共查询到19条相似文献，搜索用时 140 毫秒
1.
金飞飞 《南京气象学院学报》1980,(2)
地转适应过程就是指地转平衡破坏以后的气压场和风场作迅速调整重新达到地转平衡的过程。对于这种过程,已经有了比较充分的研究,在这些研究中曾指出:地转适应过程依赖于扰动水平尺度L,在较大尺度下(L>L_0,L_0为临界尺度)适应过程是风场向气压场调整;在较小尺度下(L相似文献
2.
在自由大气中,风压场之间基本上是满足地转平衡的,但在某些局部地区,可以出现地转偏差,而这些偏差通过惯性重力外波的频散作用将最终消灭而建立起地转平衡。这种适应过程已有很多的研究。与自由大气中的准地转气流的特征相似,在边界层中,在三种力即折向力、气压梯度力和湍流粘性力的平衡下,风场呈现Ekman气流,即风速矢量湍迹呈现Ekman螺线。类似于地转适应问题的提法,在边界层中,也存有Ekman气流的适应问题。即当初始场在某种原因下,风场、压力场之间与Ekman气流 相似文献
3.
冬夏季海面风场和海洋表层流的数值计算 总被引：2，自引：0，他引：2
设计了一个海面风场的诊断模式和海洋表层流的数值计算模式。只要输入海面气压场并利用迭代方法，即可求得海洋表面的风场和海洋场。利用１月和７月多年平均的海平面气压场，对这两个模式的性能进行了检验。结果表明，无论冬夏，用海平面气压场诊断出的海面风场与观测到的海面风场很接近，而与地转风场有很明显的区别。用海面风场和海面气压场启动的海洋表面流，与实况也较一致。本文的试验结果还表明，计算海流时，不应忽略海平面气 相似文献
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分析任意气压场在中性、非线性正压边界层中风场的调整问题。结果表明：任意初始风场，将向给定的气压调整。具体调整过程是通过绝对涡度振荡及粘性系数的耗散，其调整的时间尺度为［Ｏ（ｔ＾－３／２）］，比自由大气地转适应时间尺度［Ｏ（ｔ＾－１）］快。 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
7.
南半球环状模事件的准地转调整过程分析 总被引：1，自引：0，他引：1
本文利用NCEP/NCAR逐日再分析资料,分析了南半球环状模（SAM）事件生命过程中的准地转调整过程.由于SAM沿纬圈的水平尺度远远大于临界尺度罗斯贝变形半径,因此要求纬向风场在地转调整过程向气压场适应以达到地转平衡.研究结果表明,在纬向平均环流中,异常Ferrel环流强度的变化超前于SAM强度变化约2/16位相,异常Ferrel环流能够通过超前的整层大气质量的经向输运,改变中高纬度的质量分布装状况,导致中、高纬度地区间的位势高度梯度异常变化,而中、高纬度地区间的位势高度梯度异常发生变化就意味着SAM强度和位相发生变化;而当SAM强度和位相发生改变后,即中、高纬度地区南北方向上的位势高度梯度发生变化后,可破坏中纬度地区纬向风场与位势高度场之间的地转平衡,产生地转偏差;地转偏差产生后,又可驱动经向散度风场,造成Ferrel环流异常的变化,由此形成一个自我内部循环调整过程. 相似文献
8.
本文首先利用变分方法,考察了边界层运动能量的变化,指出经典Ekman流是在不可压缩条件下,能量积分达最小值时的一种平衡运动。这对Ekman层运动的物理本质有了进一步的认识。其次,讨论了Ekman动量近似下的Ekman层的平衡风场特征,研究了该平衡风场附近扰动的稳定性问题,结果表明,在自由大气气压场不发生扰动条件下,Ekman层中存在一类新的与惯性不稳定相类似的动力不稳定,且其不稳定性可与Ekman抽吸相联系,还讨论了一般性条件下的扰动不稳定性问题。 相似文献
9.
本文利用二阶矩湍流模式着重讨论了有地形条件下Ekman螺旋的特征，结果表明，在北半球一定的环境地转风场结构下，斜坡Ekman螺旋可以变为反时针旋转。另外，还研究了地形对稳定边界层二阶矩湍流量的结构和垂直分布的影响。 相似文献
10.
大尺度大气运动的重要特点之一,是运动处于准地转平衡状态。因此大气中必定存在着一种物理过程,使得一旦偏离平衡状态时能迅速恢复,这就是“地转适应过程”,这是四十年代C.G.Rossby首先提出的。早期的研究都认为气压场主要向风场适应,通过重力波的频散来完成。重力波将有限空间内风、压场间的不平衡能量带到了整个空间,于是单位空间中的不平衡能量就接近于零了。 相似文献
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Summary On the basis of Wu and Blumen's work (1982) on the geostrophic momentum approximation (GMA) in the planetary boundary layer (PBL) and Tan and Wu (1992, 1994) on the Ekman momentum approximation (EMA) in the PBL, some improvements about the eddy exchange coefficientK, the advective inertial force and the lower boundary condition of the PBL are developed in this paper: (1) apply theK which is a gradually varying function of height instead of a constant value in the Ekamn layer, and introduce a surface layer; (2) take the effect of the vertical advective inertial force into account; (3) the solution technique is extended from level terrain to orographically formed terrain. Under the condition of the equilibrium among four forces (the pressure — gradient force, Coriolis force, eddy viscous force and inertial force including horizontal and vertical advective inertial forces), we have obtained the analytical solutions of the distributions of the wind and the vertical velocity. The computation of an individual example shows that: (1) both the wind velocity near surface and the angle between which and the non-viscous wind are more consistent with usual observations than that of Wu and Blumen (1982); (2) comparing with the horizontal advective inertial force, the vertical advective inertial force can not be neglected, when the orography is considered, the effect of the latter is even more important than the former.With 3 Figures 相似文献
12.
