Abstract. The Meso-NH Atmospheric Simulation System is a joint e ort of the Centre National de Recherches Me te orologiques and Laboratoire d'Ae rologie. It comprises several elements; a numerical model able to simulate the atmospheric motions, ranging from the large meso-alpha scale down to the micro-scale, with a comprehensive physical package, a¯exible ®le manager, an ensemble of facilities to prepare initial states, either idealized or interpolated from meteorological analyses or forecasts, a¯exible post-processing and graphical facility to visualize the results, and an ensemble of interactive procedures to control these functions. Some of the distinctive features of this ensemble are the following: the model is currently based on the Lipps and Hemler form of the anelastic system, but may evolve towards a more accurate form of the equations system. In the future, it will allow for simultaneous simulation of several scales of motion, by the so-called``interactive grid-nesting technique''. It allows for the in-line computation and accumulation of various terms of the budget of several quantities. It allows for the transport and di usion of passive scalars, to be coupled with a chemical module. It uses the relatively new Fortran 90 compiler. It is tailored to be easily implemented on any UNIX machine. Meso-NH is designed as a research tool for small and meso-scale atmospheric processes. It is freely accessible to the research community, and we have tried to make it as``user-friendly'' as possible, and as general as possible, although these two goals sometimes appear contradictory. The present paper presents a general description of the adiabatic formulation and some of the basic validation simulations. A list of the currently available physical parametrizations and initialization methods is also given. A more precise description of these aspects will be provided in a further paper.

SUMMARYA bulk mass-flux convection parametrization for deep and shallow convection is presented that includes an efficient and straightforward treatment of numerics, moist thermodynamics and convective downdraughts. The scheme is evaluated in a single-column model context for a tropical deep-convective period and a trade-wind cumulus case. Preliminary applications in a global numerical weather-prediction model and a mesoscale model are also discussed.The results suggest that the present scheme provides reasonable solutions in terms of predicted rainfall, and tropical temperature and moisture structures. The application of the scheme to various scales is supported by the use of a convective available potential energy convective closure that assures a smooth interaction with the largescale environment and efficiently suppresses conditional instability of the second kind-like spin-up processes on the grid-scale.Finally, the theoretical and practical limits of the present approach are discussed together with possible future developments.

Abstract. This paper presents the Meso-NH model version 5.4. Meso-NH is an atmospheric non hydrostatic research model that is applied to a broad range of resolutions, from synoptic to turbulent scales, and is designed for studies of physics and chemistry. It is a limited-area model employing advanced numerical techniques, including monotonic advection schemes for scalar transport and fourth-order centered or odd-order WENO advection schemes for momentum. The model includes state-of-the-art physics parameterization schemes that are important to represent convective-scale phenomena and turbulent eddies, as well as flows at larger scales. In addition, Meso-NH has been expanded to provide capabilities for a range of Earth system prediction applications such as chemistry and aerosols, electricity and lightning, hydrology, wildland fires, volcanic eruptions, and cyclones with ocean coupling. Here, we present the main innovations to the dynamics and physics of the code since the pioneer paper of Lafore et al. (1998) and provide an overview of recent applications and couplings.

The Meso-NH Atmospheric Simulation System is a joint eort of the Centre National de Recherches Me te orologiques and Laboratoire d'Ae rologie. It comprises several elements; a numerical model able to simulate the atmospheric motions, ranging from the large meso-alpha scale down to the micro-scale, with a comprehensive physical package, a¯exible ®le manager, an ensemble of facilities to prepare initial states, either idealized or interpolated from meteorological analyses or forecasts, a¯exible post-processing and graphical facility to visualize the results, and an ensemble of interactive procedures to control these functions. Some of the distinctive features of this ensemble are the following: the model is currently based on the Lipps and Hemler form of the anelastic system, but may evolve towards a more accurate form of the equations system. In the future, it will allow for simultaneous simulation of several scales of motion, by the so-called``interactive grid-nesting technique''. It allows for the in-line computation and accumulation of various terms of the budget of several quantities. It allows for the transport and diusion of passive scalars, to be coupled with a chemical module. It uses the relatively new Fortran 90 compiler. It is tailored to be easily implemented on any UNIX machine. Meso-NH is designed as a research tool for small and meso-scale atmospheric processes. It is freely accessible to the research community, and we have tried to make it as``user-friendly'' as possible, and as general as possible, although these two goals sometimes appear contradictory. The present paper presents a general description of the adiabatic formulation and some of the basic validation simulations. A list of the currently available physical parametrizations and initialization methods is also given. A more precise description of these aspects will be provided in a further paper.