共查询到20条相似文献，搜索用时 31 毫秒
1.
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
2.
A diagnostic study of heat transfer within the lower atmosphere and between the atmosphere and the surface of the Arctic Ocean
snow/ice pack during clear-sky conditions is conducted using data from the Surface Heat Budget of the Arctic Ocean (SHEBA)
field experiment. Surface heat budgets computed for four cloudy and four clear periods show that, while the net turbulent
heat fluxes at the surface are small during the cloudy periods, during the clear-sky periods they are a considerable source
of surface heating, balancing significant portions of the conductive heat fluxes from within the snow/ice pack. Analysis of
the dynamics and thermodynamics of the lower atmosphere during the clear-sky periods reveals that a considerable portion of
the heat lost to the surface by turbulent heat fluxes is balanced by locally strong heating near the atmospheric boundary-layer
(ABL) top due to the interaction of subsiding motions with the strong overlying temperature inversions surmounting the ABL.
This heat is then entrained into the ABL and transported to the surface by turbulent mixing, maintained by a combination of
vertical wind shear and wave-turbulence interactions. The frequency of stable, clear-sky periods, particularly during the
winter, combined with these results, suggests that the downward transfer of heat through the lower atmosphere and into the
surface represents an important component of the heat budgets of the lower atmosphere and snow/ice pack over the annual cycle 相似文献
3.
J. Sanjay 《Boundary-Layer Meteorology》2008,129(1):159-177
Data collected during the Land Surface Processes Experiment (LASPEX) in a semi-arid region of the state of Gujarat in north-west
India for a clear sky day (16 May 1997) are used to assess the performance of the atmospheric boundary-layer (ABL) and land-
surface parameterizations in the fifth-generation Pennsylvania State University-National Center for Atmospheric Research (PSU-NCAR)
Mesoscale Model (MM5). The ABL turbulence parameterizations examined are the Blackadar scheme coupled to a simple soil slab
model (SSM), and the Troen-Mahrt scheme coupled to SSM or to the more sophisticated Noah land-surface model (NSM). The comparison
of several two-way nested high resolution (9-km) MM5 short term 24-h simulations indicate that, although the model is able
to capture the trend in the observed data, the computed results deviate from observations. The NSM with a modest treatment
of vegetation outperforms the SSM in capturing the observed daily variations in surface heat fluxes and aspects of ABL structure
over the tropical land surface at local scales. Detailed analysis showed that, with the incorporation of observed local vegetation
and soil characteristics, the NSM reproduced a realistic surface energy balance and near-surface temperature. It is further
found that the coupling of the NSM with the Troen-Mahrt ABL scheme leads to excessive ABL mixing and a dry bias in the model
simulations. 相似文献
4.
Samir Khanna 《Boundary-Layer Meteorology》1998,88(1):121-144
The surface layer of an atmospheric boundary layer (ABL) is most accessible to field measurements and hence its ensemble-mean structure has been well established. The Kansas field measurements were the first detailed study of this layer, providing numerous benchmark statistical profiles for a wide range of stability states. Large-eddy simulation (LES), in contrast, is most suitable for studying the mixed layer of the ABL where the energy-containing range of the vertical velocity field is well resolved. In the surface layer, typical large-eddy simulations barely resolve the energy-containing vertical-velocity fields and hence do not provide sufficient data for a detailed analysis.We carried out a nested-mesh simulation of a moderately convective ABL (-zi/L = 8) in which the lower 6% of the boundary layer had an effective grid resolution of 5123. We analyze the LES fields above the 6th vertical grid level (z = 23 m) where the vertical velocity field has a well formed inertial subrange, for a detailed comparison with the Kansas results. Various terms in the budgets of turbulent kinetic energy, temperature variance, Reynolds stress, temperature flux, and some higher order moments are compared. The agreement is generally quite good; however, we do observe certain discrepancies, particularly in the terms involving pressure fluctuations. 相似文献
5.
Analysis of Atmospheric Boundary Layer Height Characteristics over the Arctic Ocean Using the Aircraft and GPS Soundings 
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下载免费PDF全文 Utilizing aircraft sounding data collected from the Surface Heat Budget of the Arctic Ocean (SHEBA, 1998) campaign, the authors evaluated commonly-used profile methods for Arctic ABL height estimation by validating against the’true’ABL height from aircraft sounding profiles, where ABL height is defined as the top of the layer with significant turbulence. Furthermore, the best performing method was used to estimate ABL height from the one-year GPS soundings obtained during SHEBA (October 1997-October 1998). It was found that the temperature gradient method produces a reliable estimate of ABL height. Additionally, the authors determined optimal threshold values of temperature gradient for stable boundary layer (SBL) and convective boundary layer (CBL) to be 6.5 K/100 m and 1.0 K/100 m, respectively. The maximum ABL height during the year was 1150 m occurred in May. Median values of Arctic ABL height in May, June, July, and August were 400 m, 430 m, 180 m, and 320 m, respectively. Arctic ABL heights are clearly higher in the spring than in the summer. 相似文献
6.
