Structure and Dynamics of Transient Brightenings and their Relation to
Magnetic Field Geometry


Contributors: G.H. Fisher, D.W. Longcope, O.H.W. Siegmund, and 
T.A. Kucera (SUMER), J.R. Lemen (EIT), O.H.W. Siegmund and 
D. Zarro (CDS), T. R. Metcalf and L. Jiao (Mees Solar Observatory)

Scientific Justification

Active region coronae are composed of discrete isolated loops, each
defined by closed magnetic field lines.  These loops, visible in UV and
X-rays, are created by some localized heating mechanism (Rosner1978).  
Recently, Yohkoh SXT observations with high temporal resolution have 
revealed that at least some of these loops brighten suddenly, and stay 
bright for periods of minutes (Shimizu1992). These "transient brightening"
TB) events may be related to microflares (Gary1995), and could account for a 
significant fraction of the energy deposited in an active region.

We propose to study active region loops and TBs using SUMER
spectroheliograms in NV and FeXII, CDS spectroheliograms in MgX,
EIT images in FeXII and FeXV, and ground based vector magnetograms 
from the University of Hawaii's Mees Solar Observatory. Several TBs 
should be visible within a single 2' x 2' FOV.  Because of their 
relatively short lifetime, these maps must be made relatively quickly.

The high sensitivity and spatial resolution of SUMER, CDS and EIT will 
provide unprecedented detail in the study of TB's. Simultaneous imaging in 
lines at transition region and coronal temperatures will permit the study 
of the loop's structure, dynamics and energy budget.  For instance, the 
intensity of the NV line, formed in the transition region, can in some 
cases be used as a pressure diagnostic for the base of a loop (Hawley1992).  
Doppler shifts of both coronal and transition region lines provide information 
on how and where energy is being deposited.  Our goal will be to use this 
information to study the energetics and dynamics of TBs.

It is also important to understand why TBs occur along specific
isolated magnetic field lines.  We plan to coordinate the SUMER, CDS, and EIT
observations with the Imaging Vector Magnetograph (IVM) at the
University of Hawaii, which creates vector magnetograms of an active region.
The magnetic field should provide the key to understanding the energy source 
for TB's, if that source is coronal. We are particularly interested in 
magnetic features known as {\it separator field lines}
(Gorbachev1988,Longcope1996) which play a crucial role in
theories of reconnection.  If TB's are caused by reconnection they
should be located at or near separator field lines.


References

Gary, D., Hartl, M., and Shimizu, T. (1995).
Transactions, AGU 1995 Fall Meeting 76 (46), SH41B.

Gorbachev, V. and Somov, B. (1988). Solar Phys. 117, 77.

Hawley, S.L. and Fisher, G.H. (1992). ApJ Supp 78, 565.

Longcope, D.W. (1996). Solar Phys.

Rosner, R., Tucker, W.H., and Vaiana, G.S. (1978). ApJ 220, 643.

Shimizu, T., Tsuneta, S., Acton, L.W., Lemen, J.R., and Uchida, Y. (1992).
Proc. Astron. Soc. Japan 44, L147.


SUMER Observation Sequence

Initial pointing 	               A Small Bipolar Active region 
Slit                                   1 x 120 arcsec^2
Scan Area	                       122 xs 120 arcsec}^2 
Step Size	                       0.78 arcsec (full step)
Resulting Number of Scan Locations     160
Dwell Time                             2.5 sec
Duration of Scan                       421 sec
Line Selection                         NV (1242.804A)
                                       FeXII (1242.01A)
Spectral Binning                       50 -> 25
Estimated Reduction Factor
	  Selection 1 x 25 x 120 px
	  Compression  Quasilog  
	  Reduction  -> 25 x120 x 8 bits/scan


CDS Observation Sequence

Initial pointing                        A Small Bipolar Active region 
Slit                                    2 xs 120, arcsec^2 
Scan Area	                        122 x 120, arcsec^2 
Resulting Number of Scan Locations      61
Dwell Time                              5 sec
Duration of Scan                        474 sec
Line Selection                          MgX (609.79A)
                                        MgX (624.94A)
Spectral Binning                        20 px (no binning)
Compression                             Truncate to 12 bits 



EIT Observation Sequence

Initial pointing                        A Small Bipolar Active region 
Partial Frame Images                    FeXII (195A) 
                                        FeXV  (284A) 
Timing                                  195A  -- several images per minute 
                                        284A  -- one image every 10 minutes