A Study of the Flux Budget of Active Regions
              using SOHO/MDI and Ground-Based Data

Principal Investigator: Gary A. Chapman
Co-Investigators: A.M. Cookson, J.J. Dobias, D. Preminger, and S.R.
                  Walton

                            ABSTRACT
     The radiant flux from an active region is determined by the
presence of sunspots and faculae, which have different temporal
developments.  An important question in solar physics is what is
the energy budget in active regions.  An answer to this and related
questions requires uninterrupted observations, with photometrically
stable imaging, over the life of the active region.  We propose to
combine SOHO/MDI observations with ground-based images at the Ca II
K-line and other wavelengths to determine the energy budget of as
many active regions as practical.  We would also improve our
knowledge of the facular irradiance contribution to variations in
the total irradiance and we would improve our knowledge of the
center-to-limb contrast of faculae.

Scientific Plan
     To determine the energy budget of an active region,
observations are needed of the region before sunspots begin to
appear because faculae can precede sunspots.  This implies the need
for full disk imaging, probably from the ground.  However, to avoid
gaps in the data due to weather and the day-night cycle, space data
such as from SOHO are needed.  It is rather difficult to find
active regions with the proper lifetime, placed at the proper
longitude so that their entire lifetime can be observed.  It is
probably more difficult, at least from the ground, than finding a
large solar flare that can be observed in its entirety.  In the
process of determining the energy budget of active regions, we
would also determine, more accurately than in the past, the
contribution of faculae and network to irradiance variations.  For
a subset of regions, we would use the high resolution mode of the
MDI to improve our knowledge of the contrast of faculae close to
the limb.  This would permit the construction of an improved model
of the center-to-limb dependence of facular contrast.

Data Requirements
     Full disk continuum images are will be needed from the MDI
experiment on SOHO at least twice per day to monitor the irradiance
fluctuations caused by individual active regions.  It would be very
helpful to filter the MDI images over 5 to 10 minute intervals in
order to reduce the effect of convection and p-mode structure. 
This would allow more precise recovery of the contrast of facular
and network features.  In addition, high resolution images of
selected faculr regions would be needed to determine their contrast
as a function of limb distance.  These data will be combined with
daily ground-based images obtained with the two full disk
photometric telescopes at the San Fernando Observatory (SFO). 
These two telescopes, Cartesian Full Disk Telescope (CFDT)  1 and
2, have pixel sizes of 5" and 2.5", respectively.  These images
will have comparable spatial resolution with the SOI it its full
disk mode.  CFDT2 daily images are obtained at the following
wavelengths/bandpasses in Angstroms: 6723/97, 4706/87, 3934/9, and
3934/3.  An additional filter at 9970/62 will be added soon.  The
K-line images are taken in pairs separated by 7.5 minutes and are
summed to reduce the intensity of the p-modes.  Other ground-based
data that may be available will be utilized as deemed appropriate.

Data Processing
     The photometric images of selected active regions will be
processed using software developed by the SOI team and by the staff
at the SFO.  The filtering of the MDI images would best be done at
the SOI Science Support Center at Stanford.  The processing of the
calibrated and filtered images could then be carried out at SFO or
the CSUN campus using software running on HP 700 model
workstations.  Both IDL and IRAF are running on these systems. 
Data could be transported on EXABYTE tapes.  Selected images could
be sent to or retrieved from the SOI Science Support Center over a
high speed link to the CSUN campus.  The SFO and the campus are
connected by a 56 kbaud line permitting the sending of SFO images.

Science Goals
     1.  To determine the radiative energy budget for a number of
active regions over all or most of their lifetime.  This will help
our understanding of the flow of energy through the outer part of
the convection zone and will complement the results from
helioseismology.
     2.  To improve our understanding of the causes of fluctuations
in the total irradiance by collaborations with other groups and by
using spacecraft measurements of the total irradiance.  MDI images
will be very useful because of their relatively high spatial
resolution.  It should be possible to determine the irradiance
contribution of faculae without the need for proxy data, such as K-
line images.
     3.  To improve our knowledge of the facular center-to-limb
contrast, a much debated function.  This would be done using
selected high resolution MDI images with 1.25" pixels of selected
facular regions.