IONOSPHERIC ION VELOCITY DISTRIBUTIONS AND ASSOCIATED TRANSPORT-PROPERTIES IN THE PRESENCE OF AURORAL ELECTRIC-FIELD GRADIENTS

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.