SEASONAL AND SOLAR-CYCLE VARIATIONS IN HIGH-LATITUDE THERMOSPHERIC WINDS

Thermospheric wind measurements have been collected systematically every winter for over nine years from a high-latitude site at Kiruna, Sweden (67.8-degrees-N, 20.4-degrees-E). The database contains 1242 nights of data collected with a Fabry-Perot Interferometer (FPI), perhaps the largest single- site database of thermospheric winds. This analysis shows a marked seasonal and solar cycle variation. Particularly at high solar activity, sunward winds of the evening period (16 - 20 UT) are more than 50% stronger at Spring than at Autumn equinox. This large asymmetry in the behaviour of high-latitude thermospheric winds at spring and autumn equinox has not yet been predicted by model simulations.