A completely new nonhydrostatic model system known as the Advanced Regional Prediction System (ARPS) has been developed in recent years at the Center for Analysis and Prediction of Storms (CAPS) at the University of Oklahoma. The ARPS is designed from the beginning to serve as an effective tool for basic and applied research and as a system suitable for explicit prediction of convective storms as well as weather systems at other scales. The ARPS includes its own data ingest, quality control and objective analysis packages, a data assimilation system which includes single-Doppler velocity and thermodynamic retrieval algorithms, the forward prediction component, and a self-contained post-processing, diagnostic and verification package. The forward prediction component of the ARPS is a three-dimensional, nonhydrostatic compressible model formulated in generalized terrain-following coordinates. Minimum approximations are made to the original governing equations. The split-explicit scheme is used to integrate the sound-wave containing equations, which allows the horizontal domain-decomposition strategy to be efficiently implemented for distributed-memory massively parallel computers. The model performs equally well on conventional shared-memory scalar and vector processors. The model employs advanced numerical techniques, including monotonic advection schemes for scalar transport and variance-conserving fourth-order advection for other variables. The model also includes state-of-the-art physics parameterization schemes that are important for explicit prediction of convective storms as well as the prediction of flows at larger scales. Unique to this system are the consistent code styling maintained for the entire model system and thorough internal documentation. Modern software engineering practices are employed to ensure that the system is modular, extensible and easy to use. The system has been undergoing real-time prediction tests at the synoptic through storm scales in the past several years over the continental United States as well as in part of Asia, some of which included retrieved Doppler radar data and hydrometeor types in the initial condition. As the first of a two-part paper series, we describe herein the dynamic and numerical framework of the model, together with the subgrid-scale turbulence and the PBL parameterization. The model dynamic and numerical framework is then verified using idealized and realistic mountain flow cases and an idealized density current. Other physics parameterization schemes will be described in Part II, which is followed by verification against observational data of the coupled soil-vegetation model, surface layer fluxes and the PBL parameterization. Applications of the model to the simulation of an observed supercell storm and to the prediction of a real case are also found in Part II. In the latter case, a long-lasting squall line developed and propagated across the eastern part of the United States following a historical number of tornado outbreak in the state of Arkansas.

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The Advanced Regional Prediction System (ARPS) – A multi-scale nonhydrostatic atmospheric simulation and prediction model. Part I: Model dynamics and verification

After six years of scientific, technical developments and meteorological validation, the Application of Research to Operations at Mesoscale (AROME-France) convective-scale model became operational at Meteo-France at the end of 2008. This paper presents the main characteristics of this new numerical weather prediction system: the nonhydrostatic dynamical model core, detailed moist physics, and the as- sociated three-dimensional variational data assimilation (3D-Var) scheme. Dynamics options settings and variables are explained. The physical parameterizations are depicted as well as their mutual interactions. The scale-specific features of the 3D-Var scheme are shown. The performance of the forecast model is evaluated using objective scores and case studies that highlight its benefits and weaknesses.

/pdf/the-arome-france-convective-scale-operational-model-43tn89mjkn.pdf

The AROME-France Convective-Scale Operational Model

The paper describes the turbulence scheme implemented in the Meso-NH community research model, and reports on some validation studies. Since the model is intended to perform both large-eddy and mesoscale simulations, we have developed a full three-dimensional scheme, based on the original method of Redelsperger and Sommeria. A prognostic equation for the turbulent kinetic energy is used, together with conservative variables for moist non-precipitating processes. A particularity of the scheme is the use of variable turbulent Prandtl and Schmidt numbers, consistently derived from the complete set of second-order turbulent-moment equations. The results of three idealized boundary-layer simulations allowing detailed comparisons with other large-eddy simulation (LES) models are discussed, and lead to the conclusion that the model is performing satisfactorily.



The vertical flux and gradient computation can be run in isolation from the rest of the scheme, providing an efficient single-column parametrization for the mesoscale configuration of the model, if an appropriate parametrization of the eddy length-scale is used. The mixing-length specification is then the only aspect of the scheme which differs from the LES to the mesoscale configuration, and the numerical constants used for the closure terms are the same in both configurations. The scheme is run in single-column mode for the same three cases as above, and a comparison of single-column and LES results again leads to satisfactory results. It is believed that this result is original, and is due to the proper formulation of the parametrized mixing length and of the turbulent Prandtl and Schmidt numbers. In fact, a comparison of the parametrized mixing length with the length-scale of the energy-containing eddies deduced by spectral analysis of the LES shows interesting similarity.

A turbulence scheme allowing for mesoscale and large‐eddy simulations

Ecoclimap, a new complete surface parameter global dataset at a 1-km resolution, is presented. It is intended to be used to initialize the soil–vegetation–atmosphere transfer schemes (SVATs) in meteorological and climate models (at all horizontal scales). The database supports the “tile” approach, which is utilized by an increasing number of SVATs. Two hundred and fifteen ecosystems representing areas of homogeneous vegetation are derived by combining existing land cover maps and climate maps, in addition to using Advanced Very High Resolution Radiometer (AVHRR) satellite data. Then, all surface parameters are derived for each of these ecosystems using lookup tables with the annual cycle of the leaf area index (LAI) being constrained by the AVHRR information. The resulting LAI is validated against a large amount of in situ ground observations, and it is also compared to LAI derived from the International Satellite Land Surface Climatology Project (ISLSCP-2) database and the Polarization and Direc...

https://journals.ametsoc.org/doi/pdf/10.1175/1520-0442-16.9.1261

A Global Database of Land Surface Parameters at 1-km Resolution in Meteorological and Climate Models

. SURFEX is a new externalized land and ocean surface platform that describes the surface fluxes and the evolution of four types of surfaces: nature, town, inland water and ocean. It is mostly based on pre-existing, well-validated scientific models that are continuously improved. The motivation for the building of SURFEX is to use strictly identical scientific models in a high range of applications in order to mutualise the research and development efforts. SURFEX can be run in offline mode (0-D or 2-D runs) or in coupled mode (from mesoscale models to numerical weather prediction and climate models). An assimilation mode is included for numerical weather prediction and monitoring. In addition to momentum, heat and water fluxes, SURFEX is able to simulate fluxes of carbon dioxide, chemical species, continental aerosols, sea salt and snow particles. The main principles of the organisation of the surface are described first. Then, a survey is made of the scientific module (including the coupling strategy). Finally, the main applications of the code are summarised. The validation work undertaken shows that replacing the pre-existing surface models by SURFEX in these applications is usually associated with improved skill, as the numerous scientific developments contained in this community code are used to good advantage.

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The SURFEXv7.2 land and ocean surface platform for coupled or offline simulation of earth surface variables and fluxes

The Meso-NH Atmospheric Simulation Sys- tem is a joint eAort of the Centre National de Recher- ches Meteorologiques and Laboratoire d'Aerologie. 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 flexible file manager, an ensemble of facilities to prepare initial states, either idealized or interpolated from meteorological analyses or forecasts, a flexible 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 com- putation and accumulation of various terms of the budget of several quantities. It allows for the transport and diAusion 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 ini- tialization methods is also given. A more precise description of these aspects will be provided in a further paper.

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C. Fischer

Papers

The Meso-NH Atmospheric Simulation System. Part I: adiabatic formulation and control simulations