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1.
Turbulent characteristics and bulk transfer coefficients over the desert in the HEIFE area 总被引：1，自引：0，他引：1
Ichiro Tamagawa 《Boundary-Layer Meteorology》1996,77(1):1-20
Observations of surface-layer turbulence and turbulent fluxes were made over a desert in northwestern China as a part of HEIFE (HEIhe river Field Experiment). These show that the normalized variations of the vertical wind component and of the air temperature obey Monin-Obukhov similarity well, especially in free convective conditions. However, the variations of specific humidity do not obey Monin-Obukhov similarity.Mean bulk transfer coefficients of sensible heat and momentum flux are obtained as functions of stability over a wide stability range from the observed data of turbulent fluxes and mast profiles. However, the bulk transfer coefficient for water vapor could not be obtained because of the large scatter of the data. In free convective conditions, the sensible heat flux was found to be approximately proportional to the 1.4 power of temperature difference between the surface and 20m. The bulk transfer coefficient of sensible heat is also obtained as a function of the bulk Richardson number for practical convenience. 相似文献
2.
3.
S. C. Colbeck 《Boundary-Layer Meteorology》1988,44(1-2):1-12
Profiles of temperature and humidity are calculated for a snow surface being cooled by outgoing radiation assuming no wind. These suggest that fog would necessarily form to block the cooling and, even in the absence of fog, the diffusion of water vapor to the surface could not account for observed rates of surface hoar growth. Therefore turbulent transfer to an interfacial sublayer with a very large temperature gradient must occur at least intermittently. In mountainous areas, gravity drainage of air over the interfacial sublayer probably accounts for the turbulence since air currents from a regional pressure gradient appear to transfer enough heat to the surface to prevent surface hoar growth. The vapor must diffuse through a 1 mm interfacial sublayer until the crystals reach a sufficient height to interact with the drainage wind. 相似文献
4.
Monin–Obukhov similarity functions for the structure parameters of temperature and humidity are needed to derive surface heat and water vapour fluxes from scintillometer measurements and it is often assumed that the two functions are identical in the atmospheric surface layer. Nevertheless, this assumption has not yet been verified experimentally. This study investigates the dissimilarity between the turbulent transport of sensible heat and water vapour, with a specific focus on the difference between the Monin–Obukhov similarity functions for the structure parameters. Using two datasets collected over homogeneous surfaces where the surface sources of sensible heat and water vapour are well correlated, we observe that under stable and very unstable conditions, the two functions are similar. This similarity however breaks down under weakly unstable conditions; in that regime, the absolute values of the correlations between temperature and humidity are also observed to be low, most likely due to large-scale eddies that transport unsteadiness, advection or entrainment effects from the outer layer. We analyze and demonstrate how this reduction in the correlation leads to dissimilarity between the turbulent transport of these two scalars and the corresponding Monin–Obukhov similarity functions for their structure parameters. A model to derive sensible and latent heat fluxes from structure parameters without measuring the friction velocity is tested and found to work very well under moderately to strongly unstable conditions (−z/L > 0.5). Finally, we discuss the modelling of the cross-structure parameter over wet surfaces, which is crucial for correcting water vapour effects on optical scintillometer measurements and also for obtaining surface sensible and latent heat fluxes from the two-wavelength scintillometry. 相似文献
5.
HUBEX试验区近地面层的湍流输送 总被引：8，自引：1，他引：7
1998年淮河流域能量和水循环试验(HUBEX)期间曾进行了1个月的近地面层湍流观测.分析不稳定条件下湍流的统计特性和谱特征,并与Monin-Obukhov相似理论进行了比较.结果表明,不稳定的时候各湍流量的统计特征与相似理论的预期相符.虽然不稳定条件下温度和湿度涨落的相关系数很高,谱的式样也相近,但湿度谱的峰值频率高于温度谱.协谱曲线的形状显示感热通量的谱峰较宽,表现出w和T在较宽范围的强相关性,而水汽通量谱在高频段下降很快,说明水汽的输送更多地出现在低频部分.从谱相关系数可见,在近中性的时候,各尺度湍流涡的热量输送效率普遍较低,随着不稳定性增强而显著提高.分析还发现,不论不稳定性的程度如何,小尺度湍流的水汽输送效率都较低.水汽通量谱的相关系数随稳定度的变化不如热通量的谱相关系数大,表明近中性时除小尺度湍流外其他湍流涡的水汽输送效率高于热量输送. 相似文献
6.
