Abstract
Abstract. The morphology of ELF hiss events observed at low-latitude ground station Varanasi (L = 1.07, geomagnetic latitude 14°55'N) are reported, which consist of two types: (1) events which propagated in ducted mode along the geomagnetic field line corresponding to observing station Varanasi and (2) events which propagated in ducted mode along higher L-values (L = 4–6), after reaching the lower edge of ionosphere excite the Earth-ionosphere wave guide and propagate towards equator to be received at Varanasi. To understand the generation mechanism of ELF hiss, incoherent Cerenkov radiated power from the low latitude and middle latitude plasmasphere are evaluated. Considering this estimated power as an input for wave amplification through wave-particle interaction, the growth rate and amplification factor is evaluated which is too small to explain the observed wave intensity. It is suggested that some non-linear mechanism is responsible for the generation of ELF hiss.Key words. Ionosphere (equatorial ionosphere; ionosphere · magnetosphere interactions; wave · particle interactions)
Highlights
Low frequency (ELF) hiss is a well-known form of electromagnetic emissions that arises in the plasmasphere and has constant spectral density in the limited frequency band (Ellis, 1957, 1960; Helliwell, 1965; Kimura, 1967; Sazhin and Hayakawa, 1992)
Global distribution of Extremely low frequency (ELF) hiss is characterized by three principal zones of intense activity of which the ®rst is located at invariant latitudes above 70°, the second near 50° and the third below 30° (Bullough et al, 1975)
In order to explain the wide coverage of ELF hiss at ionospheric height Ondoh et al (1983), on the basis of ray tracing studies, suggested that the waves must be generated at large wave normal angles in the equatorial region near L = 4
Summary
Low frequency (ELF) hiss is a well-known form of electromagnetic emissions that arises in the plasmasphere and has constant spectral density in the limited frequency band (Ellis, 1957, 1960; Helliwell, 1965; Kimura, 1967; Sazhin and Hayakawa, 1992). Several mechanisms have been proposed from time to time to explain the generation of ELF/VLF waves (Kimura, 1967; Sonwalker and Inan, 1989; Sazhin and Hayakawa, 1992; Dragnov et al, 1993). The generation of hiss during resonance cyclotron instability between whistler mode wave and counter streaming energetic electrons is envoked (Thorne et al, 1979; Ondoh et al, 1983; Church and Thorne, 1983; Helliwell et al, 1986; Sazhin, 1987; Sonwalker and Inan, 1988; Dragnov et al, 1993). Observations of ELF hiss are reported and an attempt is made to discuss its generation mechanism.
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