2012年初欧洲严寒天气成因的分析

Cause analysis on European severe cold weather in early 2012

2012年初欧洲遭受了严重的低温严寒天气。分析表明:从对流层低层到高层持续的大气环流异常与此次严寒天气有着密切的联系,1、2月出现的北极涛动(AO)的强负异常是造成此次欧洲严寒天气的主要原因。AO负异常导致北大西洋副高异常偏强、偏东和偏北,使得暖湿空气沿副高北侧流向北极地区,极大减弱了欧洲暖湿空气的来源;同时使乌拉尔山高压强度偏强,位置偏西偏北,有利于上游偏强、偏北的大西洋副高的维持,并加强了极区冷空气南下西进,造成了南欧地区的严寒天气。AO负异常引起的地中海低压槽的加深,为北方冷空气的南下创造了有利条件,也使冷暖空气在地中海北岸交汇,从而导致亚平宁半岛和巴尔干半岛的暴雪天气。虽然La Nia事件对这次严寒天气也有一定的贡献,但AO负异常对这次严寒天气的作用远远大于La Nia事件的作用。

Analysis shows that the severe cold weather in European areas in early 2012 had close relationship with the persistent atmospheric circulation anomalies from low to high level in the tropo- sphere. The strong negative anomaly of the Arctic Oscillation （AO） in Jan. and Feb. was the main reason of this event, making the North Atlantic subtropical high extend eastward and northward together with en- hanced intensity. At the same time, it forced the warm and wet air flow along its north side to the Arctic region, which weakened the warm and wet air source in the Europe. Meanwhile, the robust Ural high pressure shifted westward and northward, sustaining the North Atlantic subtropical high, and the polar cold air was enforced to invade southward to the South Europe. The deepened trough in Mediterranean was benefit to the invasion of cold air, leading to the warm and cold air convergence at the north coast of the Mediterranean, whereas the heavy snow disaster occurred in the Appennine Peninsula and the Balkan Peninsula. The AO anomalies had much more effects on the severe cold weather than the La Ni^a did, though the latter played some roles in the weather.