ON THE FORMATION OF A PLASMA PRESSURE ANISOTROPY IN THE DAYSIDE MAGNETOSHEATH

We present a numerical solution for the momentum equation of the magne tosheath particles that describes the distribution of the pressure ani sotropy of the magnetosheath plasma in the midday meridian plane. The pressure anisotropy is a maximum near the magnetopause subsolar point (p(perpendicular to) /p(parallel to) congruent to 10). The pressure an isotropy is caused by two factors: particles with small pitch angles ( V-parallel to/V-perpendicular to) which travel along the magnetic fiel d lines away from the equatorial plane of the magnetosheath; and parti cles, after crossing the bowshock, which reach the bulk velocity compo nent directed along the magnetic field lines again, away from the magn etosheath equatorial plane. This velocity increases with increasing di stance from the subsolar point of the bow shock, and does not permit p articles with large pitch angles (V-<perpendicular to > > V-parallel t o) to move toward the equatorial plane.