A comparative study of VHF scintillation and spread F events over Natal and Fortaleza in Brazil

A comparative study is carried out of the equatorial ionospheric irregularity occurrences, as observed by range spread F events over Fortaleza (4°S, 38°W, dip latitude 1.8°) and satellite VHF signal scintillation event over Natal (5.8°S, 33.23°W, dip latitude 4.8°S) for a one‐year period 1978. Close association is observed in the occurrences and the durations of the irregularities at the two stations. Marked differences in the seasonal behavior of the occurrences of the irregularity events over these two stations are noted with respect to that over Huancayo, most important of them being that while the latter station presents equinoctial maxima in the occurrence rates (as over some African stations), the Brazilian stations show an additional and pronounced peak in December. This result is explained as possible evidence of magnetic declination control of the spread F irregularity generation and its seasonal dependence. The present results have important implications also on the coexistence of different irregularity scale sizes during equatorial plasma bubble irregularity events.