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

¹ College of Meteorology and Oceanography, National University of Defense Technology, Changsha, PR China
e-mail: dailongkang2022@126.com; 19994035@sina.com
² National Space Institute, Technical University of Denmark, Lyngby, Denmark
³ Planetary Environmental and Astrobiological Research Laboratory (PEARL), School of Atmospheric Sciences, Sun Yat-sen University, Zhuhai, PR China

Received: 12 August 2023
Accepted: 22 September 2023

Abstract

Context. The vertical eddy diffusion coefficient (K_zz) 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 K_zz, examining the variability of the cloud K_zz in both equatorial and polar regions, and evaluating the derived K_zz 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 K_zz. The global mean K_zz 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 K_zz 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 K_zz is three times as large as polar K_zz at 48 km, while polar K_zz reaches its peak below 46.5 km, where equatorial K_zz rapidly decreases as the altitude decreases.

Conclusions. We provide an estimate of the Venusian cloud K_zz based on H₂SO₄ vapor observations. Significant latitudinal variations exist in the Venusian cloud K_zz.