共查询到18条相似文献，搜索用时 656 毫秒
1.
本文研究了斜压效应对地转动量Ekman流的影响。利用两变量奇异摄动方法求得了边界层中风场及顶部垂直速度的前二级一致有效渐近解析解，解中明显地反映了斜压情形地转风随高度变化（即热成风）的影响，尤其是其中一级近似解完全由热成风影响所致。在边界层顶垂直速度的解中导出了三种由斜压效应引起的Ekman抽吸新物理因子，即热成风形变、热成内涡度及热成风涡度交叉项等抽吸因子。分析表明，这些因子只在具有水平温度梯度不均匀的系统（譬如锋区）中方能出现。文中还对锋区内上述三种抽吸因子的动力特征作了具体的分析，指出在锋区这 样的强斜压系统中，此三种抽吸因子的贡献是显著的。下一文中，我们将利用本文所得理论解对斜压效应进行具体的定量计算。 相似文献
2.
本文研究了斜压效应对地转动量Ekman流的影响。利用两变量奇异摄动方法求得了边界层中风场及顶部垂直速度的前二级一致有效渐近解析解,解中明显地反映了斜压情形地转风随高度变化(即热成风)的影响,尤其是其中一级近似解完全由热成风影响所致。在边界层顶垂直速度的解中导出了三种由斜压效应引起的Ekmon抽吸新物理因子,即热成风形变、热成风涡度及热成风涡度交叉项等抽吸因子。分析表明,这些因子只在具有水平温度梯度不均匀的系统(譬如锋区)中方能出现。文中还对锋区内上述三种抽吸因子的动力特征作了具体的分析,指出在锋区这样的强斜压系统中,此三种抽吸因子的贡献是显著的。下一文中,我们将利用本文所得理论解对斜压效应进行具体的定量计算。 相似文献
3.
本文研究了斜压性对非线性Ekman层内的风场及顶部垂直速度的影响。结果表明,斜压性将改变其非线性Ekman层内的风场及顶部垂直速度,其影响随着系统特征与热成风特征的改变而改变。在本工作中,还用地转动量近似的方法作了相应的研究,并将其结果作了相应比较。 相似文献
4.
在大气边界层中,当温度分布在水平方向不均匀时,斜压性必须予以考虑。本文在地转动量近似条件下,采用Agee[1]公式来描述湍流粘性系数K,求得斜压边界层中风场分布的解析表达式。由求得的解析解和个例的图解均分析得出一些与经典Ekman理论很不相同的动力学特征。例如,在边界层上部,冷平流使气旋中的风速随高度增大而一直增大,且一直指向低压一方,不再呈Ekman螺线状。在边界层下部,例如20米处,引进热成风将使风向改变达25°左右。这对预报边界层风场是很重要的修正。 相似文献
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6.
边界层特征参数对边界层顶垂直速度的影响 总被引：1，自引：1，他引：1
本文从正斜压及有层结时的边界层相似理论及阻力定律出发，由边界层顶垂直速度与地面湍应力的关系求出了层结、粗糙度、它们的水平梯度及地转风的水平梯度、斜压性对w的影响的解析式，可用于模式计算。计算结果表明层结影响可使w差1-２个量级，不稳定时粗糙度影响也使w差几倍。除地转涡度决定w外，地转风、层结稳定度和粗糙度及其水平梯度也起了重要作用，还讨论了斜压性的影响。 相似文献
7.
本文分别用线性与半地转斜压Ekman层模式,解析地给出由宏观外参数来估计斜压Ekman层中动能耗散即变性能量的公式。结果表明,斜压性对变性能量有较大影响,其影响程度随系统特征与热成风特征的改变而改变,从而加深了对变性能量的认识。 相似文献
8.
在边界层动力学中，涡动粘性系数是影响边界层风场结构的一个重要参数。本文利用边界层动力学中的Ekman动量近似理论，给出了涡动粘性系数随高度缓变条件下的Ekman动量近似边界层模式解，着重讨论了边界层的风场结构、水平散度、垂直涡度以及边界层顶部的垂直速度。结果分析表明：与常值涡动粘性系数情况相比，在边界层低层随高度增加的涡动粘性系数可以导致低层边界层风速随高度迅速增加，即风速垂直切变增加，同时风速矢与地转风之间的夹角减小。惯性项作用可以导致上述作用在气旋性区域减小、而在反气旋性区域增大。随高度增加的涡动粘性系数导致水平散度绝对值、垂直涡度绝对值以及边界层顶部的垂直速度绝对值在气旋性区域减小，而在反气性旋区域增大。涡动粘性系数与惯性之间的非线性相互作用是边界层动力学中重要过程。 相似文献
9.
