Based on the NCEP/ NCAR reanalysis data the interannual variability of the East Asian winter mon-soon (EAWM) is studied with a newly defined EAWM intensity index. The marked features for a strong (weak) winter monsoon...Based on the NCEP/ NCAR reanalysis data the interannual variability of the East Asian winter mon-soon (EAWM) is studied with a newly defined EAWM intensity index. The marked features for a strong (weak) winter monsoon include strong (weak) northerly winds along coastal East Asia, cold (warm) East Asian continent and surrounding sea and warm (cold) ocean from the subtropical central Pacific to the trop-ical western Pacific, high (low) pressure in East Asian continent and low (high) pressure in the adjacent ocean and deep (weak) East Asian trough at 500 hPa. These interannual variations are shown to be closely connected to the SST anomaly in the tropical Pacific, both in the western and eastern Pacific. The results suggest that the strength of the EAWM is mainly influenced by the processes associated with the SST anom-aly over the tropical Pacific. The EAWM generally becomes weak when there is a positive SST anomaly in the tropical eastern Pacific (El Ni?o), and it becomes strong when there is a negative SST anomaly (La Ni?a). Moreover, the SST anomaly in the South China Sea is found to be closely related to the EAWM and may persist to the following summer. Both the circulation at 850 hPa and the rainfall in China confirm the connection between the EAWM and the following East Asian summer monsoon. The possible reason for the recent 1998 summer flood in China is briefly discussed too. Key words East Asian winter monsoon - Interannual variability - SST - Summer monsoon This study was supported by “ National Key Programme for Developing Basic Sciences” G1998040900 part 1, and by key project (KZ 952-S1-404) of Chinese Academy of Sciences.展开更多
A strong （weak） East Asian summer monsoon （EASM） is usually concurrent with the tripole pattern of North Atlantic SST anomalies on the interannual timescale during summer, which has positive （negative） SST anoma...A strong （weak） East Asian summer monsoon （EASM） is usually concurrent with the tripole pattern of North Atlantic SST anomalies on the interannual timescale during summer, which has positive （negative） SST anomalies in the northwestern North Atlantic and negative （positive） SST anomalies in the subpolar and tropical ocean. The mechanisms responsible for this linkage are diagnosed in the present study. It is shown that a barotropie wave-train pattern occurring over the Atlantic-Eurasia region likely acts as a link between the EASM and the SST tripole during summer. This wave-train pattern is concurrent with geopotential height anomalies over the Ural Mountains, which has a substantial effect on the EASM. Diagnosis based on observations and linear dynamical model results reveals that the mechanism for maintaining the wave-train pattern involves both the anomalous diabatic heating and synoptic eddy-vorticity forcing. Since the North Atlantic SST tripole is closely coupled with the North Atlantic Oscillation （NAO）, the relationships between these two factors and the EASM are also examined. It is found that the connection of the EASM with the summer SST tripole is sensitive to the meridional location of the tripole, which is characterized by large seasonal variations due to the north-south movement of the activity centers of the NAO. The SST tripole that has a strong relationship with the EASM appears to be closely coupled with the NAO in the previous spring rather than in the simultaneous summer.展开更多
The interannual variation of Asian winter (NE) monsoon and its influence is studied using the long-term integration of Max-Plank Institute ECHAM3(T42 L19) model. The simulation well reproduces the main features of th...The interannual variation of Asian winter (NE) monsoon and its influence is studied using the long-term integration of Max-Plank Institute ECHAM3(T42 L19) model. The simulation well reproduces the main features of the climatological mean Asian winter monsoon and shows pronounced difference of atmospheric circulation between strong and weak winter monsoon and for the consecutive seasons to follow. Most striking is the appearance and persistence of an anomalous cyclonic flow over the western Pacific and enhanced Walker circulation for strong winter monsoon in agreement with the observation. The contrast in summer rainfall patterns of both East China and India can