TITLE: Correlative study of magnetic field properties and coronal plasma
composition 

J.L.R. Saba (MDI/Lockheed @SOHO EOF)
A. Fludra (CDS/RAL, JOP 21 leader)
J.T. Hoeksema (MDI/Stanford)
and other interested parties (to be determined).


ABSTRACT:
The proposed collaborative investigation uses calibrated MDI high
resolution (HR) and full disk (FD) magnetogram data, extrapolated into the
corona, in conjunction with data from SoHO coronal instruments, to address
the following question: Are trace element abundances in transition region
and coronal plasma correlated with properties of the associated magnetic
structures? For example, how do they depend on the age, height, field
strength, configuration, or evolution of those structures? Understanding 
abundance variability will improve interpretation of many kinds of solar 
data and may yield insights into how coronal plasma is supplied and heated. 
This study supports SoHO JOP 21.

TECHNICAL SUMMARY:

BACKGROUND: A variety of solar wind, solar energetic particle, and
spectroscopic studies [see, e.g., Meyer 1985] show that the composition of
the solar corona differs systematically from that in the photosphere:
Elements with low first ionization potential (FIP) are preferentially
enhanced relative to high-FIP elements (or high FIPs are preferentially 
depleted). A good quantitative model does not yet exist, but the FIP effect
is believed to reflect ion-neutral separation in a magnetic field, in a
temperature regime (~10,000 K) where low-FIPs are essentially ionized and
high-FIPs largely neutral, by a mechanism which operates on a diffusion
timescale. Variations in the magnitude of the enhancement factor, in the
threshold of the low-FIP/high-FIP transition, and in the shape of the
FIP-related distribution have been reported for different kinds of solar
structures, among structures of the same type, and within a given structure
over time. Such variability can sometimes lead to order-of-magnitude 
uncertainties in such physical quantities as emission measure derived from 
spectroscopic, multilayer, or broadband filter data. Combining MDI
magnetogram data with abundances determined from CDS and SUMER, along with
structural information from EIT and Yohkoh SXT and/or TRACE, should tell us
whether T.R. and coronal abundance variations are more related to magnetic
field strength in the differentiation region, the openness of the structures, 
or the height or age of the structures, as have been variously suggested. 
Such information should provide clues to the separation mechanism, and 
the trace element abundances may help diagnose the physical conditions in
the regions which supply material to the observed structures. 

DATA TO BE USED IN STUDY:
 - MDI data: High-resolution and sub-fields of full-disk magnetograms.
 - CDS and SUMER spectroscopic data as specified in JOP 21.
 - Cospatial images from EIT (TBD), and Yohkoh SXT and/or TRACE when
available, for geometric context, interpretation, and sanity check on
magnetic field extrapolations. 

REQUIREMENTS SUMMARY:
 - Synoptic FD_Mag and standard VC2 HR_MAG data should be adequate.
 - Frequency TBD (whenever CDS and/or SUMER abundance data are available).
 - Solar conditions: This study should be made on a wide variety of targets,
from coronal holes and quiet Sun, to bright points and active region loops.
Nonsimultaneous data can also be used to study stable targets on the limb.

TYPE OF ANALYSIS:
 - Level-1 calibration of high-resolution and sub-fields of full-disk
magnetograms, with potential extrapolations into the corona. 
 - Coregistration of MDI data with data from other instruments. Analysis of
other data sets in parallel. 


REFERENCES:
SoHO JOP 21: Elemental Abundances from EUV Spectra (JOP leader: A. Fludra)
   (http://sohowww.nascom.nasa.gov/operations/JOPs)
Meyer, J.-P., 1985, Ap. J. Suppl., 57, 151.