Dynamics of the Global-Scale Albedo Feature of Venus

Details Dynamics of the Global-Scale Albedo Feature of Venus Dynamics of the Global-Scale Albedo Feature of Venus

Dec 2003

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003dps....35.3710i&link_type=abstract

American Astronomical Society, DPS meeting #35, #37.10; Bulletin of the American Astronomical Society, Vol. 35, p.1487

Astronomy and Astrophysics

Astronomy

Scientific paper

The dominant global-scale ultraviolet feature near the Venusian cloud top has been described as the dark Y-feature (turned sideways) and identified as a Kelvin wave. At the arms of the Y, dark regions tilt toward the direction of planetary rotation (westward) with latitude. A plausible scenario of creating the contrast has ultraviolet absorbers, which are formed well below the cloud top and destroyed by photodissociation or interaction with reactive photochemicals. Such absorbers should be rarer at the cloud tops and more prevalent deeper in the atmosphere. Then, local upward/downward winds associated with the Kelvin wave would increase/decrease the amount of absorbers to produce dark/bright regions. The cause of the meridional tilt of the dark region, however, is still unclear. The absorbers transported upward from the lower atmosphere by the Kelvin wave will be advected poleward by the Hadley circulation and westward by mid-latitude jets, but even in that case the dark regions would tilt in the opposite direction near the equator if the wave travels faster than the background atmosphere.
In this study, we propose that the mean upward flow associated with the Hadley circulation supports a Kelvin wave whose zonal phase speed does not exceed the mean zonal wind speed. Such a wave will provide a 'fountain' region which moves with the background zonal flow. Then, the absorbers supplied from this region will be advected poleward and westward to form the arms of the Y. A non-linear primitive equation model on the equatorial beta-plane is used to simulate such a Kelvin wave, and the albedo pattern caused by the advection and photodissociation of absorbers is calculated. It is also shown that the Kelvin wave which is modified in the Hadley circulation induces an equatorward flux of zonal momentum, which might contribute to the maintenance of the super-rotation.

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