Modelling Mean and Turbulence Fields in the Dry Convective Boundary Layer with the Eddy-Diffusivity/Mass-Flux Approach     

Peter Hurley 《Boundary-Layer Meteorology》2007,125(3):525-536

The treatment of turbulence closure in atmospheric models is examined in the context of the dry convective boundary layer (CBL) and the eddy-diffusivity/mass-flux (EDMF) approach. The EDMF approach is implemented into a model called TAPM to use a coupled two-equation prognostic turbulence closure and the mass-flux approach to represent turbulence in the CBL. This work also extends the range of turbulence variables that can be derived from the mass-flux component of the model and uses these along with their values from the prognostic scheme to provide total turbulence fields that can be used to compare to data and/or to feed into other components of TAPM, including those needed to drive Eulerian and Lagrangian air pollution dispersion modules. Model results are presented for the afternoon of a simulated summer day and are compared to both laboratory and field observations in a mixed-layer scaled framework. The results show that the EDMF approach works well within TAPM and can provide good predictions of mean and turbulence fields, including in the upper levels of the CBL. The EDMF approach has several attractive features, including the potential to be one approach to unify the treatment of turbulence and dry and moist convection in atmospheric models.  相似文献   

Contribution of the MODIS instrument to observations of deep convective storms and stratospheric moisture detection in GOES and MSG imagery   总被引：1，自引：0，他引：1  

Martin Setvk  Robert M. Rabin  Pao K. Wang 《Atmospheric Research》2007,83(2-4):505-518

Past studies based on the NOAA/AVHRR and GOES I-M imager instruments have documented the link between certain storm top features referred to as the “cold-U/V” shape in the 10–12 μm IR band imagery and plumes of increased 3.7/3.9 μm band reflectivity. Later, similar features in the 3.7/3.9 μm band have been documented in the AVHRR/3 1.6 μm band imagery.The present work focuses on storm top observations utilizing the MODIS data. The MODIS instrument (available onboard NASA's EOS Terra and Aqua satellites) provides image data with significantly better geometrical resolution (in some of its bands) and broader range of spectral bands as compared to that from AVHRR/3 observations. One of the goals of this study is to evaluate the contribution of this new instrument to observations of convective storm tops. Besides the cloud top features linked to storm top microphysics and morphology, the paper also addresses the possibility of detection of lower stratospheric water vapor above cold convective storm tops. This issue is explored utilizing MODIS as well as GOES and MSG imagery.In addition, the paper discusses an alternative interpretation of the “cold-U/V” patterns at the top of intense storms by a mechanism of “plume masking” as suggested by some of the observations.  相似文献   

A Case Study on the Effects of Heterogeneous Soil Moisture on Mesoscale Boundary-Layer Structure in the Southern Great Plains, U.S.A. Part I: Simple Prognostic Model     

Ankur R. Desai  Kenneth J. Davis  Christoph J. Senff  Syed Ismail  Edward V. Browell  David R. Stauffer  Brian P. Reen 《Boundary-Layer Meteorology》2006,119(2):195-238

The atmospheric boundary-layer (ABL) depth was observed by airborne lidar and balloon soundings during the Southern Great Plains 1997 field study (SGP97). This paper is Part I of a two-part case study examining the relationship of surface heterogeneity to observed ABL structure. Part I focuses on observations. During two days (12–13 July 1997) following rain, midday convective ABL depth varied by as much as 1.5 km across 400 km, even with moderate winds. Variability in ABL depth was driven primarily by the spatial variation in surface buoyancy flux as measured from short towers and aircraft within the SGP97 domain. Strong correlation was found between time-integrated buoyancy flux and airborne remotely sensed surface soil moisture for the two case-study days, but only a weak correlation was found between surface energy fluxes and vegetation greenness as measured by satellite. A simple prognostic one-dimensional ABL model was applied to test to what extent the soil moisture spatial heterogeneity explained the variation in north–south ABL depth across the SGP97 domain. The model was able to better predict mean ABL depth and variations on horizontal scales of approximately 100 km using observed soil moisture instead of constant soil moisture. Subsidence, advection, convergence/divergence and spatial variability of temperature inversion strength also contributed to ABL depth variations. In Part II, assimilation of high-resolution soil moisture into a three-dimensional mesoscale model (MM5) is discussed and shown to improve predictions of ABL structure. These results have implications for ABL models and the influence of soil moisture on mesoscale meteorology  相似文献   

