共查询到20条相似文献，搜索用时 15 毫秒
1.
Increased heat fluxes near a forest edge 总被引：1，自引：0，他引：1
W. Klaassen P. B. van Breugel E. J. Moors J. P. Nieveen 《Theoretical and Applied Climatology》2002,72(3-4):231-243
Summary ?Observations of sensible and latent heat flux above forest downwind of a forest edge show these fluxes to be larger than
the available energy over the forest. The enhancement averages to 56 W m−2, or 16% of the net radiation, at fetches less than 400 m, equivalent to fetch to height ratios less than 15. The enhancement
of turbulent energy fluxes is explained by advection and increases with the difference in temperature and humidity of the
air over the upwind area as compared to the forest. The relatively high temperature and humidity of the upwind air are not
caused by high surface heat fluxes, but are explained by the relatively low aerodynamic roughness of the upwind surface. Although
the heat fluxes over forest are enhanced, the momentum fluxes are almost adjusted to the underlying forest. The different
behaviour of heat and momentum fluxes is explained by absorption of momentum by pressure gradients near the forest edge. It
is concluded that fetch requirements to obtain accurate surface fluxes from atmospheric observations need to be more stringent
for scalar fluxes as compared to momentum fluxes.
Received November 23, 2001; accepted May 13, 2002 相似文献
2.
C. Jacovides P. Kerkides G. Papaioannou F. B. Smith 《Theoretical and Applied Climatology》1992,45(2):145-154
Summary Hourly lysimetric and micrometeorological data taken over a grass surface at the Meteorological Research Unit, Cardington U.K. have been analysed. A temperature difference and measurements of wind speed at only one height, combined with an independently estimated effective roughness length allowed sensible heat and momentum fluxes determination by the profile method on an hourly basis. The estimates are compared with direct measurements of sensible heat and friction velocity obtained by the eddy correlation method. The sensible and latent heat fluxes are also modelled by the resistance method. Equations based on the Monin—Obukhov similarity theory are used to account for stability effects through various forms of parameterization Aerodynamic and surface resistances, necessary for the Penman—Monteith equation are calculated from routinely measured meteorological data. The profile method for estimation of sensible heat flux and friction velocity is found to work excellently on the discussed daytime experimental data which correspond mainly to near neutral or slightly unstable conditions.Surface latent and sensible heat fluxes can also be described very well by the resistance method. A slightly better estimate of the sensible heat flux is achieved when stability corrections are taken into account. On the contrary Penman-Monteith equation for estimating latent heat flux is insensitive to adjustments for atmospheric stability.The comparison of the various methods leads to the establishment of empirical relationships which correlate various quantities such as soil heat flux, resistances, evapotranspiration etc. to routinely measured meteorological data.With 8 Figures 相似文献
3.
Regional-Scale Heat and Water Vapour Fluxes in an Agricultural Landscape: An Evaluation of CBL Budget Methods at OASIS 总被引：1，自引：0，他引：1
Helen A. Cleugh Michael R. Raupach Peter R. Briggs Peter A. Coppin 《Boundary-Layer Meteorology》2004,110(1):99-137
This paper evaluates convective boundary layer (CBL) budget methods as a tool for estimating regionally averaged sensible and latent heat fluxes for the study region used in OASIS (Observations at Several Interacting Scales). This is an agricultural region of mixed cropping and grazing extending about 100 km west of the town of Wagga Wagga, NSW, Australia.The analysis proceeds in three stages: first, a simpleone-dimensional model of the well-mixed layer (the CBL slab model), forced with measurements of the surface heat and evaporation fluxes, is evaluated by comparing measured and modelled CBL temperature, humidity and depths. A comparison of several entrainment schemes shows that a simple model, where the entrainment kinetic energy is parameterised as a fraction (3) of the surface sensible heat flux, works well if is set to 0.5. Second, the slab model is coupled to a Penman–Monteith model of surface evaporation to predict regional scale evaporation and thence heat fluxes. Finally, the integral CBL budget approach, which is an inverse method using theone-dimensional slab model, is used to infer regional heat and evaporation fluxes from measured time series of CBL temperature and humidity.We find that the simple CBL slab model works reasonably well for predicting CBL depth and very well for CBL temperature, especially if approximate estimates of subsidence velocity and warming due to advection are included. Regional sensible heat fluxes estimated from the integral CBL method match those measured, although the method is very sensitive to measurement errors. Measurement-model differences were larger for short integration times, because the well-mixed assumptions are violated at particular times of the day. The corollary is that `whole-day' (0530–1530 h) estimates are in reasonable agreement with measured values. Integral methods could not be used to infer the regional evaporation flux directly because CBL humidity profiles were complex and often not well mixed until mid-afternoon. We recommend that regional evaporation fluxes be predicted either from a coupled Penman–Monteith – CBL slab model, or inferred as a residual term from estimates of the regionally averaged available energy and sensible heat flux. Furthermore, we show that inferring fluxes via integral methods will always be difficult when the scalar concentrations have either a large surface source and free atmosphere sink (in the case of water vapour and methane), or a large surface sink and upper level source (in the case of CO2). 相似文献
4.
