Dr. Ondrej Santolik (Institute of Atmospheric Physics and Charles University, Prague, Czech Republic)
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Observations of two types of emissions will be discussed, whistler-mode chorus and equatorial noise. Both of them are co-located with the Van Allen radiation belts and both can be important for the transfer of energy between different populations of energetic particles. Results of analysis of data from wave instruments on board the Cluster and Double Star spacecraft can help to characterize the role of wave-particle interactions connected to these natural emissions. Whistler-mode chorus has been recently shown to play a role in the process of local acceleration of electrons in the outer Van Allen radiation belt. We use a database of systematic wave measurements to develop a model of properties of whistler-mode emissions. A range of wave frequencies around one-half of the equatorial electron cyclotron frequency is investigated and the wave intensity, polarization and propagation properties are shown as a function of frequency and position. We show that, at L=4-5, the wave magnetic field power-spectral density maximizes at larger latitudes, although the source region is located at the geomagnetic equator. Equatorial noise emissions are observed in the inner magnetosphere close to the geomagnetic equator at frequencies below the local lower hybrid frequency and consist of a superposition of a large number of narrow spectral lines. We select the data with a nearly linear polarization corresponding to known properties of equatorial noise. We use a parametric model of the frequency-averaged power-spectral density as a function of the geomagnetic latitude and we analyze the data as a function of frequency. The most probable peak frequency of emissions is found below the 10th harmonic of the local proton cyclotron frequency. |
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