共查询到20条相似文献，搜索用时 46 毫秒
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二维场的高斯权重带通滤波分析 总被引：3，自引：0，他引：3
首先对任意的二维气象要素场推导出其带通滤波的响应函数，并进一步引入了带通滤波的相对响应函数。基于相对响应函数的性质，得到了权重参数Ｃ１、Ｃ２的合适选择。通过实例研究，说明由结构函数曲线选取最大响应波长的方法。实例分析结果表明，带通滤波能对暴雨、强对流天气分析提供一定帮助。 相似文献
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A new static microwave sounding unit (MSU) channel 4 weighting function is obtained from using Coupled Model Inter-comparison Project, Phase 5 (CMIP5) historical multimodel simulations as inputs into the fast Radiative Transfer Model for TOVS (RTTOV v10). For the same CMIP5 model simulations, it is demonstrated that the computed MSU channel 4 brightness temperature (T4) trends in the lower stratosphere over both the globe and the tropics using the proposed weighting function are equivalent to those calculated by RTTOV, but show more cooling than those computed using the traditional UAH (University of Alabama at Huntsville) or RSS (Remote Sensing Systems in Santa Rosa, California) static weighting functions. The new static weighting function not only reduces the computational cost, but also reveals reasons why trends using a radiative transfer model are different from those using a traditional static weighting function. This study also shows that CMIP5 model simulated T4 trends using the traditional UAH or RSS static weighting functions show less cooling than satellite observations over the globe and the tropics. Although not completely removed, this difference can be reduced using the proposed weighting function to some extent, especially over the tropics. This work aims to explore the reasons for the trend differences and to see to what extent they are related to the inaccurate weighting functions. This would also help distinguish other sources for trend errors and thus better understand the climate change in the lower stratosphere. 相似文献
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Developing a likely climate scenario from multiple regional climate model simulations with an optimal weighting factor 总被引：1，自引：0，他引：1
This study presents a performance-based comprehensive weighting factor that accounts for the skill of different regional climate models (RCMs), including the effect of the driving lateral boundary condition coming from either atmosphere–ocean global climate models (AOGCMs) or reanalyses. A differential evolution algorithm is employed to identify the optimal relative importance of five performance metrics, and corresponding weighting factors, that include the relative absolute mean error (RAME), annual cycle, spatial pattern, extremes and multi-decadal trend. Based on cumulative density functions built by weighting factors of various RCMs/AOGCMs ensemble simulations, current and future climate projections were then generated to identify the level of uncertainty in the climate scenarios. This study selected the areas of southern Ontario and Québec in Canada as a case study. The main conclusions are as follows: (1) Three performance metrics were found essential, having the greater relative importance: the RAME, annual variability and multi-decadal trend. (2) The choice of driving conditions from the AOGCM had impacts on the comprehensive weighting factor, particularly for the winter season. (3) Combining climate projections based on the weighting factors significantly increased the consistency and reduced the spread among models in the future climate changes. These results imply that the weighting factors play a more important role in reducing the effects of outliers on plausible future climate conditions in regions where there is a higher level of variability in RCM/AOGCM simulations. As a result of weighting, substantial increases in the projected warming were found in the southern part of the study area during summer, and the whole region during winter, compared to the simple equal weighting scheme from RCM runs. This study is an initial step toward developing a likelihood procedure for climate scenarios on a regional scale using equal or different probabilities for all models. 相似文献
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高,低分辨率模式对典型个例的对比预报试验 总被引：3，自引：2，他引：3
利用实时观测资料Ｔ６３模式预报产品资料，对１９９５年７－８月发生在西北地区的３次大雨、暴雨天气过程进行了高、低分痃率数值预报模式的对比预报试验。 相似文献
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P. A. Solignac A. Brut J. L. Selves J. P. Béteille J. P. Gastellu-Etchegorry 《Boundary-Layer Meteorology》2012,143(2):261-283
Large-aperture scintillometers (LAS) are often used to characterize atmospheric turbulence by measuring the structure parameter
of the refractive index Cn2{C_{n^{2}}} . However, absorption phenomena can lead to an overestimation of Cn2{C_{n^{2}}} . By applying an accurate numerical filtering technique called the Gabor transform to the signal output of a LAS, we improved
our knowledge of the accuracy of the measured Cn2{C_{n^{2}}} by determining and attenuating the contribution of absorption. Two studies are presented on a 12-day dataset using either
