共查询到19条相似文献，搜索用时 140 毫秒
1.
非均匀下垫面湍流通量观测的印痕分析 总被引：5，自引：1，他引：4
利用2005年在北京昌平区小汤山开展的非均匀下垫面观测实验的观测数据,分别处理了涡旋相关法和大孔径闪烁仪LAS测得的感热通量,并运用印痕模型对数据进行“源区”分析。分析结果表明:在复杂地表上,涡旋相关的测量值由于混杂了其他下垫面的通量信息,不能真实地反映其观测区域的湍流特征,存在着观测误差。而LAS观测出现的低估问题则与掺混高度和“源区”有关。通过用印痕方法进行数据订正后,以上问题均得到很好的改善,订正结果与LAS观测通量的线性关系良好,两者的相关系数达到0.9。实验结果验证了印痕模型在非均匀下垫面的适用性。 相似文献
2.
《高原气象》2017,(2)
利用2009—2012年在北京密云、青海阿柔、河南济源、甘肃张掖、河北馆陶和沽源的野外对比试验数据,分析了国产光学型大孔径闪烁仪的观测精度、稳定性和一致性,为国产光学型大孔径闪烁仪的后续生产和改进提供科学依据。分析结果表明:(1)以德国BLS900闪烁仪观测值作为参考值,张掖巴吉滩3套和沽源站5套国产大孔径闪烁仪样机感热通量观测值的平均均方根误差分别为19.91 W·m~(-2)和9.81 W·m~(-2);样机感热通量观测值均值与涡动相关仪观测值比较,均方根误差分别为21.08 W·m~(-2)和12.87 W·m~(-2),表明国产大孔径闪烁仪具有较好的观测精度;(2)国产大孔径闪烁仪在高温、低温、高湿或低湿的恶劣天气条件下以及长时间序列的观测均具有较好的稳定性;(3)样机观测感热通量之间的回归斜率差异较大,为6%,相关系数大于0.98,表明国产大孔径闪烁仪的一致性较好。综上所述,国产光学型大孔径闪烁仪基本达到了国外同类仪器的性能水平。 相似文献
3.
在对涡动相关仪和大孔径闪烁仪足迹模型进行敏感性分析的基础上,利用北京密云站2006年8月至2007年12月期间的观测资料,应用足迹模型对观测通量的空间代表性做了初步的分析.结果表明:涡动相关仪和大孔径闪烁仪的源区对风向、Monin-Obukhov长度,空气动力学粗糙度和观测高度/有效高度等因子比较敏感.密云站涡动相关仪的源区白天主要分布在仪器的西南与南面,而夜间则在东北与北面.大孔径闪烁仪的源区为西南一东北向分布.涡动相关仪各月源区形状不同,但大致分布在南北长1000 m、东两宽850 m的范嗣内,而LAS各月源区为西南一东北向分布,长约2060 m,最宽处约为620 m.对涡动相关仪通量有贡献的下垫面主要为园地(67%)和耕地(19%).其中园地的通量贡献比例在夏、秋季比较大,冬、春季稍小,而耕地则相反.大孔径闪烁仪的主要通量贡献源区为园地、耕地和居民地,通量贡献比例分别为49%,28%和11%.其中园地和耕地通量贡献率的变化趋势与涡动相关仪的观测结果一致,但没有涡动相关仪的变化明显. 相似文献
4.
LAS在西北干旱区荒漠均匀下垫面的观测研究 总被引：2，自引：0，他引：2
利用“古浪非均匀近地层观测试验”的仪器平行对比观测部分试验数据,首先分析荒漠均匀下垫面大孔径闪烁仪(Large Aperture Scintillometer,LAS)光径线上等间距架设的4台涡动相关仪(Eddy Covariance System,EC)观测的摩擦速度和感热通量的一致性.然后,基于4种不同下垫面建立稳定度普适函数分析,利用4台EC观测摩擦速度平均值,计算了LAS观测区域的感热通量,进而比较了LAS和EC两者观测值的差异.结果表明,4台EC观测的摩擦速度与感热通量一致性好,摩擦速度的差别＜10％,感热通量的差别在10％左右.4种稳定度普适函数计算的LAS区域感热通量在白天、夜晚与EC观测平均值变化趋势一致,但计算值偏大;TAG (Thiermann and Grassl)稳定度普适函数计算值与EC观测平均值较接近.其主要原因除不同下垫面试验所得稳定度普适函数的差异外,Kipp&Zonen LAS所测感热通量的系统性偏高不可忽视. 相似文献
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7.
