Distinct Westerly Wind Burst Features in Cyclic and Noncyclic El Niño Events and Their Association with Western-Central Pacific SST Anomalies
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Graphical Abstract
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Abstract
El Niño–Southern Oscillation (ENSO) is an oscillation of the ocean–atmosphere system in the tropical Pacific, which is argued to be energized by high-frequency stochastic atmospheric disturbances. Among these disturbances, westerly wind bursts (WWBs) play a crucial role in the development of El Niño by generating eastward-propagating downwelling Kelvin waves and suppressing the thermocline in the central-eastern equatorial Pacific. The present work elucidates distinct seasonal evolutions of WWBs during cyclic and noncyclic El Niño events, and their association with the local sea surface temperature anomalies (SSTAs). For noncyclic El Niño events, WWBs prevail over the western-central equatorial Pacific during spring of the developing year, accompanied by local warming SSTAs. In contrast, active WWBs cannot be observed until the developing summer for cyclic El Niño events. Significant differences in high-frequency WWBs and associated local deep convection appear in the developing spring season of noncyclic and cyclic El Niño events. These differences are closely linked to local SSTAs in the western-central equatorial Pacific via the stimulation of atmospheric deep convection, preceding the full manifestation of ENSO-associated large-scale SSTAs in the central-eastern tropical Pacific. The observed difference in WWBs for noncyclic and cyclic El Niño events and its association with the western-central equatorial Pacific SSTAs is realistically reproduced in a coupled general circulation model. This study enhances our comprehension of El Niño development by illustrating the intricate connection between WWBs and El Niño evolution from the ENSO cycle perspective.
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