Sharp Changes in the Ordinary Mode Microwave Emission from a Stable Sunspot: Model Analysis

In the work, interpretation is given for a microwave source associated with a stable isolated sunspot as a sample to study the sharp changes in ordinary mode microwave emission. The appropriate microwave source of the solar active region NOAA 10325 was observed with the radio telescope RATAN-600 and the Nobeyama Radio Heliograph during March 30 - April 4, 2003. The radio emission brightness in ordinary mode is shown to be depressed below the brightness of the quiet Sun when the sunspot was near the solar disk centre (April 2-3) but sharply increased in the wavelength range 1.76-2.67 cm at the longitudes |θ| > 50°.

Microwave radiation by gyroresonance mechanism is analysed in relation to the particular features of the images taken in He I 10830 Å chromospheric line (Chromospheric Helium-I Imaging Photometer) and EUV emission lines (Coronal Diagnostic Spectrometer). We have constructed a new model according to which above the sunspot's surroundings at the levels of gyroresonance emission the atmosphere is as cold as a "sunspot plume" (T ~ 10⁵-10⁶ K, N ~ 10⁹ cm^-3). As could be supposed from the He I line intensity, the central part of the sunspot atmosphere contains open magnetic field and rarefied plasma (N ~ 10⁸ cm^-3, T ~ 10^5.5-10⁶ K).