ISEE particle observations of surface waves at the magnetopause boundary layer

The dual‐spacecraft ISEE mission provides a uique opportunity to study the motions of the magnetopause and adjacent boundary layer. By comparing high‐time‐resolution energetic particle data from ISEE 1 to those of ISEE 2, the velocity and orientation of the inner boundary of the boundary layer can be determined. Two cases are presented. In one, tailward propagating sinusoidally shaped surface waves with a wavelength in excess of 42,000 km and an amplitude of ∼5000 km are found. In the other, surface waves are indicated with a wavelength of ∼40,000 km and an amplitude of ∼11,000 km having steepened nonsinusoidal shapes. The existence of such large‐amplitude waves suggests that the particle dynamics near the magnetopause support nonlinear processes.