observations show that protons and minor ions are hot (Tp>106 K, Ti>107 K) and anisotropic in coronal holes. A possible cause of the large perpendicular motions is unresolved Alfvénic fluctuations in the solar wind. Using the three-fluid 2.5D MHD model we have shown that the unresolved Alfvénic fluctuations lead to apparent proton temperature and anisotropy consistent with UVCS observations. However, \Alfven waves with realistic amplitudes can not reproduce the O5+ perpendicular temperature and anisotropy deduced from UVCS observations. We use the hybrid model to investigate constrains on the anisotropy of the minor ions. Our results suggests that the minor ions are heated and accelerated by high-frequency waves (∼103 Hz), while proton heating occurs by low frequency waves ( ∼10-3 Hz).

Cyclotron Resonances of Ions with Obliquely-Propagating Waves in CoronalHoles and the Fast Solar Wind

Hollweg, J. V.; Markovskii, S. A.

UVCS/SOHO has provided observations of protons and ions in coronal holes which suggest the operation of ion-cyclotron heating and acceleration. Many models have concentrated on the interactions of particles with parallel-propagating ion-cyclotron waves. There is of course no reason to expect parallel propagation in the corona, so we consider here some consequences of oblique propagation. Following Stix (1992), we analytically calculate the energy absorbed by an ion moving in an obliquely-propagating electromagnetic wave. Resonances occur at harmonics of the gyro frequency, though we will show that the physical interpretations are quite different for electric field polarizations in, or perpendicular to, the plane containing k and Bo (k is wavenumber and Bo is the ambient magnetic field). Surprisingly, a resonance at the fundamental frequency can occur even if the wave is right-hand circularly polarized (i.e. opposite to the sense of the gyromotion). We suggest, therefore, that resonances with the fast/whistler branch, which are often overlooked, may play a role in the heating of ions and protons in coronal holes as long as the waves are oblique. We will discuss possible sources of such waves. We will also summarize other consequences of oblique propagation for the resonant heating of coronal holes and the origin of the fast solar wind. Stix, T.H., Waves in Plasmas, AIP, New York, 1992.

Where in the Streamer Belt does the Slow Speed Wind Originate?

Strachan, L.; Suleiman, R.; Panasyuk, A. V.; Biesecker, D. A.; Kohl, J. L.

The Ulysses high latitude mission showed that the slow speed wind at solar minimum appears to come from equatorial regions in the heliosphere that are dominated by helmet streamers. However, there are few coronal measurements of the detailed latitudinal variation of the outflow velocity across a streamer. Such measurements are needed to identify the region of the streamer that gives rise to the slow speed wind. For this study we use UVCS and LASCO observations of a solar minimum streamer to make a detailed model of the outflow velocities for O+5 as a function of position angle from the streamer axis. This new work goes beyond using the OVI line ratios to define the boundaries between fast and slow wind. We constrain the coronal plasma parameters (velocities, temperature anisotropies, densities, etc.) using OVI and Ly-alpha line profiles, and white light polarized brightness data. We will discuss various possibilities for the latitudinal profile for the coronal outflow in the streamer belt. This work is supported by NASA Grant NAG5-7822 to the Smithsonian Astrophysical Observatory, by the Italian Space Agency, and by the ESA PRODEX program (Swiss contribution).

Plasma Conditions in Polar Plumes and Interplume Regions in Polar Coronal Holes

Cranmer, S. R.; Kohl, J. L.; Miralles, M.; Panasyuk, A. V.

During times of low solar activity, large polar coronal holes are observed to contain bright raylike polar plumes that appear to follow open magnetic field lines. Plumes are believed to be flux tubes that are heated impulsively at their base, which leads to a higher density, a lower outflow speed, and a lower overall temperature in the extended corona, compared to the surrounding interplume regions. Despite years of white light and spectroscopic observations, though, the differences in mass, momentum, and energy flux in plumes and between plumes are not known precisely. This poster presents an updated survey of data from the Ultraviolet Coronagraph Spectrometer (UVCS), aboard SOHO, that attempts to sort out the local plume and interplume conditions. These results will be compared with previous analyses that characterized the ``mean'' plume/interplume coronal hole, averaged over many lines of sight through varying concentrations of plumes. Limits on the relative contributions of plumes and interplume regions to the high-speed solar wind will be determined, with emphasis on the proton outflow speed in the corona and at 1 AU. Implications for theoretical models of coronal heating and solar wind acceleration will be discussed. This work is supported by the National Aeronautics and Space Administration under grant NAG5-10093 to the Smithsonian Astrophysical Observatory, by Agenzia Spaziale Italiana, and by the Swiss contribution to the ESA PRODEX program.

