Characterizing the V1 layer in the Venus ionosphere using VeRa observations from Venus Express

Abstract

The Venus Radio Science Experiment (VeRa) on the Venus Express spacecraft sounds the Venus atmosphere during Earth occultations to obtain vertical profiles of electron density in the ionosphere. The resultant profiles reveal the vertical structure of the Venus ionosphere from the topside down to below the lower layers (\u3c 115 km). On the dayside, the dominant plasma layer is the V2 layer at ~142 km, which is produced primarily by photoionization of CO2. Embedded on the bottomside of the V2 layer is the less prominent, and much less studied, V1 layer at ~127 km. The V1 layer is also produced by photoionization of CO2, but secondary ionization due to energetic photoelectrons is much more important. Here we investigate properties of the V1 layer using VeRa profiles from 2006 to 2012 during which the Sun went from the deep solar minimum of Solar Cycle 23 to the rising solar activity levels of Solar Cycle 24. We investigate how the peak electron density and peak altitude of the V1 layer depend on solar zenith angle. We also characterize the shapes of the V1 layer and show how they are related to the solar activity level. Solar spectra from the Solar EUV Experiment (SEE) instrument on the Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED) spacecraft are used to characterize the shapes of the V1 layer with solar activity