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Brown dwarfs and directly imaged giant planets exhibit significant evidencefor active atmospheric circulation, which induces a large-scale patchiness inthe cloud structure that evolves significantly over time, as evidenced byinfrared light curves and Doppler maps. These observations raise criticalquestions about the fundamental nature of the circulation, its timevariability, and the overall relationship to the circulation on Jupiter andSaturn. Jupiter and Saturn themselves exhibit numerous robust zonal (east-west)jet streams at the cloud level; moreover, both planets exhibit long-termstratospheric oscillations involving perturbations of zonal wind andtemperature that propagate downward over time on timescales of ~4 years(Jupiter) and ~15 years (Saturn). These oscillations, dubbed the QuasiQuadrennial Oscillation (QQO) for Jupiter and the Semi-Annual Oscillation (SAO)on Saturn, are thought to be analogous to the Quasi-Biennial Oscillation (QBO)on Earth, which is driven by upward propagation of equatorial waves from thetroposphere. To investigate these issues, we here present global,three-dimensional, high-resolution numerical simulations of the flow in thestratified atmosphere--overlying the convective interior--of brown dwarfs andJupiter-like planets. The effect of interior convection is parameterized byinducing small-scale, randomly varying perturbations in theradiative-convective boundary at the base of the model. In the simulations, theconvective perturbations generate atmospheric waves and turbulence thatinteract with the rotation to produce numerous zonal jets. Moreover, theequatorial stratosphere exhibits stacked eastward and westward jets thatmigrate downward over time, exactly as occurs in the terrestrial QBO, JovianQQO, and Saturnian SAO. This is the first demonstration of a QBO-likephenomenon in 3D numerical simulations of a giant planet.

Atmospheric Circulation of Brown Dwarfs and Jupiter and Saturn-like Planets: Zonal Jets, Long-term Variability, and QBO-type Oscillations