Daytime gigahertz scintillations near magnetic equator: relationship to blanketing sporadic E and gradient-drift instability

Observations made in non-equatorial regions appear to support the hypothesis that the daytime scintillation of radio signals at gigahertz (GHz) frequencies is produced by the gradient-drift instability (GDI) in the presence of a blanketing sporadic E (E-sb) layer. However, the only evidence offered, thus far, to validate this notion, has been some observations of E-sb in the vicinity of GHz scintillations. A more comprehensive evaluation requires information about electric field, together with the presence of a steep gradient, which is presumed to be that of Esb. In this regard, the region in the vicinity of the equatorial electrojet (EEJ) appears to be an ideal "laboratory" to conduct such experiments. The dominant driver of electron drift there is the same as that of the EEJ, the vertical polarization electric field, and indications are that the presence of Esb in that vicinity is controlled by a balance in horizontal transport of Esb, between the EEJ electric field and the neutral wind, as described in a model by Tsunoda (On blanketing sporadic E and polarization effects near the equatorial electrojet, 2008). In this paper, we present, for the first time, results from a comprehensive study of daytime GHz scintillations near the magnetic equator. The properties, derived from measurements, are shown, for the first time, to be consistent with a scenario in which Esb presence is dictated by the Tsunoda model, and the plasma-density irregularities responsible for GHz scintillations appear to be produced by the GDI.