Ekman动量近似下中间边界层模式中的风场结构 总被引：2，自引：0，他引：2
发展了一个准三维的、中等复杂的边界层动力学模式，该模式包含了EKman动量近似下的惯性加速度和Blackadar的非线性湍流粘性系数，它进一步改进了Tan和Wu(1993）提出的边界层理论模型。该模型在数值计算复杂性上与经典Ekman模式相类似，但由于包含了Ekman动量近似下的惯性项，使得该模式比传统Ekman模式更近于实际过程。中详细地比较了该模式与其他简化边界层模式在动力学上的差异，结果表明：在经典的Ekman模式中，由于忽略了流动的惯性项作用，导致在气旋性切变气流（反气旋性切变气流）中风速和边界层顶部的垂直速度的高估（低估），而在半地转边界层模式中，由于高估了流动惯性项的作用，结果与经典Ekman模式相反。同样，该模式可以应用于斜压边界层，对于Ekman动量下的斜压边界层风场同时具有经典斜压边界层和Ekman动量近似边界层的特征。 相似文献
10.
利用斜压两层模式研究了赤道平面近似下的低纬热带大气适应过程。指出低纬斜压大气适应过程主要受重力惯性内波控制。通过重力惯性内波对初始非地转能量的频散，使纬向运动达到地转平衡，而经向维持非地转运动，正压模式下称为半地转平衡，斜压模式下称为半热成风平衡。通过对垂直运动方程的求解，可知，垂直运动只与重力惯性内波相联系，其产生与初始斜压位涡度无关，而只与初始时刻的垂直运动和垂直运动倾向有关，半地转适应使运动趋向水平运动。讨论了半热成风平衡的建立及其物理机制，指出由于重力惯性内波激发出垂直运动，与垂直运动相联系的水平辐合辐散调整流场和温度场之间的关系，使温压场最终达到半热成风平衡。通过对适应过程终态的分析，指出平均温度场和切变流场之间的适应方向决定于初始非半地转扰动的尺度与斜压Ｒｏｓｓｂｙ变形半径有关的特征尺度的比值，当比值大于１时，切变流场向平均温度场适应；当比值小于１时，平均温度场向切变流场适应 相似文献
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With the Ekman momentum approximation,the influence of atmospheric baroclinity on the dynamics of boundarylayer is studied.Some new results are obtained.These results show that the atmospheric baroclinity plays an importantrole in altering the horizontal velocity of Ekman boundary layer and its angle with the horizontal wind velocity compo-nent near the surface.There are three different physical factors affecting the nonlinear Ekman suction,the vertical mo-tion at the top of boundary layer:first,barotropic geostrophic relative vorticity at the ground;second,the thermal windvorticity induced by the baroclinity;and third,the nonlinear interaction between the barotropic geostrophic relativevorticity and the baroclinic thermal wind vorticity.These results may provide a better physical basis for theparameterization of boundary layer and the interpretation of the numerical modeling results. 相似文献
12.
A. Wiin-Nielsen 《Boundary-Layer Meteorology》1974,6(3-4):459-476
The Ekman-Taylor problem for the planetary boundary layer is solved in the case of a thermal wind which varies linearly with height. The upper boundary condition is a vanishing ageostrophic wind, while the lower boundary condition is continuity of the stress vector across the interface between the planetary boundary layer and the surface layer. The latter condition is used to determine the magnitude and the direction of the wind at the bottom of the Ekman layer.Theoretical hodographs are compared with observed hodographs based on five years of ohservations from Ship N in the Pacific, giving fair agreement.The divergence, the vorticity, and the vertical velocity are calculated through the Ekman layer with emphasis on differences between the classical barotropic and the baroclinic cases; these differences are significant, especially in the vertical velocities as compared to the standard approximation.An extension of the present study to include thermal stratification is desirable. 相似文献
13.
