Effects of solar penetration on the annual cycle of sea surface temperature in the North Pacific

The effects of solar penetration on the annual cycle of extratropical North Pacific sea surface temperature (SST) are investigated based on coupled ocean-atmosphere model simulations. It is found that the solar penetration can significantly improve the seasonal cycle of the North Pacific SST in the model. In summer, the solar penetration can partly reduce the SST warm bias in the model by diluting the shortwave radiation to the seasonal thermocline, while in winter, it can reduce the model SST cold bias through the entrainment of the warm thermocline water into the mixed layer. The solar penetration forces significant changes not only in the ocean but also in the atmosphere. The changes in the atmospheric circulation are characterized by a baroclinic structure with ridge/trough in the lower/upper troposphere in summer and an equivalent barotropic trough in winter. As a result, the annual mean of the oceanic subtropical gyre is intensified. Our study echoes the potential importance of the ecosystem in modulating the coupled ocean-atmosphere interaction over the extratropical oceans.