On the nature of radar echoes below 95 km during counter streaming in the equatorial electrojet

Abstract

Using data obtained with a 49.92‐MHz radar on the island of Pohnpei (Federated States of Micronesia), we show that a weak, westward current exists at the base of the normal eastward electrojet. We suggest that this counter stream is driven by a downward‐directed electric field associated with positive‐charge accumulation near the base of the eastward electrojet. To explain the existence of radar echoes from this counter‐streaming region, where conditions are not conducive to irregularity generation by the gradient‐drift instability (GDI), we suggest that “seed” plasma structure may be produced by neutral turbulence. If so, the GDI could act on appropriately directed gradients in plasma density that are associated with the seed structure to generate the secondary type‐2 irregularities responsible for the radar echoes.