Statistics – Applications
Scientific paper
Dec 1996
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996esasp.392..233j&link_type=abstract
Environment Modelling for Space-based Applications, Symposium Proceedings (ESA SP-392). ESTEC Noordwijk, 18-20 September 1996. E
Statistics
Applications
6
Scientific paper
The prediction of satellite charging and other harmful effects can not be successful unless we can model and predict substorms and other kinds of auroral breakups. For this we need a high-resolution global simulation system whose only essential input consists of measured solar-wind data. GUMICS-2 ("Grand Unified Ionosphere-Magnetosphere Coupling Simulation, version 2") is a simulation system, which integrates a three-dimensional global magnetohydrodynamic (MHD) simulation box with a high-resolution model of ionospheric electrodynamics. We use a hierarchical rectangular grid, which is recursively refined according to a specified density function. The density function is such that the grid resolution is high in the near-Earth region, at the magnetopause and in the tail current sheet, while the solar wind, far tail and lobe regions have a lower resolution. The finite volume method is used in the MHD equations. The ionospheric conductivities depend on the electron precipitation, along with a dayside enhancement due to solar radiation. A model for field-aligned potential drop (current-voltage relationship) can also be defined. The most important difference between GUMICS-2 and other similar programs is the use of a locally varying time step. In the near-Earth region the Alfven speed is very high, which makes it necessary to use a very small time step, sometimes less than 10 ms. In conventional simulation methods the same time step must be used throughout the grid, but in our version of MHD the time step is locally adaptive. This results in significant reduction (at least one order of magnitude) of computing time, making it possible to use a previously unavailable resolution in the near-Earth region and in the ionosphere without increasing the computer requirements. The grid spacing in the auroral ionospheric is less than 100 km in the supercomputer versions of the model. We will present the GUMICS-2 model and show some examples of simulated events where solar wind data has been available. Comparisons with observations will be included. The problems of how to translate the MHD and ionospheric variables produced by GUMICS-2 into useful information about high-energy particle fluxes at geostationary orbit and elsewhere will also be briefly discussed.
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