HEIFE戈壁地区近地层大气的湍流结构和输送特征

根据黑河地区地气相互作用实验研究(HEIFE)1988年POP和1990年PIOP实验的观测资料,分析了戈壁地区近地层大气的湍流结构,主要是风速分量和温度方差的相似关系,以及各有关量的功率谱和湍流通量的协谱。1988年POP期间发现的戈壁近地层大气中白天经常出现的水汽由上而下输送等特殊现象,在1990年PIOP中得到进一步的验证。文中分析了有关物理机制,认为这一现象和众所周知的“绿洲效应”是戈壁-绿洲这一地区性中尺度环流影响的两个侧面。     

ON SIMILARITY AND THE TURBULENT STRUCTURE IN THE STABLE BOUNDARY LAYER

In the stably stratified boundary layer,the vertical flux profiles for momentum and heat can be obtained froman atmospheric boundary layer model which includes parameterization of the long-wave radiation.In addi-tion,the Monin-Obukhov similarity theory can be extended to the whole boundary layer by using the local tur-bulent scales L(z),U.(z)and 0.(z)in place of surface layer scales.The similarity predictions are ingood agreement with observational data.     

局地环流与大气边界层湍流相互作用的数值研究

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。     

沂蒙南部山区冬季大气边界层风、温场结构特征研究

利用现场低空探测所获得的实测资料,分析了沂蒙南部山区冬季大气边界层内的风、温场垂直分布特征以及随时间的演变特征。     

山地露天矿自然通风风流与湍流结构的数值模拟

利用建立的三维非力能量闭合的大气边界层数值模式，研究了中性层结条件下某露天矿自然通风的风流和湍流结构特征及影响因子。研究表明：坑内水平风场在坑底或采壁处受地形的影响很大，在矿采深与开口宽度比较小或者来流风速随高度的切变不大时，坑内气流为平直型，有利于通风；反之坑内则形成环流，且在环流范围内较大的湍能，不利于通风，易产生高浓度的污染物。本模式模拟的结果还与风洞模拟和高阶闭合模式模拟的结果作了检验比较     

南海台风边界层湍流小波分析

利用小波变换（WT）对香港天文台飞机观测台风“妮妲”（1604）资料进行分析,研究在不稳定、不均匀的台风边界层中湍流涡旋的垂直传输作用。在0.1～5 Hz惯性子区内横风和顺风分量功率谱密度能较好符合-5/3幂律。小波分析显示：横风的小波功率谱峰值集中在1 km之下,顺风分量的小波功率谱峰值集中在1～6km之间;眼区动量通量的主要贡献尺度为2.3 km,眼区外主要贡献尺度在1～2 km,中低层为较小尺度（<1.0km）;湍流功能(TKE)的生成尺度主要集中在4 km之下。这项研究定量描述了南海北部台风边界层各个区域湍流结构的差异特征,讨论了对台风边界层通量参数化的可能影响。     

北京大气边界层中风和温度廓线的观测研究

为了研究冬季北京城区大气边界层结构的特征,分别在城区和郊区4个观测点利用系留气艇在2001年1月5～13日和2月21～28日进行了大气廓线探测,并分析了温度和风廓线垂直变化的基本特征.初步结果显示城市热岛效应十分明显,热岛强度随高度增加而递减,近地层热岛强度在晴天最大可达到4℃左右.除了近地层郊区的风速大于城区外,城区和郊区风速的垂直分布特征有较大差异.在100～200m高度以下,城区和郊区风速和风向随高度分布都出现了明显的拐点,300 m以上高度风向和风速基本趋于一致,表明城区和郊区的风廓线均受到城市覆盖层的影响.随着北京市区的规模不断扩大,在今后探测中应考虑郊区测点的代表性.     