fixed band pass or adaptive filtering. The first consists of evaluating the best-fit filter for which the resulting Cn2{C_{n^{2}}} is independent of meteorological conditions, especially crosswind, and the second consists in accurately reconstructing the
signal to remove absorption, without losing information on Cn2{C_{n^{2}}} . A reference Cn2{C_{n^{2}}} (hereafter ‘reconstructed Cn2{C_{n^{2}}} ’) is created by accurately removing absorption from the scintillation spectrum, and is used to evaluate each filter. By
comparing the ‘reconstructed Cn2{C_{n^{2}}} ’ with a raw Cn2{C_{n^{2}}} measured with a scintillometer, in the presence of absorption, we found that the average relative contribution of absorption
to the measurement of Cn2{C_{n^{2}}} is approximately 9%. However, the absorption phenomenon is highly variable; occasionally, in the worst cases, we estimate
that the absorption phenomenon could represent 81% of the value of Cn2{C_{n^{2}}} . Some explanations for this high variability are proposed with respect to theoretical considerations. Amongst the fixed
band-pass filtering used, we conclude on the preferential use of a band-pass filter [0.2–400 Hz] for Cn2{C_{n^{2}}} , as its performance is only slightly affected by the crosswind, and that the mean absorption contribution is reduced to
5.6%, with a maximum value of 60%. Using an adaptive filter on the 12-day dataset really improves the filtering accuracy for
both points discussed—the independence of meteorological conditions and the quality of signal reconstruction. 相似文献
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The influence of random errors in turbulence measurements on scalar similarity for temperature, water vapour, \(\hbox {CO}_{2}\), and \(\hbox {NH}_{3}\) is investigated using two eddy-covariance datasets collected over a lake and a cattle feedlot. Three measures of scalar similarity, namely, the similarity constant in the flux–variance relationship, the correlation coefficient between two scalars and the relative transport efficiency, are examined. The uncertainty in the similarity constant \(C_{s}\) in the flux–variance relationship resulting from random errors in turbulence measurements is quantified based on error propagation analyses and a Monte-Carlo sampling method, which yields a distribution instead of a single value for \(C_{s}\). For different scalars, the distributions of \(C_{s}\) are found to significantly overlap, implying that scalars are transported similarly under strongly unstable conditions. The random errors in the correlation coefficients between scalars and the relative transport efficiencies are also quantified through error propagation analyses, and they increase as the atmosphere departs from neutral conditions. Furthermore, the correlation coefficients between three scalars (water vapour, \(\hbox {CO}_{2}\), and \(\hbox {NH}_{3}\)) are statistically different from unity while the relative transport efficiencies are not, which highlights the difference between these two measures of scalar similarity. The results suggest that uncertainties in these measures of scalar similarity need to be quantified when using them to diagnose the existence of dissimilarity among different scalars. 相似文献
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荒漠戈壁大气总体曳力系数和输送系数观测研究 总被引：24，自引：10，他引：14
利用“我国西北干旱区陆一气相互作用观测试验”在甘肃敦煌进行的陆面过程野外试验的观测资料,依据三种不同方法确定了干旱戈壁区动量输送的曳力系数Cd、感热和潜热交换的总体输送系数Ch和Cq。结果表明：尽管这三种方法计算的曳力系数和总体输送系数有一定的差别,但在量级上相当,尤其是Cd和Ch的平均值比较接近。本文还通过对风向的分析,剔除了附近建筑物干扰和来自绿洲湿平流的影响,得到了荒漠戈壁总体输送系数的特征及其与理查孙数的关系。 相似文献
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Simultaneous Non-linear Retrieval of Atmospheric Temperature and Absorbing Constituent Profiles from Satellite Infrared Sounder Radiances 总被引：4，自引：3，他引：1
Based on Zeng’s theory (1974), a successive linearized form of radiative transfer equation (RTE) is derived for simultaneous retrieval of atmospheric temperature and absorbing constituent profiles from satellite infrared observa-tions. It contains the temperature component weighting function and absorbing constituent (H2O, O3, CH4 etc.) com-ponent weighting functions. All these weighting functions reach maximum at their own “optimum information levels”, and make the remote sensing equations well-conditional. Then the atmospheric profiles are derived by Newton’s non-linear iteration method. Experiments of retrieval from both TIROS-N operational High Resolution Infrared Sounder (HIRS) and the simulated Atmospheric infRared Sounder (AIRS) show an significant improvement. 相似文献