Regional turbulent statistics over contrasting natural surfaces 总被引：1，自引：0，他引：1
T. J. Lyons Li Fuqin J. M. Hacker Wan-Li Cheng Huang Xinmei 《Meteorology and Atmospheric Physics》2001,78(3-4):183-194
Summary
Regional turbulent fluxes of momentum, sensible and latent heat collected over both agricultural and native vegetation in
the south west of Australia are presented. Analysis of the energy spectrum illustrates that the most energetic eddies are
between scales of 20 metres to 5 kilometres and highlights the spatial distance required to obtain representative regional
fluxes. For the sensible heat flux, this distance is a function of measurement height whereas the latent flux is also influenced
by surface variability. Statistics of these fluxes highlight that for the unstable surface layer, despite marked differences
in the underlying vegetation and the corresponding sources of heat and moisture, heat is transported more efficiently than
water vapour from the ground surface.
Received October 9, 2000/Revised April 23, 2001 相似文献
5.
对临海沙漠地区非均匀地表区域地表能量通量和蒸发(蒸散)的研究,是一个十分重要但又是一个难点问题。本文提出了1个基于卫星遥感和地面观测的参数化方案,并把其应用于沙特阿拉伯吉达地区,利用1个景的陆地资源卫星Landsat-7E^TM^ 资料进行了分析研究,得到了一些有关临海沙漠地区非均匀地表区域地表特征参数、植被参数和地表能量通量的新概念。最后讨论了所提出的参数化方案的适用范围和需改进之处。 相似文献
6.
Jens Bange Thomas Spieß Marcus Herold Frank Beyrich Barbara Hennemuth 《Boundary-Layer Meteorology》2006,121(1):127-151
Turbulent fluxes of sensible and latent heat were measured with the helicopter-borne turbulence probe Helipod over a heterogeneous landscape around the Meteorological Observatory Lindenberg during the STINHO-2 and LITFASS-2003 field experiments. Besides the determination of area-averaged heat fluxes, the analysis focused on different aspects of the response of the turbulent structure of the convective boundary layer (CBL) on the surface heterogeneity. A special flight pattern was designed to study flux profiles both over quasi-homogeneous sub-areas of the study region (representing the major land use types—forest, farmland, water) and over a typical mixture of the different surfaces. Significant differences were found between the heat fluxes over the individual surfaces along flight legs at about 80 m above ground level, in agreement with large-aperture scintillometer measurements. This flux separation was still present during some flights at levels near the middle of the CBL. Different scales for the blending height and horizontal heterogeneity were calculated, but none of them could be identified as a reliable indicator of the mixing state of the lower CBL. With the exception of the flights over water, the latent heat flux measurements generally showed a larger statistical error when compared with the sensible heat flux. Correlation coefficients a nd integral length scales were used to characterise the interplay between the vertical transport of sensible and latent heat, which was found to vary between ‘fairly correlated’ and ‘decoupled’, also depending on the soil moisture conditions. 相似文献
7.
