Arctic autumn sea ice decline and Asian winter temperature anomaly

Associations between the autumn Arctic sea ice concentration （SIC） and Asian winter temperature are discussed using the singular value decomposition analysis. Results show that in recent 33 years reduced autumn Arctic sea ice is accompanied by Asian winter temperature decrease except in the Tibetan plateau and the Arctic Ocean and the North Pacific Ocean coast. The autumn SIC reduction excites two geopotential height centers in Eurasia and the north Arctic Ocean, which are persistent from autumn to winter. The negative center is in Barents Sea/Kara Sea. The positive center is located in Mongolia. The anomalous winds are associated with geopotential height centers, providing favorable clod air for the Asian winter temperature decreasing in recent 33 years. This relationship indicates a potential long-term outlook for the Asian winter temperature decrease as the decline of the autumn sea ice in the Arctic Ocean is expected to continue as climate warms.

Change in Sea Ice Cover is Responsible for Non-Uniform Variation in Winter Temperature over East Asia

Observed winter(December–February)surface air temperature over East Asia(0°–60°N,100–140°E)(TEA)shows non-uniform variation during 1979–2013,with cooling and weak warming north and south of40°N.To understand this,the authors perform statistical analysis(linear regression and composite)on the observed data.The results suggest that reduced(increased)autumn sea ice cover in the Barents-Kara Sea(BK-ASIC)lowers(warms)TEA over northern East Asia,which is consistent with previous studies.In comparison,increased(decreased)winter sea ice cover in the Sea of Okhotsk(O-WSIC),warms(cools)the air over southern East Asia.The mechanism can be described as follows:When the BK-ASIC decreases,the East Asian winter monsoon tends to be stronger with an intensified Siberian high,leading to cooling over northern East Asia.An O-WSIC increase is associated with cold anomalies north of 50°N,altering the meridional temperature gradient between the midlatitudes and tropics,and leading to a northward shift of the East Asian jet steam in the upper troposphere.In the low atmosphere,anomalous northeasterly winds prevail north of50°N and anomalous southerly winds control the southern coast of East Asia,contributing to the weak warming over southern East Asia.Version 3 of the Community Atmosphere Model also provides evidence for the impact of increased O-WSIC on the warm southern mode of TEA.

Recent Rapid Decline of the Arctic Winter Sea Ice in the Barents–Kara Seas Owing to Combined Effects of the Ural Blocking and SST

This study investigates why the Arctic winter sea ice loss over the Barents–Kara Seas（BKS） is accelerated in the recent decade. We first divide 1979–2013 into two time periods： 1979–2000（P1） and 2001–13（P2）, with a focus on P2 and the difference between P1 and P2. The results show that during P2, the rapid decline of the sea ice over the BKS is related not only to the high sea surface temperature（SST） over the BKS, but also to the increased frequency,duration, and quasi-stationarity of the Ural blocking（UB） events. Observational analysis reveals that during P2, the UB tends to become quasi stationary and its frequency tends to increase due to the weakening（strengthening） of zonal winds over the Eurasia（North Atlantic） when the surface air temperature（SAT） anomaly over the BKS is positive probably because of the high SST. Strong downward infrared（IR） radiation is seen to occur together with the quasi-stationary and persistent UB because of the accumulation of more water vapor over the BKS. Such downward IR favors the sea ice decline over the BKS, although the high SST over the BKS plays a major role. But for P1, the UB becomes westward traveling due to the opposite distribution of zonal winds relative to P2, resulting in weak downward IR over the BKS. This may lead to a weak decline of the sea ice over the BKS. Thus, it is likely that the rapid decline of the sea ice over the BKS during P2 is attributed to the joint effects of the high SST over the BKS and the quasi-stationary and long-lived UB events.

一个反映中国大陆冬季气温变化的东亚冬季风指数的统计预测方法

利用中国160个站逐月温度、NCEP再分析和NOAA-CIRES 20世纪再分析等资料,采用统计分析方法,就反映中国东部大陆冬季一致性气温变化模态的能力方面,对多种东亚冬季风指数进行了评估,探讨了影响东亚冬季风强弱的主要前期因子及其相应的影响过程,并据此建立了一个预测冬季风指数的预测模型。研究结果表明:1981年前、后两个阶段·朱艳峰2008年定义的东亚冬季风指数都可以很好地反映中国东部大部分地区的冬季气温异常;北美大陆西侧北太平洋中纬度地区(35°—50°N,145°—130°W)的前期秋季(9—10月)海温、北极喀拉海地区(75°—82°N,65°—85°E)的前秋海冰密集度和东亚中纬度地区(30°—50°N,80°—140°E)的前秋高空(300—200 hPa)温度异常都具有较强的持续性,异常信号可从前秋一直持续到冬季,进而影响东亚冬季风的强度;根据上述3个前期因子建立了东亚冬季风统计预测模型,评估发现该模型具有较强的预测能力,可用于冬季风强度以及相应的中国东部大陆冬季气温的定性预测。

