An Analysis of the Causes of Decadal Variations of Rainfall in Shandong in Summer

The precipitation in Shandong in July, August as well as the whole summer (JJA) and the corresponding 500 hPa geopotential height fields are analyzed by means of the SVD (singular value decomposition) methodology. It is found that the general circulations in East Asia and the Western Pacific underwent decadal changes around 1979. The geopotential height, in particular over key areas like the South China Sea and the Philippines, increased after 1979. Corresponding to the changes in the geopotential height, the rainfall in Shandong started to decrease around 1979. The synthesized analysis shows that when the geopotential height at 500hPa level decreases in the key areas, the Western Pacific subtropical high shifts northward and an anticyclonic anomalous cell enforces the southerly flow over Shandong-Korea-Japan, Shandong could experience a wet period. A dry period is likely to occur when the geopotential height increases in these key areas, the subtropical high moves southward or expands westward to a great distance, and a cyclonic anomalous cell controls Shandong. Respective conceptual models for the causative mechanism are obtained for the cases of July, August and the whole summer (JJA) .

Interdecadal variability of the large-scale extreme hot event frequency over the middle and lower reaches of the Yangtze River basin and its related atmospheric patterns

Based on daily maximum temperature data from Chinese weather stations for the period 1960- 2013, the characteristics of the interdecadal variability of large-scale extreme hot event （EHE） frequency over the middle and lower reaches of the Yangtze River basin （MLYR） are analyzed. It is found that the frequency of large-scale EHE over the MLYR experiences two significant interdecadal changes, around the early 1970s and early 2000s, having a more-less-more variability shape during the past half century. Furthermore, the EHE frequency interdecadal variability-related atmospheric circulation patterns are diagnosed. The results indicate the western Pacific subtropical high could not be the dominant atmospheric circulation associated with the interdecadal variability of the large-scale EHE frequency over the MLYR. In contrast, the dominant teleconnection pattern over the Eurasian continent, which is represented by the second empirical orthogonal function mode of the 200 hPa geopotential height, is closely related to the interdecadal variability of the EHE frequency over the MLYR. The results of this study deepen our understanding of the variability of the EHE frequency over the MLYR and its possible mechanism.

Decadal Anomalies of Winter Precipitation over Southern China in Association with El Nio and La Nia

Using multiple datasets, this paper analyzes the characteristics of winter precipitation over southern China and its association with warm and cold phases of E1 Nifio-Southern Oscillation during 1948 2011. The study proves that E1 Nifio is an important external forcing factor resulting in above-normal winter precipitation in southern China. The study also reveals that the impact ofLa Nifia on the winter precipitation in southern China has a decadal variability. During the winter of La Nifia before 1980, the East Asian winter monsoon is stronger than normal with a deeper trough over East Asia, and the western Pacific subtropical high weakens with its high ridge retreating more eastward. Therefore, anomalous northerly winds dominate over southern China, leading to a cold and dry winter. During La Nifia winter after 1980, however, the East Asian trough is weaker than normal, unfavorable for the southward invasion of the winter monsoon. The India-Burma trough is intensified, and the anomalous low-level cyclone excited by La Nifia is located to the west of the Philippines. Therefore, anomalous easterly winds prevail over southern China, which increases moisture flux from the tropical oceans to southern China. Meanwhile, La Nifia after 1980 may lead to an enhanced and more northward subtropical westerly jet over East Asia in winter. Since southern China is rightly located on the right side of the jet entrance region, anomalous ascending motion dominates there through the secondary vertical circulation, favoring more winter precipitation in southern China. Therefore, a cold and wet winter, sometimes with snowy and icy weathers, would occur in southern China during La Nifia winter after 1980. Further analyses indicate that the change in the spatial distribution of sea surface temperature anomaly during the La Nifia mature phase, as well as the decadal variation of the Northern Hemisphere atmospheric circulation, would be the important reasons for the decadal variability of the La Nifia impact on the atmospheric circulation in East Asia and winter precipitation over southern China after 1980.