Positive equatorial Dst and diurnal variation of the geomagnetic field

Using a careful selection of groups of days during 1956-77, based on increasing magnitudes of positive Dst and the hourly values of equatorial geomagnetic field in the Indian region, it is shown that enhanced solar wind pressure modifies the low latitude field in a systematic manner. Apart from a linear increase in the mean level of the equatorial field, a local time dependence of the field changes with Dst + is also indicated. From a comparison of these results with those derived from the data of a station north of the Sq focus in the Indian zone, it is shown that mean level and local time dependence of the field on Dst + change in a similar manner. (author)