Interplanetary Transient Solar Wind Plasma Structures and Associated Cosmic Ray Intensity

Abstract

Abstr act: In this study the interplanetary magnetic clouds and their interaction with the Earth's magne- tosphere is presented. The magnetic clouds identified during the period 1995 - 2008 are analyzed by di- viding them in to two categories i.e. negative clouds and positive clouds. Then the superposed epoch analysis is applied to observe their association with various interplanetary and geomagnetic parameters. Dst index is taken as an indicator of geomagnetic activities. The magnetic field intensity, proton density, and proton temperature are enhanced ahead of magnetic clouds, which are preceded by a shock, while the large fluctuations in Bz component of interplanetary magnetic field are found during the period of mag- netic clouds. It is investigated that the negative magnetic clouds are generally, responsible for producing significant decrease in Dst index after just emergence of magnetic clouds, while the positive clouds pro- duce decrease after 24 to 48 hours of onset time giving clear evidence of enhanced geomagnetic activities. The magnitude of the change in the Dst index, for the case when southward fields arrive first is compara- ble to that for the case when northward fields arrive first, and the phase is such that geomagnetic activity is associated with southward fields, substantiating earlier findings.