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1.
复杂地形对对流混合层的影响 总被引：2，自引：1，他引：1
用发展后的混合层模式研究下垫面（地形和地面热力）的不均匀性对混合层结构的影响。数值实验表明,在保持了混合层模式简便和实用等特点的同时,发展后的混合层模式能够很好地反映复杂地形对混合层厚度和风速的影响。 相似文献
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利用Godas的逐月混合层深度(MLD)和中国160站逐月降水资料,分析热带太平洋混合层深度的季节变化及年际异常特征,初步探讨混合层深度异常与中国夏季降水异常的相关关系。结果表明:(1)赤道地区,东太平洋区域混合层最浅,中太平洋区域最深,且北半球秋冬季混合层比春夏季深;热带西北和西南太平洋在冬半球混合层深,夏半球浅。(2)赤道中、西太平洋混合层深度的年际异常终年都为大值区,北半球春(秋)季的热带西北太平洋(西南太平洋)也为年际异常大值区;7月年际异常最弱。(3)1、4和10月热带太平洋混合层深度年际异常与ENSO事件关系密切,在El Nio事件期间,热带太平洋东部及东北部混合层深度加深,西部及西南部减小。(4)热带太平洋混合层深度异常与中国夏季降水异常关系密切,这一关系也反映了El Nio事件与中国夏季降水的关系。即当秋冬季节发生El Nio事件时,来年El Nio事件衰减期的夏季长江中下游以南特别是洞庭湖、鄱阳湖的降水将显著偏多,江淮、华南南部降水偏少。 相似文献
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梅雨锋结构的数值模拟 总被引：5，自引：3，他引：5
利用1999年6月下旬持续性梅雨锋降水过程的全程四维同化模拟结果,深入分析梅雨锋结构的时空不均匀变化特征及其与低涡降水强度的密切关系。结果表明,梅雨锋呈现明显的中层锋和边界层锋两段锋的特征,中层梅雨锋区对降水的影响比边界层锋更为关键,中层锋的加强、锋坡增大趋于垂直、锋区垂直环流的加强和与高空急流锋区的上下贯通,有利于梅雨锋降水的加强,强降水并不出现于中层锋区最强的时段,而是发生于大范围锋区强度达峰值之后约16—24 h。中低层总变形加强与梅雨锋的加强有密切关系。组成低空急流的中低层u,v分量呈现不同的分布和演变特征,强南风中心位于900—800 hPa,呈明显的低空急流状特征,贴近暴雨区还可能出现较小尺度的急流;而强西风中心出现于中层锋前700—500 hPa,表现为高空强西风区沿锋区上界的向下延伸;低空南风急流通常与总变形同时加强。强锋段的锋前饱和高湿高能气柱、锋前中低层急流状南风区和中层西风均匀大值区等要素场呈现高度组织化的特征。梅雨锋的低层特性,如辐合、锋区强度、总变形和南风分量及降水强度等要素呈现显著的中尺度扰动特征,有明显的日变化且受长江中下游中尺度地形影响,扰动特征有随时间上传的趋势。 相似文献
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北京城市大气混合层与气溶胶垂直分布观测研究 总被引：26，自引：0，他引：26
2002年3～10月在北京大学利用微脉冲激光雷达(MPL)观测了气溶胶时空变化。提出一种反演混合层高度的方法,这种方法减小了仪器订正的误差,反演的混合层高度与探空测量结果有很好的一致性。利用该方法计算了观测期间晴天无云天气条件下的混合层高度,分析了混合层高度及其增长率的日变化、季节变化,初步研究了混合层高度和近地面气溶胶分布的相互关系,分析了表征大气扩散能力的通风系数的日变化。结果表明,利用MPL监测城市混合层是可行的和优越的。 相似文献
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1991年江淮暴雨期地气通量与混合层结构的研究 总被引：6，自引：1，他引：6
本文用１９９１年５—７月江淮及其北部地区的地面与高空资料根据３种不同的整体公式对地表通量（动量、感热和潜热通量）进行了估算，并对混合层结构进行了研究，揭示出这次持续性特大暴雨中陆面过程的一些特征，主要结果如下：１．地表通量依赖于大气稳定度，稳定度越强，地表通量越小。不稳定状况下平均地表动量通量为０．０１５４Ｎ／ｍ２，向上的感热和潜热平均值分别为２５．７Ｗ／ｍ２和１３２．３Ｗ／ｍ２；稳定状况下，地表动量通量为０．００６Ｎ／ｍ２，感热和潜热通量平均是向下输送的，分别为－１．５Ｗ／ｍ２和２．５Ｗ／ｍ２。２．地表通量与降水过程密切有关。雨期的动量通量略小于非雨期，而雨期的感热与潜热通量明显小于非雨期，雨量越大，这两种通量愈小。３．地表通量具有明显日变化。动量、感热和潜热通量的最大值出现在下午２时左右，最小值出现在凌晨２时左右。４．混合层与雨期关系密切，雨期的混合层高度较非雨期低，这时地表感热和潜热通量小；而非雨期情况相反 相似文献
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Langmuir turbulence is a complex turbulent process in the ocean upper mixed layer. The Coriolis parameter has an important effect on Langmuir turbulence through the Coriolis–Stokes force and Ekman effect, however, this effect on Langmuir turbulence has not been systematically investigated. Here, the impact of the Coriolis parameter on Langmuir turbulence with a change of latitude (LAT) from 20°N to 80°N is studied using a non-hydrostatic large eddy simulation model under an ideal condition. The results show that the ratio of the upper mixed layer depth to Ekman depth scale (RME) RME = 0.266 (LAT = 50°N) is a key value (latitude) for the modulation effect of the Coriolis parameter on the mean and turbulent statistics of Langmuir turbulence. It is found that the rate of change of the sea surface temperature, upper mixed layer depth, entrainment flux, crosswind velocity, downwind vertical momentum flux, and turbulent kinetic energy budget terms associated with Langmuir turbulence are more evident at RME ≤ 0.266 (LAT ≤ 50°N) than at RME ≥ 0.266 (LAT ≥ 50°N). However, the rate of change of the depth-averaged crosswind vertical momentum flux does not have a clear variation between RME ≤ 0.266 and RME ≥ 0.266. The complex changes of both Langmuir turbulence characteristics and influence of Langmuir turbulence on the upper mixed layer with latitude presented here may provide more information for further improving Langmuir turbulence parameterization. 相似文献