HEIFE区边界层某些结构特征

我们于１９９１年８，１０月，在ＨＥＩＦＥ实验区的三种下垫面（农田绿洲、戈壁、沙漠）上进行了边界层探测，分析结果表明，被大片戈壁或沙漠包围的绿洲在整个时次上２００－３００ｍ以下边界层内温度低于周围环境，湿度大于周围环境，绿洲“冷岛效应”明显，其影响高度可达２００ｍ。实验区的风具有明显的日变化特征。     

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。     

边界层急流型重力波─-飞机颠簸的一种形成机制

采用线性化的Boussinesq流体边界层绝热流动方程,比较一维边界层急流型重力波的垂直运动量级,讨论边界层急流型重力波中的湍流发展,认为边界层急流型重力波是造成边界层飞机颠簸的一种机制。     

用变分法修正边界层资料的数值试验

文中用变分方法修正边界层资料及模误差 ,目标函数相对于控制变量的梯度用扰动法计算 ,对利用小扰动求取梯度的方法进行了理论推导和试验分析。利用模式资料所作的数值试验表明 ,该方法能有效地修正模式自身误差 ,使模式能精确描述边界层物理过程 ,从而使调整后的初始场最好地拟合“观测资料”     

小波分析在大气边界层结构研究中的应用实例

将小波分析的方法应用于大气边界层风、温场结构的研究,表明了这种方法应用于大气边界层研究的优越性。小波分析方法与谱分析方法,多尺度分析方法可以互补。当研究不同尺度湍流的串级过程和突变气象场的位置时,小波方法更为优越。     

Wind-Tunnel Study Of Atmospheric Stable Boundary Layers Over A Rough Surface

Wind-tunnel simulations of theatmospheric stable boundary layer (SBL) developedover a rough surface were conducted by using athermally stratified wind tunnel at the Research Institutefor Applied Mechanics (RIAM), Kyushu University. Thepresent experiment is a continuation of the workcarried out in a wind tunnel at Colorado StateUniversity (CSU), where the SBL flows were developed over asmooth surface. Stably stratified flows were createdby heating the wind-tunnel airflow to a temperature ofabout 40–50°and by cooling the test-section floor toa temperature of about 10°. To simulate therough surface, a chain roughness was placed over thetest-section floor. We have investigated the buoyancyeffect on the turbulent boundary layer developed overthis rough surface for a wide range of stability,particularly focusing on the turbulence structure andtransport process in the very stable boundary layer.The present experimental results broadly confirm theresults obtained in the CSU experiment with the smoothsurface, and emphasizes the following features: thevertical profiles of turbulence statistics exhibitdifferent behaviour in two distinct stability regimes with weak and strong stability,corresponding to the difference in the verticalprofiles of the local Richardson number. The tworegimes are separated by the critical Richardsonnumber. The magnitudes in turbulence intensities andturbulent fluxes for the weak stability regime aremuch greater than those of the CSU experiments becauseof the greater surface roughness. For the very stableboundary layer, the turbulent fluxes of momentum andheat tend to vanish and wave-like motions due to theKelvin–Helmholtz instability and the rolling up andbreaking of those waves can be observed. Furthermore,the appearance of internal gravity waves is suggestedfrom cross-spectrum analyses.     

对流边界层中粒子随机扩散模式和高斯模式的比较

用粒子随机扩散模式和高斯模式模拟的对应３种源高的横风向各分浓度的结果与水槽试验的结果进行比较，发现粒子随机扩散模式能较好地模拟出水槽试验结果，说明该模式能用来模拟对流边界层的扩散，而高斯模式不能完全反映对流边界层的扩散。比较两种模式的模拟结果，发现粒子随机扩散模式由于考虑了对流边界中由卷流和热泡引起的垂直方向上湍流的非均一性，比高斯模式能较好的模拟出污染物在垂直方向上充分混合较快、水平方向上扩散范     

TURBULENCE STRUCTURE AND TRANSFER CHARACTERISTICS IN THE SURFACE LAYER OF HEIFE GOBI AREA

Based on the HEIFE 1988 and 1990 pilot observations,an analysis on the turbulence structure of Gobi surfacelayer,mainly on the similarity formulations of wind and temperature variances,the spectra and cospectracharacteristics,is presented.The phenomenon of downward water vapor flux over Gobi desert in daytime is confirmedin both observations,this and the well-known‘oasis effect’are two sides of a local mesoscale circulation.     

