Know how storm activities cause persistent weather extremes

If you thought that less severe storms in the mid-latitudes bring good news along with them, then according to a recent study these storms have a moderating effect on land temperatures.

Lead researcher Jascha Lehmann from the Potsdam Institute for Climate Impact Research said that they affect land temperatures because they bring maritime air from the oceans to the continents and a lack of them can thus favour extreme temperatures.

In the Northern Hemisphere mid-latitudes, much of the day-to-day weather variability is determined by the storm track regions located over the Atlantic and Pacific Oceans. Here, weather systems, including storms, are generated and travel eastwards to the continents. In winter, storms bring air from the relatively warm oceans to the continents and thus have a warming effect.

In summer, the effect reverses with winds bringing relatively cool and moist air from the sea. The authors show that a lack of such weather systems can thus favour more persistent heat and drought events in summer, and cold spells in winter.

Lehmann said that this summer a severe drought in China's northern bread basket region Liaoning threatened crop yields, while California has been experiencing a prolonged drought for no less than three consecutive years.

These detected changes in mid-latitude storm tracks are likely linked to changes in the jet stream and planetary waves in the atmosphere. Such dynamical changes favour certain types of weather situations in some regions and others elsewhere.

Co-author Dim Coumou said that altogether their study highlights how sensitive regional weather conditions are to any changes in large-scale atmosphere dynamics and this can have serious impacts for people on the ground.

The research is published in the Journal 'Scientific Reports.