Characteristics of diabatically influenced cyclones with high wind damage potential in Europe

Extratropical cyclones are the primary driver of midlatitude weather variability, including extreme events with heavy precipitation and severe wind gusts, potentially leading to widespread damage. Both baroclinicity and diabatic heating contribute to cyclone intensification. Examples of severe European winter storms with rapid intensification enhanced through diabatic heating include Lothar (1999), Klaus (2009), and Xynthia (2010). Diabatic heating through cloud condensational processes in extratropical cyclones is associated with the warm conveyor belt (WCB) airstream, among others. Focusing on European winter storms, this study provides a comprehensive assessment of structural differences important for cyclone intensification between cyclones that intensify to a relatively large extent through diabatic processes and cyclones that intensify mostly through baroclinic processes. Considering 247 winter storms affecting western and central Europe from 1979 to 2023, we combine a WCB diagnostic with the pressure tendency equation to quantify the influence of diabatic heating on deepening processes. Our results indicate that diabatic processes have a mean contribution to cyclone intensification of 26.1% (median at 25.3%, 25th and 75th percentiles at 15.2% and 33.4%). ... mehrCyclones with a relatively large diabatic influence (>30.7 % diabatic contribution) have similar minimum mean sea-level pressure compared with cyclones with a small diabatic influence (<20.1% diabatic contribution) but exhibit steeper deepening rates, stronger northward displacement, increased precipitation, stronger wind gusts, and more WCB activity. Moreover, they are characterised by increased moisture and warmer temperatures in the WCB inflow, facilitating stronger deepening rates driven by diabatic heating. Our results suggest that WCB activity is a valuable first indicator of the diabatic contribution to cyclone intensification. These findings may be useful for predicting and estimating the risks associated with winter storms that have a relatively large influence of diabatic processes in numerical weather predictions and climate projections.