The Blanketing Sporadic-E Near the Magnetic Equator: A Review

76-83The special features of blanketing sporadic-E (Es-b) in the magnetic equatorial region have been reviewed. Principally from evidences gathered by four different techniques; namely vertical radio sounding. VHF scatter, rocket sounding and ionospheric scintillation. The ionograms from magnetic equatorial stations show that Es-bis forbidden in this zone. It has a characteristic diurnal variation, exhibits lunar influence and seems to be intimately related to the counter-electrojet current system. The forward scatter observations on VHF show that both Es-q and Es-bare essentially in the nature of irregularities in the E-region and confirm that there is a forbidden zone for Es-bnear the magnetic equator. The backscatter radar at Jicamarca has produced evidences to suggest the formation of irregularities at the E-region heights by two different mechanisms, namely two-stream instability and gradient drift instability. The latter has been invoked to explain the formation of Es-b. Further evidences in support of this come from the rocket results which also suggest that the Es-b is probably in the nature of a cloud of irregularities. There are some suggestions that Es-b irregularities produce daytime scintillation. Some questions yet to be answered about the nature of Es-b are discussed