沙漠地区沙尘天气近地层湍流输送特征分析 总被引：12，自引：3，他引：12
利用1996－04－20－50－10在内蒙古自治区吉兰泰气象站以及1997－04－05－27在内蒙古自治区阿拉善右旗气象站观测到的风，温，湿廓线资料，应用空气动力学方法，计算了每天各观测时次的流动量通量，湍流感热通量和湍流潜热通量，并且比较分析了荒漠下垫面不同沙尘天气状况下的湍流动量通量，感热通量和潜热通量的日变化。结果表明，在沙漠地区春季无降水天气状况下，晴空条件下，白天热力湍流基于动力湍流，在近地层最重要的物质交换是湍流感热交换，浮尘天气条件下，近地层湍流输送较晴空天气条件下弱；扬沙天气条件下，近地层湍流感热交换和湍流动力量流感热通量的峰值大于交换，并且湍流动量通量的峰值较晴空峰值大将近一个量级，湍流感热通量的峰值大于浮尘天气峰值，但小于晴空条件下峰值，沙尘暴天气条件下，湍流动量通量和感热通量一样都是最重要的湍流交换，湍流交换强于扬沙天气，强的感热对沙漠地局地性沙尘暴的产生和加强起着重要作用。 相似文献
7.
一次热对流降水成因的分析和模拟 总被引：3，自引：0，他引：3
夏季受西太平洋副热带高压控制的中国大陆地区常发生热对流降水.文中首先利用TRMM卫星观测资料、地面自动站地表温度观测资料和NCEP资料分析了热对流降水的特征及其产生的背景条件;利用区域平均的水汽方程诊断了地表蒸发、水汽平流和水汽通量辐合项的贡献,分析了降水的水汽来源;进一步利用AREM区域数值预报模式,设计了4个敏感性试验,研究了陆气感热、潜热通量对降水的贡献.结果表明,在副热带高压控制的地区,白天强烈的非均匀地表感热加热可导致低层热空气块突破环境下沉气流而上升,周围空气补充形成辐合运动.低层空气的辐合上升既可引起水汽的汇聚,又可把低层的水汽输送到高层.同时非均匀陆面特征造成的非均匀感热和潜热通量的共同作用增强了大气的位势不稳定度,触发了对流,但感热通量对热对流降水的贡献比潜热通量略大.热对流降水的水汽除部分来自地表蒸发外,另一部分来自低层的水平通量辐合.定量计算表明二者对大气可降水量的贡献基本相当,而平流水汽的贡献很小. 相似文献
8.
太原城市下垫面扩张对边界层特征影响的个例研究 总被引：1，自引：0，他引：1
通过高分辨率卫星夜间灯光数据获取最新的城市地表分布,并利用高分辨率数值模式对2013年8月14~16日太原区域的一次高温过程进行研究,探讨城市下垫面扩张对大气边界层的影响。结果表明：基于DMSP/OLS夜间灯光数据对模式中地表参数修正后,能够更准确地反映太原主城区和高速公路沿线小规模建筑群的扩张,有效改善了模式的预报性能,显著提高对近地面气温、地表温度的预报能力。城市下垫面的扩张,使城区夜间升温明显,热岛强度增强。与1992年的城市化状况相比,晴空天气条件下,2012年太原城区夜间气温上升5℃,热岛强度升高2~3℃。城市下垫面扩张,改变了地表能量分配关系,使得地表感热传输明显加强,潜热通量明显减弱,城市冠层作用下的储热能力增强。边界层内部湍流交换、水汽输送等的进一步研究表明：城市地表水汽输送减弱,边界层水汽含量减少,2~4 km高度的水汽含量增加,湍流动能的影响高度增高,湍流混合加剧;14：00,城区边界层高度抬高了800 m,城市上空混合层加深,持续时间更长。 相似文献
9.
