Abstract
Arctic amplification 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 amplification” (TAA). The poleward eddy heat flux and eddy moisture flux are critical to Arctic warming. In this study, we investigate the synoptic transient eddy activity over the North Pacific 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 Pacific, which drive a meridional dipole pattern of synoptic transient wave intensity over the North Pacific, referred to as the North Pacific 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 flux transports more heat to the Arctic Circle, and the eddy heat flux diverges, increasing Arctic temperature. This mechanism highlights the need to consider synoptic transient eddy activity over the North Pacific as the link between the mean state of the North Pacific subtropical upper jet and TAA.
Highlights
Warming of the Arctic near-surface air temperature has been a clear feature of global warming in recent decades
The interdecadal poleward shift of the subtropical jet axis over the North Pacific resulted in meridional changes of zonal wind and its associated meridional gradient over the North
Synoptic transient wave activity associated with Tropospheric Arctic amplification” (TAA) during P1 and P2 showed a poleward shift of synoptic transient wave activity center over the North Pacific, and the difference between P1 and P2 displayed a meridional dipole pattern of synoptic transient wave intensities over the North Pacific, namely, the North Pacific synoptic transient wave intensity dipole (NPSTD)
Summary
Warming of the Arctic near-surface air temperature has been a clear feature of global warming in recent decades. It is of importance to investigate whether mid-latitude synoptic transient eddy activity is related to changes in the subtropical upper jet stream and favor Arctic warming in reanalysis data. We investigate changes of the relationship between synoptic transient wave activity and tropospheric Arctic temperature between a normal and warming Arctic troposphere, defined a dipole index of transient wave intensity, which is related to the changes of background of tropospheric Arctic temperature, and explore its relationship with the northern subtropical upper jet over the North Pacific and contribution to tropospheric Arctic warming. Our study highlights the role of synoptic transient wave activity in the influence of a meridional shift of the subtropical upper jet on tropospheric Arctic warming during the wintertime.
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