HCLIM is a seamless model framework developed jointly between several European national meteorological services. The model system provides flexibility as it contains a suite of different atmospheric model configurations, each adapted for different horizontal resolutions.

The framework, which facilitates observation handling, climate generation, lateral boundary coupling, and postprocessing is referred to as HCLIM, the climate version of the HIRLAM–ALADIN Research on Mesoscale Operational NWP in Euromed (HARMONIE) system.

Model description

HCLIM is developed by a consortium of national meteorological institutes in close collaboration with the HIRLAM-ALADIN NWP and ACCORD model development. HCLIM includes three different atmospheric physics packages AROME, ALARO and ALADIN, which are designed for use at different horizontal resolutions. The latest version is HCLIM43, succeeding the prior versions, HCLIM38 (Belušić et al., 2020) and HCLIM36 (Lindstedt et al., 2015; Lind et al., 2016). Proven effective in various simulations across different domains (e.g., Belušić et al., 2020; Lind et al., 2020, 2023; Wu et al., 2020; Wang et al., 2023) and international collaborative projects (e.g., Coppola et al., 2020; Ban et al., 2021; Pichelli et al., 2021; Berthou et al., 2022; Médus et al., 2022; Lipzig et al., 2023), HCLIM stands out as a robust regional climate modelling system.

HCLIM-AROME is specifically developed for use at convection permitting resolutions, resolving deep convection explicitly and is generally applied to horizontal resolutions finer than 4 km. In HCLIM-AROME, the nonhydrostatic dynamical core (Bubnova et al. 1995; Bénard et al. 2010), developed by ALADIN is used. It solves the fully compressible Euler equations using a two time level, semi-implicit, semi-Lagrangian discretization on an Arakawa A grid. In the vertical, a mass-based hybrid pressure terrain-following coordinate is used (Simmons and Burridge, 1981; Laprise, 1992).

HCLIM-AROME parameterized radiation using a two-stream approximation in model columns and the effects of surface slopes are accounted for. The shortwave radiation computations follow Fouquart and Bonnel (1980), while the longwave radiation is from a rapid radiative transfer model (RRTM) with 16 spectral bands (Mlawer et al., 1997; Iacono et al., 2008). The cloud optical properties for liquid clouds are derived from Morcrette and Fouquart (1986) and from Ebert and Curry (1992) for ice clouds. HARMONIE-AROME uses a mixed-phase microphysics scheme, the ICE3 scheme (Pinty and Jabouille 1998, Lascaux et al., 2006) with additional modifications for cold conditions called OCND2 (Müller et al., 2017), wherein cloud water and ice as well as rain, snow, and graupel are prognostic variables. Hail is assumed to behave as large graupel particles. The turbulence parameterization is the scheme called HARMONIE with RACMO Turbulence (HARATU; Lenderink and Holtslag, 2004; Bengtsson et al., 2017).

HCLIM-ALARO is typically used for grid sizes of 4 km and larger, employing the hydrostatic version of the dynamical core (Temperton et al., 2001). ALARO-0 was employed in HCLIM38. The newer version ALARO-1 (Termonia et al., 2018) has not been implemented in HCLIM to date. In HCLIM38-ALARO, the ACRANEB2 radiation scheme by Ritter and Geleyn (1992) and Mašek et al. (2016) is used. Deep convection is parameterized using the 3MT scheme (Gerard et al., 2009), which separates resolved large-scale and convective clouds to avoid double counting convective processes at higher resolutions. The turbulence parameterization is a pseudoprognostic turbulent kinetic energy (pTKE) scheme (Geleyn et al., 2006), an extension of the Louis-type vertical diffusion scheme (Louis 1979).

HCLIM-ALADIN, used as a hydrostatic model, is employed for simulations with grid spacing close to or larger than 10 km. It is the limited-area version of the global model ARPEGE, from which it inherits all dynamics and physics options, as detailed in Termonia et al. (2018). Similarly to AROME, the radiation scheme is a simplified radiation scheme adapted from ECMWF, described in Mascart and Bougeault (2011). Deep convection is parameterized following Bougeault (1985), and turbulence is accounted for using the CBR scheme (Cuxart et al., 2000) with the mixing length from Bougeault and Lacarrere (1989). Microphysics are parameterized based on Lopez (2002) and Bouteloup et al. (2005).

The surface parameterization framework in HCLIM is SURFEX [Surface externalise (Masson et al., 2013)]. The subgrid surface heterogeneity is represented by four tiles which encompass continental natural surfaces, sea, inland water and urban areas. Urban surfaces are simulated by the TEB (Town Energy Balance; Masson, 2000) scheme that is based on the Urban Canyon approach (Nunez and Oke, 1977). Natural surfaces are parameterized using the Interactions Soil-Biosphere-Atmosphere model  (ISBA, Noilhan and Planton, 1989). The inland water is simulated by the lake model FLake (Mironov et al., 2010). SURFEX is an external surface modelling system available off-line as well as coupled to atmospheric models. When coupled to an atmospheric model, SURFEX receives variables such as downward short-wave and long-wave radiation, surface air pressure, air temperature, humidity, wind and precipitation for every time step and then uses them to compute momentum and surface energy fluxes. In HCLIM43, SURFEX v8.1 is used together with land use data ECOCLIMAP Second Generation 300m (Druel et al., 2022), the sand / clay data SoilGrids250m version 2.0, and the orography data GMTED2010. A more thorough description of SURFEX v8.1 is given by Le Moigne (2018).