卫星遥感揭示的青藏高原上MCS活动特征及东移传播   总被引：8，自引：0，他引：8  

过仲阳  林珲  江吉喜  黄签  方兆宝 《遥感学报》2003,7(5):350-357

利用1998年6—8月日本GMS红外辐射亮温(Tbb)资料，对高原上中尺度对流系统(MCS)的活动进行了自动追踪，得到了高原上夏季MCS的大小、强度、活动区域及生命史、形状特征。在此基础上，利用国家气象中心高分辨率有限区域分析预报系统(HLAFS)的数值分析格点值，研究了MCS的东移传播与其周围环境场物理量之间的关系，建立了400hPa和500hPa两个层次上有利于MCS移出高原的物理量场概略模型图。  相似文献   

孟加拉湾云团影响下云南强降水分析   总被引：7，自引：6，他引：7       下载免费PDF全文

李英  张腾飞  索渺清 《气象科学》2003,23(2):185-191

2001年云南初夏洪涝与孟加拉湾(简称孟湾)云的活动密切相关，本文分析了云南强降水过程中几次孟加拉湾云团发展的大尺度动、热力背景和卫星云图的TBB特征。结果表明：孟加拉湾北上云贵高原的对流云必须得到足够的辐合和抬升动力，才能在高原维持和进一步发展；青藏高原横槽是孟加拉湾云团在云贵高原产生强降水的重要天气系统；孟加拉湾云团的发展与正压和斜压不稳定均有关系；冷空气对北上孟加拉湾云团的发展至关重要，它不但有利于水汽凝结量的增加，还有利于形成强降水天气发生的动力、热力环境；TBB分布更直观地反映了孟加拉湾云团的活动，≤-52℃的冷云覆盖区与云南强降水落区有较好的关系。  相似文献   

尘卷风的形成、结构和卷起沙尘过程的数值研究   总被引：6，自引：0，他引：6  

顾兆林  赵永志  郁永章  冯霄 《气象学报》2003,61(6):751-760

文中应用数值算法对尘卷风的发展过程进行了模拟计算与分析。通过模拟计算得到了尘卷风的内部详细结构和运动过程。研究表明尘卷风是由于地面局部增热不均匀而形成的一种特殊的旋转对流运动。在尘卷风形成的过程中 ,外围空气通过贴近地面的薄层被地面加热后流向中心部位 ,外围空气的旋转能量在中心部位得到加强形成尘卷风 ,其旋转能量是热泡原来具有的旋转能量的局部集中和一部分势能转化而形成的 ,其旋转方向是由热对流泡的初始旋转方向所决定。尘卷风是一种类兰金涡 ,旋转速度和压力的分布具有兰金组合涡的特点 ;在成熟阶段 ,尘卷风的详细结构可以粗略地分为 4个区域———地面附近的气流汇聚区域、柱状的涡核区域、旋风与地面作用形成的转角风区域以及涡核外部的外围气流区域。转角区域可以细分为两个子区域———外围的方位角风区域(在该区域 ,上升气流运动方向与轴线之间有一定的夹角 ,称为方位角 )和中心的下沉停滞气流区域。尘卷风中心的低压和急速的上升气流可使大量沙尘扬起 ,不同直径的沙尘颗粒在尘卷风的作用下运动轨迹不同 ,因此卷起不同大小沙尘的尘卷风的外形也是不同的。  相似文献   

Aridity and the Potential Physiological Response of C 3 Crops to Doubled Atmospheric Co 2 : A Simple Demonstration of the Sensitivity of the Canadian Prairies     

