利用2000—2013年MODIS-Terra卫星产品提供的气溶胶光学厚度(aerosol optical depth,AOD)资料及NCEP/NCAR再分析资料集,使用奇异值分解(singular value decomposition,SVD)方法,分析了夏季东亚地区AOD与到达地面太阳辐射(downward solar radiation flux,DSRF)相联系的主要模态,并分析了其与夏季风变化的关系。夏季多年平均的AOD分布显示,在东亚地区存在两个AOD大值区(>0.9),分别位于山东、河南、河北交界处附近以及苏中部分地区。而在福建、台湾及其附近洋面上,夏季AOD的值小于0.4。地面太阳辐射总体上呈现出由南往北递增的分布。比较发现,AOD与地面太阳辐射的气候分布较为相似。在保留季节趋势的情况下,运用SVD方法对两者进行分解,结果表明东亚地区AOD与地面太阳辐射表现出较好的正相关关系。由于相对于年际变化而言,季节趋势是更为主要的部分,因而这种同相关系可归因于季风活动的季节性进程。利用SVD1左场时间系数进行相关分析发现:6月(2013年除外),当中国东部气溶胶AOD大而地面太阳辐射亦大时,在中国东南部以及日本岛南部地区,由于气流辐合增强和存在较强的上升运动,降水偏多,而由于副高位置偏南,使得中国中东部偏北地区水汽供应偏弱,降水偏少。由于地面净太阳辐射增强,华北部分地区异常增暖。8月,大陆上空AOD为负(时间系数为负),地面太阳辐射减少,北方降水增多而南方降水减少,华北地区有一小范围的异常降温。上述结果表明北方气溶胶明显偏少时,云量增加,降水将增多,且辐射明显减弱;说明夏季风的季节进程对气溶胶、到达地面的太阳辐射变化等具有重要影响。
The relative dispersion of the cloud droplet spectra or the shape parameter is usually assumed to be a constant in the two-parameter cloud microphysical scheme, or is derived through statistical analysis. However, observations have revealed that the use of such methods is not applicable for all actual cases. In this study, formulas were derived based on cloud microphysics and the properties of gamma function to solve the average cloud droplet radius and the cloud droplet spectral shape parameter. The gamma distribution shape parameter, relative dispersion, and cloud droplet spectral distribution can be derived through solving the droplet spectral shape parameter equation using the average droplet radius, volume radius, and their ratio, thereby deriving an analytic solution. We further examined the equation for the droplet spectral shape parameter using the observational droplet spectral data, and results revealed the feasibility of the method. In addition, when the method was applied to the two-parameter cloud microphysical scheme of the Weather Research and Forecast(WRF) model to further examine its feasibility, the modeling results showed that it improved precipitation simulation performance, thereby indicating that it can be utilized in two-parameter cloud microphysical schemes.
近50年江苏冬季霾日数随时间线性增多,其距平变化在1970年代由负位相转变为正位相。这种变化可能与东亚气候突变有关。利用江苏气象站点资料和NCEP/NCAR再分析资料,结合江苏冬季霾日数的年代际变化特征,探讨其与年代际气候变化的联系。结果表明,在江苏冬季霾少发期(1961—1979年),500 h Pa高度场在欧亚中高纬地区表现为"正-负-正"的距平分布,即在乌拉尔山附近和阿留申群岛附近表现为正距平,而在贝加尔湖以东地区表现为负距平。这种"两脊一槽型"的分布有利于北方冷空气南下,冬季风较强,使江苏境内地面风速增大,有利于大气污染物扩散,同时大气净化次数有所增多,不利于霾天气发生。而在霾的多发期(1980—2010年),异常的大气环流型则相反。此外,江苏冬季霾日数对气温增暖存在可能的显著正响应。
Field experiments were conducted in 2008 and 2009 to study the effects of deficit irrigation with saline water on spring wheat growth and yield in an arid region of Northwest China. Nine treatments included three salinity levels sl, s2 and s3 （0.65, 3.2, and 6.1 dS/m） in combination with three water levels wl, w2 and w3 （375, 300, and 225 mm）. In 2008, for most treatments, deficit irrigation showed adverse effects on wheat growth; meanwhile, the effect of saline irrigation was not apparent. In 2009, growth parameters of wl treatments were not always optimal under saline irrigation. At 3.2 and 6.1 dS/m in 2008, the highest yield was obtained by wl treatments, however, in 2009, the weight of 1,000 grains and wheat yield both followed the order w2 〉 wl 〉 w3. In this study, spring wheat was sensitive to water deficit, especially at the booting to grain-filling stages, but was not significantly affected by saline irrigation and the combination of the two factors. The results demonstrated that 300-mm irrigation water with a salinity of less than 3.2 dS/m is suitable for wheat fields in the study area.
