夏、秋季北极海冰异常与秋、冬季青藏高原极端低温日数的关系及影响机理

利用1979~2012年青藏高原125个基本、基准站观测日最高及最低气温数据、Hadley中心月平均海冰覆盖率资料、ERA-Interim的风场、高度场等再分析资料,根据相关统计分析、合成分析等方法系统地分析了青藏高原地区秋、冬季冷昼和冷夜日数(低温日数)与关键影响海区海冰的关系及影响机理。结果表明,夏、秋季关键海区海冰偏少时,秋、冬季极地和青藏高原地区500 h Pa位势高度减小,中高纬西伯利亚地区位势高度增强,北极至青藏高原有明显由北向南波动通量,高压反气旋系统在西伯利亚地区形成与壮大,青藏高原以北风场呈现明显偏北风,Rossby波在青藏高原及其以北地区呈现由北向南波动形式,青藏高原以北的西风带地区Rossby波东传减缓,导致经向活动加强,北部冷空气易于通过气流向高原侵袭,秋、冬季青藏高原低温日数将偏多。

Relationship of Arctic Sea Ice Coverage Anomalies in Summer-Autumn and Extreme Cold Days over the Tibetan Plateau in Autumn-Winter and the Mechanism

In this paper, daily maximum and minimum temperature data (1979-2012) collected at 125 stations in the Tibetan Plateau are used. The observed monthly sea ice concentration field is extracted from the Hadley Centre sea ice data set (1°×1°, 1979-2012). Air temperature, geopotential height, and wind (monthly) fields are obtained from the latest reanalysis of the European Centre for Medium Range Weather Forecasts (ERA-Interim, 1°×1°, 1979-2012). Based on statistical analysis and synthesis analysis, the relationships between the numbers of cold days and cold nights in the Tibetan Plateau region and the key area sea ice fraction in the Arctic are systematically analyzed. The results show that extreme cold days in the Tibetan Plateau in autumn-winter become more frequent in the years when sea ice fraction is low in the key region in summer-autumn. It can be seen that 500 hPa geopotential height in the Arctic is positively correlated that in the Siberia but negatively correlated with that in the Tibetan Plateau. From the polar region to the Tibetan Plateau, there is an obvious flux fluctuation from north to south while the high pressure and anticyclone above the Siberia area become stronger. The Tibetan Plateau is mainly under the control of northerly flows. In the years with low sea ice fraction, the Rossby wave presents a fluctuation pattern from north to south over the Tibetan Plateau and to the north of the Tibetan Plateau, which makes the cold airmass easy to reach the Tibetan Plateau and results in more extreme cold weather days in the region.