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841.
A two-step variational method for three-dimensional wind retrieval from single Doppler radar 总被引:4,自引:0,他引:4
Summary A two-step variational method is developed to retrieve the three-dimension wind field from single-Doppler radar observation
for operational applications. The first step produces a proxy background wind field, and the second step retrieves the detailed
wind structures in data dense areas on a high-resolution grid. The background field is called proxy because it is obtained
in the first step by a spectral analysis of the same radial-wind observations that will be used in the second step and thus
the background is not independent of the observations. In the second step, the wind retrieval is constrained by the proxy
background and the advection equation of liquid water content in the cost function. Tested with a dataset collected during
Meiyu front heavy rainfall on 22 July 2002 in China, the two-step approach is shown to yield the best performance in comparison
with a single-step approach that uses either only the proxy background field or the retrieval without the proxy background. 相似文献
842.
843.
Rate constants for the reaction of hydroxyl radicals with dibromomethanehave been measured by discharge flow-resonance fluorescence technique(DF-RF) over the temperature range 288–368 K. The derived Arrheniusequation is k1=(1.51 ± 0.37)× 10-12 exp(-(720 ±60)/T) cm3 molec.-1 s-1.The tropospheric lifetime of dibromomethane has been estimated to be 0.29years. An ozone depletion potential (ODP) value of 0.10 for dibromomethanehas been obtained. 相似文献
844.
基于MODIS增强型植被指数的青海省牧草产量估产研究 总被引:5,自引:3,他引:5
利用青海省22个生态环境监测站在2003和2004年牧草生长季内各月所测的牧草鲜草产量数据,并搜集了该时段内逐日的MODIS遥感数据,通过对图像的预处理,云区识别,植被指数的计算及月最大植被指数的合成,形成了与牧草产量数据相对应的MODIS EVI数据。然后按牧草生长季和草地类型建立了牧草鲜草产量与MODIS植被指数的关系模型。结果表明,牧草产量和MODIS EVI之间存在较高的相关性,用指数函数建立产量模型效果较好。按牧草生长季建立的牧草产量检测模型比按草地类型建立的模型相关性要高。 相似文献
845.
846.
A three-dimensional variational method is proposed to simultaneously retrieve the 3-D atmospheric temperature and moisture profiles from satellite radiance measurements. To include both vertical structure and the horizontal patterns of the atmospheric temperature and moisture, an EOF technique is used to decompose the temperature and moisture field in a 3-D space. A number of numerical simulations are conducted and they demonstrate that the 3-D method is less sensitive to the observation errors compared to the 1-D method. When the observation error is more than 2.0 K, to get the best results, the truncation number for the EOF's expansion have to be restricted to 2 in the 1-D method, while it can be set as large as 40 in a 3-D method. This results in the truncation error being reduced and the retrieval accuracy being improved in the 3-D method. Compared to the 1-D method, the rms errors of the 3-D method are reduced by 48% and 36% for the temperature and moisture retrievals, respectively. Using the real satellite measured brightness temperatures at 0557 UTC 31 July 2002, the temperature and moisture profiles are retrieved over a region (20°-45°N, 100°- 125°E) and compared with 37 collocated radiosonde observations. The results show that the retrieval accuracy with a 3-D method is significantly higher than those with the 1-D method. 相似文献
847.
大气短波辐射传输研究中的辐射函数 总被引:1,自引:0,他引:1
研究大气短波辐射传输问题时,必需考虑多次散射,在计算各次散射光的递推方程中存在一个对光学厚度的特殊积分.为此,本文定义了“辐射函数”,并研究了它的数学性质,从而使得平面平行大气中散射光的逐次计算既准确又简便. 相似文献
848.
基于地面太阳短波总辐射对气溶胶光学特性和地表反照率的敏感性, 该文提出了一个评估我国气象台站总辐射资料准确度的方法。该方法选用气溶胶光学厚度和太阳天顶角较小情形下的晴天辐射资料, 从太阳直射辐射反演气溶胶光学厚度, 用于计算宽带透过率, 再从该透过率和总辐射资料反演太阳常数E0, P, 并采用E0, P对世界辐射基准 (WRR) 的偏差表示总辐射资料的不确定性。模拟结果表明:气溶胶折射率虚部和大气柱水汽含量的输入误差是两个主要的评估不确定因子。用于准确度评估的资料越多, 越有利于平滑气溶胶、水汽含量等输入参数随机误差的效应, 评估结果越合理。应用这一方法, 该文评估了2000— 2004年我国沈阳、额济纳旗、北京、乌鲁木齐、格尔木、上海和广州7个气象台站总辐射资料的准确度。7个站共有1161个太阳常数反演值, 都满足太阳天顶角余弦 (μ0) 大于0.7的条件。这些E0, P值对WRR的最大偏差为7.33%, 97.78%的E0, P值对WRR的偏差小于5%, 总平均E0, P值对WRR偏差只有-1.15 %。依据这些结果, 当μ0≥0.7时, 这些台站的晴天总辐射资料的不确定度估计为5%。 相似文献
849.
Disequilibria between 210Po and 210Pb in surface waters of the southern South China Sea and their implications 总被引:1,自引:0,他引:1
Yang Weifeng Huang Yipu Chen Min Zhang Lei Li Hongbin Liu Guangshan Qiu Yusheng 《中国科学D辑(英文版)》2006,49(1):103-112
Activities of the naturally occurring radionuclides, 210Pb and 210Po, were measured in both dissolved (<0.45 μm) and particulate (>0.45 μm) phases from surface waters of the southern South
China Sea. The average activity of particulate 210Pb, 0.23 Bq/m3 (n=23), accounted for about 12% of the total 210Pb, which corresponds with values of open oceans. Particulate 210Po, with an average activity of 0.43 Bq/m3, accounted for about 40% of the total 210Po, which was much higher than those of open and eutrophic oceans. The residence times of total 210Po and 210Pb in surface waters estimated from an irreversible steady-state model were 0.82 a and 1.16 a, respectively. The consistently
high fractionation factor calculated either by scavenging rate constants (5.42) or Kd values (6.69) suggested that a significant fractionation occurred between 210Po and 210Pb during their removal from solution to particles and that the two radionuclides had different biogeochemical cycling pathways
in the oligotrophic South China Sea. Furthermore, our results indicated that there exist different fractionation mechanisms
between 210Po and 210Pb in different marine environments: in eutrophic ocean, plankton detritus and fecal pellets are the main carrier of 210Po and 210Pb, by which 210Po and 210Pb have been scavenged and removed; while in oligotrophic ocean, microbes could become the main carrier of 210Po and fractionate 210Po and 210Pb significantly as a result of scarce plankton detritus and fecal pellets. These results suggest the use of 210Po to trace marine biogeochemical processes relating to microbial activities and the cycling of sulfur group elements (S,
Se, Te and Po). 相似文献
850.