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
... [Show full abstract] 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°S to 40°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 ˜104 km.
Corresponding nightside temperatures reach ˜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 Roldán 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
(˜100 to 130 km) and need to be updated.
