[P-PS06] [EJ] あかつき金星周回1.5年とその科学成果

[PPS06-P06] Stationary waves and slow cloud features challenge Venus's night side superrotation

*Javier Peralta¹、Ricardo Hueso²、Agustín Sánchez-Lavega²、Yeon Joo Lee¹、Antonio García-Muñoz³、Toru Kouyama⁴、Hideo Sagawa⁵、Takao Sato¹、Giuseppe Piccioni⁶、Takeshi Imamura⁷、Takehiko Satoh¹ (1.Institute of Space and Astronautical Science (ISAS), Japan Aerospace Exploration Agency (JAXA), JAPAN、2.Universidad del País Vasco (UPV/EHU), Bilbao, SPAIN、3.Zentrum für Astronomie und Astrophysik, Technische Universität Berlin, GERMANY、4.Artificial Intelligence Research Center, National Institute of Advanced Industrial Science and Technology, JAPAN、5.Faculty of Science, Kyoto Sangyo University, JAPAN、6.Istituto di Astrofisica e Planetologia Spaziali (INAF-IAPS), ITALY、7.Graduate School of Frontier Sciences, University of Tokyo, JAPAN)

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

The atmosphere of Venus rotates with velocities that at the cloud tops (65-70 km above surface) can be sixty times faster than the underlying surface, a phenomenon known as superrotation that continues to puzzle atmospheric scientists after decades of research. Whereas on Venus's dayside the cloud top motions are well determined, the night side circulation remains poorly studied except for the polar region. Here, we report first global measurements of the night side circulation of Venus at the upper cloud level from the tracking of individual features in thermal emission images at 3.8 and 5.0 microns during 2006-2008 (Venus Express/VIRTIS) and 2015 (IRTF/SpeX). Contrarily to the dayside motions dominated by mean super-rotating winds ranging -120 to -90 m/s at this altitude, night side motions are far more variable, revealing well-contrasted features moving at similar velocities than the day side features, stationary wave patterns with zonal speeds ranging from -10 to +10 m/s and a complex mixture of cloud-like features with apparent motions ranging from -80 to -40 m/s. These results defy the paradigm of an ubiquitous steady day and night stable superrotation at this altitude level and decades of numerical efforts to explain Venus's General Circulation.