Diurnal Variation in the Amplitude and Frequency of Magnetic ‘Sudden Commencements’ and ‘Sudden Impulses’ at Quetta

Abstract

The study of diurnal variation in the frequencies and amplitudes of magnetic sudden commencements (SC /sup s/) and sudden impulses (SI/sup s/) recorded at gretta (lat. 30 deg 11'N; long. 66 deg 57'E), during the period 1953--1962 indicates that SC/sup s/ and Si/sup s/ are more frequent near the sunrise and sunset hours with maxima around 08/sup h/ and 18/sup h/ local time (L.T.). This does not conform to the curves obtained by Newton and Ferraro & others which exhibit a maximum at 13/sup h/ J.T. and two minima at 08/sup h/ and 20/sup h/ L.T. respectively. The mean hourly values of the amplitude y of SC/sup S/ g Sl/sup S/ do not seem to exhibit any marked local time effect. The daytime enhancement in y and the similarity between the diurnal variation of amplitude of SC/sup S/ & SI/sup S/ and Sq-variation found at Huancayo, Kodaikanal, and Alibag is also absent. On the other hand a sharp minimum in the amplitude curve around 07/sup h/ L.T. gives weight to Ferraro's contention that during the day-lit hemisphere the higher conductivity of the ionosphere tends to shield the station below from the external magnetic field produced by corpuscular stream. No seasonalmore » variation in the monthly frequency of SC/sup s/ & SI/sup s/ is discernible but the mean monthly amplitude curve exhibits marked enhancement in the size of SC/sup s/ & SI/sup s/ during the summer months. The curves for the annual mean number and yearly mean amplitudes of SC/sup s/ & SI/sup s/ and yearly mean Sq-range show striking similarity to the curve for the annual mean sunspot numbers. A linear relation of the type y = 11.6 + 0.097s between the amplitude y and the relative sunspot numbers s was worked out for Quetta.« less