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Studies of the cloud-tops of Venus by JAXA's Akatsuki spacecraft show striking variety in wind speeds year-on-year and between the planet's northern and southern hemispheres. The first fine-scale observations of cloud-top temperatures have also revealed a tendency for clouds to converge towards the equator at night, in contrast to poleward circulation seen previously in daytime studies.
The results, which have been presented today at the EPSC-DPS Joint Meeting 2019 in Geneva, provide new insights into the mystery of why the Venusian atmosphere rotates much faster than the planet itself.
Prof - Masato - Nakamura - Project - Manager
Prof Masato Nakamura, Project Manager of Akatsuki at JAXA, said: "The Venusian 'super-rotation' is most pronounced at the tops of Venus's clouds, making this an important region for understanding the dynamics of the planet's atmosphere. The Akatsuki mission is in a highly elliptical orbit around Venus that enables the spacecraft to image both the north and south hemispheres of the planet simultaneously."
An international team of researchers has used advanced cloud-tracking and quality control techniques to analyze with high accuracy the direction and speed of cloud top winds using data collected by the Ultraviolet Imager (UVI) instrument over three years.
Study - Prof - Takeshi - Horinouchi - Hokkaido
The study, led by Prof Takeshi Horinouchi of Hokkaido University, Japan, and Dr. Yeon Joo Lee of JAXA/ISAS and TU Berlin, found that the super-rotation speed at the cloud tops not only changes over time but is different in the northern and southern hemispheres. The team also detected planetary-scale atmospheric waves at the cloud tops, which may interact with the super-rotation.
The degree of difference between the hemispheres, or "asymmetry," may be linked to a second mystery at Venus: an as-yet unidentified chemical species in the atmosphere that strongly absorbs ultraviolet radiation from the Sun.
Prof - Horinouchi - Asymmetry - Super-rotation - Speeds
Prof Horinouchi said: "The asymmetry in super-rotation speeds in cloud tops in the northern and southern hemispheres...
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