Origin of Long-period Micropulsations

Abstract

Several workers¹ have discussed the origin of micropulsations in the geomagnetic field with periods of several minutes. Recently, after the discovery of the magnetospheric tail², ideas about the origin of these micropulsations have been extended to include the effect of the tail. It has been suggested that the definite and regular shape of the geomagnetic tail will allow hydromagnetic waves of only certain discrete frequencies to propagate, which may appear as micropulsations³. A simple double-cylinder waveguide model⁴ of the tail allows the propagation of 3.3, 20 and 30 min periods. Another model⁵ of theta geometry also explains some long period micropulsations originating from the magnetospheric tail. It seems that many of the long periods, such as the 20 and 30 min periods discovered long ago in the geomagnetic field data, can now be explained by these models^3,4. Indeed, one possible source for the generation of these micropulsations is the magnetospheric tail.