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

Abstract

[1] 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.

First tomographic observations of the Midlatitude Summer Nighttime Anomaly over Japan

“…Although the effects of dusk time EIA, south Atlantic magnetic anomaly, and the locations of the midlatitude ionospheric trough and the plasmapause in the formation of WSA are proposed in the past literature [ Horvath and Essex , 2003 and references therein], their relative importance in the formation/sustenance and variability of WSA is not well understood even today. A recent study shows that the heavy ion trough often coexists with the WSA, whereas the topside ionospheric signatures of the light‐ion trough show a close correspondence with the plasmapause location [ Horvath and Lovell , 2009]. The WSA is also seen to be affected by the electron density distributions in the low‐ to midlatitude sector [ Burns et al , 2008].…”

An investigation of the northern hemisphere midlatitude nighttime plasma density enhancements and their relations to the midlatitude nighttime trough during summer

“…For the first time, that study provided observational evidence that the midlatitude heavy ion (Ni‐O + ) stagnation trough developed on its equatorward side and hence, the plasma at WSA latitudes was on convection paths. Furthermore, we also demonstrated that the plasmapause occurred on its poleward side during periods of increasing magnetic activity, and that the South Atlantic Magnetic Anomaly (SAMA) had a significant effect on both the trough and the nighttime WSA [ Horvath and Lovell , 2009a]. Also for the first time, this SAMA effect on the trough was modeled and the model reproduced the trough's poleward movement, instead of the usual equatorward movement, with increasing magnetic activity.…”

“…It contains the multiinstrument in situ plasma measurements of the DMSP‐F15 spacecraft that were collected at ∼850 km altitude along the ascending (northbound) passes. A detailed description of the DMSP orbit characteristics is given by Horvath [2006, 2007] and Horvath and Lovell [2009a, 2009b]. Along these F15 passes, the local time (LT) exhibited smaller variations between 75°N (geographic) and 75°S from 1900 LT through 2130 LT (at the equator) to midnight, respectively.…”

“… Burns et al [2008] also utilized the global COSMIC data, investigated the quiet time F2 layer behavior over the South Pacific at dusk and pointed out first that the currently accepted theories do not really explain the formation of the nighttime WSA. Our more recent investigation [ Horvath and Lovell , 2009a] utilized a complete data set of the Defense Meteorological Satellite Program (DMSP) that made it possible to track an entire nighttime WSA and its plasma environment during the 1996/1997 southern summer. For the first time, that study provided observational evidence that the midlatitude heavy ion (Ni‐O + ) stagnation trough developed on its equatorward side and hence, the plasma at WSA latitudes was on convection paths.…”

“…In order to do that, a complete DMSP data set is utilized for tracking nighttime midlatitude plasma density enhancements in the northern summer hemisphere and other ionospheric features such as the midlatitude trough, and their characteristics and plasma environments. A statistical investigation is also aimed for modeling the magnetic activity dependence of the nighttime trough in the northern summer and southern winter hemispheres, for comparing the modeled northern and southern magnetic activity dependencies, and for weighing the modeled magnetic activity dependency of the northern summer trough investigated in this study against that of the southern summer trough investigated in our previous study [ Horvath and Lovell , 2009a].…”