Enhanced impact of tropical Pacific on semi-circumpolar jet attributed to internal variability and anthropogenic forcing

The connection between the tropical and Arctic climates exerts an important impact on the climate in Northern Hemisphere. This study finds that the connection between sea surface temperature anomalies (SSTA) of the central tropical Pacific and semi-circumpolar jet have enhanced during summer after mid-1980s. Our results indicate that the internal variability of Atlantic Multidecadal Oscillation (AMO) has a major influence on the enhanced connection, while the anthropogenic greenhouse gases forcing and aerosol forcing play minor roles. During the period of positive AMO phase, the warm SSTA of central tropical Pacific elicit an enhanced anomalous cyclone in northwestern Pacific, which is favorable for reinforced poleward Rossby waves and enhanced polar vortex. The intensification of the polar vortex enhances the meridional pressure gradient, which amplifies the intensity of semi-circumpolar jet. Furthermore, the anthropogenic forcing amplifies the response of tropical lower tropospheric moisture anomalies induced by the SSTA in the tropical Pacific. These moisture anomalies generate a positive feedback loop of downward latent heat, which further intensifies the SSTA over tropical Pacific and consequently reinforces the response of the semi-circumpolar jet. The findings in this study demonstrate significant changes in Arctic-tropical connection of climates due to combined effect of internal variability and external forcings.