The morphology of lunar semi-diurnal variation in [formula omitted] near solar noon

Abstract

The variations of the midday critical frequency of the F2-layer, ƒ 0F2 , with the phase of the moon are computed for eighteen stations within about ±40° latitude during a period of low sunspot activity. The results show that the phase of the lunar variation of ƒ 0F2 is determined by the magnetic and not by the geomagnetic or the geographic latitude. The reversal from the equatorial type of variation with a maximum near 04 lunar hour to the higher latitude type with a maximum near 10 lunar hour occurs at about ±11° magnetic latitude. The variation of amplitude with latitude shows a sharp maximum on the magnetic equator, associated with the equatorial electro-jet, and two broad maxima at about ±20° magnetic latitude. The latter are closely associated with the well-known maxima in the variation of noon ƒ 0F2 with latitude.