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 ~30% of extremes at 30° latitude with local hotspots of 80%-100%.