Rt. Tsunoda et Wl. Ecklund, On the nature of radar echoes below 95 km during counter streaming in the equatorial electrojet, GEOPHYS R L, 26(17), 1999, pp. 2717-2720
Using data obtained with a 49.92-MHz radar on the island of Pohnpei (Federa
ted States of Micronesia), we show that a weak, westward current exists at
the base of the normal eastward electrojet. We suggest that this counter st
ream is driven by a downward-directed electric field associated with positi
ve-charge accumulation near the base of the eastward electrojet. To explain
the existence of radar echoes from this counter-streaming region, where co
nditions 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 echo
es.