OBSERVATION AND MODEL-CALCULATIONS OF SUNSPOT RING STRUCTURE AT 8.46 GHZ

We present Very Large Array (VLA) observations of AR 7542 which demons trate the existence of definite ring and horse-shoe structures of a su nspot in intensity (I) and polarization (V) at 8.46 GHz (3.5 cm wavele ngth) and compare them with model calculations of gyroresonance radiat ion. The VLA measurements have been made on three different days in Ju ly 1993 when AR 7542 was at three different longitudes which allows us to study the effect of viewing angle on sunspot-associated microwave emission. Model calculations of gyroresonance radiation have been carr ied out using a modified dipole model corresponding to the observed ph otospheric magnetic field strength and average temperature/electron de nsity distributions consistent with soft X-ray and EUV observations (f or the lower atmosphere) as well as theoretical assumptions (for the c orona). The calculated I and V maps were found to be generally consist ent with the radio observations. We obtain information on the magnetic scale length in vertical and horizontal directions above the sunspot and about the distribution of other plasma parameters (temperature, de nsity) inside the radio source region.