Water vapor near the cloud tops of Venus from Venus Express/VIRTIS dayside data

摘要

Observations of the dayside of Venus performed by the high spectral resolution channel (-H) of the Visible and Infrared Thermal Imaging Spectrometer (VIRTIS) on board the ESA Venus Express mission have been used to measure the altitude of the cloud tops and the water vapor abundance around this level with a spatial resolution ranging from 100 to 10km. CO _2 and H _2O bands between 2.48 and 2.60μm are analyzed to determine the cloud top altitude and water vapor abundance near this level. At low latitudes (±40°) mean water vapor abundance is equal to 3±1ppm and the corresponding cloud top altitude at 2.5μm is equal to 69.5±2km. Poleward from middle latitudes the cloud top altitude gradually decreases down to 64km, while the average H _2O abundance reaches its maximum of 5ppm at 80° of latitude with a large scatter from 1 to 15ppm. The calculated mass percentage of the sulfuric acid solution in cloud droplets of mode 2 (~1μm) particles is in the range 75-83%, being in even more narrow interval of 80-83% in low latitudes. No systematic correlation of the dark UV markings with the cloud top altitude or water vapor has been observed.