The sketch at the right and the one below illustrate the flow of charged
particles in the equatorial plane of the magnetosphere.
The interaction of the
solar wind with the
magnetosphere (through reconnection and viscous
processes) results in a bulk flow of
plasma down the
magnetotail. This flow is referred to as "convection,"
although this term is really a misnomer because convection
is a thermal process and the flow of plasma is not, being
governed instead by large-scale electric and magnetic
fields. In the plasma sheet, the direction of the convective
flow is sunward, perpendicular both to the direction of
the Earth's magnetic field (out of the screen) and to the
direction (dawn-to-dusk) of the electric field imposed on
the magnetosphere by the solar wind interaction. (The
motion of the plasma perpendicular to both the electric
and magnetic fields is known as "E-cross-B drift.") As
coupling between the solar wind and the magnetosphere
intensifies, sunward convection increases, and the
boundary separating the convective and co-rotational
(known as the "separatrix") moves inward, freeing some of the plasma
previously bound on "closed" Earth-encircling trajectories
to follow "open" convective paths toward the dayside
magnetopause. Weakening of convection enlarges the
region of near-Earth plasma that co-rotates with the Earth
and allows the magnetic field lines emptied of plasma
during periods of high convection to refill.
Figures adapted from:
Brice, N. M., Bulk motion of the magnetosphere, J. Geophys.
Res., 72, 5193, 1967; and Kavanaugh, L. D., Jr. et al.,
Plasma flow in the magnetosphere, J. Geophys. Res., 73, 5511,1968.