Equatorial and low latitude geomagnetic field oscillations in the Indian region

Abstract

Monthly mean hourly values of geomagnetic field components D, H and Z for quiet days at equatorial and low latitude stations in the Indian region are analyzed to study the salient features of geomagnetic field oscillations in magnetic elements. The data used in this analysis is from 1958 to 1993 at equatorial electrojet stations: Trivandrum & Annamalainagar, from 1970 to 1993 at Kodaikanal and from 1927 to 1997 at low latitude station Alibag. From this basic data, geomagnetic Sq ranges and summed ranges are computed and subjected to the data adaptive, noise reducing technique of Singular Spectrum Analysis (SSA). The pair of eigen vectors analyzed through SSA up to order 18 represent different oscillations of the field such as; 11-year, annual, semi-annual, 4- month, 14-month (Pole-tide) and a Quasi-Biennial Oscillation (QBO) etc. The Sq ranges, summed ranges at all the stations and monthly mean sunspot numbers for the same period are also analyzed by a band pass digital filter method in order to identify whether QBO signal at these stations is the result of dynamo winds or due to QBO like signature in the Sun’s atmosphere. It is found that, the amplitude of the signal is stronger at equatorial electrojet stations in comparison with low latitude station Alibag and may be due to solar origin.