Ultraviolet Spectroscopy of Coronal Jets Within the Fast Solar Wind

Dobrzycka, D.; Cranmer, S. R.; Raymond, J. C.; Biesecker, D. A.;Gurman, J. B.

The coronal jets are spectacular dynamic events originating from different structures in the solar corona. We present UVCS/SOHO observations of polar coronal jets. They appear to originate near flaring ultraviolet bright points within polar coronal holes that are source regions of the fast solar wind. UVCS recorded the jets as a significant enhancement in the integrated intensities of the strongest coronal emission lines: mostly H~I Lyα and O~VI λ λ 1032,1037. A number of detected jets are correlated with the EIT Fe~XII 195~{Å} and LASCO C2 white-light events. Typically, the observed H~I Lyα enhancement was up to a factor of 1.3-1.7 over the ambient corona and lasted for 20-30 minutes. The narrow profiles of the emission lines indicate that the material in the jets is cooler than the underlying corona. We modeled the observable properties of the jets to get estimates on jet plasma conditions. We discuss the model results, the initial electron temperature and the heating rate required to reproduce the observed O~VI ionization state. We also discuss connection of the polar jets to the fast solar wind. This work is supported by the National Aeronautics and Space Administration under grant NAG5--7822 to the Smithsonian Astrophysical Observatory, by Agenzia Spaziale Italiana, and by the ESA PRODEX program (Swiss contribution).

Temperatures, Densities and Ionization States of CMEs from UVCS

Raymond, J. C.

UV spectra of CMEs from SOHO/UVCS show ions ranging from H I and C II up to Fe XVIII. The ionization state is low in the densest, brightest regions. In some cases the gas cannot have been very hot during the initial mass ejection, because it could not have recombined quickly enough to form the low ionization species observed. We consider the implications for heating of the coronal gas and we discuss possible explanations for the rarity of high ionization gas in UVCS spectra compared with its prevalence in CMEs in the solar wind.

Elemental Abundances in the Inner Solar Corona Measured by SOHO/UVCS

Ko, Y.; Raymond, J. C.

The UVCS instrument aboard the SOHO spacecraft measures UV spectrum in the solar corona. The capability of observing Lyman lines of atomic hydrogen as well as lines from various elements, some with a range of ionization states, makes it possible to determine the absolute elemental abundances in both low and high FIP (First Ionization Potential) elements. We review UVCS observations of absolute abundances in various structures of the solar corona. These include streamers across its structure, at different latitudes and heights, as well as variations along the heliocentric heights above active regions.

Observations of a High-latitude Coronal Hole at Solar Maximum

M. P. Miralles, S. R. Cranmer, and J. L. Kohl

A large coronal hole at a latitude of about 60 degrees was observed above the north pole with the Ultraviolet Coronagraph Spectrometer UVCS aboard SOHO during 10--19 February 2001. These observations are part of an ongoing campaign to characterize equatorial and mid-latitude coronal holes during the active phase of the current solar cycle. Observations in HI Lyalpha and OVI 103.2 and 103.7 nm provided spectroscopic diagnostics of proton and O5+ velocity distributions. The OVI line profiles show a narrow core and broad wings. The narrow core is attributed to the foreground and background streamers. The broad wings are attributed to the coronal hole. We compare the observed line intensities and widths of this high-latitude hole with those of other solar maximum lower latitude holes and solar minimum polar coronal holes. The comparison of the line widths shows that the OVI line widths of this solar maximum hole are similar to those observed in polar coronal holes at solar minimum. The observation of extremely high ion kinetic temperatures at the north pole occurs simultaneously with the polarity change of the Suns magnetic field, as seen in recent magnetogram data. This coronal hole may represent the first manifestation of the stable polar coronal holes that will dominate the Suns open magnetic flux tubes at the next solar minimum. The re-appearance of broad OVI profiles at a time when not all of the new polarity magnetic flux has migrated to the poles is an interesting development that may provide a crucial constraint on models of extended coronal heating. This work is supported by NASA under Grant NAG5-10093 to the Smithsonian Astrophysical Observatory, by the Italian Space Agency and by PRODEX Swiss contribution.

