Abstract
DIURNAL AND SEASONAL VARIATION OF WHISTLERS AT LOW LATITUDE GROUND STATION JAMMU AND RECORDING OF VLF HISS EMISSIONS
Dr. Rajou Kumar Pandita* and Prof. Farooq Ahmed Sofi
ABSTRACT
This paper presents interesting observations based on the long term Data of whistlers and VLF hiss emission at a low latitude ground station Jammu (Geomagn. lat. 22?16? N, L = 1.17). The simultaneous observations presented in this paper are unique and are reported for the first time from low latitude ground station Jammu. The present observation of VLF emissions and whistlers along with ESD whistlers at Jammu clearly suggest that these VLF emissions are generated in the magnetosphere due to whistler mode wave-interaction with particles. This experimental study is unlikely to be the final word on the origin of these events and further experimental confirmation will, of course, be required at low latitudes. From the dispersion analysis of the day time whistlers recorded at Jammu, it is found that all the Whistlers have extremely small dispersion (ESD) in the range of 5-10 s1/2, which clearly supports non-ducted propagation. With the advent of the satellites, VLF receivers were placed on rockets and satellites. These receivers detected whistlers whose paths deviated from Earth?s magnetic field lines. Such whistlers are called unducted or non-ducted whistlers, completely in contrast with the earlier findings of ducted propagation of day-time whistlers. VLF emissions are known to originate within the ionosphere/magnetosphere but no satisfactory theory of their origin has yet been put forward. These are generally originated in the ionosphere/magnetosphere by two mechanisms, viz incoherent Cerenkov radiation mechanism and electron cyclotron resonance instability mechanism. The generation mechanism of whistler-mode VLF hiss remain controversial inspite of extensive amount of experimental and theoretical work. A number of mechanisms have been suggested for the generation of VLF hiss from time to time. Sazhin et al.,(1993) have reviewed the generation mechanism of the VLF hiss and have projected out that the most likely energy source of VLF hiss lie in the electrons at energies below 100 electron volts precipitating to the auroral ionosphere. They have shown that initially the waves are generated due to incoherent Cerenkov radiation and they are then amplified due to beam plasma instabilities in the Cerenkov resonance.
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