Geotail waveform observations of broadband/narrowband electrostatic noise in the distant tail

Abstract

Broadband electrostatic noise (BEN) and narrowband electrostatic noise (NEN) are common wave activities in the plasma sheet boundary and the tail lobe regions, respectively. Similar wave emissions can be observed in the magnetosheath region. We demonstrate the nature of these waves based on the waveform observations by the plasma wave instrument on board the Geotail spacecraft. The above observed waveforms are divided into two types of classifications. The BEN type emissions observed in the plasma sheet boundary and magnetosheath consist of a series of isolated bipolar pulses. They are termed after their waveforms as plasma sheet boundary layer electrostatic solitary waves (PSBL ESW) and magnetosheath electrostatic solitary waves (MS ESW). On the other hand, the waveforms of the NEN type emissions are quasi-monochromatic. They are termed as lobe electrostatic quasi-monochromatic waves (lobe EQMW) and magnetosheath electrostatic quasi-monochromatic waves (MS EQMW). The waveform observations with the high time resolution show that one of the common features of these waves is the burstiness. The burstiness means that their amplitudes or frequencies rapidly change of the order of a few milliseconds to a few hundreds of milliseconds. Further, we show that the PSBL ESW, lobe EQMW, MS ESW, and MS EQMW are parallel propagating waves relative to the ambient magnetic field. The similarities of the ESW and EQMW in the magnetosheath and magnetotail suggest the possibility that these waves are generated by the same generation mechanism. Copyright 1997 by the American Geophysical Union.