ON THE GRADIENT OF CORONAL MAGNETIC-FIELDS FROM RADIO OBSERVATIONS

A technique is proposed to estimate the magnetic field and its derivat ive in coronal layers above solar active regions. On the basis of the theory of quasi-transverse propagation of microwaves, the measurable d egree of circular polarization is related to the gradient of the coron al magnetic field. The relation is applied to the analyses of a set of microwave sunspot-associated sources at the time when they reverse th e sense of their circular polarization. Here we present the characteri stic values of coronal fields H=20 G, partial derivative H/partial der ivative l=10(-9) G cm(-1) at a height of 10(10) cm, estimated using sp ectral-polarization observations with the radiotelescope RATAN-600 (th eta=18 ''-36 '' at lambda lambda=2.0-4.0 cm). The steepest gradient of 2 x 10(-5) G cm(-1) at h=5 x 10(9) cm is obtained in the case of coro nal magnetic fields overlying a sunspot with a high photospheric prope r motion.