[P-PS06] [EJ] あかつき金星周回1.5年とその科学成果

[PPS06-04] A 9-day disruption on Venus's lower clouds from AKATSUKI/IR2

★招待講演

*Javier Peralta¹、Takehiko Satoh¹、Takeshi Horinouchi²、Kazunori Ogohara³、Toru Kouyama⁴、Shin-ya Murakami¹、Takeshi Imamura⁵、Kevin McGouldrick⁶、Takao Sato¹、Sanjay S Limaye⁷、Enrique García-Melendo^8,9、Agustín Sánchez-Lavega⁸、Ricardo Hueso⁸ (1.Institute of Space and Astronautical Science (ISAS), Japan Aerospace Exploration Agency (JAXA), JAPAN、2.Faculty of Environmental Earth Science, Hokkaido University, Sapporo, JAPAN、3.School of Engineering, University of Shiga Prefecture, Shiga, JAPAN、4.Artificial Intelligence Research Center, National Institute of Advanced Industrial Science and Technology, JAPAN、5.Graduate School of Frontier Sciences, University of Tokyo, JAPAN、6.University of Colorado, Boulder, CO, USA、7.OSSE, University of Wisconsin-Madison, WI, USA、8.Universidad del País Vasco (UPV/EHU), Bilbao, SPAIN、9.Fundació Observatori Esteve Duran, Barcelona, SPAIN)

キーワード：Venus, Atmosphere, Atmospheric Dynamics, Akatsuki

The lower clouds of Venus, located at ~50 km above the surface, can be observed on the night side at observing windows at 1.74 and 2.30 µm that sense the clouds' opacity to the deep thermal emission. Observations from ESA's Venus Express allowed to determine the overall dynamics at this cloud level. In contrast to the dynamics at the upper clouds, motions at this layer are less variable and do not have a clear mean meridional component. However those observations were severely constrained to mid-to-high latitudes because of the polar orbit of Venus Express. The arrival of AKATSUKI at Venus in December 2015 has allowed continuing the study of the lower clouds at wavelengths 1.74, 2.26 and 2.32 µm. Here we report the discovery of an equatorial disruption or bow between 30ºN-30ºS which appears on the nightside lower clouds of Venus every 9 terrestrial days during more than 8 months of observations. This bow introduces a dramatic and abrupt increase of the cloud opacity, reducing the thermal radiance in about a half. The bow is preceded by a narrow dark equatorial area surrounded by brighter clouds at higher latitudes and a border with frequent wave-shape and rich of shear-like features and vortices of very slow development. After the passage of the bow, lower clouds emerge as more opaque and homogeneous during days. A shallow-water model succesfully applied for the case of Jupiter and Saturn is adapted for the case of Venus to constrain the nature of this bow and explaining its evolution.