延安市冬季边界层风、温场特征分布

本文利用1985年12月25日—1986年1月9日的实测资料,分析了延安市冬季边界层风、温场特征。结果表明:延安市冬季低层逆温持续时间长、强度大,逆温持续期近地面几十米表现为混合层结构。边界层风场十分复杂,时空变化大,地面常为小风状态,风向、风速沿垂直方向有明显切变,低层流场有显著渠道效应,山谷风明显。     

BOUNDARY LAYER STRUCTURE IN TYPHOON SAOMAI (2006): UNDERSTANDING THE EFFECTS OF EXCHANGE COEFFICIENT

Recent studies have shown that surface fluxes and exchange coefficients are particularly important to models attempting to simulate the evolution and maintenance of hurricanes or typhoons.By using an advanced research version of the Weather Research and Forecasting(ARW)modeling system,this work aims to study the impact of modified exchange coefficient on the intensity and structures of typhoon Saomai(2006)over the western North Pacific.Numerical experiments with the modified and unmodified exchange coefficients are used to investigate the intensity and structure of the storm,especially the structures of the boundary layer within the storm.Results show that,compared to the unmodified experiment,the simulated typhoon in the modified experiment has a bigger deepening rate after 30-h and is the same as the observation in the last 12-h.The roughness is leveled off when wind speed is greater than 30 m/s.The momentum exchange coefficient(CD)and enthalpy exchange coefficient(CK)are leveled off too,and CD is decreased more than CK when wind speed is greater than 30 m/s.More sensible heat flux and less latent heat flux are produced.In the lower level,the modified experiment has slightly stronger outflow,stronger vertical gradient of equivalent potential temperature and substantially higher maximum tangential winds than the unmodified experiment has.The modified experiment generates larger wind speed and water vapor tendencies and transports more air of high equivalent potential temperature to the eyewall in the boundary layer.It induces more and strong convection in the eyewall,thereby leading to a stronger storm.     

边界层气溶胶气候效应的研究

用三维气候模式模拟了边界层气溶胶的气候效应。结果表明，边界层气溶胶可使大气和地表的气候状态发生明显的变化。３００ｈＰ以下气柱中气温升高，地表和土壤温度降低。在气溶胶光学厚度较大的沙漠区上空，水平风场出现气旋性差值环流，垂直上升运动也发生较多变化。降水变化与３００ｈＰａ上垂直运动的变化有很好的正相关。同时讨论了气溶胶气候效应的物理机制。     

TURBULENCE STRUCTURE AND TRANSFER CHARACTERISTICS IN THE SURFACE LAYER OF HEIFE GOBI AREA*

Based on the HEIFE 1988 and 1990 pilot observations,an analysis on the turbulence structure of Gobi surface layer,mainly on the similarity formulations of wind and temperature variances,the spectra and cospectra characteristics,is presented.The phenomenon of downward water vapor flux over Gobi desert in daytime is confirmed in both observations,this and the well-known‘oasis effect’are two sides of a local mesoscale circulation.     

A comparison of wind-tunnel experiments and numerical simulations of neutral and stratified flow over a hill

A comparison is made of numerical and experimental results for flow over two-dimensional hills in both neutral and stably stratified flow. The numerical simulations are carried out using a range of one-and-a-half order and second-order closure schemes. The performance of the various turbulence schemes in predicting both the mean and turbulent quantities over the hill is assessed by comparing the results with new wind-tunnel measurements. The wind-tunnel experiments include both neutral and stably stratified flow over two different hills with different slopes, one of which is steep enough to induce flow separation. The dataset includes measurements of the mean and turbulent parts of the flow using laser Doppler anemometry. Pressure measurements are also made across the surface of the hill. These features make the dataset an excellent test of the model performance. In general second-order turbulence schemes provide the best agreement with the experimental data, however, they can be numerically unstable for steep hills. Some modifications can be made to the standard one-and-a-half order closure scheme, which results in improved performance at a fraction of the computation cost of the second-order schemes.