The “fan” instability as a possible generating mechanism of vlf quarter-gyrofrequency emissions during the recovery phase of a magnetospheric storm |
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| Authors: | J Bo?ková P T?íska Yu A Omelchenko V D Shapiro V I Sotnikov |
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| Institution: | (1) Geophysical Institute, Czechosl. Acad. Sci., Prague;(2) Space Research Institute, Russian Acad. Sci., Moscow |
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| Abstract: | Summary VLF quarter-gyrofrequency emissions, whose experimental characteristics differ from those of discrete plasmaspheric emissions usual during active times, have been observed by low-altitude Intercosmos 24 and Magion 2 satellites within the plasmasphere during periods of quieting geomagnetic activity. A new kind of instability is proposed which could lead to the production of these emissions. It is shown that quasi-electrostatic whistler waves can be generated in the eqquatorial region due to the fan instability, with maximum growth rate and spectral energy density in a frequency band below one half of the equatorial electron gyrofrequency. The observations of low-energy electrons and plasma waves in the equatorial region within or in the vicinity of the plasmapause, which could support our hypothesis experimentally, are discussed. |
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