Content area
Full text
1. Introduction
Rainfall is an important factor in describing a regional climate given its substantial impact on human life. Rainfall distribution is extremely inhomogeneous and localized. However, rainfall from a climatological point of view is usually controlled by large-scale phenomena. For instance, the Asian monsoon system dominates the precipitation over the western North Pacific and East Asian (WNP–EA) sector, our current area of interest. This monsoon system has a strong annual cycle, with a wet season in the boreal summer, a dry season in the boreal winter, and two transition seasons between the wet and dry seasons. This annual variation is termed “the slow annual cycle,” which is commonly associated with solar insolation (e.g., LinHo and Wang 2002, hereafter LW02). A well-known feature of double peaks of heavy rainfall in the wet phase is usually found over the WNP–EA sector. The first peak is associated with the mei-yu–baiu rainfall, and the second with the WNP summer monsoon and typhoon rainfall. This variation within the wet phase of the Asian monsoon system is termed the fast annual cycle (Ding and Chan 2005; LW02). Thus, five natural rainy periods associated with the annual cycle are usually found over the WNP–EA sector (Chen and Chen 2003; LW02; Yeh and Chen 2000).
The Asian summer monsoon system includes several subregional systems—the Indian, East Asian, and WNP summer monsoons (Wang and LinHo 2002)—and covers the major rainy season over this region, so there have been many studies that have focused on this rainy period (e.g., Annamalai et al. 1999; Chou 2003; Ding 1992; Ding and Chan 2005; Li and Yanai 1996; Murakami 1987; Webster et al. 1998; Yasunari and Seki 1992 and references therein). In contrast, relatively less attention has been given to the rainfall variations in the other periods such as winter, fall, and spring. Nevertheless, the precipitation variations in these seasons merit further investigation. For instance, the spring rain in this region has a distinct characteristic; its rainfall is also very significant (Tian and Yasunari 1998). Some studies (Hung et al. 2004; Jiang et al. 2003) show that the spring rainfall over the WNP–EA has a strong interannual variation associated with El Niño–Southern Oscillation (ENSO) and an interdecadal variation associated with the Pacific decadal oscillation (PDO). Other studies...