The brightness temperature distribution of microwave emission in a solar active region generally shows a ring structure, with a dip at the centre. However, no dip was found in the Nobeyama Radioheliograph left handed circular polarization (LCP) image on 1992 August 18; instead, there was a peak. This is a completely LCP source with Zero right-handed circular polarization (RCP). We examine this structure on terms of the joint effect of gyroresonance and bremsstrahlung mechanism with a raised electron density above the central part of the sunspot, and the commonly assumed temperature and vertical dipole magnetic filed modes. The raised electron density is found to be 1.4×10^11cm^-3 at the chromosphere base.
展开▼