SEBS模型在黄淮海地区地表能量通量估算中的应用 总被引：1，自引：0，他引：1
在对SEBS模型的有关参数进行订正的基础上,利用MODIS遥感数据结合地表气象观测数据,对黄淮海地区地表能量通量进行了估算。将SEBS估算结果先与北京顺义定量遥感综合试验(QRSLSP/Shunyi)实测结果进行对比分析,然后与郑州的大孔径闪烁仪(LAS)观测的感热通量进行对比分析。结果表明,SEBS估算的通量与二者的实测结果相当一致。因此,利用改进后的SEBS模型估算的黄淮海地区地表能量通量具有一定的精度,可满足区域日蒸散量计算等的需求。 相似文献
8.
首先把显热通量作为地表能量平衡的一部分,通过每半小时平均净辐射、潜热通量和土壤热通量的观测值来计算显热通量。然后,采用迭代法解显热通量的空气动力方程,并且考虑到非流线体(热量和动量交换粗糙高度的不同)和稳定度(地表和空气温度的不同)对空气动力阻力的校正,得到空气动力地表温度。这时会发现,在稳定(不稳定)大气条件下的空气动力温度比红外测温观测值要低(高)。而且,在阻力-能量平衡方程中用红外温度估算潜热通量时,这个估算值与观测值,通过回归分析,显示出高度的线性相关(r=0.96)与适中的标准差(47Wm~(-2)) 相似文献
9.
利用2008年6月11～30日在金塔开展的"绿洲系统非均匀下垫面能量水分交换和边界层过程观测与理论研究"期间第一阶段戈壁下垫面大孔径闪烁仪(LAS)的观测资料,用混合对流方法和自由对流方法分别计算了戈壁感热通量。结果表明,对于利用LAS资料计算地表感热通量的方法中,混合对流方法相对于自由对流方法更加适用,且混合对流方法中Andreas给出的参数相对于DeBruin的参数更加适用于戈壁下垫面。此外,LAS测得的感热通量相对涡动相关方法的值较大,提高了地表能量闭合度。 相似文献
10.
利用2000~2007年四川省乐至县大口径闪烁仪(Large Aperture Scintillometer,LAS)观测资料,对比分析了降水日与非降水日、干旱日与非干旱日地表热量通量的时间变化特征。分析结果表明:非降水日显热通量具有明显的日变化特征,最大值出现在13:00左右,降水日显热通量的日变化受降水影响,降水使显热通量减小;非降水日的月平均显热通量有2个峰值,分别出现在5月和8月,最小值在1月;降水日也有2个明显的月平均显热通量峰值,它们是4月和7月,12月最小;夏秋交替的9月非降水日与降水日的显热通量差异最大;干旱日和非干旱日的显热通量都是1月最小,干旱日8月显热通量最大,非干旱日是4月最大;6~10月干旱与非干旱日的显热通量具有明显差异;干旱越严重的月份,月平均显热通量越偏大;相同时次的显热通量平均值,干旱日较非干旱日的明显偏大。 相似文献
11.
