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The Northern Hemisphere (NH) stratospheric signals of eastern Pacific (EP) and central Pacific (CP) El Niño events are investigated in stratosphere-resolving historical simulations from phase 5 of the Coupled Model Intercomparison Project (CMIP5), together with the role of the stratosphere in driving tropospheric El Niño teleconnections in NH climate. The large number of events in each composite addresses some of the previously reported concerns related to the short observational record. The results shown here highlight the importance of the seasonal evolution of the NH stratospheric signals for understanding the EP and CP surface impacts. CMIP5 models show a significantly warmer and weaker polar vortex during EP El Niño. No significant polar stratospheric response is found during CP El Niño. This is a result of differences in the timing of the intensification of the climatological wavenumber 1 through constructive interference, which occurs earlier in EP than CP events, related to the anomalous enhancement and earlier development of the Pacific-North American pattern in EP events. The northward extension of the Aleutian low and the stronger and eastward location of the high over eastern Canada during EP events are key in explaining the differences in upward wave propagation between the two types of El Niño. The influence of the polar stratosphere in driving tropospheric anomalies in the North Atlantic European region is clearly shown during EP El Niño events, facilitated by the occurrence of stratospheric summer warmings, the frequency of which is significantly higher in this case. In contrast, CMIP5 results do not support a stratospheric pathway for a remote influence of CP events on NH teleconnections. [ABSTRACT FROM AUTHOR]

The Brewer–Dobson circulation strengthens in the lowermost tropical stratosphere during warm El Niño–Southern Oscillation (ENSO) events. Dynamical analyses using the most recent version of the Whole Atmosphere Community Climate Model show that this is due mainly to anomalous forcing by orographic gravity waves, which maximizes in the Northern Hemisphere subtropics between 18 and 22 km, especially during the strongest warm ENSO episodes. Anomalies in the meridional gradient of temperature in the upper troposphere and lower stratosphere (UTLS) are produced during warm ENSO events, accompanied by anomalies in the location and intensity of the subtropical jets. This anomalous wind pattern alters the propagation and dissipation of the parameterized gravity waves, which ultimately force increases in tropical upwelling in the lowermost stratosphere. During cold ENSO events a similar signal, but of opposite sign, is present in the model simulations. The signals in ozone and water vapor produced by ENSO events in the UTLS are also investigated. [ABSTRACT FROM AUTHOR]