Japan Geoscience Union Meeting 2019

Presentation information

[E] Oral

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

[P-PS05] Recent advances of Venus science

Mon. May 27, 2019 1:45 PM - 3:15 PM A03 (TOKYO BAY MAKUHARI HALL)

convener:Takehiko Satoh(Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency), Takeshi Horinouchi(Faculty of Environmental Earth Science, Hokkaido University), Masaru Yamamoto(Research Institute for Applied Mechanics, Kyushu University), Kevin McGouldrick(University of Colorado Boulder), Chairperson:Kevin McGouldrick

1:45 PM - 2:00 PM

[PPS05-12] Cloud top structure of Venus retrieved from the Akatsuki IR2 dayside observations

★Invited Papers

*Takao M. Sato1, Takehiko Satoh2, Hideo Sagawa3, Naohiro Manago2, Yeon Joo Lee, Shin-ya Murakami2, Kazunori Ogohara4, George HASHIMOTO5, Yasumasa Kasaba6, Atsushi Yamazaki2, Manabu Yamada7, Shigeto Watanabe1, Takeshi Imamura8, Masato Nakamura2 (1.Hokkaido Information University, 2.ISAS/JAXA, 3.Kyoto Sangyo University, 4.University of Shiga Prefecture, 5.Okayama University, 6.Tohoku University, 7.Chiba Institute of Technology, 8.The University of Tokyo)

Keywords:Venus, atmosphere, clouds, Akatsuki, near-infrared, radiative transfer

We present the cloud top structure of Venus retrieved from a total of 93 dayside images acquired at a wide variety of solar phase angles (0-120 deg) by the 2.02-μm channel of the 2-μm Camera (IR2) onboard Japanese Venus orbiter, Akatsuki, during the period from April 4 to May 25, 2016. Since the 2.02-μm channel locates in a CO2 absorption band, the sunlight reflected from Venus allows us to determine the cloud top altitude corresponding to unit aerosol optical depth at 2.02 μm with radiative transfer calculation. Firstly, the observed solar phase angle dependence and zonal variation of the reflected sunlight in the equatorial region were used to construct a baseline model characterized by cloud top altitude , Mode 2 radius , and cloud scale height which are 70.287 km, 1.26 μm and 5.1 km, respectively. Secondly, individual cloud top altitudes were retrieved with the assumption that the last two values are valid for the entire planet. The latitudinal structure of cloud top altitude is symmetrical with respect to the equator: the averaged cloud top locates at a constant altitude of 68-70 km equatorward of ±45 deg but rapidly drops in latitudes of 50-60 deg and reaches 61 km poleward of ±70 deg. The averaged cloud top in the equatorial region indicates the tendency to increase from early morning (~7 h) and reach a maximum near early afternoon (~14 h) and decrease toward late afternoon (~17 h). The magnitude of the change is in the order of 1 km. After high-pass filtering of the cloud top altitude maps, small-amplitude features including stationary structures occur within several hundred meters and typically show less contrast than those at two channels (283 and 365 nm) of the Ultraviolet Imager (UVI). Although the long, zonal or tilted streaky features poleward of ~45 deg are clearly identifiable, the features in low and middle latitudes are usually faint and do not necessarily appear as the local variation in cloud top altitude where mottled and patchy patterns are seen in the UV channels, suggesting the existence of convection and turbulence at the cloud top level.