** Title:

          Average Magnetic Helicity of Active Regions: 
          What is the Role of Convection Zone Dynamics?


** Lead Investigator: 

          Richard C. Canfield, Institute for Astronomy, U. Hawaii
          2680 Woodlawn Drive, Honolulu, HI96822


** Other Team Members: 

          Alexei Pevtsov, Institute for Astronomy, U. Hawaii
          2680 Woodlawn Drive, Honolulu, HI96822

          Frank Hill, National Solar Observatory, 
          P.O. Box 26732, Tucson AZ 85726-6732

          SOI-funded NSO Junior Scientist (tbd), NSO


** SOI Coordinator: 
          
          tbd (Bogart?)
          

** SSSC Lead Programmer: 

          tbd (Sa?)


** Abstract/Technical Summary: 

The goal of this study is to determine the relationship of the average
magnetic helicity density of active regions to large-scale motions
observable in the convection zone directly beneath and around them. The
SOI data to be analyzed will comprise several 3-5 day long time series of
full-disk and high-resolution Doppler images obtained in the presence of
sunspots.  This will be used in conjunction with ground-based vector
magnetograms.  The SOI data analysis will use ring diagrams, while the
magnetogram analysis will be done outside of SOI.


** Investigation Plan: 
 
Helicity is a fundamental attribute of magnetic fields in laboratory and
astrophysical plasmas.  In the Sun, preliminary work implies that magnetic
helicity observed at photospheric levels [ref H2] is due to two effects:
shear at great depth and strong perturbations in the convection zone [refs
H3, H4, H5]. The goal of this study is to determine the relationship of
the average magnetic helicity of active regions to large-scale motions
observable in the convection zone directly beneath and around them.

The approach is observational and has two aspects:
(1) magnetic helicity, based on vector magnetograms made from the ground,
through which the average photospheric helicity density and chirality 
(sense of twist, right or left) of active regions will be determined;
(2) dynamics, based on photospheric oscillations observations made with
SOI, through which subphotospheric shear and kinetic vorticity will be
inferred.

The average magnetic helicity measurements require spectrograph-based Stokes
polarimeter observations; typical filter-based vector magnetographs cannot
correct for well-known under-resolution and magneto-optical effects that
distort helicity determinations.  Data reduction techniques for the
spectroscopic polarimetric observations and local helicity density
calculations [ref H1] and analysis techniques for inference of the
active-region-average helicity density from the local measurements have
already been developed [ref H2].

The dynamics observations will use ring-diagram analysis of high-degree
modes. This technique is under intensive development at NSO, U.  Colorado,
and within the SOI team itself [refs D1, D2, D3, D4]. Results using
ground-based data have already produced evidence of both shear layers and
spiraling Ekman-like flows in the outer convection zone which could quite
easily produce magnetic helicity [refs D2, D5].

This project requires cotemporal and cospatial magnetic helicity and
convection-zone dynamics observations for a period of several successive
days, when one or more spotted active regions are present on the disk
within about 45 degrees of the central meridian.  The schedule for the
dynamics observations requires at least one time series of full-disk
Doppler images of 3-5 days duration with the required activity present for
the entire time span. Preferably, these images will be extracted from the
Dynamics program data stream, thereby providing a nearly unbroken sequence
of images around the clock. If the activity levels during the Dynamics
program are insufficient, then Campaign data can be substituted. Selected
3-5 day time series of Campaign high-resolution Doppler images containing
active regions can also be used for the study.

The analysis of the data using ring diagrams is already installed in the
SOI SSSC, and the same algorithms can be used for our program. One 
difference will be the specific selection of the area of analysis -- we
will be targeting specific active regions rather than fully covering the
solar disk.

The schedule for the helicity observations needs to be adapted to the
solar activity and SOHO mission operations constraints (tbd).  The
helicity observations will be based on vector magnetograms obtained at
Mees Solar Observatory and NSO/SP.  The former are gathered on a daily
basis, and therefore require no scheduling.  We have proposed to make the
latter on a bumping basis, and expect to start within one or two days of
the time a "go" response is made to our request.  A proposal has been
submitted for two weeks of observing time in each quarter of the next
year, starting in the fourth quarter of this 1995.  No time is required
for development of analysis tools.  The analysis of a week's data from
Mees is only a few days' work; the analysis of a week's data from NSO is a
few weeks' work.

Once the subsurface flow field has been estimated, it will be used to
predict the magnetic helicity at the surface. This can then be compared to
the actual helicity observed in the vector magnetograms. Discrepancies can
hopefully be used to improve the model and increase our understanding of
the formation of magnetic helicity within active regions, and thereby
contribute to our knowledge of the solar dynamo.


** References:

H1. Pevtsov, A.A., Canfield, R.C., & Metcalf, T.R. 1994a,
``Patterns of Helicity in Solar Active Regions'' ApJ, 425, L117.

H2. Pevtsov, A.A., Canfield, R.C., & Metcalf, T.R. 1994a,
``Latitudinal Variation of Helicity of Photospheric Fields'' 
ApJ, 440, L109.

H3. Canfield, R.C., Pevtsov, A.A., Acton, L.W. 1995,
``Helicity of Active Regions in the Photosphere and Corona'' 
Eos Trans. AGU, 76(17), Spring Meet. Suppl., S235.

H4. Pevtsov, A.A., Canfield, R.C., & Metcalf, T.R. 1995,
``Helicity of Photospheric Magnetic Fields'' 
Eos Trans. AGU, 76(17), Spring Meet. Suppl., S228.

H5. Pevtsov, A.A., Canfield, R.C., & Glatzmaier, G.A 1995,
``Signatures of Convection in Solar Magnetic Helicity'' 
in Geophysical and Astrophysical Convection Workshop, 
October 10-13, National Center for Atmospheric Research, Boulder.

D1. Hill, F. 1988, ``Rings And Trumpets: Three-Dimensional Power
Spectra Of Solar Oscillations'' ApJ, 333, 996.

D2. Hill, F. 1990, ``A Map Of The Horizontal Flows In The Solar
Convection Zone'', Solar Physics, 128, 321.

D3. Haber, D.A., Toomre, J., Gough, D.O., and Hill, F. 1995, ``Local
Area Analysis Of High-Degree Solar Oscillations: New Ring Fitting
Procedures'', Proc. 4th SOHO Workshop: Helioseismology, in press.

D4. Bogart, R.S., Sa, L.A.D., Duvall, T.L., Haber, D.A., Toomre, J., and
Hill, F. 1995, ``Plane-Wave Analysis Of Solar Acoustic-Gravity Waves: A
(Slightly) New Approach'', Proc. 4th SOHO Workshop: Helioseismology, in
press.

D5. Patron, J., Hill, F., Rhodes, E.J., Korzennik, S.G., and Cacciani,
A. 1995, ``Velocity Fields Within The Solar Convection Zone: Evidence
>From Ring Diagram Analysis Of Mt. Wilson Dopplergrams'', ApJ, in press.