R. P. Patel

An experimental study of hiss-triggered chorus emissions at low latitude

Hiss-triggered chorus emissions recorded at low-latitude ground station Gulmarg (geomag. lat., 24°26N; geomag. long., 147°09E, L = 1.28) on March 8, 1986 are reported. From the detailed spectral analysis of these emissions, it is found that the chorus is hiss-triggered and each chorus element has tendency to originate from the hiss band. Based on the theory of Helliwell, and previous satellite VLF data, a possible generation mechanism of low-latitude hiss-triggered chorus emissions is proposed. An attempt has been made to find out the chorus source location and the length of resonance region from which the various parameters associated with generation mechanism are determined.

Triggered emissions observed at Varanasi (India)

Abstract Whistler triggered emissions recorded at a low latitude station e.g. Varanasi are described. The study covers various aspects of these emissions including riser, riser followed by constant frequency emissions, hiss and oscillating tones. Analysis shows that the whistlers have propagated along paths with L -values lying between L =1.9 and 2.4, suggesting that these whistlers are to be regarded as mid-latitude whistlers. These waves could have propagated along the geomagnetic field lines either in a ducted mode or in a pro-longitudinal mode. The measured intensity of the triggered emissions is either equal to or more than that of the source wave and also varies from one event to another. It is proposed that these emissions are generated through a process of resonant interaction of the whistler waves with energetic electrons. Parameters related to this interaction are computed for different values of L and wave amplitude. The proposed mechanism explains some aspects of the dynamic spectra.

Observation of very low frequency emissions at Indian Antarctic station, Maitri

Recently, we have succeeded in recording VLF emissions at the Indian Antarctic station, Maitri (geom. lat. 62°S, geom. long. 57.23°E,L = 45) using a T-type antenna, pre/main amplifiers and digital audio tape recorder. VLF hiss in the frequency ranges 11–13 kHz and 13–14.5 kHz and some riser-type emissions in the frequency range 3–5 kHz and magnetospheric lines at about 6.2, 8.0 and 9.2 kHz are reported for the first time. The generation and propagation mechanism of these emissions are discussed briefly.

Characteristics of discrete VLF falling-tone chorus emissions observed at low latitude ground station Jammu

The discrete VLF chorus emissions recorded at low latitude ground station Jammu (geomag. lat. = 22°26′N, L = 1.17) are reported and their characteristics based on spectral analysis have been carried out. These discrete chorus emissions are falling tone emissions which are rarely observed at low latitude ground stations. These discrete chorus emissions are generated during a strong geomagnetic storm period of 2–7 May, 1998. We have computed the frequency sweep rate, repetition period and source region of the individual chorus elements. It is observed that the sweep rate increases with time.