有两个关键偶尔在北方冬季温带环流模式。一个是-[阻塞流][1]导致封锁反气旋的形成和一个可以测量的位置通过这个指数——“阻塞事件”(中共封锁指数)[2]。另一个是(突然平流层变暖)[3]。为了把这一个需要看温度变化在北极平流层通常在10 hPa等压面。如果温度变化超过50到70度的天气尺度和温度变化是快速的3 - 4天就有一个突然的变暖的可能性。关注后者,因为目前有可能2019年1月突然平流层变暖可能导致平流层极涡分裂。基于此同行评议参考——(平流层涡流位移的影响和分裂表面气候][4]它实际上是导致极地平流层对流层变异性通过垂直传播罗斯比波[5]。背后的数学很复杂但也提要在线性理论(准地转势涡度方程)。其中一些垂直传播波可以旅行到中间层。[这些课堂讲稿罗斯比波][6]提到罗斯比波不能传播如果平均纬向风垂直东风或如果他们是西风,超过一定的速度。 It is only the wintertime atmosphere that permits Rossby waves to reach the stratosphere and deposit energy and hence sudden stratospheric warmings are only observed after boreal fall. In the northern hemisphere most vertically propagating Rossby waves arise due to the topography and in the southern hemisphere the sudden stratospheric warmings are a rarity due to lack of topographical features. The last sudden stratospheric warming over the southern hemisphere was in 2002. The resulting stratospheric anomalies can in return influence surface climate but the mechanism on how exactly this occurs is the still the matter of scientific research. One of the theories that are currently popular is the [Wave mean flows interactions][7]. This can be easily summarized as how planetary scale Rossby waves influence the circulating zonal flows around a planet. The other theory is wave reflections at the tropopause. So what is the net result of either of the above two possibilities ? The net result is how they affect mid latitude storms. Storms could either become more intense or shift equatorward or there could be extremely cold air advection spells as the stratospheric air gets mixed with the troposheric air. On the rarity of polar vortex splits - well they are coupled to sudden stratospheric warmings. If you are asking about the climatology of SSWs [observations are currently split between El Ninos and La Ninas][8]. It is also not unusual that the polar vortex not split at all but be merely be pushed equatorward. Sudden stratospheric warmings happen almost every other year. The long term effect that this could cause is extended spells of extremely cold weather and when the summer returns the polar vortex shrinks in size giving rise to the easterly wind circulation at the poles. [1]: https://en.wikipedia.org/wiki/Block_(meteorology) [2]: https://www.cpc.ncep.noaa.gov/products/precip/CWlink/MJO/block.shtml [3]: https://en.wikipedia.org/wiki/Sudden_stratospheric_warming [4]: https://journals.ametsoc.org/doi/pdf/10.1175/JCLI-D-12-00030.1 [5]: http://www-eaps.mit.edu/~rap/courses/12831_notes/3.pdf [6]: http://snowball.millersville.edu/~adecaria/ESCI343/esci343_lesson11_rossby_waves.pdf [7]: http://pordlabs.ucsd.edu/pcessi/theory2016/TEM_Vallis.pdf [8]: https://academiccommons.columbia.edu/doi/10.7916/D8QJ7TFG