General circulation of Venus from a long-term synoptic study of tropospheric CO by Venus Express/VIRTIS

The understanding of spatial and temporal variations in tropospheric abundances of the trace gas carbon monoxide (CO) is key to understanding the deep atmospheric circulation on Venus. CO is entrained in the global circulation, as well as being key ingredients in the multi-reaction chemical cycle that creates and destroys the sulfuric acid that is a primary constituent of the clouds. Long-term temporal variations of CO across Venus' disc would provide critical insights and constraints into the large-scale circulation and cloud forming processes in the troposphere. Here, we present an in-depth look at the CO as a function of latitude, longitude and local time as seen by the VIRTIS-M-IR instrument onboard the Venus Express spacecraft during its three years of operation. We find that CO is slightly enhanced on the dusk hemisphere near the poles (by ∼2 ppmv) and the equatorial concentrations from 22:00 - 03:00 are also elevated. Longitudinal variations of CO are largely absent, except for a potential correlation of anomalous CO around Themis Regio. These observations provide the most stringent constraints yet on global dynamics and CO chemistry of the deep troposphere on Venus.