ABSTRACT
The present work deals with the detailed study of very low frequency (VLF) phenomena at Indian base station Maitri, Antarctica, from 1997 to 2002. Antarctica is an ideal place for monitoring whistler and VLF phenomena. Earlier work in related areas of research reveals that various transient discrete emissions such as risers, fallers, and hooks have been reported at Antarctica. At Maitri, we have observed such phenomena frequently and discuss the diurnal variation of their occurrence. Certain types of VLF emissions can be correlated with auroral phenomena. During the XVII–XXII Indian Antarctic Expeditions, analysis of the discrete VLF emissions observed during daytime at Maitri reveals several facts. Discrete chorus emissions have been observed for the first time during daytime at Maitri. The computed value of df/dt is found to be 2 kHz/sec, which is within the range of observed value as reported by other workers. From detailed spectral analyses, it is found that periodic emissions are observed in the frequency range of 2.5–6.8 kHz. The measured period of the periodic VLF emissions recorded at Maitri lies typically in the range of 0.1 to 0.5 sec. These periodic emissions show a non-dispersive character. There were typically two different types of periodic VLF signatures observed, purely “discrete rising tones” within a frequency range of 2 kHz, and “burst-type” periodic emissions with the upper and lower bands of frequencies. It is thus observed that all emission parameters are found to lie almost within the range of our observed parameters of discrete VLF emission at Maitri. VLF hiss in the frequency range 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 also reported for the first time. The propagation mechanisms of these emissions are discussed briefly.
