Arctic amplifcation refers to the greater surface warming of the Arctic than of other regions during recent decades. A similar phenomenon occurs in the troposphere and is termed “tropospheric Arctic amplifcation” (TAA). The poleward eddy heat fux and eddy moisture fux are critical to Arctic warming. In this study, we investigate the synoptic transient eddy activity over the North Pacifc associated with TAA and its relationship with the subtropical jet stream, and propose the following

mechanism. A poleward shift of the subtropical jet axis results in anomalies of the meridional gradient of zonal wind over the North Pacifc, which drive a meridional dipole pattern of synoptic transient wave intensity over the North Pacifc, referred to as the North Pacifc Synoptic Transient wave intensity Dipole (NPSTD). The NPSTD index underwent an interdecadal shift in the late 1990s accompanying that of the subtropical jet stream. During the positive phase of the NPSTD index, synoptic

eddy heat fux transports more heat to the Arctic Circle, and the eddy heat fux diverges, increasing Arctic temperature. This mechanism highlights the need to consider synoptic transient eddy activity over the North Pacifc as the link between the mean state of the North Pacifc subtropical upper jet and TAA.