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AGU: Journal of Geophysical Research, Space Physics

 

Keywords

  • radiation belts
  • electron acceleration
  • wave acceleration
  • chorus waves
  • pitch angle diffusion

Index Terms

  • Magnetospheric Physics: Radiation belts
  • Magnetospheric Physics: Magnetic storms and substorms
  • Magnetospheric Physics: Energetic particles: precipitating
  • Magnetospheric Physics: Energetic particles: trapped
  • Magnetospheric Physics: Plasma waves and instabilities
Abstract
Cited By (85)
 

Abstract

Timescale for radiation belt electron acceleration by whistler mode chorus waves

Richard B. Horne

British Antarctic Survey, Cambridge, UK

Richard M. Thorne

Department of Atmospheric Sciences, University of California, Los Angeles, California, USA

Sarah A. Glauert

British Antarctic Survey, Cambridge, UK

Jay M. Albert

Space Vehicles Directorate, Air Force Research Laboratory, Hanscom Air Force Base, Massachusetts, USA

Nigel P. Meredith

Mullard Space Science Laboratory, University College London, Dorking, UK

Roger R. Anderson

Department of Physics and Astronomy, University of Iowa, Iowa City, Iowa, USA

Electron acceleration inside the Earth's magnetosphere is required to explain increases in the ∼MeV radiation belt electron flux during magnetically disturbed periods. Recent studies show that electron acceleration by whistler mode chorus waves becomes most efficient just outside the plasmapause, near L = 4.5, where peaks in the electron phase space density are observed. We present CRRES data on the spatial distribution of chorus emissions during active conditions. The wave data are used to calculate the pitch angle and energy diffusion rates in three magnetic local time (MLT) sectors and to obtain a timescale for acceleration. We show that chorus emissions in the prenoon sector accelerate electrons most efficiently at latitudes above 15° for equatorial pitch angles between 20° and 60°. As electrons drift around the Earth, they are scattered to large pitch angles and further accelerated by chorus on the nightside in the equatorial region. The timescale to accelerate electrons by whistler mode chorus and increase the flux at 1 MeV by an order of magnitude is approximately 1 day, in agreement with satellite observations during the recovery phase of storms. During wave acceleration the electrons undergo many drift orbits and the resulting pitch angle distributions are energy-dependent. Chorus scattering should produce pitch angle distributions that are either flat-topped or butterfly-shaped. The results provide strong support for the wave acceleration theory.

Received 28 September 2004; accepted 13 January 2005; published 31 March 2005.

Citation: Horne, R. B., R. M. Thorne, S. A. Glauert, J. M. Albert, N. P. Meredith, and R. R. Anderson (2005), Timescale for radiation belt electron acceleration by whistler mode chorus waves, J. Geophys. Res., 110, A03225, doi:10.1029/2004JA010811.

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