JOP 110: Structure of the Poles During Magnetic Transition



STRUCTURE OF THE SOLAR POLES DURING THE MAGNETIC TRANSITION


	C. DeForest; A. Fludra; C. Kankelborg; B. Thompson
	
	Point of contact: C. DeForest, zowie@urania.nascom.nasa.gov


	Introduction

The Sun is currently observed to have near zero net magnetic field; it is undergoing
the inversion of its dipole field, and the poles have near zero net signed magnetic flux.
Simultaneously, we are near the annual maximum "B" angle of 7.25 degrees, allowing a 
near-optimum view of the North pole of the Sun.

As the last vestiges of the bulk field are neutralized and
reversed, the overlying coronal structures are converting from open to
closed and back to open field configurations in a uniquely coherent,
large-scale reorganization.  The goal of this JOP is to characterize
both the magnetic and lower coronal structure of the poles during this
unique time in the solar cycle as the polar coronal holes shrink, disappear,
and (ultimately) reform.  

By collecting coronal data in an organized manner, we hope to characterize both the
mesoscopic structure of the magnetic reversal and the coronal response to the changing
flux linkages.  TRACE and EIT will provide global and local structures to compare with
magnetic field models.  By recording images near the pole at multiple wavelengths, TRACE
will provide an indication of ionization temperature in the observed structures.  Reference
spectra from CDS will provide composition and temperature diagnostics for specific times.

This JOP addresses the following specific questions:

	Is there a difference in the small-scale magnetic activity
	(``magnetic carpet'') between "normal" quiet sun and the transitioning
	polar zone?  Polar coronal holes at solar minimum exhibit
	distinct differences in flux concentration size and location compared 
	to normal mid-latitude quiet sun; but the transitioning poles have not
	yet been well characterized with single continuous, seeing-free dataset.

	How do the boundaries of the polar coronal holes evolve as the 
	hole shrinks toward the pole?  Does the edge of the coronal
	hole maintain connection with a particular part of the
	surface, or does it move across surface features as do the
	boundaries of low latitude coronal holes?

	How do the unique magnetic conditions and global-scale reconnections affect
	the local coronal material near the poles?

	Is there an obvservable difference in the supergranulation pattern
	at the pole compared to other times and/or places?  If so, how does it affect
	the small- and mid-scale structure of the magentic field
	and, in turn, of the corona?

	What happens to the open field lines emerging from the pole?  As the
	coronal hole constricts, do field lines visibly "snap" outward, producing
	ejecta different than ``normal'' CMEs?  By comparing motions
	near the surface with coronal images higher up, we will be able to perform 
	a sensitive search for such rapidly moving structures.




	Instruments' contributions:

MDI: will record surface magnetograms and dopplergrams
continuously for five days at a one-minute cadence.  The northern 3/4
of the disk will be imaged.  The doppler signal will allow tracking of
the supergranular pattern and comparison with similar datasets
collected during solar minimum.  The magnetogram data will be averaged
to 16 or 32 minute bins during post processing to increase
signal-to-noise ratio.

EIT: The normal EIT synoptic "CME watch" program will suffice to
record global structures and relate them to magnetic fields.

TRACE: will record images in 195A, 171A, and 1550 (full
3-wavelength sequence) on a 5-10 minute cadence over the very pole of
the Sun.  Pointing will be 3/4 on-disk and 1/2 (approx. 2 arc min)
over the limb, centered on the Pole.  Deep-exposure ("coronal hole")
AEC settings will be used.

CDS: will record periodic reference spectra in a single slit
position on the central meridian, extending from just above the limb
to the bottom of the TRACE field of view.

LASCO: The normal LASCO C-2 synoptic sequence will suffice to monitor evolution
of open structures (and their demise) in the middle corona

Scheduling constraints:

This JOP is intended to be run during the 5-day continuous DSN contact starting
Wednesday, 25-Aug-1999.  At least 3 days of TRACE and CDS support are requested.
The TRACE sequence may be interrupted periodically but brevity of interruptions is
desirable as motions of the coronal hole boundary take place on timescales of tens 
of minutes.  CDS support is for intermittent "snapshot" spectra and may be interleaved
freely with other projects, though several spectra per day are requested.  EIT and 
LASCO will, presumably, continue their synoptic programs throughout.