Dennis Baldocchi 《Boundary-Layer Meteorology》1992,61(1-2):113-144
An integrated canopy micrometeorological model is described for calculating CO2, water vapor and sensible heat exchange rates and scalar concentration profiles over and within a crop canopy. The integrated model employs a Lagrangian random walk algorithm to calculate turbulent diffusion. The integrated model extends previous Lagrangian modelling efforts by employing biochemical, physiological and micrometeorological principles to evaluate vegetative sources and sinks. Model simulations of water vapor, CO2 and sensible heat flux densities are tested against measurements made over a soybean canopy, while calculations of scalar profiles are tested against measurements made above and within the canopy. The model simulates energy and mass fluxes and scalar profiles above the canopy successfully. On the other hand, model calculations of scalar profiles inside the canopy do not match measurements.The tested Lagrangian model is also used to evaluate simpler modelling schemes, as needed for regional and global applications. Simple, half-order closure modelling schemes (which assume a constant scalar profile in the canopy) do not yield large errors in the computation of latent heat (LE) and CO2 (F
c
) flux densities. Small errors occur because the source-sink formulation of LE andF
c are relatively insensitive to changes in scalar concentrations and the scalar gradients are small. On the other hand, complicated modelling frames may be needed to calculate sensible heat flux densities; the source-sink formulation of sensible heat is closely coupled to the within-canopy air temperature profile. 相似文献
10.
Estimation of Turbulent Fluxes Using the Flux-Variance Method over an Alpine Meadow Surface in the Eastern Tibetan Plateau 总被引：1，自引：0，他引：1
The flux-variance similarity relation and the vertical transfer of scalars exhibit dissimilarity over different types of surfaces,resulting in different parameterization approaches of relative transport efficiency among scalars to estimate turbulent fluxes using the flux-variance method.We investigated these issues using eddycovariance measurements over an open,homogeneous and flat grassland in the eastern Tibetan Plateau in summer under intermediate hydrological conditions during rainy season.In unstable conditions,the temperature,water vapor,and CO2 followed the flux-variance similarity relation,but did not show in precisely the same way due to different roles(active or passive) of these scalars.Similarity constants of temperature,water vapor and CO2 were found to be 1.12,1.19 and 1.17,respectively.Heat transportation was more efficient than water vapor and CO2.Based on the estimated sensible heat flux,five parameterization methods of relative transport efficiency of heat to water vapor and CO2 were examined to estimate latent heat and CO2 fluxes.The strategy of local determination of flux-variance similarity relation is recommended for the estimation of latent heat and CO2 fluxes.This approach is better for representing the averaged relative transport efficiency,and technically easier to apply,compared to other more complex ones. 相似文献
11.
Osamu Tsukamoto 《Boundary-Layer Meteorology》1986,35(4):349-368
The turbulent structure of the planetary boundary layer (PBL) is investigated based on measurements from a 213 m meteorological tower. It is found that the sensible heat flux decreases with height, resulting in a temperature increase during the daytime. On the other hand, the water vapor flux is almost constant with height and the diurnal variation of specific humidity is not so clear. Time variations of sensible heat flux and water vapor flux are closely correlated to the variation of net radiation and some differences are seen in their response times. Transient processes in the mixed layer including those related to the moisture structure are also investigated during periods of development and disappearance of the layer. 相似文献
12.
