自由大气的扰动对边界层结构影响的二维数值研究

在中性正压的行星边界层中,考虑边界层顶的负随时空变化的一般情况,在的假定下,用数值方法解边界层运动方程得到风及边界层某些参数的分布。还计算了边界层顶垂直速度,发现和Charney等人的结果不同。     

非定常,水平非均匀的正压EKman边界层的动力特征

除了动量的局地变化和水平平流之外,本文讨论了动量垂直输送和β-效应在均质正压的Ekman边界层中的作用。利用奇异摄动方法,得到了精确到O(R_0~2)的Ekman边界层中水平风场的垂直结构和边界层顶垂直速度的解析表达式,对解的非定常和水平非均匀特征作了定性讨论。用一迭加在均匀西风气流上的园形、定常涡旋场的定量计算表明,动量垂直输送和β-效应对Ekman边界层中水平风速分布、边界层厚度及边界层顶垂直速度均有明显的影响。     

变化涡动沾性系数的Ekman动量近似模式风场结构

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。     

地形与斜压边界层的动力分析

利用摄动方法,解析求解了含有地形的非线性斜压行星边界层的风场及其顶部的垂直速度。将所得结果与其它工作比较,说明了斜压性、地形和非线性平流对边界层中风场分布和顶部垂直速度的影响。     

正压边界层中的风压场相互调整

本文考虑正压边界层顶的垂直质量输送,将边界层与自由大气联系起来,研究这两层之间的风压场的相互作用所得到定常状态下的风压场,并算得了边界层顶的垂直速度。这些结果与经典Ekman边界层是有明显区别的。     

边界层抽吸引起的旋转减弱

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。     

基于风廓线仪的华南地区夏季边界层湍流统计特征研究

采用双权重算法,使用2015年6—8月我国东南部业务风廓线雷达资料,通过湍流脉动垂直速度方差和偏度的计算和分析,对晴空和低云主导情况下的边界层湍流特征以及中小尺度局地环流对于边界层湍流的影响进行研究。主要结论如下:(1)晴天情况下垂直速度标准差和垂直速度偏度都具有明显的日变化特征,湍流主要由下垫面加热驱动发展;(2)在低云主导情况下,湍流明显弱于晴天对流边界层的湍流强度,边界层内湍流的发展不仅受地面加热的影响,而且在边界层上部存在明显的自上而下发展的湍流,这主要是由于边界层顶云辐射冷却造成的;(3)除了上述两种情况,边界层湍流发展同时受到局地中小尺度环流或者天气系统的影响,因而呈现出更多的复杂性。      

大气对流边界层中热力湍流过程的研究

本文利用实测资料讨论了对流边界层内的湍流结构,重点分析复盖递温层附近风速和温度的方差以及垂直速度三阶矩的垂直分布。此外,还讨论了对流边界层顶部附近温度的垂直分布,得出温度梯度随高度分布呈—2次幂关系。     

不等距垂直分层的垂直速度订正

本文讨论了不等距气压垂直分层情况下的垂直速度的修正公式,计算并比较了它与沿用等距订正公式的结果的差异。结果表明: 1.不论哪一种积分方法,其两种订正结果高原和平原地区是有差别的,高原地区的偏差值相对地比平原大。 2.除P_T=0hPa时从下往上积分外,其它积分法都是垂直气压厚度△P值越大,两种订正结果的偏差值|△ω′|越大。 3.从下往上积分法不等距订正公式比等距订正公式求得的垂直速度在低层显著增大,而在高层则显著减小。 4.从上往下积分法两订正结果在某些层次某些网格点上出现符号相反的情况。 5.两种订正结果的差异在从上往下积分法中明显比从下往上积分法中的大。偏差值|△ω|最大者约在21.0×10~(-4)hPa·s~(-1)以上。 因此,本文对目前气象台站广泛采用的O′Brienc订正法在不等距分层情况下的使用,有重要参考价值。     

风廓线雷达垂直径向速度应用初探

利用北京风廓线雷达五波束探测中的垂直波束资料,进行了垂直速度在预报中的应用研究。通过对垂直速度的分级显示,配合地面气象记录,对不同的天气个例进行分析,结果表明:平稳晴空的天气风廓线雷达所测量的垂直速度很小,基本上在±1m·s~(-1)范围内;而有降水时,风廓线雷达所测得边界层的垂直速度基本上都是朝向地面的,不同相态降水粒子的垂直下落速度有明显的差别。分析表明风廓线雷达垂直速度的探测对研究晴空大气的垂直运动、判断降水粒子相态和降水预报有应用价值。     

WIND DISTRIBUTION IN THE NONLINEAR PLANETARY BOUNDARY LAYER OF A CIRCULAR VORTEX

In the PBL of a circular vortex in which the gradient wind is a function of radius,the equations ofmotion are solved under the assumption of K=l~2|(?)V/(?)_z|.The distribution of the wind and someboundary layer parameters are obtained.The vertical velocity at the top of PBL is also computed andcompared with other studies.     

