Abstract
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 10o from the geomagnetic equator and the maximum occurrence rate of EN is during the daytime especially in the afternoon sector.