An Actively Controlled Wind Tunnel And Its Application To The Reproduction Of The Atmospheric Boundary Layer     

Cao Shuyang  Akira Nishi  Kimitaka Hirano  Shigehira Ozono  Hiromori Miyagi  Hiromori Kikugawa  Yuji Matsuda  Yasuo Wakasugi 《Boundary-Layer Meteorology》2001,101(1):61-76

An actively controlled wind tunnel equipped with multiple fansand airfoils has been developed, mainly for the purpose of reproducing the atmospheric boundary layer (ABL) for wind engineering applications. Various fluctuating flows can be achieved in this wind tunnel by altering the input data of the fans and airfoils through computer control. In this study, the ABL is physically simulated in this wind tunnel, and particular attention ispaid to the simulation of the profile of Reynolds stress. The method of generating the fluctuating flow and the experimental results of reproducing the ABL are presented. As the results show, the spatial distribution of Reynolds stress is satisfactorily simulated, and the profiles of other statisticalturbulent parameters, such as mean velocity, turbulent intensity, integral scale and power spectrum are successfully reproduced simultaneously.  相似文献   

An Approximate Analytical Solution For The Baroclinic And Variable Eddy Diffusivity Semi-Geostrophic Ekman Boundary Layer     

Zhe-Min Tan 《Boundary-Layer Meteorology》2001,98(3):361-385

The WKB method has been used to develop an approximate solutionof the semi-geostrophic Ekman boundary layer with height-dependenteddy viscosity and a baroclinic pressure field. The approximate solutionretains the same simple form as the classical Ekman solution. Behavioursof the approximate solution are discussed for different eddy viscosityand the pressure systems. These features show that wind structure inthe semi-geostrophic Ekman boundary layer depends on the interactionbetween the inertial acceleration, variable eddy viscosity and baroclinicpressure gradient. Anticyclonic shear has an acceleration effect on theair motion in the boundary layer, while cyclonic shear has a decelerationeffect. Decreasing pressure gradient with height results in a super-geostrophicpeak in the wind speed profile, however the increasing pressure gradient withheight may remove the peak. Anticyclonic shear and decreasing the variableeddy viscosity with height has an enhanced effect on the peak.Variable eddy viscosity and inertial acceleration has an important role in thedivergence and vorticity in the boundary layer and the vertical motion at the top of the boundary layer that is called Ekman pumping. Compared to the constanteddy viscosity case, the variable eddy diffusivity reduces the absolute value ofEkman pumping, especially in the case of eddy viscosity initially increasing with height. The difference in the Ekman pumping produced by different eddy diffusivity assumptions is intensified in anticyclonic flow and reduced in cyclonic flow.  相似文献   

Why Is the Climate Forcing of Sulfate Aerosols So Uncertain?   总被引：2，自引：0，他引：2  

Hu Rongming  Serge Planton  Michel Déque  Pascal Marquet  Alain Braun 《大气科学进展》2001,18(6):1103-1120

l. IntroductionAlthough the aerosol has been recognized as an important factor which has innuence onthe past, present and future climate for a long time, it still has much uncertainty in assessingits climate forcing. The direct radiative forcing of sulfate aerosols has been estimated rangingfrom --0.3 W/ m2 to --0.9 W/ m2 in recent publications (Charlson et al., l992, Kiehl andBriegleb l993; Taylor and Penner 1994, Boucher and Anderson l995, Kieh1 and Rodhe l995;Chuang et al., l997, Penne…  相似文献   

地磁场对1999年9月空间天气大事件的响应   总被引：1，自引：0，他引：1  

王文 《地震地磁观测与研究》2001,22(6):13-17

1999年9月22－25日发生一个大磁暴（Dst=-164nT).磁暴主相开始的头1小时伴随有丰富的Pc型地磁脉动，包括Pc2,Pc3,Pc4等。在行星际磁场Bz由北向转向南向后，磁暴主相开始，南向分量达到最大值后大约2小时，地磁H分量达到最小值，恢复相开始，并且，这次磁暴与太阳风各参数以及星际电场也存在一定的对应关系。  相似文献   

毛乌素沙地植被覆盖率与风蚀输沙率定量关系   总被引：54，自引：2，他引：54  

黄富祥  牛海山  王明星  王跃思  丁国栋 《地理学报》2001,56(6):700-710

基于毛乌素沙地不同植被覆盖条件下的风蚀输沙率实地观测数据，借鉴国外最新的建模思想，采用Matlab5.3软件对数据进行非线性回归，建立毛乌素沙地植被覆盖率与风蚀输沙率之间的定量关系模型，比较系统地考察了植被覆盖对沙粒起动风速和风蚀输沙率的影响，确定了不同风速下的有效植被覆盖率。结果表明，在毛乌素沙地要有效减少和防治风蚀，植被覆盖率必须达到40－50％的水平，而要保证在最高风速下风蚀输沙得到有效控制，植被覆盖率必须达到60－70％的水平。  相似文献   