UVCS Observations of the July 14 CME

Raymond, J C; Ko, Y; Vourlidas, A; Ciaravella, A

UVCS detected highly blue-shifted Lyman Alpha and faint O VI emission at 3.5 and 4 solar radii. The spatially narrow region of Ly alpha emission shows blue-shifts up to 1000 km/s and modest line broadening. Comparison of the speed in the plane of the sky to the Doppler shift indicates an angle to the line of sight of 27 degrees. We compare with LASCO data and discuss the particle densities and the excitation mechanisms of the UV lines.

Characteristics of the Fast and Slow Solar Wind at Solar Maximum South of 20 deg Latitude

Habbal, S R; Woo, R; Vial, J; Fineschi, S

The superior conjunctions of the Galileo and Cassini spacecraft in May 2000, reaching 2 and 3 $R_s$, respectively, south of the ecliptic at the closest approach points, offered a rare opportunity for coordinated SOHO/UVCS and SUMER, and TRACE observations with radio occultation measurements. Ulysses observations at latitudes around 50 deg south were also available during that time period. A number of high latitude streamers, as evidenced from LASCO white light images, intercepted the line of sight during that approximate two week time interval. While SUMER observations were limited to within 1.5 $R_s$ and to -70 deg S, UVCS observations covered the southern hemisphere from 1.1 to 5 $R_s$. By integrating the results of the remote sensing and in situ measurements, we show to what extent inferences of the characteristics of the fast and slow solar wind, in the inner corona at high latitudes, can be affected by line of sight integration effects during solar maximum.

Constraints on the O^5+ Anisotropy in the Solar Corona

Ofman, L; Vinas, A; Gary, S P

Velocity distributions of O^5+ ions derived from Ultraviolet Coronagraph Spectrometer (UVCS) observations in coronal holes indicate that the O^5+ are highly anisotropic (T_{\perp i}/T_{\parallel i}\approx30-300$ at 3.5 R_\odot). The observations provide empirical values for the electron density and the ion temperatures. It is well known that the electromagnetic ion-cyclotron instability is driven by temperature anisotropy. The instability leads to the rapid decrease of anisotropy and transfer of some kinetic energy of the particles into the magnetic field fluctuations. Here we use linear theory and hybrid simulations combined with the empirical values of the densities and the temperatures to investigate the ion-cyclotron instability of the anisotropic minor ions in the coronal hole plasma. We find that an initial O^5+ anisotropy of 50 decreases by an order of magnitude within $\sim$300-900 proton cyclotron periods (3-9 s). Thus, the ion-cyclotron instabi lity constrains the anisotropy of O^5+ ions that can be sustained in the solar corona.

UVCS Outflow Velocity Measurements During the Third Whole Sun Month Campaign

Strachan, L; Panasyuk, A V; Kohl, J L; Biesecker, D A

We present results for outflow velocity measurements obtained in different coronal structures with the Ultraviolet Coronagraph Spectrometer on SOHO during the Third Whole Sun Month Campaign (18 Aug. to 14 Sept. 1999). Ion velocities were obtained from heliocentric heights of 1.5 to 3.5 solar radii. This is the coronal region where it is believed that much of the solar wind acceleration takes place however there are few velocity measurements at these heights since this region is not readily accessible to other techniques for measuring outflow velocities. In our analysis we determine day-to-day variations of oxygen ion outflow speeds at selected latitudes in the corona and compare these measurements with IPS and in situ measurements made at much greater heliocentric distances. The comparison of the outflow speeds are used to provide information on the nature of the solar wind acceleration from different coronal regions during the rise to solar maximum. This work is supported by NASA Grant NAG5-7822 to the Smithsonian Astrophysical Observatory, by the Italian Space Agency, and by the ESA PRODEX program (Swiss contribution)

