A mechanism for the low nightside temperatures in the Venus thermosphere

A mechanism is proposed and discussed that may account for the extraordinarily low temperatures in the nightside upper atmosphere of Venus: cooling by the emission of infrared radiation in the rotational band of the H2O molecule, which represents a minor constituent of the atmosphere. A theoretical model for quantitative description has been devised which yields height profiles of the temperature and the CO2, CO, O, H2O abundances in the layer 100-170 km near the antisolar point. Along with molecular heat conduction, the model includes processes which may warm and cool the upper atmosphere, including: infrared radiational cooling in the H2O rotational band, the 15 micron CO2 band, the CO rotational band, and the 63 micron line of atomic oxygen; warming by the infrared radiation of the lower atmosphere in the 15 micron CO2 band; and wind energy transport.