Richard A. Dobbins 《Boundary-Layer Meteorology》1977,11(1):39-54
Data from low-level soundings over Cambridge, U.S.A. were selected on the basis of an Ekman-like variation of the wind vector with altitude combined with evidence of a barotropic atmosphere. The method of geostrophic departure was used to determine the shear-stress distribution. The analysis yields the dimensionless properties of the barotropic Ekman layer under neutral and stable stratification. Some important results include: the geostrophic drag coefficient displays no dependence on the degree of static stability; the dimensionless height of the boundary layer decreases with increasing stability in agreement with the prediction of Zilitinkevich; the properties of the urban surface layer, where the roughness elements are multistory buildings, show no dependence on atmospheric stability under the moderate wind conditions which display the Ekman-like wind profile; and the directions of the horizontal shear stress and the vertical derivative of the velocity vector usually tend to be parallel only near the surface layer. Values of the two constants of the Rossby number similarity theory are found for the neutral barotropic Ekman layer at a surface Rossby number equal to 2 × 105. The implications of the work with respect to wind-tunnel simulation of the flow over models of urban areas are discussed. 相似文献
14.
William Blumen 《Boundary-Layer Meteorology》2001,99(3):509-519
The traditional Ekman boundary-layer parameterization is introduced into the quasigeostrophic Eady baroclinic instability model and into the deformation flow model, to couple the planetary boundary layer with the inviscid interior flow aloft. An explicit time-dependent version of this parameterization is then introduced into an unbalanced zero potential vorticity model to evaluate the initial transient response. It is noted that the adaptation of the geostrophic flow to the same parameterization is different in each of the balanced models. The characteristic flow response reflects thedifferent constraints imposed by each model. Further, the zero potential vorticity condition constrains the evolution of the baroclinic geostrophic part of the flow, which leads to an unphysical flow response when the Ekman boundary-layer parameterization is employed with this unbalanced model. The barotropic part of the flow does, however, evolve in a physically consistent manner spinning down to reflect the introduction of low momentum air pumped into the interior from the boundary layer. Moreover, the transient spin-up processis shown to have an insignificant effect on this spin-down process. 相似文献
15.
Dynamics of nonlinear baroclinic Ekman boundary layer 总被引：2，自引：0，他引：2
By the geostrophic momentum approximation, the wind structure and vertical motion within the non-linear baroclinic Ekman layer matching with the surface layer are determined. A comparison of the Ekman solution with the classical one is made. It is demonstrated that the contributions of baroclinity, stratification and nonlinear effects to the wind profile within the layer are all of definite importance. 相似文献
16.
边界层动力学中的Ekman动量近似 总被引：3，自引：3，他引：3
自由大气中,大气运动的基本状态是地转风,近年来发展的地转动量近似,是为了进一步研究非均匀地转流的动力学问题,然而,在边界层大气中,运动的基本状态是经典的Ekman流,所以对边界层运动来说,地转动量近似是不合适的,需作一推广。本文提出了一种所谓Ekman动量近似,它相似于自由大气中的地转动量近似,并讨论了Ekman动量近似的物理基础,对边界层的风场结构及边界屋顶部的垂直速度也作了详细分析。 相似文献
17.
In this paper, Wu and Blumen’s boundary layer geostrophic momentum approximation model (Wu and Blumen, 1982) is applied to baroclinic and non-neutral PBL, the motion equations for the PBL under the geostrophic momentum approximation are solved, in which the eddy transfer coefficient is a function of the distributions of the wind and temperature. The results are compared with those in barotropic and neutral conditions with the geostrophic momentum approximation. It is found that in the baroclinic condition, the wind distribution has both the characteristics of a steady, homogeneous and baroclinic PBL and those caused by the geostrophic momentum approximation. Those in non-neutral conditions show that they retain the intrinsic characteristics for the wind in non-neutral PBL, at the same time, the effects of the large-scale advection and local variation are also included. We can predict the wind in the non-neutral and baroclinic PBL by use of the geostrophic mo-mentum approximation when the temporal and spatial distributions of the geostrophic wind, as well as the po-tential temperatures and their variation rates at the upper and lower boundary of the PBL are given by large-scale model. Finally, the model is extended to the case over sea surface. 相似文献
18.
ZHAO Ming 《Acta Meteorologica Sinica》2002,16(2):215-225
The motion equation of atmospheric boundary layer with cold front surface under geostrophic momentum approximation is solved and some characteristics of the stream field for the cold front surface in the boundary layer are derived,for example,the slope of the cold front surface increases with the increases of geostrophic vorticity and the temporal tendency of geostrophic wind speed,and also increases with the decrease of the component of thermal wind speed along the motion direction of the front:the stream field above and below the cold front surface in the boundary layer depends on the slope of the front surface,geostrophic wind speed and its temporal and spatial distributions.A common characteristic is that there exist updraft motion above the cold front surface and downdraft motion below it. 相似文献