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Streamer Evaporation
Wu, S. T.; Suess, S. T.; Wang, A. -H. +1 more
Streamer evaporation is the consequence of heating in ideal MHD models because plasma is weakly contained by the magnetic field. Heating causes inflation, opening of field lines, and release of solar wind. It was discovered in simulations and, due to the absence of loss mechanisms, the ultimate end point is the complete evaporation of the streamer…
Characterization of Solar Coronal Holes and Plumes Using Spectroscopic Diagnostic Techniques Applied to SOHO/CDS Observations
Del Zanna, G.; Bromage, B. J. I.
Results from a series of SOHO/Coronal Diagnostic Spectrometer (CDS) observations of coronal holes and plumes are presented, including analysis of a low-latitude plume observed in August 1996. Spectroscopic diagnostic techniques using the CHIANTI atomic database are applied to derive the plasma parameters: electron density, temperature, and element…
Working Group 1 Report: Solar Wind Models from the Sun to 1 AU: Constraints by "in situ" and Remote Sensing Measurements
Marsch, E.; Leer, E.
The goal of Working Group 1 was to discuss constraints on solar wind models. The topics for discussion, outlined by Eckart Marsch in his introduction, were: (1) what heats the corona, (2) what is the role of waves, (3) what determines the solar wind mass flux, (4) can stationary, multi-fluid models describe the fast and slow solar wind, or (5) do …
Coronal Hole Properties Observed with SUMER
Solanki, S. K.; Wilhelm, K.; Schühle, U. +5 more
We analyze SUMER spectra of 14 lines belonging to 12 ions, obtained on both sides of the boundary of polar coronal holes as well as at other locations along the limb. We compare line intensities, shifts and widths in coronal holes with values obtained in the quiet Sun. We find that with increasing formation temperature, spectral lines show an incr…
Coronal Heating: a Comparison of Ion-cyclotron and Gravity Damping Models
Poletto, G.; Cuseri, I.; Mullan, D.
SOHO/UVCS data indicate that minor ions in the corona are heated more than hydrogen, and that coronal heating results in T⊥ larger than T‖. Analogous behavior has been known from in situ measurements in solar wind for many years. Here we compare and contrast two mechanisms which have been proposed to account for the above beh…
Properties of Coronal Hole/Streamer Boundaries and Adjacent Regions as Observed by SPARTAN 201
Guhathakurta, M.; Strachan, L.; Kohl, J. L. +4 more
The Spartan 201 flights from 1993 to 1995 provided us with observations in H I Lyman-α of several coronal hole/streamer boundaries and adjacent streamers during the declining phase of the current solar cycle: Analysis of the latitudinal dependence of the line intensities clearly shows that there is a boundary region at the coronal hole/streamer in…
Two-fluid 2.5D MHD Simulations of the Fast Solar Wind in Coronal Holes and the Relation to UVCS Observations
Davila, J. M.; Ofman, L.
Recent SOHO/UVCS observations indicate that the perpendicular proton and ion temperatures are much larger than electron temperatures. In the present study we simulate numerically the solar wind flow in a coronal hole with the two-fluid approach. We investigate the effects of electron and proton temperatures on the solar wind acceleration by nonlin…
Working Group 4 Report: Composition and Elemental Abundance Variations in the Solar Atmosphere and Solar Wind
Bochsler, Peter; Mason, Helen E.
This paper contains a summary of the topics treated in the working group on abundance variations in the solar atmosphere and in the solar wind. The FIP bias (overabundance of particles with low First Ionization Potentials over photospheric abundances) in coronal holes and coronal hole associated solar wind amounts to values between 1 and 2. The FI…
Constraints on Coronal Outflow Velocities Derived from UVCS Doppler Dimming Measurements and in-Situ Charge State Data
Romoli, M.; Dobrzycka, D.; Biesecker, D. A. +6 more
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 solar radii, were determined from 3-…
Coronal Heating by Magnetic Explosions
Falconer, D. A.; Moore, R. L.; Porter, J. G. +1 more
From magnetic fields and coronal heating observed in flares, active regions, quiet regions, and coronal holes, we propose that exploding sheared core magnetic fields are the drivers of most of the dynamics and heating of the solar atmosphere, ranging from the largest and most powerful coronal mass ejections and flares, to the vigorous microflaring…