夏季长江中下游流域性极端日降水事件的环流异常特征及其与非极端事件的比较  

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

作　　者：韩洁[1,2,3] 管兆勇[1,2] 李明刚[1,2] 

机构地区：[1]宝鸡市气象局,陕西宝鸡721006 [2]南京信息工程大学大气科学学院,江苏南京210044 [3]南京信息工程大学气象灾害省部共建教育部重点实验室,江苏南京210044

出　　处：《热带气象学报》2012年第3期367-378,共12页Journal of Tropical Meteorology

基　　金：国家科技支撑计划项目课题(2007BAC29B02);江苏省"青蓝工程创新团队"项目共同资助

摘　　要：利用1979—2008年夏季(6—8月)的NCEP/NCAR再分析逐日资料与中国743测站的逐日降水资料,对长江中下游地区流域性极端降水(99百分位,也称为极端强降水)、85～90百分位、75～80百分位降水事件进行合成分析,比较了不同百分位降水事件的环流异常特征。结果表明:长江中下游地区流域性极端日降水量的99百分位阈值为25 mm/d。各类降水事件在梅雨汛期出现频率较高。1990年代以后的极端日降水事件明显偏多。在各百分位降水事件中,在对流层中、低层,长江中下游地区均受气旋性异常环流控制,但对流层高层异常环流特征明显不同。无论在低层还是高层,极端事件的异常环流比非极端事件的异常环流强。不同百分位降水事件的水汽主要来源亦有所不同。极端降水事件中,由孟加拉湾直接辐散至长江流域的水汽较强,而在非极端降水事件中,则是来自南海地区的水汽明显偏强。非绝热加热率<Q1>、<Q2>与<Q1>-<Q2>的异常分布在各百分位降水事件中的分布较为一致,但强度随降水强度的减小而明显减小。另外,极端日降水事件与85～90百分位的降水事件在太平洋上都存在着北负南正的海温分布,但极端降水事件相应的海温异常明显偏强。而在75～80百分位降水事件中,海温并未出现明显异常。说明极端日降水事件的形成与较强的局地环流异常、与中纬度和热带西太平洋-南海区域的环流异常直接相关,与太平洋海温异常存在可能的密切联系,而非极端事件则主要与局地性异常环流有关。这些结果有利于人们认识和预测极端日降水事件的发生。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 the circulation anomalies have been investigated for both daily precipitation extreme （DPE） events, and the non-extreme （NEDP） events of daily precipitation on a regional scale in the middle and lower reaches of Yangtze river in the present study. The DPE events are defined as events whose precipitation amounts are above the 99 percentile in a rearranged time series in ascending order in precipitation amount of the regional mean daily precipitation in the river reaches whereas the non-extremes are defined here as the events whose percentiles are from 85 to 90 and from 75 to 80 in the same time series of precipitation. Our results showed that the threshold of the precipitation amount of the DPEs is 25 mm/d. The occurrences of DPEs in the river reaches change on both interannual and weekly scales. Both the DPE and NEDP events tend to occur more frequently in Meiyu/Baiu period, especially after the 1990s. The circulation anomalies in DPE and NEDP events show some similar distributions such as an anomalous anticyclone over the Southern China Sea and northwestern Pacific, an anomalous cyclone over regions northwest of the precipitation area, and the divergent flow emanating from the rainfall area outward at the upper troposphere. However, different features are clearly seen between these two types of events by big differences in both the intensity and location of the anomalous circulation. The anomalous circulations of the DPE events are intensified as compared to those of the NEDP events. The anomalous circulations in the upper troposphere in the DPE events match more effectively with the anomalous circulations in the lower troposphere than those in the NEDP events. Different sources of water vapor are found to be related to different types of precipitation events; the vapor is from the Bay of Bengal in the DPE events whereas it is from the South China Se

关 键 词：气候学 极端降水 非极端降水 环流特征 长江中下游 海温 

分 类 号：P426.6[天文地球—大气科学及气象学]