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Ann. Geophys., 22, 2587-2595, 2004
www.ann-geophys.net/22/2587/2004/
© European Geosciences Union 2004
Systematic analysis of equatorial noise below the lower hybrid frequency
O. Santolík1, F. Němec1, K. Gereová1, E. Macúšová1, Y. de Conchy2, and N. Cornilleau-Wehrlin3
1Faculty of Mathematics and Physics, Charles University, V Holešovičkách 2, Prague, CZ-18000, Czech Republic
2LESIA/Observatoire de Paris-Meudon, F-92195, Meudon Cedex, France
3CETP/IPSL, 10/12 Avenue de L’Europe, Vélizy, F-78140, France
Abstract. We report results of a systematic analysis of a large number
of observations of equatorial noise between the local proton
cyclotron frequency and the local lower hybrid frequency. The
analysis is based on the data collected by the
STAFF-SA instruments on board the four
Cluster spacecraft. The data set covers
their first two years of measurement in the
equatorial magnetosphere at radial distances between 3.9 and 5 Earth
radii. Inspection of 781 perigee passages shows that the occurrence
rate of equatorial noise is approximately 60%.
We identify equatorial noise by selecting data
with nearly linearly polarized magnetic field fluctuations.
These waves are found within 10° of the geomagnetic equator,
consistent with the published past observations.
Our results show that equatorial noise
has the most intense magnetic field fluctuations among all the
natural emissions in the given interval of frequencies and latitudes.
Electric field fluctuations of equatorial noise are also more intense
compared to the average of all detected waves. Equatorial noise thus can
play a non-negligible role in the dynamics of
the internal magnetosphere.
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