Meridional Distribution of CO, H2O, and H2SO4 in the Venus' Atmosphere: A Two-Dimensional Model Incorporating Transport and Chemical Reaction

Abstract

We developed a 2-dimensional model of Venus' atmosphere which calculates meridional distributions of chemical species such as CO, $H_2$O, and $H_2{\text{SO}}_4$. To calculate the meridional distribution of chemically active species, we combined chemical model, cloud model, and transport model. Partitioning between gas and liquid phase is calculated assuming vapor-liquid equilibrium, and the number density of cloud droplet is calculated by taking coagulation into account. Our model demonstrated that the meridional distributions of CO and $H_2$O are sensitive to the circulation of the Venus' atmosphere. Observed meridional distribution of CO indicates that there is a large scale meridional circulation from the lower (below 20 km altitude) to the upper (around 80 km altitude) atmosphere. Also observed concentration of $H_2$O vapor above the cloud top suggests that meridional circulation ventilates the air above the cloud top on a time scale of 600 days. In our model, thick clouds at low latitudes are maintained by meridional circulation, while thick clouds at high latitudes are caused by latitudinal temperature gradient and horizontal transport of $H_2{\text{SO}}_4$ vapor.