Constructing the BEST High-Resolution Synoptic Maps from MDI

J.T. Hoeksema, Y. Liu, X.P. Zhao, A. Amexcua

Synoptic maps provide a global view of the solar magnetic field.  However,
what constitutes the 'best' possible synoptic map depends on the
application. Traditional charts are compiled from data observed close to
central meridian from magnetograms observed over a 27-day solar rotation.
But with higher resolution data, a whole new set of details must be
addressed when assembling such maps.  Small-scale features move and evolve
on the time scale over which the maps are constructed.  The fluctuating
background noise level is comparable to the smallest features.  Projection
effects and sensitivity variations of different sorts complicate the
effort.  And what about the polar field? (See accompanying poster by Liu et
al.)  Parts of the Sun cannot be seen.  We describe methods for assembling
the best maps possible by accounting for image sensitivity, image scale,
corrupt pixels, differential rotation, geometric field projection, zero
offset, varying noise characteristics of MDI magnetograms, and polar field
interpolation.