SOHO/UVCS Observations of a Coronal Jet During the Third Whole Sun Month Campaign

Ko, Y; Raymond, J C; Gibson, S; Strachan, L; Alexander, D; Fletcher, L; Holzer, T; Gilbert, H; Burkepile, J; St. Cyr, O C; Thompson, B

On August 26 1999, a coronal jet occurred at the north west limb near a sigmoid action region which has been the target for a joint observation plan during the third Whole Sun Month Campaign. This jet was observed by several instruments at the limb (SOHO/CDS, SOHO/EIT, TRACE, MLSO/CHIP, MLSO/PICS), at 1.7 Ro (SOHO/UVCS), and at the outer corona (SOHO/LASCO). At 1.7 Ro, the intensities of Lyman alpha, Lyman beta in the jet increased by as large a factor of 100 compared with the background corona, while those for O VI 1032 and O VI 1037 increased by a factor of 2. C III 977 and N III 991 lines also brightened significantly. The line shift in the lines indicates that the line-of-sight velocity in the jet started from ~150 km/sec blue shift and ended at ~120 km/sec red shift. This line-of-sight motion seen at 1.7 Ro apparently was opposite that observed when the jet emerged from the limb. In this paper, we present the observation by SOHO/UVCS and discuss the dynamic structure and physical properties of this jet as it passed through 1.7 Ro. Comparisons will be shown with the observations from other instruments. This work is supported by NASA Grant number NAG5-7822

Tracing Coronal Hole Boundaries into the Solar Wind

von Steiger, R; Zurbuchen, T H; Antonucci, E; Geiss, J; Raymond, J; Riley, P

Coronal hole boundaries are being studied using a combined set of composition data from SOHO/UVCS, Ulysses/SWICS, and ACE/SWICS. The following questions will be addressed: (1) How sharp are these boundaries, and why are they so sharp; (2) What are the dynamics and the degree of the observed superradial expansion, and are there systematic variations and sub-structures inside coronal holes; (3) How can the data be used to constrain models of generation of solar wind. These questions should be considered in the context of more general questions such as (A) What is the cause of the FIP effect and its difference between fast and slow wind; (B) How does the He/H abundance ratio drop by a factor of 1.5--2 between the outer convective zone and the slow wind. We concentrate on two time periods from mid-1996 to mid-1997. The boundaries are identified using the following coronal and solar wind quantities: Coronal Carrington rotation synoptic maps of kinetic properties (speed, temperatures), O/H ratio, electron density, and radial speed profiles from UVCS, as well as interplanetary parameters such as differential speeds, non-thermal temperature distributions, elemental ratios (Si/O, O/H, ...), and ionic ratios (O7+/O6+, C6+/C5+, ...) from SWICS. The connection between solar and heliospheric data is performed using MHD simulations to account for the dynamical evolution of the streams in the heliosphere. This paper gives a progress report of an ISSI International Team on coronal hole boundaries.

UVCS Observations of a High Latitude Streamer From 2-11 November 1999

L. Strachan, M.P. Miralles, R. Frazin, J.L. Kohl

A high latitude coronal streamer was observed with the Ultraviolet Coronagraph Spectrometer UVCS on SOHO for ten days during the period 2 -- 11 November 1999. The streamer was formed above a filament channel on the disk and, at the start of the observations, was located on the east limb at a position angle of about 150 deg. During the following ten days the streamer moved across the face of the Sun andand presented different aspect angles to the observed line of sight. We compare UVCS measurements of intensities and line widths of H Ly-alpha and O VI profiles obtained from 1.5 to 3.0 solar radii with equatorial streamer observations made near solar minimum. This work demonstrates that geometry effects are important when interpreting spectroscopic observations of coronal structures. In the future these observations will be used to model ion velocity distributions and outflow velocities in these high latitude streamer structures. This work is supported in part by NASA under grant NAG5-7822 to the Smithsonian Astrophysical Observatory, by the Italian Space Agency, and by Swiss funding agencies.

