COMPARISONS OF CIRCULATION ANOMALIES BETWEEN THE DAILY PRECIPITATION EXTREME AND NON-EXTREME EVENTS IN THE MIDDLE AND LOWER REACHES OF YANGTZE RIVER IN BOREAL SUMMER

Based on the NCEP/NCAR reanalysis dataset and in situ meteorological observations of daily precipitation in boreal summer from 1979 to 2008, the features of circulation anomalies have been investigated using the composite analysis for the extreme events and non-extreme events of regional mean daily rainfall(RMDR) occurring over the midand lower- Yangtze valley(MLYV). The extreme RMDR(ERMDR) events are the events at and above the percentile99 in the rearranged time-series of the RMDR with ascending order of rainfall amount. The non-extreme RMDR events are those at the percentiles 90-85 and 80-75 separately. Our results suggest that the threshold value is 25 mm/day for the ERMDR at percentile 99. Precipitation at all the percentiles is found to occur more frequently in the Meiyu rainfall season in MLYV, and the ERMDR events have occurred with higher frequency since the 1990 s. For the percentiles-associated events, the MLYV is under the control of an anomalous cyclonic circulation in the mid- and lower- troposphere with vastly different anomalous circulation at higher levels. However, at both low and high levels, the ERMDR events-related anomalous circulation is stronger compared to that linked to the non-ERMDR events. The dominant sources of water vapor differ between the ERMDR and non-ERMDR events. During the ERMDR events plentiful water vapor is transported from the Bay of Bengal into the MLYV directly by divergence while there is distinctly increased water vapor from the South China Sea(SCS) in non-RMERMDR episodes. The diabatic heating rates < Q1>, < Q2> and< Q1>- < Q2> have their anomalous patterns and are consistent with each other for these percentiles but their strength decreases markedly with the drop of rainfall intensity. For the precipitation at percentiles 99 and 90-85, the sea surface temperature anomalies(SSTA) in the Pacific distribute positively(negatively) in the south(north), and are stronger when the ERMDR emerges, with little or no SSTA as the events at percentile 80-75 occur. Besides, these results suggest that the genesis of the ERMDR event is directly related to intense local circulation anomalies and the circulation anomalies over the Pacific and SCS in tropical to mid-latitudes, and probably linked with the Pacific SSTA closely while the non-ERMDR events are mainly associated with the anomalous circulation on a local basis. The findings here help understand and predict the happening of ERMDR events over the MLYV.     

利用GMS－4红外云图资料定量测量淮河流域汛期降水

提出和介绍了利用ＧＭＳ－４红外云图资料定量测量淮河流域汛期降水的ＣＴ－ＴＲＣ（ｃｌｏｕｄｔｏｐｔｅｍｐｅｒａｔｕｒｅｒａｉｎｆｕｌｌｃｕｒｖｅ，云顶温度－降水量曲线）方法及实现步骤，并结合个例进行了分析。     

El Nino事件对其衰减阶段夏季中国降水季节内演变的影响及其机理

利用1979—2007年NOAA重建海温逐月资料和中国160站夏季降水资料,使用扩展奇异值分解（extended singular value decomposition,ESVD）方法,研究了冬季热带太平洋海温异常与次年夏季中国降水异常季节内演变型之间的关系,指出前冬El Nino事件是与次年夏季中国降水季节内变化相联系的最重要的热带太平洋海温异常模态。相应的降水异常季节内变化情况为：6月在长江以南为正异常,江淮流域有负异常;7月在华南沿海有负降水异常,而正异常北进到长江流域,华北地区也出现正降水异常;8月在长江南北分别为少雨和多雨。进一步研究前冬El Nino事件与次年春夏印度洋、太平洋海温异常、对流层低层风场异常以及副热带高压等的联系,结果表明：El Nio事件发生的次年春夏,热带西太平洋周边存在东负西正的海温异常分布;西太平洋反气旋异常较强;副高在6月、7月偏西偏北,但在8月迅速南退。虽然与El Nino事件相联系的6月与7月、8月的降水型不同,但是西太平洋反气旋异常带来的充沛水汽造成7月长江流域雨季多雨,8月副高迅速南退带来的又一次长江流域降水,造成了El Nino事件发生次年夏季长江流域涝而华南沿海旱的夏季平均降水异常型。     

GPS折射率资料在梅雨锋暴雨数值模拟中的应用

运用WRF三维变分同化系统同化GPS掩星折射率资料,并应用到2007年7月4—6日梅雨锋暴雨个例中进行数值模拟试验,以此考察GPS掩星折射率资料在梅雨锋暴雨数值模拟中的应用。同化结果表明：GPS掩星折射率资料对初始资料的调整主要是中低层湿度场,对于温度场和高度场的调整都是从底层到高层逐渐增大;加入GPS掩星折射率资料对降水预报有所改进,这与中低层湿度场的初始调整有关系;从对模拟结果进行诊断和结构分析中可以发现负散度增量和正涡度增量与降水中心和区域有很好的对应,同化资料之后对于各降水中心地区增强了产生降水的动力条件。     

台风云娜后部强降水分析

通过对中尺度自动站、常规气象要素、1°×1°NCEP格点资料和多普勒雷达资料的诊断分析,发现台风云娜登陆后西行路径对其后部的强降水起了关键性作用;高层辐散和低层辐合差加大,抽吸作用加强,上升运动加剧是后部降水加强的动力原因;沿海较冷的温度场配合台风后部强烈的东南偏南水汽输送,是台风后部降水加强的热力原因;台风后部海面上形成北上的螺旋雨带是造成台风后部强降水的直接原因;浙江东部地形与台风后部强烈的东南偏南水汽输送正交是造成台风后部降水增幅的重要原因。该分析结果对今后台风预报服务实际工作具有一定的参考作用。     

