Study On Water Vapor Transport And Its Inter-annual And Inter-decadal Variation Of South China First Rainy Season By Lagrangian Method

This study simulated the moisture transport process of South China during its first rainy season using a Lagrangian airflow trajectory model(Hybrid Single Particle Lagrangian Integrated Trajectory:HYSPLIT),combining with "air parcel trace method","E-P diagnostics method" and "areal source-receptor attribution method",to determine the moisture transport characteristics of South China during first rainy season and its relationship with South China Sea summer monsoon(SCSSM)firstly,and then analyzed the relationship between water vapor transport and sea surface temperature during the first flood season of South China under different time scales.The main conclusions are summarized as follows:(1)Using the Lagrangian method to analyze the climatic characteristics of water vapor transport of South China during its first flood season,it is found that water vapor mainly comes from the Northern Indian Ocean,the BOB-South China Sea and the Philippine Ocean,and the eastern part of China.(2)It is found that the moisture transport paths and sources of South China are closely related to the onset of SCSSM.Divided by SCSSM onset dates.Before the onset of SCSSM,West Pacific(WP)contributes most to the moisture transport of South China.After the onset of SCSSM,the results show that moisture transport path locates southwest to South China.Indian Ocean(IO)contributes the most moisture to South China.Eastern China(EC)also has a certain contribute to South China.The change of the western Pacific subtropical high and the circulation adjustment over the Indian Peninsula after the onset of SCSSM is the main cause of the moisture transport variation of South China during its first rainy season.(3)The water vapor transport of South China first rainy season has obvious annual variations.Before the onset of SCSSM,the moisture transport over Western Pacific region has a significant interannual change during South China first rainy season.While after the onset of SCSSM,Bay of Bengal has a significant change.Besides,interannual water vapor transport is closely related to ENSO before the onset of the South China Sea summer monsoon.Due to the Western Pacific subtropical high lying more south during El Nino years than during La Nina years,the location of eastly moisture transport path is correspondingly more to the south during El Nino years than it is during La Nina years,resulting in the contribution of the northwest Pacific to the water vapor during El Nino years slightly lower than that of La Nina years.(4)The water vapor transport of South China first rainy season has obvious annual variations.The water vapor transport during the first flood season of South China in 1961-2012 can be divided into three stages,and the trends before and after the onset of the SCSSM are approximately the opposite.Before the onset of the South China Sea summer monsoon,the water vapor transport during the first rainy season of South China is closely related to PDO in the previous autumn.During PDO warm phase,moisture content is consistently more over all key regions than its is during PDO cold phase.Note that only in northwestern Pacific(NWP,north of 200° N),moisture is less than it is during PDO cold phase.As a result,southwestern Pacific(SWP,south of 20° N)is the main moisture source of South China first rainy season before the onset of SCSSM during PDO warm phase.While the eastern part of China,the Bay of Bengal,South China sea and the offshore of China are the main moisture source during PDO cold phase.