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Abstract Quasi‐random vertical displacement fluctuations, caused by the spectrum of non‐breaking gravity waves, mix the atmosphere, similar to turbulence, which induces significant vertical transport of heat and constituents in the upper atmosphere. Multi‐decade observations of temperature, made between 85 and 100 km with a Na lidar at Colorado State University (CSU, 40.6°N, 105.1°W), are used to derive the seasonal variations of the wave‐induced thermal (KH) and constituent (KWave) diffusivities. Both show strong annual oscillations with maxima in winter, which increase with increasing altitude.KHandKWaveexhibit summer minima of ∼40 and ∼70 m2s−1, respectively, that are approximately constant with altitude. In winter,KHvaries from ∼50 at 85 to ∼180 m2s−1at 100 km, whileKWavevaries from ∼110 at 85 to ∼340 m2s−1at 100 km. These values are much larger than the eddy diffusivity (Kzz∼ 35 m2s−1) predicted for this site by the Whole Atmosphere Community Climate Model. The CSU diffusivities are comparable to similar measurements made at other mid‐latitude mountain sites in both hemispheres, and derived from global observations of atomic O. However, the seasonal variations differ from the O observations, which may reflect differences in wave sources at these sites and the different approaches employed to derive the wave diffusivities. Even so, the CSU results demonstrate that heat and constituent transport by unresolved, non‐breaking gravity waves are important processes that need to be incorporated in global chemistry models to properly characterize the thermal and constituent structure of the upper atmosphere.
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Impact of Atmospheric Compressibility and Stokes Drift on the Vertical Transport of Heat and Constituents by Gravity Waves
Abstract 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. KHand KWaveare typically much larger than the eddy diffusivity (Kzz), arising from the turbulence generated by breaking waves, and can exceed several hundred m2s−1in 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.
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- PAR ID:
- 10500323
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Journal of Geophysical Research: Atmospheres
- Volume:
- 129
- Issue:
- 8
- ISSN:
- 2169-897X
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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