Constructing the BEST High-Resolution Synoptic Maps from MDI

1
Constructing the BEST High-Resolution Synoptic
Maps from MDI J.T. Hoeksema, Y. Liu, X.P.
Zhao, A. Amezcua Stanford University
Carrington Rotation 2055 April 2007 RADIAL
FIELD
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.
Process for Constructing Synoptic
Chart Announcing New Level 1.8 MDI
Magnetograms For each 96-minute MDI magnetogram,
we correct for Uniform Zero Offset due to
Shutter Jitter (Existing) Bad Cosmic Ray Pixels
(New, rare) MDI saturation (Not yet
implemented) Calibration using UCLA rescaling
mask (New) In heliographic remapping
processing Convert from Line-of-sight to radial
(assumption). Adjust Carrington mapping for
differential rotation Ulrich Boyden (Solar
Phys. 235, 17, 2006) Zhao et al., in prep,
2006/7) Radial Field Synoptic Chart
Construction Combine remapped radial
magnetograms Select for uniform effective
integration time (equivalent to 20 one-minute
magnetograms) Use data closest to central
meridian Statistically test and eliminate cosmic
ray corruption Options Polar field
interpolation (See adjacent poster)