Abstract
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.
Highlights
Equatorial noise is an intense natural emission of electromagnetic plasma waves observed within a few Earth radii (RE) of geocentric radial distance, and always recorded very close to the geomagnetic equator
We use the data collected by the “spatiotemporal analysis of field fluctuations” (STAFF-SA) instruments on board the four Cluster spacecraft operated by the European Space Agency (ESA)
We have proven that equatorial noise is the most intense electromagnetic emission within 30◦ of the geomagnetic equator, in the frequency range between fH+ and flh, and in the range of radial distances between 4 and 5 RE
Summary
Equatorial noise is an intense natural emission of electromagnetic plasma waves observed within a few Earth radii (RE) of geocentric radial distance, and always recorded very close to the geomagnetic equator. Multipoint observations of equatorial noise by the four Cluster spacecraft have been presented by CornilleauWehrlin et al (2003) and Santolık et al (2002). We present the first results of our systematic analysis of a large number of observations of equatorial noise. These emissions are, together with the whistler mode chorus, among the most intense electromagnetic waves observed in the low-latitude region of the Earth’s magnetosphere, and their sensitivity to the variations of the geomagnetic activity indicates their importance for the “space weather” applications, i.e. prediction of fluxes of energetic particles as a consequence of variations of the solar input (Andreet al., 2002).
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