The present work analyzes the effect of aerosols on the evolution of the atmospheric boundary layer (ABL) over Shangdianzi in Beijing.A one-dimensional ABL model and a radiative transfer scheme are incorporated to develop the structure of the ABL.The diurnal variation of the atmospheric radiative budget,atmospheric heating rate,sensible and latent heat fluxes,surface and the 2 m air temperatures as well as the ABL height,and its perturbations due to the aerosols with different single-scattering albedo (SSA) are studied by comparing the aerosol-laden atmosphere to the clean atmosphere.The results show that the absorbing aerosols cause less reduction in surface evaporation relative to that by scatting aerosols,and both surface temperature and 2 m temperature decrease from the clean atmosphere to the aerosol-laden atmosphere.The greater the aerosol absorption,the more stable the surface layer.After 12:00 am,the 2 m temperature increases for strong absorption aerosols.In the meantime,there is a slight decrease in the 2 m temperature for purely scattering aerosols due to radiative cooling.The purely scattering aerosols decrease the ABL temperature and enhance the capping inversion,further reducing the ABL height. 相似文献
7.
8.
Maria Tombrou Aggeliki Dandou Costas Helmis Evaggelos Akylas George Angelopoulos Helena Flocas Vasiliki Assimakopoulos Nikolaos Soulakellis 《Boundary-Layer Meteorology》2007,124(1):61-79
In the present study, an attempt is made to assess the atmospheric boundary-layer (ABL) depth over an urban area, as derived
from different ABL schemes employed by the mesoscale model MM5. Furthermore, the relationship of the mixing height, as depicted
by the measurements, to the calculated ABL depth or other features of the ABL structure, is also examined. In particular,
the diurnal evolution of ABL depth is examined over the greater Athens area, employing four different ABL schemes plus a modified
version, whereby urban features are considered. Measurements for two selected days, when convective conditions prevailed and
a strong sea-breeze cell developed, were used for comparison. It was found that the calculated eddy viscosity profile seems
to better indicate the mixing height in both cases, where either a deep convective boundary layer develops, or a more confined
internal boundary layer is formed. For the urban scheme, the incorporation of both anthropogenic and storage heat release
provides promising results for urban applications. 相似文献
9.
10.
This paper presents a new method to estimate the height of the atmospheric boundary layer(ABL) by using COSMIC radio occultation bending angle(BA) data. Using the numerical differentiation method combined with the regularization technique, the first derivative of BA profiles is retrieved, and the height at which the first derivative of BA has the global minimum is defined to be the ABL height. To reflect the reliability of estimated ABL heights, the sharpness parameter is introduced, according to the relative minimum of the BA derivative. Then, it is applied to four months of COSMIC BA data(January, April, July, and October in 2008), and the ABL heights estimated are compared with two kinds of ABL heights from COSMIC products and with the heights determined by the finite difference method upon the refractivity data. For sharp ABL tops(large sharpness parameters), there is little difference between the ABL heights determined by different methods, i.e.,the uncertainties are small; whereas, for non-sharp ABL tops(small sharpness parameters), big differences exist in the ABL heights obtained by different methods, which means large uncertainties for different methods. In addition, the new method can detect thin ABLs and provide a reference ABL height in the cases eliminated by other methods. Thus, the application of the numerical differentiation method combined with the regularization technique to COSMIC BA data is an appropriate choice and has further application value. 相似文献
11.
One-dimensional turbulence (ODT) is a single-column simulation in which vertical motions are represented by an unsteady advective process, rather than their customary representation by a diffusive process. No space or time averaging of mesh-resolved motions is invoked. Molecular-transport scales can be resolved in ODT simulations of laboratory-scale flows, but this resolution of these scales is prohibitively expensive in ODT simulations of the atmospheric boundary layer (ABL), except possibly in small subregions of a non-uniform mesh.Here, two methods for ODT simulation of the ABL on uniform meshes are described and applied to the GABLS (GEWEX Atmospheric Boundary Layer Study; GEWEX is the Global Energy and Water Cycle Experiment) stable boundary-layer intercomparison case. One method involves resolution of the roughness scale using a fixed eddy viscosity to represent subgrid motions. The other method, which is implemented at lower spatial resolution, involves a variable eddy viscosity determined by the local mesh-resolved flow, as in multi-dimensional large-eddy simulation (LES). When run at typical LES resolution, it reproduces some of the key high-resolution results, but its fidelity is lower in some important respects. It is concluded that a more elaborate empirically based representation of the subgrid physics, closely analogous to closures currently employed in LES of the ABL, might improve its performance substantially, yielding a cost-effective ABL simulation tool. Prospects for further application of ODT to the ABL, including possible use of ODT as a near-surface subgrid closure framework for general circulation modeling, are assessed. 相似文献
12.
