Decadal Relationship Between Arctic SAT and AMOC Changes Modulated by the North Pacific Oscillation

The faster warming for Arctic Ocean surface air temperature (SAT) relative to that at lower latitude is connected with various processes, including local radiation feedback, poleward oceanic and atmospheric heat transport. It is unclear how combinations of different low-frequency internal climate modes influence Arctic amplification on the decadal timescale. Here, the decadal Arctic SAT variation, its connection with the Atlantic meridional overturning circulation (AMOC) and possible underlying mechanisms, are investigated based on several independent observational proxies, pre-industrial experiments, and historical large ensembles of two CMIP6 models. Our study suggests that AMOC and Arctic SAT vary in phase on the decadal timescale, whereas this relationship is insignificant at the interannual timescale. Further analysis shows that the AMOC accompanied with cross-basin oceanic water/heat transport between Atlantic and Arctic would alter air-sea interface exchange over the melting ice regions, and then amplified poleward atmospheric heat and moisture transports. The resulting enhanced downward longwave radiation ultimately warms the Arctic SAT. Additionally, the decadal-scale North Pacific Oscillation (NPO) can modulate the relationship between AMOC and Arctic SAT by influencing poleward moisture transport and cross-basin circulation. Specifically, the phase shift of combined NPO and AMOC can contribute 14%-41% covariance relationship between AMOC and Arctic SAT. Our study provides potential sources for predicting the Arctic climate and constraining its uncertainty in future projections. The Arctic has warmed faster than lower latitudes and is capable of influencing weather and climate. Previous studies suggest that Atlantic meridional overturning circulation (AMOC) can induce warming over the Arctic region, however, the underlying mechanism for AMOC influencing Arctic SAT and whether their relationship is stable are still unclear. In this study, we have identified the relationship between the AMOC and Arctic SAT during 1950-2014 on the decadal scale. Our results demonstrate that AMOC changes in phase with the Arctic SAT, which is dominated by surface downward longwave radiation resulting from poleward moisture and heat transport, and air-ice-sea interaction associated with AMOC. Additionally, the North Pacific Oscillation (NPO) can modulate the correlation between AMOC and Arctic SAT by influencing the meridional eddy advection of water vapor and cross-basin processes. Specifically, the phase shift of combined NPO and AMOC can contribute 14%-41% covariance relationship between AMOC and Arctic SAT. The Atlantic meridional overturning circulation (AMOC) change in phase with the Arctic surface air temperature (SAT) during 1950-2014 on a decadal timescale in multiple observations Decadal Arctic SAT change associated with AMOC is dominated by surface downward longwave radiation, evaporation and poleward moisture transport The North Pacific Oscillation accompanied with the cross-basin processes modulates the relationship between AMOC and Arctic SAT