摘要
用NCEP再分析资料和纬向平均的局地经向环流线性诊断模式 ,模拟了 1 980～1 999年 4～ 6月南海夏季风经向环流的建立和演变过程 ,并结合统计方法分析了模式输出的各物理因子和外界影响 (主要为越赤道气流 )在激发南海夏季风经向环流过程中的作用和贡献。结果表明 :( 1 )依 1 980～ 1 999年 4～ 6月经向环流指数的逐日演变情况判断得出 ,南海地区 4～ 6月经向风中有 48%为地转成分 ,非地转成分占 5 2 % ;若从 2 0年平均的经向环流指数逐候演变情况来看 ,4月 1候到 6候南海地区经向风中有 94%为非地转成分 ,而且 5月份非地转经向环流指数与总经向环流指数的变化趋势也比较一致。因此表明 ,引起经向风地转偏差的因子在南海夏季风的酝酿和爆发过程中的作用尤其重要。 ( 2 )对南海地区非地转经向环流指数的贡献 ,主要来自外界影响 (主要由越赤道气流体现 )和 4个物理因子 ,即与温度层结和垂直运动有关的热量垂直输送 ,纬向温度平流 ,潜热加热作用以及西风动量经向输送 ,其余 1 2个物理因子贡献较小。( 3) 2 0年中有 1 5年与外界影响有关的经向环流指数在南海夏季风爆发前一周内出现最明显的突变性加强 ,剩下的 5年则是与热量垂直输送作用有关的经向环流指数出现较明显的突变性加强 ,其余
Based on the NCEP reanalysis data, the monsoon meridional circulations over the South China Sea (SCS) from April to June in 20 years (1980—1999) are simulated with the local meridional circulation model. The physical factors' contributions to the circulation are analyzed with the linear model outputs and the index representing the intensity of the monsoon circulation. The results show that geostrophic component (pressure gradient force) accounts for 48% and ageostrophic component for 52% of the intensity of the monsoon circulation in terms of the index. The open boundary effect (or the effect of cross-equatorial flow) on the SCS monsoon meridional circulation is crucial according to the numerical outputs. Among the 16 physical factors responsible for the ageostrophic component of meridional wind, the main factors are the vertical transport of heat, the zonal transport of the heat, the latent heating and the meridional transport of the westerly momentum. The suddenly increasing influences of these factors are closely related to the onset of SCS summer monsoon. Fifteen years out of twenty years, the rapidly enhancement of cross-equatorial flow is prior to the SCS summer monsoon onset. In the other five years, the vertical transport of heat plays the main role.
出处
《气候与环境研究》
CSCD
2004年第4期605-618,共14页
Climatic and Environmental Research
基金
国家自然科学基金资助项目 40 2 75 0 2 6和 40 1 75 0 1 8资助
关键词
南海夏季风
经向环流
演变机制
诊断分析
South China Sea summer monsoon
meridional circulation
evolution mechanism
diagnostic study of monsoon
