Dayside thermal structure of Venus' upper atmosphere characterized by a global model

Observations of Venus' dayside thermal structure are being conducted through ground based observatories. These temperature measurements, along with those from several instruments onboard the current Venus Express mission, are augmenting the previous thermal structure data from past missions (e.g., Veneras', Pioneer Venus Orbiter, Pioneer Venus Probes). These recent ground-based and VEx observations reveal the Venus dayside lower thermosphere to be considerably warmer and dynamically important than previously understood. In this study, a three dimensional general circulation model, the Venus Thermospheric General Circulation Model (VTGCM), is used to provide dayside temperature predictions for comparison to these recent ground based observations. Such a comparison serves to identify and quantify the underlying thermal processes responsible for the observed dayside temperature structure. The VTGCM reproduces the dayside temperatures observed near 110 km at noon from 40 degrees S to 40 degrees N very well. In addition, the global winds generated by these warm dayside temperatures are shown to give rise to dayside upwelling (divergence) and nightside subsidence (convergence) resulting in nightside warming near the anti-solar point at similar to 104 km. Corresponding nightside temperatures reach similar to 198 K, in accord with averaged measurements. This agreement implies (1) it is important for GCMs to include the updated radiative heating and cooling rates presented in Roldan et al. (2000) and (2) the current VTS3 and VIRA empirical models are in-sufficient in representing the warm regions observed in the thermal structure of the dayside lower thermosphere (similar to 100 to 130 km) and need to be updated.