Self-consistent retrieval of temperature profiles and cloud structure in the northern hemisphere of Venus using VIRTIS/VEX and PMV/VENERA-15 radiation measurements

Abstract

Improved radiative transfer simulation and multi-window retrieval procedures (MWR) are described that are applied to investigate thermal structure and cloud features in the nightside atmosphere of Venus over the northern hemisphere. Comparative analyses of spectroscopic data, which were recorded independently in different parts of the infrared spectrum by the Visible and InfraRed Thermal Imaging Spectrometer (VIRTIS-M-IR) aboard ESA's Venus Express space probe and the Profile Measuring Instrument for Venus (PMV, Fourier spectrometer FS-1/4) during the earlier Soviet Venera-15 experiment, are combined with self-consistent temperature profile and cloud parameter retrievals. MWR performance is studied using synthetic spectra at different latitudes and for different atmospheric temperature profiles and cloud parameters. VIRTIS and PMV retrieval result comparisons are used to determine constraints on physical state parameter variations, especially on applicability of different cloud models. An analytically parameterized initial model of four-modal cloud altitude distributions is proposed. Together with retrieved cloud parameters, which encompass individual mode factors and cloud upper altitude boundary, it permits optimum fits of measured radiances and brightness temperatures in the 4.3 and 15 µm CO₂ bands utilized for atmospheric temperature profile retrievals. A new multi-spectrum retrieval (MSR) method (Kappel et al., 2012, Kappel, in press) provides deep atmosphere CO₂ opacity correction parameters, which affect cloud parameter retrievals from short-wavelength emission windows.