共查询到19条相似文献，搜索用时 93 毫秒
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本文介绍了下垫面粗糙度突变时内边界层的形成过程,阐述了内边界层研究的意义,总结和分析了内边界层在理论研究、实验和观测以及数值模拟方面的主要成果。 相似文献
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本文在边界层顶垂直速度正比于地转涡度和地转风速,并与下垫面粗糙度有关的前提下,研究了边界层抽吸引起的涡度变化,在圆对称气压系统内得到了不同粗糙度情况下的涡度场和气压场的变化速率,修正了经典理论的结果。在湍流交换系数是地转风速及高度的函数的前提下,推导了地形存在时边界层顶垂直速度的公式,并用来讨论地形存在时的旋转减弱问题。 相似文献
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胡非 《南京气象学院学报》1989,(4)
本文在定常和中性层结条件下,利用有限元方法研究了下垫面粗糙度分布有阶跃变化的边界层问题。得到平均风场、气压变化以及湍流交换系数的主要分布特征,模拟出内边界层的发展规律。并将有关结果与观测事实作了比较。 相似文献
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Temperature oscillations observed in the stable boundary layer over four different underlying surfaces 
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下载免费PDF全文 《大气和海洋科学快报》2017,(3)
夜间边界层内的温度时空特征决定了边界层的稳定性。由于稳定边界层的间歇性和复杂性,模式在夜间的参数化方案还不完善,研究夜间边界层的温度变化有助于改进模式在夜间的表现。本文利用四座在不同下垫面上的气象塔的数据,研究了夜间边界层中的温度波动。研究表明,无论是海边、草原还是沙漠下垫面,夜间形成的稳定边界层中,振幅大约2摄氏度,周期在数分钟的温度波动非常频繁地出现。而在北京,由于城市下垫面较大的热容量和人为热源使得稳定边界层不容易形成,温度波动也较弱。用布朗特维萨拉频率代表的静力稳定度是影响温度脉动强弱的重要因子。 相似文献
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本文建立了一个二维定常大气中尺度数值模式，并用该模式讨论了由下垫面粗糙分布非均匀（局地动力强迫）和温度分布非均匀（局地热力强迫）而产生的局地大气环流与大气边界层湍流的相互作用。结果指出：下垫面存在温度分布非均匀时运动方程中的湍流交换项与水平气压梯项一样可促使局地热力环境的形成，由粗糙度分布非均匀强迫产生的局地环流与由下垫面温度分布非均匀强迫产和的局地热力环流间的非线笥相互作用是通过湍流交换实现的。 相似文献
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森林下垫面陆面物理过程及局地气候效应的数值模拟试验 总被引：5，自引：0，他引：5
文中基于大气边界层和植被冠层微气象学基本原理 ,建立了一个森林植被效应的陆面物理过程和二维大气边界层数值模式。并应用该模式进行了植被和土壤含水量等生物和生理过程在陆面过程和局地气候效应方面的数值模拟试验。所得数值模拟试验结果与实际情况相吻合。结果表明 ,应用该模式可获得植被温度、植被冠层内空气温度、地表温度日变化特征 ;森林下垫面大气边界层风速、位温、比湿、湍流交换系数的时空分布和日变化特征。该模式还可应用于不同下垫面 ,模拟陆面物理过程与大气边界层相互作用机制及其局地气候效应的研究 ,这将为气候模式与生物圈的耦合研究奠定一个良好的基础。 相似文献
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利用2007年4月17日-2008年4月16日兰州大学半干旱气候与环境观测站边界层气象塔的风速、 风向、 温度、 气压、 湿度等观测资料, 采用经典的廓线法和风速、 风向标准差法, 分别计算了中性大气层结下观测站下垫面粗糙度长度, 并得到了具有黄土高原地理特征的地表粗糙度及其时空变化特征。计算结果表明, 季节变化对粗糙度的影响幅度可达0.159 m, 空间非均一性对粗糙度的影响幅度可达0.155 m。测站附近粗糙度春季为0.017 m, 夏季为0.062 m, 秋季为0.065 m, 冬季为0.018 m。测站西北方向上游粗糙度春季为0.17 m, 夏季为0.22 m, 秋季为0.34 m, 冬季为0.05 m。测站东南方向上游粗糙度春季为0.11 m, 夏季为0.17 m, 秋季为0.19 m, 冬季为0.05 m。该站下垫面粗糙度计算宜选用风速为6±1.5 m·s-1, 风向变化30°范围内的数据。 相似文献
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利用大涡模式模拟了对流边界层结构演变以及深对流触发过程。通过改变鲍恩比的敏感性试验研究不同大气初始状况下湿润和干旱下垫面湍流特征及其对深对流触发过程的影响。结果表明:干旱下垫面的混合层干而暖,厚度较大;湿润下垫面相反。由于地表感热通量对热力湍流形成的作用更大,干旱下垫面上湍流混合和夹卷作用更强,使得水汽和相当位温在边界层内分布更均一,而在边界层顶有较大的负扰动;干旱下垫面上对流强度较湿润下垫面大,但均表现为泡状对流,水平方向上呈网状结构。不同下垫面上深对流的发生与大气初始状况有关,当初始时刻1—3 km的逆温强度较弱时（0.15 K/（100 m））,边界层内湍流迅速发展,深对流首先在干旱下垫面发生,但因对流有效位能较小,云层厚度小于湿润下垫面。当1—3 km的逆温强度增加到0.55 K/（100 m）时,云层形成时间较晚,云层厚度明显减小,仅当边界层顶的比湿较大时,有深对流发生,但仍首先发生在干旱下垫面,考虑贯穿对流在边界层顶引起的较强冷却作用,云层厚度大于湿润下垫面。 相似文献
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The internal boundary layer — A review 总被引：2，自引：2，他引：0
J. R. Garratt 《Boundary-Layer Meteorology》1990,50(1-4):171-203
A review is given of relevant work on the internal boundary layer (IBL) associated with:
- Small-scale flow in neutral conditions across an abrupt change in surface roughness,
- Small-scale flow in non-neutral conditions across an abrupt change in surface roughness, temperature or heat/moisture flux,
- Mesoscale flow, with emphasis on flow across the coastline for both convective and stably stratified conditions.
