Theory for modeling the equatorial evening ionosphere and the origin of the shear in the horizontal plasma flow

Abstract

Companion papers in this series present (1) the role of equatorial E region postsunset ionosphere, (2) the origin of horizontal plasma shear flow in the postsunset equatorial ionosphere (this paper), (3) the Coloured Bubbles experiments results, and (4) computer simulations of artificial initiation of plasma density depletions (bubbles) in the equatorial ionosphere. Within this paper, equations describing the time evolution of the equatorial ionosphere are developed using flux tube integrated and flux tube weighted quantities which model the chemistry, dynamics, and electrodynamics of the equatorial ionosphere. The resulting two‐dimensional set of equations can be used to investigate equatorial electric fields neglecting small‐scale phenomena (λ < 1 km). An immediate result derived from the integrated current equations is an equation describing the physics of the shear in the horizontal flow of the equatorial plasma during the evening hours. The profile of the horizontal flow has three important contributing terms relating to the neutral wind dynamo, Hall conduction, and the equatorial electrojet current divergence. Using a one‐dimensional model of the velocity shear equation and the integrated ionospheric transport equations, a time history of the development of the shear feature during the postsunset hours is presented. The one‐dimensional model results are compared to the velocity shear measurements from the Coloured Bubbles experiments.

Three-dimensional simulation of equatorial spread-F with meridional wind effects

“…(5), we have neglected Hall-conductance terms relative to Pedersen-conductance terms and have neglected ∂/∂p terms relative to ∂/∂φ terms on the right-hand side. Equation (5) is similar to that derived in Haerendel et al (1992).…”

Plasma bubble zonal velocity variations with solar activity in the Brazilian region

“…Assuming that the last term of Eq. (1) is small for most local times, except near the solar terminator below the F-region ledge (Eccles, 1998), it is assumed to be null and consequently, the zonal plasma drift velocity will depend essentially on the intensity of the zonal wind velocity U P ϕ (Haerendel et al, 1992;Eccles, 1998). So, since during the solar maximum activity the pressure gradients produced by the solar heating are greater and the wind becomes more intense, the zonal plasma drift velocities are expected to be larger in this period as observed in Table 2, where one can also seen that shows that the deceleration is consistently higher in spring (October to December) than in summer (January to March) and that the velocities tend to decrease faster with local time during solar minimum than during solar maximum.…”

Climatology and modeling of ionospheric scintillations and irregularity zonal drifts at the equatorial anomaly crest region

“…In contrast, the irregularity zonal drifts estimated during the December solstice months of the years 2004 to 2007 presented quite similar behavior to that observed during the equinoxes of the year 2005. The marked differences are the comparatively larger mean velocities during early evening (from ∼ 100 to 120 m s −1 ) followed by a brief initial increase until reaching the peak velocities between 21:00 and 22:00 LT. Table 1 It is well known that at low latitudes the field-linemapped ionospheric vertical electric field is responsible for the zonal motions of the ambient plasma (Haerendel et al, 1992). Since the maximum contribution of the scintillationproducing irregularities occurs at the heights of peak electron density, any change in the evening peak of the F region is expect to affect the dynamic evolution of these irregularities.…”

“…Since the maximum contribution of the scintillationproducing irregularities occurs at the heights of peak electron density, any change in the evening peak of the F region is expect to affect the dynamic evolution of these irregularities. Theoretical formulations have predicted that the nighttime eastward irregularity drift, which can be considered equivalent to the background plasma drift, depends essentially on a ratio of flux-tube-integrated Pedersen conductivity weighted by the F-region zonal neutral wind velocity (Anderson and Mendillo, 1983;Haerendel et al, 1992;Eccles, 1998;Santos et al, 2016). Thus, the years with larger mean irregularity zonal velocities during the December solstice (summer) months over Cachoeira Paulista are possibly associated with a stronger vertical polarization electric field owing to a larger thermospheric zonal wind, which then drives the irregularities zonally.…”