Characteristics Of Planetary Wave Propagation In Absorbing And Reflecting SSW And Its Relation With Winter Cold Waves In Northern Hemisphere

In order to explore the relationship between different types of stratospheric sudden warming(SSW)events and winter cold wave in the northern hemisphere more futher,the changes of temperature and wind fields and the vertical propagation characteristics of planetary waves during 47 stratospheric explosive warming events in the 39 years from 1980 to 2018 were classified using ERA-Interim reanalysis data from the European Center,with emphasis on the winter of 2015 and 2016.Taking two SSWs in winter as examples,the propagation characteristics of planetary waves in absorbing and reflecting SSWs and their relationship with cold waves in different regions of northern hemisphere in winter are discussed..The conclusions are as follows:There are 47 SSWs during 1980-2014 including 24 absorbing SSWs and 23 reflecting SSWs.Early in the process,the upper stratosphere is in non-reflective state with strong west wind for absorbing SSW,which is favourable to upward propagation of planetary waves in troposphere,while upper stratosphere is in reflective state with obvious east wind for reflecting SSW,which prevents upward propagation of planetary wave and promote its downward propagation.In the later period,the upper troposphere dominated by upward planetary wave in absorbing SSW,while it dominated by downward planetary wave in reflecting SSW.SSW is usually accompanied by strong sub-planetary scale disturbances(high resistance)and triggers surface cold waves.8% of the 24 absorpting SSW events strengthened the original cold wave,67% events transferred planetary waves triggered the new cold wave,and 25% events both strengthened the original cold wave and triggered the new cold wave;Though 13% of the 23 reflective SSW events strengthened the original cold wave,65% events transferred planetary waves triggered the new cold wave,and 22% events both strengthened the original cold wave and triggered the new cold wave.The cold wave in North America 2015 with long duration and strong intensity is affected by a absorbing SSW.During that time,a deep high stratospheric Atlantic pressure is established by flux of planetary waves which propagate in tropospheric Europe and Atlantic region.And the flux of planetary wave action causes the high pressure to develop downward.The upward planetary waves also cause the deep high pressure in both upstream and downstream area in North America.Under this Deep(through stratosphere and troposphere)blocking condition,north wind lead the cold air to North America.On the other hand,the upward propagation of planetary wave promoted by absorbing SSW cause the energy aggregation of planetary wave energy,which promote the blocking state exist and make the cold wave long and strong.The cold wave in East Asia 2016 with short duration and weak intensity is affected by a reflecting SSW.During that time,reflecting SSW prevents continuous upward propagation of planetary wave in Europe and Atlantic region and promote its downward propagation.The planetary wave in Alaska propagate downward and eastward to the region of Ural Mountains and then promote the development of high pressure,which cause the blocking state.The north wind in east of the high pressure lead the cold air to East Asia.Due to prevention by reflecting SSW,the energy of planetary wave can not aggregate.The duration and intensity of both blocking high and cold wave is short and weak.