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The bandpass eddy covariance method has been used to measure the turbulent flux of scalar quantities using a slow-responsescalar sensor. The method issimilar in principle to the traditional eddy correlation method but includes the estimation of high-frequency components of the flux on the basis of cospectral similarity in the atmospheric surface layer. In order to investigate the performance of the method, measurements of the water vapour flux over a forest with the bandpass eddy covariance method and the direct eddy correlation method were compared. The flux obtained by the bandpass eddy covariance method agreed with that by the eddy correlation method within ±20% for most cases, in spite of a rather slow sensor-response of the adopted hygrometer. This result supports its relevance to a long-term continuous operation, since a stable, low-maintenance,general-purpose sensor canbe utilized for scalar quantities. Oneweak point of the method isits difficulty in principle to measure the correct flux when the magnitude of the sensible heat flux is very small, because the method uses the sensible heat flux as a standard reference for the prediction of undetectable high-frequency components of the scalar flux. An advanced method is then presented to increase its robustness. In the new method, output signals from a slow-response sensor are corrected using empirical frequency-responsefunctions for the sensor,thereby extending the width of the bandpass frequency region where components of the flux are directly measured (not predicted). The advanced method produced correct fluxes for all cases including the cases of small sensible heat flux. The advanced bandpass eddy covariance method is thus appropriate for along-term measurement of the scalar fluxes. 相似文献
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本文利用高空常规资料,格距为150km,取λ_(max)=1500km的带通滤波器对长江三角洲地区的暴雨云团所处的环境场(包括风场,高度场和温度场)进行尺度分离,讨论中尺度扰动场与暴雨云团的关系。 相似文献
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Deliang CHEN Tinghai OU Lebing GONG Chong-Yu XU LI Weijing Chang-Hoi Ho QIAN Weihong 《大气科学进展》2010,27(6):1221-1232
Climate research relies heavily on good quality
instrumental data; for modeling efforts gridded data are needed. So
far, relatively little effort has been made to create gridded
climate data for China. This is especially true for high-resolution
daily data. This work, focuses on identifying an accurate method to
produce gridded daily precipitation in China based on the observed
data at 753 stations for the period 1951--2005. Five interpolation
methods, including ordinary nearest neighbor, local polynomial,
radial basis function, inverse distance weighting, and ordinary
kriging, have been used and compared. Cross-validation shows that
the ordinary kriging based on seasonal semi-variograms gives the
best performance, closely followed by the inverse distance weighting
with a power of 2. Finally the ordinary kriging is chosen to
interpolate the station data to a 18 km×18 km grid system
covering the whole country. Precipitation for each 0.5o×0.5o latitude-longitude block is then obtained by averaging
the values at the grid nodes within the block. Owing to the higher
station density in the eastern part of the country, the
interpolation errors are much smaller than those in the west (west
of 100oE). Excluding 145 stations in the western region, the
daily, monthly, and annual relative mean absolute errors of the
interpolation for the remaining 608 stations are 74%, 29%, and
16%, respectively. The interpolated daily precipitation has been
made available on the internet for the scientific community. 相似文献
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利用CRTM (Community Radiative Transfer Model) 快速辐射传输模式对NOAA-K系列卫星的AMSU-A通道亮温进行正演模拟,重点研究云粒子类型、云高、云厚度等云参数对微波亮温模拟的影响。结果表明:改变云粒子类型时,云水和雨水对模拟亮温影响较大,模拟亮温值比晴空高1 K;霰、雪、冰、雹等固态粒子对模拟亮温的影响较小,模拟亮温值略低于晴空无云情况;云层光学厚度较大时,各通道亮温受云层影响的情况取决于权重函数峰值高度和云顶高度的配置;多个高度存在云时,若最上层云较厚 (2 km),光学厚度大,相应通道亮温取决于最上层云,较低层云对亮温不产生影响;云层变薄,光学厚度减小,高度低于云层或略高于云顶的通道亮温随云层厚度的变化明显,若通道高度远高于云顶,云层厚度的变化对于其亮温模拟的影响很小。 相似文献
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Precipitation over the Tibetan Plateau (TP) is important to local and downstream ecosystems. Based on a weighting method considering model skill and independence, changes in the TP precipitation for near-term (2021–40), mid-term (2041–60) and long-term (2081–2100) under shared socio-economic pathways (SSP1-1.9, SSP1-2.6, SSP2-4.5, SSSP3-7.0, SSP5-8.5) are projected with 27 models from the latest Sixth Phase of the Couple Model Intercomparison Project. The annual mean precipitation is projected to increase by 7.4%–21.6% under five SSPs with a stronger change in the northern TP by the end of the 21st century relative to the present climatology. Changes in the TP precipitation at seasonal scales show a similar moistening trend to that of annual mean precipitation, except for the drying trend in winter precipitation along the southern edges of the TP. Weighting generally suggests a slightly stronger increase in TP precipitation with reduced model uncertainty compared to equally-weighted projections. The effect of weighting exhibits spatial and seasonal differences. Seasonally, weighting leads to a prevailing enhancement of increase in spring precipitation over the TP. Spatially, the influence of weighting is more remarkable over the northwestern TP regarding the annual, summer and autumn precipitation. Differences between weighted and original MMEs can give us more confidence in a stronger increase in precipitation over the TP, especially for the season of spring and the region of the northwestern TP, which requires additional attention in decision making. 相似文献