On Blanketing Sporadic E and Polarization Effects Near the Equatorial Electrojet

Abstract

A number of puzzling features have been observed that occur during the day in the vicinity of the equatorial electrojet (EEJ). They include (1) an equatorial belt, essentially collocated with the EEJ, that is virtually devoid of blanketing sporadic E (E_sb); (2) appearances of E_sb within that “forbidden” belt but only when the EEJ is weak or reversed (i.e., a counterelectrojet); (3) occasional appearances of a secondary current layer above the EEJ; and (4) observations at 4.3°N dip latitude of a latitudinal tilt in the bottomside E layer on one occasion and an unexpectedly large electron drift velocity on another. These features are shown to be accountable if the usual framework for electrodynamics in this region is modified to include the following: (1) transport of E_sb that is controlled by a shear in the neutral wind with a crucial contribution from the polarization electric field of the EEJ; (2) the formation of an equatorward boundary for E_sb by a dynamical balance between the neutral wind and the polarization electric field; (3) a buildup in conductivity within a band-like region, just poleward of the E_sb boundary, from an accumulation of metallic ions; and (4) the appearance of a secondary polarization electric field across the band of enhanced conductivity and current flow throughout the region pervaded by that secondary electric field.