摘要:利用1959～2017年ERA40/ERA-Interim逐日再分析资料和国家气候中心的逐日站点资料，针对发生在当年11月至次年3月（NDJFM）的全国性持续低温事件（EPECEs），分析了热带外环流的变化特征，以及平流层—对流层相互作用。结果表明，全国性EPECEs可划分为冷空气在乌拉尔山—西伯利亚关键区堆积和冷空气爆发以及消亡三个阶段，分别与对流层中层乌拉尔山—西伯利亚一带大型斜脊的建立、发展和崩溃以及平流层极涡强度的恢复、维持和再次减弱相对应，其中伴随着显著的平流层—对流层相互作用。首先，以大西洋地区异常扰动为主的热带外对流层形成2波型行星波异常，并上传影响平流层；随后在平流层2波调整为1波型的过程中，出现了行星波的异常下传以及平流层极涡强度的恢复，在对流层形成的1波型的高度正异常中心位于东欧地区，有利于乌拉尔山高度脊的建立以及源于北冰洋的冷空气在高压脊前形成堆积；随后由于平流层极涡强度维持，对流层行星波上传持续受到抑制，并主要在欧洲一带出现显著的异常向下反射，对应对流层1波型高度正异常中心逐步东移至中西伯利亚地区，从而有助于乌拉尔山脊向下游发展成一个横跨西伯利亚地区的大型斜脊，冷空气堆积区也东移到中西伯利亚地区。进入冷空气爆发阶段，随着斜脊前的大型横槽与上游移来的短波槽形成阶梯槽形势，横槽很快转竖引导低层冷空气向我国大范围爆发；同时大型斜脊的维持也使行星波再次出现1波型异常上传，影响平流层极涡再次减弱。最后，随着冷空气爆发，大型槽脊迅速崩溃，对流层波动减弱，低层气团的经向输送也随之减弱，EPECEs消亡。
关键词:全国性持续极端低温/
大型斜脊/
平流层—对流层相互作用
Abstract:Using the ERA40/ERA-interim daily-mean reanalysis data and the daily station data from National Climate Center, this study explores the stratosphere-troposphere interaction processes during nationwide Extensive and Persistent Extreme Cold Events (EPECEs). The results show that nationwide EPECEs usually experience three stages: (1) Cold air accumulation in Urals-Siberia area, (2) cold outbreak, and (3) cold-decay, which corresponds respectively to the formation, the development and the collapse of the Urals-Siberia tilted ridge in the middle troposphere, as well as the recovering, the persistence and the re-weakening of the stratospheric polar vortex. Firstly, a wavenumber-2-type anomaly pattern, mainly dominated by disturbances in Atlantic, appears in the extratropical troposphere and propagates upwards to weaken the stratospheric polar vortex. Subsequently, when the wavenumber-2-type anomaly pattern changes to a wavenumber-1-type in the stratosphere, wave propagation turns to downward while the stratospheric polar vortex recovers its strength. Followed is a wavenumber-1-type anomaly pattern in the troposphere with its positive pole centered in the eastern Europe which helps the establishment of a Ural blocking and accumulation of cold air from the Arctic Ocean in front of the blocking. Thereafter, with the eastward shifting of the positive pole of the wavenumber-1-type anomaly pattern to central Siberia, a large-scale tilted ridge arching across the Siberia is established. The cold-air accumulation area thus also moves eastward to central Siberia. Before the cold-air outbreak, a trench structure is formed by the large-scale transversal trough downstream of the ridge and an upstream short-wave trough. Cold air outbreaks into China as the transversal trough quickly turns into a vertical form. Meanwhile, the stratospheric polar vortex weakens again due to the enhanced upward wave propagation related to the persisting large-scale tilted ridge in the troposphere. Finally, with the collapsing of the blocking and troughs, meridional transport of cold air diminishes and EPECEs decays.
Key words:Nationwide EPECEs (nationwide Extensive and Persistent Extreme Cold Events)/
Large-scale tilted ridge/
Stratosphere–troposphere interaction
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