Nighttime ionospheric radio scintillations and vertical drifts at the magnetic equator

Abstract

The scintillation of VHF radio waves traversing the equatorial ionosphere is largely a nighttime phenomenon starting shortly after sunset and reaching maximum occurrence around 2100-2200 LT. Comparing the F-region vertical drift velocities (produced by the east-west electric field) at Jicamarca and the amplitude scintillation of VHF radio waves at Huancayo, it has been shown that besides the usual pre-midnight events, any abnormal reversal of the equatorial horizontal electric field to the eastward direction at night is followed by the occurrence of intense VHF scintillation with a delay in time of the order of an hour. Temporary reversals of the electric field lasting less than half an hour do not seem to develop irregularities of strong enough intensity to produce scintillations.