北极地区极昼气候突变现象及转型成因研究

基于1979—2018年的NCEP-DOE Reanalysis II逐日再分析数据,采用模糊C均值聚类算法(Fuzzy C-Means Algorithm, FCMA)将北极地区极昼期间的气候分为寒干型、半寒干型、半暖湿型及暖湿型4种。在夏季北极海冰快速减少的气候背景下,这4种气候型控制的区域也相应发生了明显变化。其中,寒干型气候面积以-7.241×10~4 km~2·a~(-1)的速率快速减少;半寒干型气候面积以6.489×10~4 km~2·a~(-1)的速率快速增加,且洋面上的气候型变化比陆地更为显著。1999年前后,北极地区主控气候发生突变现象:由寒干型气候为主转化为半寒干型气候为主,尤其在楚科奇海和东西伯利亚海表现突出。成因分析表明海冰面积—净短波辐射—大气增暖增湿—向下长波辐射—气候型转变之间存在密切联系,极昼期海冰面积异常减少对其气候转型突变起到了重要作用。

Analysis of Arctic abrupt climatic change and the causes of the climatic type transition during the polar day

Based on the daily NCEP-DOE Reanalysis II data from 1979 to 2018, the Fuzzy C-Means Algorithm (FCMA) was used to classify the climate during the Arctic polar day into four climate types, which were the cold-dry type, the semi-cold-dry type, the semi-warm-wet type, and the warm-wet type. Results show that under the climate background of rapid reduction of Arctic sea ice in summer, the regions controlled by these four climate types also change significantly. Among them, the area of the cold-dry type decreases rapidly with the rate up to -7.241×10⁴ km²·a^-1, the semi-cold-dry type increases at a rate of 6.489×10⁴ km²·a^-1,and the climate change on the ocean is more significant than that on the land. Around 1999, the dominant climate in the Arctic changed from cold-dry type to semi-cold-dry type, especially in the Chukchi Sea and East Siberian Sea. The genetic analysis shows that there is a close relationship between sea ice area, net short wave radiation, atmospheric warming and humidification, downward long-wave radiation as well as climate type transformation, moreover, the abnormal decreasing of sea ice area in polar day plays an important role in the abrupt change of climate transformation.