  In this letter we report three-dimensional particle-in-cell simulations of
the interaction between a nonpenetrable magnetosheath jet and the magnetopause,
for northward interplanetary magnetic field. The magnetopause is modeled as a
tangential discontinuity with no magnetic shear. We investigate the deflection
of the plasma jet in the direction tangential to the magnetopause. We find that
as the frontal edge of the jet interacts with the magnetopause, the electrons
and ions are scattered in opposite directions, tangential to the magnetopause,
by the energy-dependent gradient-B drift. This effect is more effective on the
nonthermal particles that tend to accumulate at the two sides of the jet and
sustain a polarization electric field in the direction normal to the
discontinuity surface. The electric drift of the bulk of particles under the
action of this polarization electric field explains the deflection and
counterstreaming at the impact of the plasma jet on the tangential
discontinuity.
