Electron cyclotron waves in the presence of parallel electric fields in the Earth’s auroral plasma

S Kumar,A K Gwal,S K Dixit

doi:10.1007/s005850050417

Abstract

The electron cyclotron waves that originate at low altitudes (<0.5 RE) and observed by ground facilities have been studied in the presence of a weak parallel electric field in auroral magnetoplasma consisting of trapped energetic auroral electrons and cold background electrons of ionospheric origin. The model distribution for auroral trapped electrons is taken as Maxwellian ring distribution. An expression for the growth rate has been obtained in the presence of parallel electric field assuming that the real frequency in the whistler mode is not affected by the presence of the electric field. The results show that waves grow (or damp) in amplitude for a parallel (or antiparallel) electric field. The influence of the electric field is more pronounced at a shorter wavelength spectrum. An increase in population of energetic electrons increases the growth rate and thus, plays a significant role in the wave excitation process in the auroral regions.

Highlights

The electric fields which were first proposed by Alfven and Falthammar (1963) from theoretical arguments are an important parameter in the study of magnetospheric plasma and associated wave phenomena
Block and Falthammar (1990) from the Viking observations reported that weaker parallel electric fields of the order of few mV/m to 20 mV/m are more common, with a duration that can be as long as tens of seconds
A detailed description of parallel electric fields is out of the scope of the present study, it is well established that parallel electric fields occur in the auroral zone

Summary

Introduction

The electric fields which were first proposed by Alfven and Falthammar (1963) from theoretical arguments are an important parameter in the study of magnetospheric plasma and associated wave phenomena. The observations made indicate the presence of electric fields aligned parallel to the magnetic field lines in Earth’s magnetoplasma (Mozer et al, 1980; Block et al, 1987; Falthammar, 1989; Matsuoka et al, 1991; Tsuruda et al, 1994). In the present work, dealing with linear wave-particle approach, we report the effect of parallel electric field on the propagation of electron cyclotron waves in auroral magnetosphere observed by ground facilities near Fairbanks, Alaska. These observations are reported by Benson et al (1988). S. Kumar et al.: Electron cyclotron waves in the presence of parallel electric field in the Earth’s auroral plasma complex temperature 1#. The external magnetic field (Davidson, 1983; Wu et al, 1989) in the presence of parallel electric field can be written as: ck "1#(n /n)(

Distribution function

Expression for growth rate

Results and discussion