The interannual variation of the ionospheric solar quiet (Sq) current system is examined. A dense magnetometer network over Japan enables the accurate determination of the central position of the northern Sq current loop or the Sq current focus, during 1999–2015. It is found that the Sq focus latitude undergoes an interannual variation of ±2° with a period of approximately 28 months, similar to the quasi-biennial oscillation (QBO) in the tropical lower stratosphere. The QBO-like variation of Sq is particularly evident during 2005–2013. No corresponding interannual variability is found in solar extreme ultraviolet radiation. Comparisons with tidal winds, derived from a whole-atmosphere model, reveal that the QBO-like variation of the Sq current focus is highly correlated with the amplitude variations of migrating and nonmigrating diurnal tides in the lower thermosphere. The results suggest that the stratospheric QBO can influence the ionospheric wind dynamo through the QBO modulation of tides.
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