共查询到20条相似文献，搜索用时 31 毫秒
1.
Estimating the Random Error in Eddy-Covariance Based Fluxes and Other Turbulence Statistics: The Filtering Method 总被引：1，自引：1，他引：0
A spatially local decomposition of turbulent fluxes based on properties of spatial filters is used to develop a new method of estimating random error in turbulent moments of any order. The proposed error estimation method does not require an estimate of the integral time scale, which can be highly sensitive to the method used to calculate it. The error estimation method is validated using synthetic flux data with a known ensemble mean and intercompared with existing methods using data from the Advection Horizontal Array Turbulence Study (AHATS). Typical errors for a 27.3-min block of data collected at a height of 8 m are found to be approximately 10% for the heat flux and 7–15% for variances. The error in the momentum flux increases rapidly with increasing atmospheric instability, reaching values of 40% or greater for unstable conditions. A new method based on filtering is also proposed to estimate integral time scales of turbulent quantities. 相似文献
2.
采用一种基于相似误差的模式后处理方法,对2011年10月18日—2012年1月5日WRF模式24 h预报的陕西延长风电场风速进行误差订正。该方法通过寻找与当前预报相似的历史预报来进行误差订正,克服了一般基于时间顺序的误差订正方法的不足,即不能处理由于天气系统的剧烈转变引起的预报误差的快速变化。相似误差订正方法减小了预报的均方根误差和中心均方根误差,相对原始预报分别减小9%和10%左右。该方法不仅可以减小系统误差,还可以减小随机误差,从而提高预报准确率。同时,订正结果相对原始预报具有更好的Taylor图模态相关。相似误差订正方法对风能预报敏感区的订正效果更为显著,均方根误差和中心均方根误差分别减小了12%和22%左右。该方法尤其适用于基于风能模式预报的风速误差订正,同时该方法对其他的预测系统和预报变量也有很好的应用潜力。 相似文献
3.
L. Haimberger B. Ahrens F. Hamelbeck M. Hantel 《Meteorology and Atmospheric Physics》2001,77(1-4):167-184
Summary Diagnostic time-mean budgets of energy and water are evaluated in many atmospheric process studies. The errors of budget-derived
quantities like sub-gridscale fluxes or diabatic heating are governed by the errors of the budgets. Here we consider 3D-budgets
on the meso-β scale over Europe. They are compiled from analyses of state quantities available from forecast centres.
In the present study we found that the mandatory 6 hours sampling interval between synoptic observations is the main error
source for routine time-mean budgets. The errors have been quantified (i) by first sampling forecast data of the German Europamodell every 5 minutes and averaging them over 12 hours (reference budget), and (ii) by sampling the same data only every 6 hours and averaging these also over 12 hours (routine budget). With this method we find that routine budgets in single atmospheric meso-β scale columns show relative random errors
of typically 200% and systematic errors of up to 20%, exclusively due to undersampling. Thus routine budgets, if applied to
specific days at individual locations, cannot be expected to yield useful results, except perhaps for cases with extremely
strong signal. Compositing over several hundreds of columns with similar weather reduces the random budget error down to about
50%; this seems to be the best one can achieve for routine budgets. The systematic error of some budget quantities is caused
by a correlation between the time of occurence of certain processes (mainly convection) and the sampling times. While this
error cannot be reduced through compositing, we find that it can be crudely estimated by using different time averaging methods.
As application for this method we determine sub-gridscale budget quantities over the BALTEX catchment (August-September 1995)
for an ensemble of convectively active and an ensemble of rain-active columns. For the ensemble mean profiles we find, in
terms of the diagnosed sub-gridscale test quantities diabatic heating and vertical moist enthalpy flux divergence, that their
accuracy is sufficient to detect statistically significant differences between both ensembles. The diabatic heating is about
the same for both ensembles, while the flux divergence in the convective ensemble is about three times as large as in the
rain ensemble.
Received November 7, 2001 Revised April 4, 2001 相似文献
4.