Surface turbulent flux measurements over the Loess Plateau for a semi-arid climate change study 总被引：2，自引：0，他引：2
In order to provide high quality data for climate change studies, the data quality of turbulent flux measurements at the station
of SACOL (Semi-Arid Climate & Environment Observatory of Lanzhou University), which is located on a semi-arid grassland over
the Loess Plateau in China, has been analyzed in detail. The effects of different procedures of the flux corrections on CO2, momentum, and latent and sensible heat fluxes were assessed. The result showed that coordinate rotation has a great influence
on the momentum flux but little on scalar fluxes. For coordinate rotation using the planar fit method, different regression
planes should be determined for different wind direction sectors due to the heterogeneous nature of the ground surface. Sonic
temperature correction decreased the sensible heat flux by about 9%, while WPL correction (correction for density fluctuations)
increased the latent heat flux by about 10%. WPL correction is also particularly important for CO2 fluxes. Other procedures of flux corrections, such as the time delay correction and frequency response correction, do not
significantly influence the turbulent fluxes. Furthermore, quality tests on stationarity and turbulence development conditions
were discussed. Parameterizations of integral turbulent characteristics (ITC) were tested and a specific parameterization
scheme was provided for SACOL. The ITC test on turbulence development conditions was suggested to be applied only for the
vertical velocity. The combined results of the quality tests showed that about 62%–65% of the total data were of high quality
for the latent heat flux and CO2 flux, and as much as about 76% for the sensible heat flux. For the momentum flux, however, only about 35% of the data were
of high quality. 相似文献
8.
南疆沙漠腹地大气边界层湍流通量特征的观测研究 总被引：4，自引：0，他引：4
利用新疆塔中站2006年4月、8月的三维风速。温度和水汽脉动资料,运用涡旋相关法计算得到了春、夏季塔中10m高度的动量、感热和潜热通量。结果表明,塔中地区地表热量输送以感热输送为主。春季每天的最大感热通量变化范围为120—320W·m^-2,月平均值为220W·m^-2;夏季最大感热通量的变化范围为140—340W·m^-2,月平均值为230W·m^-2。感热通量值在夜间为负,白天为正,符号的改变出现在日出、日落前后。夏季潜热通量最大值一般为20—60W·m^-2,平均值为27W·m^-2,潜热通量比感热通量小一个量级。春季动量通量的平均值为-0．063W·m^-2,夏季动量通量的平均值为-0．091W·m^-2。日变化规律比较明显,日出后,动量向下传输增大,在09-10时（地方时）出现一个最大值,随后动量向下传输并开始减小。 相似文献
9.
In this study, the performances of the Community Atmosphere Model (CAM) and Pleim–Xiu (PX) surface layer parameterization schemes are investigated by using field observations. The parameterization schemes are evaluated against continuous momentum and sensible heat flux observations measured at two flat and homogeneous grassland sites in the suburb of Nanjing, eastern China. The observations were conducted from 30 December 2014 to 18 April 2017 at Jiangxinzhou and from 9 February 2015 to 26 March 2018 at Jiangning. It is found that the momentum flux is overall in good agreement with the observation, and the sensible heat flux is overestimated. The parameterizations of the momentum and sensible heat fluxes well capture the diurnal and seasonal patterns seen in the observations at the two sites. At Jiangxinzhou, the PX parameterization underestimates the momentum flux throughout the day and the CAM parameterization slightly overestimates it around the noon, while they underestimate the momentum flux throughout the year. The two parameterizations overestimate the sensible heat flux in the daytime as well as over the entire year. At Jiangning, the two parameterizations overestimate the momentum flux throughout the day and the sensible heat flux in the daytime, and overestimate both of them over the entire year. The two parameterizations are not significantly different from each other in reproducing the turbulent fluxes at the same site, while they perform differently at the two sites in terms of statistics. In addition, the parameterized fluxes increase with increased roughness length. 相似文献
10.
The estimation of the sensible heatflux from thermal infrared temperature requires anestimate of the excess resistance to be added to theaerodynamic resistance to the transfer of heat fromthe surface. This excess resistance can be expressedin terms of kB-1. An earlier studysuggested that the sensible heat flux over semi-aridregions could be derived from satellite thermalinfrared temperature using a value of kB-1= 7. Values of kB-1 were derived frommeasurements of sensible heat flux, radiometricsurface temperature, air temperature and wind speedtaken over millet, savannah and open forest sitesduring HAPEX-Sahel. These were comparable to valuesderived over similar sites during a previous study. Sensible and latent heat fluxes were estimated usingno excess resistance, kB-1 = 7 andkB-1 set to the values derived from theHAPEX-Sahel data set. There was an improvement on theestimated fluxes when an excess resistance wasincorporated. However, there was no apparentdifference between the errors in the estimated fluxeswith kB-1 set to either the derived orfixed values. This provides additional support forthe use of kB-1 = 7 in the derivation ofsurface fluxes from satellite data for sparsecanopies. 相似文献
11.
