Influence of the Northern Hemisphere annular mode on ENSO

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The influence of the Northern Hemisphere annular mode(NAM) on the El Nino/Southern Oscillation(ENSO) was examined using 41-year reanalysis data and an atmospheric general circulation model(AGCM). Significant lag correlations between the NAM index for spring and the Nino-3 index for the following winter were revealed. An anomalous lower tropospheric westerly associated with modulation of the westerly wind burst(WWB) over the western tropical Pacific in spring often coincided with the positive phase of the NAM and extended eastward during summer and autumn. Then, warm sea surface temperature(SST) anomalies reflecting El Nino appeared over the eastern tropical Pacific in early winter. In an AGCM experiment in which SSTs were fixed as a climatological-mean monthly distribution, the interannual modulation of WWB was significantly associated with NAM variability in spring, supporting the possible influence of the NAM in spring on an ENSO outbreak the following winter.