Impact of Westerly Wind Bursts on ENSO Based on a Hybrid Coupled Model: Part I – ENSO Simulation

Abstract

ABSTRACT Westerly wind bursts (WWBs), usually occurring in the tropical Pacific region during the beginning and advancement of El Niño events, play a vital role in El Niño–Southern Oscillation (ENSO). In this study, we use a hybrid coupled model (HCM) for the tropical Pacific Ocean–atmosphere system to investigate the impact of WWBs on ENSO. To achieve this goal, we performed two experiments: first, the standard version of the HCM is integrated for years without prescribed WWBs events; and second, the WWBs are added to the HCM, which are constructed using observational data and WWB parameterization schemes. Results show that when WWBs are added to the HCM not only can a more realistic climatology of sea surface temperature (SST) in both spatial structure and temporal amplitudes be generated but also better ENSO features can be generated than with the HCM alone. The former is mainly reflected in the simulation of the SST seasonal cycle in the eastern Pacific and a reduction in the bias toward the cold tongue in the equatorial eastern Pacific, whereas the latter includes an improvement in a broad spectrum of ENSO features, such as ENSO amplitude, phase locking, asymmetry, and diversity. In particular, when WWBs are added to the HCM, the model can capture central Pacific ENSO events, which are absent in the original HCM. On the other hand, WWBs have little impact on cold events because very few WWBs occur during the cold phase of ENSO. Furthermore, the possible physical mechanisms responsible for these improvements as a result of adding WWBs are discussed.