Abstract

wave circular polarization of the active region (AR) NOAA 7260 on 21-23August 1992 is analyzed. Two-dimensional images at 1.76cm with spatial resolution of theta=10'' from the Nobeyama radioheliograph and one-dimensional scans at 9wavelengths in the range of 1.81-3.43cm and theta=16.3''-31.1'' from the radio telescope RATAN-600 were used. An inversion of the sense of circular polarization through the wavelength range was recorded on 22August. It is shown that both the wavelength and the time dependence of the inversion are consistent with quasi-transverse (QT) propagation of the radiation in the solar corona. From this, the strength of the coronal magnetic field in the active region was found to be H=20-65G at a height of h= (5.7-8.7)x109cm above the photosphere on 22 and 30August and 125G at the lower height of (3.7-6.4)x109cm on 23August. We present a new technique, based on the radio mapping (in both StokesI and V) of an AR undergoing circular polarization inversion; applying this method to the Nobeyama data we obtained, for the first time, a magnetogram of the coronal magnetic field. For AR7260 we found values in the range of 70-100G at heights of (4-6)x109cm on 23August, adopting a constant value of NLalpha (where N is the electron density and Lalpha is the scale of the coronal field divergence) of 2.5x1018cm-2. We compare our results with force-free extrapolations of the photospheric magnetic field from a MSFC magnetogram obtained on 20August.