First incoherent‐scatter measurements of the equatorial E layer obtained with the ALTAIR radar

We describe the first incoherent-scatter (IS) radar measurements made of the daytime E layer at equatorial latitudes. Using ALTAIR, a steerable IS radar located in the Kwajalein Atoll, we not only show that the E-layer profiles are consistent with those obtained in situ by rockets, we present the first direct evidence of a latitudinal gradient in plasma density in the bottomside E layer that extended from 3°N dip latitude to beyond 6°N. We suggest that the gradient involves the electrodynamic transport of metallic ions, e.g., the gradient could be produced by the equatorial metallic-ion fountain or possibly by the dumping of metallic ions at the base of the E layer by the wind-shear mechanism for sporadic E. We close with a brief discussion of the implications of such a gradient on the equatorial electrojet.

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