Atmospheric Boundary-Layer Dynamics with Constant Bowen Ratio 总被引：1，自引：1，他引：0
Amilcare Porporato 《Boundary-Layer Meteorology》2009,132(2):227-240
Motivated by the observation that the diurnal evolution of sensible and latent heat fluxes tends to maintain a constant Bowen
ratio, we derive approximate solutions of the ordinary differential equations of a simplified atmospheric boundary-layer (ABL)
model. Neglecting the early morning transition, the potential temperature and specific humidity of the mixed layer are found
to be linearly related to the ABL height. Similar behaviour is followed by the inversion strengths of temperature and humidity
at the top of the ABL. The potential temperature of the mixed layer depends on the entrainment parameter and the free-atmosphere
temperature lapse rate, while the specific humidity also depends on the free-atmosphere humidity lapse rate and the Bowen
ratio. The temporal dynamics appear only implicitly in the evolution of the height of the boundary layer, which in turn depends
on the time-integrated surface sensible heat flux. Studying the limiting behaviour of the Bowen ratio for very low and very
large values of net available energy, we also show how the tendency to maintain constant Bowen ratio during midday hours stems
from its relative insensitivity to the atmospheric conditions for large values of net available energy. The analytical expression
for the diurnal evolution of the ABL obtained with constant Bowen ratio is simple and provides a benchmark for the results
of more complex models. 相似文献
13.
The temperature and wind profiles in abaroclinic atmospheric boundary layer (ABL) are investigated.Assuming stationary conditions, the turbulent state in the ABL forstable and neutral conditions is uniquely determined by the Rossbynumber, the external stratification parameter and two externalbaroclinic parameters. A simple two-layer baroclinic model isdeveloped. It consists of a surface layer (SL) and overlyingEkman-type layer. The system of dynamic and heat transfer equations isclosed using K-theory. In the SL the turbulent exchangecoefficient is consistent with the results of similarity theorywhile in the Ekman layer it is assumed constant. The universalfunctions in the resistance, heat and humidity transfer laws arededuced from the analytical solutions for the wind and temperatureprofiles. The solutions of the ABL resistance laws for theinternal ABL parameters, necessary for the calculations of the ABLprofiles, are approximated in terms of the external ABLparameters. Favourable agreement of model results with theavailable experimental data is demonstrated. 相似文献
14.
建立了一个农林复合带地区一维非静力大气边界层能量闭合模式，对1000m以下的大气边界层内的风、温、湿作了24h的预报，并对下垫面3种不同参数化方案(农作物、森林、无植被)的输出结果与实测值进行了分析和比较；同时通过敏感性试验，突出比较了农作物和森林下垫面对大气边界层垂直流场，湍流垂直交换和湍能的影响。结果表明，本模式能改善边界层风速、位温和湿度预报的模拟效果，下垫面植被对边界层气象要素大小和分布有显著的作用，对湍能垂直分布有一定影响。 相似文献
15.
主要从理论、试验角度对大气边界层的研究进行了简要的回顾,尤其对近年来倍受关注的非均匀地表条件下的边界层研究进行了较详细的介绍,并对大气边界层的研究进行了展望。20世纪50年代,Monin和Obukhov提出的Monin-Obukhov相似理论,为现代大气边界层物理学奠定了基础。之后进行的多次大型综合性外场试验,不仅揭示和发现了大气边界层中的许多现象和规律,也验证和发展了Monin-Obukhov相似理论。80年代以后,非均匀地表条件下的大气边界层研究越来越受到关注,一些新的现象被揭示,新的问题被提出,同时也提出了一些新的概念和研究方法。未来10 a,除大气湍流机理等需长期坚持研究外,还应进一步开展非均匀复杂下垫面边界层研究、城市边界层研究和局地边界层气象预报研究。 相似文献
16.