also be discerned in the simulation. Comparison of three sets of experiments with different SST shows that the forcing from the anomalies of global SST makes a major contribution to the interannual variability of Asiao winter monsoon and, in particular, to the interseasonal persistence of the salient features of circulation. The SSTA over the tropical western Pacific also plays an important part of its own in modulating the Walker circulation and the extratropical flow patterns. The apparent effect of strong NE monsoon is to enhance the convection over the tropical western Pacific. This effect, on the one hand, leads to a strengthening of SE trades to the east and extra westerly flow to the west, thus favorable to maintaining a specific pattern of SSTA. On the other hand, the thermal forcing associated with the SSTA acts to strengthen the extratropical flow pattern which is, in turn, conducive to stronger monsoon activity. The result seems to suggest a certain self-sustained regime in the air-sea system, which is characterized by two related interactions, namely the air-sea and tropical-extratropical interactions with intermittent outburst of NE cold surge as linkage. There is a connection between the strength of the Asian winter monsoon and the precipitation over China in the following summer. Links between these two variabilities are mainly throug展开更多
The present study investigates the influence of South China Sea （SCS） SST and ENSO on winter （January-February-March; JFM） rainfall over South China and its dynamic processes by using station observations for the ...The present study investigates the influence of South China Sea （SCS） SST and ENSO on winter （January-February-March; JFM） rainfall over South China and its dynamic processes by using station observations for the period 1951-2003, Met Office Hadley Center SST data for the period 1900-2008, and ERA-40 reanalysis data for the period 1958-2002. It is found that JFM rainfall over South China has a sig- nificant correlation with Nio-3 and SCS SST. Analyses show that in El Nio or positive SCS SST anomaly years, southwesterly anomalies at 700 hPa dominate over the South China Sea, which in turn transports more moisture into South China and favors increased rainfall. A partial regression analysis indicates that the independent ENSO influence on winter rainfall occurs mainly over South China, whereas SCS SST has a larger independent influence on winter rainfall in northern part of South China. The temperature over South China shows an obvious decrease at 300 hPa and an increase near the surface, with the former induced by Nio-3 and the latter SCS SST anomalies. This enhances the convective instability and weakens the potential vorticity （PV）, which explains the strengthening of ascending motion and the increase of JFM rainfall over South China.展开更多
文摘Based on the NCEP/ NCAR reanalysis data the interannual variability of the East Asian winter mon-soon (EAWM) is studied with a newly defined EAWM intensity index. The marked features for a strong (weak) winter monsoon include strong (weak) northerly winds along coastal East Asia, cold (warm) East Asian continent and surrounding sea and warm (cold) ocean from the subtropical central Pacific to the trop-ical western Pacific, high (low) pressure in East Asian continent and low (high) pressure in the adjacent ocean and deep (weak) East Asian trough at 500 hPa. These interannual variations are shown to be closely connected to the SST anomaly in the tropical Pacific, both in the western and eastern Pacific. The results suggest that the strength of the EAWM is mainly influenced by the processes associated with the SST anom-aly over the tropical Pacific. The EAWM generally becomes weak when there is a positive SST anomaly in the tropical eastern Pacific (El Ni?o), and it becomes strong when there is a negative SST anomaly (La Ni?a). Moreover, the SST anomaly in the South China Sea is found to be closely related to the EAWM and may persist to the following summer. Both the circulation at 850 hPa and the rainfall in China confirm the connection between the EAWM and the following East Asian summer monsoon. The possible reason for the recent 1998 summer flood in China is briefly discussed too. Key words East Asian winter monsoon - Interannual variability - SST - Summer monsoon This study was supported by “ National Key Programme for Developing Basic Sciences” G1998040900 part 1, and by key project (KZ 952-S1-404) of Chinese Academy of Sciences.