采用与实测较接近的二次函数来表达Ｅｋｍａｎ层中的湍流粘性系数Ｋ，在圆形气压场条件下，求得了山地上空边界层中的风速，进而求得散度、涡度和垂直速度等场变量随高度的分布。并作图分析了这些场变量的一些动力学特征。改进了以往在求解析解时，略去运动方程中湍流粘性力项中的关于高度的一阶导数项，以及取山坡面上风速为零作下边界条件等欠合理欠精确的做法。所求得的风速、散度、涡度和垂直速度均用简单的初等函数表示出来，有助于边界层参数化和深化对边界层动力学的认识。 相似文献
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本文提出一个在中性情况下边界层数值模式中考虑背景风压场影响的方法。背景风压场的水平非均匀影响了边界层运动方程中的惯性力项及边界层的上界风速。本文把三维问题用一种线性化方法简化为一维问题，只要知道背景气压场的空间分布，即可求出考虑了背景场影响的边界层风场。 相似文献
14.
By use of the small parameter expansion method, the nonlinear planetary boundary layer (PBL) is studied in this paper. The PBL is divided into the surface layer and the Ekman layer, which is divided into several sublayers. In the surface-layer, the eddy coefficient K is taken as a linear function of height; in the Ekman layer, different constant K values are taken within different sublayers: these values are determined from O'Brien's formula (O'Brien, 1970) approximately. Under the upper and lower boundary conditions and the continuity conditions of the wind velocities and turbulent stresses at each boundary between sublayers, analytical expressions for wind velocity in all sublayers and the vertical velocity at the top of the PBL are obtained. A specific example of steady axisymmetrical circular high and low pressure areas is analysed, and some new conclusions are obtained. The results are in better agreement with reality than previous results. This example also shows that the vertical velocity at the top of the PBL caused by friction approaches zero near the center of a high or low pressure system for this model, but attains its maximum absolute values near the center of the high or low pressure area for Wu's (1984) model. This is due to the fact that in our model, the geostrophic wind speed near the center of this specific vortex approaches zero, which causes the wind shear and the friction effect to be very weak. Therefore the wind distribution in the PBL is very sensitive to the type of eddy coefficient. 相似文献
15.
The analytical solutions of the PBL wind distribution under the equilibrium of four forces including both horizontal and vertical advections are obtained in this paper using small parameter method. Utilizing this simple PBL model, we also compute the wind spirals of a certain circular vortex over level ground and over a west-east ranged mountain, respectively. The results show that when there exsits large-scale orographic forcing, vertical advection may exert considerable influence on the wind distribution of PEL, the angle between geostrophic flow and surface wind, and the height of the top of PBL 相似文献
16.
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17.
A numerical model was developed to simulate neutrally stratified air flow over and through a forest edge. The spatially averaged equations for turbulent flow in vegetation canopies are derived as the governing equations. A first-order closure scheme with the capability of accounting for the bulk momentum transport process in vegetation canopies is employed. The averaged equations are solved numerically by a fractional time-step method and successive relaxation. The asymptotic solution in time is regarded as the steady-state solution. Comparisons of model output to the field measurements of Raynor (1971) indicate that the model provides a realistic mean flow.Momentum balance computations show that the pressure gradient induced by the wind blowing against the forest edge is significant and has the same order of magnitude as the drag force in the edge region. The edge effect involves the generation of drag forces, the appearance of a large pressure gradient, the upward deflection of mean flow and the transport of momentum into the edge of the canopy. 相似文献
18.
赵鸣 《热带气象学报(英文版)》1997,3(2):202-206
This paper suggests a method to eompute the verticaI velocity at the top of PBL Jn low latitude areas by use of the wind data on(sea)surfaca and some characteristics of the vcrtical velocity are shownThe results show the important rolcs played by the incrtial forces and β effect 相似文献
19.
雷达资料同化在局地强对流预报中的应用 总被引：4，自引：1，他引：3
采用ARPS模式的资料分析系统ADAS同化多普勒雷达径向速度和反射率因子资料,分析两者对初始场的改进作用,并应用于WRF中尺度模式中对2012年8月21日江西省一次局地强对流过程进行了模拟试验。分析结果表明:（1）ADAS同化系统能够利用雷达径向速度和反射率因子资料有效增加初始场中的中小尺度风场信息和云、水物质含量,并通过湿绝热或非绝热初始化对温度场、湿度场和风场进行调整,使初始场在动力和热力上达到平衡。（2）同化径向速度后对改善模式初始场的动力场有重要贡献,而对大气水凝物和降水的预报影响较小;同化反射率因子的主要作用是调整初始场中的水凝物场和热力场,有效缩短了模式的“ spin-up”时间,明显改进了定量降水预报;同时同化雷达径向速度和反射率因子后,初始场中快速调整出了中小尺度风场水平辐合、垂直运动以及合理的温、湿分布,对3小时内雨带形状、降水落区及定量降水的预报与实况更接近。（3）模拟试验表明,同时同化径向速度和反射率因子能成功模拟出本次对流单体风暴的中β尺度三维空间分布结构及其演变过程,中低层切变线的辐合抬升强迫作用是对流单体风暴组织、发展和维持的主要动力机制之一,对流凝结潜热加热在对流单体风暴的发生发展中发挥了重要作用。因此,雷达资料同化对提高临近数值天气预报的准确率以及对强对流天气系统的模拟能力具有重要意义。 相似文献