Response of the thermosphere and ionosphere to geomagnetic storms

摘要: Four numerical simulations have been performed, at equinox, using a coupled thermosphere-ionosphere model, to illustrate the response of upper atmosphere geomagnetic storms. The storms are characterized by an increase in magnetospheric energy input high latitude for 12-hour period; each storm commences different universal time (UT). initial is that Joule heating raises temperature thermosphere and ion drag drives high-velocity neutral winds. heat source global wind surge, from both polar regions, which propagates low latitudes into opposite hemisphere. surge has character large-scale gravity wave with phase speed about 600 m s−1. Behind circulation magnitude 100 s −1 established middle latitudes, indicating onset manifestations same phenomena. A dominant feature penetration hemisphere where it poleward winds few hours. preference night sector longitude magnetic pole therefore depends on UT start storm. second meridional develops after interaction but also restricted, this case buildup zonal via Coriolis interaction. Conservation angular momentum may limit extreme cases. divergent field upwelling composition change height pressure surfaces. bulge responds background storm-induced horizontal winds; does not simply rotate Earth. During disturbance modulates location bulge; during recovery induce diurnal variation its position. Equatorward sunlight produce positive ionospheric changes main driving Negative phases caused increases molecular nitrogen regions sunlight, strength local input. Regions ionosphere persist period due decreases mean mass previous downwelling. Ion density changes, expressed as ratio disturbed quiet values, exhibit driven explains ac component observed negative phase.