Nelson Luís Dias Bianca Luhm Crivellaro Marcelo Chamecki 《Boundary-Layer Meteorology》2018,168(3):387-416
The Hurst phenomenon is a well-known feature of long-range persistence first observed in hydrological and geophysical time series by E. Hurst in the 1950s. It has also been found in several cases in turbulence time series measured in the wind tunnel, the atmosphere, and in rivers. Here, we conduct a systematic investigation of the value of the Hurst coefficient H in atmospheric surface-layer data, and its impact on the estimation of random errors. We show that usually \(H > 0.5\), which implies the non-existence (in the statistical sense) of the integral time scale. Since the integral time scale is present in the Lumley–Panofsky equation for the estimation of random errors, this has important practical consequences. We estimated H in two principal ways: (1) with an extension of the recently proposed filtering method to estimate the random error (\(H_p\)), and (2) with the classical rescaled range introduced by Hurst (\(H_R\)). Other estimators were tried but were found less able to capture the statistical behaviour of the large scales of turbulence. Using data from three micrometeorological campaigns we found that both first- and second-order turbulence statistics display the Hurst phenomenon. Usually, \(H_R\) is larger than \(H_p\) for the same dataset, raising the question that one, or even both, of these estimators, may be biased. For the relative error, we found that the errors estimated with the approach adopted by us, that we call the relaxed filtering method, and that takes into account the occurrence of the Hurst phenomenon, are larger than both the filtering method and the classical Lumley–Panofsky estimates. Finally, we found that there is no apparent relationship between H and the Obukhov stability parameter. The relative errors, however, do show stability dependence, particularly in the case of the error of the kinematic momentum flux in unstable conditions, and that of the kinematic sensible heat flux in stable conditions. 相似文献
5.
整体传输公式是一种常用的计算洋面海气通量的方法。在作气候平均计算时,存在两种平均方法:方法一F_1=AB及方法二F_2=AB。显然,方法一是合理的,而方法二是对方法一的近似。本文利用COADS资料针对不同的平均时间计算分析了方法二对方法一的近似程度,结果表明:利用方法二计算长期气候平均,平滑时间超过5天则对计算结果必须进行订正;对感热和潜热通量,月平均方法二在20％的精度内可代替方法一,而旬平均方法二则可在10％的精度内代替方法一;动量通量月平均和旬平均精度分别为40％和20％。因此方法二在计算月平均动量通量时必须作订正,或直接用方法一进行计算,本文同时计算比较了1972年(E1 Nino年)和1975年(非E1 Nino年)太平洋洋面的各项能量及总能量收支,发现1972年洋面能量收支年变化幅度比1975年小得多,其差别主要决定于感热和潜热的变化。 相似文献
6.
How Well Can We Measure the Vertical Wind Speed? Implications for Fluxes of Energy and Mass 总被引：2，自引：2，他引：0
John Kochendorfer Tilden P. Meyers John Frank William J. Massman Mark W. Heuer 《Boundary-Layer Meteorology》2012,145(2):383-398
Sonic anemometers are capable of measuring the wind speed in all three dimensions at high frequencies (10–50 Hz), and are relied upon to estimate eddy-covariance-based fluxes of mass and energy over a wide variety of surfaces and ecosystems. In this study, wind-velocity measurement errors from a three-dimensional sonic anemometer with a non-orthogonal transducer orientation were estimated for over 100 combinations of angle-of-attack and wind direction using a novel technique to measure the true angle-of-attack and wind speed within the turbulent atmospheric surface layer. Corrections to the vertical wind speed varied from −5 to 37% for all angles-of-attack and wind directions examined. When applied to eddy-covariance data from three NOAA flux sites, the wind-velocity corrections increased the magnitude of CO2 fluxes, sensible heat fluxes, and latent heat fluxes by ≈11%, with the actual magnitude of flux corrections dependent upon sonic anemometer, surface type, and scalar. A sonic anemometer that uses vertically aligned transducers to measure the vertical wind speed was also tested at four angles-of-attack, and corrections to the vertical wind speed measured using this anemometer were within ±1% of zero. Sensible heat fluxes over a forest canopy measured using this anemometer were 15% greater than sensible heat fluxes measured using a sonic anemometer with a non-orthogonal transducer orientation. These results indicate that sensors with a non-orthogonal transducer orientation, which includes the majority of the research-grade three-dimensional sonic anemometers currently in use, should be redesigned to minimize sine errors by measuring the vertical wind speed using one pair of vertically aligned transducers. 相似文献
7.
该文实现了一种极轨气象卫星的自动地标导航方法。地标导航能够纠正由于姿态而引起的定位误差。首先根据当前轨道遥感卫星图像中海洋、陆地、河流等地物特征能量的概率分布情况,利用全球模板,建立地标库,然后通过最大相关系数方法计算地标偏移量,从而获得姿态偏差,之后利用计算得到的姿态偏差对遥感卫星图像重新导航,获得地理定位结果。利用FY-1D扫描辐射计的遥感数据对方法进行检验,结果表明:该文所提出的自动地标导航方法可以有效纠正由姿态而引起的定位误差,达到像素级的定位精度。该方法能够突破传统地标导航方法需要丰富的遥感卫星历史资料的限制,拓展传统地标导航方法的适应范围。该方法已在我国2008年5月发射的新一代极轨气象卫星FY-3号上得到应用,并将在下一代静止轨道气象卫星FY-4号上进一步开发。 相似文献
8.
