Cyclone phase space diagrams dedicated to extratropical cyclones studies

Cyclones’ tracking algorithms are commonly used to study the life cycle of extratropical cyclones and their evolution with climate change in both reanalyses and climate models. Such a framework allows the computation of valuable diagnostics such as maps of genesis, lysis, and track densities, statistical analyses or also centered-cyclone composites. Cyclone phase space diagrams, i.e representations of a cyclone in a multidimensional parameters’ space, can be also diagnosed and are particularly illuminating. This has been extensively investigated for tropical cyclones, but much less in the context of extratropical cyclones. The cyclone phase space diagrams of Hart (2003) have shown to be useful to study tropical cyclones and particularly extratropical transitions, but they are not well adapted to study extratropical cyclones themselves and to separate them into different categories, as we will illustrate with different individual cases of mid-latitude and Arctic cyclones. Our aim is to present a new set of cyclone phase space diagrams that are as simple as possible and can be easily computed from climate model or reanalyses outputs. It includes a refinement of the cyclone core temperature of Hart (2003) that takes into account the non-axisymmetric character of extratropical cyclones, the thermal asymmetry parameter of Hart (2003), and additional parameters, related to baroclinic growth such as the baroclinic conversion rate, the baroclinicity, and the vertical tilt of baroclinic disturbances. Such diagrams will be presented with a large set of extratropical cyclones tracked with the ‘TempestExtremes’ algorithm applied to ECMWF-ERA5 reanalysis datasets. A few statistical analyses conducted with the diagrams will be presented as well.