Sunspot cycle and seasonal variations in the position and intensity of the equatorial electro] et in the Indian region

Abstract

Recent views on the equatorial electrojet are briefly reviewed. Seasonal and annual values of the quiet day ranges of H and Z are calculated for the four Indian magnetic observatories, Alibag, Annamalainagar, Kodaikanal and Trivandrum for all the years for which data are available. Ranges H and Z on quiet days are shown diagrammatically for the years of sunspot maximum and sunspot minimum. Mean annual values of half-width of the equatorial electrojet have been calculated using Kodaikanal and Annamalainagar data. A comparison is made with earlier studies. It is inferred that the half-width is of the order of 300 km in the Indian region. The correlation between half-width and sunspot number is insignificant. The correlation coefficient between current intensity and sunspot number is very high, suggesting almost a linear relationship. Taking the rSq(Z) value, excess of the lowest daytime hourly value of Z, over its night-time value, on a local day nearest to the international quiet day, as an indication of the proximity of the station to the jet center, it is inferred that the jet moves opposite the sun, in agreement with the findings of Price & Wilkins (1963) and of Mason (1963). A comparison of the electrojet current intensity at different longitudes shows that the intensity is highest in the South American region and lowest in the Indian and Central Pacific areas.