The goals of Working Group B are to determine the quantitative plasma parameters (densities, temperatures, outflow velocities for electrons, protons, and ions) based on empirical constraints derived from observations of several coronal and in situ instruments.
There will be an attempt to relate plasma parameters determined by different instruments that may use different methods for their quantitative determinations. In this way, the conditions in the corona can be determined from the base at 1 Rsun out to the region of solar wind acceleration (2 Rsun and beyond).
An important result from this work will be the development of a self-consistent empirical description of the 3D corona that can be used to test theoretical models of coronal heating and solar wind acceleration in open and closed magnetic field regions of the corona.
We began the workshop by identifying the known techniques that are being used to derive densities, temperatures, and outflow velocities for the electrons and ions in the corona. Not surprisingly, there were numerous techniques used by the various instruments. Almost all of the techniques have instrumental effects that must be well-understood before final results can be achieved. In addition, assumptions about the conditions in the corona, like optical depths, spherical symmetry, or volume of emitting plasma, must be made in order to get some of the results.
Nonetheless, we came up with a list that is a useful start until it becomes clearer what techniques can work. The plasma parameters and the techniques used to derive them are shown below:
2. CDS (Bromage, Del Zanna) 17 Aug + additional dates NCH, and Boundary of NCH (on disk and above limb) Ne, Te, Diff EM 27 Aug - Equatorial extension of NCH
3. SUMER (Warren, Hassler) 21 Aug, 28 Aug - Full Disk (S VI) Reference Spectrum of NCH (Offlimb and Disk) 27 Aug Non thermal Vel, line shifts; Ne, Te sensitive ratios Full Disk Images out to 1.3 Rsun 5 lines in NCH (obtained once per week during WSM) scale ht. temps from line intensities aim to separate thermal and nonthermal temps.
4. UVCS (Strachan, Giordano, Dobrycka) FOV from 1.5 to 3 Rsun 17 Aug +/- 3 days on W Limb; NCH 24 Aug NCH LOS Velocity distr. for H and O5+ outflow velocites H, O5+ (from Doppler dimming) CH Boundaries in intensity, line widths Daily Synoptic Maps in intensities, line widths H Lya, OVI 1032,1037 Special Obs.: radial scans every 30 deg around Sun
5. C1/C2/MLSO (Gibson, Zidowidt) 17 Aug; 24 Aug Ne (van de Hulst; magnetostatic) Teff 2 ways (vdeH; force balance model) densities from emission measure of Fe XIV Daily synoptic maps
6. SXT (Alexander), EIT (Thompson) disk to 1.25 Rsun Te from filter ratios emission measure used to get Ne, Te (with assumed est. for emission volume; Irreg. factor) synoptic maps in intensity, temperature
7. SWICS/Ulysses (Ko, Galvin) ion speeds, charge states, ion temperatures, T(freeze-in) 1 month of high speed wind (before DOY 256) DOY 257 - 262: slow wind (CR 1913 long. 255 - 200 deg) 4+ days of data of steady decrease from fast to slow wind
To simplify the data analysis effort, we chose two periods from the Whole Sun Month to focus our efforts. The main period is the week centered on 17 August 1996 when there was a stable equatorial streamer on the West Limb of the Sun. This streamer is ideal since it appears to be one that can be treated by an axisymmetric model for the densities. The second observing period was on 24 August 1996 where several of the instruments made observations of the north coronal hole. The north coronal hole was larger and had less foreground and background structures of higher density along the line of sight. Therefore, the north coronal hole model will be used as the model for the solar minimum polar coronal hole.
Densities and temperatures from white light data
The next step is to compare the results from the different methods, where there are common observation dates, and to consolidate the results so that the coverage in spatial extent (radial and azimuthal) is as complete as possible. We don't expect that the picture will fit together perfectly but we will strive for self-consistency whenever possible using only basic assumptions to relate the various derived quantities to each other.
We hope to incorporate some of the results from the 3-D modeling group in order to get infer global properties of the corona from the specific regions that we will analyze in some detail. There is also some overlap with the work from Working Group C which is studying the equatorial coronal hole on the disk. The offlimb observations may be useful as well, if it can be shown that any foreground and background emission can be removed.
The final product from this Working Group, an empirical description of the physical conditions of coronal holes and streamers, can be used by theoretical modelers in two ways (at least). One way to that the empirical model can be used is to use the derived physical quantities as inputs into a theoretical model so that the particular model can be made as realistic as possible. The second way to use the empirical model is to take a subset ot the physical parameters determined by the observations and then use theory to predict what the other physical quantities should be. Only those theories that can predict the derived quantities (within the uncertainties of their mean values) can be called successful.
Much work remains to be done but I feel that we are off to a good start. The success of the working group will depend on how well each member can keep in touch with others working on similar topics. The cross fertilization of ideas should benifit the group as whole and hopefully produce some significant progress in the understanding of how the corona is heated and accelerated to form the solar wind.
Leonard Strachan