Venus dayside ionospheric conditions: Effects of ionospheric magnetic field and solar EUV flux

Abstract

The Venus ionosphere is influenced by both solar EUV and solar wind conditions. Using in situ measurements of solar EUV flux, we investigate the extent of the EUV‐contributed modulation of dayside conditions as measured by the Pioneer Venus orbiter Langmuir probe experiment. We use data from the low altitude dayside ionosphere (150‐200 km altitude, 0600‐1800 local solar time), normalized by a new empirical model of the ionosphere. We also introduce a new method for measuring the EUV flux at Venus that relies on the photoelectron emission from the Langmuir probe sensor in regions far above the ionosphere. Using these data we find that the EUV flux strongly affects ionospheric electron number density, Ne, but influences electron temperature, Te, very little. After removing this EUV dependence from the data, we examine the role of ionospheric magnetic fields in modulating dayside conditions, and we find that the presence or absence of large scale horizontal fields has no significant affect on Ne and Te at these altitudes. This is because the ions are collision dominated at these altitudes, and vertical diffusive transport is unimpeded by magnetic fields of the observed magnitudes.