Gross deformation of the dayside magnetopause

On July 24, 1996, the entire magnetosheath moved past the Interball‐1 spacecraft twice within 7 min. Such rapid transits through the magnetosheath suggest the passage of an antisunward‐moving boundary wave with an amplitude in excess of 5 R E . A wave of this amplitude requires an order of magnitude decrease in the pressure confining the magnetosphere. Such decreases have been reported only in conjunction with hot flow anomalies, features accompanying interplanetary magnetic field discontinuities, bounded by narrow shocks, and identified on the basis of heated deflected flows transverse to the Earth‐Sun line. We identify all these features just outside the Interball‐1 magnetopause crossings on July 24, 1996.