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A.P. Showman (Univ. Arizona)
The question of what causes the persistent east-west jets on Jupiter, Saturn, Uranus, and Neptune remains one of the most important unsolved problems in planetary science. Two-dimensional models of turbulent motion show that, under the appropriate conditions, small-scale energy reorganizes itself into large-scale jets. And since the 1970s it has been repeatedly suggested that the required small-scale turbulence can be supplied by moist convection (i.e., thunderstorms). However, the dynamical models have been too simple to properly test this idea for the giant planets. The source of turbulence in the models is not consistent with the expected physics of moist convection. Jovian thunderstorms are localized and produce isolated clouds that expand in a few days to diameters of 1000--5000 km. In published simulations, however, the forcing is usually applied randomly as a perturbation of vorticity or mass that is broadly distributed (with some characteristic wavelength) over all spatial regions, and not surprisingly these simulations do not produce realistic jets. Moreover, published studies have to date used forcing that is not affected by the flow, whereas Jovian thunderstorms typically occur within cyclonic regions, indicating that the large-scale flow influences the locations of convection. Here I present preliminary numerical simulations of Jupiter's atmospheric flow that adopt a realistic, yet simple, parameterization of moist convection that allows the convection to interact with the flow. The goals are to determine (1) do jets of the correct shape and speed occur, and if so, what is the nature of the inverse cascade that produces them? (2) How does the flow feed back on the moist convection --- for example, does the moist convection predominantly occur in cyclonic regions? To allow systematic diagnosis of the horizontal dynamics and of the parameterization's behavior in a simplified setting, I initially adopt the shallow-water model. Future simulations will use the full primitive equations with many vertical layers and investigate the vertical structure resulting from the convection.
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Bulletin of the American Astronomical Society, 34, #3< br> © 2002. The American Astronomical Soceity.