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对流边界层的大涡模拟研究 总被引：5，自引：0，他引：5
本文建立了一个均匀平坦地面上对流边界层的大涡模式,模式考虑了水汽,采用了考虑浮力和固壁影响订正的一阶闭合。并用所建模式进行了由热扰动发展的对流边界层的模拟及其对地表热状况变化响应的初步探讨性模拟工作。通过模拟认为,模式较好地反映了对流边界层的主要结构。 相似文献
10.
The entrainment flux ratio A e and the inversion layer (IL) thickness are two key parameters in a mixed layer model. A e is defined as the ratio of the entrainment heat flux at the mixed layer top to the surface heat flux. The IL is the layer between the mixed layer and the free atmosphere. In this study, a parameterization of A e is derived from the TKE budget in the firstorder model for a well-developed CBL under the condition of linearly sheared geostrophic velocity with a zero value at the surface. It is also appropriate for a CBL under the condition of geostrophic velocity remaining constant with height. LESs are conducted under the above two conditions to determine the coefficients in the parameterization scheme. Results suggest that about 43% of the shear-produced TKE in the IL is available for entrainment, while the shear-produced TKE in the mixed layer and surface layer have little effect on entrainment. Based on this scheme, a new scale of convective turbulence velocity is proposed and applied to parameterize the IL thickness. The LES outputs for the CBLs under the condition of linearly sheared geostrophic velocity with a non-zero surface value are used to verify the performance of the parameterization scheme. It is found that the parameterized A e and IL thickness agree well with the LES outputs. 相似文献
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大地形上边界层流场的动力学研究 总被引：1，自引：1，他引：1
本文应用边界层气象学中Estoque数值模式关于湍流交换系数及分层的处理方法,求得了大地形存在时定常边界展方程的零、一级解析解,并用来得到大地形存在时边界层的散度场、垂直速度场,改进了前人的结果。 相似文献
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This study aims to explore the relative role of oceanic dynamics and surface heat fluxes in the warming of southern Arabian Sea and southwest Indian Ocean during the development of Indian Ocean Dipole (IOD) events by using National Center for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) daily reanalysis data and Global Ocean Data Assimilation System (GODAS) monthly mean ocean reanalysis data from 1982 to 2013, based on regression analysis, Empirical Orthogonal Function (EOF) analysis and combined with a 2? layer dynamic upper-ocean model. The results show that during the initial stage of IOD events, warm downwelling Rossby waves excited by an anomalous anticyclone over the west Indian Peninsula, southwest Indian Ocean and southeast Indian Ocean lead to the warming of the mixed layer by reducing entrainment cooling. An anomalous anticyclone over the west Indian Peninsula weakens the wind over the Arabian Sea and Somali coast, which helps decrease the sea surface heat loss and shallow the surface mixed layer, and also contributes to the sea surface temperature (SST) warming in the southern Arabian Sea by inhibiting entrainment. The weakened winds increase the SST along the Somali coast by inhibiting upwelling and zonal advection. The wind and net sea surface heat flux anomalies are not significant over the southwest Indian Ocean. During the antecedent stage of IOD events, the warming of the southern Arabian Sea is closely connected with the reduction of entrainment cooling caused by the Rossby waves and the weakened wind. With the appearance of an equatorial easterly wind anomaly, the warming of the southwest Indian Ocean is not only driven by weaker entrainment cooling caused by the Rossby waves, but also by the meridional heat transport carried by Ekman flow. The anomalous sea surface heat flux plays a key role to damp the warming of the west pole of the IOD. 相似文献
