Formation Mechanism of Warm SST Anomalies in 2010s Around Hawaii

Abstract

AbstractWarm sea surface temperature (SST) anomalies have been observed in the subtropical North Pacific around Hawaii in the recent decade, appearing from 2013. We examined the formation mechanisms of the warm SST anomalies in terms of relative contribution of atmospheric surface forcing and oceanic dynamics, using the latest reanalysis products from ECMWF (ERA5 for atmosphere and ORAS5 for ocean). Results of the mixed layer temperature budget diagnosis in the target area (10–20°N and 180°–160°W) indicates that contributions from anomalous latent heat fluxes to the subtropical SST anomalies are dominant. Oceanic advective contributions play a secondary role, dampen the SST anomalies, and are negatively correlated (r = −0.38) with the latent heat fluxes. For example, the +1.0 K SST increased from 2011 to 2015 results from +1.5 K contributions from sum of surface heat flux and −0.5 K from meridional oceanic advection. The anti‐correlation between atmospheric forcing and oceanic meridional advection reflects co‐variations of wind‐driven latent heat flux and meridional Ekman advection due to the weakening of the zonal component of the surface winds.