Extended Influence of Midlatitude Cyclones on Global Cold Extremes

Cold temperature extremes, causing damage to industry, agriculture and human health, are often associated with midlatitude cyclones. Here, we quantify the relation between cyclones and cold extremes by highlighting two cyclone-associated dynamical features that may, differently, induce cold extremes. Namely, slantwise-descending dry intrusions (DIs) advect cold air equatorward into the cyclone's cold sector, and upper-tropospheric troughs, diagnosed as cyclonic potential vorticity (PV) anomalies, induce cold anomalies directly below. By objectively-identified DI outflows and cyclonic PV anomalies for 1979-2019 in ERA5 reanalysis, their climatological association with the 5% lowest 2-m temperature is globally quantified. We find that in midlatitudes upper PV anomalies dominate cold extremes, while DIs dominate extremes in the subtropics and even the tropics. The rare overlap between the two features can potentially act as a strong predictor for cold extremes, accompanying similar to 30% of extremes at 30(degrees) latitude with local hotspots of 80%-100%.

Automated summary

This study quantifies the relationship between midlatitude cyclones and cold extremes, finding that upper potential vorticity anomalies dominate cold extremes in midlatitudes, while slantwise-descending dry intrusions dominate extremes in subtropics and even tropics.