Modeling of nonstationary electron precipitation by the whistler cyclotron instability

A G Demekhov,V Y Trakhtengerts,J Manninen,E E Titova,T Turunen,A A Lyubchich

doi:10.1007/s00585-998-1455-1

A G Demekhov, V Y Trakhtengerts + Show 4 more

Open Access

https://doi.org/10.1007/s00585-998-1455-1

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Abstract

Abstract. We study a simple self-consistent model of a whistler cyclotron maser derived from the full set of quasi-linear equations. We employ numerical calculations to demonstrate dependencies of pulsation regimes of whistler-mode wave interactions with energetic electrons on plasma parameters. Possible temporal evolution of those regimes in real conditions is discussed; calculations are compared with case-study experimental data on energetic electron precipitation pulsations. A reasonable agreement of the model results and the observations has been found.Key words. Magnetospheric physics (Auroral phenomena; Energetic particles · precipitating; Storms and substorms)

Highlights

It is well known that the whistler cyclotron instability (WCI) is an important agent of energetic electron precipitation from the radiation belts
Due to the complexity of the self-consistent theory of WCI it seems fruitful to employ simpli®ed models which enable a quick means of obtaining estimations and rapid choice of parameters that provide the best agreement with the experiment
As shown by Trakhtengerts et al (1986), Demekhov (1991), Demekhov and Trakhtengerts (1994), the distribution function of energetic electrons can strongly vary in these regimes, as well as wave spectrum shape, so using a full pitch-angle distribution seems necessary for proper treatment of the loss cone ®lling eect in the case of moderate diusion

Summary

Introduction

It is well known that the whistler cyclotron instability (WCI) is an important agent of energetic electron precipitation from the radiation belts. One of its interesting features is existence of nonstationary (pulsating) regimes in presence of a constant free energy source which may be, e.g., due to drift of injected energetic electrons into an instability region or local acceleration mechanisms These pulsations can be damped or undamped and they are believed to account for some types of experimentally observed phenomena such as pulsating auroral patches (for a review of observations see, e.g., Sandahl (1984), theoretical investigation has been reported by Trakhtengerts et al. Due to the complexity of the self-consistent theory of WCI it seems fruitful to employ simpli®ed models which enable a quick means of obtaining estimations and rapid choice of parameters that provide the best agreement with the experiment Such models have been suggested and analyzed, e.g., by Bespalov and Trakhtengerts (1976), Schulz (1974), Davidson (1979), Bespalov (1981), and Davidson and Chiu (1986). We show that using the multilevel WCI equations, the qualitative dierence of precipitation time patterns between these events can be consistently attributed to the dierence in the recorded plasma parameters

Basic equations and their properties

Parameters of pulsations

Calculation results

Discussion

Conclusion