根据1998年南海季风试验西沙海面铁塔梯度观测资料，利用总体（Bulk）系数法和多层结通量廓线法对西沙海面的海-气通量进行了估算，得出两种方法估算的潜热通量、感热通量基本一致。总体系数法估算的潜热通量比多层结通量廓线法略大1～3 W·m-2，感热通量小0～1.5 W·m-2。一般而言，季风爆发期间潜热输送逐渐增加；季风爆发前期夜间潜热通量比季风爆发后期大；季风爆发后期，白天潜热通量明显大于爆发初期和中期。感热通量季风爆发前海面向大气输送，爆发后期大气向海面输送。动量通量和摩擦速度随风速增加。 相似文献
12.
甘肃马衔山区陆面过程与降水的研究 总被引：1，自引：0，他引：1
采用定西的麦田微气象观测,定西、兰州的辐射观测和马衔山区34个气象、水文和雨量站的气候资料,结合NOAA-16卫星的AVHRR资料以及反演的地表植被盖度和反射率,并用SEBAL算法推导出夏季地表净辐射、感热、潜热、土壤热通量密度的区域分布特征,并分析陆面过程对降水的影响。结果表明:本区降水的空间分布与夏季植被盖度对应最好,相关系数高达0.722,其次是土壤热通量和潜热通量,相关系数分别为-0.65和0.615。这表明森林通过降低地表反射率和表面温度,不仅增加地表净辐射,而且减少其用于感热和土壤热通量的消耗。由于林区地表水分多,从而将接收较多的太阳辐射能主要用于蒸散,增加边界层中的水汽。故林区降水远大于植被稀疏的半干旱黄土梁。 相似文献
13.
The impact of sea waves on sensible heat and momentum fluxes is described. The approach is based on the conservation of heat and momentum in the marine atmospheric surface layer. The experimental fact that the drag coefficient above the sea increases considerably with increasing wind speed, while the exchange coefficient for sensible heat (Stanton number) remains virtually independent of wind speed, is explained by a different balance of the turbulent and the wave-induced parts in the total fluxes of momentum and sensible heat.Organised motions induced by waves support the wave-induced stress which dominates the surface momentum flux. These organised motions do not contribute to the vertical flux of heat. The heat flux above waves is determined, in part, by the influence of waves upon the turbulence diffusivity.The turbulence diffusivity is altered by waves in an indirect way. The wave-induced stress dominates the surface flux and decays rapidly with height. Therefore the turbulent stress above waves is no longer constant with height. That changes the balance of the turbulent kinetic energy and of the dissipation rate and, hence the diffusivity.The dependence of the exchange coefficient for heat on wind speed is usually parameterized in terms of a constant Stanton number. However, an increase of the exchange coefficient with wind speed is not ruled out by field measurements and could be parametrized in terms of a constant temperature roughness length. Because of the large scatter, field data do not allow us to establish the actual dependence. The exchange coefficient for sensible heat, calculated from the model, is virtually independent of wind speed in the range of 3–10 ms-1. For wind speeds above 10 ms-1 an increase of 10% is obtained, which is smaller than that following from the constant roughness length parameterization.The investigation was in part supported by the Netherlands Geosciences Foundation (GOA) with financial aid from the Netherlands Organization for Scientific Research (NWO). 相似文献
14.
Estimation of areally-averaged surface fluxes 总被引：6，自引：1，他引：6
Martin Claussen 《Boundary-Layer Meteorology》1991,54(4):387-410
The concept of blending height is used to estimate areally averaged surface fluxes of momentum and heat in a stratified, horizontally inhomogeneous surface-layer flow. This concept is based on the assumption that at sufficiently large heights above a heterogeneous surface, subsequent surface modifications will not be recognizable in the flow individually, but overall flux and mean profiles will represent the surface condition of a large area. The height at which the flow becomes approximately independent of horizontal position is called blending height according to Wieringa (1986).Here, it is proposed to classify the ground surface in a surface-layer grid box of a larger-scale model into several land-use categories. Surface momentum and heat fluxes should be estimated for each category at the blending height. The grid-averaged surface fluxes are to be obtained by the average of surface fluxes on each land-use surface weighted by its fractional area. The postulate of computing the surface fluxes at the blending height leads to a new formulation of turbulent transfer coefficients.The proposed parameterization has been tested by employing a small-scale numerical model as a surface-layer grid box of a hypothesized larger-scale model. Several quite different flow configurations have been studied in order to investigate the performance of the new parameterization. Generally, the relative errors of estimated averaged surface fluxes are found to be well within ±10%. 相似文献
15.