瞬时经圈环流与西风带环流变化的关系

用一九七六年冬半年八个个例,对纬圈平均非热成风,瞬时经圈环流和西风带环流变化的关系进行了个例分析和统计分析。指出。当纬圈平均非热成风产生率为较大的负值时,出现逆瞬时经圈环流,并有利于长波的阻尼和纬向环流的维持或加强;反之,当为正值时,出现正瞬时经圈环流,并有利于长波的发展和纬向环流的减弱或崩溃。对于上述关系,本文还从物理上进行了初步的讨论。     

The diurnal wind variation in a variable eddy viscosity semi-geostrophic Ekman boundary-layer model: Analytical study

Summary ?A time-dependent semi-geostrophic Ekman boundary-layer model (SG), including slowly varying eddy diffusivity with height and inertial term effects, is developed to investigate the diurnal wind variation in the planetary boundary layer (PBL). An approximate analytical solution of this model is derived by using the WKB method, which extends the Tan and Farahani (1998)’s solution by including the vertical variable eddy viscosity. The features of the diurnal wind variation in the PBL mainly depend on three factors: the latitude, horizontal momentum advection and eddy viscosity. The vertical variable eddy viscosity has little influence on diurnal wind variation in the PBL at the low latitude, however its effect may be exacerbated in the mid- and high latitudes. In comparing with the constant eddy viscosity case, the decreasing (increasing) with height eddy viscosity produces a large (small) maximum wind speed (MWS) in the PBL, however, the eddy viscosity that has a mid-layer peak in the vertical gives rise to a higher height of occurrence of MWS. For the boundary-layer wind structure, there is a singular point when the modified SG inertial oscillation frequency η equals the forcing frequency ω. The isotachs of boundary-layer wind speed have almost no tilt to left or right relative to time evolution and the occurrence time of the MWS is the earliest at the singular point. The feature will be enhanced in the decreasing with height eddy viscosity case and weakened in the eddy viscosity initially increasing with height case. Received April 6, 2001; accepted December 27, 2001     

平流层垂直运动的计算方法与1958年1月平流层热源热汇的分布

本文利用平流层平均温压场的资料,用定常情况下的热力方程计算了1958年1月份北半球平流层各层(10—200毫巴)的冷热源分布。发现平流层中层的冷热源分布和流场一样,是以波数为1,2的超长波系统占优势的。文中还讨论了这些大尺度冷热源的地理分布以及它们和气压系统相互配置的关系。 为了计算平流层中与垂直运动相平衡的加热分量,本文提出了一个把涡度方程自大气顶向下逐层积分的计算垂直运动的新方法。结果证明,这种计算方法对于计算平流层的垂直运动是比较适宜的。     

Analysis of wind vertical component characteristics in the stratosphere

Height, time, and latitude dependences are analyzed of zonal mean vertical component of wind velocity for the period of 1992–2006 from the UKMO atmospheric general circulation model. It is shown that the ascending wind speed can provide vertical transport, against gravity, of rather large (up to 3–5μm) aerosol particles with density to 1.0–1.5 g/cm³ in the stratosphere and mesosphere. The wind velocity vertical component is supposedly a significant factor of particle motion up to 30–40–km levels and can affect sedimentation rate and residence time of the aerosol particles in the stratosphere. Structure of the mean vertical component of wind velocity allows occurrence of dynamically stable aerosol layers in the middle stratosphere.     

一次暴雨过程大气边界层结构的数值分析

1979年7月28日河北唐山地区的强暴雨,10小时总降水量达430mm,降水强度大,从时间和空间上都非常集中。这次太平洋副热带高压北侧暖区发生的强暴雨引起国内气象界的普遍重视。游景炎,陆一强等对这次暴雨过程的大尺度环境、中尺度结构进行了详细分析并分别讨论了边界层急流、强对流性云团以及地形等的作用。游景炎根据地面天气图的分析,发现明显的雷暴高压和中尺度低压。这种中尺度系统在大气边界层内如何表现呢?这次暴雨系统延伸多高呢?各种物理量输送和分布的特性     

The wind field in the nonlinear multilayer planetary boundary layer

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.     

Classification of the stratified atmospheric boundary layers at Molve (Croatia) based on the similarity theory

Summary The stability parameter μ is suggested as the one which is determinable with satisfying accuracy for routine application by means of commonly accessible meteorological data at the Molve location (Croatia). The similarity functions applied for vertical wind speed simulation in the planetary boundary layer (PBL) at Molve were useful for the determination of local stability classes. Universal similarity functions were applied for unstable and neutral stability, whereas local similarity functions were established for stable stratification. Wind speed simulations were performed using two types of wind models. The Monin-Obukhov similarity theory was included in both types. However, it turned out that for the operative determination of the stability of the 35 m deep lowest layer, the stability parameter μ was locally a better stability parameter than the Monin-Obukhov parameter z/L. That was possibly because 35 m deep lowest layer sometimes (depending upon stability) includes a large proportion of the Ekman layer and parameter μ is originally designed for the deeper part of PBL than z/L that is originally designed for the surface layer. At Molve, the input data for local wind models as well as for the stability parameter μ were wind speed at 35 m and temperature at 2 and 35 m above the ground.