Geophys. Res. Lett. (2016)

Credit: Rainer Lesniewski / Alamy Stock Vector

Atmospheric fronts — the sharp boundaries between air masses of different thermal properties — are associated with high-impact extreme weather in the mid-latitudes. Their passage, for example, often triggers intense precipitation and strong winds, with potentially severe socio-economic impacts.

Sebastian Schemm from the University of Bergen, Norway, and co-authors investigate recent changes in frontal system behaviour using gridded data based on observations and satellite retrievals. While the total annual number of fronts has not altered over the period 1979–2014, the authors find a systematic increase in the frequency of strong and extreme fronts traversing Europe during summer and autumn. This change, they argue, can be linked to increasing atmospheric humidity gradients. Strengthened frontal systems are also found to have enhanced frontal precipitation rates, and may therefore be one factor contributing to the observed increases in extreme rainfall events over Europe. No similar frontal trends are evident over North America. These findings continue to highlight the importance of assessing both dynamic and thermodynamic atmospheric properties when diagnosing contemporary and future hydroclimate variability.