ИСТИНА

Effects on the geomagnetic field produced by high speed streams from coronal holes are clearly seen in variations of the hourly indices from Canadian magnetic observatories. Quantitative description of the coronal holes activity has been proposed and tested by correlation analysis on the sets of solar wind and geomagnetic data. Preliminary results are reported on the correlation coefficient (CC) analysis between areas of coronal holes derived from SOHO and STEREO images, solar wind speed at ACE and STEREO spacecraft, and magnetic hourly ranges from 3 observatories located in polar, auroral and subauroral zones. Monthly mean probability to have CC above ordinary threshold value 0.5 increases by 17-21% when sporadic activity periods are eliminated from analysis. Yearly mean CC between daily values of polar magnetic indices and measured solar wind speed increases by 10-15% when regular geomagnetic variations over the year are removed from daily averaged values. This study opens further ways to increase the quality of forecasts for recurrent polar and auroral activity and global quiet days.