Electrodynamics of the equatorial evening ionosphere: 2. Conductivity influences on convection, current, and electrodynamic energy flow

Abstract

We analyze how the evening equatorial plasma vortex and the prereversal enhancement (PRE) of the vertical drift are influenced by the distributions of conductivity in the E and F regions in relation to the wind, through numerical simulations with the thermosphere-ionosphere-electrodynamics general circulation model coupled with the global ionosphere-plasmasphere model. The nightside electric potential satisfies an approximate minimization principle that unifies the connection of the horizontal and vertical components of plasma convection to the wind and conductivity distributions. The relative roles of E and F region conductivities on the convection and current closure are clarified. Evening time F region zonal winds at latitudes that encompass the equatorial ionization anomaly (EIA) region provide the main energy source to drive the convection, including the PRE. The E region helps regulate both the meridional and the zonal convection through drag on the meridional convection associated with Cowling current. For large nighttime E region conductivities, additional drag on the zonal convection comes from the Pedersen conductance. The minimization principle favors meridional plasma inflow to the EIA region from lower rather than higher magnetic apex heights, so long as the E region Cowling conductance is not too large. This upward/poleward inflow maximizes on field lines that traverse the lower F layer near the equatorward edge of the EIA region, producing a PRE with maximum vertical velocity within the equatorial F layer.

Modeling the ionospheric prereversal enhancement by using coupled thermosphere‐ionosphere data assimilation

“…They demonstrate that the E × B vertical drift could be improved from “climatology” to “weather” for strong PRE by assimilating GPS‐TEC data. In some recent studies, upward plasma drift is shown to be a part of the evening plasma convection vortex driven by the neutral wind and ion drag effects [e.g., Kudeki and Bhattacharyya , ; Rodrigues et al ., ; Heelis et al ., ; Richmond et al ., ; Richmond and Fang , ]. The evening plasma vortex results from the eastward plasma flow at F layer height, the westward plasma flow in the E layer, and the vertical plasma flow that plays a role in balancing the zonal plasma shear.…”

Electrodynamics of the equatorial evening ionosphere: 1. Importance of winds in different regions

“…The role that E region conductivity plays in the electrodynamics of the nightside F region also requires further clarification. These questions are addressed in a companion paper [ Richmond and Fang , ].…”

West wall structuring of equatorial plasma bubbles simulated by three‐dimensional HIRB model

“…Because of the limited model configuration that uses a periodic boundary condition in a zonal direction, the model does not simulate a real evening condition in which a nighttime (daytime) condition should be applied at the eastern (western) boundary. The actual electrodynamics in the equatorial evening ionosphere is very complex and still being eagerly investigated [ Richmond et al , ; Richmond and Fang , ; Eccles et al , ]. The plasma shear flow is tightly coupled with the prereversal enhancement of vertical plasma drift as a consequence of the complex current closure system [ Haerendel and Eccles , ; Haerendel et al , ; Eccles et al , ].…”