Abstract Results from a 1D kinetic simulation, for the first time, unveil the generation and time evolution of the downward parallel electric fields stemming from the coupling between modified electron acoustic waves (MEAWs) and dispersive Alfvén waves (DAWs). Under the incidence of long‐period Alfvén waves carrying downward field‐aligned currents, a parallel potential drop forms in the transition region between magnetospheric hot electrons and ionospheric cold electrons, accelerating cold electrons upward. These accelerated electrons progressively replace hot electrons as the main current carrier. Parametric investigations show that the ratio of potential drop to downward field‐aligned current increases with hot‐electron temperature and decreases with hot electron density, and is several (7–8) times smaller than that for upward currents because less potential drop is required for more abundant cold electrons to reach the same current magnitude. These results unify the generation of E

in both current polarities in the same DAW‐MEAW coupling framework.

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