四川盆地暴雨对初值敏感性的模拟研究

本文基于区域暴雨数值预报模式AREM,针对2007年7月发生在四川地区的多次强降水过程进行数值试验,检验了NCEP和站点资料（STN）初始分析场资料预报结果,发现由于台站资料稀少,NCEP资料在四川地区的评分较高。讨论了四川盆地降水对初值的高度敏感性,揭示了四川盆地降水对初值中各个物理量场的不同敏感性,其中,降水对初值中湿度场的响应最为显著。初值不仅决定着降水的范围和强度,还对降水的发生时间产生明显影响。     

Effects of rainfall intensity fluctuations on infiltration and runoff: rainfall simulation on dryland soils,Fowlers Gap,Australia

Small plots and a dripper rainfall simulator were used to explore the significance of the intensity fluctuations (‘event profile’) within simulated rainfall events on infiltration and runoff from bare, crusted dryland soils. Rainfall was applied at mean rain rates of 10 mm/h. Fourteen simulated rainfall events each involved more than 5000 changes of intensity and included multipeak events with a 25‐mm/h peak of intensity early in the event or late in the event and an event that included a temporary cessation of rain. These are all event profiles commonly seen in natural rain but rarely addressed in rainfall simulation. A rectangular event profile of constant intensity, as commonly used in rainfall simulation experiments, was also adopted for comparative purposes. Results demonstrate that event profile exerts an important effect on infiltration and runoff for these soils and rainfall event profiles. ‘Uniform’ events of unvarying intensity yielded the lowest total runoff, the lowest peak runoff rate and the lowest runoff ratio (0.13). These parameters increased for ‘early peak’ profiles (runoff ratio 0.24) and reached maxima for ‘late peak’ profiles (runoff ratio 0.50). Differences in runoff ratio and peak runoff rate between the ‘uniform’ event profile and those of varying intensity were all statistically significant at p ≤ 0.01. Compared with ‘uniform’ runs, the varying intensity runs yielded larger runoff ratios and peak runoff rates, exceeding those of the ‘uniform’ events by 85%–570%. These results suggest that for small‐plot studies of infiltration and erosion, the continued use of constant rainfall intensity simulations may be sacrificing important information and misrepresenting the mechanisms involved in runoff generation. The implications of these findings for the ecohydrology of the research site, an area of contour‐aligned banded vegetation in which runoff and runon are of critical importance, are highlighted. Copyright © 2011 John Wiley & Sons, Ltd.     

RELATIONSHIPS BETWEEN SPRING KUROSHIO SSTA AND SUMMER RAINFALL IN CHINA

Based on the data of SST and NCEP/NCAR reanalysis data, the relationship is analyzed of spring SSTA in the Kuroshio region with summer precipitation in China, summer 500 hPa field and water vapor transport, using the methods of Morlet wave, correlation and composite analysis. The results show that annual and interdecadal change of spring SST in the Kuroshio region is distinct. Spring SST displays a significantly increasing trend and there exist different periodic oscillations in the Kuroshio region, with the 23-year periodic oscillation being the most obvious. Troughs and ridges in the mid- and higher- latitudes turn deeper in high Kuroshio SSTA years. At the same time, the western Pacific subtropical high strengthens and stretches westwards. As a result, the warm / wet air from the west of the subtropical high locates in the mid- and lower- reaches of the Yangtze River and south China and summer rainfall in the above regions increases accordingly. Composite anomalous water vapor flux fields indicate that the vapor transport from the South China Sea and western Pacific and the vapor from the north converge over the mid- and lower- reaches of the Yangtze River and south China, which results in the increase of the summer rainfall in the mid- and lower- reaches of the Yangtze River and south China. On the contrary, the summer rainfall in the mid- and lower- reaches of the Yangtze River and south China decreases correspondingly in low Kuroshio SSTA years.     

The Dipole Mode of the Summer Rainfall over East China during 1958–2001

By examining the second leading mode(EOF2)of the summer rainfall in China during 1958–2001 and associated circulations,the authors found that this prominent mode was a dipole pattern with rainfall decreasing to the north of the Yangtze River and increasing to the south.This reverse relationship of the rainfalls to the north and to the south of the Yangtze River was related with the meridional circulations within East Asia and the neighboring region,excited by SST in the South China Sea-northwestern Pacific....     

双线偏振多普勒天气雷达遥测降水强度和液态含水量的方法和精度研究

利用雨滴谱的Г分布和散射计算模式,研究了C波段双线偏振多普勒天气雷达遥测降水强度、液态含水量和识别降水粒子相态的方法,给出了利用反射率因子ZH、差分反射率因子ZDR、差传播相移KDP反演降水强度和液态含水量的三种公式以及这三个物理量的关系公式,并从雨滴谱的变化和雷达测量误差两方面比较了几种方法的测雨精度.结果表明:雨滴谱在很大范围变化时,利用ZDR和KDP可以很好地反演出降水强度和液态含水量,它受滴谱分布的影响不大,它的探测精度优于(ZH,ZDR)方法.单参数KDP方法优于传统的Z-R关系方法.同时给出的ZH与ZDR和KDP关系公式也基本不受雨滴谱变化的影响,它可以用于降水粒子相态的识别.双参数方法的测量误差主要来源于雷达测量ZDR和KDP的误差,特别是KDP的误差,改善KDP的测量误差是发挥双线偏振多普勒雷达探测降水强度或液态含水量潜力的关键.