The velocity and particle density of solar wind related with the geomagnetic disturbances during 2008-2010

It has been established that the geomagnetic disturbances are closely related to the solar wind velocity. They have an inverse correlation, i.e. the geomagnetic disturbance, which is represented by the Dst index, will have a lower value with the higher solar wind speed. However, the detailed correlation, particularly on their time profile, has not been known yet. We analyze the time profile of the solar wind and geomagnetic disturbance by comparing the correlation between the solar wind and the geomagnetic (Dst index) time profiles. We also analyze the correlation between the plasma density and the geomagnetic disturbance. We analyzed the solar wind velocity and density data from Advanced Composition Explorer (ACE) satellite around the disturbed days. The geomagnetic disturbance (Dst index) data are obtained from the World Data Center for Geomagnetism Kyoto, for the period of 2008-2010. We selected the event which has Dst index ≤ 30 nT. By using this criterion we found 41 geomagnetic disturbance events. The negative correlation between the solar wind and Dst index time profiles means that solar wind speed will increase when the geomangetic field is more depressed. On the contrary, the density profile shows the positive correlation with the Dst index. which means that the density will increase when the disturbance becomes stronger. However, the increasing or decreasing parameters did not occur simultaneously.