Abstract
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.
Highlights
The thermospheric meridional wind is one of the keys to understanding the variability of the coupled Ionosphere–Thermosphere (IT) system
3.1 Data-Model Comparison The zonal ion drift velocities calculated by the Subauroral Polarization Streams (SAPS)-Thermosphere Ionosphere Electrodynamics General Circulation Model (TIEGCM) and the TIEGCM at 00 universal times (UTs) on 18 March 2015 are given in Figures 1a and 1b, respectively
The DMSP-observed SAPS are reasonably consistent with the ones modeled in the SAPS-TIEGCM, but with small differences
Summary
The thermospheric meridional wind is one of the keys to understanding the variability of the coupled Ionosphere–Thermosphere (IT) system It can influence the ionosphere by moving the plasma along the magnetic field lines (Rishbeth, 1967), by the ionospheric wind dynamo (Blanc and Richmond, 1980), and by other ion-neutral interaction processes (Richmond et al, 1992; Zhang SR et al, 2017), including the flywheel effect (Lyons et al, 1985; Odom et al, 1997; Richmond et al, 2003; Ridley, 2005; Deng Y et al, 2014). SAPS are described as westward plasma jets (PJ, Galperin et al, 1974) or subauroral ion drifts (SAID, Anderson et al, 1993). They are located in a latitudinally narrow region and are observed from dusk to early morning. As reported by Wang WB et al (2012), an empirical model of SAPS was imposed in the Thermosphere Ionosphere Electrodynamics General Circulation Model (SAPS-TIEGCM) to simulate SAPS effects on the IT system during a period of geomagnetically moderate activ-
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