摘要
通过对1998年南海季风爆发过程中大尺度风场、温度场、厚度场、地面气压场以及视热源与视水汽汇的演变分析研究了对流活动对大尺度场的作用,结果表明:大尺度环流与中尺度对流活动之间可能存在着一种正反馈机制。在季风爆发早期,大尺度背景与中尺度对流活动的关系主要表现为前者为季风爆发以及中尺度对流活动的发生提供有利的天气和动力条件;季风爆发后期持续的大范围中尺度对流活动反过来会对大尺度环流存在明显的反馈作用。由对流活动强烈发展产生的凝结潜热释放在南海北部造成了显著的大气加热,使对流层中上层出现一明显的加热中心,这导致:(1)南海上空经向温度梯度由高层向低层发生反向,形成北高南低的温度梯度,从而使大尺度环流发生季节性改变;(2)相应南海北部地面气压不断加深,形成宽广的季风槽和明显的减压区,促使副热带高压从南海地区最后撤离;(3)随着中低层低压环流的不断发展,对流系统和降水区进一步加强并向南扩展,有利于南海季风在南海中、南部地区爆发和维持;(4)季风槽的加深使其南侧的季风气流与水汽输送进一步加强,促使季风爆发过程达到盛期。
The apparent heat sources, apparent moisture sinks and large-scale wind, temperature as well as surface pressure during the summer monsoon onset over the northern South China Sea （SCS） in 1998 were investigated. The results suggested that there was a kind of positive feedback mechanism between large-scale circulations and meso-scale convective systems （MCSs）. At the early stage of the monsoon onset, the large-scale background provided favorable synoptic and dynamic conditions for the summer monsoon onset and formation of meso-scale convective activities; whereas after the summer monsoon onset, occurrence of persistent and large-scale mesoscale convective activities produced obvious feedback effect on large-scale circulations. Because of the release of latent heating driven by enhanced convective activities, the intense atmospheric heating appeared over the northern SCS, which resulted in： （1） the meridional temperature gradient over the SCS reversed from upper-level to low-level and then the large-scale circulations were changed seasonally; （2） correspondingly, the surface pressure over the northern SCS deepened continually and formed broad monsoon trough and obvious pressure-reducing areas, thus making the subtropical high moving out of the SCS eventually; （3） with the development of the low pressure circulations in the middle and low troposphere, the MCSs further enhanced and extended southward, which was favorable to the SCS monsoon onset and maintaining over the middle and southern SCS; （4） the deepening of monsoon trough promoted strengthening of the monsoon flow and moisture transport on the southern side of it, consequently the monsoon onset reaching prevalence.
出处
《气象学报》
CAS
CSCD
北大核心
2005年第4期443-454,共12页
Acta Meteorologica Sinica
基金
中国科学技术部攀登项目A"南海季风试验"
