基于客观识别的冬季南支槽强度年际变化及其与南方降水的关联性

Interannual Variation of South Branch Trough Intensity in Winter Based on Objective Identification and Its Relationship with Precipitation

利用欧洲中心ERA-Interim逐日再分析资料,基于南支槽客观识别方法定义了一个南支槽强度指数,并结合格点降水资料,对1980—2019年冬季南支槽强度的年际变化特征及其与中国降水、大气环流和水汽输送的联系进行了研究。结果表明:(1)南支槽强度变化主要呈准4年周期。(2)赤道中东太平洋海温是影响南支槽年际变化的一个重要因素,与南支槽强度有很强的负相关关系,其中Nino 3区的海温变化对南支槽强度的影响更显著。(3)南支槽偏强年从云南南部到华南一带降水量较常年偏多,其中广东、湖南和江西南部至福建一带降水量较常年偏多30 mm以上;南支槽偏弱年西南至华南一带降水较常年偏少,其中广东、广西东部降水量较常年偏少30 mm以上。(4)南支槽偏强年时存在两支异常水汽输送路径,一支为从赤道以北至10°N,从60°E延伸至菲律宾附近的异常强西风水汽输送带;另一支位于20°N附近,由南支槽的槽前西南气流将孟加拉湾地区水汽输送到我国境内,是冬季西南与华南的主要水汽通道。

Based on the ERAInterim reanalysis data,an intensity index of the South Branch Trough(SBT)is defined by the result of the objective identification method of the SBT.The relationships between the interannual variations of the SBT intensity and the precipitation,atmospheric circulation,and water vapour transport during 1980-2019 are investigated in this study.The results show:(1)The intensity index of the SBT mainly characterizes interannual variations with the quasi4year cycle.(2)The sea surface temperature in the central equatorial Pacific is an important factor affecting the interannual variations of the SBT,which has a significant negative correlation with the intensity of the SBT,especially the SST over the Nino 3 region.(3)When the intensity of the SBT is stronger,the precipitation from southern Yunnan to South China is more than normal,especially in Guangdong,southern Hunan,southern Jiangxi,and southern Fujian,which is 30 mm more than normal.When the intensity of SBT is weaker,the precipitation in Southwest China to South China is less than normal.In particular,the precipitation in central Guangdong and Guangxi is over 30 mm less than normal.(4)There are two water vapour transport paths with strong intensity of SBT.One is the water vapour conveying belt with anomalously strong westerly wind extending from the north of the equator to 10°N and 60°E to the Philippines.The other branch is located near 20°N,and the southwest airflow in front of the SBT transports the water vapour from the Bay of Bengal area to China,which is the main water vapour channel of Southwest and South China in winter.