Sanjay S. Limaye. Lead

1 July 2013 – 31 December 2014

The recent ISSI publication, “Towards Understanding the Climate of Venus” discussed the scientific obstacles in reproducing the observed properties of the atmosphere of Venus that describe its climate. One of the key obstacles is a better knowledge of deposition of energy in the atmosphere of Venus (Titov et al., 2012). Predominantly this energy deposition takes place in the thick cloud/aerosol layer of Venus that extends from ~ 48 to 80 km through the incident solar radiation and to a smaller extent from the absorption of the emitted radiation by the surface and lower atmosphere. The large number thermal profiles obtained from Venus Express experiments hold the potential for exploiting the relationship to learn about the energy deposition in regions where it has not been explicitly measured or impractical to measure. The required observations of the spatial variability of the radiative forcing are not yet available and this along with the knowledge of the distribution of aerosols/clouds and trace species responsible absorption of energy along with a knowledge of the detailed global structure of the thermal structure of the atmosphere of Venus is a critical component of the information required to understand the planet’s current climate as well as clues to its past and future states.

Since then a huge amount of thermal structure data has been obtained from multiple instruments on ESA’s Venus Express (VEX) orbiter mission. The VEX data come from retrieval of temperature profiles from SPICAV/SOIR stellar/solar and VeRa radio occultations and from the passive remote sensing by the VIRTIS instrument. The results of these three experiments vary in their intrinsic properties – altitude coverage, spatial and temporal sampling and resolution and accuracy. Thus assembling a self-consistent three-dimensional thermal structure model requires that the results from these experiments be compared, evaluated and integrated in the context of simple physical models. This activity requires that the different experiment groups will present, discuss and suggest a three dimensional model will be of immense value for future research on understanding the atmospheric state of the Venus atmosphere in terms of its dynamical, chemical and physical properties.

Nearly three decades ago, an international effort led to the adoption of the Venus International Reference Atmosphere (VIRA) was published in 1985 after the significant data returned by the Pioneer Venus Orbiter and Probes and the earlier Venera missions (Kliore et al., 1985). The vertical thermal structure is one component of the reference model which relied primarily on the three Pioneer Venus Small Probes, the Large Probe profiles as well as several hundred retrieved temperature profiles from the Pioneer Venus Orbiter radio occultation data collected during 1978 – 1982.

A companion proposal is being submitted to ISSI (A. C. Vandaele and Korablev) to review the variability of trace species (SO2 and H2O) and another (Wilson and Marcq) consider the role of aerosols/clouds in the atmosphere of Venus. The ambient thermal structure is expected to play a role in determining the abundances of such species. This proposal will consider primarily the thermal structure of the atmosphere of Venus with a goal to arrive at an integrated model from the different measurement approaches that is not only self-consistent, but also consistent with the observed clouds/aerosols from the available observations. We expect that the effort will identify areas where further observations may be needed to resolve any inconsistencies in the available observations.