Mechanisms of the disappearance of sea surface temperature fronts in the subtropical North Pacific Ocean

Abstract

AbstractThe disappearance mechanisms of subtropical sea surface temperature (SST) fronts occurring from May to August were examined quantitatively using a simple mixed‐layer model. Weekly 2.5° data sets were matched up between satellite and in situ observations, including cloud‐free SST from Advanced Microwave Scanning Radiometer‐Earth Observing System (AMSR‐E) and Global Temperature and Salinity Profile Program (GTSPP) data. A 1.5 mixed‐layer model used in this study assumed that the temporal variation of the SST gradient was controlled by the resultant effect among the net heat flux, temperature advection (including Ekman and geostrophic), and the temperature entrainment at the bottom of the mixed layer. The net heat flux was found to provide a dominant contribution to the weakening of the SST front (decreasing SST gradient), while the temperature advection and the bottom entrainment were relatively weak. Decomposition of the net heat flux revealed that the meridional gradient of the latent heat flux is a direct factor in the weakening of the SST front, while the shortwave radiation could have indirect effects. The meridional gradient of the latent heat flux is induced by southerly winds, which in turn causes the weakening and disappearance of the SST front. Comparison of weekly and monthly averaged SST gradient modeling results with in situ observations demonstrated that the weekly SST gradient in the model agrees closely with AMSR‐E observations, but there was a large difference between the monthly SST gradient in the model and in the observations.