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大气混合层高度的模式计算和分析 总被引：3，自引：1，他引：2
设计了一套描述混合对流层平均状况的平板模式．模拟了混合层平均要素随时间的演变过程。采用能量学方法,通过考虑影响混合层演变的浮力、风切变及下沉等因子,对混合层高度随时间变化的过程进行数值模拟计算,并与实际观测资料比较。结果表明．模式可以较好地应用于实际业务预报中,同时改进了模式的计算方法．分析了各种物理参数对混合层高度变化的不同影响和物理成因。 相似文献
14.
In this paper,mixed layer height and certain mean elements are predicted by using a dry mixed layer model.Their variation with time and some basic properties are discussed.The model is tested with the 1967 Australian Wangara experimental data.Comparison of the calculated results with the observed data is conducted.The aim of this paper is to build a predictive model describing the basic properties of the mixed layer and attempts to formulate a boundary layer parameterization scheme suitable for the numerical weather prediction model. 相似文献
15.
根据2000—2005年逐日4个时次的常规气象资料,采用国家标准GB/T 3840—91中规定的方法计算并分析了重庆主城区大气混合层厚度的频率分布、时间变化等基本特征;在此基础上,进一步以2005年为例分析了混合层厚度与空气污染指数的相关关系。结果表明:重庆市大气混合层厚度以0—800 m范围出现频率最高,多年平均值为428 m;混合层厚度的季节变化和日变化特征明显。与1980—1990年相比,2000—2005年期间年平均混合层厚度总体上有所增加。混合层厚度与空气污染指数的相关性分析显示,月平均混合层厚度和月平均API呈显著负相关(r=-0.72);分析表明,大气混合层厚度是影响城市空气质量的重要因素。 相似文献
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The aquatic eco-environment is significantly affected by temporal and spatial variation of the mixed layer depth(MLD) in large shallow lakes.In the present study,we simulated the three-dimensional water temperature of Taihu Lake with an unstructured grid with a finite-volume coastal ocean model(FVCOM) using wind speed,wind direction,short-wave radiation and other meteorological data measured during 13-18 August 2008.The simulated results were consistent with the measurements.The temporal and spatial distribution of the MLD and the possible relevant mechanisms were analyzed on the basis of the water temperature profile data of Taihu Lake.The results indicated that diurnal stratification might be established through the combined effect of the hydrodynamic conditions induced by wind and the heat exchange between air and water.Compared with the net heat flux,the changes of the MLD were delayed approximately two hours.Furthermore,there were significant spatial differences of the MLD in Taihu Lake due to the combined impact of thermal and hydrodynamic forces.Briefly,diurnal stratification formed relatively easily in Gonghu Bay,Zhushan Bay,Xukou Bay and East Taihu Bay,and the surface mixed layer was thin.The center of the lake region had the deepest surface mixed layer due to the strong mixing process.In addition,Meiliang Bay showed a medium depth of the surface mixed layer.Our analysis indicated that the spatial difference in the hydrodynamic action was probably the major cause for the spatial variation of the MLD in Taihu Lake. 相似文献
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AN EVALUATION OF SEVERAL TURBULENCE SCHEMES FOR THE PREDICTION OF MEAN AND TURBULENT FIELDS IN COMPLEX TERRAIN 总被引：2，自引：0，他引：2
PETER J. HURLEY 《Boundary-Layer Meteorology》1997,83(1):43-73