城市边界层动量和保守物通量的特征 总被引：2，自引：0，他引：2
利用2005年1-5月北京325 m气象塔47 m高度的湍流脉动资料(风速、温度、水汽和CO2),对城市边界层冠层内的湍流运动统计特征(相似关系、高阶矩、通量和谱等)进行了分析。其中,谱分析的结果表明,城市冠层内稳定度对湍流谱的影响比较小,而水平风速的影响比较大。因此,速度和温度的相似关系在夜间稳定条件下也成立。但是,由于水汽和CO2还受其他因素的影响,相似关系并不适用。更高阶矩的研究表明它们的陡峭度与偏斜度之间存在平方关系。而水汽和CO2之间也存在差异,它们的通量日变化特征明显不同,CO2通量的日变化更能体现人类活动的影响。同时,感热通量、潜热通量和CO2通量存在季节变化,尤其是潜热通量季节差异很大。 相似文献
13.
利用位于青藏高原东侧理塘大气综合观测站2008年观测资料,分析了高寒草甸下垫面上地表通量的时间变化特征,确定了温度、水汽和CO2的归一化标准差在不稳定情况下随稳定度变化的通量方差关系,应用通量方差法对感热、潜热和CO2通量进行了计算,并与涡旋相关系统的观测结果进行了比较。结果表明：地表通量月平均日变化呈较为规则的日循环特征,季节变化特征也很明显,雨季（5-9月）潜热大于感热,干季则以感热为主,CO2通量以6-9月值最大。在不稳定条件下,温度、水汽和CO2的归一化标准差随稳定度的变化均满足-1/3规律,其通量方差相似性常数分别为1.2,1.4和0.9。通量方差法估算出的通量值与涡旋相关观测得到的通量值有较好的一致性,但感热通量的效果优于潜热通量和CO2通量。该方法高估了感热通量尤其是潜热通量,而低估了CO2通量。采用直接观测的感热通量值计算潜热通量和CO2通量可改善计算结果。 相似文献
14.
根据“第三次青藏高原大气科学试验” 2014年7、8月青藏高原西南部狮泉河站、东南部林芝站的3 m涡动相关系统原始数据和10 Hz湍流资料以及中国气象局台站观测资料、JRA-55（Japanese 55-year Reanalysis）逐日再分析资料、GPCP（Global Precipitation Climatology Project）全球降水逐日观测资料,分别讨论了这两个站在10~20天低频振荡的天气背景下其干、湿位相近地层气象要素的日变化特征以及湍流变化特征。结果表明:两站高低空环流场、水汽通量场、热源的10~20天低频分量在其干、湿位相期间的配置相反。低频地表感热和潜热的不同变化对降水的影响分别在高原西部和东部有不同表现。狮泉河站的低频振荡在纬向上自西向东传播,而林芝站的低频振荡在纬向上自东向西传播,结果表明这两个站分别存在两种不同起源的低频振荡。两站干、湿位相的近地面气象要素以及湍流通量具有明显的日变化特征,通常温度极大值出现在午后14时（北京时,下同）,但狮泉河站干、湿位相的温度极大值均出现在夜间20时;由波文比可知,狮泉河站湿位相全天以潜热为主导,干位相期间,06时之前以潜热为主,06时之后以感热为主;林芝站干、湿位相均为08时之前以感热为主,08时之后以潜热为主。两站湍流平均动能与平均风速正相关,垂直动量表现为向下传输,热量和水汽表现为向上传输。 相似文献
15.
A Note on the Flux-Variance Similarity Relationships for Heat and Water Vapour in the Unstable Atmospheric Surface Layer 总被引：12，自引：11，他引：1
Atmospheric surface layer (ASL) experiments over the past 10 years demonstrate that the flux-variance similarity functions for water vapour are consistently larger in magnitude than their temperature counterpart. In addition, latent heat flux calculations using the flux-variance method do not compare as favorably to eddy- correlation measurements when compared to their sensible heat counterpart. These two findings, in concert with measured heat to water vapour transport efficiencies in excess of unity, are commonly used as evidence of dissimilarity between heat and water vapour transport in the unstable atmospheric surface layer. In this note, it is demonstrated that even if near equality in flux-profile similarity functions for heat and water vapour is satisfied, the flux-variance similarity functions for water vapour are larger in magnitude than temperature for a planar, homogeneous, unstably-stratified turbulent boundary-layer flow. 相似文献
16.
