Impact of summer-hemisphere E-region dynamo on the day-to-day variability of equatorial pre-reversal enhancement

The pre-reversal enhancement (PRE) of equatorial F-region vertical drift varies strongly day-to-day and with longitude, but the tidal origin of this variability remains debated. Classical theory (CFM, HCDM, EEJ) attributes PRE primarily to F-region zonal winds interacting with the dusk terminator conductivity gradient, with migrating tides (DW1, SW2) usually invoked as the dominant drivers of variability.
Using the SAED coupled ionosphere-electrodynamics model in a series of controlled single-tide-varying experiments- in which one tidal mode varies day-to-day while all other modes and the background conductivities are held fixed- we attribute day-to-day PRE variability to specific tides and identify the responsible pathway. This configuration explicitly removes the classical Eccles mechanisms as sources of day-to-day variability, since the terminator conductivity gradient is identical every day.
Cross-tide analysis at low latitudes shows that non-migrating tides in the summer-hemisphere E-region at dusk significantly drive the day-to-day PRE variability. The mechanism is a "terminator-amplifier" acting on E-region tidal winds: day-to-day amplitude and phase variations of these tides produce dusk-wind anomalies that the fixed terminator conductivity gradient amplifies PRE perturbations.
This new pathway highlights that in addition to the classical F-region Eccles mechanisms in which the F-region dynamo sets the climatological baseline PRE, the sunlit summer-hemisphere E-region dynamo also significantly modulates and drives the day-to-day variability of equatorial PRE.