IONOSPHERIC STORM SIMULATIONS DRIVEN BY MAGNETOSPHERIC MHD AND BY EMPIRICAL-MODELS WITH DATA COMPARISONS

The results of two ionospheric simulations are compared with each othe r and with ionospheric observations of the southern hemisphere for the magnetic cloud passage event of January 14, 1988, For most of the eve nt one simulation agrees with observations, while the other does not. Electric fields and electron precipitation patterns generated by a mag netospheric MHD model are used as inputs to a physical model of the io nosphere in the successful simulation, while empirical electric fields and electron precipitation are used as the inputs for the second simu lation. In spite of ionospheric summer conditions a large and deep pol ar hole is developed. This is seen in the in situ plasma observations made by the DMSP-F8 satellite. The hole is surprisingly present during both northward and southward IMF conditions. It is deepest for the st orm phase of the southward IMF period. A well-defined tongue of ioniza tion is formed during this period. These features have been reproduced by the TDIM-MHD simulation and to a lesser extent by the TDIM-empiric al simulation. However, the model simulations have not been able to ge nerate a storm enhanced density where one was observed by DMSP-F8 duri ng the initial phase of the storm. The differences between the two F r egion ionospheric simulations are attributed to differences in the mag netospheric electric fields and precipitation patterns used as inputs. This study provides a unique first simulation of the ionosphere's res ponse to self-consistent electric field and auroral precipitation patt erns over a 24-hour period that leads into a major geomagnetic storm.