[P-PS04] Advancing the science of Venus in the golden age of exploration

[PPS04-13] Temperature Retrievals from Akatsuki LIR Measurements and Initial Comparisons with Akatsuki Radio Science

*Armin Kleinboehl¹, Shigeru Suzuki¹, Makoto Taguchi², Norihiko Sugimoto³, Takao Sato⁴, Takehiko Satoh⁵, Takeshi Imamura⁶ (1.Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA, 2.Rikkyo University, Tokyo, Japan, 3.Keio University, Yokohama, Japan, 4.Hokkaido Information University, Sapporo, Japan, 5.Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, Sagamihara, Japan, 6.The University of Tokyo, Kashiwa, Japan)

Keywords:Venus, atmospheric temperature, Akatsuki

Thermal infrared measurements with the Longwave Infrared Camera (LIR) on Akatsuki have revolutionized our understanding of Venus with the discovery of stationary waves and the characterization of thermal tides in Venus’ middle atmosphere. A limitation of these measurements is that data only exist as brightness temperatures measured by the camera and any information pertaining to the altitude range to which the measurements are sensitive is not available to date. This limits our understanding of Venus’ weather and climate that can be gained from these thermal infrared measurements.
The Venus sulfuric acid cloud layer is the predominant source of absorption in the 8-12 μm wavelength window covered by LIR. Hence, the derivation of atmospheric temperatures requires an understanding of the cloud cover and its vertical distribution. We use a cloud top height climatology based on measurements of the CO₂ column density above the clouds by the Akatsuki IR2 camera at a wavelength of 2.02 μm in April and May 2016 as input to retrieve atmospheric temperatures from thermal infrared images and characterize their vertical sensitivity.
Here we present retrievals of atmospheric temperatures from Venus images by LIR, together with their weighting functions that give the vertical sensitivity of the measurement. The retrieval algorithm is based on the one created for the Mars Climate Sounder, which has been adapted for the Venus atmosphere. It calculates absorption by sulfuric acid cloud layers based on the latitudinally dependent cloud climatology from IR2, using vertical profiles of temperature from the AFES-Venus General Circulation Model as a first guess. We illustrate the sensitivity of the LIR temperature retrieval by discussing examples at various emission angles and provide initial comparisons with temperatures retrieved from nearly-coincident measurements by the Akatsuki Radio Science investigation.