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A finite-volume numerical model is employed to investigate the adaptation of the atmospheric boundary layer to a change in
the underlying surface roughness, such as that existing in the transition from land to the free surface of a water body. Numerical
results are validated by comparison with neutral stratification atmospheric data and compared with the internal boundary-layer
(IBL) heights computed using a number of existing empirical formulae. The numerical analysis allows an extension of the fetch
range in which the existing formulae, calibrated only by comparison with short fetch data, may be applied. An argument is
offered that the spatial variability of the water surface roughness should be also taken into account for the IBL development
over the surface of a water body. 相似文献
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Heinz -Theo Mengelkamp 《Boundary-Layer Meteorology》1991,57(4):323-341
A three-dimensional, non-hydrostatic mesoscale model is used to study boundary-layer structure over an area characterized by the city of Copenhagen, the Øresund strait, and adjacent coastal farmland. Simulations are compared with data obtained on June 5, 1984 during the Øresund experiment.Under moderately strong wind conditions, a stable internal boundary layer (IBL) developed over the Øresund strait during the day. Near-surface winds decelerate over water due to diminished vertical momentum transfer.The turbulent kinetic energy field closely reflects the surface roughness distribution due to the imposed relatively strong wind forcing. TKE budgets over water, farmland and a city area are discussed by inspection of vertical profiles of the individual terms. The buoyancy term is used to indicate IBL heights because it changes sign at the boundary between different stability regimes. Measured and simulated dissipation rates show a decrease in the transition zone as the air travels over water and an abrupt increase when the IBL over a downwind city area is intersected. The top of the stable IBL is characterized by a minimum in the vertical TKE profile. 相似文献
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Martin Claussen 《Boundary-Layer Meteorology》1987,40(1-2):31-86
Modification of a turbulent flow upstream of a change in surface roughness has been studied by means of a stream function-vorticity model.A flow reduction is found upstream of a step change in surface roughness when a fluid flows from a smooth onto a rough surface. Above that layer and above the region of flow reduction downstream of a smooth-rough transition, a flow acceleration is observed. Similar flow modification can be seen at a rough-smooth transition with the exception that flow reduction and flow acceleration are reversed. Within a fetch of –500 < x/z
0< + 500 (z
0 is the maximum roughness length, the roughness transition is located at x/z
0 = 0), flow reduction (flow acceleration) upstream of a roughness transition is one order of magnitude smaller than the flow reduction (flow acceleration) downstream of a smooth-rough (rough-smooth) transition. The flow acceleration (flow reduction) above that layer is two orders of magnitude.The internal boundary layer (IBL) for horizontal mean velocity extends to roughly 300z
0 upstream of a roughness transition, whereas the IBL for turbulent shear stress as well as the distortion of flow equilibrium extend almost twice as far. For the friction velocity, an undershooting (overshooting) with respect to upstream equilibrium is predicted which precedes overshooting (undershooting) over new equilibrium just behind a roughness transition.The flow modification over a finite fetch of modified roughness is weaker than over a corresponding fetch downstream of a single step change in roughness and the flow stays closer to upstream equilibrium. Even in front of the first roughness change of a finite fetch of modified roughness, a distortion of flow equilibrium due to the second, downwind roughness change can be observed. 相似文献
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The notion of an internal boundary layer (IBL) appeared in studies of local advection within the atmospheric boundary layer when air flows over a change in surface conditions. These include surface roughness, thermal and moisture properties. An ability to predict the height of the IBL interface in the atmosphere under neutral stability, accompanied by certain assumptions on the form of the mean flow parameters, have been a means of obtaining information on the velocity profile after step changes in roughness for more than half a century. A compendium of IBL formulae is presented. The approach based on the diffusion analogy of Miyake receives close attention. The empirical expression of Savelyev and Taylor (2001, Boundary Layer Meteorol. 101, 293–301) suggested that turbulent diffusion is not the only factor that influences IBL growth. An argument is offered that an additional element, mean vertical velocity or streamline displacement, should be taken into account. Vertical velocity is parameterized in terms of horizontal velocity differences employing continuity constraints and scaling. Published data are analyzed from a new point of view, which produces two new neutral stratification formulae. The first implies that the roughness lengths of adjacent surfaces are equally important and a combined length scale can be constructed. In addition new formulae to predict the height of the region of diabatic flow affected by a step change in surface conditions are obtained as an extension of the neutral flow case. 相似文献
