摘要
近几十年来长江下游地区夏季(6—8月)降水量呈现出显著上升的变化趋势,利用1961—2020年夏季台站降水资料,通过降水项分解法,定量分析了该降水趋势的可能影响因素。结果表明:1)长江下游地区夏季降水的上升趋势主要是由日降水量显著增加造成,而日降水量显著增加主要与整层水汽垂直梯度增大和垂直上升速度增强所导致的降水增加有关;2)长江下游地区对流层低层大气温度因地面升温的加热作用而显著上升,高层大气温度受亚太振荡相位正转负的影响而下降,使得高、低层大气的温差变大,低层大气比湿升高、高层大气比湿降低,导致整层水汽垂直梯度增加,为局地降水的增强提供了充沛的水汽条件;低层大气异常辐合加之显著增长的不稳定能量为垂直上升运动的增强和对流性降水的增加提供了有利的动力和热力条件,从而造成了长江下游地区夏季降水的显著上升趋势。
The lower reaches of the Yangtze River(28°—33°N,116°—123°E)are economically developed and prone to frequent summer(June-August)flooding disasters.Studying the variability of summer precipitation in this region is of great significance.In recent decades,summer precipitation in this area has increased significantly.This study quantitatively analyzes the factors influencing this trend using precipitation term decomposition,based on observed summer precipitation from 1961 to 2020,TC best track datasets,and hourly mean reanalysis data from the European Centre for Medium-Range Weather Forecasts Reanalysis Version 5(ERA5).The results show that:(1)From 1961 to 2020,the average annual precipitation increase reaches 3.54 mm/year(passing the 95%significance test),with a growth rate of 38.1%.The variance contribution of the linear trend accounts for 20.7%of the total variance of summer precipitation.The increasing trend of daily precipitation reached 0.04 mm/day(passing the 95%significance test),which is the primary for the significant increase in summer precipitation in this region.(2)Precipitation term decomposition reveals that the variability of summer precipitation is influenced by vertical velocity,horizontal motion,water vapor,and evaporation.Among these,significant upward trends in water vapor and vertical velocity contribute to the increase in daily precipitation by 0.039 mm/day(passing the 99%significance test)and 0.019 mm/day(passing the 95%significance test),respectively.This is primarily related to the increased vertical gradient of water vapor and the enhancement of vertical rise velocity.(3)The temperature of the lower atmosphere has risen due to the ground warming,while the upper atmosphere has cooled due to the phase change of the Asia-Pacific Oscillation(from a positive phase to a negative phase).The ability of the atmosphere to retain moisture is directly proportional to temperature.The intensified temperature difference between the upper and lower levels of the atmosphere increases the vertical gradient of water vapor,providing abundant moisture for increased precipitation.Additionally,abnormal positive vorticity in the upper atmosphere(200 hPa)and abnormal negative vorticity in the lower atmosphere(850 hPa)indicate that large-scale circulation does not favor the strengthening of upward motion.However,the anomalous convergence in the lower atmosphere,combined with increased instability energy due to mesoscale system variations,offers favorable dynamic and thermodynamic conditions for enhanced vertical rise velocity and increased convective precipitation in the summer.Previous studies have lacked quantitative analysis of the dynamic and thermodynamic factors affecting summer precipitation trends in the lower reaches of the Yangtze River.This paper quantifies the contributions of water vapor and vertical velocity variability to the summer precipitation trend,providing a theoretical basis for understanding precipitation changes in the context of global warming.
作者
杜如意
宋雨佳
赵传湖
黄菲
王国复
DU Ruyi;SONG Yujia;ZHAO Chuanhu;HUANG Fei;WANG Guofu(College of Oceanic and Atmospheric Sciences,Ocean University of China,Qingdao 266100,China;Physical Oceanography Laboratory/Frontiers Science Center for Deep Ocean Multispheres and Earth System,Qingdao 266100,China;Pilot National Laboratory for Marine Science and Technology(Qingdao),Qingdao 266237,China;National Climate Centre,Beijing 100081,China)
出处
《大气科学学报》
CSCD
北大核心
2024年第4期557-569,共13页
Transactions of Atmospheric Sciences
基金
国家自然科学基金项目(41975061)
山东省自然科学基金重大基础研究项目(ZR2019ZD12)。
关键词
长江下游地区
夏季降水
降水项分解
比湿垂直梯度
垂直上升速度
lower reaches of the Yangtze River
summer precipitation
precipitation-term decomposition
specific humidity vertical gradient
vertical velocity
