A global magnetic potential model for Venus' ionosphere

Abstract

Venus represents the prototype for a class of objects whose interaction with the solar wind is characterized by the dominance of an ionospheric obstacle to the magnetized plasma. Though the interaction region between the bow shock and the ionopause boundary of Venus has been extensively studied and successfully modeled, the ionosphere itself, especially on the night side, has only been the subject of piecemeal models. These models either restrict themselves to two dimensions, or treat only one ionospheric phenomenon at a time. However, it is possible to combine the information from these models of the ionosphere into a coherent three dimensional model of the large-scale fields of the Venerean ionosphere. The model, which makes use of magnetic potentials to insure the proper continuity relations of field across boundaries and to insure the magnetic field is globally divergenceless, is developed by breaking the field into altitude-independent toroidal, poloidal, and flow-parallel components. These components are fit to terminator characteristics that can be specified by a very few number of parameters, and to an approximate adherence to Newtonian pressure balance at the dayside ionopause. Finally, the altitude profiles of the field are inserted into the model as the potentials are renormalized and fit to a more exacting ionopause boundary condition on the dayside determined by a gasdynamic treatment of the magnetosheath. In addition, methods of applying the model to similar objects are discussed.