Assessment of HARMONIE-AROME in the simulation of the convective activity associated to a subtropical transition using satellite data

Subtropical transition events (STT) are a challenge for forecasting and research due to the hybrid characteristics they give to the cyclones. The ability and skillfulness of the HARMONIE-AROME model to reproduce the cloud structure and convection associated to the October 2014 STT is here evaluated. Brightness temperature, cloud top height and accumulated precipitation are assessed against satellite data using traditional skill scores and object-based techniques specific to forecasting spatial evaluation. The results present differences in the simulation of the cyclone between the periods before and after the transition. They also show a very good performance of the model in the location of the events and a good simulation of the intensity of the variables. The performance is sub-optimal for the estimation of the sizes of the convective objects. Brightness temperature and cloud top heights yield very good results in general, with a slight overestimation in both cases. However, the model struggles to capture the accumulated precipitation. There is scarce work evaluating the HARMONIE-AROME model in this type of events; nevertheless, the results are in line with those produced by the simulations with other numerical models. The overall performance of the model is very adequate, although it might be hindered by the internal stability of the model produced by the deep-convection computation.