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
16.
Measurements made as part of studies of the evolution of the planetary boundary layer (the Sangamon experiments of 1975 and 1976) are used to compare the surface eddy fluxes of heat and momentum over adjacent fields of soybeans and maize. Although the maize canopy was much taller and rougher than that of the soybeans, daytime eddy fluxes of momentum over the maize exceeded those over the soybeans by only about 35%, in good agreement with predictions based on PBL similarity theory. Heat flux was about 10% greater over the maize, probably as a consequence of greater evaporation over the soybeans. Infrared surface temperatures generally differed by less than 0.4 °C and net radiation by less than 10%. For the soybean canopy, the momentum displacement height was found to be located at approximately 90% of the crop height, and the roughness length was about 5%. The roughness length for sensible heat transfer was found to be 2–3% of the soybean canopy height. For the maize canopy, the momentum displacement height was about 60% of the crop height, and the roughness length about 7%.Work supported under the auspices of the U.S. Department of Energy. 相似文献
17.
With the marine ship observation data set obtained by three cruise-phases of Chinese Xi-angyanghong 5 from November 5,1992 to February 19,1993 in the TOGA-COARE IOP at 2°S,156°E.the sea surface fluxes at this point are estimated by three different bulk schemes.Firstly.aquasi-linear relation is found between the neutral drag coefficients and wind speed.Then,the sta-bility-dependent drag and heat transfer coefficients are solved in the iterative method.Based onthus-derived transfer coefficients,the momentum,sensible and latent heat fluxes are calculated.In the warm pool region,the fluxes corresponding to the westeily winds are much greater thanthose of the easterly trade winds.The magnitude of sea surface fluxes depends upon the atmo-spheric stability as well,in particular in the case of weak wind condition.The estimated sea sur-face net heat budget shows that considerable amount of heat transport from ocean to atmosphere ismainly produced by the effective longwave radiation,latent and sensible heat fluxes.Among themthe value of latent heat flux is the largest and the sensible heat flux is the smallest.Finally,an ac-curacy analysis is made by direct measurements with the eddy-correlation method on the JapaneseR/V Hakuho board at the same time.It is shown that the bulk-derived fluxes are acceptable withmuch confidence.The estimated effective longwave radiation is used to compare with those by di-rect observations on Xiangyanghong 5.This research is compared with TOGA investigation in thetropical western Pacific. 相似文献
18.
关于用台站资料估算西北干旱区夏季感热通量的热力参数化比较 总被引：2，自引：0，他引：2
气象台站观测的气象要素可能受城市化等因子的影响而与野外试验站的观测存在一定的差异,这影响野外试验获取的热力参数直接应用于西北干旱区台站感热通量的估算。本文选取了一些常用的热力参数化方案(包括Z10、B82、Z98、Y08和Z12等方案),通过敦煌站夏季估算的感热通量与野外观测的比较以及对整个西北干旱区夏季感热通量的估算,评价了这些热力参数化对动量粗糙度的敏感性和在西北干旱区的适用性。结果显示,热力输送系数取定值的方案计算西北干旱区的感热通量可能存在较大不确定;台站的动量粗糙度可能受城市化等因子的影响,但在感热通量计算时建议取台站下垫面的动量粗糙度;Y08方案估算的感热通量相对比较合理,可以用来研究西北干旱区的夏季地表感热输送特征。 相似文献
19.
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
20.
Daily and zonal (latitudinal belt) averages of heat and momentum fluxes were computed using bulk aerodynamic formulae, from the meteorological parameters measured onboard M. S. Thuleland during the sixth Indian scientific expedition to Antarctica (26th November, 1986 to 22nd March, 1987). Both estimates showed significant variations, the momentum flux showing the largest variation. The maximum values of sensible and latent heat fluxes were observed over the 30°–40° S and 10°–20° S zones during the southern summer and fall respectively while the minimum values of latent heat flux were observed in the 60°–70° S zone for both seasons. The sensible heat flux minimum was observed in the 50°°60° S and 60°–70° S zones for summer and fall, respectively. Higher momentum flux values over the 40°–50° S zone in summer shifted to the 50°–60° S zone during fall. 相似文献