A Joint Impact on Water Vapor Transport over South China during the Pre-Rainy Season by ENSO and PDO

Abstract

Based on precipitation data from 60 stations in South China (SC) and NCEP reanalysis data, the Hybrid Single-Particle Lagrangian Integrated Trajectory model (HYSPLIT_4.9) is used to analyze the difference of water vapor transport tracks, water vapor sources, and their precipitation contribution rate to frontal/monsoon precipitation, with four combinations of ENSO and PDO phase for a period of 53 years (1960–2012). The results show that: (1) For the frontal precipitation, in the Pacific Decadal Oscillation positive phase (PDO+), there is a great positive water vapor difference between ENSO+ (the positive ENSO phase) and ENSO− (the negative ENSO phase) over the tropical Indian Ocean (IO), the Bay of Bengal (BOB), the South China Sea (SCS) and the western Pacific (WP), the distribution of the difference is adjusted for PDO− (the negative PDO phase). For monsoon precipitation, when PDO and ENSO are in phase resonance, water vapor gathers over IO-BOB-SCS. (2) For the frontal precipitation, both PDO+ and PDO−, compare with ENSO+, more water vapor from SCS for ENSO−, but the southward water vapor transport anomaly over the western part of BOB-SCS-ocean east of the Philippines, which leads a decline in precipitation contribution rate of SCS water vapor. Both ENSO+ and ENSO−, compare with PDO−, more water vapor comes from IO-BOB for PDO+, but their precipitation contribution rates are lower. (3) For the summer monsoon precipitation, SCS and IO are important rain contributor sources. Regardless of the PDO phase, compared with ENSO+, there is more water vapor from the IO and WP for ENSO−, the easterly anomaly in the south of the stronger subtropical high brings more water vapor from WP to SC, the strong westerly anomalies in the IO-BOB-SCS increases IO water vapor transporting to SC, so water vapor precipitation contribution rates of IO and WP are higher. Both ENSO+ and ENSO−, compare with PDO−, more water vapor comes from SCS and EC for PDO+, but their precipitation contribution rates are lower. (4) The water vapor transport process of precipitation in PFS over SC is jointly affected by ENSO and PDO.