Importance of cold and dry surges in substantiating the NAM and ENSO relationship



[1] We propose a possible mechanism for the influence of the Northern Hemisphere annular mode/Arctic Oscillation (NAM/AO) on westerly wind bursts (WWB). Using 26-year reanalysis data, we statistically demonstrate and evidentially confirm that the NAM intensifies WWB through Asian cold and dry surges. Twin cyclones with anomalous westerlies and updrafts were dominant in the western tropical Pacific in positive NAM years. This structure was caused by the inflow of cold and dry advections associated with cold and dry surges, which excited anomalous heat transport from the western tropical Pacific Ocean. This thermodynamic structure is similar to that of the Matsuno-Gill pattern. Observational evidence indicates that the surge associated with the NAM is a probable cause of El Niño outbreaks through the intensification of WWB, stemming from the WWB association with the Matsuno-Gill pattern.