Performance of various similarity functions for nondimensional wind and temperature profiles in the surface layer in stable conditions   总被引：3，自引：0，他引：3  

Maithili Sharan  Aditi 《Atmospheric Research》2009,94(2):246-253

The linear functions for non-dimensional wind and temperature profiles are commonly used to describe the surface layer fluxes in atmospheric models. However, their applicability is limited to smaller values of the stability parameter z/L (where z is the height above ground and L is the Obukhov length) i.e. z/L < 1.0. These linear functions have been modified (Webb 1970, Quart. J. Roy. Meteor. Soc. 96, 67–90; Clarke 1970, Quart. J. Roy. Meteor. Soc. 96, 91–114; Hicks 1976, Quart. J. Roy. Meteor. Soc. 102, 535–551; Beljaars and Holtslag 1991, J. Appl. Meteorol. 30, 327–341; Cheng and Brutsaert 2005, Boundary-Layer Meteorol. 114, 519–538) over the years for calculating fluxes when z/L > 1.0 under strongly stable conditions. In view of this, the objective of the present study is to analyze the performance of these similarity functions to compute surface fluxes in stable conditions.The meteorological observations from the Cooperative Atmosphere-Surface Exchange Study (CASES-99) experiment are utilized for computing the surface fluxes in stable conditions. The computed fluxes are found to be reasonably close to those observed. The ratio of observed to computed fluxes reveals that the computed fluxes are close to the observations for all the similarity functions for z/L < 1.0 whereas the computed values show relatively a large scatter from observations for z/L > 1.0. The computed values of u and heat flux do not show significant differences from those observed at 99% confidence limit. The performance of all the similarity functions considered here is found to be comparable to each other in strongly stable conditions.  相似文献   

老风口风资源分析及风资料应用评价     

马玲霞  王秀琴  陈建新 《沙漠与绿洲气象(新疆气象)》2009,3(3):44-48

通过对老风口风区2001--2005年风观测数据的统计整理,建立各类风要素值的数据库,分析和探讨老风口风能资源的分布特征、可利用的理论指标及评价,结果表明：老风口作为风能较丰富的地区之一,风能季节性变化明显,风向变化相对稳定,平均风能密度和有效风能密度分别达到了150W／m^2和200W／m^2以上,是风能资源开发利用较有价值的地区。随着环境保护和生态治理的不断深入,老风口无污染的风能资源,在生态治理、风力发电等多方面,有着很大的可持续利用的潜力。  相似文献   

风廓线雷达估算大气返回信号功率方法研究   总被引：3，自引：1，他引：2  

马建立  阮征  葛润生  何建新 《气象科技》2009,37(1):89-92

基于风廓线雷达大气返回信号功率谱中噪声电平的估算方法,统计分析了北京延庆对流层风廓线雷达（CFL-08）2006年10～12月的探测数据。对该频段风廓线雷达环境噪声的空间和时间变化进行了分析,观测期间环境噪声在5km以下随高度递减,10月的平均环境噪声大于11月、12月的平均分布。给出目前风廓线雷达用信噪比估算大气返回信号功率的两种方法,并对两种方法进行了环境噪声的剔除,经过修正后的大气返回信号功率输出结果趋于一致。  相似文献   

基于风廓线雷达资料的暴雨天气过程分析   总被引：4，自引：1，他引：3  

董保举  刘劲松  高月忠 《气象科技》2009,37(4):411-414

2008年6月1～2日大理市暴雨过程的风廓线雷达资料和每小时的雨量资料分析发现：暴雨过程具有明显的中小尺度系统影响特征,雷达水平风廓线资料可以很直观地显示随时间变化风场的垂直结构;高空气流的向下脉动与降水强度的增强有着紧密的联系;风廓线雷达产品（垂直速度、折射率结构常数和信号噪声比）清楚地反映降水的开始、结束以及降水的强度。  相似文献   

Long term variations in the mesospheric mean flow observed at Grahamstown (South Africa) and Adelaide (Australia)     

S.B. Malinga  L.M.G. Poole  R.A. Vincent 《Journal of Atmospheric and Solar》2004,66(18):1745

The seasonal and interannual behaviour of monthly mean winds at a height of 90 km recorded at Grahamstown (33.3°S, 26.5°E) and Adelaide (34.5°S, 138.5°E) between 1987 and 1994 are compared. The zonal wind is found to be consistently stronger at Grahamstown and is always eastward, whereas at Adelaide it sometimes reverses. Maxima tend to occur near the solstices, the primary maximum during summer at Grahamstown, in agreement with satellite results, and during winter at Adelaide. The meridional wind also tends to be stronger at Grahamstown, but at both stations is predominantly northward with a maximum in summer and generally not as strong as the zonal component. This seasonal behaviour is reasonably well understood in terms of the interaction of the mean flow with gravity waves propagating up from below, with coriolis forces also playing an important role in the case of the meridional wind. Satellite observations do not generally support the idea that longitudinal differences between the stations could be attributed to the presence of a tropospheric/stratospheric stationary wave. It is suggested that these differences are more probably associated with local effects. Interannual zonal wind patterns at the two sites are similar over the summer months but are less well correlated during the rest of the year. The underlying causes of this variability are not well understood but are most probably global in nature, at least during the summer.  相似文献   

Observational and Numerical Study on the Influence of Large-Scale Flow Direction and Coastline Shape on Sea-Breeze Evolution     

Robert C. Gilliam  Sethu Raman  Dev Dutta S. Niyogi 《Boundary-Layer Meteorology》2004,111(2):275-300

