Ion temperature anisotropy and heat flow in the Venus lower ionosphere

Abstract

Motivated by the recent observations of supersonic ion flow in the Venus ionosphere near the terminator, we have studied the extent to which such a flow can induce an ion temperature anisotropy and a diffusion‐thermal heat flow. Our calculations indicate that appreciable ion temperature anisotropies can be induced at altitudes below about 220 km. The temperature anisotropy is with respect to the ion‐neutral relative drift velocity vector, with the ion temperature parallel to the relative drift velocity greater than the perpendicular ion temperature. The parallel to perpendicular ion temperature ratio is likely to be in the range of from 2 to 4, depending on the ionospheric conditions. We have also found that in the same ionospheric region the ion neutral relative drift induces a diffusion‐thermal heat flow that is considerably more important than ordinary ion thermal conduction. Consequently, diffusion‐thermal heat flow could have an appreciable effect on the ion energy balance in the Venus lower ionosphere.