Climate Fact: Jet Stream Secrets
Could lessons from its 44-year climatology improve our forecasts of cold snaps?
Jet streams are the air traffic controllers of Earth’s weather. These fast-moving “rivers of air” meander through the atmosphere’s landscape, pushing around mountains and valleys of high and low pressure. The jet stream’s position can be a great clue for predicting some types of extreme weather. An international team of scientists showed that when the average position of the Polar Jet falls below 44°N in winter months, the chances of an extreme cold snap nearly double for the Mountain West and triple across Europe. And these odds remain in place for nine days – even if the jet stream moves! Even more amazingly, these odds quadruple in Europe for the most severe, record-breaking cold snaps that represent the coldest one percent of all recorded temperatures from 1957 to 2001. However, when the Polar Jet inches northward between 44°N and 53°N, the odds of a European cold snap actually decrease and the U.S. remains unaffected. These jet stream secrets could be strong, medium-range forecasting tools for meteorologists since these results are derived from almost 50 years of observational data. But climatologists can use these results as well. As our climate changes, the zonal mean Polar Jet is expected to shift northward, and that could reduce the frequency of extreme cold snaps across Europe and Greenland. That could be good news for ice since the southerly Polar Jet position (below 44°N) greatly increases the chance of very mild temperatures in Greenland.
The Polar Jet Stream. Video courtesy of NASA.
(Source: Mahlstein, I., O. Martius, C. Chevalier, and D. Ginsbourger, 2012. “Changes in the odds of extreme events in the Atlantic basin depending on the position of the extratropical jet.” Geophysical Research Letters, 39:L22805, doi:10.1029/2012GL053993)