The atmosphere of Venus displays extreme equatorial superrotation, in that upper-level winds over the equator blow in the direction of planetary rotation at speeds nearly a hundred times greater than the absolute motion of the solid surface. This project is based on the idea that the phenomenon of equatorial superrotation is not confined to slowly rotating planets, such as Venus, but, given sufficiently strong solar tides, occurs on Earth. Very strong tides could result from the presence of dense dust clouds, such as were produced by the asteroid impact believed to have caused the extinction of the dinosaurs. The stratospheric overturning circulation in the presence of equatorial superrotation may have played an important role in spreading the dust cloud over the entire globe, and, therefore, in causing the extinctions. Atmospheric superrotation could also be important for the response of the climate to a nuclear exchange (so-called "nuclear winter") or to extreme vulcanism.
Zhu has demonstrated, in an idealized two-dimensional (latitude-altitude) model, that strong solar tides in the stratosphere can cause Earth's atmosphere to superrotate. Now he and his collaborators will conduct a set of exploratory experiments using a three-dimensional global climate model with a well resolved stratosphere, incorporating stratospheric particles with distributions and physical properties relevant to volcano super-eruptions. These experiments will test, in a fully three-dimensional dynamical context, the new and intriguing hypothesis that tidal forcing from strong solar absorption in the stratosphere can cause equatorial superrotation on Earth.
The results of this work should be of general interest to the public, and the investigators plan to describe them in an article in a general-audience science magazine.
