Low Cloud-SST Feedback over the Subtropical Northeast Pacific and the Remote Effect on ENSO Variability

Low clouds frequent the subtropical northeastern Pacific Ocean (NEP) and interact with the local sea sur-face temperature (SST) to form positive feedback. Wind fluctuations drive SST variability through wind-evaporation-SST (WES) feedback, and surface evaporation also acts to damp SST. This study investigates the relative contributions of these feedbacks to NEP SST variability. Over the summer NEP, the low cloud-SST feedback is so large that it exceeds the evap-orative damping and amplifies summertime SST variations. The WES feedback causes the locally enhanced SST variability to propagate southwestward from the NEP low cloud deck, modulating El Nin similar to o-Southern Oscillation (ENSO) occurrence upon reaching the equator. As a result, a second-year El Nin similar to o tends to occur when there are significant warm SST anoma-lies over the subtropical NEP in summer following an antecedent El Nin similar to o event and a second-year La Nin similar to a tends to occur when there are significant cold SST anomalies over the subtropical NEP in summer following an antecedent La Nin similar to a event The mediating role of the NEP low cloud-SST feedback is confirmed in a cloud-locking experiment with the Community Earth System Model, version 1 (CESM1). When the cloud-ocean coupling is disabled, SST variability over the NEP weak-ens and the modulating effect on ENSO vanishes. The nonlocal effect of the NEP low cloud-SST feedback on ENSO has important implications for climate prediction.

Automated summary

It is found that the interaction between low clouds and sea surface temperature (SST) in the northeastern Pacific Ocean (NEP) leads to positive feedback and amplifies SST variations. Wind fluctuations and surface evaporation contribute to the variability of SST through wind-evaporation-SST (WES) feedback. The study confirmed the mediating role of the NEP low cloud-SST feedback in modulating ENSO.