“weather” Variability of Close-in Extrasolar Giant Planets

Shallow-water numerical simulations show that the atmospheric circulation of the close-in extrasolar giant planet (EGP) HD 209458 b is characterized by moving circumpolar vortices and few bands/jets (in contrast with ∼ 10 bands/jets and absence of polar vortices on cloud-top Jupiter and Saturn). The large spatial scales of moving circulation structures on HD 209458 b may generate detectable variability of the planet’s atmospheric signatures. In this Letter, we generalize these results to other close-in EGPs, by noting that shallow-water dynamics is essentially specified by the values of the Rossby (Ro) and Burger (Bu) dimensionless numbers. The range of likely values of Ro (∼ 10 –10) and Bu (∼ 1–200) for the atmospheric flow of known close-in EGPs indicates that their circulation should be qualitatively similar to that of HD 209458 b. This results mostly from the slow rotation of these tidally-synchronized planets. Subject headings: planetary systems – planets and satellites: general – stars: atmospheres – turbulence