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

• Published in: Journal of Geophysical Research: Space Physics
• Main Authors: Horvath, Ildiko, Lovell, Brian C.
• Other Authors: Robert L. Lysak
• Format: Article in Journal/Newspaper
• Language: English
• Published: American Geophysical Union 2009
• Subjects: Mid-latitude trough; Northern mid-latitude night-time plasma enhancements; Plasmasphere-ionosphere coupling; 810199 Defence not elsewhere classified; 970102 Expanding Knowledge in the Physical Sciences; 020107 Mesospheric; Ionospheric and Magnetospheric Physics; Weddell Sea; Weddell
• Online Access: https://espace.library.uq.edu.au/view/UQ:185448/UQ185448_OA.pdf; https://espace.library.uq.edu.au/view/UQ:185448

This study has utilized regional surface maps and field-aligned latitudinal profiles derived from multiinstrument DMSP-F15 data. It investigates northern midlatitude plasma enhancements in the nighttime topside ionosphere during summer and their relation to the midlatitude heavy ion stagnation trough. The tracked midlatitude summer enhancements showed significant longitudinal variations. Their best development occurred in the 50°N-60°N/110°E- 170°E (geographic) region. Proven by Coupled Thermosphere-Ionosphere Plasmasphere wind velocity simulations, equatorward winds were strongest there. This region is the northern hemisphere equivalent of the Weddell Sea Anomalys (WSA) locality. There, northern summer plasma enhancements resembled the nighttime WSA, a southern summer equinoctial phenomenon, and thus were named as WSA-like feature. Their plasma density increased mainly owing to the mechanical or direct effects of the equatorward winds. However, as results show, the WSA-like feature was an ordinary northern midlatitude nighttime enhancement occurring in summer. This was further confirmed by the WSA-like features relation to the trough and by the troughs movement. Over the northern hemisphere, the summer trough appeared at (62.461 ± 2.93) °N (geomagnetic), poleward of the WSA-like feature and other midlatitude plasma enhancements, and moved equatorward with a rate of (0.097 ± 0.04) °N/nT when magnetic activity increased. As our previous WSA investigation indicates, the southern summer trough develops at lower latitudes, at (47.1564 ± 2.16) °S, equatorward of the nighttime WSA and moves poleward with a rate of (0.0497 ± 0.003) °S/nT with increasing magnetic activity under the combined influence of the nighttime WSA and South Atlantic Magnetic Anomaly. Copyright 2009 by the American Geophysical Union.