1998 Spring AGU meeting and A.A.S. Solar Physics Div. Meeting,Boston, May 25-29

Study of the Latitudinal Dependence of H I Ly-alpha and O VI Emission - Evidence for the Super-Radial Geometry of the Outflow in the Polar Coronal Holes.

D.Dobrzycka, L.Strachan, A.Panasyuk, S.R.Cranmer, J.L.Kohl, & M.Romoli

The observations obtained during the Whole Sun Month (WSM) campaign (Aug.10 - Sept.08, 1996) provide us with detailed information about the Sun and solar corona near the minimum of solar activity. This data set is especially important for analysis of the latitudinal dependence of the emission from the solar corona, since at solar minimum the polar coronal holes are large, stable structures and streamers are long lasting features occupying a narrow region in the equatorial plane. We present our analysis of the UVCS/SOHO data acquired during the period of the WSM campaign. We describe the distribution of the H I Ly-alpha and O VI (\lambda\lambda 1032,1037) emission as a function of both latitude and radius and derive characteristic plasma parameters like velocities along the line of sight and kinetic temperatures. We put constraints on the boundaries of the polar coronal holes by modeling them with flow tubes that expand radially or super-radially and compare our results with constraints from other instruments. We also model the latitudinal distribution of the Ly-alpha and O VI line intensities assuming outflow either along purely radial or non-radial flux tubes. This work was supported by NASA under Grant NAG5-3192 to the Smithsonian Astrophysical Observatory, by the Italian Space Agency, and by Swiss Funding Agencies.

A. Fludra, L. Strachan, D. Alexander, F. Bagenal, D.A. Biesecker, D. Dobrzycka, A.B. Galvin, S. Gibson, D. Hassler, Y-K. Ko, A.V. Panasyuk, B. Thompson, H. Warren, G. Del Zanna, S. Zidowitz, E. Antonucci, B.J.I. Bromage, S. Giordano

We present empirical results for temperatures, densities, and outflow velocities of constituents of the solar corona from 1 to 3 R_\odot in polar coronal holes and an equatorial streamer. Data were obtained from a variety of space and ground-based instruments during August 1996 as part of the SOHO Whole Sun Month Campaign. From white light data obtained with the SOHO/LASCO/C2 and HAO/Mauna Loa coronagraphs, we determine electron densities and compare them to those determined from the density-sensitive EUV line ratio of Si IX 350/342 Å\ observed by the SOHO/Coronal Diagnostic Spectrometer (CDS). Moreover, from the white light density profiles we calculate temperature profiles and compare to temperature diagnostic information from EUV lines and soft X-ray images from Yohkoh. H I Ly \alpha and O VI 1032/1037 Å\ intensities from the SOHO Ultraviolet Coronagraph Spectrometer (UVCS) are used to estimate both the direction and magnitude of plasma outflow velocities in coronal holes and streamers above 1.5 R_\odot. The velocities are derived using densities from white light coronagraph data and coronal electron temperature estimates derived from Ulysses/SWICS ion composition data. Near the base of the corona we find the white light and spectral analysis produce consistent density and temperature information. In the extended corona we find results consistent with high outflow velocities and a superradial outflow geometry in polar coronal holes.

Y-K Ko, A B Galvin, S Gibson & L Strachan

The solar wind ionic charge states are frozen-in in the inner solar corona within 5 solar radii. The freeze-in process, thus the frozen-in ionic charge states, depends on the electron temperature, electron density and the ion velocity in the ion's freeze-in region. Therefore the observed solar wind ionic charge states can be used to infer the physical properties in the inner solar corona where important solar wind heating and acceleration mechanisms are believed to take place. During the SOHO Whole Sun Month Campaign, Ulysses observed high speed solar wind from the north polar coronal hole. With the electron density profile derived from the LASCO/C2 and HAO/Mark 3 coronagraphs and the outflow velocities derived from the UVCS instrument, we model the electron temperature profile in the north polar coronal hole constrained by the above and the solar wind ionic charge states data observed by the SWICS instrument onboard Ulysses.

