“…[2] A quasi-27-day periodicity in various atmospheric, ionospheric, and magnetospheric parameters has previously been reported in numerous studies, some dating to before the space age [e.g., Bartels, 1950;Langehesse, 1953;Chkhetiya, 1975;Akasofu et al, 1988;Hapgood, 1993;Pancheva et al, 1991;Bowman, 1996;Rich et al, 2003;Apostolov et al, 2004;Hocke, 2008, and references therein]. The $27-day solar rotation period is clearly connected with recurrent periodicity in ionospheric disturbances.…”