The Role of Clouds in Shaping Tropical Pacific Response Pattern to Extratropical Thermal Forcing

Extratropical influences on tropical sea surface temperature (SST) have implications for decadal predictability. We implement a cloud-locking technique to highlight the critical role of clouds in shaping the tropical SST response to extratropical thermal forcing. With heating imposed over either the extratropical Northern Atlantic or Pacific, Hadley Cells respond similarly that the trades strengthen south of the rainband. The wind-evaporation-SST (WES) feedback leads to cooling over the southern subtropics, which is enhanced in the southeastern Pacific due to the positive feedback between SST and stratiform clouds. Cloud-locking experiments show that zonal contrasts in SST and cloud feedbacks in the Pacific enhance the zonal surface winds, leading to increased evaporation and strengthens zonal SST difference. We propose that the meridional and zonal SST gradients are tightly linked via WES effects and the cloud-radiative-SST feedbacks, which are largely determined by the climatological rainband position and the spatial distribution of cloud properties.

Automated summary

This study investigates the critical role of clouds in shaping the tropical SST response to extratropical thermal forcing using a cloud-locking technique. It is found that heating imposed over the extratropical Northern Atlantic or Pacific leads to a strengthening of the Hadley Cells and trades south of the rainband. The wind-evaporation-SST feedback results in cooling over the southern subtropics, with enhanced cooling in the southeastern Pacific due to positive feedback between SST and stratiform clouds. Cloud-locking experiments reveal that zonal contrasts in SST and cloud feedbacks in the Pacific enhance zonal surface winds, leading to increased evaporation and strengthening of zonal SST difference. The study proposes that the meridional and zonal SST gradients are tightly linked via WES effects and cloud-radiative-SST feedbacks, which are determined by the climatological rainband position and the spatial distribution of cloud properties.