Net Radiation in the Atmosphere of Venus: Measurements and Interpretation

Net flux radiometer measurements in the atmosphere of Venus question the effectiveness of the greenhouse mechanism in maintaining the high surface temperature. To search for possible instrumental explanations, new spare instrument tests were conducted. These tests uncovered an error mechanism that is defined well enough in the upper atmosphere to make approximate corrections for the large transient errors initiated at the time of instrument deployment. No direct evidence for significant errors in the lower atmosphere was found. The observed net radiative energy loss near the surface is found not to violate the assumption of a steady state atmosphere. Comparisons of the corrected flux profiles with radiative transfer calculations support the following conclusions: a new source of infrared opacity in the upper cloud is required, possibly a submicron haze; the infrared opacity of the lower cloud is too small for the cloud particles to be concentrated sulfuric acid; the mean water vapor mixing ratio is of the order of several tenths of a per cent immediately below the clouds and of the order of a few parts per million near the surface; water vapor amounts vary greatly from probe to probe, by nearly two orders of magnitude at some levels; there are thin layers of opacity in the subadiabatic layer between 35 and 48 km; and, finally, the north probe flux profile depression near 60 km may be partly a result of temperature inversions immediately above.