利用模式三维预报变量,结合地面要素预报产品,采用2 m温度三维插值方法进行地形订正,以确保预报与观测三维空间上的一致性,在地形订正基础上,利用历史月均预报误差作为参考误差,剔除模式系统性误差,获取具备日变化特征的预报产品。基于陕西地区复杂地形条件下的典型观测站点,利用2016年8月28日48 h预报个例进行对比分析发现,三维插值方法有效改善了地形差异引起的评估误导问题,但无法改进模式预报的日变化趋势,进一步采用系统性误差订正后,日变化特征明显改善,特别是前24 h预报效果体现出与实况良好的一致性及更佳的预报技巧。通过2016年夏季统计评估表明,误差订正后的2 m温度预报产品有效改善了周期性误差振荡,均方根误差稳定在2 K左右,显示出明显的改进优势。 相似文献
9.
Annual mean ocean surface heat fluxes have been studied as a function of horizontal resolution in the ECMWF model (cycle 33) and compared with Oberhuber's COADS (1959–1979) based empirical estimates. The model has been run at resolutions of T21, T42, T63 and T106 for 15 months with prescribed monthly varying climatological SST and sea ice. The T42 simulation was extended to 2 years, which enabled us to determine that many differences between the resolution runs were significant and could not be explained by the fact that individual realizations of an ensemble of years can be expected to give different estimates of the annual mean climate state. In addition to systematic differences between the modeled and the observed fluxes, the simulated fields of surface shortwave and longwave radiation showed much more spatial variability than the observed estimates. In the case of the longwave radiation this may be attributable more to deficiencies in the observations than to errors in the model. The modeled latent and sensible heat fields were in better agreement with observations. The primary conclusion concerning the dependence of ocean surface fluxes on resolution is that the T21 simulation differed significantly from the higher resolution runs, especially in the tropics. Although the differences among the three higher resolution simulations were generally small over most of the world ocean, there were local areas with large differences. It appears, therefore, that in relation to ocean surface heat fluxes, a resolution greater than T42 may not be justified for climate model simulations, although the locally large differences found between the higher resolution runs suggest that convergence has not been achieved everywhere even at T106. 相似文献
10.
11.
The Global Soil Wetness Project (GSWP) is an international initiative aimed at producing global data sets of soil wetness and energy and water fluxes by driving land surface models with state-of-the-art 1° by 1° atmospheric forcing and land surface parameters. It also provides a unique opportunity to develop and test land surface parameterizations at the global scale, using multi-year off-line simulations that are not affected by the systematic errors found in atmospheric models. Nevertheless, the accuracy and reliability of the 10?year GSWP-2 atmospheric forcing remain questionable. A first comparison using the high-resolution Rhône-AGGregation (Rhône-AGG) database reveals that the baseline GSWP-2 precipitation forcing is drastically overestimated over the Rhône river basin. Hydrological simulations driven with each dataset and using the ISBA land surface model and the MODCOU river routing model are also compared. The simulated river discharges are validated against a dense network of river gauges and are generally less realistic when using the GSWP-2 instead of the Rhône-AGG precipitation forcing. Secondly, the GSWP-2 precipitation forcing is compared with three alternative data sets (GPCP-2, CRU-2, CMAP) at the global scale. Moreover, the results of a global sensitivity study to the precipitation forcing conducted with six land surface models are shown. The TRIP river routing model is used to convert daily runoff from all models into river discharges, which are compared at 80 gauging stations distributed over the globe. In agreement with the regional evaluation, the results reveal that the baseline GSWP-2 precipitation forcing is generally overestimated over the mid and high latitudes, which implies systematic errors in the simulated discharges. This study reveals that the empirical wind corrections applied to the GSWP-2 precipitation forcing are exaggerated, whereas the GPCP satellite adjustments seem to be useful for simulating realistic annual mean river discharges over the East Siberian river basins. 相似文献
12.
