Determination of the eddy diffusion in the Venusian clouds from VeRa sulfuric acid observations

Abstract

Context. The vertical eddy diffusion coefficient (Kzz) characterizing the efficiency of vertical atmospheric mixing is essential for 1D planetary atmospheric modeling, but poorly constrained in the Venusian clouds, where our ability to observe tracer gases is limited. The Venusian clouds are mainly composed of H2SO4, which has significant mass cycles in this region. A critical process herein is that the H2SO4 vapor abundance in the middle and lower clouds of Venus is regulated by both condensation and eddy diffusion processes. Aims. This study is devoted to proposing a novel approach to estimating the Venusian cloud Kzz, examining the variability of the cloud Kzz in both equatorial and polar regions, and evaluating the derived Kzz through the implementation of a 1D photochemical model. Methods. The H2SO4 vapor data used in this study were obtained from observations conducted by Venus Express. A novel approach that relies on the premise that both eddy diffusion and condensation regulate the abundance of H2SO4 vapor was then applied to estimate the Venusian cloud Kzz. The global mean Kzz and its latitudinal variation were discussed. A 1D photochemistry-diffusion model was applied to evaluate the estimations. Results. Our calculations indicate that the global mean Kzz reaches 5 × 108 cm2 s−1 in the lower clouds, which is an order of magnitude larger than several observation-based estimations and model results. It rapidly decreases as the altitude increases above 54 km. Equatorial Kzz is three times as large as polar Kzz at 48 km, while polar Kzz reaches its peak below 46.5 km, where equatorial Kzz rapidly decreases as the altitude decreases. Conclusions. We provide an estimate of the Venusian cloud Kzz based on H2SO4 vapor observations. Significant latitudinal variations exist in the Venusian cloud Kzz.