A prognostic three-dimensional mesoscale model has been developed andused in one- and two-dimensional modes to evaluate ten local turbulenceclosure schemes. The schemes ranged from first-order to the two-equationprognostic schemes. Predictions by the models were compared for aone-dimensional convective boundary layer using mixed layer scaling andmeasurements to interpret the results. Two-dimensional simulations were alsoperformed for a sea-breeze flow and for flow over a hill. The results showedthat for all of the models considered, minor differences were produced in themean meteorological fields and in the vertical scalar fluxes, but majordifferences were apparent in the velocity variances and dissipation rate.Predicted tracer concentrations were very sensitive to the turbulence modelformulation for dispersion from a point source in the convective boundarylayer, particularly for the prediction of maximum concentrations. Predictedtracer concentrations from a surface volume source for the two-dimensionalsimulations were similar for all models, although the degree of mixing in themorning growth period produced some differences. Generally, good results forthe mean meteorological fields can be obtained with first-order schemes, evenif they underpredict the magnitude of turbulence in the convective boundarylayer, and reasonable tracer concentrations can also be obtained with thesemodels provided near-source effects are not important. The two-equationprognostic models performed best for the prediction of turbulence in theconvective boundary layer. 相似文献
18.
使用1998—2016年大西洋40个飓风2 032个GPS下投式探空仪观测数据,以距离海岸线300 km为界分为近海和远洋两组,利用合成分析方法探讨了飓风边界层特征高度的差异。边界层特征高度的定义方法包括最大切向风高度、入流层高度、混合层高度和理查森数法高度。对比分析不同定义方法下近海和远洋边界层高度,结果表明：根据最大切向风和入流层强度定义的边界层高度,近海边界层高度低于远洋边界层高度,且近海边界层高度随径向增加至2倍最大风速半径后趋于稳定;基于混合层定义的边界层高度明显低于动力边界层高度,且近海与远洋混合边界层特征高度无明显差异;近海理查森数边界层高度在最大风速半径内与远洋的无明显差异,而在最大风速半径外略高于远洋的。 相似文献
19.
A new method for deduction of the sensible heat flux is validated with three sets of published SODAR （sound detection and ranging） data. Although the related expressions have previously been confirmed by the author with surface layer data, they have not yet been validated with observations from the boundary layer before this work. In the study, selected SODAR data are used to test the method for the convective boundary layer. The sensible heat flux （SHF） retrieved from SODAR data is found to decrease linearly with height in the mixed layer. The surface sensible heat fluxes derived from the deduced sensible heat flux profiles under convective conditions agree well with those measured by the eddy correlation method. The characteristics of SHF profiles deduced from SODAR data in different places reflect the background meteorology and terrain. The upper part of the SHF profile （SHFP） for a complicated terrain is found to have a different slope from the lower part. It is suggested that the former reflects the advective characteristic of turbulence in upwind topography. A similarity relationship for the estimation of SHFP in a well mixed layer with surface SHF and zero-heat-flux layer height is presented. 相似文献
20.
海洋生物过程在海洋吸收大气二氧化碳中的作用 总被引：5，自引：0，他引：5
使用一个包括浮游生物（植物、动物和细菌）和无生命氮（有机碎片、溶解有机氮、硝酸盐和铵）的食物网来描述发生在海洋上层的生物过程。并将该生物模式分别用在佛罗里达海峡的一个固定位置和从佛罗里达海峡（２４°Ｎ,８０°Ｗ）流经挪威海（６８°Ｎ,１０°Ｅ）（扩展湾流体系,ＥＧＳＳ）的一个水块中,研究了海洋中上述的生物过程对水块吸收大气二氧化碳的影响。水块模式的结果十分明显地表明了海洋中的水华季,比包括浮游植物－浮游动物－硝酸盐体系得到的峰陡,结果更合理。扩展湾流体系中平均净初级生产力为４３ｇＣｍ－２ａ－１,小于观测值。模拟的总碱度,总二氧化碳和二氧化碳分压落在观测值的范围内,在水块吸收大气ＣＯ２的总量中生物泵的作用约占１６％。 相似文献