Vertical circulation and thermospheric composition: a modelling study

H. Rishbeth, I. C. F. Müller-Wodarg
1999 Annales Geophysicae  
The coupled thermosphere-ionosphere-plasmasphere model CTIP is used to study the global threedimensional circulation and its eect on neutral composition in the midlatitude F-layer. At equinox, the vertical air motion is basically up by day, down by night, and the atomic oxygen/molecular nitrogen OaN 2 concentration ratio is symmetrical about the equator. At solstice there is a summer-to-winter¯ow of air, with downwelling at subauroral latitudes in winter that produces regions of large OaN 2
more » ... of large OaN 2 ratio. Because the thermospheric circulation is in¯uenced by the highlatitude energy inputs, which are related to the geometry of the Earth's magnetic ®eld, the latitude of the downwelling regions varies with longitude. The downwelling regions give rise to large F2-layer electron densities when they are sunlit, but not when they are in darkness, with implications for the distribution of seasonal and semiannual variations of the F2-layer. It is also found that the vertical distributions of O and N 2 may depart appreciably from diusive equilibrium at heights up to about 160 km, especially in the summer hemisphere where there is strong upwelling.
doi:10.1007/s00585-999-0794-x fatcat:wvcskqkcwvdnvjyhehvsadvvke