In this study radar, surface observations and numericalsimulations are used to examine the inland penetrationand intensity of the sea breeze during various large-scaleflow regimes along the curved coastline of the Carolinas,U.S.A. The results clearly indicate that the flow directionrelative to the curved coastline has a significant effecton the sea-breeze evolution.Overall, during northerly flow regimes alongthe curved North Carolina coast, observationsand numerical simulations show that the sea-breezefront has a tendency to remain close to the south-facingcoast. During these same flow regimes the frontmoves further inland relative to the east-facingcoast. The sea-breeze front during westerly flowcases progressed further inland relative to the southcoast and less so from the east-facing coastline.South-westerly flow allows the sea breeze to moveinland from both coastlines but the coastal shapeinfluence makes the inland penetration less fromthe easterly facing beaches. During periods of lightonshore flow (south-east), the sea breeze movesconsiderable distances inland but is not discernableuntil later in the afternoon. The simulations indicatedthat the sea-breeze intensity is greatest (least) when thelarge-scale flow direction has an offshore (onshore)component. Model results indicate the existence of astrong front well inland in the late afternoon duringlight onshore flow. Also noted was that the simulatedsea-breeze front develops earlier in the afternoon duringoffshore regimes and later in the day as the large-scaleflow becomes more onshore. It is concluded that thecoastline shape and coast-relative flow direction areimportant factors in determining how the sea-breezecirculation evolves spatially.  相似文献   

一次强暴雨形成的动力机制   总被引：6，自引：0，他引：6  

官元红  周伟灿  张兴强 《南京气象学院学报》2004,27(6):728-734

分析了1998年7月武汉强暴雨的天气演变特征，并从理论上探讨了强暴雨形成的动力机制。结果表明：低空急流先于暴雨生成，暴雨最强时低空急流也最强；高空急流入口区右侧及低空急流左侧非热成风梯度的存在，使得中尺度不稳定波的波振幅出现空间不稳定现象，高空急流右侧不稳定波的波振幅和低空急流左侧不稳定波的波振幅向暴雨区增加，暴雨区恰为这两支波叠加后振幅最大的区域，高低空急流耦合下的非热成风、中尺度对流-对称不稳定可能是这类强暴雨产生的动力原因之一。  相似文献   

Estimation of Site Effects in Beijing City   总被引：6，自引：0，他引：6  

Z. Ding  Y. T. Chen  G. F. Panza 《Pure and Applied Geophysics》2004,161(5-6):1107-1123

— For the realistic modeling of the seismic ground motion in lateral heterogeneous anelastic media, the database of 3-D geophysical structures for Beijing City has been built up to model the seismic ground motion in the City, caused by the 1976 Tangshan and the 1998 Zhangbei earthquakes. The hybrid method, which combines the modal summation and the finite-difference algorithms, is used in the simulation. The modeling of the seismic ground motion, for both the Tangshan and the Zhangbei earthquakes, shows that the thick Quaternary sedimentary cover amplifies the peak values and increases the duration of the seismic ground motion in the northwestern part of the City. Therefore the thickness of the Quaternary sediments in Beijing City is the key factor controling the local ground effects. Four zones are defined on the base of the different thickness of the Quaternary sediments. The response spectra for each zone are computed, indicating that peak spectral values as high as 0.1 g are compatible with past seismicity and can be well exceeded if an event similar to the 1697 Sanhe-Pinggu occurs.  相似文献   

Use of microtremor measurement for assessing site effects in Northern Belgium – interpretation of the observed intensity during the MS = 5.0 June 11 1938 earthquake     

F. Nguyen  G. Van Rompaey  H. Teerlynck  M. Van Camp  D. Jongmans  T. Camelbeeck 《Journal of Seismology》2004,8(1):41-56

To provide quantitative information on site effects in the northern part of Belgium, forty-seven H/V microtremor measurements were performed with 5 second seismometers over an area of about 15.000 km². Most of the results show a northward regular increase of the fundamental period in agreement with the augmentation of the Mesozoic and Cainozoic soft sedimentsthickness from a few meters 40 km south of Brussels to 900 m at the Netherlands-Belgium border. The measured resonance frequency values wereconsistent with theoretical computations performed at different sites onthe basis of existing information and shallow seismic experiments. At oneparticular site (Uccle) where borehole data were available, microtremor measurements using an array of four seismological stations with differentapertures allowed to obtain the low frequency part of the Rayleigh wave dispersion curve, extending the range covered by the analysis of surfacewaves artificially generated. The Vs profile derived from the surface waveinversion corroborates the 1 Hz natural frequency of the site. Comparison of these results with the macroseismic information concerning the M_S = 5.0 1938 earthquake which occurred 50 km west of Brussels,confirmed the hypothesis that the geological structure of the Brabant massifis likely to control damage distribution during such an earthquake. Comparisonbetween the intensity map of the 1938 earthquake and the resonance period ofsediments obtained by our microtremor study shows a clear relation betweenthe two parameters. During the 1938 earthquake, site effects played a prominent role due to the dimension of the source whose corner frequency wasabout 1 Hz.  相似文献   

岩石Kaiser效应测地应力原理中的若干问题研究   总被引：3，自引：0，他引：3  

刘峥  巫虹 《上海国土资源》2004,(3):38-41,56

该文通过对几种不同类型岩石的实验研究，提出了关于在围压条件下影响岩石Kaiser效应的若干问题，分析了它们的声发射特征，为深部地应力测量提供了一种新的解决方法。  相似文献