An Interdecadal Change in the Influence of the NAO on Atlantic-Induced Arctic Daily Warming around the Mid-1980s

Abstract

After approaching 0°C owing to an Atlantic storm at the end of 2015, the Arctic temperature approached freezing again in 2022, indicating that Arctic daily warming events remain a concern. The NCEP/NCAR Reanalysis dataset was used to investigate the influence of the NAO on the Arctic winter daily warming events induced by Atlantic storms, known as the Atlantic pattern-Arctic Rapid Tropospheric Daily Warming (Atlantic-RTDW) event. Atlantic-RTDW events are triggered by Atlantic storms that transport warm and humid air masses moving into the Arctic. Furthermore, an interdecadal change in the influence of NAO on Atlantic-RTDW-event frequency was observed around the mid-1980s. Specifically, before the mid-1980s (pre-transition period), 500-hPa southerly (northerly) wind anomalies occupied the North Atlantic (NA) in the positive (negative) phase of NAO, which increased (decreased) the Atlantic-RTDW events occurrence by steering Atlantic storms into (away from) the Arctic; thus, the NAO could potentially influence the Atlantic-RTDW-event frequency. However, the relationship between the NAO and the Atlantic-RTDW-event frequency has weakened since the mid-1980s (post-transition period). In the post-transition period, such 500-hPa southerly (northerly) wind anomalies over the NA hardly existed in the positive (negative) phase of NAO, which was attributed to a stronger Atlantic Storm Track (AST) activity intensity than that in the pre-transition period. During this period, the strong AST induced an enhanced NAO-related cyclone via transient eddy-mean flow interactions, resulting in the disappearance of southerly and northerly wind anomalies over the NA.

摘 要

在 2015 年底大西洋风暴导致北极气温接近 0°C 之后, 2022 年北极气温再次接近冰点, 这表明北极日变暖事件仍然令人担忧. 本文使用 NCEP/NCAR 再分析数据集, 研究 NAO 对大西洋风暴引起的北极冬季日增暖事件的影响, 即 Atlantic-RTDW 事件. Atlantic-RTDW 事件是由大西洋风暴触发的, 这些风暴将温暖潮湿的气团输送到北极. 在 20 世纪 80 年代中期左右, 北大西洋涛动 (NAO) 对 Atlantic-RTDW 事件频率的影响发生了年代际变化. 具体而言, 在 20 世纪 80 年代中期之前, 当 NAO 处于正 (负) 相位时, 500-hPa 异常的南风 (北风) 占据了北大西洋, 这将通过引导大西洋风暴进入 (远离) 北极, 增加 (减少) 了 Atlantic-RTDW 事件的发生; 因此, NAO 可能会影响 Atlantic-RTDW 事件的发生频率. 然而, NAO 和 Atlantic-RTDW 事件频率之间的关系自 20 世纪 80 年代中期之后减弱. 在 20 世纪 80 年代中期之后, 当 NAO 处于正 (负) 相位时, 北大西洋上空几乎不存在 500-hPa 异常的南风 (北风), 这归因于比之前更强的大西洋风暴轴强度. 在此期间, 更强的大西洋风暴轴通过涡流相互作用使与 NAO 相关的气旋增强, 导致北大西洋上空异常的南风和北风消失.

Electronic Supplementary Material to

An Interdecadal Change in the Influence of the NAO on Atlantic-Induced Arctic Daily Warming around the Mid-1980s