Sunspot Dependence of the Noon Bite-out Phenomenon of the F2Region at Equatorial Latitudes

The effect of sunspot activity on the noon bite-out phenomenon is investigated for a number of equatorial stations during the period 1958–64. It-is well known that for equatorial stations the forenoon peak of the noon bite-out phenomenon is prominent during sunspot maximum period and the afternoon peak is prominent during sunspot minimum period. The magnitudes of the two peaks are almost the same during certain sunspot period and this is referred to as the ‘Critical sunspot number’. It is observed that this critical sunspot number increases systematically with decreasing |L—I|, where L and I are the geographic latitude and magnetic dip respectively.