Properties of small-amplitude electron phase-space holes observed by Polar

摘要

We present Polar Plasma Wave Instrument (PWI) measurements of electrostatic solitary waves in the high-altitude polar magnetosphere. These waves are electrostatic pulses that move parallel (and antiparallel) to the geomagnetic field and are similar to waves detected in many regions of the magnetosphere by other spacecraft. The PWI instantaneous dynamic range was 72 dB with an added 30 dB obtained by changing gain states. This large dynamic range enables the study of amplitude-size relations up to a maximum electric field of 44 mV/m in the lowest gain state as well as enabling the investigation of small-amplitude waves (<0.1 mV/m). The Polar PWI data indicate that these small-amplitude solitary waves have typical scale sizes the order of the Debye length, velocities the order of the electron thermal speed, and electrostatic potentials that are small compared with the electron thermal energy per charge ( k B T e /e). Statistical distributions of the wave properties are presented, and the properties are compared with theoretical predictions of electron phase-space holes and electron-acoustic solitons. BGK-type analysis of electron holes predicts a relationship between the minimum allowed scale size and the amplitude and velocity. The observed solitary waves are consistent with these predictions.