Circulation of Venusian Atmosphere at 90-110 km Based on Apparent Motions of the O₂ 1.27 µm Nightglow From VIRTIS-M (Venus Express) Data

Abstract

The paper is devoted to the investigation of Venus mesosphere circulation at 90-110 km altitudes, where tracking of the O₂(a¹Δ_g) 1.27 μm nightglow is practically the only method of studying the circulation. The images of the nightglow were obtained by VIRTIS-M on Venus Express over the course of more than 2 years. The resulting global mean velocity vector field covers the nightside between latitudes 75°S-20°N and local time 19-5 h. The main observed mode of circulation is two opposite flows from terminators to midnight; however, the wind speed in the eastward direction from the morning side exceeds the westward (evening) by 20-30 m/s, and the streams "meet" at 22.5 ± 0.5 h. The influence of underlying topography was suggested in some cases: Above mountain regions, flows behave as if they encounter an "obstacle" and "wrap around" highlands. Instances of circular motion were discovered, encompassing areas of 1,500-4,000 km.