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ALARO-0 model

The international ALADIN (Aire Limitée Adaptation Dynamique Développement International) consortium (ALADIN, 1997) has over the past two decades developed a Limited-Area Model (LAM) to serve the specific needs of its participating partners. Currently this consortium consists of 16 partners, covering Europe and the Mediterranean region and including some North African countries. The code of the ALADIN model (Bubnová et al., 1995) is mostly shared with the code of the French global ARPEGE (Action de Recherche Petite Echelle Grande Echelle) model and the IFS (Integrated orecast System) of ECMWF (European Centre for Medium-Range Weather Forecasts). The lateral boundary conditions (LBCs) of the operational ALADIN model configurations are imposed by the Davies scheme (Davies, 1976; Termonia et al., 2012) at regular time intervals of 3 h (Termonia et al., 2009) with LBC data provided by the Coupled Model Intercomparison Project Phase 5 (CMIP5) climate runs of the CNRM ARPEGE model.

At the RMI, ALADIN has been further developed with a physics parameterization package called ALARO, which has been designed specifically to be run at convection-permitting resolutions. The key concept behind this package lies in the precipitation and cloud scheme called modular multiscale microphysics and transport (3MT), developed by Gerard and Geleyn (2005), Gerard (2007) and Gerard et al. (2009). The ALARO model version ALARO-0, which is used for CORDEX.be, utilizes a semi-Lagrangian horizontal diffusion scheme called SLHD (Váña et al., 2008), some pseudo-prognostic Turbulent Kinetic Energy (TKE) scheme (pTKE, i.e. a Louis-type scheme for stability dependencies, but with memory, advection and auto-diffusion of the overall intensity of turbulence) and a statistical sedimentation scheme for precipitation within a prognostic-type scheme for microphysics (Geleyn et al., 2008). The ALARO physics package is coupled to the dynamics of the ALADIN model via a physics–dynamics interface based on a flux-conservative formulation of the equations proposed by Catry et al. (2007). The configuration of the model with these physics runs operationally in a number of countries of the ALADIN and HIRLAM consortia for the national NWP applications.

The multiscale behaviour of 3MT has been validated in a NWP context up to a spatial resolution of 4 km (see Gerard et al., 2009). In a climate context, the ALARO-0 model has also been validated, and more specifically for maximum temperature (Hamdi et al., 2012) and extreme precipitation (De Troch et al., 2013; De Troch, 2016). It was found that the multiscale performance of the model in the simulation of daily precipitation, does not hold for the simulation of subdaily precipitation. Furthermore, it was demonstrated that the highest-resolution simulations of ALARO-0 at 4 km benefit from added value in the description of several characteristics of subdaily precipitation, such as the diurnal cycle, heavy precipitation amounts, and important scaling properties (De Troch, 2016). Finally, in a recent validation study of Giot et al. (2016), ALARO-0 has been tested within the EURO-CORDEX framework. The performance of the model is quantified through several metrics which are compared to metrics from an ensemble of 17 other EURO-CORDEX experiments. The results demonstrated that the model is capable of correctly representing the precipitation and temperature climate variables for the European region in an acceptable way as most of the ALARO-0 scores lie within the existing ensemble (Giot et al., 2016).