全球变暖背景下南海夏季风变化特征

Characteristics of the South China Sea summer monsoon under global warming

南海夏季风的爆发和推进影响着中国夏季雨带的进程。采用美国国家环境预报中心(National Centers for Environmental Prediction,NCEP)和美国国家大气研究中心(National Center for Atmospheric Research,NCAR)再分析资料分析全球变暖前、后南海夏季风的演变特征。研究结果表明,全球变暖导致南海夏季风减弱,主要出现以下特征:(1)南海夏季风的平均建立时间提早,平均撤退时间推迟,历时长度更长,持续时间有上升趋势。(2)南海夏季风爆发后(6—9月),南海西北部对流层低层(700 hPa以下)由海陆热力差异导致的局地环流在全球变暖后有减弱趋势,进入中国华南和西南地区的西南夏季风有所减弱。(3)夏季风盛行期间,西南风携孟加拉湾水汽经过中南半岛进入中国南海的水汽呈减少趋势,且从南海输入华南的水汽减少,导致中国东部降水变化趋势存在空间差异。(4)南海夏季风指数表明,南海夏季风对南海中南部以及华南东部的影响加强,而对南海北部和西南地区的影响强度明显减弱。

The onset and advance of the South China Sea summer monsoon affect the process of the summer rain belt in China.The NCEP(National Centers for Environmental Prediction)/NCAR(National Center for Atmospheric Research)reanalysis data are used to analyze the characteristics of changes in the South China Sea summer monsoon before/after global warming.The results show that the South China Sea summer monsoon is weakened after global warming,and the main features are as follows.(1)The average establishment time of the South China Sea summer monsoon is earlier,the average retreat time is delayed,the duration is longer,and the duration has an upward trend.(2)After the onset of the South China Sea summer monsoon(between June and September),the local circulation in the lower troposphere(below 700 hPa)in the northwest of the South China Sea caused by the thermal difference between land and sea tends to weaken after global warming,and the southwest summer monsoon entering South China and Southwest China tends to weaken.(3)During the prevailing summer monsoon,the southwest wind carrying water vapor from the Bay of Bengal into the South China Sea through the Indo-China Peninsula shows a decreasing trend,and the decrease in water vapor entering South China from the South China Sea leads to spatial differences in precipitation trends in eastern China.(4)The South China Sea summer monsoon index shows that the influence of the South China Sea summer monsoon on the south-central part of the South China Sea and the east of South China is strengthened,while the influence on the north of the South China Sea and Southwest China is weakened.