Rotation rate of high latitude and near polar coronal holes

Abstract

For the period of 1997-2006, coronal holes detected in the SOHO/EIT 195 $\AA$ full disk calibrated images are used to compute the rotation rates of high latitude and near polar coronal holes and, their latitudinal variation is investigated. We find that, for different latitude zones between $80^{o}$ north and $75^{o}$ south, for all their area, the number of days observed on the solar disk, and their latitudes, coronal holes rotate rigidly. Estimated magnitudes of sidereal rotation rate of the coronal holes are: $13.051 \pm 0.206$ deg/day for the equator, $12.993 \pm 0.064$ deg/day in the region of higher latitudes and, $12.999 \pm 0.329$ deg/day near the polar regions. For all the latitudes and the area, we have also investigated the annual variation of rotation rates of these coronal holes. We find that, for all the years, coronal holes rotate rigidly and their magnitude of equatorial, high latitude and polar region rotation rates are independent of magnitude of solar activity.