NAWDIC – DICHOTOMI

DICHOTOMI aims at better understanding the formation of damaging surface winds in the dry intrusion and cloud head regions of extratropical cyclones. Several factors are known to be important, such as static stability, wind shear, surface heat fluxes, evaporative cooling, and sea state conditions. However, their relative roles in downward momentum transport is disputed. The project is part of the international North Atlantic Waveguide, Dry Intrusion, and Downstream Impact Campaign (NAWDIC) whose objective is to better understand and model physical processes associated with the triggering of wintertime high-impact weather in the North Atlantic-European region. To achieve this ambitious goal, the international NAWDIC community will deploy airborne and ground-based platforms over the North Atlantic in winter 2025/26. DICHOTOMI consists of deploying (1) the French ATR42 and the German Cessna F406 research aircrafts from Ireland and France, equipped with state-of-the-art remote-sensing and in-situ instruments, and (2) two ground-based observational platforms along the French and Irish coasts, composed of networks of Doppler wind lidars, water vapor lidars and Doppler cloud radars. Synergies between the aircraft and ground-based observing systems will provide unique and complementary measurements of fine-scale wind structures, clouds and surface characteristics in extratropical cyclones. A hierarchy of limited area models will be run for selected case studies with horizontal grid spacing ranging from 10 km (parameterized convection) and 1 km (storm resolving) to 100 m (large-eddy simulation). The model representation of cloud microphysics, convection, turbulence, air-sea fluxes and wind gusts will be confronted to observations. In addition to improving our knowledge of the underlying processes, the project will provide guidance in the development of physical parameterizations in weather and climate models.