Determination of Area-Averaged Sensible Heat Fluxes with a Large Aperture Scintillometer over a Heterogeneous Surface – Flevoland Field Experiment     

W. M. L. Meijninger  O. K. Hartogensis  W. Kohsiek  J. C. B. Hoedjes  R. M. Zuurbier  H. A. R. De Bruin 《Boundary-Layer Meteorology》2002,105(1):37-62

To test the applicability of the scintillation method over a heterogeneous area an experiment was carried out in the summer of 1998 in Flevoland (The Netherlands). In the patchy area only four crops were grown namely sugar beet, potatoes, wheat and onions. From eddy covariance measurements it was found that the heterogeneity was mainly caused by differences in thermal properties. No variations in the aerodynamics roughness length were observed. Two large aperture scintillometers were installed at a height of 11.6 and 20.4 m. A good resemblance was found between the sensible heat fluxes derived from both LAS instruments and the area-averaged fluxes obtained from the in-situ eddy covariance measurements. The slight underestimation of the lower LAS could be assessed using a blending height model and an analytical footprint model. The results also indicated that when scintillometer measurements are made below the blending height the violation to Monin–Obukhov Similarity Theory is small and that reasonable fluxes can be obtained from path-averaged structure parameters.  相似文献   

Measurements Of Turbulence Transfer In The Near-Surface Layer Over The Southeastern Tibetan Plateau   总被引：5，自引：0，他引：5  

Lingen Bian  Zhiqiu Gao  Qiangde Xu  Longhua Lu  Yanjie Cheng 《Boundary-Layer Meteorology》2002,102(2):281-300

Turbulent flux measurements at Qamdo site over the Tibetan Plateau during TIPEX from May 18 to June 30, 1998 are presented. Sensible heat dominated,accounting for about 66% of the available energy (the sum of net radiation and soil heat flux) prior to the monsoon(dry period), reducing to about 31%, with latent heat increased to about 56% of available energy,in the monsoon season (wet period). Surface energy budget closure on average was about 0.80 (0.85)prior to the monsoon and 0.89 (0.76) during the monsoon using eddy correlation (profile) methods. The sum of latent and sensible heat fluxes calculated from the flux-profilemethod was smaller by about 15% than that from eddy correlation. Martano's method is used toestimate the surface aerodynamic roughness length z₀ and zero plane displacement d from singlelevel sonic anemometer data, giving d = 0.12 m and z₀ = 0.08 m. The overall neutral dragcoefficient (C_DN) and scalar coefficient (C_HN) were found to be C_DN = 0.0055and C_HN = 0.0059 in the southeastern area of Tibet. Their variations with the mean wind speed at 10 m are discussed.  相似文献   

An OGCM Simulation of Seasonal and Interannual Variabilities in the Surface—Layer Pacific of the Equatorial Band   总被引：1，自引：0，他引：1  

Boyin Huang  Zhengyu Liu 《大气科学进展》2002,19(2):219-235

The heat budget is analyzed in the surface-layer (0-50 m) Pacific of the equatorial band (10°S-10°N),using the simulation of an ocean general circulation model from 1945 to 1993. The analysis indicates that downward net surface heat flux from the atmosphere and ocean advective heat fluxes play distinct roles in seasonal and interannual variabilities of surface-layer ocean temperature. The surface heat flux dominantly determines the ocean temperature in the seasonal time-scale. But, it has a negative feedback to the ocean temperature in the interannual time-scale. The interannual variability of ocean temperature is largely associated with the cold advection from off-equatorial divergent flow in the central Pacific and from upwelling in the cold tongue. Both the surface heat flux and ocean advective heat fluxes are important to the ocean temperature during an El Nino event. The ocean advective heat fluxes are further associated with local westward trade wind in the central Pacific. These results are largely consistent with some regional observational analyses.  相似文献   

A simple yet more accurate model to calculate solar radiative flux in the inhomogeneous atmosphere     

Qiu Jinhuan 《大气科学进展》2002,19(3):433-447

A simple yet more accurate semiempirical model is developed to calculate solar radiative flux in the optically inhomogeneous atmosphere. In the model a parameterized expression of spherical reflectance and transmitance of the atmosphere is confirmed, and the weighted single scatter albedo and weighted asymmetric factor are introduced to fit four empirical correction factors responsible for radiative fluxes in the inhomogeneous atmosphere. For both clean and turbid models, there are 120060 sets of radiative flux simulations for accuracy checks of the model, which cover 0-50 cloud optical depths, 0-0.8 surface reflectance, Junge and Log-normal aerosol size distributions, and 0-0.05 imaginary parts of aerosol refractive indexes. In case of the homogeneous atmosphere, standard errors of the 120060 upward fluxes from the present model are 1.08% and 1.04% for clean and turbid aerosol models, respectively; and those of the downward fluxes are 4.12% and 3.31%. In case of the inhomogeneous atmosphere, standard errors of the upw ard fluxes from the present model are 3.01% and 3.48% for clean and turbid aerosol models.respectively; and those of the downward fluxes are 4.54% and 4.89%, showing a much better accuracy than the results calculated by using an assumption of the homogeneous atmosphere.  相似文献   

New evidence for a relation between wind stress and wave age from measurements during ASGAMAGE   总被引：7，自引：0，他引：7  

W.A. Oost  G.J. Komen  C.M.J. Jacobs  C. Van Oort 《Boundary-Layer Meteorology》2002,103(3):409-438

