zdlawrence replied to Paul's topic in Forecast models, atmosphere, stratosphere & global driversYeah, this was just a mistake that was posted on Twitter. The Charlton & Polvani 2007 paper specifically says: "... cases where the zonal mean zonal winds become easterly but do not return to westerly for at least 10 consecutive days before 30 April are assumed to be final warmings, and as such are discarded. This criterion ensures that following SSWs, a coherent stratospheric vortex is reestablished." The upcoming event will classify as a mid-winter SSW. How quickly the stratospheric circulation "recovers" after it remains to be seen, but forecasts (ensembles included) show it taking anywhere from 4-10+ days before circulation returns to westerly.
zdlawrence replied to Paul's topic in Forecast models, atmosphere, stratosphere & global driversJust want to address two points here: Amy Butler agreed that the Mar 2016 "major final warming" was a wave-driven event, but since the circulation never recovered, it just cannot be included on her table of CP07 events. Amy Butler has never said that the CP07 definition for SSWs is the "best" or "standard" definition -- it's just one of many definitions, but it is commonly used in the literature (see her paper on defining SSWs, http://journals.ametsoc.org/doi/abs/10.1175/BAMS-D-13-00173.1). I think her compendium of CP07 SSW dates is most helpful as a way to prevent errors in research & the literature; there are some small intricacies in the CP07 definition that do matter (see my next point below). I don't think her compendium was ever advertised as or intended to be the "definitive" list of events. Regarding the Feb 2017 event, I think the reason it's not an event in MERRA-2 is that the CP07 classification uses daily mean zonal mean zonal winds at 10mb 60N. They specifically say: "The first day on which the daily mean zonal mean zonal wind at 60°N and 10 hPa is easterly is defined as the central date of the warming." (see http://journals.ametsoc.org/doi/abs/10.1175/JCLI3996.1). If I wasn't on travel I would confirm, but since I can't, I would bet that averaging U1060 over the full 8 times per day of MERRA-2 would give a positive value. If anything, the above goes to show how any definition can be inadequate in specific situations, but that's just a side-effect of being consistent (i.e., true to the definition no matter what).