HDO and SO2 thermal mapping on Venus above and within the clouds

Sulfur dioxide and water vapor, two key species of Venus photochemistry, are known to exhibit significant spatial and temporal variations above the cloud top. We have started an observing campaign using the TEXES high-resolution imaging spectrometer at the NASA InfraRed Telescope Facility to map sulfur dioxide over the disk of Venus at two different wavelengths, 7 μm (probing atop the H2SO4 cloud) and 19 μm (probing a few kilometers below within the clouds). Observations took place on January 10-12, 2012 (evening terminator) and October 4-5, 2012 (morning terminator). Both HDO and SO2 lines are identified in our 7-μm spectra and SO2 is also easily identified at 19 μm. The CO2 lines at 7 and 19 μm are used to infer the thermal structure.An isothermal/inversion layer is present at high latitudes (above 60N and S) in the polar collars, much more visible when the morning terminator is observed; such an effect was not detected in October 2012. The HDO map is relatively uniform over the disk of Venus, with a mean mixing ratio of about 1 ppm above the clouds (P < 100 mbars. In contrast, the SO2 maps at 19 μm show intensity variations by a factor of about 2 over the disk within the cloud, less patchy than observed above the cloud top at 7 μm. In addition, the SO2 maps seem to indicate significant temporal changes within an hour. There is evidence for a cutoff in the SO2 vertical distribution several kilometers above the cloud top, also previously observed by SPICAV/SOIR aboard Venus Express and predicted by photochemical models. New observations have been obtained on February 26 -March 1, 2014, when the diameter of Venus was 34 arcsec. Another run is planned on July 6-9, 2014.