A Photochemical Model for the Venus Atmosphere at 47-112 km

Details A Photochemical Model for the Venus Atmosphere at 47-112 km A Photochemical Model for the Venus Atmosphere at 47-112 km

Dec 2011

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011agufm.p11g..06k&link_type=abstract

American Geophysical Union, Fall Meeting 2011, abstract #P11G-06

Physics

[0343] Atmospheric Composition And Structure / Planetary Atmospheres, [6295] Planetary Sciences: Solar System Objects / Venus

Scientific paper

The model is intended to respond to the recent findings in the Venus atmosphere from the Venus Express and ground-based submillimeter and infrared observations. It extends down to 47 km for comparison with the kinetic model for the lower atmosphere (Krasnopolsky, V.A., 2007, Icarus 191, 25-37) and to use its data as the boundary conditions. The model numerical accuracy is significantly improved by reduction of the altitude step from 2 km in the previous models to 0.5 km. Effects of the NUV absorber are approximated using the detailed photometric observations at 365 nm from Venera 14. The H2O profile is not fixed but calculated in the model. The model involves odd nitrogen and OCS chemistries based on the detected NO and OCS abundances. The number of the reactions is significantly reduced by removing of unimportant processes. Column rates for all reactions are given, and balances of production and loss may be analyzed in detail for each species. The calculated vertical profiles of CO, H2O, HCl, SO2, SO, OCS and of the O2 dayglow at 1.27 μm generally agree with the existing observational data; some differences are briefly discussed. The OH dayglow is ~30 kR, brighter than the OH nightglow by a factor of 4. The H + O3 process dominates in the nightglow excitation and O + HO2 in the dayglow, because of the reduction of ozone by photolysis. The model is extremely sensitive to small variations of eddy diffusion near 60 km: the calculated variations of SO2, SO, and OCS at and above the cloud tops are within a factor of ~30. Variations of the SO2/H2O ratio at the lower boundary have similar but weaker effect: variations within a factor of ~4 are induced by changes of SO2/H2O by ±5%. Therefore the observed variations of sulfur species originate from minor variations of the atmospheric dynamics near the cloud layer and do not require volcanism. NO cycles are responsible for production of a quarter of O2, SO2, and Cl2 in the atmosphere. A net effect of photochemistry in the middle atmosphere is the consumption of CO2, SO2, and HCl from and return of CO, H2SO4, and SO2Cl2 to the lower atmosphere. These processes may be balanced by thermochemistry in the lower atmosphere even without outgassing from the interior, though the latter is not ruled out by our models.
Variations of observable species induced by variations of eddy breakpoint he and SO2 at 47 km

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