The influence of anisotropic F region ion velocity distributions on ionospheric ion outflows into the magnetosphere

The contribution to the fieldionospheric F region and sources of the heavy ions aligned ionospheric ion momentum equation, due to which are accelerated to several electron volts at coupling between pressure anisotropy and the greater altitudes and subsequently flow from the inhomogeneous geomagnetic field, is investigated. ionosphere into the magnetosphere. In order to We term this contribution the "hydrodynamic mirror look at this suggestion in more detail, this paper force" and investigate its dependence on the ion drift and the resulting deformations of the ion velocity distribution function from an isotropic form. It is shown that this extra upforce increases rapidly with ion drift relative to the neutral gas but is not highly dependent on the ion-neutral collision model employed. An example of a burst of flow observed by EISCAT, thought to be the ionospheric signature of a flux transfer event at the magnetopause, is studied in detail and it is shown that the nonthermal plasma which results is subject to a hydrodynamic mirror force which is roughly 10% of the gravitational downforce. In addition, predictions by the coupled University College London Sheffield University model of the ionosphere and thermosphere show that the hydrodynamic mirror force in the auroral oval is up to 3% of the gravitational force for Kp of about 3, rising to 10% following a sudden increase in cross-cap potential. The spatial distribution of the upforce shows peaks in the cusp region and in the post-midnight auroral oval, similar to that of assesses the role of temperature anisotropy on plasma dynamics in an inhomogeneous geomagnetic