Solar quiescent prominences at 10.7 GHz

Abstract

Filaments on the Sun, which are dark linear features in the light of the Fraunhofer Hα line, are a mysterious feature of the solar surface. They are blade-like extensions of the chromosphere projecting to a height of 40,000 km into the corona, and may extend for up to 200,000 km along the surface. The fact that they may persist for a year or so, disappear abruptly and then reappear in the same positions shows that they are superficial indicators of deeper phenomena. There have been several reports^1–4 of reduced brightness in the radio spectrum associated with the Hα filaments, leading to the widely accepted view that filaments are associated with broad dark radio features. This picture is, however, contradicated by our observations at 10.7 GHz of one solar filament during the solar eclipse of 12 October 1977.