Venusl Chemical and Dynamical Processes in the Stratosphere and Mesosphere

Abstract

Photochemical models for the Venus clouds are presented and discussed. We illustrate models for sulfuric acid density as a function of altitude based on a proposed photochemical scheme. Emphasis is placed on two competing removal mechanisms for sulfur atoms above the visible clouds:The first reaction (which forms the major oxygen sink in the visible cloud region) requires reasonable O₂ concentrations and leads to sulfuric acid production. The second reaction occurs in regions where O₂ is severely depleted and leads to elemental sulfur production. Quantitative estimates of the balance between these two competing processes are presented together with a discussion of the complete sulfur and oxygen cycles on the planet. We propose that the dark regions in the ultraviolet on Venus are oxygen-depleted regions where a significant amount of ultraviolet-absorbing sulfur is being produced. We also discuss observations of particle densities on Venus and their implications for vertical mixing rates. Transient internal gravity waves are a likely process for vertical mixing above the altitude z ≈ 80 km and we suggest that the vertical eddy-mixing coefficient is given by (D2) where H is the atmospheric density scale height. This suggests the turbopause should lie near or below 136 km. The dispersion relation for internal gravity waves in regions of wind shear suggests vertical mixing can be accomplished by transient thermally or mechanically-forced waves with horizontal wavelengths ≳20 km.