Magnetic field compression at the dayside magnetopause

The degree of compression sustained by the solar wind field as it convects to the magnetopause has been determined empirically with magnetometer data from ISEE 3 in the solar wind and ISEE 1 in the magnetosheath. At the stagnation point, the strength BSH of the magnetosheath field may be expressed as which implies that BSH is equal to the geometric mean of the stagnation field strength BST and the shocked solar wind field, approximated by 4 BSWt For the usual spiral pattern of the solar wind field, BSH on the duskside of the magnetopause is about 20% stronger than it is on the dawnside. No dependence of BSH on the sign of the north‐south component of the solar wind field is apparent.