Séminaire
For confidence to be achieved in future projections of extra-tropical cyclones we need to be sure that climate models can represent them in the current climate. However, this representation should be considered through the dynamical and diabatic processes operating within cyclones rather than just the statistics. Using CMIP6 and higher resolution configurations of the IPSL and CNRM climate models run in “weather-forecast” mode in depth case studies of a rapidly-deepening cyclone sampled during the NAWDEX (North Atlantic Waveguide and Downstream impact EXperiment) field campaign is considered. Differences between the simulations and the analysis is associated with the representation of initial cyclogenesis. The quasi-geostrophic omega equation is then used to separate the contributions between dynamical and diabatic processes in the development of the cyclones. The results show that for both cyclones and all simulations the strongest deepening stage is first dominated by diabatic processes and then dynamical processes. Contrary to expectations, there is no obvious stronger contribution of diabatic processes with increased resolution, instead the dynamic processes increase with importance. The climate models are also compared against observations made during the NAWDEX campaign, and indicate that the models produce too much supercooled liquid. These cases show that further work into the representation of cyclones in climate models, focusing on baroclinic interaction and latent heating is required to improve confidence in the projections for the behaviour of extra-tropical cyclones in the future.
helene.rouby@ens.fr