open access

https://hdl.handle.net/2115/88500

Gigantic Vortices From Barotropic Instability Observed in the Atmosphere of Venus

英語

planetary atmospheres

2023-01-28

American Geophysical Union

Geophysical Research Letters

50(2)

e2022GL101633

Until recently, the lower to middle cloud region of Venus had been supposed to be dynamically quiet, accommodating nearly steady superrotating westward flow. However, observations of the regions by Akatsuki, the latest Venus orbiter operating since 2015, have revealed a variety of cloud features indicative of vortices and waves. Here we report another, and arguably the most conspicuous, example. Akatsuki's near-infrared imager IR2 captured gigantic vortices rotating cyclonically on 25 August 2016. By using winds estimated by cloud tracking, the feature is shown to be quantitatively consistent with barotropic instability. The size of the vortices (similar to 1,000 km) and their spacing (similar to 2,500 km) are more than several times greater than the vortex-like features reported previously from the observations of Venus, and they are also greater than the largest barotropic instability observed in the Earth's troposphere. Hydrodynamical instabilities play important roles in the general circulation of the Earth and planetary atmospheres. Barotropic instability is a kind of instability that arises from horizontal differences in predominantly parallel horizontal flows. We report herewith the first concrete evidence of its occurrence in the atmosphere of Venus. Before this study, reports are limited to vortex-like cloud features whose appearance is consistent with this instability, but no analyses of flows have been conducted before. The cloud feature like a vortex street reported in this study has a spatial scale far greater than any of previously reported ones, and our study shows that it is dynamically consistent with barotropic instability.

学術雑誌論文

Version of Record

0094-8276

AA00657102