The framework, which facilitates observation handling, climate generation, lateral boundary coupling, and postprocessing required is referred to as the HIRLAM–ALADIN Research on Mesoscale Operatinal NWP in Euromed (HARMONIE) system.
In HARMONIE, the nonhydrostatic dynamical core (Bubnova et al. 1995; Benard 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).
HARMONIE-AROME is specifically developed to be run at convection permitting resolutions resolving deep convection explicitly and is generally applied to a resolution of around 2 km.
HARMONIE-AROME parameterizes radiation using a two-stream approximation in model columns and the effects of surface slopes are accounted for. Shortwave and longwave spectral computations follow Fouquart and Bonnel (1980) and Mlawer et al. (1997), respectively, and 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), 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 was developed by Cuxart et al. (2000) and is based on a prognostic TKE equation combined with a diagnostic mixing length L.
HARMONIE-ALARO-0 is often used from grid sizes of 4 km and larger and hence use the hydrostatic version of the dynamical core. Differences between HARMONIE-ALARO-0 and HARMONIE-AROME appear primarily in the atmospheric physics. In HARMONIE-ALARO-0, radiation is parameterized using the two-stream scheme developed by Ritter and Geleyn (1992) with optical cloud properties following Masek (2005). Deep convection in HARMONIE-ALARO-0 is not explicitly resolved and uses the 3MT parameterization scheme. In standard parameterizations, separate schemes are used for deep convection and for ‘‘nonconvective’’ (i.e., resolved large scale) clouds, with microphysical conversion to precipitation treated separately in each scheme. However, at ever-higher resolution, the risk of double counting convective processes (both through resolved and parameterized parts) increases, and 3MT handles this by formally separating the two different contributions. The microphysical processes handle five prognostic water phases, where autoconversion and evaporation are computed level by level (Gerard et al. 2009). The turbulence parameterization is a pseudoprognostic turbulent kinetic energy (pTKE) scheme, which is an extension of the Louis-type vertical diffusion scheme (Louis 1979).
The surface parametrisation framework in HARMONIE is SURFEX [Surface externalise (Masson et al., 2013)]. It originates from the ISBA (Interactions Soil-Biosphere-Atmosphere) surface scheme (Noilhan and Planton, 1989) and 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 air temperature, humidity, wind and precipitation for every time step and then uses them to compute momentum and surface energy fluxes. Land surface properties in SURFEX are taken from the ECOCLIMAP database (Champeaux et al., 2005). A more thorough description of SURFEX is found in (Le Moigne, 2012).
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