In this study, using the ECMWF reanalysis data, the possible linkage between the Pacific-North American teleconnection pattern （PNA） and the North Atlantic Oscillation （NAO） during boreal winter （December- Febru...In this study, using the ECMWF reanalysis data, the possible linkage between the Pacific-North American teleconnection pattern （PNA） and the North Atlantic Oscillation （NAO） during boreal winter （December- February） is investigated. The PNA and the NAO pattern are obtained by performing Rotated Empirical Orthogonal Function （REOF） analysis on an anomalous daily mean 300-hPa geopotential height field. The composite daily NAO indices show that the NAO indices are prone to be negative （positive） when the contemporary PNA indices are extremely positive （negative）. The correlation coefficients between the daily PNA and NAO indices also confirm that, indeed, there is a significant anti-correlation between the PNA and NAO indices. The correlation peaks at a lag of 0 days （meaning contemporary correlation）, and its value is 0.202. Analyses of a newly defined Rossby wave breaking index and diagnostics of the stream function tendency equation indicate that the anti-correlation between PNA and NAO may be caused by the anomalous Rossby wave breaking events associated with the PNA pattern.展开更多
This study uses multiple sea surface temperature （SST） datasets to perform a parallel comparison of three super El Nifios and their effects on the stratosphere. The results show that, different from ordinary El Nifi...This study uses multiple sea surface temperature （SST） datasets to perform a parallel comparison of three super El Nifios and their effects on the stratosphere. The results show that, different from ordinary El Nifios, warm SST anomalies appear earliest in the western tropical Pacific and precede the super El Nifio peak by more than 18 months. In the previous winter, relative to the mature phase of El Nifio, as a precursor, North Pacific Oscillation-like circulation anomalies are observed. A Pacific-North America （PNA） teleconnection appears in the extratropical troposphere during the mature phase, in spite of the subtle differences between the intensities, as well as the zonal position, of the PNA lobes. Related to the negative rainfall response over the tropical Indian Ocean, the PNA teleconnection in the winter of 1997/98 is the strongest among the three super El Nifios. The northern winter stratosphere shows large anomalies in the polar cap temperature and the circumpolar westerly, if the interferences from other factors are linearly filtered from the circulation data. Associated with the positive PNA response in a super El Nino winter, positive polar cap temperature anomalies and circumpolar easterly anomalies, though different in timing, are also observed in the mature winters of the three super El Nifios. The stratospheric polar vortex in the next winter relative to the 1982/83 and 1997/98 events is also anomalously weaker and warmer, and the stratospheric circulation conditions remain to be seen in the coming winter following the mature phase of the 2015/16 event.展开更多
A comparison of sensitivity in extratropical circulation in the Northern Hemisphere （NH） and Southern Hemisphere （SH） is conducted through observational analyses and diagnostic linear model experiments for two typ...A comparison of sensitivity in extratropical circulation in the Northern Hemisphere （NH） and Southern Hemisphere （SH） is conducted through observational analyses and diagnostic linear model experiments for two types of El Ni（n）o events,the traditional El Ni（n）o with the strongest warmth in the eastern tropical Pacific （EP El Ni（n）o） and the El Ni（n）o Modoki with the strongest warmth in the central tropical Pacific （CP El Ni（n）o）.It is shown that CP El Ni（n）o favors the occurrence of a negative-phase Northern Annular Mode （NAM）,while EP El Ni（n）o favors that of the Pacific-North American （PNA） pattern.In SH,both EP and CP El Ni（n）o induce a negative phase Southern Annular Mode （SAM）.However,the former has a greater amplitude,which is consistent with the stronger sea surface temperature （SST） warmth.The difference in the two types of El Ni（n）o events in NH may originate from the dependence of heating-induced extratropical response on the location of initial heating,which may be associated with activity of the stationary wave.In SH,the lack of sensitivity to the location of heating can be associated with weaker activity of the stationary wave therein.展开更多
文摘In this study, using the ECMWF reanalysis data, the possible linkage between the Pacific-North American teleconnection pattern （PNA） and the North Atlantic Oscillation （NAO） during boreal winter （December- February） is investigated. The PNA and the NAO pattern are obtained by performing Rotated Empirical Orthogonal Function （REOF） analysis on an anomalous daily mean 300-hPa geopotential height field. The composite daily NAO indices show that the NAO indices are prone to be negative （positive） when the contemporary PNA indices are extremely positive （negative）. The correlation coefficients between the daily PNA and NAO indices also confirm that, indeed, there is a significant anti-correlation between the PNA and NAO indices. The correlation peaks at a lag of 0 days （meaning contemporary correlation）, and its value is 0.202. Analyses of a newly defined Rossby wave breaking index and diagnostics of the stream function tendency equation indicate that the anti-correlation between PNA and NAO may be caused by the anomalous Rossby wave breaking events associated with the PNA pattern.
