都市における運動量フラックスの鉛直分布とシアー関数 Shear function and vertical profile of momentum flux over an urban canopy

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Abstract

メソ気象モデルでは,都市一大気間の熱・エネルギーの乱流交換過程は,平板モデルと同様に取り扱われ,従来から提案されているモニンーオブコフ相似則がそのまま拡張適用されている.風洞実験により建物模型キャノピー内外の乱流特性が調べられているが,フィールドに拡張する際に不可欠である大気安定度依存性にまで言及しているものは数少なく,平原や森林で数多く提案されているモニンーオブコフ相似則が,都市においても適用できる保証はない.本報では住宅街でのタワー観測による運動量フラックスと風速勾配の関係およびシアー関数について検討した.

In this paper, we evaluate the applicability of flux-gradient relationships for momentum and heat for urban boundary layers within the Monin-Obukhov similarity (MOS) theory framework. Although the theory is widely used for smooth wall boundary layers, it is not known how well the theory works for urban layers. To address this problem, wemeasured the vertical profiles of wind velocity, air temperature, and fluxes of heat and momentum over a residential area and compared the results to theory. We found the following: (1) The non-dimensional horizontal wind speed has good agreement with the stratified logarithmic profile predicted using the semi-empirical Monin-Obukov similarity (MOS) function, when it was scaled by the surface friction velocity that is derived from the shear stress extrapolated to the roof-top level. (2) The scaled gradient of horizontal windspeed followed a conventional semiempirical function for a flat surface above the canopy, whereas, in the vicinity of the canopy height it was larger than the commonly-used empirical relationship. (3) The potential temperature profile above the canopy shows dependency on the atmospheric stability and the scaled gradient of temperature is in good agreement with a conventional shear function for heat. In the case of heat, the dependency on height was not found. (4) The flux-gradient relationship for momentumand heat was rather similar to that for flat surfaces than that for vegetated canopies.

Journal

  • Proceeding of Annual Conference

    Proceeding of Annual Conference 16(0), 262-263, 2003

    THE JAPAN SOCIETY OF HYDROLOGY AND WATER RESOURCES

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