On the origin and characteristic features of the V1 layer in Venus ionosphere using Akatsuki radio science experiment and the one-dimensional photochemical model

Abstract

ABSTRACT Using the radio science experiment onboard the Akatsuki spacecraft and an in-house developed one-dimensional photochemical model (1D-PCM) characteristic features of the V1 layer in Venus ionosphere, which peaks ∼125 km, have been studied. The shape of a V1 layer is highly variable; it can appear from mere as a slope change below the V2 layer to a clear prominent layer peak. We simulated the observations using 1D-PCM and found that the model solar X-ray flux at 1.5–3 nm and 5–10 nm bands need to be enhanced by a factor of 2–4 to reproduce a V1 layer. The model simulations also show that major ions below 135 km are O$_2^+$ and NO+ with O$_2^+$ increasing linearly up to ∼135 km, while NO+ peaks at around 127 km. Our analysis shows that for a case when the V1 layer appears as a slope change below the V2 layer, O$_2^+$ ions are the dominant ions, whereas the NO+ ions are the major ion when a clear V1 peak appears. When both the ion densities are comparable, the layer appears as a ledge.