等熵位涡揭示的一次强寒潮过程中高层扰动特征

Disturbance features of mid-upper troposphere during a strong cold wave event revealed by isentropic potential vorticity analysis

采用欧洲中心提供的ERA-Interim每日4次再分析资料,对2016年1月下旬的一次强寒潮事件进行等熵位涡分析。结果表明,此次强寒潮的爆发以动力对流层顶下降、高位涡下传为特征,位涡扰动的强度和时间曲线的转折点对寒潮的酝酿和爆发有指示意义。此次强寒潮过程的冷空气可追溯到欧亚北部的新地岛附近和亚洲东北部的对流层顶,两股具有高位涡的冷空气在贝加尔湖附近合并堆积,在转竖横槽的引导下向南爆发,形成强寒潮。伴随寒潮过程的酝酿和爆发,高位涡强冷空气向下、向南传播,并伴随急流向下伸展。高位涡柱对应强烈发展并下伸的正涡度柱,表明高位涡引起的垂直拉伸导致显著的旋转增强,对应涡后横槽的强烈加深。对流层顶呈现大振幅波动,来自高层的信号较低层出现得更早、更强,在动力对流层顶上的信号比500 h Pa表现得更为清楚。

By employing isentropic potential vorticity analysis, the disturbance features of mid-upper troposphere during a strong cold wave event in January 2016 are analyzed with ECMWF ERA-Interim reanalysis data. Results reveal that the out-break of the strong cold wave was characterized by dropping of the dynamical tropopause and downward extending of PV, and the disturbance of PV can be a good indicator for the brewing and out-breaking of cold wave. The cold air of the strong cold wave, which originated from the tropopause in vicinity of Novaya Zemlya in the north Eurasia and northeast of Asia, combined and accumulated nearby Lake Baikal, finally broke out southward as the cold trough transformed from transversal into upright. With the brewing and out-breaking of the strong cold wave, the cold air of high PV propagated downward and southward, with jet stream extending downward. The transversal trough intensively deepened, as the air column of high PV and cyclonic vorticity rapidly stretching downward, indicating the strengthening of cyclonic rotation as a result of vertical stretching of high PV. The dynamic tropopause exhibited large amplitude of disturbance. The disturbance signal from the upper levels appeared earlier and stronger, and the signal in the dynamic tropopause was more pronounce than that at 500 hPa.