A comparative study on the Venusian Atmospheric Thermal Structure using observations and models

We present a long-term analysis of the Venusian atmospheric thermal structure between 45-80 km combining data from Venus Express and Akatsuki Radio Science payloads for periods spanning 2006-2024. The thermal structure is crucial for our comprehensive understanding of the atmosphere, providing better constraints for the cloud structure, radiative transfer algorithms and the general circulation models. The temperature profiles derived from the Radio Occultation (RO) measurements are compared with climatological mean outputs from the Venus International Reference Atmosphere (VIRA) and the Venus Climate Database (VCD). Large deviations exceeding 10K between RO observations and model outputs are seen at the high latitudes in both the hemispheres. A long term trend analysis of the annually averaged temperature profiles reveals a quasi-sinusoidal variability over the years across the low to mid latitude regions. To test the possible role of cloud albedo in modulating the thermal structure, VCD albedo settings are varied mimicking the observations obtained by Venus Express and Akatsuki. We find that VCD is able to partially explain the variability, especially in the lower altitudes, although large deviations with RO still occur above cloud tops. Our study highlights the need to update the existing climatological models with the latest available datasets, as well as to improve our understanding of the underlying physical processes governing the chemical and dynamical processes in the atmosphere.