The Role of Coupled Feedbacks in the Decadal Variability of the Southern Hemisphere Eddy-Driven Jet

Recent work has suggested that tropical Pacific decadal variability and external forcings have had a comparable influence on the observed changes in the Southern Hemisphere summertime eddy-driven jet over the satellite era. Here we contrast the zonally asymmetric response of the Southern Hemisphere eddy-driven jet to tropical Pacific decadal variability by designing an atmosphere-only PAC-A experiment using the Community Atmosphere Model version 5 (CAM5) and comparing it with the fully coupled Community Earth System Model Version 1 (CESM1) tropical Pacific pacemaker (PAC-C) experiments. In both frameworks, the tropical Pacific sea surface temperature (SST) anomalies are identical (model climatology plus observed anomalies), which allows the PAC-C and PAC-A experiments to be used to estimate the impact of coupling on teleconnections from the tropical Pacific to the Southern Hemisphere extratropics. The observed summertime South Pacific jet intensification is reproduced in both coupled and uncoupled experiments, indicating that the central and eastern tropical Pacific (hereafter, tropical Pacific) SST impacts the South Pacific jet mainly via direct atmospheric teleconnections. By contrast, only the coupled PAC-C captures the summertime poleward shift of the South Atlantic-Indian jet, suggesting that air-sea coupling is essential in driving the teleconnections between tropical Pacific SST anomalies and South Atlantic-Indian jet variations.

Automated summary

This study contrasts the response of the Southern Hemisphere eddy-driven jet to tropical Pacific decadal variability, finding that the South Pacific jet is mainly influenced by direct atmospheric teleconnections from the central and eastern tropical Pacific SST. The coupled PAC-C experiment captures the poleward shift of the South Atlantic-Indian jet, indicating that air-sea coupling plays a crucial role in driving the teleconnections between tropical Pacific SST anomalies and South Atlantic-Indian jet variations.