Decadal Characteristics Of Summer Eurasian Blockings And Its Possible Relation To Precipitation Over China

On the basis of observations investigation is conducted on the decadal characteristics of summer Eurasian blockings and its possible relation to precipitation over China. The main results are:(1) The summer Eurasian blockings exist pronounced annual variation. Through comparing the blockings over Okhotsk, Baikal, Ural regions and Europe, it shows that the activities of blockings over Europe are more while those over Baikal are less.(2) The summer Eurasian blockings exist pronounced decadal variation. Their periods and amplitudes are different from each other, in that the period of blockings in Okhotsk region is longer, yet in Ural region it is shorter, and both blockings in Baikal and Europe have two periods. The long-term trends of blockings over the four regions are not obvious.(3) It can be seen from the correlation and composite analyses that on the decadal timescale, more (less) blockings over Okhotsk region in summer are closely related to floodings(droughts) to the south of Changjiang River, and droughts (floodings) over the Hanshui River and the Weishui River;more(less) blockings over Baikal region in summer are in close relation to floodings(droughts) over the Huanghe- Huaihe River and the Changjiang- Huaihe River, and droughts(floodings) to the south of Changjiang River;more(less) blockings over Ural region in summer are closely associated with floodings(droughts) over the Weishui River, and droughts(floodings) over the large areas to the south of Changjiang River and in South China;more(less) blockings over Europe in summer are in close relation to floodings(droughts) to the large regions in South China, and droughts(floodings) over the Hanshui River and the Weishui River.(4) On the decadal timescale, the possible mechanisms of impacts of the summer Eurasian blockings anomalies on the precipitation in China are as follows: when blockings over Okhotsk and Europe in summer are more, rainfall in the Hanshui River and the Weishui River is scarce because although northerly prevails inthis region, there is no water vapor convergence;rainfall in the areas to the south of Changjiang River is plentiful because northerly prevails and warm moist air from the ocean converges in this region. When blockings over Baikal in summer are more, rainfall in the Huanghe- Huaihe River and the Changjiang- Huaihe River is abundant since northerly prevails and warm moist air from the ocean converges in this region;rainfall in the areas to the south of Changjiang River is scarce since southerly prevails and there is no water vapor convergence in this region. When blockings over Ural region in summer are more, rainfall in the Weishui River and to its west is abundant since northerly prevails and warm moist air from the ocean converges in this region;rainfall in the areas to the south of Changjiang River is scarce since southerly prevails and there is no water vapor convergence in this region. Furthermore, when blockings over Okhotsk and Baikal in summer are more, the West Pacific Subtropical High (WPSH) is stronger and larger in area. Therefore, WPSH may be an important reason for the more rainfall in the areas to the south of Changjiang River, in the Huanghe- Huaihe River and in the Changjiang- Huaihe River. The correlation of WPSH and blockings over both Ural region and Europe in summer is not obvious.