Synoptic cyclones in mid- and high-latitudes govern dynamics of the meridional energy fluxes in the earth’s climate system (Trenberth and Stepaniak, 2004; Fan et al., 2015). Extra-tropical storms (see figure 2 ) are an integral part of synoptic meteorology with ample theories about their dynamics and life cycles, see the extended review by Shultz et al. (2019), “Extratropical Cyclones: A Century of Research on Meteorology’s Centerpiece”.
There is strong evidence that storms control stagnating planetary waves in the atmosphere, thus, being responsible for seasonal weather extremes (heat and cold waves) over Europe, parts of Asia and the Arctic (Nakamura et al., 1997; Pfahl et al., 2015; Cohen et al., 2020). Atlantic storm activity was historically high in the mid-1990s, and after some decrease, is rising again (Wang et al., 2011).
In this context, we cannot ignore the number of extra-tropical storms reaching tropical depression status and how this might change in the future. In the North Atlantic, there are more than 10 extratropical storms every year with hurricane-force winds (e.g. Hanafin et al., 2012, Masselink et al., 2016). A consensus is emerging among climate modelers (e.g. Bengtsson, 2006) that the world's changing climate will lead to a poleward shift in extratropical storm tracks, with no overall intensification of extratropical cyclonicity, but considerable regional changes associated with this poleward shift. Climate models further predict increased Atlantic storminess due to the northeastward extension of the North Atlantic storm track (Li et al., 2018). These changes protrude to the very high Arctic where previously extreme winds were infrequent whereas other high-latitude regions see decrease of storminess (Wickström et al., 2020).
Extra Tropical Cyclone