亚洲夏季风爆发的基本气候特征分析

利用统一的亚洲热带夏季风爆发指标,重新制作了季风爆发日期的推进图,确证了亚洲热带夏季风最早在热带东印度洋与中印半岛中南部爆发的观点,这发生在26候(5月10日前后),28候(5月20日前后)在南海地区相继爆发,这两个地区的爆发是属同一季风系的不同爆发阶段。以后通过对海陆热力对比、季节内振荡等多方面的分析,对夏季风的爆发机制问题进行了深入的研究,提出了气候学意义下影响亚洲热带夏季风爆发的关键影响因子。在此基础上,给出了夏季风最早在热带东印度洋-中印半岛-南海地区爆发机理的一种概念模式图,即大气环流的季节进程是季风爆发的背景条件;而中印半岛及其邻近地区对流活动和感热与潜热加热的迅速增强与北推、印缅槽的强烈加深,以及高原东部地区的西风暖平流作用是夏季风爆发的主要驱动力,其结果是使经向温度梯度首先在这个地区反向并建立强的上升运动区,使热带季风和降水迅速发展和加强;来自不同源地的低频30—60 d和10—20 d季节内振荡的锁相则是夏季风爆发的一种触发因子,正是这些因子的共同作用导致了亚洲热带夏季风在这个地区的最早爆发。

ANALYSIS OF THE BASIC FEATURES OF THE ONSET OF ASIAN SUMMER MONSOON

A relatively systematic climatological research on onset of the Asian tropical summer monsoon(ATSM) was carried out.Based on a unified index for onset of the ATSM,the advancing of the whole ATSM was newly made and then further documented was the view that the ATSM breaks out firstly over the tropical eastern Indian Ocean and the middle and south part of the Indo-China Peninsula in the 26th pentad(about May 10),then successively over the South China Sea(SCS) in the 28th pentad(around May 20),and it seems that the onsets over the above two regions belong to the different stages of the same monsoon system.Then,the onset mechanism of ATSM was further investigated by the comprehensive analysis on the land-sea thermodynamic contrast,intra-seasonal oscillation and so on,and the several key factors climatologically influencing the ATSM onset are put forward.Based on these results,a possible climatological schematic map for the onset of ATSM firstly over the tropical eastern Indian Ocean-the Indo-China Peninsula-the SCS is also presented.Namely the seasonal evolution of the atmospheric circulation is the background of the monsoon onset;the enhancement and northward advance of convections and of the vertical transfer of sensible heat and latent heat over the Indo-China Peninsula and neighboring areas,the dramatic deepening of the India-Burma trough,and the westerly warm advection over the eastern Tibetan Plateau are the major driving forces for the summer monsoon onset,which make the longitudinal gradient of temperature reversed firstly and ascending motion vigorous over this region,then the tropical monsoon and precipitation rapidly enhanced;and the phase-lock between the 30-60 day and 10-20 day low frequency oscillations originated from different sources is a triggering factor for the summer monsoon onset.It is just the joint effect of these factors that induces the earliest onset of ATSM over this region.