Read on Twitter
The big question looms once again: Will there be a sudden stratospheric warming (SSW) this winter, and if yes, when? Anybody can participate in the SSW competition, I’ll explain how — a thread. 1/11
What is a SSW? It’s a disruption of the infamous “polar vortex” in the stratosphere, at heights between about 10-50km above the Earth’s surface. Kind of like in this illustration, but not really: https://i.kym-cdn.com/photos/images/original/000/803/771/d67.jpg
Why do we care about SSWs? They can influence our weather for several weeks, with freezing cold in northern Europe and storms in southern Europe. Here’s an example of the change in surface temperatures after the 2018 SSW event. see also: https://simonleewx.com/2018/11/13/the-stratosphere-why-do-we-care/
How often do SSW events occur? Roughly every 2 years, but with high decadal variability. 4/11
In which season do SSW events occur? Mostly in December - February, with rare occurrences in November and March. 5/11
How predictable are SSWs? Sometimes not more than a few days, but generally not more than 2 weeks, Fig by @DrAHButler in https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2019JD030920
On longer timescales, remote effects can affect the strength of the polar vortex. The chance of a SSW increases for El Nino, easterly QBO, and MJO phase 6. These factors are not currently looking favorable for an SSW. Fig. by Chaim Garfinkel https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2019JD030923
What has happened so far this winter? The polar vortex has had a healthy start into winter with average to strong winds. But wave disturbances are increasing now, threatening to disrupt the vortex. https://acd-ext.gsfc.nasa.gov/Data_services/met/metdata/annual/merra2/flux/vt45_75n_100_2020_merra2.pdf
The troposphere has also prepared: High geopotential height disturbances over Northern Eurasia tend to precede SSW events, and they’re predicted to be present for the next three weeks — but will it be sufficient for an SSW event? https://simonleewx.com/cfsv2_weekly-anomalies/
So here’s the challenge: Will there be a SSW this winter (defined as the day of reversal of the zonal mean zonal wind at 60N and 10hPa), and if yes, on which day? Place your bet by replying to this tweet by December 9!
More information:
Stratosphere forecast by @zd1awrence:
https://www.stratobserve.com
Stratosphere forecast by @simonleewx:
https://simonleewx.com
Stratosphere forecast by @HannahAttard:
http://www.atmos.albany.edu/student/hattard/realtime.php
Polar vortex blog by @judah47: https://www.aer.com/science-research/climate-weather/arctic-oscillation/
Stratosphere forecast by @zd1awrence:
https://www.stratobserve.com
Stratosphere forecast by @simonleewx:
https://simonleewx.com
Stratosphere forecast by @HannahAttard:
http://www.atmos.albany.edu/student/hattard/realtime.php
Polar vortex blog by @judah47: https://www.aer.com/science-research/climate-weather/arctic-oscillation/
