On 21 June 2020, an annular solar eclipse will traverse the low latitudes from Africa to Southeast Asia. The highest latitude of the maximum eclipse obscuration is approximately 30°. This low-latitude solar eclipse provides a unique and unprecedented opportunity to explore the impact of the eclipse on the low-latitude ionosphere–thermosphere (I–T) system, especially in the equatorial ionization anomaly region. In this study, we describe a quantitative prediction of the impact of this upcoming solar eclipse on the I–T system by using Thermosphere–Ionosphere–Electrodynamics General Circulation Model simulations. A prominent total electron content (TEC) enhancement of around 2 TEC units occurs in the equatorial ionization anomaly region even when this region is still in the shadow of the eclipse. This TEC enhancement lasts for nearly 4.5 hours, long after the solar eclipse has ended. Further model control simulations indicate that the TEC increase is mainly caused by the eclipse-induced transequatorial plasma transport associated with northward neutral wind perturbations, which result from eclipse-induced pressure gradient changes. The results illustrate that the effect of the solar eclipse on the I–T system is not transient and linear but should be considered a dynamically and energetically coupled system.
The present work uses the Thermosphere Ionosphere Electrodynamics General Circulation Model (TIEGCM), under geomagnetically disturbed conditions that are closely related to the southward interplanetary magnetic field (IMF), to investigate how the nighttime poleward wind (30°–50° magnetic latitude and 19–22 magnetic local time) responds to subauroral polarization streams (SAPS) that commence at different universal times (UTs). The SAPS effects on the poleward winds show a remarkable UT variation, with weaker magnitudes at 00 and 12 UT than at 06 and 18 UT. The strongest poleward wind emerges when SAPS commence at 06 UT, and the weakest poleward wind develops when SAPS occur at 00 UT. A diagnostic analysis of model results shows that the pressure gradient is more prominent for the developing of the poleward wind at 00 and 12 UT. Meanwhile, the effect of ion drag is important in the modulation of the poleward wind velocity at 06 and 18 UT. This is caused by the misalignment of the geomagnetic and geographic coordinate systems, resulting in a large component of ion drag in the geographically northward (southward) direction due to channel orientation of the SAPS at 06 and 18 UT (00 and 12 UT). The Coriolis force effect induced by westward winds maximizes (minimizes) when SAPS commence at 12 UT (00 UT). The centrifugal force due to the accelerated westward winds shows similar UT variations as the Coriolis force, but with an opposite effect.