An extreme rainstorm hit southern China during 13–17 December 2013, with a record-breaking daily rainfall rate, large spatial extent, and unusually long persistence. We examined what induced this heavy rainfall proce...An extreme rainstorm hit southern China during 13–17 December 2013, with a record-breaking daily rainfall rate, large spatial extent, and unusually long persistence. We examined what induced this heavy rainfall process, based on observed rainfall data and NCEP–NCAR reanalysis data through composite and diagnostic methods. The results showed that a Rossby waveguide within the subtropical westerly jet caused the event. The Rossby wave originated from strong cold air intrusion into the subtropical westerly jet over the eastern Mediterranean. With the enhancement and northward shift of the Middle East westerly jet, the Rossby wave propagated slowly eastward and deepened the India–Burma trough, which transported a large amount of moisture from the Bay of Bengal and South China Sea to southern China. Strong divergence in the upper troposphere, caused by the enhancement of the East Asian westerly jet, also favored the heavy rainfall process over Southeast China. In addition, the Rossby wave was associated with a negative-to-positive phase shift and enhancement of the North Atlantic Oscillation, but convergence in the eastern Mediterranean played the key role in the eastward propagation of the Rossby wave within the subtropical westerly jet.展开更多
As the strongest subseasonal atmospheric variability during boreal winter, three remarkable sudden stratospheric major warming(SSW) events in the 2000 s are investigated in terms of the Brewer–Dobson circulation(BDC)...As the strongest subseasonal atmospheric variability during boreal winter, three remarkable sudden stratospheric major warming(SSW) events in the 2000 s are investigated in terms of the Brewer–Dobson circulation(BDC) response. Our study shows that the changes of cross-isentropic velocity during the SSWs are not only confined to the polar region, but also extend to the whole Northern Hemisphere: enhanced descent in the polar region, as well as enhanced ascent in the tropics. When the acceleration of the deep branch of the BDC descends to the middle stratosphere, its strength rapidly decreases over a period of one to two weeks. The acceleration of the deep branch of the BDC is driven by the enhanced planetary wave activity in the mid-to-high-latitude stratosphere. Different from the rapid response of the deep branch of the BDC, tropical upwelling in the lower stratosphere accelerates up to 20%–40% compared with the climatology, 20–30 days after the onset of the SSWs,and the acceleration lasts for one to three months. The enhancement of tropical upwelling is associated with the large-scale wave-breaking in the subtropics interacting with the midlatitude and tropical Quasi-Biennial Oscillation–related mean flow.展开更多
The second EOF(EOF2) mode of interannual variation in summer rainfall over East China is characterized by inverse rainfall changes between South China(SC) and the Yellow River-Huaihe River valleys(YH).However,un...The second EOF(EOF2) mode of interannual variation in summer rainfall over East China is characterized by inverse rainfall changes between South China(SC) and the Yellow River-Huaihe River valleys(YH).However,understanding of the EOF2 mode is still limited.In this study,the authors identify that the EOF2 mode physically depicts the latitudinal variation of the climatological summer-mean rainy belt along the Yangtze River valley(YRRB),based on a 160-station rainfall dataset in China for the period 1951-2011.The latitudinal variation of the YRRB is mostly attributed to two different rainfall patterns:one reflects the seesaw(SS) rainfall changes between the YH and SC(SS pattern),and the other features rainfall anomalies concentrated in SC only(SC pattern).Corresponding to a southward shift of the YRRB,the SS pattern,with above-normal rainfall in SC and below-normal rainfall in the YH,is related to a cyclonic anomaly centered over the SC-East China Sea region,with a northerly anomaly blowing from the YH to SC;while the SC pattern,with above-normal rainfall in SC,is related to an anticyclonic anomaly over the western North Pacific(WNP),corresponding to an enhanced southwest monsoon over SC.The cyclonic anomaly,related to the SS pattern,is induced by a near-barotropic eastward propagating wave train along the Asian upper-tropospheric westerly jet,originating from the mid-high latitudes of the North Atlantic.The anticyclonic anomaly,for the SC pattern,is related to suppressed rainfall in the WNP.展开更多
