Equatorial evening prereversal electric field enhancement and sporadic E layer disruption:: A manifestation of E and F region coupling -: art. no. 1254

An investigation of the evening prereversal enhancement in the equatorial zonal electric field (PRE) based on ionosonde data show that the PRE development process is coupled with the sporadic E layer formation in the evening over Fortaleza. Larger PRE amplitudes are associated with disruption of the Es layer, whereas for smaller PRE amplitudes such disruption does not occur, in general. The Es layer disruption does not occur also when the PRE amplitude decreases or is inhibited under a disturbance dynamo electric field. The disruption of these layers is followed by their reconstitution after a break of similar to3 hours. An examination of the relative role of the electric field and winds on ion velocity convergence process shows that the Es layer formation from a shearing (or height-independent and westward) zonal wind is directly influenced by a vertical electric field (but not by zonal electric field). Measurements of the Es patch zonal drift velocities by a digital ionosonde seem to support the role of a westward wind in the Es layer formation. The observed association between the PRE and Es layer disruption/formation is shown to arise from sunset-related vertical electric field development originating from the E and F region electrodynamic coupling processes. The results demonstrate the competing influences of the vertical electric field and the zonal wind in the evening Es layer processes. Since the PRE is responsible for the equatorial spread F (ESF) development, its relationship with the Es layer is discussed in the context of the day-to-day variability of the ESF.