GHOST

GHOST (the Geophysical High-Order Suite for Turbulence) is an accurate and highly scalable pseudospectral code that solves a variety of PDEs often encountered in studies of turbulent flows. It is mainly developed by Pablo Mininni and Duane Rosenberg, with contributions from many users. The code uses a hybrid parallelization method combining MPI and OpenMP (GHOST also has support for GPUs using CUDA). This allows the code to run efficiently in laptops and small clusters, as well as to scale up to over 100,000 CPU cores in production runs in supercomputers. The hybrid parallelization method used in GHOST was recognized by two awards: an NCAR/CISL award, and the best paper award (technology track) at the TeraGrid 2010 conference.

The most recent release found in the "master" branch supports elongated periodic domains with arbitrary linear sizes (including cubic domains), and arbitrary spatial resolutions in each spatial direction (in three dimensions). We also maintain a stable branch with GHOST ver. 1, that only supports cubic periodic domains with NxNxN grid points.

GHOST can solve PDEs in periodic domains in two and three dimensions, to tackle many problems including:

• Compressible and incompressible hydrodynamic equations.
• Compressible and incompressible magnetohydrodynamic (MHD) equations.
• Hall-MHD equations and other kinetic plasma effects.
• Rotating flows.
• Rotating and stratified flows using the Boussinesq approximation.
• Passive scalars.
• Superfluids and Bose-Einstein condensates using the Gross-Pitaevskii Equation (GPE).
• Ginzburg-Landau equations.
• Integration of many types of particles.
• Several subgrid scale (SGS) models.

GHOST can integrate trajectories of Lagrangian particles, test particles (charged particles in a conducting fluid or a plasma), and inertial particles. It also includes two types of SGS models: one group of models derived from regularizations of the primitive equations of motion (Lagrangian Averaged, Clark, and Leray models), and another group of models based on computation of eddy viscosity and eddy noise using the Eddy-Damped Quasi-Normal Markovian approximation.

GHOST is mostly written in Fortran 90/95, with some C bindings, code in Fortran 2003 for the particles, and code in CUDA for GPUs. To build the main code, without particles and without GPU support, only a C and a Fortran 95 compiler are required. More details on how to compile GHOST can be found in the directory 3D/src/README.txt. GHOST also includes examples of scripts in Python, Matlab, IDL, and Mathematica, to do post-analysis of the numerical simulations. Moreover, it can be used together with VAPOR (the Visualization and Analysis Platform for Ocean, Atmosphere, and Solar Researchers) to do still frame renderings and animations. VAPOR provides an interactive environment for 3D visualization of GHOST outputs, allowing powerful analysis of turbulent flows in systems with 3D graphics cards (https://www.vapor.ucar.edu/).