IPDP geomagnetic pulsations and their relation to coronal holes and high speed solar wind streams

Abstract

The frequency of occurrence of intervals of pulsations of diminishing periods (IPDP) has shown a very surprising inverse relation to the sunspot number. In this paper we take the annual frequency of occurrence of IPDPs at Sodankyla station for the period 1974 to 1985 and find that they correlate positively with coronal hole area with a correlation coefficient of 0. 77. This suggests a physical relationship between this kind of pulsations and the high speed streams (HSSs) in the solar wind coming from the holes. We compare the annual rate of IPDPs to the annual number of coronal-hole associated HSSs having a velocity equal to or higher than 550 km/s for the period from 1974 to 1982. We find a good agreement during the descending part of il solar cycle and around the maximum, but during the minimum and the first years of the ascending phase IPDPs were mme frequent than HSSs. We conclude that IPDPs are related to some solar wind characteristics in HSSs and we discuss a possible reason for the differences during the minimum.