Stable ‘pancake’ distributions of low energy electrons in the plasma trough

Abstract

WAVE–PARTICLE interactions have been recognised as the likely key to processes which control the dynamics of the Earth's magnetosphere and trigger auroral precipitation¹. The GEOS 1 and GEOS 2 satellites carry wave and particle measuring instruments which permit a full exploration of interactions occurring in the equatorial magnetosphere out to a distance of 7 R_E (ref. 2). The large variety of plasma wave phenomena has been reviewed by Southwood³ and Christiansen et al.⁴ have reported on emissions observed by GEOS 1. The geostationary position was expected to be an oasis of important wave–particle phenomena because it is in that region of the magnetosphere where cold plasma, originating from the ionosphere, mixes with hot plasma–sheet particles⁵. The large amount of data now emanating from GEOS 2 more than meets expectations, a number of relatively exotic particle distributions are being observed together with clearly associated wave spectra. Here, we report on one significant example.