From Pekka.Janhunen@fmi.fiTue Aug 20 11:50:37 1996 Date: Fri, 12 Apr 1996 16:21:15 +0300 (EET DST) From: Pekka.Janhunen@fmi.fi To: confburo@vmprofs.estec.esa.nl Subject: Space env. symposium (18-20 Sept) abstract GUMICS-3 - a global ionosphere-magnetosphere coupling simulation with high ionospheric resolution Pekka Janhunen (*) Finnish Meteorological Institute, Department of Geophysics P.O.B. 503, FIN-00101, Helsinki, Finland. Preference: ORAL The prediction of satellite charging and other harmful effects can not be succesful 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 timestep. In the near-Earth region the Alfven speed is very high, which makes it necessary to use a very small timestep, sometimes less than 10 ms. In conventional simulation methods the same timestep must be used throughout the grid, but in our version of MHD the timestep 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. (*) Also at: Swedish Institute of Space Physics, Uppsala Division, 755 91, Uppsala, Sweden ______________________________________________________________ Pekka Janhunen tel (+358) 0 1929 535 Finnish Meteorological Institute fax (+358) 0 1929 539 Department of Geophysics tlx 124436 EFKL FI P.O.Box 503, FIN-00101 Helsinki, Finland Pekka.Janhunen@fmi.fi http://www.geo.fmi.fi See also http://www.geo.fmi.fi/prog/tela.html ______________________________________________________________