J L Kohl, S Fineschi, R Esser, A Ciaravella, S Cranmer, L D Gardner, A Modigliani, R Suleiman & G Noci

The SOHO Ultraviolet Coronagraph Spectrometer (UVCS/SOHO) is being used to measure spectral line profiles in polar coronal holes. The measurements include HI 121.6 nm, O VI 103.2 nm and 103.7 nm and Mg X 62.5 nm. Measurements of O VI profiles above 2.2 R_\odot and Mg X profiles above 1.75 R_\odot are presented for the first time. The measurements are used to determine the velocity distribution of the corresponding ions along the lines-of-sight. The velocities are much different for the various particles with O⁵⁺ having the largest most probable speeds at heliocentric heights above 1.8 R_\odot. Mg⁹⁺ is found to have most probable speeds above 1.8 R_\odot that fall between those of O⁵⁺ and the smaller H^0 values. The derived velocity distributions for O⁵⁺ and Mg⁹⁺ do not appear to be dominated by transverse wave motions. The possibility that the velocity distributions are caused by ion cyclotron resonance with high frequency MHD waves is being investigated. Some details of the observations and the use of the UVCS instrument will be presented. Information for gaining access to UVCS data and the data analysis software as well as information about how to arrange for specialized UVCS observations will also be presented. 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.

A V Panasyuk

Synoptic observations from the Ultraviolet Coronagraph Spectrometer (UVCS) on SOHO are used to obtain profiles and intensities (integrated along the line-of-sight) for a number of emission lines in the corona including H I Ly\alpha and the O~VI doublet at 1032/1037 Å\.\ The UVCS synoptic program makes a scan around the Sun once per day, covering heights from 1.5 to 3 R_\sun in the equatorial regions and heights from 1.5 to 2.5 R_\sun in the polar and midlatitude regions. Presented here are the results of the first attempt at global 3D reconstruction of the emissivity distribution for Ly\alpha and O~VI lines in the extended solar corona. The reliability of the reconstruction technique and the uncertainties of the computed emissivities are also discussed. This work is supported by the National Aeronautics and Space Administration under grant NAG5-3192 to the Smithsonian Astrophysical Observatory.

R M Suleiman, J L Kohl, R Frazin, A Ciaravella, S R Cranmer, L D Gardner, R Hauck, A V Panasyuk, P L Smith & G Noci

The Ultraviolet Coronagraph Spectrometer (UVCS) aboard the SOHO spacecraft is designed to probe the solar corona from 1.25 to 10 R_\odot from sun center through the observation of ultraviolet spectral lines. In polar coronal holes, H I Lyman \alpha is the most intense observable line with UVCS above 3.0 R_\odot. This is the region where the outflowing coronal plasma becomes nearly collisionless and the ionization balance is believed to be frozen. At these heights, the H^0 velocity distribution may not be representative of the proton distribution because the characteristic time for charge transfer between H^0 and protons becomes longer than that for the outflow through, for example, a density scale height. Hence, the H^0 velocity distribution may not be directly affected by transverse wave motion or wave damping. In this paper we present measurements of H I Lyman \alpha line profiles in coronal holes from 3.5 to above 6.0 R_\odot. 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.

L Strachan, A V Panasyuk, D Dobrzycka, S Gibson, D A Biesecker, Y-K Ko, A B Galvin, M Romoli, J L Kohl

We constrain coronal outflow velocity solutions, resolved along the line-of-sight, by using Doppler dimming models of H I Lyman alpha and O VI 1032/1037 Å\ 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 Whole Sun Month Campaign (10~Aug. -- 8~Sep. 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 O⁵⁺ outflow velocities which are determined from an analysis of the the O~VI line ratios. This analysis is less sensitive to the uncertainties in the electron density and independent of the ionization balance and elemental abundance than the analyses which use individual spectral lines. This work is supported in part by NASA under grant NAG-3192 to the Smithsonian Astrophysical Observatory, by the Italian Space Agency and by Swiss funding agencies.

