OpenGGCM

The Open Geospace General Circulation Model (Open GGCM) was originally developed as a magnetohydrodynamic (MHD) model of Earth's magnetosphere at UCLA in the early 1990's by J. Raeder. Besides solving the resistive MHD equations in the magnetosphere the model included a rather crude ionospheric boundary condition consisting of a ionosphere potential solver that served to close the magnetospheric field-aligned currents in the ionosphere and thus coupled magnetospheric convection with ionospheric convection. Subsequently the ionosphere end of the model was improved by adding a magnetosphere-ionosphere coupling module that not only mapped the field-aligned currents into the ionosphere and the potential back into the magnetosphere, but also computed electron precipitation parameters and the ionospheric Hall and Pedersen conductances using empirical relations in a self-consistent manner. In the late 90's this model was coupled with CTIM (Coupled Thermosphere Ionosphere Model, developed by T. Fuller-Rowell, NOAA/SEC), a sophisticated three-dimensional dynamical models of the thermosphere and ionosphere. CTIM takes the potential and the electron precipitation parameters from the MHD model and provides in turn the conductances and the ionospheric dynamo current to the potential solver. CTIM thus replaces the empirical conductance calculations with first-principle calculations. However, it also adds substantial physics to the model, and its outputs are highly relevant space weather parameters, such as the ionospheric electron parameters (Nmf2, hmf2) and neutral densities and composition. The coupled model was known for some time as the UCLA/NOAA GGCM and is now Open GGCM.

The model does not include the energetic particle drift and ring current physics. Thus, results within about 5 RE from Earth are generally meaningless. Likewise, there is no plasmasphere. This should not affect the dynamics of the magnetosphere much, however, wave propagation through the inner magnetosphere is affected. Also, the model uses a `Boris correction' to keep time steps manageable. As a consequence wave propagation in the inner magnetosphere is artificially slowed. The developers do not provide any guarantee for the correctness of model results. There are many more caveats of various natures than listed here. Users of the model are therefore highly encouraged to contact the developers and discuss results with them prior to any publication. Users should also consult the Open GGCM web site.

Inputs to Open GGCM are solar wind plasma and magnetic field conditions propagated from a solar wind monitor satellite to the upstream simulation box boundary. The Earth magnetic field is approximated by a dipole with fixed orientation during the entire simulation run. The orientation angle can be specified independently from the time interval simulated.

The output of the model consists of snapshots of the full 3d grid of the primary variables (density, pressure, velocity, magnetic field, current density), snapshots on pre-defined 2d cuts perpendicular to any of the axes, snapshots of the ionospheric quantities (FAC, potential, electron precipitation fluxes and energies, ground magnetic perturbations), and if run with CTIM, also snapshots of the CTIM variables (neutral density, composition, winds, temperature, ion and electron densities and temperatures). Since the output can be virtually unlimited a judicious choice must be made before each run of which parameters are needed for analysis and at which cadence. It is easily possible to create 100GB or more with one run.