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Thin film methods and X ray energy dispersive technique were applied to analyze sulfate-containing particles in Beijing in order to examine their features and sources. Atmospheric aerosol particles were collected on electron mi-croscope meshes according to two size ranges: coarse particles (r>0.5μm) and fine particles (0.5μm≥r≥0.1μm) by using a two-stage impactor. It was found fiat more than seventy percent of the fine particles and about twenty percent of the coarse particles were sulfate-containing particles. These particles were formed mainly through heterogeneous nucleation. The element composition analyses revealed that the atmospheric aerosol particles in Beijing were domi-nated by crustal particles and construction dust.  相似文献   
Geophysical data sets are growing at an ever-increasing rate, requiring computationally efficient data selection(thinning)methods to preserve essential information. Satellites, such as Wind Sat, provide large data sets for assessing the accuracy and computational efficiency of data selection techniques. A new data thinning technique, based on support vector regression(SVR), is developed and tested. To manage large on-line satellite data streams, observations from Wind Sat are formed into subsets by Voronoi tessellation and then each is thinned by SVR(TSVR). Three experiments are performed. The first confirms the viability of TSVR for a relatively small sample, comparing it to several commonly used data thinning methods(random selection, averaging and Barnes filtering), producing a 10% thinning rate(90% data reduction), low mean absolute errors(MAE) and large correlations with the original data. A second experiment, using a larger dataset, shows TSVR retrievals with MAE < 1 m s-1and correlations 0.98. TSVR was an order of magnitude faster than the commonly used thinning methods. A third experiment applies a two-stage pipeline to TSVR, to accommodate online data. The pipeline subsets reconstruct the wind field with the same accuracy as the second experiment, is an order of magnitude faster than the nonpipeline TSVR. Therefore, pipeline TSVR is two orders of magnitude faster than commonly used thinning methods that ingest the entire data set. This study demonstrates that TSVR pipeline thinning is an accurate and computationally efficient alternative to commonly used data selection techniques.  相似文献   
As part of a joint effort to construct an atmospheric forcing dataset for mainland China with high spatiotemporal reso- lution, a new approach is proposed to construct gridded near-surface temperature, relative humidity, wind speed and surface pressure with a resolution of 1 km× 1 km. The approach comprises two steps: (1) fit a partial thin-plate smoothing spline with orography and reanalysis data as explanatory variables to ground-based observations for estimating a trend surface; (2) apply a simple kriging procedure to the residual for trend surface correction. The proposed approach is applied to observations collected at approximately 700 stations over mainland China. The generated forcing fields are compared with the corresponding components of the National Centers for Environmental Predic- tion (NCEP) Climate Forecast System Reanalysis dataset and the Princeton meteorological forcing dataset. The comparison shows that, both within the station network and within the resolutions of the two gridded datasets, the interpolation errors of the proposed approach are markedly smaller than the two gridded datasets.  相似文献   