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

We present empirical models based on UVCS/SOHO observational data for several plasma parameters in the fast solar wind emerging from near-solar-minimum polar coronal holes. We also discuss the constraints on various theoretical processes of coronal heating and acceleration, and present preliminary kinetic models of the velocity distributions. UVCS/SOHO has measured hydrogen kinetic temperatures in polar coronal holes in excess of 3 million K, and O^(5+) ion kinetic temperatures of at least 200 million K. The velocity distributions parallel to the open magnetic field are smaller than those perpendicular to the field, possibly implying temperature anisotropy ratios of order 100 for minor ions. In addition, Doppler dimming and pumping of the emission line intensities indicates that the O^(5+) ions may have higher outflow velocities than the protons; the ions may reach 500 km/s by a radius of 4 solar radii.

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 the observed plasma conditions. This resonant wave damping produces anisotropic velocity-space diffusion and a significant outward acceleration in addition to that provided to ions by the magnetic mirror force. Because different ions have different resonant frequencies, they receive different amounts of heating and acceleration as a function of radius. Thus, the more ionic species that are observed, the greater the extent in frequency space the wave spectrum can be inferred and spatially mapped.

 Coronal observations made by the SOHO telescopes provide unprecedented information on coronal dynamics including corona mass ejections. The best images and spectra are obtained for events that take place within 30 degrees of the plane of the sky. It is difficult to combine analyses of these data with analyses of in-situ data on CME debris in interplanetary space because in-situ data are generally available only for events aimed at Earth. However, the NEAR (Near-Earth Asteroid Rendezvous) spacecraft trajectory to the asteroid Eros provides opportunities to combine interplanetary magnetic field observations well off the Sun-Earth line with SOHO coronal imaging. We present an analysis of a CME that was ejected off the west limb of the Sun on August 13, 1997. As observed by the SOHO telescopes, various features in the CME propagated outward with gradual acceleration so that at 29 solar radii, velocities of the features ranged between 260 and about 500 km/s, as projected into the observation plane. At this time the NEAR spacecraft was 58 to the west of the Sun-Earth line at a distance of 1.78 AU from the Sun. On August 20, 1997, the NEAR magnetometer observed a magnetic cloud with a clear flux rope signature for about 6 hours. The flux rope was embedded in the CME disturbance witch lasted approximately 30 hours at NEAR. The cloud arrival time at NEAR corresponds to time-averaged propagation speeds of 400 - 500 km/s. This strongly indicates that NEAR observed the magnetic cloud associated with the August 13 CME. The magnetic cloud field had right- hand helicity. The CME appears to have originated with the disappearance of a southern-hemisphere filament at 45 degrees west longitude. Southern- hemisphere filaments usually, have right-hand helicity. Since the twist of the field is known, we are searching for rotational motions in the CME which could indicate whether the CME fields are twisting up or unwinding. All in all, this study demonstrates the type of analyses that can be performed using coronal imaging and in-situ observations from spacecraft at widely separated heliolongitudes. Opportunities for such analyses are very rare now, and they are hindered by limited data sets in the best of cases, but they will be abundant during the Solar Stereo Mission.

