Boundary-Layer Entrainment Estimation Through Assimilation of Radiosonde and Micrometeorological Data into a Mixed-Layer Model     

Steven A. Margulis  Dara Entekhabi 《Boundary-Layer Meteorology》2004,110(3):405-433

In this study we estimate boundary-layer growth and entrainment bycombining radiosonde and micrometeorological observations with asimple coupled boundary-layer and land surface model. A variational(smoothing) approach is used to find the optimal estimate ofentrainment over the daytime window. This method is appealingbecause it accounts for the uncertainty in the various data streams,while enforcing the dynamics of the model (i.e., water and energybudgets in the boundary layer, mixed-layer growth, etc.). Thetraditional variational framework was modified in this study toinclude an ensemble approach, which not only yields a (mean) estimateof entrainment, but a measure of its uncertainty as well. Themethodology is applied to a field experiment site in Kansas. Resultsfrom this study indicate a much larger ratio of entrainment to surfacefluxes compared to early literature values from other sites. However,our results are consistent with recent estimates at the site usingindependent estimation methods. In tests where radiosonde data werewithheld, reasonable skill in entrainment estimation was still shown,suggesting the potential for more widespread applications where onlymicrometeorological data are available. Finally, the data assimilationframework presented here has not traditionally been used inatmospheric boundary-layer studies, and may provide a useful approachfor studying other aspects of the boundary layer in the future.  相似文献   

Turbulence Structures Over The Marginal Ice Zone Under Flow Parallel To The Ice Edge: Measurements And Parameterizations     

C. Drüe  G. Heinemann 《Boundary-Layer Meteorology》2002,102(1):83-116

Three aircraft-based studies of boundary-layer fronts (BLFs) werecarried out during the experiment KABEG in April 1997 near thesea-ice edge over the Davis Strait. The boundary-layer flow wasparallel to the ice edge and hence two independent turbulent regimescould develop in an identical synoptic framework, separated by thefrontal zone along the ice edge. The zone of strongest crosswindhorizontal gradients was typically 20 km wide, while the downstreamscale of the BLF was observed to be several hundreds of kilometres.For two of the three cases the investigation of turbulence structureswas possible and the results are given herein.Horizontal and vertical profiles of turbulent fluxes and other turbulentquantities are presented. A spectral analysis reveals the coexistence ofsmall-scale turbulence with roll motions. These roll motions can behidden or can be visible as cloud streets. The associated transportmechanisms are highly relevant for the choice of suitable averagingintervals for turbulent flux calculations and model validation.Parameterizations for the vertical velocity variance, countergradienttransport, sea surface roughness and eddy diffusivity are evaluatedand compared for this baroclinic strong-wind convective boundary-layerenvironment. Analogously, drag coefficients and bulk transfer coefficientsare derived from measurements.  相似文献   

一个用于气候模式的简单冻土过程参数化方案的建立和检验   总被引：13，自引：0，他引：13  

Zhang Yu  Lu Shihua 《大气科学进展》2002,19(3):513-527

在NCAR／LSM的基础上，发展了一个简单的冻土过程参数化方案，并使用苏联6个站的水气象观测资料考察了耦合了新方案模式的气候效应。在新方案中，加入了对含冰量的求解和在相变过程中的能量变化;并使用Johanson的方案替代了模式中原有的土壤导热率的参数化方案，考虑了含冰量对土壤水热性质的影响。原模式和改进后模式的模拟结果的比较得到，冻土过程方案能够合理的模拟土壤列中的能量收支及水热性质随含冰量的变化。随着入渗的减少和径流的增加，春季的土壤湿度减小。因此，热通量的分配和土壤温度也产生了相应的变化。  相似文献   

Cumulus convection and lateral boundary conditions in a limited area model     

E N Rajagopal  S S Singh 《Journal of Earth System Science》1991,100(3):235-253

Three versions of Kuo's cumulus parameterization have been tested in a limited area model to investigate their comparative performances. Results show that the version of Anthes produces better forecasts than those produced by other versions. To identify a suitable scheme of lateral boundary conditions for the limited area model, impact of two time-invariant and two time-dependent boundary conditions have been examined. The forecasts suggest that the time-dependent tendency modification scheme, based on large-scale tendencies obtained from observed data, is a better boundary scheme for the model. Furthermore, the forecast produced with the revised version of the model incorporating improved versions of Kuo's scheme and lateral boundary conditions shows an overall improvement.  相似文献   

参数化的多次散射激光雷达方程和它的反演理论 Ⅰ:方程     

邱金桓  H.Quenzel  M.Wiegner 《大气科学》1992,(5)

本文提出了一个参数化的多次散射激光雷达方程,该方程基于本文引出的四个因子,即几何消光因子、消光分布因子、前向散射因子和后向散射因子.前两个因子表征多次散射成分对大气消光系数分布、激光的发散角和接收视场角以及接收孔径的依赖关系,后两个因子表征多次散射成分对散射相函数的依赖关系.这个参数化多次散射雷达方程在241个数值试验中得以检验,这些试验包含很宽的大气条件和雷达几何参数,包括14个大气散射相函数,均匀和不均匀的大气消光系数分布,0.5至1之间变化的一次散射反照率,地基和空间站激光雷达两种情形.数值试验表明,在小于4的光学厚度内参数化的解和Monte-Carlo解之间的标准偏差小于27％,而本模式的计算时间比Monte-Carlo方法偏小4个数量级左右.本模式不仅适合于研究多次散射对激光回波信号和激光大气遥感的效应,而且对于考虑多次散射的激光大气探测而言,是一个合适的应用模式.  相似文献   

