Title: 
==============
 Proposal for global analysis of the magnetic field evolution during the period of instability of a filament.  

Lead Investigator:
=======
Brigitte Schmieder

Team Members:
==================
	Pierre Mein, Jean-Marie Malherbe, 
P. Demoulin, J.E. Wiik, and Lidia van
 Driel-Gesztelyi, J.C.Vial,
T. Kucera and A. Poland

Local Coordinator:
==================
Craig DeForest and Julia Saba

Lead Programmer:
=====


Technical Summary:
==================
 
        
Scientific background:

The solar corona is extremely complex. Besides coronal loops
within active regions (ARs), there are loops which connect different
ARs, even across the equator, as well as loops which connect ARs to
quiet Sun several arcminutes away (Strong et al. 1994, Strong 1994).
When a structure becomes unstable and starts to expand, it will very
probably meet and interact with other magnetic loops. Such events may 
lead to a re-organization of the coronal structure. On a short time
scale( a few hours to a day), such re-organization has been observed 
following filament eruptions or disparition brusques (Watanabe et al.
1992, McAllister et al 1992, Tsuneta et al. 1992, Watanabe et al. 1993,
Kahn et al. 1993, Hanaoka et al. 1994). In some cases, small transient
coronal holes were reported to form as a result of such events (Watanabe
et al. 1992, 1994).

Since observations of multiple  layers of the solar atmosphere are 
required to understand such events (Schmieder 1992, Raadu and Schmieder
1988), we propose to study combined data on disparition brusques from 
the corona (Yohkoh/SXT), the transition region (SOHO/CDS, SUMER, and 
EIT ), the chromosphere (MSDP, Tenerife), and the photosphere (SOHO/MDI).
MSDP provides spectral data in Halpha and Ca lines
in 2 D (typically 0.5 by 4 arc min)

Past observations:

We obtained good data during the coordinated filament campaigns (JOP 17) with 
Yohkoh and SOHO in the periods June 3-9, 1996, and September 20-29, 1996.
In June, the MSDP spectrograph at the Pic Du Midi telescope observed
active regions and filaments (Malherbe, Roudier). In September, three
telescopes in the Canary Islands were involved in an international 
ground-based campaign: the German telescope VTT with our MSDP spectrograph
(P. Mein, Schmieder, Malherbe), the Gregory (Magnetic field - Germans from
Freiburg, the  Swedish telescope (Engvold and J.E. Wiik).
Successful observations were also made by CDS and SUMER instruments on SOHO
(T.Kucera and A. Poland) and by the SXT on Yohkoh.

We observed some disparition brusque and a large loop with Yohkoh
 on September 25-26, large filament and  emerging flux
near disk center on June 7-9.

Future Observations:
We plan to have two weeks of campaigns in 1997 one in June and one in 
September and we hope that MDI could support them. After some preliminary
work on the existing data we would be able to be more precise in our request.



Proposal Text:
=======================
	
MDI data sets needed:

Daily full-disk magnetograms in the interval 0700-1100 UT (or the closest one
available) for the preiods Sept 24-27, 1996. and June 3-9, 1996.


Planned use of MDI data:

We plan to use the technique developed by Demoulin to extrapolate the
magnetic field and define the "quasi-separatrix" over the
 active region (Demoulin and Priest 1996 and references herein) to
 understand the conditions of the filament eruptions.


See Also:
=========
 Raadu M., Schmieder B., Mein N., Gesztelyi L: 1988. A and A 197,289       in press.
  D\'emoulin, P., H\'enoux, J.C., Priest, E.R. and Mandrini, C.H.:
  1996, aA et A {308}{643}
 D\'emoulin, P., Bagal\'a, L.G., Mandrini, C.H., H\'enoux, J.C. and
         Rovira, M.G.:  \aetap{97}