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

The Northern Hemisphere (NH) polar stratospheric response to Central Pacific El Nino (CP-El Nino) 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 Nino. In fact, the CP-El Nino 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 Nino 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 Nino and explain why different responses to CP-El Nino have been reported previously.