Abstract
Warm 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 are relatively small, dampen the SST anomalies, and are
negatively correlated (r = –0.38) with the latent heat fluxes. For
example, the +1.0K SST increased from 2011 to 2015 results from +1.5K
contributions from sum of surface heat flux and –0.5K 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.