Data from the 1996 ASGAMAGE experiment, performed in the southern North Sea at research platform Meetpost Noordwijk (MPN), are analysed for the parameters affecting the momentum flux. The stress turns out to be quadratically related to the 10-m wind speed and linearly to the wind speed at a wavelength related level. The Charnock parameter (dimensionless roughness length) shows a pronounced correlation with wave age. This implies, due to a coupling between wave age and the steepness of the waves, a connection between the stress and the steepness. We find that our North Sea results are consistent withopen ocean observations. For a given wind speed the mean stress at MPN turns out to be higher because the wave age there is in general lower. We define and give an expression for a drag coefficient at a wavelength related level that can be calculated straightforwardly from the wave age and then reduced to a standard level.  相似文献   

An OGCM Simulation of Seasonal and Interannual Variabilities in the Surface-Layer Pacific of the Equatorial Band     

Boyin Huang  Zhengyu Liu Department of Atmospheric  Oceanic Sciences  University of Wisconsin-Madison W. Dayton St.  Madison  WI-  U.S.A. 《大气科学进展》2002,(2)

l. IntroductionThe physical mechanisms contro1ling t]de El Nifio event have been studied based on ob-servations in the equatorial Pacific (Weare l983; Reed l986; Hayes et al. l99l; McPhadenand Picaut l990; Frankignoul et al. 1996; Weisberg and Wang l997). One of the most impor-tant issues is whether the surface heat flux ojr ocean advective heat fluxes are dominant in con-trolling the sea surface temperature (SST). Some studies indicated that the SST is mainly con-trolled by the surface…  相似文献   

青藏高原北部的大气加热场特征   总被引：12，自引：9，他引：12  

季国良  顾本文  吕兰芝 《高原气象》2002,21(3):238-242

利用五道梁1994－1997年的实际观测资料，结合一些经验计算公式计算得到了1994－1997年青藏高原北部地区的大气加热场强度。结果表明，从4年平均情况来看，高原北部地区4－8月大气加热场为热源，10月－2月为冷源，3月和9月为转换时期；就年平均大气加热场强度年际变化来看，1994年和1995年为大气冷源，1996年和1997年则为大气热源；高原北部的大气加热场强度的年际变化主由地面感热输送的年际变化所决定。  相似文献   

Quantifying CO₂ fluxes from soil surfaces to the atmosphere     

L. K. Kabwe  M. J. Hendry  G. W. Wilson  J. R. Lawrence 《Journal of Hydrology》2002,260(1-4):1-14

Measurements of CO₂ fluxes from ground surface of the atmosphere (soil respiration) are needed to quantify biotic and abiotic reaction rates in unsaturated zones and to gain insight into the importance of these processes on global warming. The use of three techniques (dynamic closed chambers, static chambers, and gradient calculations) to determine soil respiration was assessed by measuring fluxes of microbially produced CO₂ from an unsaturated mesocosm (2.4 m dia.×3.2 m thick) and two unsaturated minicosms (0.58 m dia.×1.2 m thick), one maintained at 18–23 °C (HT) and the other at 5 °C (LT). By injecting known and constant CO₂ fluxes into the bottom of the HT minicosm and measuring the resulting fluxes, it was shown that the dynamic closed chamber (DCCS) technique yielded accurate measurements of fluxes over the range observed from natural unsaturated media. Over this same range, results showed that the concentration gradient method yielded reasonable estimates of fluxes but its accuracy was limited by uncertainties in both the concentration gradient and the gaseous diffusion coefficient in the soil atmosphere. The static chamber method underestimated the actual flux at higher CO₂ fluxes and when adsorption times of >24 h were used.  相似文献   

Exchange flux of total gaseous mercury between air and natural water surfaces in summer season   总被引：5，自引：0，他引：5  

冯新斌  Jonas Sommar 《中国科学D辑(英文版)》2002,45(3):211-220

The exchanges of mercury between surface and air are of significance in the biogeochemical cycling of Hg in the environment, but there are still few reliable data on air/surface exchange in aquatic systems. Field measurement campaigns over seawater surface at Kristineberg Marine Research Station (KMRS) and over Hovg?rds?n River surface at Knobesholm in southwestern Sweden were conducted to measure mercury flux using a dynamic flux chamber technique coupled with automatic mercury vapor-phase analyzers. Both sites show net emissions during summer time. Mercury fluxes measured over both river and seawater surfaces exhibit a consistently diurnal pattern with maximum fluxes during the daytime period and minimum fluxes during the nighttime period. At freshwater site, mercury flux is strongly correlated with the intensity of net solar radiation, and negatively correlated with relative humidity. A typical exponential relationship between mercury flux and water temperature was observed at freshwater measurement site. At seawater site, a strong correlation between mercury flux and intensity of solar radiation was obtained. The driving force of mercury emission from water surface to air is the super-saturation of dissolved gaseous mercury in aqueous phase.  相似文献   

新疆地区侏罗系中低变质煤储层吸附特征及煤层气资源前景   总被引：11，自引：2，他引：11  

胡宝林  杨起  刘大锰  车遥  黄文辉  蔚运江  宋晓梅 《现代地质》2002,16(1):77-82

利用高压吸附仪对新疆主要沉积盆地侏罗系煤储层的甲烷吸附能力进行了测试。测试结果表明中低变质煤的吸附能力普遍较低 ,且吸附能力随煤镜质组反射率值的增加而增加 ,随煤中水分的增加而减小 ,其原因与煤的微孔特征有关。根据煤储层的吸附兰氏体积 ,新疆侏罗系煤储层可分为 4类区 ,并认为新疆具有煤层气资源前景的地区分布在煤的吸附兰氏体积大于 12m3 /t的第三类区及第四类区  相似文献