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

摘要

This study has utilized regional surface maps and field-aligned latitudinal profilesderived from multiinstrument DMSP-F 15 data. It investigates northern midlatitude plasmaenhancements in the nighttime topside ionosphere during summer and their relationto the midlatitude heavy ion stagnation trough. The tracked midlatitude summerenhancements showed significant longitudinal variations. Their best developmentoccurred in the 50°N-60°N/110°E-170°E (geographic) region. Proven by CoupledThermosphere-Ionosphere Plasmasphere wind velocity simulations, equatorward windswere strongest there. This region is the northern hemisphere equivalent of the Weddell SeaAnomaly's (WSA) locality. There, northern summer plasma enhancements resembled thenighttime WSA, a southern summer equinoctial phenomenon, and thus were named asWSA-like feature. Their plasma density increased mainly owing to the mechanical ordirect effects of the equatorward winds. However, as results show, the WSA-like featurewas an ordinary northern midlatitude nighttime enhancement occurring in summer.This was further confirmed by the WSA-like feature's relation to the trough and by thetrough's movement. Over the northern hemisphere, the summer trough appeared at(62.461 ± 2.93)°N (geomagnetic), poleward of the WSA-like feature and other midlatitudeplasma enhancements, and moved equatorward with a rate of (0.097 ± 0,04)°N/nT whenmagnetic activity increased. As our previous WSA investigation indicates, the southernsummer trough develops at lower latitudes, at (47.1564 + 2.16)°S, equatorward of thenighttime WSA and moves poleward with a rate of (0.0497 ± 0.003)°S/nT with increasingmagnetic activity under the combined influence of the nighttime WSA and South AtlanticMagnetic Anomaly.