UVCS Observations of Solar Wind and its Modeling
Steven R. Cranmer
This presentation will review the dramatic new understanding of
the solar wind that has come from the past decade of UVCS/SOHO
observations, analysis, and theoretical work. In many ways,
there is a key synergy between the two very different kinds of
remote-sensing measurements discussed here.
(1) The high-resolution solar disk measurements of Yohkoh and
Solar-B reveal the complex lower boundary conditions for solar
mass loss. (2) Coronagraph measurements in the wind's
acceleration region (especially in combination with spectroscopy)
allow the highly dynamic nonequilibrium evolution of the plasma
to be followed as the asymptotic conditions in interplanetary
space are established. Both kinds of observations are needed
for a complete understanding of the expansion of the Sun's
atmosphere. This presentation gives a brief survey of UVCS/SOHO
results, including evidence for preferential acceleration of
heavy ions in coronal holes, ion temperatures exceeding
100 million K at large heights, and extreme departures from
Maxwellian velocity distributions in both fast and slow solar
wind streams. UVCS also provided the first detailed plasma
diagnostics of coronal mass ejections in the extended corona,
yielding new insights into the roles of shock waves,
current sheets, and helicity conservation in the evolution of
solar eruptions.
Correspondence
Steven Cramer (scranmer@cfa.harvard.edu), Harvard-Smithsonian Center for Astrophysics
presentation
invited