The diurnal variation of sizes of sudden commencements and impulses in the Kodaikanal magnetograms

Abstract

Combined data of sudden commencements (SCs) and sudden impulses (SIs) recorded at Kodaikanal (geomagnetic latitude 0.60N) during the period 1949-57 have been analysed in order to study the relationship between the diurnal variation (DV) in the amplitudes of the impulses and the DV in the horizontal component of the earth's magnetic field (the Sq variations in H) There is a statistically significant daytime enhancement in se sizes similar to the enhancement in Sq variation. Furthermore, this enhancement is larger on days with larger Sf variation than on days with smaller Sq variation. These results confirm those obtained by Forbush and Vestine (1955) at Huancayo, another station near the geomagnetic equator.