Distinct growth rates of the two ENSO types

Abstract:

El Niño-Southern Oscillation (ENSO) events can be grouped into two types based on their sea surface temperature anomaly (SSTA) spatial patterns, i.e., eastern-Pacific (EP) and central-Pacific (CP) types. In this study, we propose a new method to empirically diagnose linear growth rates of the EP and CP ENSO types due to a limitation of applying the traditional Bjerknes stability (BJ) index method simply to these two types. We spatially project the peak-time symmetric component of the mixed-layer oceanic heat budget terms onto the ENSO-related SSTA patterns to estimate the ENSO grow rate. After validating the method by comparing it with the BJ index, we show that the growth rate is positive for the CP ENSO type and weakly negative for the EP ENSO type, contributed by different feedback terms. The CMIP5-based multi-model ensemble mean shows similar characteristics as the reanalysis for the EP ENSO type rather than CP ENSO type.