Enhancement of the lunar tide in the noon critical frequency of the F2 layer over the magnetic equator

The luna r semi-diurn al variations in t he midday values of the crit ical frequency (foFz) a nd t he height of t he m aximum electron densi.ty (h p F2) are d erived for t he t wo chains of equator ial sta t ions in So ut h America a nd India for t he pen od 195758. T he latlt udm al variation of the ampli t ude of t he lun ar semi-diurn al va riation in Jo li'z shows a sharp maximum over t he mag netic equ ator in both of t he longit ud e zo nes. There is a n indication of sy.s tema tic va ria t ion in t he a mpli t ude wit h longit ude a long t he m agnetIC eClu ator, ~he maximum occuring in t he Sout h America n zone .(about 0.63. Mc/s) and t he m~ nllnum 111 t he I ndian zo ne (about 0.33 Mc/s). Similar 10nglt udll1al van a tlOns ha ve bee n ll1 d,cate~ 111 t he lL~~ ar semi-diurnal vari ations of t he hori zo ntal compo nent of t he Ear t h 's m agnetIC fi eld . 1he latit udin al vari ation of t he a mpli t ude of t he lunar s.en~i-di~rnal vari ation .of ~pF? is opposite t o t hat of f oF2• The enh a ncement of t he lun ar van atlOn III t he Fz layer IO Dlza t lOll over the m ag ne tic equator appears to be associated wi th t he eq uatorial electrojet.