本文利用WRF模式及其3DVAR同化系统,以2008年4月20日00时-23日00时的江苏近海10 m风场为研究个例,对QuikSCAT、WindSAT、多源测风融合数据进行同化试验,通过比较WRF-3DVAR同化系统对模拟风场初始场和预报场的改进,检验了同化不同类型资料后WRF模式对研究区域内单点及区域近地层风速的预报效果。结果表明:同化试验对初始场有改进,且对预报场的改进较FNL资料明显;不同资料对风场模拟的影响不同,同化星星、星地多源融合资料效果最佳,QuikSCAT次之,WindSAT最差。此外,在模式分辨率一定的情况下,提高观测资料的分辨率并不一定能够改善模拟效果,资料的稀疏分辨率存在最佳选择。  相似文献   
ATOVS资料同化方案对暴雨模拟效果的影响   总被引:3,自引:1,他引:2       下载免费PDF全文
张斌  张立凤  熊春晖 《大气科学》2014,38(5):1017-1027
本文利用WRF模式及其3DVar同化系统,以2009年6月29日00时到30日00时的湖北鹤峰暴雨为研究个例,对ATOVS探测器的AMSU-A、AMSU-B和HIRS三类资料进行了不同的同化方案试验。结果表明:同化ATOVS三类资料对暴雨模拟的影响不同,HIRS资料对暴雨模拟效果改进最大,AMSU-B次之,AMSU-A最小。同时同化ATOVS三类资料时,AMSU-A资料起主要作用,其同化效果与同时同化ATOVS三类资料相近,优化组合同化AMSU-B和HIRS资料的效果最好。同化ATOVS不同资料对初始要素场的影响不同,AMSU-A资料主要影响大气温度场,AMSU-B资料对中高空要素场的影响较大,HIRS资料对低空湿度场及风场的协同改变最有利于降水模拟的改善。同时ATOVS资料的稀疏分辨率也是影响同化效果的一个因子,在模式分辨率不变时,同化资料稀疏分辨率可能存在最佳选择。  相似文献   
在全天空红外-可见光云像观测反演方法基础上,针对已往阈值法判断高云的局限性,提出改进的算法。对可见光图像可利用以太阳-天顶为连线的主平面两边相元特性的对称性来判断云的存在,对红外成像仪可利用同一仰角扫描时所得不同方位角亮温分布的非均匀性来判断云的存在。以北京2011年1 3月观测资料为基础,选择原阈值法未能判别出来的案例进行再处理,全天空可见光成像观测仪高云判别能力最高可达73.9%,全天空扫描式红外成像仪可达70.1%。该工作为天空的高云识别提供新的复合算法。  相似文献   
用小波变换提取雷达回波图像中的辐合特征线   总被引:1,自引:1,他引:0  
采用小波变换的方法对滨州雷达资料的反射率图像进行处理,得到特征线增强后的图像,将其输入自动预报系统实现特征识别,可为雷暴预报提供初步资料。  相似文献   
Many forest management methods alterstand density uniformly. The effectsof such a change on the wind andturbulence regimes in the forest arecritical to a number of processes governingthe stability of the stand and itsmicroclimate. We measured wind speed andturbulence statistics with a Dantec tri-axialhot-film probe in model forests of variousdensities (31–333 trees m-2), created byremoving whole trees in a regular pattern in awind tunnel, and compared them with similarmeasurements made with propeller anemometers insimilarly thinned plots (156–625 trees ha-1)within a Sitka spruce stand in Scotland. The results agree well, in general, with measurements made inother such studies with diverse canopy types.The systematic variations with density and verticalleaf-area distribution (which differed betweenwind-tunnel and field trees) in our work can explainmuch of the variability shown in scaled profiles ofbasic turbulence statistics reported in theliterature. The wind tunnel and field results are shown to be in good agreement overalldespite the difference in vertical leaf-areadistribution. Within-canopy and isolated-treedrag coefficients in the wind tunnel showthat tree-scale shelter effects increase astree density increases. The measurements indicatethat turbulence in the canopy is dominated bylarge-scale structures with dimensions of the sameorder as the height of the canopy as found inother studies but suggest that inter-tree spacing also modulates the size of these structures. These structures are associated with the sweeps that dominatemomentum exchange in the canopy and it is thisfact that allows the tri-axial probe to operate sowell despite the relatively narrow range of anglesin which the wind vector is correctly measured. Theratio of streamwise periodicity of these structuresto vorticity thickness varies systematically withtree density in the range 2.7–5.1, which spans theexpected range of 3.5–5 found in a laboratorymixing-layer, suggesting that tree spacing imposes another relevant length scale. This test andothers show that the results are in agreement withthe idea that canopy turbulence resembles that of a mixing layer even though they disagree with, and challenge the linear relationship between, streamwise periodicity andshear length scale presented recently in theliterature. The measurements are also in goodoverall agreement with simple drag models presented recently by other researchers.  相似文献   
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