Abstract
In the present work, we analyze the competition between tidal winds and electric fields in the formation of blanketing sporadic E layers (Esb) over Sao Luis, Brazil (2° 31′ S, 44° 16′ W), a quasi-equatorial station. To investigate this competition, we have used an ionospheric E region model (MIRE) that is able to model the Esb layers taking into account the E region winds and electric fields. The model calculates the densities for the main molecular and metallic ions by solving the continuity and momentum equations for each of the species. Thus, the main purpose of this analysis is to verify the electric fields role in the occurrence or disruption of Esb layers through simulations. The first results of the simulations show that the Esb layer is usually present when only the tidal winds were considered. In addition, when the zonal component of the electric field is introduced in the simulation, the Esb layers do not show significant changes. However, the simulations show the disruption of the Esb layers when the vertical electric field is included. In this study, we present two specific cases in which Esb layers appear during some hours over Sao Luis. We can see that these layers appear when the vertical electric field was weak, which means that the tidal components were more effective during these hours. Therefore, the vertical component of the electric field is the main agent responsible for the Esb layer disruption.
Highlights
The ionospheric E region frequently shows patches of enhanced electron density, known as sporadic E layers (Es)
We have included the zonal and/or the vertical electric field components in order to evaluate their influence on the sporadic E formation or disruption process
On January 2005, the Esb layer is formed above 130 km around 1600 universal time (UT) and descends to approximately 98 km at 1100–1200 UT
Summary
The ionospheric E region frequently shows patches of enhanced electron density, known as sporadic E layers (Es). These layers are observed from 90 to 130 km, and they have a large variability that depends on the altitude and latitude. The Es layers are constituted of metallic ions (like Mg+, Si+, Fe+, Ca+, Na+), and they have different formation mechanism according to the region of the globe where they are detected, i.e., equatorial, middle/ low latitude, and auroral (Whitehead 1961; Layzer 1972; Kopp 1997; Mathews 1998; Haldoupis 2011). The Esq traces on ionograms are associated with the Equatorial Electrojet Current (EEJ) plasma instabilities (Forbes 1981), mainly the gradient drift instability (Type II irregularities) driven by the vertical polarization electric field produced by a Hall current as well as by the vertical density gradient (Chandra and Rastogi 1975; Reddy and Devasia 1973)
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