The Paradox of Filamented Coronal Hole Flow but Uniform High Speed Wind

 S. T. Suess, S. Parhi, R. L. Moore
NASA Marshall Space Flight Center, Mail Stop ES82, Huntsville, AL 35812 USA

 Plumes and rays in coronal holes are nearly radially aligned density striations that follow the ambient magnetic field. They have long been known, but have gained new interest with growing awareness that coronal hole flow is inherently filamentary. In retrospect, filamentary flow should have been no surprise. This is because $\beta\ll1$ in coronal holes inside $\sim 10\ R_\odot$, allowing the flow to be filamentary down to the smallest scale of photospheric magnetic activity. While the magnetic field itself is locally smooth across any height above ca. 50,000 km, SOHO/MDI has shown that the photospheric magnetic field is a complex array of rapidly evolving small bipoles that are constantly emerging, evolving, and cancelling. The resulting activity is manifested in microflares, concentrated in the magnetic network, that produce impulsive injections at the footpoints of coronal field lines. The uneven distribution of this activity in space and time is the source of coronal hole filamentation. What is surprising is that the radial flow speed also exhibits filamentary structure. It is not well described as smooth, spherically symmetric, diverging flow, but instead ranges from 300 to over 1000 km/s at 5.5 $R_\odot$ among field-aligned filaments like those seen in plumes and rays [Feldman et al., JGR, Dec. 1997]. This is completely unlike the constant high speed solar wind reported beyond 0.3 AU. Consequently, plumes and filamentary structure must be strongly mixed, and the mixing must be far along by 0.3 AU to be consistent with Helios observations. The paradox is what causes the mixing? Existing models of coronal heating and solar wind acceleration hardly address this issue. One possibility we are investigating is the MHD Kelvin-Helmholtz instability, to which the shear between plumes and interplume corona is expected to become unstable at 5-10 $R_\odot$. This instability can be simulated and followed far into the nonlinear regime and may lead to Alfv\'enic fluctuations like those seen at 1 AU.

UVCS/SOHO Observations of the 13 August 1997 Coronal Mass Ejection 

L. Strachan, J. C. Raymond, S. Fineschi, A. Modigliani, R. O'Neal, G. Noci, J. L. KohlThe Ultraviolet Coronagraph Spectrometer (UVCS) on the Solar and Heliospheric Observatory (SOHO) satellite observed a large coronal mass ejection (CME) that erupted near the west limb of the Sun on 13 Aug 1997 at 01:13 UT. The dense core of the CME material reached 8 solar radii at approximately 22:16 UT and was observed with the UVCS Lyman alpha and OVI spectrometer channels. Spectral profiles were obtained in H I Ly-alpha, H I Ly-beta, O VI 1032, O VI 1037, and other weaker lines. In some cases, the line intensities increased by more than an order of magnitude and there were also significant changes to the line widths and line ratios during the CME event. A preliminary analysis of the data and a discussion on the CME dynamics and morphology will be presented. 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.

A Search for Coronal Origins of Solar Wind Streams Observed During the Whole Sun Month

A. J. Lazarus, J.T. Steinberg, D.A. Biesecker, R.J. Forsyth, A.B. Galvin, F.M. Ipavich, S.E. Gibson, R.P. Lepping, A. Szabo, B.J. Thompson, K.W. Ogilvie, A. Lecinski, D.M. Hassler, P. Riley, J.T. Hoeksema, X.P. Zhao, L. Strachan, Jr., B.V. Jackson, P.J. Hick, M. Kojima

 Several solar wind streams having speeds in excess of 500 km/s were observed from the Wind, SOHO, and Ulysses 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). The magnetic field map determined by the Michelson Doppler Imager (MDI) of the Solar Oscillations Investigation shows no obvious associations other than polarity with the extent of the CH region, as might be expected since it observes photospheric rather than coronal features. The CH boundaries do seem to match fairly well with the computed locations of open field in the potential field model of the large-scale field. 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.

Spectroscopic Measurements of the High Speed Solar Wind Near the Sun With UVCS/SOHO 

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

The SOHO Ultraviolet Coronagraph Spectrometer (UVCS/SOHO) is being used to observe polar coronal holes at heliocentric heights up to 4 solar radii. Spectroscopic diagnostic techniques are used to determine proton and minor ion velocity distributions along the line of sight and outflow velocities. Polarized radiance measurements of visible light are used to determine electron densities. Observations at 1.7 solar radii in H I 121.57 nm, O VI 103.19 nm and 103.76 nm indicate intensity enhancements which appear to be polar plumes. Values for the line of sight velocity distributions for H I, O VI, and Mg X, derived from the line profiles, will be presented. Outflow velocities for H I and O VI derived from Doppler dimming also will be given. Limits on the radial velocity distribution of O VI derived from the intensity ratio of the O VI doublet will be discussed. This work is supported by NASA under Grant NAG5-3192 to the Smithsonian Astrophysical Observatory, by the Italian Space Agency, and by Switzerland.