JpGU-AGU Joint Meeting 2020

Presentation information

[E] Oral

P (Space and Planetary Sciences ) » P-PS Planetary Sciences

[P-PS06] Science of Venus: Venus Express, Akatsuki, and beyond

convener:Takehiko Satoh(Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency), Kevin McGouldrick(University of Colorado Boulder), Hideo Sagawa(Kyoto Sangyo University), Thomas Widemann(Observatoire De Paris)

[PPS06-11] Dayside cloud top structure of Venus retrieved from Akatsuki IR2 observations

*Takao M. Sato1, Takehiko Satoh2, Hideo Sagawa3, Naohiro Manago4, Yeon Joo Lee5, Shin-ya Murakami2, Kazunori Ogohara6, George HASHIMOTO7, Yasumasa Kasaba8, Atsushi Yamazaki2, Manabu Yamada9, Shigeto Watanabe1, Takeshi Imamura10, Masato Nakamura2 (1.Hokkaido Information University, 2.ISAS/JAXA, 3.Kyoto Sangyo University, 4.Chiba University, 5.Technische Universität Berlin, 6.The University of Shiga Prefecture, 7.Okayama Unviersity, 8.Tohoku University, 9.Chiba Institute of Technology, 10.The University of Tokyo)

Keywords:Venus, atmosphere, cloud structure, infrared observations, radiative transfer, Akatsuki

We describe the dayside cloud top structure of Venus as retrieved from 93 images acquired at a wide variety of solar phase angles (0–120 deg) using the 2.02-μm channel of the 2-μm camera (IR2) onboard the Venus orbiter, Akatsuki, from April 4 to May 25, 2016. Since the 2.02-μm channel is located in a CO2 absorption band, the sunlight reflected from Venus allowed us to determine the cloud top altitude corresponding to a unit aerosol optical depth at 2.02 μm. First, the observed solar phase angle dependence and the center-to-limb variation of the reflected sunlight in the region equatorward of 30 deg were used to construct a spatially averaged cloud top structure characterized by cloud top altitude , Mode 2 modal radius , and cloud scale height , which were 70.4 km, 1.06 μm, and 5.3 km, respectively. Second, cloud top altitudes at individual locations were retrieved on a pixel-by-pixel basis with an assumption that and were uniform for the entire planet. The latitudinal structure of the cloud top altitude was symmetric with respect to the equator. The average cloud top altitude was 70.5 km in the equatorial region and showed a gradual decrease of ~2 km by the 45 deg latitude. It rapidly dropped at latitudes of 50–60 deg and reached 61 km in latitudes of 70–75 deg. The average cloud top altitude in the region equatorward of 30 deg showed negligible local time dependence, with changes up to 1 km at most. Local variations in cloud top altitude, including stationary gravity wave features, occurred within several hundreds of meters. Although long zonal or tilted streaky features poleward of ~45 deg were clearly identifiable, features in the low and middle latitudes were usually subtle. These did not necessarily appear as local variations at the cloud top level, where mottled and patchy UV patterns were observed, suggestive of convection and turbulence at the cloud top level.