Jp. Stmaurice et al., IONOSPHERIC ION VELOCITY DISTRIBUTIONS AND ASSOCIATED TRANSPORT-PROPERTIES IN THE PRESENCE OF AURORAL ELECTRIC-FIELD GRADIENTS, J GEO R-S P, 99(A10), 1994, pp. 19527-19548
We have studied the response of the ionospheric F region to intense ho
rizontal gradients in the convection electric field, using a kinetic t
heory of the ion gas. In the boundary regions where the electric field
changes rapidly in space, we have found that the local ion velocity d
istribution can become markedly asymmetric in a direction that is perp
endicular to that of the magnetic field. The degree of asymmetry depen
ds on the local electric field and on the magnitude of the shears. The
re is also a marked contrast between situations for which the electric
field increases in its own direction as opposed to when it decreases
along that direction. An integral part of our kinetic solution is the
presence of a time-dependent ion density, associated with a change in
the net charge and therefore with the divergence of the electric field
. This is a result of current continuity requirements for the problem
at hand. A more unexpected results is that the mean ion drift differs
markedly from the local value of the E x B drift as well. This behavio
r could lead to strong Hall currents in the regions of convection shea
rs and cause a Farley-Buneman type of instability at F region heights.
Other findings include the fact that the ion temperature varies marke
dly from one situation to another and is strongly three-dimensionally
anisotropic. Finally, strong ion heat flows can be induced in the E x
B direction even though the plasma is strongly magnetized.