The Budget of Turbulent Kinetic Energy in the Urban Roughness Sublayer
The Budget of Turbulent Kinetic Energy in the Urban Roughness Sublayer
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DOI：
10.1007/s10546-009-9359-5
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发表时间：
2009-05-01
影响因子：
4.3
通讯作者：
Vogt, Roland
中科院分区：
文献类型：
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作者：
Christen, Andreas;Rotach, Mathias W.;Vogt, Roland
对瑞士巴塞尔两个城市站点的全面观测进行了分析，以确定在城市大气中产生、重新定位和消散湍流动能(TKE)的不同过程的规模。两个塔配备了六个超声波风速仪，每个塔都采样了城市粗糙度亚层中的水流，即从街道峡谷底部到平均建筑高度的大约2.5倍。这项观测研究建议将城市粗糙度亚层概念性地划分为三层：(1)最高屋顶上方的层，在那里TKE的本地浮力生产和本地切变生产被当地的粘性耗散率所抵消，尺度湍流统计接近地表；(2)平均建筑物高度周围的层具有明显的偏折平均风廓线，TKE的强切变和尾迹生产，动量的湍流交换更有效，TKE通过输送过程显著输出；(3)较低的街道峡谷，通过输送过程输入TKE，本地生产可以忽略不计。平均积分速度方差随城市粗糙度次表层高度的变化而显著变化，反映了在特定高度产生或迁移TKE的驱动过程。观测到的TKE预算条款和速度变化的轮廓与植被冠层内和之上的观测结果有许多相似之处。
Full-scale observations from two urban sites in Basel, Switzerland were analysed to identify the magnitude of different processes that create, relocate, and dissipate turbulent kinetic energy (TKE) in the urban atmosphere. Two towers equipped with a profile of six ultrasonic anemometers each sampled the flow in the urban roughness sublayer, i.e. from street canyon base up to roughly 2.5 times the mean building height. This observational study suggests a conceptual division of the urban roughness sublayer into three layers: (1) the layer above the highest roofs, where local buoyancy production and local shear production of TKE are counterbalanced by local viscous dissipation rate and scaled turbulence statistics are close to to surface-layer values; (2) the layer around mean building height with a distinct inflexional mean wind profile, a strong shear and wake production of TKE, a more efficient turbulent exchange of momentum, and a notable export of TKE by transport processes; (3) the lower street canyon with imported TKE by transport processes and negligible local production. Averaged integral velocity variances vary significantly with height in the urban roughness sublayer and reflect the driving processes that create or relocate TKE at a particular height. The observed profiles of the terms of the TKE budget and the velocity variances show many similarities to observations within and above vegetation canopies.