Mechanisms underlying the prereversal enhancement of the vertical plasma drift in the low‐latitude ionosphere

Abstract

The evening prereversal enhancement (PRE) of the vertical plasma drift has important consequences for the Appleton density anomaly and the stability of the nighttime ionosphere. Simplified simulations were used to review the three competing theories of the PRE origin, to explore their relative importance, and to indentify their interdependence. The mechanisms involved in the generation and climatology of the PRE are, first, a curl-free electric field response to rapid changes in the vertical electric field associated with the nighttime F region dynamo; second, a divergence of Hall currents in the E region away from the magnetic equator; and, third, the moderating effect of the large Cowling conductivities in the equatorial E region. The simulations indicate that the equatorial Cowling conductivity creates an important current path that limits the other two mechanisms prior to equatorial sunset and releases them after equatorial sunset. The curl-free mechanism is the dominant mechanism when the terminator and magnetic meridian are aligned in part due to the accelerating F region zonal wind. When the solar terminator is not aligned with the magnetic meridian, there is an interaction involving all three mechanisms contributing to the magnitude and timing of the PRE. Finally, the altitude profile of the PRE decays more quickly with altitude when the curl-free mechanism dominates as compared to when the Hall current mechanism dominates.

The dawn enhancement of the equatorial ionospheric vertical plasma drift

“…Recently, the simulation result of Eccles et al . [] illustrated that both the Hall current divergence mechanism in conjugated E regions and the curl‐free electric field mechanism (proposed by Eccles []) can play a vital role in development stages of the PRE. The curl‐free electric field mechanism may contribute to the dawn enhancement as a result of the similarity between the dawn enhancement and the PRE.…”

“…With regard to the sunset PRE, many investigations have been conducted to focus mostly on the solar activity dependence [e.g., Fejer et al ., , , ; Kil et al ., ; Santos et al ., ], the longitudinal‐seasonal variations [e.g., Abdu et al ., , ; Fejer et al ., , ; Batista et al ., ; Su et al ., ; Ren et al ., ; Kil et al ., ], the peak local time [e.g., Abdu et al ., ; Batista et al ., ; Kil and Oh , ], the occurrence [e.g., Su et al ., ; Kil and Oh , ], and the mechanisms responsible for its formation [e.g., Rishbeth , ; Farley et al ., ; Haerendel and Eccles , ; Eccles , , ].…”

Diurnal evolution of the F region electron density local time gradient at low and middle latitudes resolved by the Swarm constellation

“…However, after sunset the E region conductance decays quickly, while the F region decays slowly persisting through the night. The F region neutral wind dynamo can generate large vertical electric fields during night [ Rishbeth , , ; Eccles et al ., ].…”

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

“…The zonal plasma drift velocity over the magnetic equator is westward/eastward at lower/higher altitudes, resulting in a vortex flow with upward/downward drifts at the western/eastern sides of the vortex center [ Kudeki and Bhattacharyya , ]. The mechanism of the shear flow was studied theoretically [ Haerendel and Eccles , ; Haerendel et al , ; Eccles et al , ] and numerically [ Hysell et al , ; Rodrigues et al , ] and is attributed to the complex current closure system near the sunset terminator. It is also suggested that the shear flow itself can play a major role in seeding the EPBs by a shear instability mechanism [ Hysell and Kudeki , ; Hysell et al , ; Aveiro and Hysell , ].…”