台灣地區的颱風與梅雨為主要的降雨天氣系統，而梅雨則與西南季風產生密切相關。但台灣秋冬為東北季風盛行區，東北季風肇始與其相伴隨的秋雨，亦常有異常降水出現。當秋季雨量不足時，亦會造成台灣北部地區來年春耕及民生用水的缺乏，因此秋季之降雨對台灣地區的用水，尤其北部影響甚大，雖然台灣秋季現象的降雨，並不似梅雨現象來得明顯，但有些年份產生豪大雨，仍造成局部地區的災害，有些年份，降雨量甚小，也致來年春季各地用水不足，因此本研究特別針對秋季豪大雨與降雨甚少，甚至幾乎未降雨的特殊秋霖天氣現象加以探討，以分析探討其天氣特性。首先由經向環流分析，藉以界定台灣地區秋霖的起始時間，研究發現9月份係北方系統逐漸抵達台灣北部地區，從而影響台灣地區的秋季降雨現象，可謂台灣秋霖的起始月份。
而本研究除統計資料分析探討外，並以個案探討研究秋霖天氣特性，其中影響的天氣系統包括低壓槽、鋒面、南支槽以及渦旋偶極子的低層北風噴效應等，另由氣候環流系統的分析，則發現秋霖多雨年與少雨年的重力位高度場，在台灣地區出現正距平與負距平反相的現象。
The main weather rainfall systems of Taiwan are typhoon and Mei-Yu systems. And the rainfall of Mei-Yu season is closely related to the southwest monsoon. In winter Taiwan is northeast monsoon season and it’s also accompanying with rainfall in this season. If the autumn rainfall of north Taiwan is not enough, it will cause northern Taiwan lack of water for people's livelihood of next year. In this study will focus on autumn rains of Taiwan areas. So the climate characteristics of autumn rainfall is the major factor in this research. From the longtiudeal analysis which can difine the period of Taiwan's autumn rain season is begin from September.
In this study except the data analysis, the cases study are also given, such as tropic trough, indian-china trough, vortex dipole and north-east monsoon weather system. And then the the rainy and dry seasons of autumn rain are also investigated. The results show that the characteristicof autumn rain is opposite. In rainy autumn, the geopotential high field is negative abnormal. In dry autumn, the geopotential high is positive abnormal.