V. Puygrenier F. Lohou B. Campistron F. Saïd G. Pigeon B. Bnech D. Sera 《Atmospheric Research》2005,74(1-4):329-353
Surface and remote-sensing instruments deployed during ESCOMPTE experiment over the Marseille area, along the Mediterranean coast, were used to investigate the fine structure of the atmospheric boundary layer (ABL) during sea-breeze circulation in relation to pollutant transport and diffusion. Six sea-breeze events are analyzed with a particular focus on 25 June 2001.Advection of cool and humid marine air over land has a profound influence on the daytime ABL characteristics. This impact decreases rapidly with the inland distance from the sea. Nearby the coast (3 km inland), the mixing height Zi rises up to 750 m and falls down after 15:00 (UT) when the breeze flow reaches its maximum intensity. A more classical evolution of the ABL is observed at only 11-km inland where Zi culminates in the morning and stabilizes in the afternoon at about 1000 m height.Fine inspection of the data revealed an oscillation of the sea-breeze with a period about 2 h 47 min. This feature, clearly discernable for 3 days at least, is present in several atmospheric variables such as wind, temperature, not only at the ground but also aloft in the ABL as observed by sodar/RASS and UHF wind profilers. In particular, the mixing height Zi deduced from UHF profilers observations is affected also by the same periodicity. This pulsated sea-breeze is observed principally above Marseille and, at the northern and eastern shores of the Berre pond.In summary, the periodic intrusion over land of cool marine air modifies the structure of the ABL in the vicinity of the coast from the point of view of stability, turbulent motions and pollutants concentration. An explanation of the source of this pulsated sea-breeze is suggested. 相似文献
17.
This paper is the second of a series devoted to the observation and analysis of coherent structures in the cloudy Atmospheric Boundary Layer (ABL) such as horizontal rolls or thermal cells. In the first paper, the TRAC (Turbulence Radar Aircraft Cells) experiment which is the observational support of this investigation based on coupled radar-aircraft measurements, was presented along with an overview of the main results of this campaign held in June 1993 in France. Here the analysis is focused on the spatial characteristics (length-scale, orientation ... ) of the coherent structures, their temporal evolution and vertical distribution deduced from the radar reflectivity fields acquired in clear air at several levels for five different ABLs. For that, an original and efficient image processing method able to extract the major mode of the organisation was developed. These characteristics are examined in relation to the dynamic and thermodynamic state of the ABL using mean and turbulent information as observed by the in-situ aircraft. These experimental results are the basis of a future Large Eddy Simulation modeling of an organised ABL which is in progress and will be the concern of the third paper in the series. 相似文献
18.
基于旋翼无人机开展大气边界层观测可为气象要素和大气污染物垂直结构的研究提供具有高时空解析能力的新方法,有助于深入理解低层大气物理化学变化机制。本文详述了旋翼无人机在开展大气边界层环境气象垂直观测实验的应用及优势。基于自主研发的旋翼无人机环境气象观测平台,通过开展传感器在无人机上不同的搭载位置,以及旋翼无人机与探空气球、高塔的对比观测实验,明确了旋翼无人机对气象环境观测的影响及合理的搭载方式。研究进一步在湖北重污染天气条件下开展了0—1000 m的大气边界层垂直观测,并研发了基于旋翼无人机姿态数据的大气边界层气象要素及污染物垂直观测的订正方法。结果表明:实验获取了2—10 m垂直分辨率的高质量大气廓线数据,可精细捕捉大气边界层及其逆温层高度和污染物浓度等要素的垂直变化特征。本文旨在为无人机观测的科研应用提供一种技术可行且数据可靠的观测手段。 相似文献
19.
Aircraft observations of the atmospheric boundary layer (ABL) over Arctic sea ice were made during non-stationary conditions
of cold-air advection with a cloud edge retreating through the study region. The sea-ice concentration, roughness, and ABL
stratification varied in space. In the ABL heat budget, 80% of the Eulerian change in time was explained by cold-air advection
and 20% by diabatic heating. With the cloud cover and inflow potential temperature profile prescribed as a function of time,
the air temperature and near-surface fluxes of heat and momentum were well simulated by the applied two-dimensional mesoscale
model. Model sensitivity tests demonstrated that several factors can be active in generating unstable stratification in the
ABL over the Arctic sea ice in March. In this case, the upward sensible heat flux resulted from the combined effect of clouds,
leads, and cold-air advection. These three factors interacted non-linearly with each other. From the point of view of ABL
temperatures, the lead effect was far less important than the cloud effect, which influenced the temperature profiles via
cloud-top radiative cooling and radiative heating of the snow surface. The steady-state simulations demonstrated that under
overcast skies the evolution towards a deep, well-mixed ABL may take place through the merging of two mixed layers one related
to mostly shear-driven surface mixing and the other to buoyancy-driven top-down mixing due to cloud-top radiative cooling. 相似文献