Primary Study About the Relationships Between Coronal Holes' Parameters and the Correlative Geomagnetic Disturbances

Data from the SOHO EIT284 images are used to analyze the development of coronal holes which existed from 1996 to 2005. In order to investigate the relationship between the coronal hole and earth effect, the correlativity of the coronal hole parameters including coronal holes＇ area and longitude span, with solar wind parameters and geomagnetic index were examined. Our investigation shows that： The correlation between coronal holes＇ longitude extend （20°N-20°S） and geomagnetic disturbance duration is very good. For coronal holes that appeared in 2002, the linear-correlation coefficient is 0.91, and for a long-lived recurrent coronal hole that existed for 15 Carrington rotations from 2002 to 2003, the Pearson Coefficient is 0.934. There is poor correlation between coronal holes＇ areas and maximum solar wind speed in the high speed stream. This result is different from the result that Nolte found in 1976. This might remind us that the solar wind speed in the high speed stream is not only related to the coronal holes＇ areas. The relationship between the high speed stream and the coronal hole must be much more complex. The correlations between the yearly averaged maximum solar wind speed in CHHSS （Coronal Hole-High Speed Stream） and the yearly averaged corresponding geomagnetic field index, for example, Ap index and Kp index are good, especially for the declining phase of solar activity cycle 23. But to the individual samples, fast velocity does not mean intense geomagnetic disturbance, which means that solar wind velocity is not the only major role that causes earth effect. From the study of a recurrent coronal hole that existed for fifteen Carrington rotations, we found that the daily average velocity maximum v^-max shows somewhat correlation to Kp maximum during the the geomagnetic disturbance. The linear-correlation coefficient is about 0.604.