Abstract
Our statistical study is based on a compilation of the daily
Nobeyama
Radioheliograph full-disk
maps obtained at 17 GHz between July 1992 -- December 1994. It includes
533 active regions,
20% of which appear to have gyroresonance cores during some part of
their disk crossing. At least
one of the regions reaches coronal temperatures (T>10(6) K) while
several others show a
polarization reversal at the extreme limb. Our study indicates that the
gyroresonance cores are
polarized in the sense of the x-mode and are due to s=3 (B=2024 G)
and/or s=4 (B=1518 G)
gyroresonance absorption in the transition region and/or corona. We also
investigate the
dependence between various physical quantities such as brightness
temperature, degree of
polarization, spot area, photospheric magnetic field and heliographic
longitude and comment on the
polarization reversals at the limb. A more detailed study of individual
active regions, that have
been also observed with the Owens Valley Solar Array, will follow.