Younger Dryas Glaciation in Söderåsen, South Sweden: An Analysis of Meteorologic and Topographic Controls     

Ole Humlum 《Geografiska Annaler: Series A, Physical Geography》1997,79(1-2):1-15

In Söderåsen, South Sweden, various geomorphological investigations indicate that small, local glaciers were initiated at very low altitudes within the Skäralid rock canyon during the Younger Dryas period. Wind polish on boulders indicates that this period was characterised by easterly winds and drifting snow. Some new field observations are presented and the Söderåsen Younger Dryas reglaciation hypothesis is tested by means of empirical knowledge on glacier equilibrium line climate and an analytic geographical information system (GIS) experiment. The GIS analysis demonstrates that the deeply incised rock canyon represents a pronounced radiation shelter, while the empirical analysis emphasises the importance of strong snow drift from the east during the winter. Together, the two analyses indicate that the inferred Söderåsen Younger Dryas reglaciation is possible from a palaeoclimatic point of view, although conditions for glaciation may have been marginal to those of rock glacier initiation.  相似文献   

FURTHER STUDY ON THE PROPERTIES OF OPERATORS OF ATMOSPHERIC EQUATIONS AND THE EXISTENCE OF ATTRACTOR_*     

Li Jianping  Chou Jifan 《Acta Meteorologica Sinica》1997,11(2):216-223

The equivalent operator equation is derived from the full primitive nonlinear equations of the atmospheric motion and the properties and physical senses of the operators are studied.In the infinite dimensional Hilbert space,the global asymptotic behavior of the atmosphere system with the non-stationary external forcing is studied under the assumption of the bounded external forcing.The existence theorems of the global absorbing set and the global attractor are obtained.Thus,the conclusions deduced from the large-scale atmosphere(Li and Chou 1996a;1996b) are extended to the general atmosphere.  相似文献   

NUMERICAL STUDY ON THE LOCAL WIND STRUCTURES FORCED BY THE COMPLEX TERRAIN OF QINGDAO AREA   总被引：1，自引：0，他引：1       下载免费PDF全文

Wu Zengmao  K. Heinke Schlunzen 《Acta Meteorologica Sinica》1992,6(3):355-366

In this paper, some 2-D features of the down- and up-slope winds and sea-land-breeze generated over the com-plex terrain of the Qingdao area and the interaction between them are numerically analysed by use of a 2-Dnon-hydrostatic mesoscale model. The simulated results in the west-east vertical cross-section show that (1) when thelarge-scale wind is a southerly gentle one, the generated easterly down-slope wind is much stronger than with an oppo-site background wind, and the down-slope wind can trigger and intensify the land breeze corresponding to the easterncoast of Jiaozhou Bay; (2) a gentle westerly background wind will reduce the eastward sea breeze and up-slope windduring the daytime due to a cold advection, but shows a little effect on the mesoscale circulation formed in the nighttime.  相似文献   

FIELD STUDY ON WIND EROSION IN THE NORTHWESTSHANXI PROVINCE     

LI Jianhua 《国际泥沙研究》1992,(1)

Field study on wind erosion in the hilly regions with gentle slope in the Northwest Shanxi Province has been carried out from 1983 through 1988. Based on the data observed in the field, quantitative analyses of the wind erosion and the effects of the wind-break forest are presented in this paper in detail. Most of the strong windy days occur in the period of March to May. The coincidence of drought and strong wind in the Spring days with no vegetative cover at all on the loose top soil lead to severe wind erosion in this region. The rate of soil erosion is as high as 12800 t / km2. Major characteristics of wind and other meteorological factors are given in graphs and tables. Wind-break forest reduces the wind velocity by 51. 1 %. Consequently, the amount of wind erosion is reduced by 90% and the dust content in the atmosphere is reduced by 97. 1 % in comparison with those measured in the farmland. This paper provides a preliminary summary on the result of data analyses of wind erosion on the Loess Plateau. It can serve as scientific basis for control of the wind erosion in regions of similar conditions.  相似文献   

坡风热力不稳定条件的讨论     

段德寅  潘良宝 《地理研究》1992,11(3):12-15

本文在文献^[1,2]的基础上,说明坡风是一种耗散结构,并对形成坡风的热力不稳定条件进行了初步讨论,给出了临界瑞利数Rc作为坡风热力不稳定的判据。  相似文献