Analysis of Venus Express optical extinction due to aerosols in the upper haze of Venus

Observations by the SPICAV/SOIR instruments aboard the Venus Express (VEx) spacecraft have revealed that the upper haze (UH) of Venus, between 70 and 90 km, is variable on the order of days to weeks and that it is populated by two particle modes. Gao et al. (submitted, Icarus, 2013) posit that one mode is made up of cloud particles that have diffused upwards from the main sulfuric acid cloud deck below, while the other mode is generated in situ by nucleation of sulfuric acid droplets on meteoric dust. They also propose that the observed variability in the UH is caused in part by vertical transient winds. They test this hypothesis by simulating a column of the Venus atmosphere from 40 to 100 km above the surface using a model based upon the Community Aerosol and Radiation Model for Atmospheres (CARMA). In this work, we significantly extend the analysis using the new more detailed SOIR/VeRa VEx temperature profiles which better constrain the observed strong CO2 15-micron cooling emission and 4.3-μm near-IR heating in Venus' atmosphere (and consistent with Venus Thermospheric General Circulation Model (VTGCM) simulations of Brecht et al. (2011)). We discuss our new results in context of the recent VEx observations (Wilquet et al., Icarus 217, 2012) with an intercomparison with the PVO data. We will also discuss similarities and differences arising from the PVO and VEx epochs where they exist. Additionally we report on our efforts self-consistently applying the VTGCM to constrain the degree to which effects due to vertical transient wind simulations can establish variability timescales and number density profiles that match VEx observations.