An Explanation of the Nightside Ionospheric Structure of Venus.

Hybrid simulations of Venus have produced nightside structure. It is believed these are the first simulations to produce the structure reported by spacecraft such as the Pioneer Venus Orbiter (PVO). The simulations reveal that the structure is created by the ∇ P_e ambipolar electric field when it aligns with local IMF (interplanetary magnetic field) direction. Thus, the orientation of the IMF in and near the ionosphere controls where on the nightside the tail structure will occur. The structure size and density is found to agree well with that measured by the PVO spacecraft. Further, comparisons with ion energy and velocity distributions also agree well with the summary conclusions from a variety of PVO papers and with some nightside observations by Venus Express. The agreement between the data and simulations lends confidence that the simulation results have merit. [ABSTRACT FROM AUTHOR]