ENSO amplitude modulation related to Pacific decadal variability

Abstract

Decadal modulation of El Niño/Southern Oscillation (ENSO) amplitude is reproduced by a long-term simulation with an atmosphere-ocean general circulation model. A frequency of the modulation is in phase with Pacific decadal variability (PDV). A detailed analysis of the budget of sea surface temperature (SST) shows that effect of a change in anomalous zonal advection of mean temperature correlated to ENSO development has a dominant role in low-frequency modulation of ENSO. That is because an equatorial zonal SST gradient changes periodically in the PDV cycle as a change in the background mean state for ENSO. Such characteristics are consistent with an observed climate shift and changes in ENSO characteristics that occurred in mid-1970s. Copyright 2009 by the American Geophysical Union.