Solar activity dependency of multiday oscillations in the nighttime thermospheric winds observed by Fabry‐Perot interferometer

An 11 year (1989–1995 and 2010–2013) nighttime thermospheric wind (at ~250 km) data set from Fabry‐Perot interferometer at Millstone Hill (42.6°N, 71.5°W) is used to investigate multiday oscillations (6–30 days) in the thermospheric nighttime winds. Dependencies of multiday oscillations on solar radiation ( F 10.7 ), solar wind speed (SW), and geomagnetic activity ( Kp ) are determined. We found that (1) there exist prominent quasi 27 day oscillations in the thermospheric zonal (meridional) wind, which appears to be more correlated to the same periodic oscillations in Kp and SW than in F 10.7 during the solar maximum (solar declining phase and minimum); (2) quasi 13.5 day oscillations in the zonal wind occur during the solar maximum and increasing phases and are also more correlated to the same periodic oscillations in Kp and SW; and (3) in general, the correlations of the multiday oscillations in the thermospheric winds are more correlated with Kp and SW than F 10.7 . Our analyses also show that the zonal wind is more sensitive to SW than the meridional wind. We further find that (4) for high F 10.7 , the premidnight zonal wind is more westward toward increasing SW; for low F 10.7 , the postmidnight zonal wind is also more westward toward increasing SW; and (5) meridional winds tend to be more southward with increasing SW for medium and high F 10.7 .