Occurrence of Winter Stratospheric Sudden Warming Events and the Seasonal Timing of Spring Stratospheric Final Warming

Abstract:

Based on the NCEP–NCAR reanalysis dataset covering 1958–2012, this paper demonstrates a statistically

significant relationship between the occurrence of major stratospheric sudden warming events (SSWs) in

midwinter and the seasonal timing of stratospheric final warming events (SFWs) in spring. Specifically, early

spring SFWs that on average occur in early March tend to be preceded by non-SSW winters, while late spring

SFWs that on average take place up until early May are mostly preceded by SSW events in midwinter. Though

the occurrence (absence) of SSW events in midwinter may not always be followed by late (early) SFWs in

spring, there is a much higher (lower) probability of late SFWs than early SFWs in spring after SSW (non-

SSW) winters, particularly when the winter SSWs occur no earlier than early January or in the period from

late January to early February. Diagnosis shows that, corresponding to an SSW (non-SSW) winter and the

following late (early)-SFW spring, intensity of planetary wave activity in the stratosphere tends to evolve out

of phase from midwinter to the following spring, being anomalously stronger (weaker) in winter and

anomalously weaker (stronger) in spring. Furthermore, the strengthening of the western Eurasian high, which

appears during early to mid-January in late-SFW years but does not appear until late February to mid-March

in early-SFW years, always precedes the strengthening of planetary wave activity in the stratosphere and thus

acts as a tropospheric precursor to the seasonal timing of SFWs.