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 B SH of the magnetosheath field may be expressed as which implies that B SH is equal to the geometric mean of the stagnation field strength B ST and the shocked solar wind field, approximated by 4 B SW t For the usual spiral pattern of the solar wind field, B SH on the duskside of the magnetopause is about 20% stronger than it is on the dawnside. No dependence of B SH on the sign of the north‐south component of the solar wind field is apparent.