Radio emission of loop structures on the sun at near-critical frequencies

An exact formula is derived for the optical thickness of an inhomogeneous plasma layer (Epstein layer) that simulates a loop structure on the sun for a wave of TE polarization and oblique incidence. Constraints on the angle of incidence on the current layer are found for which the formula for optical thickness also describes well the case of TM polarization. Elementary coronal-loop models are examined and it is shown that the radioemission intensity spectrum without allowance for the magnetic field can have a broad peak at frequencies close to the plasma frequency at the center of the layer. A comparison with observation data is performed.St. Petersburg State University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 36, No. 6, pp. 467–474, June, 1993.