The eect of the high-speed stream following the corotating interaction region on the geomagnetic activities

The high-speed stream following the corotating interaction regions (CIRs) was analyzed. As a result of the analysis, it is found that the geomagnetic ®eld is continuously disturbed in the high-speed stream in question. The geomagnetic disturbances with long duration recurred several rotations between December 1993 and June 1994. These disturbances were associated with a large recurrent coronal hole expanding from the south pole of the Sun. High-speed solar wind from this coronal hole was observed by the IMP-8 satellite during this period. However, the observed intensities of the geomagnetic disturbances were di€erent for each recurrent period. This is explained by the seasonal e€ect. The disturbed geomagnetic condition continued in the highspeed stream after the passage of the CIRs. The long duration of these disturbances can be explained by the continuous energy input into the Earth's magnetosphere from the high-speed regions following the CIRs. This kind of long-duration geomagnetic disturbance in association with coronal holes has been observed in the declining phase of other solar cycles. The relation between the coronal-hole area and the maximum solar-wind velocity is not good for the well-developed large coronal hole analyzed here.