摘要:

A nondimensional form of the temperature spectrum in a convective near‐surface layer was derived empirically as a function of stability parameter ξ =z/Land surface wave parameter γ =u*/(gz)1/2, under the assumption of horizontal isotropy, wherezis the depth of the measurement,Lis the Monin‐Obukhov length scale,u*is the surface friction velocity, andgis the acceleration due to gravity. The wave number‐weighted, one‐dimensional spectrum had +1 slope at low wave numbers and −2/3 slope at high wave numbers (characteristic of an inertial subrange). Spectral levels in the −2/3 range varied with γ, and the spectrum width was a function of ξ. The wavelength of the spectral peak decreased as −ξ (>0) increased. The variation of spectral level in the inertial subrange suggested that dissipation due to wave breaking was enhanced by a factor of 1.7 at 2‐m depth for a wind speed of 10 m s−1. Root‐mean‐square temperature fluctuations at 2‐m depth versus −ξ were in excellent agreement with atmospheric surface layer observations and agreed moderately well (within 30%) with the results of large‐eddy simulation experiments. Root‐mean‐square fluctuations were proportional to (−ξ)−1/3for −ξ>0.4, consistent with the predictions of similarity theory. The skewness of temperature fluctuations varied with −ξ, qualitatively similar to variation in the atmospheric surface layer. The skewness of the horizontal gradient of temperature at 2‐m depth varied relative to the wind direction and was well

ISSN:0148-0227    

DOI:10.1029/2003JC002066

年代:2004

数据来源: WILEY