Interdecadal Variability in Summer Precipitation over East China during the Past 100 Years and Its Possible Causes

In this paper, the interdecadal variations of rainfall over North China, the Yangtze River valley, and South China during the past 100 years are examined using weather station data. The results show that the rainfall over these three regions underwent simultaneous shifts in the early 1910 s, the early 1920s, the middle 1940 s, the middle 1960s, the late 1970 s, and the early 1990 s, although there are different interdecadal shifting periods. During the past 100 years the distribution patterns of summer rainfall over eastern China are primarily characterized by dipoles, such as "positive south and negative north" or "positive north and negative south" in different interdecadal periods. Furthermore, the probability of the totally reverse distribution patterns during two adjacent interdecadal periods is higher (60%) whether they are dipolar or tripolar. In addition, summer Pacific Decadal Oscillation (PDO), winter Arctic Oscillation (AO), and spring arctic sea ice also showed synchronous shifts around the late 1920s, the middle 1940s, the late 1970s, and the middle 1990s, consistent with the shifting periods of summer precipitation over three regions of eastern China, suggesting that PDO, AO, and arctic sea ice have played a synergetic role in the interdecadal variation of summer rainfall over eastern China during the past 100 years.
At interdecadal time scales, PDO in summer is significantly negatively correlated with summer rainfall in North China. The interdecadal variability of PDO may generate interdecadal wave trains of Pacific-Japan (PJ) interconnection pattern at 500-hPa geopotential height and atmospheric circulation in the 850-hPa wind field, which is similar to that affecting the interdecadal variation of summer rainfall over North China. Consequently, summer rainfall over North China showed interdecadal variation. The AO in wintertime is significantly positively correlated with summer rainfall over the Yangtze River valley. When AO enters its positive interdecadal phase from winter to spring, it causes an increase of precipitation and a decrease in temperature over the southern Eurasian continent. The cold and wet state over the southern Eurasian continent persists from winter to summer because of the memory of soil humidity. It causes the weakening of sea-land contrast in summer. As a result, the East Asian summer monsoon experiences interdecadal weakening. Correspondingly, the rainfall over the Yangtze River valley shows interdecadal increase. Spring Arctic sea ice is significantly negatively correlated with summer rainfall over South China. Interdecadal variation in Arctic sea ice can generate interdecadal wave trains of the Eurasia-South China interconnection pattern associated with the anomalous propagation of stationary Rossby waves at 500-hPa geopotential height, which affects the interdecadal variation in rainfall over South China.