Sudden Stratospheric Warmings (SSWs)

Sudden stratospheric warmings (SSWs) are large scale events that are of first-order importance to understanding the wintertime dynamical variability in the polar stratosphere. These dramatic events were first observed by Richard Scherhag, who initially called them "the explosion-like warming of the stratosphere", during February 1952 in Berlin, Germany. SSWs have been known as "Berlin phenomenon" during the first decades after their discovery, until the term SSW got established and widely accepted. It is interesting that the acronym SSW is sometimes spelled out as "stratospheric sudden warming", however given there is no tropospheric analog of SSWs it seems more appropriate to use "sudden stratospheric warming" (as in the sub-class of stratospheric warmings that occur suddenly). SSWs are marked by a reversal of the polar cap circulation on the order of days with an associated warming that can be as large as 50 K on the same timescale. The wind reversal is a downward propagating feature that begins near the stratopause (~50 km altitude) and that descends to the lowest levels of the stratosphere (~15 km altitude).

Animation of mid-stratospheric (~30 km altitude) circulation of the entire cold season 2008-2009 (blue shading shows cold polar vortex air, the strongest vortex split SSW event on record took place in late January 2009), this is an extensive animation and may take a bit to load in your browser - please be patient

Past SSW events (will be updated to include more recent events soon)

all animations below are for potential vorticity (PV, a measure of the vortex swirl) on the 530 K isentropic surface (~21 km altitude); high values of PV in blue with the black contour marking the approximate edge of the polar vortex

[note, the animations may take a bit to load - please be patient]