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Anna Maria Sempreviva S. E. Larsen N. G. Mortensen I. Troen 《Boundary-Layer Meteorology》1990,50(1-4):205-225
When air blows across a change in surface roughness, an internal boundary layer (IBL) develops within which the wind adapts to the new surface. This process is well described for short fetches, > 1 km. However, few data exist for large fetches on how the IBL grows to become a new equilibrium boundary layer where again the drag laws can be used to estimate the surface wind.To study this problem, data have been sampled for two years from four 30-m meteorological masts placed from 0 to 30 km inland from the North Sea coast of Jutland in Denmark. The present analysis is limited to neutral stratification, and the surface roughness is the main parameter. The analysis of wind data and two simple models, a surface layer and a planetary boundary layer (PBL) model, are described.Results from both models are discussed and compared with data analysis. Model parameters have been evaluated and the model sensitivity to those parameters has been investigated. Using the model parameters, a large-scale roughness length has been estimated.Istituto Di Fisica dell' Atmosfera I.F.A. — CNR, Rome, Italy. 相似文献
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John L. Walmsley 《Boundary-Layer Meteorology》1989,47(1-4):251-262
The height of the internal boundary layer (IBL) downwind of a step change in surface roughness is computed using formulae of Elliott (1958), Jackson (1976) and Panofsky and Dutton (1984). The results are compared with neutral-stratification atmospheric data extracted from the set of wind-tunnel and atmospheric data summarized by Jackson (1976) as well as neutral-stratification data presented by Peterson et al. (1979) and new data measured at Cherrywood, Ontario. It is found that the Panofsky-Dutton formulation gives the least root-mean-square (RMS) absolute errors for atmospheric applications. 相似文献
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Martin Claussen 《Boundary-Layer Meteorology》1991,54(1-2):1-27
Micro-scale turbulent transport processes over the marginal ice zone have been studied by use of a two-dimensional numerical model. It has been found that internal boundary layers (IBLs) of horizontal mean velocity, temperature, and specific humidity reveal a near field and a far field. In the near field, the change in surface roughness dominates the height and growth rate of a velocity IBL. The change in surface heat flux governs the near field of a temperature and humidity IBL. In the far field, approximately x/¦L
*2
¦ ~ 20, where L
*2 is the downstream Obukhov length, the downstream stratification more and more influences the growth rate of IBLs basically by modifying the eddy viscosity.Above more complex terrain consisting of an ensemble of ice strips and leads, a merging height h
M
develops, below which the horizontal variability of the surface modification is clearly observed; h
M
varies with the length scale L of surface modification approximately in proportion to h
M
/L ~ 1/20 – 1/10, as a rule of thumb. Above the merging height, an enveloping IBL exists, whose growth depends on the ice cover, i.e., on the integral of surface modification, but changes very little with L.Local advection of momentum, heat, and moisture clearly affects the local surface heat fluxes. Sensible and latent heat fluxes are found to show also a near and far field. However, if areally averaged surface fluxes are to be deduced from grid-averaged flow variables, then details of local advection can be neglected to a reasonably good approximation. 相似文献
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A warm on-ice air flow from the open water over the Arctic sea ice in the Fram Straitwas, for the first time, systematically measured on 12 March 1998 by aircraft in thelowest 3 km over a 300-km long distance. The air mass modification and the processesinvolved are discussed.Over the water, air temperature was lower than water temperature so that a convectiveboundary layer (CBL) was present as initial condition. As soon as the CBL passed theice edge, a shallow stable internal boundary layer (IBL) was formed. In the residual CBL, turbulence and pre-existing convective clouds dissolved within about 20 km. Within about the same distance, due to the transition from unstable to stable stratification, the influence of surface friction increased in the IBL and decreased above the IBL with consequent generation of a low-level jet at IBL top. The IBL was strongly stratified with respect to both temperature and wind. The wind shear was around 0.1 s-1 so that the Richardson number in the IBL was subcritical and turbulence was generated. The IBL top grew to about 145 m over 230 km distance. The growth of the IBL was not monotonic and was influenced by (a) inhomogeneous ice surface temperatures causedby both different ice thickness and changes in the cloud conditions, and (b) leads in theice deck. At the front side of the on-ice flow, the air mass boundary between the warmair and the cold Arctic air was sharp (12 K over 10 km) at low levels and tilted withheight. Observations suggest that the stratified IBL was lifted as a slab on top of thecold air. 相似文献