热带气象学报2012，Vol.28Issue(3)：367-378,12.DOI:10.3969/j.issn.1004-4965.2012.03.009
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
摘要
Abstract
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 Sea in the NEDP events. The apparent diabatic heating and vapor sources in these two types of events are examined, which show stronger net heating over the northern flank of the rainfall area and stronger cooling in northwestern Pacific in the DPE events. The stronger cooing over oceans facilitates the maintenance of an anomalous anticyclone over the southeastern coastal areas. Interestingly, very significant sea surface temperature anomalies (SSTA) are observed in the Pacific in the DPE other than the NEDP events, which look similar to the SSTA pattern of El Nino episodes. Both the anomalous circulation and SSTA patterns in the DPE events are more significant statistically in large areas than those in the NEDP events. Almost no significant signals (0.05 level of confidence) are found in SSTA in the NEDP events. The weaker significance of both circulation anomalies and SSTA in the NEDP events suggest that the NEDP events are more probably induced by the local circulation anomalies than by both the local and remote forcing from the middle latitudes and tropics.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Key words
climatology/ daily precipitation extremes/ non-extreme precipitation events/ atmospheric circulation/ middle and lower reaches of Yangtze River/ SST分类
天文与地球科学引用本文复制引用
韩洁,管兆勇,李明刚..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[J].热带气象学报,2012,28(3):367-378,12.基金项目
国家科技支撑计划项目课题(2007BAC29B02) （2007BAC29B02）
江苏省“青蓝工程创新团队”项目共同资助 （）