A THREE-DIMENSIONAL ELASTIC NESTED-GRID MESO-(β-γ)SCALE ATMOSPHERIC MODEL——PART Ⅰ:MODEL DESCRIPTION          下载免费PDF全文

Liu Yubao  Zhou Xiuji  Hu Zhijin 《Acta Meteorologica Sinica》1993,7(3):257-272

A three-dimensional elastic nonhydrostatic mesoscale(β-γ) model with nested-grid is presented.It uses a set of full equations in terrain-following coordinates as its basic dynamic frame,which is solved with a time-splitting algorithm for acoustic and gravity waves.The model physical parameterization includes a K-theory subgrid eddy mixing for cloud and free atmosphere,a bulk planetary boundary layer parameterization,and three types of sofisticated cloud microphysics schemes with double-parameters for hail-bearing clouds,warm clouds and snowing clouds respectively.The model is designed to be used flexibly for simulations of a variety of meso-and small-scale atmospheric processes,and can be improved as a regional and local operational NWP system in future.  相似文献   

PARAMETERIZATION OF SOLAR RADIATIVE FLUX CALCULATION IN THE ATMOSPHERE          下载免费PDF全文

Zhao Gaoxiang  Wang Hongqi 《Acta Meteorologica Sinica》1994,8(1):79-88

Based on the two-stream approximation a broad-band parameterization scheme for solar radiative flux calculationis presented.The whole solar spectral region from 0.2 to 3.58 μm is divided into three broad spectral intervals.The effec-tive broad-band optical depths and single scattering albedos in the atmosphere in each spectral interval can be obtainedusing parameterized formulae from known atmospheric parameters.The overlapping scattering and/or absorption ef-fects of two atmospheric constituents are considered properly.In the consideration of radiative effect of clouds in theatmosphere the single scattering albedos and backscattering parameters of clouds in each broad spectral interval are giv-en preliminarily and the cloud optical depths are determined according to the cloud liquid water content.  相似文献   

On the bulk parameterization of snow and its application to the quantitative studies of precipitation growth     

Wojciech W. Grabowski 《Pure and Applied Geophysics》1988,127(1):79-92

Appropriate formulation of bulk parameterization of snow growth and evaporation based on observational characteristics of snow particles is presented. The parameterization is compared to that of S. A. Rutledge and P. V. Hobbs and to detailed treatment in which snow particles are assumed to grow or evaporate in each size bin separately. On the contrary to bulk parameterization of rain, snow diffusional growth or evaporation is accurately represented in the suggested bulk formulation, but growth by riming is overpredicted. Integrations of water budget equations in a one-dimensional updraft have shown that quantitative results, e.g., precipitation intensity, cloudwater content, supersaturation with respect to ice, depend on the parameterization scheme employed, which suggests that comparisons of field measurements with parameterized model outputs is usually not straightforward.  相似文献   

Modeling the Global Thermohaline Circulation     

Hiroyasu Hasumi 《Journal of Oceanography》2002,58(1):25-33

This paper reviews recent progress and problems in modeling the thermohaline circulation of the world ocean by use of z-coordinate ocean general circulation models. Discussions focus on four issues: sea surface forcing, mixing in the deep ocean interior, eddy-induced tracer transport, and bottom boundary layer processes. Although some widely used techniques and parameterizations deal with these issues, some aspects are still overlooked and more sophistication is certainly required. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   

Parameterization for the depth of the entrainment zone above the convectively mixed layer   总被引：1，自引：0，他引：1  

SUN Jianning  JIANG Weimei  CHEN Ziyun  YUAN Renmin 《大气科学进展》2005,22(1):114-121

It has been noted that when the convective Richardson number Ri* is used to characterize the depth of the entrainment zone, various parameterization schemes can be obtained. This situation is often attributed to the invalidity of parcel theory. However, evidence shows that the convective Richardson number Ri^* might be an improper characteristic scaling parameter for the entrainment process. An attempt to use an innovative parameter to parameterize the entrainment-zone thickness has been made in this paper.Based on the examination of the data of water-tank experiments and atmospheric measurements, it is found that the total lapse rate of potential temperature across the entrainment zone is proportional to that of the capping inversion layer. Inserting this relationship into the so-called parcel theory, it thus gives a new parameterization scheme for the depth of the entrainment zone. This scheme includes the lapse rate of the capping inversion layer that plays an important role in the entrainment process. Its physical representation is reasonable. The new scheme gives a better ordering of the data measured in both watertank and atmosphere as compared with the traditional method using Ri^*. These indicate that the parcel theory can describe the entrainment process suitably and that the new parameter is better than Ri^*.  相似文献