The lower hybrid drift instability at the magnetopause

When the interplanetary magnetic field is northward, wave‐particle cross‐field transport may contribute to solar wind‐magnetosphere coupling. Such transport is studied here through the use of hybrid computer simulations (particle ions, fluid electrons with nonzero mass) carried out in the x‐y plane of a plasma with a density gradient in the x direction, no average iow speed, and a magnetic field B = B(x)ž. At early times, the lower hybrid drift instability grows on the gradient. However, at times long compared to an ion gyroperiod, the fluctuations coalesce to longer wavelengths in the y‐direction and nondiffusive density x‐profiles emerge which exhibit “plateaus” and “inclusions” qualitatively similar to those observed by ISEE near the magnetopause. These results call into question critical assumptions of quasilinear theories of cross‐field transport by this instability.