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.

北极放大是指近几十年来北极比其他地区更大的表面变暖。在对流层中也发生了类似的现象，被称为“对流层北极放大”（TAA）。极地涡流和涡流是北极变暖的关键。在这项研究中，我们调查了北太平洋与TAA相关的天气短暂涡流活动及其与副热带急流的关系，并提出了以下机理。副热带喷气轴的极移导致北太平洋上纬向风子午梯度的异常，从而驱动了北太平洋上的天气瞬变波强度的子午偶极子模式，称为北太平洋天气瞬变波强度偶极子（NPSTD）。NPSTD指数在1990年代后期伴随着副热带急流的变化而发生了年代际变化。在NPSTD指数的正值阶段，天气涡流将更多的热量传递到北极圈，涡流的热量发散，从而增加了北极的温度。该机制强调需要将北太平洋的天气瞬变涡旋活动视为北太平洋副热带高压高空急流的平均状态与TAA之间的联系。