With the methods of correlation and composite analyses, Ju et al. discussed the relationship between low-frequency oscillation in the summer monsoon region in East Asia and droughts/floods in the middle and lower reac...With the methods of correlation and composite analyses, Ju et al. discussed the relationship between low-frequency oscillation in the summer monsoon region in East Asia and droughts/floods in the middle and lower reaches of the Yangtze River and found that strong monsoon years usually cause more rain in the region. Studying the interdecadal variation of precipitation in three rain zones over south China, the valley of Yangtze River and north China, Tan et al. showed that mid- and higher- latitude circulation and SST have important effect on the precipitation associated with summer monsoon in east China. With data of north Pacific SST and characteristic subtropical high, Cai et al.discovered that the anomalies of precipitation distribution in rainy seasons were directly affected by the activity of the subtropical high. As shown in an observational study, anti-correlation was found between the rainfall in the middle and lower reaches of the Yangtze River during the Mei-yu season and the frequency of TCs in northwest Pacific, including the South China Sea, in the prime of summer . The less active maritime TCs are, the more southward the westerly zone is over the Asian mid- latitudes. It is favorable for the Southwest Monsoon to transport moisture towards the region the Yangtze and Huaihe Rivers and for frontal rains to stagnate over the middle and lower reaches of the Yangtze, increasing the rainfall during Mei-yu. Otherwise, the mid-latitude westerly is located more northward, frontal rains develop north of the Yangtze River, the Mei-yu season shortens and rainfall decreases. Statistically studying the effect of South China Sea TCs and directionturning TCs on the Mei-yu season from 1980 to 1991, Kang et al.showed that 85% of the TCs had significant effect on Mei-yu and 35% of them would cause it to end. In addition, the Chinese meteorologists have long noted the cut-off role of TCs in the transportation of moisture by Southwest Monsoon to the Mei-yu fronts in the Yangtze and Huaihe Rivers. They found that TCs active offshore China would usually take moisture from the Bay of Bengal and cut off the transportation of moisture and transformation of energy for the frontal areas of Mei-yu, weakening, or even break and end the precipitation （like TC 9106, or Zeke）, but there were few TCs over offshore waters or even the west Pacific when Mei-yu was active. As shown in a numerical study, the disturbance of Zeke triggered a horizontal flow field at lower troposphere that weakened the Southwest Monsoon and further decreased its moisture transportation to the region of Yangtze and Huaihe Rivers and the convergence of moisture flux there. At the same time, the typhoon had indirect impact on the Mei-yu through its effect on the subtropical high.展开更多
The feature of the decadal movement of the Meiyu belt and their association with East Asia atmospheric circulation for the period of 1979―2007 is examined in this study. It is shown that the Meiyu belt of China has a...The feature of the decadal movement of the Meiyu belt and their association with East Asia atmospheric circulation for the period of 1979―2007 is examined in this study. It is shown that the Meiyu belt of China has a decadal shift in the late 1990s. There is a remarkable difference between the periods before and after 1999, with the Meiyu belt mainly located to the south of the Yangtze River valley before 1999, but afterward mainly located in the Huaihe River valley. At the same time, a distinctive tropospheric warming and stratospheric cooling trend is found in the mid-latitudes of East Asia, which causes the upper tropospheric pressure surfaces upward bulging and the tropoause elevated in the subtropics and associated widening of the subtropical area over East Asia. Accompanying the subtropics widening, the subtropical westerly jet over East Asia shifts northward and the East Asia tropical Hadley circulation expands poleward, which results in the northward shift of the Meiyu belt.展开更多
基金Natural Science Foundation of China (40505011) Project of Shanghai Science andTechnology Committee (05DZ05815)
文摘With the methods of correlation and composite analyses, Ju et al. discussed the relationship between low-frequency oscillation in the summer monsoon region in East Asia and droughts/floods in the middle and lower reaches of the Yangtze River and found that strong monsoon years usually cause more rain in the region. Studying the interdecadal variation of precipitation in three rain zones over south China, the valley of Yangtze River and north China, Tan et al. showed that mid- and higher- latitude circulation and SST have important effect on the precipitation associated with summer monsoon in east China. With data of north Pacific SST and characteristic subtropical high, Cai et al.discovered that the anomalies of precipitation distribution in rainy seasons were directly affected by the activity of the subtropical high. As shown in an observational study, anti-correlation was found between the rainfall in the middle and lower reaches of the Yangtze River during the Mei-yu season and the frequency of TCs in northwest Pacific, including the South China Sea, in the prime of summer . The less active maritime TCs are, the more southward the westerly zone is over the Asian mid- latitudes. It is favorable for the Southwest Monsoon to transport moisture towards the region the Yangtze and Huaihe Rivers and for frontal rains to stagnate over the middle and lower reaches of the Yangtze, increasing the rainfall during Mei-yu. Otherwise, the mid-latitude westerly is located more northward, frontal rains develop north of the Yangtze River, the Mei-yu season shortens and rainfall decreases. Statistically studying the effect of South China Sea TCs and directionturning TCs on the Mei-yu season from 1980 to 1991, Kang et al.showed that 85% of the TCs had significant effect on Mei-yu and 35% of them would cause it to end. In addition, the Chinese meteorologists have long noted the cut-off role of TCs in the transportation of moisture by Southwest Monsoon to the Mei-yu fronts in the Yangtze and Huaihe Rivers. They found that TCs active offshore China would usually take moisture from the Bay of Bengal and cut off the transportation of moisture and transformation of energy for the frontal areas of Mei-yu, weakening, or even break and end the precipitation （like TC 9106, or Zeke）, but there were few TCs over offshore waters or even the west Pacific when Mei-yu was active. As shown in a numerical study, the disturbance of Zeke triggered a horizontal flow field at lower troposphere that weakened the Southwest Monsoon and further decreased its moisture transportation to the region of Yangtze and Huaihe Rivers and the convergence of moisture flux there. At the same time, the typhoon had indirect impact on the Mei-yu through its effect on the subtropical high.
基金Supported jointly by National Basic Research Program of China (Grant No. 2006CB403604)the National Key Technology R&D Program (Grant Nos. 2007BAC03A01 and 2006BAC02B04)
文摘The feature of the decadal movement of the Meiyu belt and their association with East Asia atmospheric circulation for the period of 1979―2007 is examined in this study. It is shown that the Meiyu belt of China has a decadal shift in the late 1990s. There is a remarkable difference between the periods before and after 1999, with the Meiyu belt mainly located to the south of the Yangtze River valley before 1999, but afterward mainly located in the Huaihe River valley. At the same time, a distinctive tropospheric warming and stratospheric cooling trend is found in the mid-latitudes of East Asia, which causes the upper tropospheric pressure surfaces upward bulging and the tropoause elevated in the subtropics and associated widening of the subtropical area over East Asia. Accompanying the subtropics widening, the subtropical westerly jet over East Asia shifts northward and the East Asia tropical Hadley circulation expands poleward, which results in the northward shift of the Meiyu belt.
