ENSO bimodality and extremes


GRL, 46, 4883– 4893, DOI:10.1029/2019GL082270

Key points: 1) Large changes in higher order moments of El Nino-Southern Oscillation (ENSO) variability in the historical record; 2) Strong bimodality in El Nino SST linked to westerly wind bursts; 3) Strongest easterly wind bursts occur during the extreme El Nino, not La Nina, years.

Tropical sea surface temperature (SST) and winds vary on a wide range of timescales, and have a substantial impact on weather and climate across the globe.” Here we study the variability of SST and zonal wind during ENSO between 1982 and 2014. We focus on changes in extreme statistics using higher-order moments of SST and zonal winds. We find hat ENSO characteristics exhibit bimodal distributions and fat tailts with extreme warm and cold temperatures in 1982-1999, but not during 2000-2014. The changes in the distributions coincide with changes in the intensity of ENSO events and the phase of the Interdecadal Pacific Oscillation (IPO). We also find that the strongest Easterly Wind Bursts occur during extreme El Ninos and not during La Ninas. Maps of SST kurtosis can serve as a diagnostic for the thermocline feedback mechanism responsible for the differences in ENSO diversity between the two periods.