Investigating the relationships among the South Atlantic Magnetic Anomaly, southern nighttime midlatitude trough, and nighttime Weddell Sea Anomaly during southern summer

Abstract

This study utilized the multi‐instrument data of the Defense Meteorological Satellite Program to investigate the evening/nighttime topside ionosphere during the 1996/1997 southern summer. A series of regional surface maps were constructed and permitted the tracking of the topside ionosphere's plasma density features, plasma composition, thermal structures, and vertical and horizontal plasma flows. These maps tracked a complete nighttime Weddell Sea Anomaly (WSA) and strong horizontal plasma flows that registered the high‐conductivity regions of the South Atlantic Magnetic Anomaly (SAMA). These regions developed over the southeastern Pacific, just equatorward of the WSA, and over the South Atlantic. A heavy‐ion stagnation trough developed poleward of the SAMA affected regions. Thus, the trough appeared on the WSA's equatorward side. During periods of increasing magnetic activity, the plasmapause was the WSA's poleward boundary. A statistical study modeled the trough's magnetic activity dependence and revealed a strong east‐west hemispherical difference that was due to the SAMA effects. When the AE6 was 0 nT, the trough appeared at (57.49 ± 2.82)°S (geomagnetic) over the southwestern hemisphere. Owing to the SAMA's special electrodynamic effects, the trough developed at lower latitudes, (42.39 ± 3.04)°S, over the southeastern hemisphere. Meanwhile, the plasmapause occurred at ∼(62.5 ± 4)°S, and the WSA's peak appeared at ∼(56.2 ± 4)°S. Hence, there was a ∼20° (lat) separation between the trough and the plasmapause over the southeastern hemisphere. Between 210°E and 330°E (geographic), the WSA filled this gap. With increasing magnetic activity, the trough in the SAMA affected regions moved poleward at a rate of (0.0157 ± 0.004)°S/nT. Elsewhere, it had a (0.0196 ± 0.002)°S/nT equatorward movement.