DCMIP2016: a review of non-hydrostatic dynamical core design and intercomparison of participating models

Atmospheric dynamical cores are a fundamental component of global atmospheric modeling systems and are responsible for capturing the dynamical behavior of the Earth's atmosphere via numerical integration of the Navier-Stokes equations. These systems have existed in one form or another for over half of a century, with the earliest discretizations having now evolved into a complex ecosystem of algorithms and computational strategies. In essence, no two dynamical cores are alike, and their individual successes suggest that no perfect model exists. To better understand modern dynamical cores, this paper aims to provide a comprehensive review of 11 non-hydrostatic dynamical cores, drawn from modeling centers and groups that participated in the 2016 Dynamical Core Model Intercomparison Project (DCMIP) workshop and summer school. This review includes a choice of model grid, variable placement, vertical coordinate, prognostic equations, temporal discretization, and the diffusion, stabilization, filters, and fixers employed by each syste

The ICON-1.2 hydrostatic atmospheric dynamical core on triangular grids – Part 1: Formulation and performance of the baseline version

Abstract. As part of a broader effort to develop next-generation models for numerical weather prediction and climate applications, a hydrostatic atmospheric dynamical core is developed as an intermediate step to evaluate a finite-difference discretization of the primitive equations on spherical icosahedral grids. Based on the need for mass-conserving discretizations for multi-resolution modelling as well as scalability and efficiency on massively parallel computing architectures, the dynamical core is built on triangular C-grids using relatively small discretization stencils. This paper presents the formulation and performance of the baseline version of the new dynamical core, focusing on properties of the numerical solutions in the setting of globally uniform resolution. Theoretical analysis reveals that the discrete divergence operator defined on a single triangular cell using the Gauss theorem is only first-order accurate, and introduces grid-scale noise to the discrete model. The noise can be suppressed by fourth-order hyper-diffusion of the horizontal wind field using a time-step and grid-size-dependent diffusion coefficient, at the expense of stronger damping than in the reference spectral model. A series of idealized tests of different complexity are performed. In the deterministic baroclinic wave test, solutions from the new dynamical core show the expected sensitivity to horizontal resolution, and converge to the reference solution at R2B6 (35 km grid spacing). In a dry climate test, the dynamical core correctly reproduces key features of the meridional heat and momentum transport by baroclinic eddies. In the aqua-planet simulations at 140 km resolution, the new model is able to reproduce the same equatorial wave propagation characteristics as in the reference spectral model, including the sensitivity of such characteristics to the meridional sea surface temperature profile. These results suggest that the triangular-C discretization provides a reasonable basis for further development. The main issues that need to be addressed are the grid-scale noise from the divergence operator which requires strong damping, and a phase error of the baroclinic wave at medium and low resolutions

Un modèle de transport et de chimie atmosphérique à grande échelle adapté aux calculateurs massivement parallèles

