Seasonal and solar cycle variations in high‐ latitude thermospheric winds

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Abstract
Thermospheric wind measurements have been collected systematically every winter for over nine years from a high‐latitude site at Kiruna, Sweden (67.8°N, 20.4°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.