Does Extreme El Niño Have a Different Effect on the Stratosphere in Boreal Winter Than Its Moderate Counterpart?

Abstract: A robust impact of El Niño on the Northern Hemisphere (NH) polar stratosphere has been demonstrated by previous studies, although whether this applies to extreme El Niño is uncertain. The time evolution of the response of the NH stratospheric vortex to extreme El Niño, compared with that to moderate eastern Pacific El Niño, is addressed by means of composite analysis using the National Centers for Environmental Prediction/Department of Energy reanalysis data set from 1980 to 2016. Lead‐lag analysis indicates that the El Niño signal actually leads the stratospheric response by ~2 months. Considering the time lag, the signal of December‐January‐February El Niño in the NH stratospheric vortex should mature in the February‐March‐April season (late winter/early spring). The patterns of circulation and temperature for late winter/early spring during extreme and moderate El Niño events are significant, exhibiting similar structure. The results are confirmed with the Whole Atmosphere Community Climate Model version 4 model, which is forced with observed SSTs of extreme and moderate El Niño in winter (December‐January‐February) to analyze the day‐to‐day propagation of their signals. Note that the magnitudes of the stratospheric responses are much larger in the case of extreme El Niño, as stronger upward propagation of planetary waves leads to a weaker northern polar vortex than during moderate El Niño events. [ABSTRACT FROM AUTHOR]