Experimental determination of turbulent fluxes over the heterogeneous LITFASS area: Selected results from the LITFASS-98 experiment 总被引：1，自引：0，他引：1
F. Beyrich S. H. Richter U. Weisensee W. Kohsiek H. Lohse H. A. R. de Bruin Th. Foken M. Göckede F. Berger R. Vogt E. Batchvarova 《Theoretical and Applied Climatology》2002,73(1-2):19-34
Summary ?During the LITFASS-98 experiment, local flux measurements were performed over five different types of underlying surface
(grass, barley, triticale, pine forest, water) in a heterogeneous landscape using eddy covariance and profile techniques over
a three week time period in June, 1998. Estimates of the area-integrated sensible heat flux during daytime were obtained from
continuous measurements with a large aperture scintillometer (LAS) along a 4.7 km path. The calculation of a mean diurnal
cycle of the fluxes during the experiment revealed significant differences between the main land use classes. A land-use weighted
average of the sensible heat flux was found to be in good agreement with the LAS based estimate, which in turn was supported
by other regionally integrated flux estimates from budget considerations and aircraft measurements for a few case studies.
The profiles of turbulent quantities measured along a 99 m-tower significantly deviate from “idealised” profiles measured
over homogeneous terrain. Peculiarities in the profile structure could be attributed to the heterogeneity of the terrain,
namely to the differences in the surface characteristics of the footprint areas for the different tower levels.
Received June 6, 2001; revised January 15, 2002; accepted April 4, 2002 相似文献
12.
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
13.
W. M. L. Meijninger F. Beyrich A. Lüdi W. Kohsiek H. A. R. De. Bruin 《Boundary-Layer Meteorology》2006,121(1):89-110
The performance of a combined large aperture scintillometer (LAS) and a millimetre wave scintillometer (MWS) for estimating surface fluxes of sensible and latent heat over natural landscape is investigated, using data gathered during LITFASS-2003. For this purpose the LAS–MWS system was installed in a moderate heterogeneous landscape over a path length of 4.7 km with an effective beam height of 43 m. The derived surface fluxes have been compared with aggregated eddy-covariance (EC) measurements. The fluxes of sensible and latent heat from the LAS–MWS combination, as well as sensible heat fluxes of the single LAS, agreed fairly well with the EC-based fluxes, considering the uncertainties of the similarity stability functions and observed energy imbalance. 相似文献
14.
Mariusz Zieliński Krzysztof Fortuniak Włodzimierz Pawlak Mariusz Siedlecki 《Boundary-Layer Meteorology》2017,164(2):281-301
The sensible heat flux (H) is determined using large-aperture scintillometer (LAS) measurements over a city centre for eight different computation scenarios. The scenarios are based on different approaches of the mean rooftop-level \((z_{H})\) estimation for the LAS path. Here, \(z_{H}\) is determined separately for wind directions perpendicular (two zones) and parallel (one zone) to the optical beam to reflect the variation in topography and building height on both sides of the LAS path. Two methods of \(z_{H}\) estimation are analyzed: (1) average building profiles; (2) weighted-average building height within a 250 m radius from points located every 50 m along the optical beam, or the centre of a certain zone (in the case of a wind direction perpendicular to the path). The sensible heat flux is computed separately using the friction velocity determined with the eddy-covariance method and the iterative procedure. The sensitivity of the sensible heat flux and the extent of the scintillometer source area to different computation scenarios are analyzed. Differences reaching up to 7% between heat fluxes computed with different scenarios were found. The mean rooftop-level estimation method has a smaller influence on the sensible heat flux (?4 to 5%) than the area used for the \(z_{H}\) computation (?5 to 7%). For the source-area extent, the discrepancies between respective scenarios reached a similar magnitude. The results demonstrate the value of the approach in which \(z_{H}\) is estimated separately for wind directions parallel and perpendicular to the LAS optical beam. 相似文献
15.
J. -P. Lagouarde M. Irvine J. -M. Bonnefond C. S. B. Grimmond N. Long T. R. Oke J. A. Salmond B. Offerle 《Boundary-Layer Meteorology》2006,118(3):449-476
Abtract Sensible heat flux estimated by Large Aperture Scintillometry (LAS) has been tested against the more traditional eddy covariance technique over Marseille city centre, a reasonably homogeneous surface. Over the 3 week test period fluxes were found to be similar, yet less noisy for the LAS due to the spatial integration. No systematic bias between the estimates was found as a function of wind direction, indicating the homogeneity of the site. Sensitivity analysis of the required aerodynamic parameters shows that careful attention must be paid to the displacement height along the measurement path. Spatial variability of surface sensible heat flux is studied via a second LAS measurement path over the city. 相似文献
16.
