THE EFFECT OF FORESHOCK ON THE MOTION OF THE DAYSIDE MAGNETOPAUSE

The role of the foreshock or quasi parallel shock in causing motions o f the magnetopause is studied using both the number of crossings of th e magnetopause found as ISEE 1 and 2 passed through the expected regio n of the magnetopause on each orbit and by determining the minimum and maximum distances to the magnetopause on each pass. Downstream of the afternoon magnetosheath and bow shock, a region free from foreshock e ffects for typical interplanetary magnetic field (IMF) directions, the north-south component of the IMF controls these motions. On the morni ng side additional oscillation in the magnetopause position is found f or both northward and southward IMF. We interpret these increased moti ons as driven by the pressure variations in and behind the foreshock r egion or quasi-parallel shock. These results are consistent with other studies of foreshock effects on the magnetosphere which show little e ffect On erosion of the magnetopause or flux transfer event occurrence .