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Ann. Geophys., 24, 1725-1735, 2006
www.ann-geophys.net/24/1725/2006/
© European Geosciences Union 2006
Electron velocity distribution and lion roars in the magnetosheath
W. Masood1,2,3, S. J. Schwartz4, M. Maksimovic5, and A. N. Fazakerley6
1Astronomy Unit, Queen Mary, University of London, UK
2Government College University (GCU), Lahore, Pakistan
3PRD, PINSTECH, P.O.Nilore, Islamabad, Pakistan
4The Blackett Laboratory, Imperial College London, UK
5DESPA, Observatoire de Paris, France
6Mullard Space Science Laboratory, University College London, UK
Abstract. Whistler waves which are termed "lion roars" in the magnetosheath are
studied using data obtained by the Spectrum Analyser (SA) of the
Spatio-Temporal Analysis of Field Fluctuations (STAFF) experiment aboard
Cluster. Kinetic theory is then employed to obtain the theoretical expression
for the whistler wave with electron temperature anisotropy which is believed
to trigger lion roars in the magnetosheath. This allows us to compare theory
and data. This paper for the first time studies the details of the electron
velocity distribution function as measured by the Plasma Electron And Current
Experiment (PEACE) in order to investigate the underlying causes for the
different types of lion roars found in the data. Our results show that while
some instances of lion roars could be locally generated, the source of others
must be more remote regions of the magnetosheath.
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