Motions of particle microstructures in the magnetopause boundary layer

Particle flux data acquired by the ISEE 1 and 2 spacecraft reveal many of magnitude changes within the magnetopause boundary layer that occur during less than 1/4 s of time. These changes define small-scale particle structure, or microstructures within the region, many of which are apparently inclusions of plasma from adjacent regions. Particle structures resolved by the high time resolution data include groups with periods as short as 0.375 s. An estimate is derived for the motion of the microstructures with respect to an oscillatory inner boundary for four afternoon sector boundary layer crossings by measuring interspacecraft time differences as the features propagate past the satellites. On average the microstructures move toward the tail of the magnetosphere in concert with the wavy large-scale inner boundary. Furthermore, the orientations of the edges of the structures maintain an aspect similar to that of the boundary. These characteristics are expected for magnetohydrodynamic plasma flows that generate vorticity due to velocity shear stresses.