Bursts of whistler mode waves in the upstream of the bow shock: Geotail observations

Details Bursts of whistler mode waves in the upstream of the bow shock: Geotail observations Bursts of whistler mode waves in the upstream of the bow shock: Geotail observations

Sep 1998

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1998jgr...10320529z&link_type=abstract

Journal of Geophysical Research, Volume 103, Issue A9, p. 20529-20540

Physics

Plasma Physics

4

Radio Science: Waves In Plasma, Space Plasma Physics: Shock Waves, Space Plasma Physics: Wave/Particle Interactions, Magnetospheric Physics: Plasma Waves And Instabilities

Scientific paper

Bursts of narrowband and short-lived electromagnetic waves are frequently observed in the upstream (the electron foreshock and the pure solar wind) by the waveform capture instrument on board Geotail satellite. The electromagnetic waves with frequencies above 10 Hz are all right-hand circularly polarized and identified as whistler mode waves. We call the waves narrowband and short-lived whistlers (NSW). Nearly all the NSW in the electron foreshock propagate in a downstream direction parallel to the ambient magnetic field (B0) with an average θkB of 16°, where θkB is an angle between NSW wave vector and the B0. Their frequencies cover a range from 0.05 to 1.0Ωe with an average of 0.35Ωe, where Ωe is a local electron cyclotron frequency. Their amplitudes range from a few picoteslas to 100 pT with an average of 23 pT. Because of their parallel propagation, the NSW must be excited by electron cyclotron resonance. These features of the NSW suggest existence of electron beams which travel in an upstream direction parallel to the B0 and which have a temperature anisotropy. Kinetic energies of the beams range from a few eV to about 200 eV (28 eV on average). All these characteristics of the electron beams revealed from the NSW are consistent with ISEE and WIND particle observations. The competition between electrostatic and whistler instabilities and the finite size of the beams are very likely the reasons why the NSW are short-lived. These NSW can be well explained by a modeled electron beam with a losscone distribution in the electron foreshock. The NSW in solar wind are very similar to those in the electron foreshock. However, they have larger amplitudes (34 pT on average), lower frequencies (0.24Ωe on average), and higher cyclotron resonant energy (100 eV on average). They are very likely excited by halo electrons or nonlocal sources in the solar wind.

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