基金supported by the Startup Foundation for Introducing Talent of Nanjing University of Information Science and Technology (Grant No. 2016r060)the National Key Research and Development Program (Grant No. 2016YFA0602104)+2 种基金the National Natural Science Foundation of China (Grant Nos. 41575041, 41430533 and 91437105)the Chinese Academy of Sciences (Grant No. XDA11010402)the China Meteorological Administration Special Public Welfare Research Fund (Grant No. GYHY201406001)
文摘This study uses multiple sea surface temperature （SST） datasets to perform a parallel comparison of three super El Nifios and their effects on the stratosphere. The results show that, different from ordinary El Nifios, warm SST anomalies appear earliest in the western tropical Pacific and precede the super El Nifio peak by more than 18 months. In the previous winter, relative to the mature phase of El Nifio, as a precursor, North Pacific Oscillation-like circulation anomalies are observed. A Pacific-North America （PNA） teleconnection appears in the extratropical troposphere during the mature phase, in spite of the subtle differences between the intensities, as well as the zonal position, of the PNA lobes. Related to the negative rainfall response over the tropical Indian Ocean, the PNA teleconnection in the winter of 1997/98 is the strongest among the three super El Nifios. The northern winter stratosphere shows large anomalies in the polar cap temperature and the circumpolar westerly, if the interferences from other factors are linearly filtered from the circulation data. Associated with the positive PNA response in a super El Nino winter, positive polar cap temperature anomalies and circumpolar easterly anomalies, though different in timing, are also observed in the mature winters of the three super El Nifios. The stratospheric polar vortex in the next winter relative to the 1982/83 and 1997/98 events is also anomalously weaker and warmer, and the stratospheric circulation conditions remain to be seen in the coming winter following the mature phase of the 2015/16 event.
基金supported by the National Natural Science Foundation of China(41205048)the National Basic Research Program of China,"Structures,Variability and Climatic Impacts of Ocean Circulation and Warm Pool in the Tropical Pacific Ocean"(2012CB417403)the Special Project of Chinese Academy of Sciences(XDA11010401)
文摘A comparison of sensitivity in extratropical circulation in the Northern Hemisphere （NH） and Southern Hemisphere （SH） is conducted through observational analyses and diagnostic linear model experiments for two types of El Ni（n）o events,the traditional El Ni（n）o with the strongest warmth in the eastern tropical Pacific （EP El Ni（n）o） and the El Ni（n）o Modoki with the strongest warmth in the central tropical Pacific （CP El Ni（n）o）.It is shown that CP El Ni（n）o favors the occurrence of a negative-phase Northern Annular Mode （NAM）,while EP El Ni（n）o favors that of the Pacific-North American （PNA） pattern.In SH,both EP and CP El Ni（n）o induce a negative phase Southern Annular Mode （SAM）.However,the former has a greater amplitude,which is consistent with the stronger sea surface temperature （SST） warmth.The difference in the two types of El Ni（n）o events in NH may originate from the dependence of heating-induced extratropical response on the location of initial heating,which may be associated with activity of the stationary wave.In SH,the lack of sensitivity to the location of heating can be associated with weaker activity of the stationary wave therein.
