The Influence of the Extratropical Atmospheric Disturbances on ENSO

Abstract

AbstractThe composite analysis of the 5 major ENSO events since 1980s show that, through the meridional wind anomaly, the extratropical atmospheric disturbances play a role in triggering the occurrence as well as in the development and decay of ENSO. The extratropical atmospheric disturbances interact with ENSO although they are influenced by ENSO. Before the occurrence of ENSO, due to the anticyclonic anomaly in midlatitude of the South Indian Ocean, the anticyclonic anomaly over Australia tends to be enhanced through the dispersion of Rossby wave; In the meantime, the equatorial convergence of the southerly anomaly off the east of Australia and the northerly anomaly in the Philippine excite the onsets of the westerly anomaly in the equatorial western Pacific and the occurrence of ENSO. Afterwards, the cyclonic anomaly in the Southeast Pacific and the associated southerly anomaly further enhance the westerly anomaly in the equatorial middle and eastern Pacific and the development of ENSO. In the mature phase of ENSO, the cyclonic anomaly in the Southeast Pacific together with the South Oscillation is weakened due to the eastward movement of the anticyclonic anomaly to the east of Australia. Moreover, the cyclonic Aleutian anomaly, in particular the wind anomaly in the subtropical North Pacific, enhances the upwelling of sea water and decreases sea surface temperature in the equatorial middle and eastern Pacific, and therefore plays a role in the decay of ENSO.