What is the relative impact of nudging and online coupling on meteorological variables, pollutant concentrations and aerosol optical properties?

Meteorological and chemical modelling at the regional scale often involve the nudging of the modelled meteorology towards reanalysis fields and meteo-chemical coupling to properly consider the interactions between aerosols, clouds and radiation. Both types of processes can change the meteorology, but not for the same reasons and not necessarily in the same way. To assess the possible interactions between nudging and online coupling, several simulations are carried out with the WRF–CHIMERE (Weather Research and Forecasting) model in its offline and online configurations. Through comparison with measurements, we show that the use of nudging significantly improves the model performances. We also show that coupling changes the results much less than nudging. Finally, we show that when nudging is used, it limits the variability in the results due to coupling.