Magnetopause characteristics during a four‐hour interval of multiple crossings observed with GEOTAIL

This paper presents multiple magnetopause crossings observed with Geotail on October 17, 1992. On this day Geotail skimmed the magnetopause in the dawn flank sector (the spacecraft had a speed of ∼0.7 km/s normal to the nominal magnetopause) and crossed the magnetopause more than 45 times in four hours. When the magnetopause crossings were observed, the interplanetary magnetic field was southerly directed. For the large number of crossings we have examined the magnetopause normal directions by using the minimum variance analysis technique, and as a result we have confirmed in a statistical sense a clear inbound/outbound dependence of the magnetopause orientation consistent with the tailward‐moving recurrent bumps in the magnetopause. In addition, there is an implication that the northward (southward) flow along the magnetopause occured for the inward (outward) directed magnetic field component normal to the magnetopause.