南海夏季风期间水汽输送的气候特征

通过分析NCEP/NCAR 1973～1998年(共26年)4～8月的再分析比湿场和风场资料,研究了南海夏季风期间的水汽输送特征.夏季,东亚上空水汽水平输送特征在各月有很大差异,这是夏季风环流系统演变的结果.孟加拉湾南部地区是中国长江中下游和南海地区重要的水汽源地,来自上游孟加拉湾南部地区的水汽输送对南海季风的爆发具有重要意义.经向水汽输送主要有利于20～30°N之间华南地区的水汽辐合.从总的收支看,南海地区是一个水汽汇区.南海季风爆发早晚年的水汽输送通道存在明显差别.在爆发偏早年,从赤道印度洋到南海地区的输送通道建立早且维持时间长,4～5月南海易成为水汽辐合区;在偏晚年,南海地区水汽则是辐散的,不利于形成季风性降水.南海季风爆发早晚年与长江中下游旱涝年的水汽输送有一定联系.

Climatological Characteristics of Moisture Transport during Summer Monsoon over South China Sea

Climatological characteristics are investigated for moisture transport during summer mon-soon over the South China Sea (SCS) based on NCEP/ NCAR reanalysis data for the period of 1973~1998. It is found that the significant difference of moisture transport over East Asia exist between months due to evolutions of monsoon circulation. The moisture transports coming from the upstream of Indian Ocean play important roles in the SCS moisture budget, the SCS monsoon onset and the South China precipitation. Meridional transport is favorable to moisture convergence over South China between 200N and 300N. The SCS is a moisture sink area. Moisture transport channels in early onsetyears are significantly different from that in delayed onset years. For early onset years, the moisture passageway from the equatorial Indian Ocean to the SCS occurs earlier and maintains for a longer time, the SCS is liable to become moisture convergence region in the period of April~ May. For delayed years, the moisture over the SCS remains divergent in the end of Spring and the beginning of Summer, which is not favorable to the SCS monsoon.