The longitudinal location of precipitation anomalies over the equatorial Pacific shows a distinctive feature with the westernmost location for La Niña, the easternmost location for eastern Pacific (EP) El Niño, and somewhere between for central Pacific (CP) El Niño, even though the center of the sea surface temperature anomaly (SSTA) for La Niña is located slightly east of that of CP El Niño. The mechanisms for such a precipitation diversity were investigated through idealized model simulations and moisture and moist static energy budget analyses. It is revealed that the boundary layer convergence anomalies associated with the precipitation diversity are mainly induced by underlying SSTA through the Lindzen–Nigam mechanism, that is, their longitudinal locations are mainly controlled by the meridional and zonal distributions of the ENSO SSTA. The westward shift of the precipitation anomaly center during La Niña relative to that during CP El Niño is primarily caused by the combined effects of nonlinear zonal moist enthalpy advection anomalies and the Lindzen–Nigam mechanism mentioned above. Such a zonal diversity is further enhanced by the “convection–cloud–longwave radiation” feedback, the SST-induced latent heat flux anomalies, and the advection of mean moist enthalpy by anomalous winds. This diversity in the longitudinal location of precipitation anomalies has contributions to the diversities in the longitudinal locations of anomalous Walker circulation and western North Pacific anomalous anticyclone/cyclone among the three types of ENSO.
In this study, we investigate the relative contributions of dynamical forcings, particularly the eastern and central‐western Pacific winds, and thermodynamical forcings to the evolution of the 2017 extreme coastal El Niño using observations and modeling experiments. We show that the competing effects of anomalous eastern Pacific westerlies and central‐western Pacific easterlies and their resulting downwelling and upwelling equatorial Kelvin waves are essential for the evolution of the event, together with alongshore anomalous northerlies which suppress coastal upwelling and reduce latent heat release as discussed in previous studies. We find that eastern Pacific zonal wind anomalies are about twice as effective in generating a coastal response as central‐western Pacific anomalies, thus compensating for their usually smaller magnitude. While the 2017 event exemplified these competing effects, they were also found to be important in other coastal and basin‐scale El Niño events, thus contributing to the mechanisms responsible for El Niño diversity.
more » « less- Award ID(s):
- 1902970
- NSF-PAR ID:
- 10372672
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Geophysical Research Letters
- Volume:
- 49
- Issue:
- 15
- ISSN:
- 0094-8276
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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