Role of high speed solar wind streams in cosmic ray decreases

Abstract

The high-speed solar wind streams lasting for several days are observed by satellites and spacecraft. These streams produce geomagnetic disturbances and changes in the level of cosmic ray intensity. High-speed plasma streams identified in the solar wind measurements can be separated into two categories: coronal-hole-associated streams and flare-generated streams. The influence of two types of high speed solar wind streams- coronal-hole and solar-flare-associated on cosmic ray intensity has been studies using the neutron monitor data of three different neu- tron monitoring stations. Cosmic ray intensity data together with solar wind plasma and interplanetary magnetic field data were subjected to superposed epoch analysis with respect of these two types of high-speed solar wind streams. Variations in cosmic ray intensity influenced by coronal hole streams are much smaller than the typically Forbush like depressions. During these events the interplanetary magnetic field strength (B) and solar wind speed observed to increase. However, a significant correlation has been observed between disturbance storm time index (Dst) with geomagnetic activity index (Ap) and plasma temperature with plasma density.