Simulation of the sporadic E layer response to prereversal associated evening vertical electric field enhancement near dip equator

Abstract

The role of the molecular and metallic ions in the formation of sporadic E layers (Es layers) has been an active area of research for many years. Ionosonde data of the Es layer parameter, fbEs (the blanketing frequency of sporadic layer), and ftEs (the top frequency of Es trace), obtained over the Brazilian sites, Fortaleza, and São Luis, show that the diurnal variations of these parameters often present a disruption that is coincident with the evening prereversal electric field/vertical drift enhancement, to reappear after about 2 hours. In this work we have developed a model of the E region with the objective to describe all the phases of the life cycle of the sporadic layer and its relation to the evening vertical electric field enhancement that is associated with the development of the prereversal zonal electric field enhancement. The model calculates the densities of NO+, O +2, O+, N+2, and Fe + in the height region 86-140 km by simultaneously solving the continuity and momentum equations for each of the species. For low latitudes this model shows that winds and electric fields each play distinct roles in the vertical transport of plasma leading to Es layer formation. The results of our numerical simulation confirm the dominant role of the vertical electric field as the cause of the inhibition/disruption of the sporadic layer in the evening. More specifically, the results reveal that an upward directed (positive) vertical electric field is capable of disrupting an ongoing sporadic layer, whereas a downward (negative) electric field favors its formation or even intensification, thus corroborating the conclusions of the recent study by Abdu et al. (2003). Copyright 2007 by the American Geophysical Union.