Simulations of the behaviour of the polar thermosphere and ionosphere for northward IMF

Details Simulations of the behaviour of the polar thermosphere and ionosphere for northward IMF Simulations of the behaviour of the polar thermosphere and ionosphere for northward IMF

Feb 1994

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994jatp...56..297r&link_type=abstract

Journal of Atmospheric and Terrestrial Physics (ISSN 0021-9169), vol. 56, no. 2, p. 297-318

Physics

3

Electric Fields, Interplanetary Magnetic Fields, Ionospheres, Magnetic Field Configurations, Magnetohydrodynamic Flow, Polar Regions, Solar Wind, Thermosphere, Atmospheric Circulation, Atmospheric Models, Atmospheric Pressure, Computerized Simulation, Convective Flow, Flow Distribution, Solar Terrestrial Interactions

Scientific paper

The dynamics and structure of the polar thermosphere and ionosphere within the polar regions are strongly influenced by the magnetospheric electric field. The convection of ionospheric plasma imposed by this electric field generates a large-scale thermospheric circulation which tends to follow the pattern of the ionospheric circulation itself. The magnetospheric electric field pattern is strongly influenced by the magnitude and direction of the interpanetary magnetic field (IMF), and by the dynamic pressure of the solar wind. Previous numerical simulations of the thermospheric response to magnetospheric activity have used available models of auroral precipitation and magnetospheric electric fields appropriate for a southward-directed IMF. In this study, the University College London (UCL)/Sheffield coupled thermosphere/ionosphere model has been used, including convection electric field models for a northward IMF configuration. During periods of persistent strong northward IMF B(sub z) regions of sunward thermospheric winds (up to 200 m/s) may occur deep within the polar cap, reversing the generally anti-sunward polar cap winds driven by low-latitude solar EUV heating and enhanced by geomagnetic forcing under all conditions of southward IMF B(sub z). The development of sunward polar cap winds requires persistent northward IMF and enhanced solar wind dynamic pressure for at least 2-4 h, and the magnitude of the northward IMF component should exceed approximately 5 nT. Sunward winds will occur preferentially on the dawn (dusk) side of the polar cap for IMF B(sub y) negative (positive) in the northern hemisphere (reverse in the southern hemisphere). The magnitude of sunward polar cap winds will be significantly modulated by UT and season, reflecting E- and F-region plasma densities. For example, in northern mid-winter, sunward polar cap winds will tend to be a factor of two stronger around 1800 UT, when the geomagnetic polar cusp is sunlit, then at 0600 UT, when the entire polar cap is in darkness.

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