关于东亚副热带季风和热带季风的再认识

Reinvestigations on the East Asian Subtropical Monsoon and Tropical Monsoon

利用NCEP/NCAR再分析数据集和CMAP(Climate Prediction Center Merged Analysis of Precipitation)降水资料,分析了东亚副热带夏季风与热带夏季风的区别和联系,以及两者相互作用问题,深入讨论了东亚副热带季风的本质。分析发现东亚副热带夏季风建立早于热带夏季风,于3月中旬已经开始建立。两者是相互独立的两个过程,前者并非是后者向北推进的结果;相反,前者建立后的突然南压有利于后者的爆发。副热带夏季风为渐进式建立,但撤退迅速;热带夏季风爆发突然,但撤退缓慢。副热带夏季风的建立以偏南风的建立为特征,而热带夏季风的建立以偏东风向偏西风转变为特征。热带夏季风的建立时间取决于经向海陆热力差异转向,而东亚副热带夏季风则更依赖于纬向海陆热力差异的逆转。亚洲大陆(含青藏高原)与西太平洋之间的纬向海陆热力差异的季节逆转无论对东亚副热带夏季风还是热带夏季风均有重要作用。

The East Asian monsoon consists of the subtropical monsoon and the tropical monsoon, whose interaction has not been paid attention to. NCEP/NCAR reanalysis dataset and CMAP （Climate Prediction Center Merged Analysis of Precipitation） rain data are used to investigate differences and relationship between the East Asian subtropical monsoon and the tropical monsoon in order to discuss the essence of the subtropical monsoon. Analyses find that the onset of the subtropical monsoon is in middle March, earlier than that of the tropical monsoon. They are independent on each other, the subtropical monsoon is not the northward branch of the tropical monsoon, by contraries, the former onset is propitious to the latter breakout. The subtropical monsoon sets up step by step but retreats rapidly, while the tropical monsoon breaks out suddenly but withdraws slowly. The subtropical/tropical monsoon onset is characterized by southerly/westerly beginning, which lies on zonal/meridional land-sea thermal contrast reverse. Heating source over the Tibetan Plateau and zonal land-sea thermal difference play important roles not only in the subtropical monsoon, but also in the tropical monsoon.