Summary
An analysis of the VLF atmospherics at 10, 20 and 30 kHz recorded over the tropical station Calcutta exhibits stepped-falls during sunrise of which the first two steps observed before ground sunrise are relatively weak while the last one called the main stepped-fall observed around ground sunrise is always clearly visible. Results show that the fall of the main-step as well as its duration are greater than those of the other two steps. The average duration for the third, second and main steps are respectively 21, 31 and 54 minutes. The magnitudes of the fall are frequency dependent, being maximum at 30 kHz. They have also been found to be less during the summer and monsoon months than in winter. The results have been interpreted by considering the source activity and the nature of propagation involved.
Zusammenfassung
Eine Untersuchung der auf der tropischen Station Kalkutta registrierten VLF-Atmospherics bei 10, 20 and 30 kHz zeigte eine stufenweise Abnahme bei Sonnenaufgang, wobei die ersten zwei Stufen vor Sonnenaufgang relativ schwach entwickelt sind, während die letzte bei Sonnenaufgang beobachtete Hauptstufe immer sehr klar sichtbar ist. Die Ergebnisse der Untersuchung zeigen, daß der Abfall in der Hauptstufe wie auch seine Ausdauer größer war als in den zwei anderen Stufen. Die mittlere Dauer der ersten, zweiten und der Hauptstufe betrug entsprechend 21, 31 und 54 Minuten. Die Größen des Abfalls sind frequenzabhängig und haben ihr Maximum bei 30 kHz. Sie sind während der Sommer- und Monsunmonate kleiner als im Winter. Die Ergebnisse werden mit Berucksichtigung der Quellenaktivität und der Natur der Ausbreitung interpretiert.
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Sarkar, S.K., Bhattacharya, A.B. & Sen, A.K. Some studies on the stepped fall of atmospherics during sunrise. Arch. Met. Geoph. Biocl. A. 30, 279–288 (1981). https://doi.org/10.1007/BF02257849
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DOI: https://doi.org/10.1007/BF02257849