We present in this thesis the development of a large-scale bidimensional atmospheric transport scheme designed for parallel architectures with scalability in mind. The current version, named Pangolin, contains a bi-dimensional advection and a simple linear chemistry scheme for stratospheric ozone and will serve as a basis for a future CTM. For mass-preservation, a van Leer finite-volume scheme was chosen for advection and extended to 2D with operator splitting. To ensure mass preservation, winds are corrected in a preprocessing step. We aim at addressing the "pole issue" of the traditional regular latitude-longitude by presenting a new quasi-area-preserving grid mapping the sphere uniformly. The parallelization of the model is based on the advection operator and a custom domain-decomposition algorithm is presented here to attain load-balancing in a message-passing context. To run efficiently on current and future parallel architectures, algebraic features of the grid are exploited in the advection scheme and parallelization algorithm to favor the cheaper costs of flops versus data movement. The model is validated on algebraic test cases and compared to other state-of-the-art schemes using a recent benchmark. Pangolin is also compared to the CTM of Météo-France, MOCAGE, using a linear ozone scheme and isentropic coordinates.Cette thèse présente un modèle bi-dimensionnel pour le transport atmosphérique à grande échelle, nommé Pangolin, conçu pour passer à l'échelle sur les achitectures parallèles. La version actuelle comporte une advection 2D ainsi qu'un schéma linéaire de chimie et servira de base pour un modèle de chimie-transport (MCT). Pour obtenir la conservation de la masse, un schéma en volume-finis de type van Leer a été retenu pour l'advection et étendu au cas 2D en utilisant des opérateurs alternés. La conservation de la masse est assurée en corrigeant les vents en amont. Nous proposons une solution au problème "des pôles" de la grille régulière latitude-longitude grâce à une nouvelle grille préservant approximativement les aires des cellules et couvrant la sphère uniformément. La parallélisation du modèle se base sur l'advection et utilise un algorithme de décomposition de domaines spécialement adapté à la grille. Cela permet d'obtenir l'équilibrage de la charge de calcul avec MPI, une librairie d'échanges de messages. Pour que les performances soient à la hauteur sur les architectures parallèles actuelles et futures, les propriétés analytiques de la grille sont exploitées pour le schéma d'advection et la parallélisation en privilégiant le moindre coût des flops par rapport aux mouvement de données. Le modèle est validé sur des cas tests analytiques et comparé à des schémas de transport à l'aide d'un comparatif récemment publié. Pangolin est aussi comparé au MCT de Météo-France via un schéma linéaire d'ozone et l'utilisation de coordonnées isentropes

A two-fluid single-column model of the dry, shear-free, convective boundary layer

This is the final version. Available on open access from Wiley via the DOI in this record.A single-column model of the dry, shear-free, convective boundary layer is presented in which nonlocal transports by coherent structures such as thermals are represented by the partitioning of the fluid into two components, updraft and environment, each with a full set of prognostic dynamical equations. Local eddy diffusive transport and entrainment and detrainment are represented by parameterizations similar to those used in Eddy Diffusivity Mass Flux schemes. The inclusion of vertical diffusion of the vertical velocity is shown to be important for suppressing an instability inherent in the governing equations. A semi-implicit semi-Lagrangian numerical solution method is presented and shown to be stable for large acoustic and diffusive Courant numbers, though it becomes unstable for large advective Courant numbers. The solutions are able to capture key physical features of the dry convective boundary layer. Some of the numerical challenges posed by sharp features in the solution are discussed, and areas where the model could be improved are highlighted.Natural Environment Research Council (NERC

Multiple physical elements to determine the gravitational-wave signatures of core-collapse supernovae

We review recent progress in the theoretical predictions of gravitational waves (GWs) of core-collapse supernovae. Following a brief summary of the methods in the numerical modeling, we summarize multiple physical elements that determine the GW signatures which have been considered to be important in extracting the information of the long-veiled explosion mechanism from the observation of the GWs. We conclude with a summary of the most urgent tasks to make the dream come true.Comment: 48 pages, 16 figures, to appear in a special issue of Comptes Rendus Physique "Gravitational Waves (from detectors to astrophysics)

The first Met Office Unified Model-JULES Regional Atmosphere and Land configuration, RAL1

This is the final version. Available on open access from the European Geosciences Union via the DOI in this recordIn this paper we define the first Regional Atmosphere and Land (RAL) science configuration for kilometre-scale modelling using the Unified Model (UM) as the basis for the atmosphere and the Joint UK Land Environment Simulator (JULES) for the land. RAL1 defines the science configuration of the dynamics and physics schemes of the atmosphere and land. This configuration will provide a model baseline for any future weather or climate model developments to be described against, and it is the intention that from this point forward significant changes to the system will be documented in the literature. This reproduces the process used for global configurations of the UM, which was first documented as a science configuration in 2011. While it is our goal to have a single defined configuration of the model that performs effectively in all regions, this has not yet been possible. Currently we define two sub-releases, one for mid-latitudes (RAL1-M) and one for tropical regions (RAL1-T). The differences between RAL1-M and RAL1-T are documented, and where appropriate we define how the model configuration relates to the corresponding configuration of the global forecasting model