In recent years, the socio-economic impacts of winter extreme climate events have underscored the importance of winter climate anomalies in Southwest China （SWC）. The spatio-temporal variability of surface air tempe...In recent years, the socio-economic impacts of winter extreme climate events have underscored the importance of winter climate anomalies in Southwest China （SWC）. The spatio-temporal variability of surface air temperature （SAT） and precipitation in SWC and their possible causes have been investigated in this paper based on observational data from 1961 to 2010. The results indicate that SAT anomalies in SWC have two dominate modes, one is homogenous, and the other a zonal dipole. The former is caused by the anomalies of East Asian winter monsoon; the latter arises from the anomalies of both subtropical west Pacific high and regional cold air in lower troposphere. The most dominant mode of precipitation anomalies in SWC is homogenous and it has a high correlation with northern hemisphere annular mode （NAM, AO）. Neither NAM nor ENSO has significant impacts on SAT in SWC. The anomalies of NAM are associated with the anomalies of tropical circulations, and therefore precipitation over the SWC. When NAM is in positive （negative） phase, the winter precipitation is more （less） than normal in SWC. Winter precipitation increase over the whole SWC is associated with the El Nino. However, during La Nina winter, the pattern is not uniform. There is an increase in precipitation over the central parts and a decrease in western and eastern parts of SWC. The severe drought in SWC in winter 2010 is more likely caused by anomalies of NAM, not El Nino.展开更多
In order to study the origin of the spatial structure of the Northern Hemisphere Annular Mode （NAM）,a linear stochastic model is constructed empirically from the output of a GCM run.Optimal stochastic forcing in ter...In order to study the origin of the spatial structure of the Northern Hemisphere Annular Mode （NAM）,a linear stochastic model is constructed empirically from the output of a GCM run.Optimal stochastic forcing in terms of the maximum variance contribution,which may be potentially related to the maintenance of the NAM,is investigated.Theoretical analysis on the dominant non-modal response to the stochastic forcing shows that this dominance is jointly decided by the properties of forcing and the non-modal growth （decay）.The results of computation demonstrate that the eddy forcing corresponding to the instantaneous rapid growth of the NAM,which is indicated by the instantaneous stochastic optimum,has a roughly similar but significantly different annular structure like that of the NAM.On the other hand,the eddy forcing corresponding to the stationary variance of the NAM,which is indicated by the asymptotic stochastic optimum,has a totally different structure from that of the NAM.These results,together with our general discussion on the relationship between the spatial structure of forcing and response,suggest that one should be careful when explaining the spatial structure of the NAM by that of the eddy forcing.展开更多
基金National Natural Science Foundation of China, No.40875060 No.60832012 Basic Research and Operation Program of institute of Plateau Meteorology, China Meteorological Administration, No.BROP201017 Acknowledgements We thank Hyacinth Cyprain Nnamchi for his kind help in improving our English writing.
文摘In recent years, the socio-economic impacts of winter extreme climate events have underscored the importance of winter climate anomalies in Southwest China （SWC）. The spatio-temporal variability of surface air temperature （SAT） and precipitation in SWC and their possible causes have been investigated in this paper based on observational data from 1961 to 2010. The results indicate that SAT anomalies in SWC have two dominate modes, one is homogenous, and the other a zonal dipole. The former is caused by the anomalies of East Asian winter monsoon; the latter arises from the anomalies of both subtropical west Pacific high and regional cold air in lower troposphere. The most dominant mode of precipitation anomalies in SWC is homogenous and it has a high correlation with northern hemisphere annular mode （NAM, AO）. Neither NAM nor ENSO has significant impacts on SAT in SWC. The anomalies of NAM are associated with the anomalies of tropical circulations, and therefore precipitation over the SWC. When NAM is in positive （negative） phase, the winter precipitation is more （less） than normal in SWC. Winter precipitation increase over the whole SWC is associated with the El Nino. However, during La Nina winter, the pattern is not uniform. There is an increase in precipitation over the central parts and a decrease in western and eastern parts of SWC. The severe drought in SWC in winter 2010 is more likely caused by anomalies of NAM, not El Nino.
基金Supported by the National Natural Science Foundation of China under Grant Nos.40940022 and 40775033the National Key Basic Research and Development Project of China under Grant No.2009CB421503+2 种基金the Special Scientific Research Project for Public Interest of China under Grant No.GYHY200806009the LaSW Fund of the Chinese Academy of Meteorological Sciences (2008)the Qinglan Project of Jiangsu Province of China (2009)
文摘In order to study the origin of the spatial structure of the Northern Hemisphere Annular Mode （NAM）,a linear stochastic model is constructed empirically from the output of a GCM run.Optimal stochastic forcing in terms of the maximum variance contribution,which may be potentially related to the maintenance of the NAM,is investigated.Theoretical analysis on the dominant non-modal response to the stochastic forcing shows that this dominance is jointly decided by the properties of forcing and the non-modal growth （decay）.The results of computation demonstrate that the eddy forcing corresponding to the instantaneous rapid growth of the NAM,which is indicated by the instantaneous stochastic optimum,has a roughly similar but significantly different annular structure like that of the NAM.On the other hand,the eddy forcing corresponding to the stationary variance of the NAM,which is indicated by the asymptotic stochastic optimum,has a totally different structure from that of the NAM.These results,together with our general discussion on the relationship between the spatial structure of forcing and response,suggest that one should be careful when explaining the spatial structure of the NAM by that of the eddy forcing.
