The prereversal enhancement of the zonal electric field in the equatorial ionosphere

Abstract

The electric fields in the ionospheric E and F regions near the magnetic equator often show a strong eastward enhancement shortly after sunset and before the eastward (normally) daytime field reverses to westward. Several theoretical models of the low-latitude fields suggest that this enhancement is caused mainly or entirely by F region winds (the F region dynamo), but some authors have suggested that it could be produced solely by E region tidal winds. We give here additional calculations and arguments in support of the F region source. The enhancement of the eastward field for an eastward F region wind tums out to be a simple direct consequence of the fact that after sunset the ionospheric conductivity decreases far more rapidly in the E region than in the F region. 13,72313,724 FARLEY ET AL.' BRIEF REPORT

Simulation of the pre‐reversal enhancement in the low latitude vertical ion drifts

“…In fact, the F regin wind was nearly zero at 18 LT, close to the time of maximum P RE development. At solar cycle maximum, the rapid drop in the E region conductivity near sunset was accompanied by a marked gradient in the F region wind which turned eastward well before sunset, a scenario similar to that described by Farley et al [1986].…”

Response of the equatorial ionosphere at dusk to penetration electric fields during intense magnetic storms

“…Further, near the magnetic equator, under normal conditions, the neutral wind dynamo also develops enhanced zonal electric field across the terminator because of the conductivity gradient as has been observed and modeled by several authors [Heelis et al, 1974;Farley et al, 1986;Fejer et al, 1979Fejer et al, , 2005. As such, at dusk, the eastward penetration electric field may add to the eastward electric field because of the neutral wind dynamo.…”

On the nature of low‐latitude Es influencing the genesis of equatorial plasma bubble

“…Farley et al [1986] regarded the divergence of Hall current in the low-latitude E region in the evening hours to be capable of generating eastward zonal field required for prereversal enhancement (PRE) in the zonal electric field. Then the divergence of Hall current would require zonal gradient in the E region conductivity, presumably linked with spatially inhomogeneous sporadic E activity.…”