Index of Solar Radio Burst Activity at 10.7 cm

Abstract

IT is now well established that the solar radio emission consists of (a) a basic component from the undisturbed Sun remaining constant for a considerable time; (b) a slowly varying component emitted from active centres on the solar surface showing a slow day to day variation in intensity; and (c) a rapidly varying component of short duration known as “bursts”. These bursts are closely correlated to flares and other centres of activity on the solar surface and are observed for a very wide range of frequencies covering centimetre and decimetre as well as metre wave bands. Although spectral studies have given much information about the mechanism of generation of radio bursts in the solar atmosphere at metre wavelengths, contributions from spot frequency observations are still regarded as valuable, particularly at microwave frequencies where bursts are of much simpler character and wider band-width. Furthermore, radio bursts in this frequency range are also accompanied by the enhanced emission of X-rays and ultraviolet rays of the electromagnetic spectrum and particles of different energies the various influences of which on the Earth are now well known. The significant role of microwave radio bursts in solar and geophysical studies can thus be appreciated and has led to the evaluation of an index of radio burst activity at 10.7 cm which, it is hoped, would supplement other indices of solar activity that already exist.