采用漂浮通量箱法和扩散模型法同步地观测了模拟内陆水体在不同条件下的CH4和N2O的水-气交换通量,旨在比较两类方法取得结果的异同。结果显示:这两类方法所测得的绝大多数CH4排放通量都与水中溶解氧呈显著线性负相关(显著性系数P0.001)。同时N2O排放通量与表层水温及水中铵态氮、硝态氮、溶解碳和溶解氧的关系可用包含所有上述水环境因素的Arrhenius动力学方程来表达,这些因素可以共同解释86%~90%的N2O通量变化(P0.0001),且不同方法测定的N2O通量的表观活化能和对表层水温的敏感系数分别介于47~59 kJ mol-1和1.92~2.27之间;扩散模型法所获得的CH4和N2O通量分别是箱法测定值的13%~175%和15%~240%,差异程度因模型而异;不同模型取得通量间相差20%~1200%,平均相差2.3倍。上述结果表明:仅用一种模型方法来取得CH4或N2O排放通量易形成较大偏差;不同扩散模型法和箱法测定的通量在反映CH4和N2O排放的内在规律方面具有一致性,但它们对真实气体通量的测量是否都存在不同程度的系统误差,尚需进一步研究。 相似文献
13.
In this study, we evaluate the ability of the Weather Research and Forecasting model to simulate surface energy fluxes in the southeast Pacific stratocumulus region. A total of 18 simulations is performed for the period of October to November 2008, with various combinations of boundary layer, microphysics, and cumulus schemes. Simulated surface energy fluxes are compared to those measured during VOCALS-REx. Using a process-based model evaluation, errors in surface fluxes are attributed to errors in cloud properties. Net surface flux errors are mostly traceable to errors in cloud liquid water path (LWPcld), which produce biases in downward shortwave radiation. Two mechanisms controlling LWPcld are diagnosed. One involves microphysics schemes, which control LWPcld through the production of raindrops. The second mechanism involves boundary layer and cumulus schemes, which control moisture available for cloud by regulating boundary layer height. In this study, we demonstrate that when parameterizations are appropriately chosen, the stratocumulus deck and the related surface energy fluxes are reasonably well represented. In the most realistic experiments, the net surface flux is underestimated by about 10 W m?2. This remaining low bias is due to a systematic overestimation of the total surface cooling due to sensible and latent heat fluxes in our simulations. There does not appear to be a single physical reason for this bias. Finally, our results also suggest that inaccurate representation of boundary layer height is an important factor limiting further gains in model realism. 相似文献
14.
Two situations observed during the second Aerosol Characterization Experiment (ACE-2) are analysed from aircraft measurements in the broken stratocumulus (Sc)-topped marine boundary layer. The first one (26 June 1997), characterized by a non-polluted, oceanic air mass, presents a decoupling between the Sc layer (1400–1520 m) and the turbulent mixed layer, this latter extending from the surface up to 580 m. In contrast, the second case (9 July 1997), during which continental air had been advected over the experimental area, presents a well-coupled layer extending from the surface up to the top of the Sc layer(910 m). This coupling, uncommon in this area in the middle of the day, isrelated to the relative shallowness of the boundary layer. For both situations,it is shown that the turbulent fluxes can be computed with reasonably goodaccuracy (better than 10 %), taking into account both the random and thesystematic errors involved in the eddy-correlation technique. Estimationof random error is based on the computation of the integral scale of thecovariance, and systematic error is estimated from the parameterizationof Mann and Lenschow. The fluxes show that the buoyancy, as a sourceof turbulence, is due to latent heat flux rather than sensible heat flux,with values comparable to previous experiments in the Azores-Canariesbasin. In addition, we propose a method to analyse, for coupled situations,the relationship between the fractional cloudiness and the organization ofthe turbulent field below the clouds. This method is based on a conditionalsampling technique. It is shown that this organization cannot be deducedfrom the analysis of the velocity signal, which is dominated by turbulence.However, when the signals are conditionally sampled according to thepresence or absence of clouds, a weak cloud-related organization can beshown, and the cloud-related transports quantified; the values found areof the order of 10 % of the total transfers, i.e. the same order of magnitude asthe errors on the total flux computation. The method developed is thereforepromising, provided that the uncertainties can be reduced by analyzing a highamount of data. 相似文献
15.
Twenty-two months (July 1983-April 1985) of surface heat fluxes predicted at day 1 from a numerical weather prediction system have been processed. Monthly means and monthly standard deviations of available surface short-wave, long-wave, latent and sensible heat fluxes as well as annual means have been computed. The global mean of the annual net sea-surface heat flux is about 40 Wm–2 and is therefore far from equilibrium. When used to force an oceanic model, these fluxes would tend to warm the ocean and would produce an unrealistic transport of heat by the oceanic general circulation. They therefore need to be corrected. This correction appears feasible because the main difference between these fluxes and long-term climatologies appears largely independent of the month and the latitude. This suggests that the errors have a systematic origin. The corrected fluxes allow both the reproduction of a realistic seasonal migration of the zero net heat-flux line and the reproduction of the annual meridional heat transport in the different oceans, within the range of previous estimates. 相似文献
16.