宁夏冬季极端低温事件特征及其与秋季北极海冰异常的联系

利用1961-2018年我国宁夏全区平均逐日观测最高和最低气温数据,英国哈德莱(Hadley)中心的逐月海冰密集度资料,美国国家环境预报中心/国家大气研究中心(NCEP/NCAR)的逐月大气再分析资料以及中国气象局国家气候中心的逐月东亚冬季风指数和西伯利亚高压指数系统地研究了宁夏冬季极端低温事件的特征及其与北极关键影响区域海冰异常的联系。结果表明:20世纪60年代以来,宁夏冬季冷日与冷夜频次呈现明显的减少趋势,极端低温事件强度总体趋于减弱,日极端低温升高趋势较为明显。秋季北极海冰异常与之后冬季海冰异常显著相关,前秋海冰异常通过季节持续性实现对后期冬季大气环流的影响,进而影响冬季气温。前期秋季拉普捷夫海-东西伯利亚海海冰密集度偏小、格陵兰海海冰密度偏大时,冬季西伯利亚高压指数和冬季风指数偏强,有利于宁夏日极端低温事件频次偏多;500 hPa高度场上,极地-欧亚大陆-阿留申地区有一个显著的“L”型的位相波列形态,使得北极与欧亚大陆中高纬地区的位势高度差减弱,中高纬地区西风气流偏弱,减弱的西风使得经向活动加强,利于北极的冷空气向低纬地区侵袭;在海平面气压场上,西伯利亚地区气压偏高,冷空气由极地挤压至中高纬度地区,造成冷空气南下,有利于宁夏冬季发生极端低温事件。

2016年宁夏冬季气温异常及其成因分析

利用1961—2016年宁夏20个气象站冬季逐月气温资料,英国气象局哈德莱Hadley中心秋季逐月海冰密集度资料,美国国家环境预报中心/国家大气研究中心(NCEP/NCAR)冬季逐月大气再分析资料,分析2016年宁夏冬季气温异常特征及其成因。结果表明:2016年冬季,宁夏气温创1961年以来同期最高。2016年500 hPa欧亚中高纬地区纬向环流明显,乌拉尔山阻塞高压异常偏弱,中国大陆上空位势高度场异常偏强,极涡偏向大西洋欧洲区和北美大陆;东亚冬季风指数为-1. 29 m·s^(-1),为1961年以来第5低值;西伯利亚高压强度距平为-1. 5 h Pa,为2000年以来第2低值。秋季格陵兰海冰密集度偏低,导致东亚冬季风偏弱;500 h Pa位势高度场上北极、欧亚大陆和阿留申地区呈现"-+-"的波列形态,使得北极与欧亚大陆中高纬地区的位势高度差增强,中高纬西风气流偏强,纬向活动加强;海平面气压场上西伯利亚高压偏弱,不利于北极冷空气向低纬地区侵袭,使得2016年冬季宁夏气温异常偏高。

北极海冰异常对中国冬季气温的影响研究进展

在全球不断变暖的大背景下，北极地区的气候系统发生了比其它地区更为显著的变化，北极海冰是其中最重要的指示和衡量标准，了解北极海冰的变化趋势已成为全球关注的焦点。笔者综述了北极海冰急剧变化的可能原因，并在此基础上归纳了影响中国气温的主要因素。北极海冰偏多的年份中国经常出现暖冬；反之，北极海冰偏少的年份中国经常出现冷冬。

Skillful prediction of winter Arctic Oscillation from previous summer in a linear empirical model

The winter Arctic Oscillation(WAO),as a primary atmospheric variability mode in the Northern Hemisphere,plays a key role in influencing mid-high-latitude climate variations.However,current dynamical seasonal forecasting systems have limited skills in predicting WAO with lead time longer than two months.In this study,we design a linear empirical model using two effective precursors from anomalies of the Arctic sea ice concentration(SIC)and the tropical sea surface temperature(SST)initiated in preceding late summer(August)which are both significantly correlated with WAO in recent four decades.This model can provide a skillful prediction of WAO at about half-year lead started from previous summer and perform much better than the dynamical models.Such a significantly prolonged lead time is owed to the stable precursor signals extracted from the SIC and SST anomalies over specific areas,which can persist from previous August and be further enhanced through autumn months.Validation results show that this model can produce a 20-year independent-validated prediction skill of 0.45 for 1999–2018 and a 39-year cross-validated skill of 0.67 for 1980–2018,providing a potentially effective tool for earlier predictions of winter climate variations at mid-high latitudes.