基金jointly supported by the National Basic Research Program of China (Grant Nos. 2010CB950404, 2013CB430203, 2010CB950501 and 2012CB955901)the National Natural Science Foundation of China (Grant No. 41205058)+1 种基金the China Postdoctoral Science Foundation (Grant No. 2012M510634)the National Science and Technology Support Program of China (Grant No. 2009BAC51B05)
文摘A strong （weak） East Asian summer monsoon （EASM） is usually concurrent with the tripole pattern of North Atlantic SST anomalies on the interannual timescale during summer, which has positive （negative） SST anomalies in the northwestern North Atlantic and negative （positive） SST anomalies in the subpolar and tropical ocean. The mechanisms responsible for this linkage are diagnosed in the present study. It is shown that a barotropie wave-train pattern occurring over the Atlantic-Eurasia region likely acts as a link between the EASM and the SST tripole during summer. This wave-train pattern is concurrent with geopotential height anomalies over the Ural Mountains, which has a substantial effect on the EASM. Diagnosis based on observations and linear dynamical model results reveals that the mechanism for maintaining the wave-train pattern involves both the anomalous diabatic heating and synoptic eddy-vorticity forcing. Since the North Atlantic SST tripole is closely coupled with the North Atlantic Oscillation （NAO）, the relationships between these two factors and the EASM are also examined. It is found that the connection of the EASM with the summer SST tripole is sensitive to the meridional location of the tripole, which is characterized by large seasonal variations due to the north-south movement of the activity centers of the NAO. The SST tripole that has a strong relationship with the EASM appears to be closely coupled with the NAO in the previous spring rather than in the simultaneous summer.
文摘The interannual variation of Asian winter (NE) monsoon and its influence is studied using the long-term integration of Max-Plank Institute ECHAM3(T42 L19) model. The simulation well reproduces the main features of the climatological mean Asian winter monsoon and shows pronounced difference of atmospheric circulation between strong and weak winter monsoon and for the consecutive seasons to follow. Most striking is the appearance and persistence of an anomalous cyclonic flow over the western Pacific and enhanced Walker circulation for strong winter monsoon in agreement with the observation. The contrast in summer rainfall patterns of both East China and India can also be discerned in the simulation. Comparison of three sets of experiments with different SST shows that the forcing from the anomalies of global SST makes a major contribution to the interannual variability of Asiao winter monsoon and, in particular, to the interseasonal persistence of the salient features of circulation. The SSTA over the tropical western Pacific also plays an important part of its own in modulating the Walker circulation and the extratropical flow patterns. The apparent effect of strong NE monsoon is to enhance the convection over the tropical western Pacific. This effect, on the one hand, leads to a strengthening of SE trades to the east and extra westerly flow to the west, thus favorable to maintaining a specific pattern of SSTA. On the other hand, the thermal forcing associated with the SSTA acts to strengthen the extratropical flow pattern which is, in turn, conducive to stronger monsoon activity. The result seems to suggest a certain self-sustained regime in the air-sea system, which is characterized by two related interactions, namely the air-sea and tropical-extratropical interactions with intermittent outburst of NE cold surge as linkage. There is a connection between the strength of the Asian winter monsoon and the precipitation over China in the following summer. Links between these two variabilities are mainly throug
基金supported by the National Basic Research Program of China (Grant No. 2009CB421405) the National Natural Science Foundation of China (Grant Nos. 40730952 and40905027)+1 种基金 the Program of Knowledge Innovation for the third period of the Chinese Academy of Sciences (GrantNo. KZCX2-YW-220)City University of Hong Kong Strategic Research Grants 7002231 and 7002329
文摘The present study investigates the influence of South China Sea （SCS） SST and ENSO on winter （January-February-March; JFM） rainfall over South China and its dynamic processes by using station observations for the period 1951-2003, Met Office Hadley Center SST data for the period 1900-2008, and ERA-40 reanalysis data for the period 1958-2002. It is found that JFM rainfall over South China has a sig- nificant correlation with Nio-3 and SCS SST. Analyses show that in El Nio or positive SCS SST anomaly years, southwesterly anomalies at 700 hPa dominate over the South China Sea, which in turn transports more moisture into South China and favors increased rainfall. A partial regression analysis indicates that the independent ENSO influence on winter rainfall occurs mainly over South China, whereas SCS SST has a larger independent influence on winter rainfall in northern part of South China. The temperature over South China shows an obvious decrease at 300 hPa and an increase near the surface, with the former induced by Nio-3 and the latter SCS SST anomalies. This enhances the convective instability and weakens the potential vorticity （PV）, which explains the strengthening of ascending motion and the increase of JFM rainfall over South China.
