Hydromagnetic emissions, X-ray bursts, and electron bunches: 2. Theoretical interpretation

Abstract

The existence of bunches of monoenergetic electrons oscillating back and forth along field lines in the magnetosphere has been suggested by a number of workers to explain various geophysical phenomena. The simultaneous occurrence of x-ray and hydromagnetic emission bursts (regular oscillatory micropulsations at frequencies in the range 1-2 cps) immediately after sudden commencements and during magnetically disturbed periods, as discussed in part 1, raises the possibility that hm emissions could be generated by such electron bunches. A model is presented that considers certain aspects of the motion of geomagnetically trapped electrons relevant to the production of hm emissions by electron bunches. A new result is the calculation of electron motion in a dipole field confined to the interior of a sphere (as a first approximation to the solar wind cavity). The model calculations are applied to experimental results discussed in part 1, and it is shown that the electrons responsible for the x-ray burst after the sudden commencement of June 27, 1960, could have produced the hm emission burst at that time, and that the maximum observed hm emission frequency as a function of geomagnetic latitude is consistent with the calculated value. Hydromagnetic emissions during magnetically quiet times are characterizedmore » by a fine structure containing overlapping bands of rapidly increasing frequency. This is tentatively interpreted as indicating rapid acceleration of electron bunches; hence, if the model is correct, hm emissions will provide a powerful tool for studying the acceleration mechanism for electrons in the magnetosphere.« less