Sudden Commencement amplitudes and Storm ranges in the Indian equatorial belt

Abstract

For the highly active period of solar cycle 19, amplitudes of storm sudden commencements (SSC) at the three stations in the Indian equatorial region are examined. Storms with a large main phase are found to accompany sudden commencements occurring during the day time. The equatorial enhancement in SSC amplitudes in the horizontal force is found to be almost uniform from 2.7° magnetic latitude to the dip equator except for a few hours centred on local noon. In the vertical force, the enhancement at Trivandrum near the dip equator is found to be extremely large. The occurrence of storms with large ranges in the vertical force and the seasonal characteristics of the ranges ate also investigated. An unexpected quasi-periodic variation in ranges in the vertical force has been found at Kodaikanal. Probable causes of large amplitudes of SSCs and storm ranges in the vertical force are discussed.