The Bowen-ratio profile method for calculating total carbon dioxide, latent heat, and sensible heat flux density above a corn crop was used by measuring temperature, water vapor, and CO2 concentrations at several heights in the aerodynamic boundary layer of the crop. The ratio (α) of sensible heat flux density to carbon dioxide flux density as well as the Bowen ratio (β) were used in the computations. The two ratios, α and β were determined graphically from the slopes of linear plots of temperature vs CO2 concentration and vs water vapor. Each of the energy flux densities was computed from the two ratios and net radiation minus soil heat flux density. An analysis of probable error was performed on the Bowen-ratio profile method to evaluate the accuracy of the flux density estimates. Less than 10% error was found for latent heat flux density and less than 15% for carbon dioxide flux density under normal midday conditions for the instrumentation used. However, the carbon dioxide flux density error increased to over 40% when the sensible heat flux was small. 相似文献
17.
18.
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
19.
The radiative forcings and feedbacks that determine Earth’s climate sensitivity are typically defined at the top-of-atmosphere (TOA) or tropopause, yet climate sensitivity itself refers to a change in temperature at the surface. In this paper, we describe how TOA radiative perturbations translate into surface temperature changes. It is shown using first principles that radiation changes at the TOA can be equated with the change in energy stored by the oceans and land surface. This ocean and land heat uptake in turn involves an adjustment of the surface radiative and non-radiative energy fluxes, with the latter being comprised of the turbulent exchange of latent and sensible heat between the surface and atmosphere. We employ the radiative kernel technique to decompose TOA radiative feedbacks in the IPCC Fourth Assessment Report climate models into components associated with changes in radiative heating of the atmosphere and of the surface. (We consider the equilibrium response of atmosphere-mixed layer ocean models subjected to an instantaneous doubling of atmospheric CO2). It is shown that most feedbacks, i.e., the temperature, water vapor and cloud feedbacks, (as well as CO2 forcing) affect primarily the turbulent energy exchange at the surface rather than the radiative energy exchange. Specifically, the temperature feedback increases the surface turbulent (radiative) energy loss by 2.87 W m?2 K?1 (0.60 W m?2 K?1) in the multimodel mean; the water vapor feedback decreases the surface turbulent energy loss by 1.07 W m?2 K?1 and increases the surface radiative heating by 0.89 W m?2 K?1; and the cloud feedback decreases both the turbulent energy loss and the radiative heating at the surface by 0.43 and 0.24 W m?2 K?1, respectively. Since changes to the surface turbulent energy exchange are dominated in the global mean sense by changes in surface evaporation, these results serve to highlight the fundamental importance of the global water cycle to Earth’s climate sensitivity. 相似文献
20.
使用鄱阳湖北部70 m气象塔湍流和梯度观测数据,分析了2011年6月6日夜间一次暴雨过程中近地面边界层特征.结果表明,此次过程是在高空低槽和西南急流的天气背景下,受鄱阳湖复杂地表影响产生的局地性强降水.强降水发生前受东南暖平流影响,近地面边界层中水汽累积,不稳定性增加;强降水过程中,近地层感热、潜热通量迅速增加,同时,近地面层湍流动量通量下传和水平输送增加,鄱阳湖的水汽输送加强降水强度.另外,强降水过程中,近地面湍流动能迅速增大并达到最大值,而平均动能的增大发生在强降水结束后,表明地表作用明显,近地面边界层的湍流场为暴雨提供动力条件.尺度分析表明,强降水前,中尺度动量通量占主要地位,降水过程中湍流动量通量显著加强. 相似文献