Whistler waves in Freja observations

Abstract

Several examples of whistler wave packets accompanied by density cavities are detected in F4 experiments of Freja satellite. The density depletion seems to be a fixed structure in space from the cross-correlation of two Langmuir probes. The wavelet analysis shows the frequency drift from 1 kHz (below the low-hybrid frequency) to 200 Hz (below the proton cyclotron frequency). The wave packets are always associated with an extremely low frequency component at 20-30 Hz (around the oxygen ion cyclotron frequency). The method of the minimum variance is used to calculate the oblique propagation of the wave packets with an angle decreased from 31 to 17 degrees between the wave vector and the ambient magnetic field. The right polarization of the wave packets is shown in the direction of the ambient magnetic field. Moreover, the phase velocity of the wave packets is inversely proportional to the frequency. These features may support the formation of envelope solitary whistler waves. Copyright 2004 by the American Geophysical Union.