| Abstrakt: |
Vertical transport of heat and atmospheric constituents by gravity waves plays a crucial role in shaping the thermal and constituent structure of the middle atmosphere. We show that atmospheric mixing by non‐breaking waves can be described as a diffusion process where the potential temperature (KH) and constituent (KWave) diffusivities depend on the compressibility of the wave fluctuations and the vertical Stokes drift imparted to the atmosphere by the wave spectrum. KH and KWave are typically much larger than the eddy diffusivity (Kzz), arising from the turbulence generated by breaking waves, and can exceed several hundred m2s−1 in regions of strong wave dissipation. We also show that the total diffusion of heat and constituents caused by waves, turbulence, and the thermal motion of molecules, is enhanced in the presence of non‐breaking waves by a factor that is proportional to the variance of the wave‐driven lapse rate fluctuations. Diffusion enhancements of both heat and constituents of 50% or more can be experienced in regions of low atmospheric stability, where the lapse rate fluctuations are large. These important transport effects are not currently included in most global chemistry‐climate models, which typically only consider the eddy diffusion that is induced when the unresolved, but parameterized waves, experience dissipation. We show that the theoretical results compare favorably with observations of the mesopause region at midlatitudes and describe how the theory may be used to more fully account for the unresolved wave transport in global models. Plain Language Summary: Winds blowing over topography and weather systems in the lower atmosphere can generate waves that propagate into the upper atmosphere to the edge of space, where their amplitudes become very large in response to decreasing atmospheric density. These waves drive the global circulation of the middle and upper atmosphere and can even affect satellite orbits and space weather. They also play very important roles in transporting heat and constituents vertically by mixing the atmosphere, which causes diffusion, and by inducing a net vertical motion, called Stokes drift. Unfortunately, global chemistry‐climate models cannot resolve the important small‐scale waves, which make the largest contributions to wave transport. Existing models account for wave transport by simply calculating the eddy mixing by turbulence that arises when waves break. We develop a general theory to describe wave‐driven diffusion and advection of heat and constituents in the atmosphere and show how the theory can be used to estimate the transport caused by unresolved, non‐breaking waves in atmospheric models. These results are important because they demonstrate the significance of wave transport, apart from simple eddy mixing, and provide a method for incorporating this crucial, but currently missing process, in future global chemistry‐climate models. Key Points: Non‐breaking gravity waves induce strong vertical transport that depends on compressibility of wave fluctuations and wave‐driven Stokes driftTheory compares favorably with observations of the mesopause region at midlatitudesResults can be used to parameterize transport of heat & constituents induced by unresolved waves in global chemistry‐climate models [ABSTRACT FROM AUTHOR] |
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