Generation of radio noise in the vicinity of the earth

Abstract : A tentative classification of possible sources of radio noise in the vicinity of the earth ay be obtai ed by examining separately available sources of power and known mechanism for conversion of this power. Among the former we may list high-energy electrons such as those trapped in the Van Allen belts; the solar wind; bursts of high-energy particles ejected by the sun; shock waves in the interplanetary medium originating on the sun; and the rotational energy of the earth. Mechanisms of conversion may be classified as direct, such as synchrotron and Cerenkov radiation, and indirect. Indirect conversion involves the excitation of an intermediate state by the available sources of power and subsequent radiation by this state. This intermediate sta e may be localized heating, the formation of unstable current patterns, the acceleration of particles, or the generation of waves which are themselves nonradiative, such as plasma oscillations. The following mechanisms which are relevant to the generation of radio noise receive special attention: Cerenkov radiation, two-stream instability, and the coupling of waves by inhomogeneity and nonlinearity. (Author)