Solar-cycle modifications of the effects of thermospheric winds on the height of the F2-layer over Antarctica

Results of analysis of the diurnal variations of hmF2 for Argentine Islands (65°15'S, 64°16'W) and Halley Bay (75°30'S, 26°40'W) are presented. It is shown that, for summer months, the diurnal variations can be approximated by simple sinusoidal functions, the phases of which vary smoothly with solar activity. This behaviour can be explained in terms of the effects of thermospheric winds; it results partly from a change in the relative importance of ‘ion drag’ and Coriolis force, and partly from changes in the chemistry which controls the characteristic time required for the layer to respond to the wind. A comparison of observations and theory suggests that the local solar time at which the thermospheric pressure maximum occurs does not vary with solar activity.

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