1978-2017年秋季北极海冰对中国大陆地区冬季极端低温事件的影响

Effects of Arctic sea ice in the previous autumn on winter extreme low temperature events in the Chinese Mainland region from 1978 to 2017

利用1978-2017年英国Hadley中心的海冰密集度资料、中国地面站点观测资料及欧洲中期天气预报中心的ERA5再分析资料,结合天气系统定量化表征指数,分析北极放大效应背景下前期秋季海冰变化对冬季中国大陆地区极端低温发生的影响及可能的机制.结果表明,在极地放大效应的背景下,当前期秋季巴伦支海-喀拉海和拉普捷夫海北部-东西伯利亚海东部-楚科奇海海域的海冰偏少时,中国大陆地区极端低温形势加剧,华南地区极端低温频次显著增多,北方地区低温强度明显增强.相对于海冰高值年,海冰低值年西伯利亚冷高压控制范围扩张且强度增强,西伯利亚高压指数由-0.48增至0.50;850 hPa风场上中国以北区域的偏北风增强,东亚冬季风综合指数由-0.56增至0.72;乌拉尔山地区阻塞形势更明显,瞬时阻塞比高值年高6 d.动力诊断分析显示, 500 hPa等压面上乌拉尔山阻塞关键区和北大西洋区存在相对涡度的显著负异常、中高纬度经向温度梯度异常高值中心和Rossby波作用通量扰动异常,能够解释在极地放大效应背景下,北极海冰减少时,有利于乌拉尔山阻塞高压的建立、发展以及与极地高压的合并,使得入侵中国大陆地区的极地冷空气增强,极端低温事件增多、增强.

Based on sea ice concentration(SIC) from the Hadley Center in the UK, the surface observation data from China and the ERA5 reanalysis data from the European Centre for medium-range weather forecasts during 1978-2017, as well as using the quantified representative index of the weather systems,the effects of the early autumn sea ice change on winter extreme low temperature weather in the Chinese Mainland region effect and its possible mechanism were analyzed under the background of Arctic amplification. The results showed that when the SIC was low in the Barents-Kara Sea and the north of Lapteveast of East Siberian-Chukchi Sea in the previous autumn, the winter extreme low temperature weather increased and intensified in the Chinese Mainland region as the whole. Its frequency was significantly increased in southern China, and intensity was significantly intensified in northern China. Compared with that in years with a high SIC, in low SIC years the control range of the Siberian high(SH) expanded and its intensity became stronger, and the composite value of the standardized SH intensity increased from-0.48 to 0.50. The northerly wind over the north of China enhanced in the 850 hPa wind field, corre-s ponding to the increase of the standardized integrated index of the East Asian winter monsoon composite value from-0.56 to 0.72. The Ural blocking(UB) mountain was more obvious, where the blockingi ndex was 6 days more. In the 500 hPa isobaric surface, there was a relative vorticity, a significantly negative anomaly and an abnormally high center of the meridional temperature gradient between the mid and high latitudes and Rossby waves activity flux anomalies in the UB region and the North Atlantic area,which was beneficial to the establishment and development of UB and its merger with the polar high,which strengthened the cold air intruding into the Chinese Mainland region and resulted in more and heavier extreme cold weather days there under the Arctic amplification effect.