Astronomy and Astrophysics – Astrophysics
Scientific paper
Nov 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006ihy..worke.139s&link_type=abstract
2nd UN/NASA Workshop on International Heliophysical Year and Basic Space Science. Proceedings of the conference held 27 Novembe
Astronomy and Astrophysics
Astrophysics
Scientific paper
abhay_s@rediffmail.com Whistler precursor is an interesting type of discrete VLF emissions, usually a rising tone, which is observed before the whistler with which it appears to be associated with. They are closely associated with a lightning discharge in the same hemisphere and with two-hop whistlers generated by the same sphere. In this paper, whistler precursors observed at low latitude ground station Gulmarg (geomag. Latitude 240 10/ N, L=1.23) are explained. A possible generation mechanism based on parametric reflection of VLF whistler wave is proposed. In this process a reflected whistler wave arises when an intense whistler mode wave decays into quasi-electrostatic short- scale waves, one LHR wave and the other ion acoustic wave, through the process of parametric decay instability. Also reflection of whistler wave may arise during the interaction of natural whistler wave, with ion cyclotron or ion acoustic waves. The reflection mechanism is equivalent to backward transformation of the LHR and ionic waves into a whistler-mode wave. This leads to partial reflection of the initial ducted whistler whistler wave from an altitude where the whistler wave frequency coincides with the local lower hybrid resonance frequency. The reflected whistler wave is ducted along the same duct as the initial whistler wave, and propagates to the ground-based receivers from two points. Such a reflection will produce the precursors with a specific hook-like shape on a spectrogram. This mechanism explains most of the observed properties of the precursors well. We have also computed the growth rate of the wave and the electric field amplitude of ion cyclotron waves. These results are discussed in the light of recent published works.
Singh Abhay K.
Singh Kesar
Singh Rahul
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