Role of Stratospheric Sudden Warmings on the response to Central Pacific El Niño

The Northern Hemisphere (NH) polar stratospheric response to Central Pacific El Niño (CP-El Niño) events remains unclear. Contradictory results have been reported depending on the definition and events considered. We show that this is due to the prominent role of Stratospheric Sudden Warmings (SSWs), whose signal dominates the NH winter polar stratospheric response to CP-El Niño. In fact, the CP-El Niño signal is robust when the events are classified according to the occurrence of SSWs and displays opposite response in winters with and without SSWs. In the absence of SSWs, polar stratospheric responses to Central Pacific and Eastern Pacific El Niño are clearly distinguishable in early winter, in relation to differences in the Pacific-North American pattern. Our results demonstrate that the occurrence of SSWs needs to be taken into account when studying the stratospheric response to CP-El Niño and explain why different responses to CP-El Niño have been reported previously.