Abstract
By using the NCEP/NCAR re-analysis data from 1990 to 2019 and the daily precipitation data of CN05.1 gridded observation dataset, the high and low level circulation characteristics and their influence on the onset and precipitation of Meiyu in Jiangsu Province in recent 30 years are studied. Comparing Meiyu in the 2010s with that in the 1990s, it is found that during the 2010s Meiyu was characterized by a late arrival and less precipitation. There were obviously earlier Meiyu years in the 1990s, while no extremely early Meiyu year existed in the 2010s, which was mainly caused by the late northward jump of the upper jet and the ridge line of the western Pacific subtropical high (WPSH hereinafter) in the 2010s. Compared with the 1990s, the 2010s witnessed an eastward position of the South Asia high and a westward position of the subtropical westerly jet during the Meiyu period, which are not conducive to precipitation in the Yangtze-Huaihe region. At the same time, the cold air flowing southward to the Yangtze-Huaihe region was hindered in the 2010s due to the change of blocking in the middle troposphere. In the 2010s, the water vapor transport and the vertical transportation weakened, resulting in the decrease of precipitation in the Yangtze-Huaihe region.
Highlights
Each summer, the northward advancement of the East Asian monsoon effects a rainy season of continuous precipitation in the Yangtze-Huaihe region in China, which is called Meiyu
Frequent occurrences of drought and flood disasters can be seen in the YangtzeHuaihe region, and those in June and July are mostly related to the abnormal Meiyu in that year [1,2]
According to the 9-year moving average of the Meiyu onset time of Jiangsu Province from 1961 to 2019 (Figure 1), it can be seen that the overall change trend in the 59 years can be divided into two stages
Summary
The northward advancement of the East Asian monsoon effects a rainy season of continuous precipitation in the Yangtze-Huaihe region in China, which is called Meiyu. In 2018, the YangtzeHuaihe region had a late Meiyu and less precipitation due to the northerly subtropical upper jet in East Asia, the WPSH, the atypical blocking situation in the middle to high latitudes, and the late onset of the summer monsoon [13,14]. The year 2017 had a stronger East Asian trough, weaker summer monsoon, and stronger WPSH, resulting in a later Meiyu onset, earlier Meiyu ending, and shorter length and less amount of precipitation in the Yangtze-Huaihe region [15,16]. Since the 1990s, the onset of Meiyu over the Yangtze-Huaihe region has been delayed, the temporal features and precipitation process of the Meiyu have changed, and the circulation background shows characteristics different from the past. By comparing the characteristics of Meiyu in the 2010s to those in the 1990s, this work discusses the interdecadal evolution of Meiyu in recent 30 years, and further reveals the variation pattern and mechanism of Meiyu
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