Sensible (H) and latent (LvE) heat fluxes are obtained by a combined energy budget – similarity model applied to observations from Melle in Belgium and Cabauw in The Netherlands. The sensitivity to both the stability functions and the accuracy of input data is investigated. In a first step, fluxes are calculated for a selection of stability functions and compared to values obtained with pre-defined (reference) functions. For the diurnal fluxes higher than 10 W m−2 in 1996 at Melle, the root-mean-square rmsreaches 9 W m−2 for H and 6 W m−2 for LvE, depending on the chosen functions. A lesser sensitivity is obtained at Cabauw and can be explained by lower absolute values of the stability parameter ζ (L involving the Obukhov length) mainly induced by higher mean wind speeds. Different stability bins are also considered. It is concluded that a more accurate assessment of the stability functions is already desirable for absolute values of L above a few metres. These values are not so scarce at Melle and should be captured in the future by an increasing number of new developing long-term measurement stations. In a second step, a statistical approach is proposed with errors depicted by both systematic biases and random fluctuations represented by means of Gaussian distributions. The results show that very accurate measurements are needed in order to maintain the mean annual value of the bias and rms below 5–10 W m−2, and thus to allow the discrimination between the sensitivity to errors on input data and to the stability functions selection. 相似文献
17.
Thomas Foken 《Boundary-Layer Meteorology》2006,119(3):431-447
In weak wind stable conditions, eddy-correlation fluxes calculated using conventional averaging times of 5 min or longer to define the perturbations are severely contaminated by poorly sampled mesoscale motions. A method is developed to identify the averaging time for each individual data record that captures the turbulence while excluding most of the mesoscale motions. The method is based on multiresolution decomposition of the heat flux, and provides an objective procedure for selecting the averaging time for calculating eddy-correlation fluxes. Eddy-correlation data collected in weak turbulence conditions over grass, snow, a pine forest and the ocean are used to demonstrate the approach.When the small-scale turbulence and mesoscale motions are clearly separated by a gap region in the heat flux cospectra, the variable window width reduces the influence of nonstationarity by more effectively filtering out mesoscale motions compared to traditional methods using constant averaging time. For records where turbulence and mesoscale motions overlap in scale, the method is not well posed, although such records occur infrequently for our datasets. These ambiguous cases correspond to significant nonstationarity at scales that overlap with turbulence scales. The improved turbulence fluxes calculated with the proposed method are the appropriate fluxes for evaluating flux-gradient relationships and Monin–Obukov similarity theory for developing improved model parameterizations of turbulence for weakly turbulent flows 相似文献
18.
19.
卫星资料凭着卫星遥感的全球性、连续性和高频次观测等优势,成为一种重要的非常规资料源,但卫星观测仍然存在各种各样的观测误差,其中包含由于观测偶然性所造成的统计学上的随机误差及仪器本身和辐射传输模式等造成的系统性偏差,这些误差在很大程度上影响了卫星资料的质量。文中提出了一种能有效订正卫星观测资料系统性偏差的梯度信息同化算法,该方法用一个梯度算子进行模式变量与观测变量的梯度变换,从而达到订正系统性偏差的目的。本文利用WRF（Weather Research Forecast）模式及其同化模式WRFDA（WRF Data Assimilation system）,以及AIRS（Atmospheric Infrared Sounder）资料,对台风“圆规”进行了实际的数值模拟和同化试验,数值结果表明,梯度信息同化方法能明显改善台风路径的模拟,在处理可信度较低的资料时仍然适用。另外,通过同化诊断分析,发现卫星资料的系统性偏差对于台风数值模拟有较大影响,而文中提出的梯度信息同化方法能较好的解决此类问题。 相似文献
20.
A MODEL OF INTEGRATED RANDOM INITIAL VALUES AND RANDOM FORCING AND ITS PRELIMINARY EXPERIMENT 
下载免费PDF全文
下载免费PDF全文 A simple quasi-geostrophic barotropic vorticity equation model is used as the dynamic frame of themodel in this paper.Considering that there are many random errors in model's initial values of meteorolo-gical data,and that it is not perfectly complete about model's physical processes (for example,take no ac-count of the interaction between atmosphere and underlying surface,radiation,etc.),we add the random for-ced term to the model and use the Monte-Carlo method with random initial values.A statistical-dynamicintegrated model is thus built up,and a numerical forecasting experiment of 500hPa monthly mean height fieldof January 1983 has been carried out.The experiment result proves that the forecasting result of the model,considering random forcing and random initial values at the same time,is better than that by the pure dynamicmodel,the random initial value model and the random forced model. 相似文献