Quasi-periodic VLF emissions observed during daytime at a low latitude Indian ground station Jammu

Abstract

This paper reports quasi-periodic pulsing hiss emissions recorded during daytime in the frequency range of 50 Hz-15 kHz at low latitude station Jammu (geomag. lat. = 22 • 26 N; L = 1.17). It is noted that pulsing VLF emissions are a rare phenomena at low latitudes. The various spectrograms of pulsing VLF hiss emissions presented in this paper clearly show band limited spectrums regularly pulsing with almost equal period of the order of few seconds in the frequency range of ∼ 3-8 kHz. Generation and propagation mechanism of these emissions are briefly discussed.

An explanation of the observation of whistler-mode chorus emissions at the Indian Antarctic station, Maitri (L=4.5)

“…By analyzing POLAR satellite data, Lauben et al [9] studied various source characteristics of chorus emissions and indicated the source region near the magnetic equator. The upper boundary frequency (UBF) method [35] has generally been used to find the location of the ground observed VLF emissions [13,20]. The upper boundary frequency of the ground observed VLF emissions is determined on the assumption of a dipolar geomagnetic field configuration by the half electron gyrofrequency region, irrespective of the observation station.…”

“…These emissions usually consist of a succession of discrete elements with rising frequency and occur at frequencies below the local electron gyrofrequency with the typical duration of chorus events being 0.5-1 h [1]. Although it is generally accepted that the generation mechanism of these emissions is connected with the cyclotron instability of whistler-mode waves and radiation belt electrons [2][3][4], the generation mechanism of these emissions and the formation of a spectrum of separate elements are still a subject of active experimental and theoretical research [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20]. Gyroresonant interactions of electrons with chorus emissions play an important role in the physics of the Earth's radiation belts.…”

“…Thus, the detailed generation process of chorus emissions remains to be fully identified. Although VLF emissions are often observed at the Indian Antarctic station, Maitri [20,27,28], chorus emissions are rarely observed. In this paper, we present the observation of chorus emissions at the Indian Antarctic station, Maitri, during a quiet period on 5 February 2001.…”