北极海冰融化影响东亚冬季天气和气候的研究进展以及学术争论焦点问题

北极历来是影响东亚冬季天气、气候的关键区域之一。北极表面增暖要比全球平均快2~3倍，即所谓北极的放大效应。随着全球增暖的持续以及北极海冰的持续融化，北极的生态环境正在发生显著的变化，进而可能对北半球中、低纬度的天气、气候产生影响。本文概述了有关北极海冰融化影响冬季东亚天气、气候的主要研究进展，特别是自2000年以来，北极海冰异常偏少影响东亚冬季气候变率以及极端严寒事件的可能途径、存在的科学问题，以及学术界的争论焦点。秋、冬季节是北极海冰快速形成时期，此时北极海冰对大气环流的影响要强于大气对海冰的影响。近二十年来的研究结果表明，北极海冰异常偏少，不仅影响北冰洋局地的气温和降水变化，而且通过复杂的相互作用和反馈过程，对北半球中、低纬度的天气、气候产生影响。北极海冰通过以下两个可能机制来影响东亚冬季的天气、气候:（1）北极海冰的负反馈机制；（2）由海冰异常偏少引起的平流层-对流层相互作用机制。秋、冬季节北极海冰持续异常偏少，特别是，巴伦支海-喀拉海海冰异常偏少，既可以加强冬季西伯利亚高压（东亚冬季风偏强），也可以导致冬季风偏弱。导致海冰影响不确定性的部分原因是:（1）夏季北极大气环流状态影响北极海冰异常偏少对冬季大气环流的反馈效果；（2）冬季大气环流对北极海冰异常偏少响应的位置、强度不同造成的。秋、冬季节北极海冰持续异常偏少，在适宜的条件下（例如，前期夏季北极大气环流的热力和动力条件，有利于加强北极海冰偏少对冬季大气的反馈作用），可以激发出有利于冬季亚洲大陆极端严寒过程的大气环流异常。目前学术界争论焦点主要集中在以下两个方面:（1）关于北极增暖、北极海冰融化对中纬度区域影响的争论；（2）关于1980年代后期以来，冬季欧亚大陆表面气温呈现降温趋势的原因。目前，有关北极海冰融化影响冬季欧亚大陆次季节变化以及极端天气、气候事件的过程和机制，我们认知非常有限，亟需开展深入细致的研究。

Progresses in the Impact Study of Arctic Sea Ice Loss on Wintertime Weather and Climate Variability over East Asia and Key Academic Disputes

The Arctic is a crucial region that influences weather and climate over East Asia during the wintertime. The rate of Arctic surface warming is 2-3 times faster than that of the global mean, which is referred to as Arctic amplification. Accompanied by global warming and Arctic sea ice loss, the ecological environment in the Arctic has been changing rapidly. Such changes would possibly influence weather and climate in the mid-and low-latitudes of the Northern Hemisphere. This paper summarizes major advances in the impact study of Arctic sea ice loss on weather and climate in the wintertime. Since 2000, special attention is paid to possible pathways, scientific problems, and key issues in the study of how Arctic sea ice loss affects the wintertime climate variability and extreme cold events.Autumn and winter are freezing seasons when the impact of Arctic sea ice on the atmosphere is stronger than the impact of atmosphere on Arctic sea ice. Over the past two decades, many studies have demonstrated that Arctic sea ice loss not only affects local air temperature and precipitation over the Arctic Ocean, but also influences weather and climate in the mid-and low-latitudes of the Northern Hemisphere due to complicated interactions and feedback processes. Arctic sea ice influences weather and climate over East Asia through two mechanisms:(1) The negative feedback process; (2) the stratosphere-troposphere interaction induced by Arctic sea ice loss. Persistent loss of Arctic sea ice from autumn to winter, particularly in the Barents-Kara Seas, can either enhance the Siberian high or weaken the East Asian winter monsoon. Uncertainties in the impact of Arctic sea ice loss on the wintertime atmosphere can be attributed to the following two reasons:(1) Arctic atmospheric circulation condition in the preceding summer influences the feedback of the persistent less sea ice on the winter atmospheric circulation variability; (2) there exist differences in both the location and strength of wintertime atmospheric response to persistent less sea ice. Under suitable conditions (for example, Arctic atmospheric circulation conditions in the preceding summer are favorable for strengthening the negative feedback of less sea ice), persistent autumn-winter loss of sea ice leads to large-scale wintertime circulation anomalies that favor the occurrence of extreme cold event over Asia.At present, the focuses of disputes in the academic community are mainly concentrated on the following two aspects:(1) The impacts of Arctic warming and Arctic sea ice loss on the mid-latitudes; (2) the reasons for the declining trend in winter surface air temperature over Eurasia since the late 1980s. Indeed, the processes and mechanisms for impacts of Arctic sea ice loss on sub-seasonal variation and extreme cold event over Eurasia still remain unclear, and these problems need to be investigated in the future.