Statistical Study of Solar Wind Parameters and Evolution of Dst Variations during 19-23 Solar Cycles in Relation with Cosmic Ray Variations

Abstract

We have studied the long-term variations of equatorial Dst index in 19-23 solar cycles to display favorable conditions in interplanetary space, which can have an influence on cosmic ray variation and climate change. In this connection the solar wind and interplanetary magnetic field parameters obtained from the OMNI and Ulysses databases, geomagnetic activity represented by Dst index from beginning 1957 to the end 2010 were used in our study. Yearly and 27-day average variations of Dst index and the solar wind parameters were compared with cosmic ray data from IZMIRAN and Oulu neutron monitors during the 19-23 solar cycles. During the descending phases of these solar cycles the long-lasting solar wind high speed streams occurred frequently and were the primary contributors to the recurrent Dst variations. We study cosmic ray (CR) variations in connection with evolution of Dst variations as the final product of solar wind - magnetosphere interaction because the important drivers of geomagnetic storms as CMEs (coronal mass ejections) and CIRs (corotating interaction regions) undergo very strong changes during their propagation to the Earth. Since Forbush observed decreases in the CR count rate it was shown good correlation between CR and Dst index during individual geomagnetic storms. For long-term variations of CR in a number of papers a good correlation between CR and sunspot numbers was shown but these results do not adequately reflect CR intensity variations and peculiarities concerned with the solar wind arrival to 1 AU. We show that long-term Dst variations in these solar cycles were correlated with cosmic ray count rate and can be used for prediction of CR variations. Climate change in connection with evolution of Dst variations is discussed