The jet stream that brought in Storm Eunice is moving northwards

New research shows that the average winter northern hemisphere jet stream position over the North Atlantic and Eurasia has moved northwards by up to 330 kilometres and the mean winter jet speed has increased by 8% to 132 miles per hour, during the 141-year period from 1871-2011.

Just this week the jet stream has brought storms Dudley, Eunice and Franklin to the UK. Jet streams are fast bands of air which flow around the globe around ten thousand metres above Earth’s surface. They have a significant influence on storm activity and temperature patterns across the northern hemisphere which can impact the weather through strong winds and flooding events.  This is the longest regional study of the northern hemisphere jet stream and the trends observed are potential indicators of climate change.

The study, published in Climate Dynamics, provides a comparison of the Northern Hemisphere jet stream across oceans and continents and finds that jet stream trends vary on a regional and seasonal basis. Between 1871 and 2011 the average winter movement in jet stream latitude over the North Atlantic was from 44° to 47° north with a 10 mph increase in speed to 132 miles per hour, but no increases were observed over the North Pacific.

The study was led by Dr. Samantha Hallam, from Maynooth University in Ireland whilst undertaking a PhD at the University of Southampton. Dr Hallam said:  “Significant increases in winter jet latitude and speed are observed over the North Atlantic and Eurasia.  These changes are consistent with the decreasing temperature and increasing pressure gradients observed between the equator and the Arctic over the period, and likely associated with the warming Arctic winters.”

“Over the North Pacific, no increase in jet latitude or speed are observed, however, changes in the North Pacific sea surface temperatures explains over 50% of the variability in jet latitude.”

The results highlight that northern hemisphere jet variability and trends differ on a regional basis across the North Atlantic, North Pacific, Eurasia and North America. This is important for making climate predictions and in developing plans to combat climate change.

These findings are the result of a statistical analysis of the 250mb jet stream using the Twentieth Century Reanalysis dataset.

The research was supported by the Marine Institute and funded by the Irish Government under the JPI Climate and JPI Ocean joint call and the Natural Environmental Research Council, and involved collaboration between The Irish Climate Analysis Research Units (ICARUS) at Maynooth University in Ireland, University of Southampton, UK and National Oceanography Centre, UK.