基金supported by the National Natural Science Foundation of China (NSFC) (Grant Nos. 41276002 and 41130859)the National Basic Research Program of China (Grant Nos. 2012CB955603 and 2013CB956201)+1 种基金the NSFC–Shandong Joint Fund for Marine Science Research Centers (Grant No. U1406401)the Fund for Open Research Programs of the Key Laboratory of Meteorological Disaster (Nanjing University of Information Science and Technology), Ministry of Education (KLME1301)
文摘An extreme rainstorm hit southern China during 13–17 December 2013, with a record-breaking daily rainfall rate, large spatial extent, and unusually long persistence. We examined what induced this heavy rainfall process, based on observed rainfall data and NCEP–NCAR reanalysis data through composite and diagnostic methods. The results showed that a Rossby waveguide within the subtropical westerly jet caused the event. The Rossby wave originated from strong cold air intrusion into the subtropical westerly jet over the eastern Mediterranean. With the enhancement and northward shift of the Middle East westerly jet, the Rossby wave propagated slowly eastward and deepened the India–Burma trough, which transported a large amount of moisture from the Bay of Bengal and South China Sea to southern China. Strong divergence in the upper troposphere, caused by the enhancement of the East Asian westerly jet, also favored the heavy rainfall process over Southeast China. In addition, the Rossby wave was associated with a negative-to-positive phase shift and enhancement of the North Atlantic Oscillation, but convergence in the eastern Mediterranean played the key role in the eastward propagation of the Rossby wave within the subtropical westerly jet.
文摘As the strongest subseasonal atmospheric variability during boreal winter, three remarkable sudden stratospheric major warming(SSW) events in the 2000 s are investigated in terms of the Brewer–Dobson circulation(BDC) response. Our study shows that the changes of cross-isentropic velocity during the SSWs are not only confined to the polar region, but also extend to the whole Northern Hemisphere: enhanced descent in the polar region, as well as enhanced ascent in the tropics. When the acceleration of the deep branch of the BDC descends to the middle stratosphere, its strength rapidly decreases over a period of one to two weeks. The acceleration of the deep branch of the BDC is driven by the enhanced planetary wave activity in the mid-to-high-latitude stratosphere. Different from the rapid response of the deep branch of the BDC, tropical upwelling in the lower stratosphere accelerates up to 20%–40% compared with the climatology, 20–30 days after the onset of the SSWs,and the acceleration lasts for one to three months. The enhancement of tropical upwelling is associated with the large-scale wave-breaking in the subtropics interacting with the midlatitude and tropical Quasi-Biennial Oscillation–related mean flow.
基金supported by the National Natural Science Foundation of China (Grant Nos. 41375086 and 41320104007)
文摘The second EOF(EOF2) mode of interannual variation in summer rainfall over East China is characterized by inverse rainfall changes between South China(SC) and the Yellow River-Huaihe River valleys(YH).However,understanding of the EOF2 mode is still limited.In this study,the authors identify that the EOF2 mode physically depicts the latitudinal variation of the climatological summer-mean rainy belt along the Yangtze River valley(YRRB),based on a 160-station rainfall dataset in China for the period 1951-2011.The latitudinal variation of the YRRB is mostly attributed to two different rainfall patterns:one reflects the seesaw(SS) rainfall changes between the YH and SC(SS pattern),and the other features rainfall anomalies concentrated in SC only(SC pattern).Corresponding to a southward shift of the YRRB,the SS pattern,with above-normal rainfall in SC and below-normal rainfall in the YH,is related to a cyclonic anomaly centered over the SC-East China Sea region,with a northerly anomaly blowing from the YH to SC;while the SC pattern,with above-normal rainfall in SC,is related to an anticyclonic anomaly over the western North Pacific(WNP),corresponding to an enhanced southwest monsoon over SC.The cyclonic anomaly,related to the SS pattern,is induced by a near-barotropic eastward propagating wave train along the Asian upper-tropospheric westerly jet,originating from the mid-high latitudes of the North Atlantic.The anticyclonic anomaly,for the SC pattern,is related to suppressed rainfall in the WNP.