Breaking Waves and Global-Scale Chemical Transport in the Earth's Atmosphere, with Spinoffs for the Sun's Interior

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The atmosphere used to be thought of using classical ideas about turbulence that looked back to analogies with gas kinetic theory, involving among other things an assumption that departures from spatial homogeneity are weak. This led to problematic notions like `negative eddy viscosity'. However, more recent advances in understanding the global-scale atmospheric circulation have shown the importance of recognizing - as essential, leading-order features - the strong spatial inhomogeneity of atmospheric turbulence together with the crucial role of wave propagation. For this purpose one can usefully draw a rough analogy with an ocean beach, where (a) turbulence in the surf zone owes its existence to waves arriving from elsewhere, and where (b) the spatial inhomogeneity of that turbulence is an essential feature of what is called wave dissipation by breaking. There is a phase-coherent interaction between the waves and the highly inhomogeneous tubulence. One well known consequence is the generation of mean currents along beaches by the convergence of the radiation stress or wave-induced momentum transport. For the global atmospheric circulation, the two most important kinds of waves are internal gravity waves and Rossby or vorticity waves. The chirality of Rossby waves, tied to the sense of the Earth's rotation, results in an angular momentum transport that is intrinsically one-signed and therefore ratchet-like, producing via Coriolis effects an inexorable `gyroscopic pumping' of air systematically poleward that dominates, for instance, the global-scale transport of chlorofluorocarbons and other long-lived greenhouse gases in the stratosphere. The Rossby-wave counterpart to oceabeach wave breaking involves not 3-dimensional but `layerwise 2-dimensional' turbulence, producing inhomogeneous mixing, quasi-horizontally along stratification surfaces, of a spin-like material invariant called the Rossby-Ertel potential vorticity. Some of the same considerations apply to the fluid dynamics of the Sun's stably stratified radiative interior. Together with recent helioseismic data they are forcing us to a novel conclusion: the Sun not merely can, but must, have in its radiative interior a poloidal magnetic field that is strong enough (~1 guass or 10^<-4> tesla by a preliminary rough estimate) to reshape, drastically, the circulation and differential rotation in the interior. This has farreaching consequences for understanding solar spindown history and internal variability, and for performing helioseismic inversions. It is helping to disentangle magnetic from soundspeed effects in the inversions, and should yield otherwise unobtainable information about differential rotation in the Sun's deepest interior. It suggests a possible new resolution of the lithium-burning enigma.
理論物理学刊行会の論文
1998-06-28

Breaking Waves and Global-Scale Chemical Transport in the Earth's Atmosphere, with Spinoffs for the Sun's Interior

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