Editing Sudden stratospheric warming (section)

== Dynamics ==
SSW events are often associated with strong [[Rossby waves|Rossby wave]] events in the [[troposphere]], which can intrude into the stratosphere if they become strong enough. Strong Rossby waves are usually associated with strong systems and temperature gradients, so it is common to see SSW events associated with particularly strong [[Low-pressure area|areas of low pressure]]. The resultant intrusion of warm, tropospheric air into the stratosphere has a dramatic effect on normal winter stratospheric wind patterns, changing the westerly winds and warming the aloft stratospheric temperatures, disrupting the polar vortex.<ref>{{cite journal |title=On the transfer of energy in stationary mountain waves |year=1960 |last1=Eliassen |first1=A |last2=Palm |first2=T |journal=Geofysiske Publikasjoner |volume=22 |pages=1023}}</ref> This is a big reason why SSW events are far more common in the northern hemisphere. Because the northern hemisphere has much more land than the southern hemisphere does, the sharp temperature gradients that induce strong Rossby wave activity seldom exist. <ref>{{cite journal |doi=10.1007/BF02987584 |pmid=12515343 |title=The southern hemisphere ozone hole split in 2002 |year=2002 |last1=Varotsos |first1=C. |journal=Environmental Science and Pollution Research |volume=9 |issue=6 |pages=375–376 |bibcode=2002ESPR....9..375V |s2cid=45351011 }}</ref><ref>{{cite journal |doi=10.1175/JAS-3313.1 |title=Simulations of Dynamics and Transport during the September 2002 Antarctic Major Warming |year=2005 |last1=Manney |first1=Gloria L. |last2=Sabutis |first2=Joseph L. |last3=Allen |first3=Douglas R. |last4=Lahoz |first4=William A. |last5=Scaife |first5=Adam A. |last6=Randall |first6=Cora E. |last7=Pawson |first7=Steven |last8=Naujokat |first8=Barbara |last9=Swinbank |first9=Richard |journal=Journal of the Atmospheric Sciences |volume=62 |issue=3 |pages=690 |bibcode = 2005JAtS...62..690M |s2cid=119492652 |doi-access=free }}</ref><ref>{{Cite journal |doi = 10.1038/d41586-019-02985-8|title = Rare warming over Antarctica reveals power of stratospheric models|journal = Nature|volume = 574|issue = 7777|pages = 160–161|year = 2019|last1 = Lewis|first1 = Dyani|pmid = 31595070|bibcode = 2019Natur.574..160L|doi-access = free}}</ref><ref>{{cite web |last1=CSIRO |title=New research centre focuses on the 'ocean hemisphere' |url=https://www.csiro.au/en/news/all/articles/2017/may/cshor#:~:text=More%20than%2080%20per%20cent,largely%20unmeasured%20and%20poorly%20understood. |website=www.csiro.au |language=en}}</ref>   

Strong Rossby wave events are often associated with a [[Block (meteorology)|meteorological blocking pattern]], which causes the waves to grow large enough to protrude into the stratosphere. The magnitude of the Rossby wave has significant influence over the strength of the SSW event. However, if the main stratospheric flow turns easterly, it prevents the Rossby wave from continuing its stratospheric intrusion. This blockage releases substantial amounts of energy that force the polar vortex to collapse, which explains why most polar-vortex collapses are major SSW events. <ref>{{cite journal |doi=10.1029/JZ066i001p00083 |title=Propagation of planetary-scale disturbances from the lower into the upper atmosphere |year=1961 |last1=Charney |first1=J. G. |last2=Drazin |first2=P. G. |journal=Journal of Geophysical Research |volume=66 |issue=1 |pages=83–109|bibcode = 1961JGR....66...83C |s2cid=129826760 }}</ref><ref name=":2">{{cite journal |last1=Lim |first1=Eun-Pa |last2=Hendon |first2=Harry H. |last3=Butler |first3=Amy H. |last4=Thompson |first4=David W. J. |last5=Lawrence |first5=Zachary D. |last6=Scaife |first6=Adam A. |last7=Shepherd |first7=Theodore G. |last8=Polichtchouk |first8=Inna |last9=Nakamura |first9=Hisashi |last10=Kobayashi |first10=Chiaki |last11=Comer |first11=Ruth |last12=Coy |first12=Lawrence |last13=Dowdy |first13=Andrew |last14=Garreaud |first14=Rene D. |last15=Newman |first15=Paul A. |date=June 2021 |title=The 2019 Southern Hemisphere Stratospheric Polar Vortex Weakening and Its Impacts |journal=Bulletin of the American Meteorological Society |volume=102 |issue=6 |pages=E1150–E1171 |bibcode=2021BAMS..102E1150L |doi=10.1175/BAMS-D-20-0112.1 |last16=Wang |first16=Guomin}}</ref><ref>{{cite journal |last1=Hartmann |first1=Dennis L. |last2=Mechoso |first2=Carlos R. |last3=Yamazaki |first3=Koji |title=Observations of Wave-Mean Flow Interaction in the Southern Hemisphere |journal=Journal of the Atmospheric Sciences |date=February 1984 |volume=41 |issue=3 |pages=351–362 |doi=10.1175/1520-0469(1984)041<0351:OOWMFI>2.0.CO;2|bibcode=1984JAtS...41..351H |doi-access=free }}</ref>   

A correlation exists between SSW events and the [[quasi-biennial oscillation]] (QBO). If the QBO is in its easterly phase, the [[atmospheric waveguide]] is set up in a way that causes upward-propagating [[Rossby waves]] to focus more on the [[polar vortex]]. This helps intensify their interaction with the mean flow, thus boosting the probability of an SSW event occurring.<ref name="Southern Hemisphere SSW">{{cite journal |last1=Shen |first1=Xiaocen |last2=Wang |first2=Lin |last3=Osprey |first3=Scott |date=2020 |title=The Southern Hemisphere sudden stratospheric warming of September 2019 |journal=Science Bulletin |volume=65 |issue=21 |pages=1800–1802 |bibcode=2020SciBu..65.1800S |doi=10.1016/j.scib.2020.06.028 |pmid=36659119 |doi-access=free}}</ref><ref name=":1" />