The fine structure of the front side magnetopause during two successive crossings

The fine structure of two magnetopause crossings observed on November 10, 1977, is studied in detail as representative of a class of magnetopause observations. A so‐called magnetopause layer is observed between the magnetosheath and the magnetosphere. Changes in the magnetic field indicate that there are current sheets on each side of this magnetopause layer, and therefore does not show the smooth features of a rotational discontinuity observed on other occasions. The magnetopause layer is characterized by an irregular and a magnetosheath‐like energy distribution, part of the time with increased flow and energy compared with the magnetosheath. The flow direction deviates considerably from that of the magnetosheath. No boundary layer plasma is observed on the magnetospheric field lines inside the magnetopause layer in the cases discussed. Electromagnetic energy is dissipated at the two edges of the magnetopause layer where the current layers are observed. The two crossings are tentatively interpreted to take place on the two sides of the X line that moved because of a change of the inclination of the magnetosheath magnetic field.