Venus Terminator Temperature Structure: Venus Express SOIR and VTGCM Comparisons
Abstract
Venus Express SOIR terminator profiles of CO2 densities and temperatures have been organized and presented for 100+ selected orbits obtained between 2006-2011. The SOIR instrument measures CO2 absorption across a broad spectral window. The observed atmospheric transmittance spectra are subsequently inverted to obtain vertical density (and inferred temperature) profiles at the Venusian terminator over approximately 70 to 160 km. These recently recalibrated measurements continue to show a striking permanent temperature minimum (at 125 km) and a weaker temperature maximum (over 100-115 km). These features are reflected in the corresponding CO2 density profiles, and provide detailed constraints for global circulation models of the upper atmosphere. New Venus Thermospheric General Circulation Model (VTGCM) simulations are conducted for conditions appropriate to these SOIR measurements. In particular, solar minimum fluxes are specified and mean values of eddy diffusion and wave drag parameters are utilized. Recent upgrades to the VTGCM code now include more realistic lower boundary conditions at 70 km near cloud tops. Model temperature profiles are extracted from the terminators that correspond to five latitude bins presently used in the SOIR data analysis. Averaging of VTGCM temperature profiles in each of these bins (at each terminator) is conducted to match SOIR sampling. Comparisons of these SOIR and VTGCM temperature profiles are made. Most notably, the observed temperature minimum near 125 km and the weaker temperature maximum over 100-115 km are generally reproduced by the VTGCM at the correct pressure level. However, magnitudes of simulated and measured temperatures are somewhat different. In addition, VTGCM evening terminator (ET) temperatures are simulated to be modestly warmer than corresponding morning terminator (MT) values, a result of stronger ET than MT zonal winds at/above about 130 km. The SOIR terminator temperatures thusfar only reveal rather weak ET versus MT asymmetries above 140 km. Details of the underlying thermal balance processes are identified that give rise to these VTGCM simulated temperatures.
- Publication:
-
AAS/Division for Planetary Sciences Meeting Abstracts #45
- Pub Date:
- October 2013
- Bibcode:
- 2013DPS....4511812B