[P-PS02] Recent advances of Venus science and coming decades

[PPS02-16] Identification and characterization of quiescent cloud region "CALM" in the Akatsuki and Venus Express data

*Takehiko Satoh^1,2, Choon Wei Vun^3,2, Takeshi Horinouchi⁴, Kevin McGouldrick⁵, Takao M. Sato⁶ (1.Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, 2.Dept of Space and Astronautical Science, SOKENDAI, 3.ZMP Inc., 4.Hokkaido University, 5.University of Colorado, Boulder, 6.Hokkaido Information University)

Keywords:cloud, microphysics, sulfuric acid, Akatsuki, Venus Express

"CALM" was identified in the Akatsuki IR2 data acquired during Orbits 24 and 25 (August 2016) once data (in 2.26- and 1.735-um filters) were plotted in a special coordinates: the horizontal axis is logarithm of radiance at 2.26 um while vertical axis (basically logarithm of radiance at 1.735 um) has been sheared such that the curve corresponding to varying amount of Mode 3 particles becomes almost level (M3L = Mode 3 Leveled). CALM appears as a concentration of data points in this correlation plot (Clouds Aligned Linearly in M3L coordinates) and is interpreted as relatively quiescent region in which aerosol sizes are determined by equilibrium. Because IR2 stopped working in December 2016, the available data set is limited. To identify more CALM-like regions and to characterize them, we have examined the data acquired by VIRTIS-M onboard Venus Express. Examples of CALM-like regions in VEx/VIRTIS-M data will be presented along with physical insights obtained through comparison with Akatsuki/IR2 data.