“北极放大”现象驱动因素及其影响的研究进展综述

A Review of the Research Progress on the Drivers of the"Arctic amplification"Phenomenon and Its Influence

21世纪以来,受全球变暖的影响,北极近地表快速升温,升温速率可达全球平均水平的2倍,称为“北极放大”(Arctic Amplification,AA)现象。本文首先探讨了北极放大效应产生的原因:在局地气候反馈方面,海冰减少导致开阔水面增多,水体吸收太阳辐射增多使海-气相互作用增强,海冰进一步融化,形成正反馈;由于北极地区绝对温度较低,根据普朗克黑体辐射定律,普朗克反馈在北极为负反馈,促进北极放大效应;开阔水面和增温使北极地区大气湿度增加导致云量增多,从而使下行长波辐射增加,促使近地面层升温,这种水汽和云反馈对北极变暖的贡献有显著的季节性,主要发生在冬季;在北极以外地区水汽和热量的极向输送方面,温度的升高使大气柱增厚,高层气压梯度的变化引起纬向风变化,纬向分量减少,经向分量增加,形成槽脊,较低纬度地区可通过槽脊实现与北极的热量和水汽交换。此外,北极涛动(Arctic Oscillation,AO)与北大西洋涛动(North Atlantic Oscillation,NAO)也被证实与北极变暖有关。大西洋经向翻转环流(Atlantic Meridional Overturning Circulation,AMOC)异常曾被认为是北极变暖的驱动因素,而近期研究表明其更可能是北极变暖导致的结果。与此同时,“北极放大”现象会通过影响大气环流对中纬度地区甚至全球气候产生影响。北极变暖会导致东亚冬季严寒和北美东部冷事件的发生,形成“暖北极-冷欧亚”的格局并影响北美冬季气候波的形成。目前认为北极变暖与海冰减退可以通过两种机制影响中纬度地区:一是通过影响气压场的分布改变纬向风,使阻塞事件增加;二是通过对流层-平流层耦合作用影响北半球大气环流。但以上两种机制还存在争议。

Since the 21st century,due to global warming,the Arctic near-surface temperature increases rapidly,the warming rate can reach more than twice the global average rate,known as the"Arctic amplification"(AA)phenomenon.This paper discusses the causes of the Arctic amplification effect from three aspects:first,in the Arctic climate feedback,the decrease of sea ice leads to the increase of open sea surface,the absorption of solar radiation increases,the sea-air interaction is enhanced,and the sea ice melts further.This is positive feedback.Second,due to the low absolute temperature in the Arctic,according to Planck’s radiation law,Planck feedback is negative in the Arctic,but it promotes the Arctic amplification effect.Third,more open sea and higher temperature increase the humidity and the number of clouds in the Arctic.Due to the greenhouse effect of water vapor,the lower wave radiation increases,and it promotes the near-surface layer heating.Water vapor and cloud feedback on the Arctic warming contribution has significant seasonality,mainly occurring in winter.The increase of temperature thickens the atmospheric column.The change of the upper-pressure gradient causes the change of zonal wind,the zonal component decreases and the meridional component increases,forms the ridge,through which the lower latitude region can exchange heat and water vapor with the Arctic.The Arctic Oscillation(AO)and the North Atlantic Oscillation(NAO)have also been confirmed related to Arctic warming.The Atlantic Meridional Overturning Circulation(AMOC)anomaly was once thought to be the driver of Arctic warming.Recent studies suggest it is more likely to be the result of Arctic warming.The Arctic amplification influences mid-latitude and even global climates by affecting atmospheric circulation.Warming in the Arctic strengthens the Siberian High,the growth of the duration of the Siberian High and its expansion into East Asia result in enhanced cold advection in the coastal areas of East Asia and adjacent seas in winter,affecting the East Asian Winter Wind System(EAWM)and promoting the flow of cold air to East Asia.It will result in severe winter cold in East Asia,forming a"warm Arctic-cold Eurasian"pattern.In addition,Arctic warming leads to cold events in eastern North America,corresponding to the 250 hPa anomalous elevation field,forming low troughs.Winter climate waves can be formed by those low troughs and high ridges over the northeastern Pacific Ocean or Greenland.It is believed that Arctic warming and sea ice loss can affect the mid-latitudes through two mechanisms:first,Arctic warming changes the zonal wind by affecting the pressure field,then increases the blocking event.However,the research shows that the effect of this mechanism on the mid-latitude is not significant.Second,it affects the atmospheric circulation of the northern hemisphere through trophic-stratospheric coupling,but this mechanism is still controversial.However,due to flaws in research methods and uncertainty in the data,the factors affecting the Arctic amplification effect are still controversial.For example,many studies believe that ice and snow albedo feedback is the core factor driving the“Arctic amplification”phenomenon,and other factors indirectly affect the Arctic amplification through sea ice and snow melting.Some studies have shown that even without considering the role of sea ice,the Arctic amplification phenomenon is still significant.Therefore,it is particularly important to improve research methods and the quality and accuracy of data.Finally,the existing problems are put forward.