R. L. Raddatz 《Boundary-Layer Meteorology》2003,107(2):483-496

Since cultivated annual C₃ field crops cover about50% of the land surface of the Canadian Prairie grassland eco-climatic zone, this vegetationinfluences the aridity of the climate during the growing season. The physiological response of these cropsto a doubling of the atmospheric concentration of CO₂ may be a doubling of canopyresistance. If this physiological effect is not counteracted by interactive feedbacks, such as increasedleaf area, evapotranspiration rates could be reduced. To demonstrate the sensitivity of thearidity of the Prairie climate to this potential physiological effect, representative spring wheatgrowing-season soil moisture and Bowen ratio curves for a doubled canopy resistance(2 × CO₂) scenario were compared with a control (1 × CO₂) scenario.Lower evapotranspiration in the 2 × CO₂ scenario: (1) Increased root-zone soilmoisture levels, and (2) weakened the atmospheric component of the hydrologic cycle by raisingBowen ratios, which reduces the convective available energy, and reduces the regionalcontribution to the atmospheric water vapour over the Prairies. A weakened hydrologic cycleimplies less rainfall, and possibly, lower soil moisture levels. Thus, the net impact of a doublingof the atmospheric concentration of CO₂ on the aridity of the Canadian Prairies is uncertain.This simple sensitivity demonstration did not consider most of the potential feedback mechanisms,nor interactions of other processes. Nevertheless, the result illustrates that the physiologicaleffect should be explicitly included in climate change models for the Canadian Prairies.  相似文献   

A Theoretical Model for the Study of Convective Turbulence Decay and Comparison with Large-Eddy Simulation Data     

A. Goulart  G. Degrazia  U. Rizza  D. Anfossi 《Boundary-Layer Meteorology》2003,107(1):143-155

The development of a theoretical model fora decaying convective boundary layeris considered. The model relies on thedynamical energy spectrumequation in which the buoyancy andinertial transfer terms are retained,and a closure assumptionmade for both. The parameterization for thebuoyancy term is given providing a factorizationbetween the energy source termand its temporal decay. Regarding the inertialtransfer term a hypothesis ofsuperposition is used to describe theconvective energy source and time variationof velocity correlation separately.The solution of the budget equation for theturbulent kinetic energy spectrum is possible,given the three-dimensional initial energyspectrum. This is doneutilizing a version of the Kristensen et al.(see Boundary-Layer Meteorol. 47, 149–193)model valid for non-isotropic turbulence. During thedecay the locus of the spectralpeak remains at about the sameposition as the heat flux decreases.Comparison of the theoretical modelis performed against large-eddy simulationdata for a decaying convectiveboundary layer.  相似文献   

Turbulence and Coherent Organizations in the Atmospheric Boundary Layer: A Radar-Aircraft Experimental Approach     

F. Lohou  B. Campistron  A. Druilhet  P. Foster  J.P. Pages 《Boundary-Layer Meteorology》1998,86(1):147-179

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An Analytical Slab Model for the Growth of the Coastal Thermal Internal Boundary Layer Under Near-Neutral Onshore Flow Conditions     

Ashok K. Luhar 《Boundary-Layer Meteorology》1998,88(1):103-120

Analytical parameterisations of the thermal internal boundary-layer (TIBL) height based on the slab approach are widely used in coastal dispersion models. However, they tend to a singular behaviour when the stability of the onshore flow is close to neutral. Assuming that convective turbulence dominates mixing, we derive a more general analytical model that is valid for both stable and neutral onshore flows. The model is based on the existing framework for the slab approach but involving the Zilitinkevich correction (or the spin-up term). The height variation of the onshore flow lapse rate is accounted for in the model by including an initial TIBL height. An algebraic form of the model also includes the mechanical mixing contribution to the TIBL growth and is, therefore, suitable for use when the overland surface heat flux is small and friction velocity large. The new analytical model is tested with field measurements taken under near-neutral onshore flow conditions. The performance of the model is shown to be better than a commonly used TIBL parameterisation scheme.  相似文献