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Observations of brown dwarfs and relatively isolated young extrasolar giantplanets have provided unprecedented details to probe atmospheric dynamics in anew regime. Questions about mechanisms governing global circulation remain tobe addressed. Previous studies have shown that small-scale, randomly varyingthermal perturbations resulting from interactions between convection and theoverlying stratified layers can drive zonal jet streams, waves, and turbulence.Here, we improve upon our previous general circulation model by using atwo-stream grey radiative transfer scheme to represent more realistic heatingand cooling rates. We examine the formation of zonal jets and their timeevolution, and vertical mixing of passive tracers including clouds and chemicalspecies. Under relatively weak radiative and frictional dissipation, robustzonal jets with speeds up to a few hundred $\rm m\;s^{-1}$ are typicaloutcomes. The off-equatorial jets tend to be pressure-independent while theequatorial jets exhibit significant vertical wind shear. Models with strongdissipation inhibit jet formation and have isotropic turbulence inoff-equatorial regions. Quasi-periodic oscillations of the equatorial flow withperiods ranging from tens of days to months are prevalent at relatively lowatmospheric temperatures. Sub-micron cloud particles can be transported toseveral scale heights above the condensation level, while larger particles formthinner layers. Cloud decks are inhomogeneous near their cloud tops. Chemicaltracers with chemical timescales $>10^5$ s can be driven out of equilibrium.The equivalent vertical diffusion coefficients, $K_{\mathrm{zz}}$, for theglobal-mean tracer, are diagnosed from our models and are typically on theorder of $1\sim10^2\rm m^2\;s^{-1}$. Finally, we derive an analytic estimationof $K_{\mathrm{zz}}$ for different types of tracers under relevant conditions.

Jet Streams and Tracer Mixing in the Atmospheres of Brown Dwarfs and Isolated Young Giant Planets