Propagation of electromagnetic ion cyclotron wave energy in the magnetosphere

Abstract

Recent satellite and conjugate observations of Pc 1 electromagnetic ion cyclotron (EMIC) waves have cast doubt on the validity of the long‐standing bouncing wave packet (BWP) model that describes their propagation in the magnetosphere. A study was undertaken using the Combined Release and Radiation Effects Satellite (CRRES) E and B field data to further the understanding of the propagation characteristics of Pc 1 EMIC waves in the middle magnetosphere. CRRES covered the region L = 3.5–8.0, magnetic latitude up to ±30°, and magnetic local time 1400–0800. From 6464 hours of observation a total of 248 EMIC wave events were identified. For the first time the Poynting vector for Pc 1 EMIC waves is presented in the dynamic spectral domain permitting the study of energy propagation of simultaneous waves located in different frequency bands. The maximum wave energy flux for the events was 25 μW/m2, averaging range 1.3 μW/m2, with the direction of wave energy propagation independent of wave frequency but dependent on magnetic latitude. EMIC wave energy propagation was bidirectional both away and toward the equator, for events observed below 11° ∣MLat∣. Unidirectional wave energy propagation away from the equator was observed for all events located above 11° ∣MLat∣. This supports the concept of unidirectional EMIC wave energy propagation away from a broad source region centered on the geomagnetic equator. No measurable energy was observed propagating equatorward beyond the source region, in contradiction to the BWP paradigm.