Sudden Stratospheric Warming May Trigger “Beast From the East”

The stratospheric potential vorticity field on February 10, 2018. The Stratospheric Polar Vortex is about to split in two, and the weakening of the vortex was followed around two weeks later by a severe cold air outbreak over Europe known as the Beast from the East. Data from ERA-Interim reanalysis (Dee et al., 2011).
Credit: University of Bristol

A new study led by researchers at the Universities of Bristol, Exeter, and Bath helps to shed light on the winter weather we may soon have in store following a dramatic meteorological event currently unfolding high above the North Pole.

Weather forecasting models were predicting with increasing confidence that a sudden stratospheric warming (SSW) event would take place on January 5, 2021, and indeed, experts confirmed that it is underway.

The stratosphere is the layer of the atmosphere from around 10-50km above the earth’s surface. SSW events are some of the most extreme of atmospheric phenomena and can see polar stratospheric temperature increase by up to 50°C over the course of a few days. Such events can bring very cold weather, which often result in snowstorms.

The infamous 2018 “Beast from the East” is a stark reminder of what an SSW can bring. The disturbance in the stratosphere can be transmitted downward and if this continues to the earth’s surface, there can be a shift in the jet stream, leading to unusually cold weather across Europe and Northern Asia. It can take a number of weeks for the signal to reach the surface, or the process may only take a few days.

The study, published in the Journal of Geophysical Research and funded by the Natural Environment Research Council (NERC), involved the analysis of 40 observed SSW events that occurred over the last 60 years. Researchers developed a novel method for tracking the signal of an SSW downward from its onset in the stratosphere to the surface.

Findings in the paper, “Tracking the stratosphere-to-surface impact of Sudden Stratospheric Warmings” suggest split events tend to be associated with colder weather over north west Europe and Siberia.

Lead author of the study, Dr. Richard Hall, said there was an increased chance of extreme cold, and potentially snow, over the next week or two.:

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