Dawit A. Zeweldi Mekonnen Gebremichael Junming Wang Theodore Sammis Jan Kleissl David Miller 《Boundary-Layer Meteorology》2010,135(1):151-159
Scintillometers are becoming increasingly popular for the validation of satellite remote sensing sensible heat-flux estimates due to the comparable spatial resolutions. However, it is important to gain confidence in the accuracy of the sensible heat-flux measurements obtained by the scintillometer. Large aperture scintillometer (LAS) and eddy-covariance (EC) measurements were collected over a homogeneous, dry and semi-arid region near Las Cruces, New Mexico, USA, where the homogeneity allowed direct comparison of the two instruments despite their differences in footprint sizes. The differences between the sensible heat-flux measured by both LAS and EC systems fall within the differences between two EC systems. We conclude that the large aperture scintillometer is a reliable system for measuring sensible heat flux in a dry semiarid region. 相似文献
17.
A scaling factor, S, is derived to account for the difference in path-weighted measurement heights of a combined system consisting of a large-aperture
scintillometer (LAS) and a millimetre-wave scintillometer (MWS), operating at wavelengths of 0.88 μm and about 3 mm respectively,
and designed to determine the area-averaged latent heat flux. This work extends an earlier derivation of Z
ef
, the effective height for the LAS yielding the area-averaged sensible heat flux. The LAS and MWS have different path-weighting
functions, therefore, in general, it is expected that the path-weighted beam heights are different, for paths other than with
the beam parallel to the land surface. Their difference will depend on the detail of the experimental set-up. The objective
is to introduce a scaling factor that transforms the MWS refractive-index structure parameter measurement to the same path-weighted
height of the LAS measurement. By applying S as a prelude to the calculation of the temperature and humidity structure parameters, and the sensible and latent heat fluxes,
these quantities are made representative of the same measurement height, thus simplifying the application of two-wavelength
scintillometry. The equations presented here enable the analysis of LAS-MWS paths such that they can be selected to optimize
S towards its ideal value of unity. For this purpose we provide a new analytical approximation of the LAS path-weighting function.
The importance of accounting for S is demonstrated by example applications over varying topography as well as for slanted beams. 相似文献
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19.
Integrated Sensible Heat Flux Measurements of a Two-Surface Composite Landscape using Scintillometry 总被引：1，自引：0，他引：1
J.-P. Lagouarde J.-M. Bonnefond Y. H. Kerr K. J. McAneney M. Irvine 《Boundary-Layer Meteorology》2002,105(1):5-35
The potential of the LAS (large aperture scintillometry) method for measuring sensible heat flux (H) directly integrated over a two-field composite surface is evaluated. We describe a field experiment performed within the Alpilles/ReSeDa project in the south-east of France over a composite surface made up of wheat and bare soil (451 and 216 m long respectively) using two 0.15-m diameter scintillometers mounted at heights of 2.05 and 4.54 m. When compared against reference values obtained by the eddy correlation technique, LAS-measured sensible heat flux reveals a systematic overestimation of about 10%. A simple model describing the integration of the scintillometer signal along the beam for a two-field composite surface is described. A simulation of the experiment confirms that the bias observed isrelated to non-linearities in the integration process in relation with thebell-shape sensitivity curve of the instrument to the structure parameter for the refractive index it measures. The model is used to test the sensitivity of the LAS-derived H values to the composition of the pathlength (ratio of both surfaces) and to the contrast in sensible heat flux and roughness length between the two fields. Sensitivity tests to the aggregation scheme for roughness length (two of them are tested) and to the measurement height are also presented. The composition of the surface in combination with the contrast in sensible heat flux (in direct relation with the contrast in latent heat flux) explains most of the bias, with possible deviations ranging from -50 up to 80 W m-2. A tentative semi-empirical method for correcting the bias is suggested, which only requires a crude estimate of the contrast in component sensible heat fluxes along the pathlength. 相似文献