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Occurrence Rate of Equatorial Noise Emissions as a Function of the McIlwain's Parameter
Hrbáčková, Zuzana ; Santolík, Ondřej
We report results of a statistical analysis of equatorial noise (EN) emissions based on the data set collected by the four Cluster spacecraft between January 2001 and December 2010. We have investigated a large range of the McIl- wain’s parameter from L 1 to L 11 thanks to the change of orbital parameters of the Cluster mission. We have processed data from the STAFF-SA instruments which analyze measurements of electric and magnetic field fluctuations onboard and provide us with hermitian spectral matrices. We have used linear polarization of magnetic field fluctuations as a selection criterion. Propagation in the vicinity of the geomagnetic equator has been used as an additional criterion for recognition of EN. We have identified about 6000 equatorial passages of all four spacecraft during the investigated time period and about 2000 passages in which we observed EN emissions. We demonstrate that EN can occur almost at all the analyzed L shells. However, the occurrence rate at L shells below 2 and above 8.5 is very low. At L shells above 10 the occurrence rate is zero. We show that EN is dependent on the magnetic local time.
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Statistical analysis of equatorial noise emissions as a function of magnetic local time
Hrbáčková, Zuzana ; Němec, F. ; Santolík, Ondřej
The four spacecraft of the Cluster mission collect a unique data set since January 2001. We process the time period from January 2001 to December 2009. The spacecraft changed their orbits over the last few years, resulting in the data set with excellent coverage of a wide range of radial distances from the Earth, especially in the equatorial plane. We focus on the statistical analysis of whistler-mode waves called the equatorial noise (EN). These intense wave emissions are generated by unstable ion distributions. They propagate close to the geomagnetic equator at frequencies between the local proton cyclotron frequency and the lower hybrid frequency. Polarization of the magnetic field fluctuations corresponding to these emissions is linear. We processed data from the STAFF-SA instruments which preanalyze data from electric and magnetic field fluctuations onboard and provide us hermitian spectral matrices. We use the data measured at radial distances from about 2 to 11 RE to show the dependence of the occurrence of EN on the magnetic local time (MLT). We show from the statistical analysis that EN is occurred at all research radial distances within 10◦ from the geomagnetic equator and the maximum occurrence rate of EN is during the daytime especially in the afternoon sector.
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Systematic Analysis of Equatorial Noise Using Data of the Cluster Mission
Hrbáčková, Zuzana
The four spacecraft of the Cluster mission are collecting a unique data set. We use data measured between 2002 and 2009. These data are unique not only by their quantity but also because the spacecraft changed their orbits during their operational phase and therefore we have data from a large area around the Earth. We focus our analysis on observations of equatorial noise (EN) which is an intense electromagnetic emission generated by unstable ion distributions. It occurs in the inner magnetosphere and propagates close to the geomagnetic equator between the local proton cyclotron frequency and local lower hybrid frequency. We make systematic analysis of EN using data from the STAFF-SA instruments onboard the four spacecraft of the Cluster mission.
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