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Based on the electron density, field‐aligned currents (FACs) and ion drift velocity data from the Swarm‐A satellite during 2013–2018, we investigate the features of the high‐latitude trough in the Southern Hemisphere. The results show that the high‐latitude trough in the Southern Hemisphere is a persistent postmidnight feature in winter. It is observed mainly in the eastern longitudes under low solar activity conditions and in a smaller longitudinal range under high solar activity conditions. The high‐latitude trough moves to higher latitudes at later local times, which is more obvious under low solar activity conditions. We also find that the features of FACs and ion drift velocity distribution in the high‐latitude trough region depend on longitude. In the longitude sector of 0°–70°E, the high‐latitude trough positions are always located at the poleward boundary of the downward FAC region, and collocated with the convection reversal boundary in the postmidnight region. In the longitude sector of 80°–130°E, the high‐latitude trough positions are located at the poleward boundary of the downward FAC region in the midnight region and at the strong westward or antisunward ion flow region in the postmidnight region. It is suggested that the high‐latitude trough formation and evolution is possibly associated with downward FACs, flow stagnation in the convection reversal boundary, and westward or antisunward ion flow. Plain Language Summary: Ionospheric troughs are depletions of the nighttime F region plasma density around the auroral and polar regions. The presence of the trough has a significant impact on the radio transmission. There are two types of troughs: the midlatitude trough and the high‐latitude trough. The midlatitude trough locates on the equatorward side of the auroral oval, and the high‐latitude trough locates within the auroral oval or polar cap. The features and formation mechanisms of the high‐latitude trough in the Southern Hemisphere are not yet clear. This study uses a new multiparameter data set gathered by the Swarm‐A satellite to find out the features and formation mechanisms of the high‐latitude trough in the Southern Hemisphere. We found that the high‐latitude trough in the Southern Hemisphere is a persistent postmidnight feature in winter. It is observed mainly in the eastern longitudes. The features of FACs and ion drift velocity distribution in the high‐latitude trough region depend on longitude. The formation and evolution of the high‐latitude trough is suggested to be associated with downward FACs, flow stagnation in the convection reversal boundary, and westward or antisunward ion flow. Key Points: The high‐latitude trough is a persistent postmidnight feature in winter in the Southern HemisphereThe high‐latitude trough is observed mainly in the eastern longitudesThere is a longitude dependence of features of FACs and ion drift velocity distribution in the high‐latitude trough region [ABSTRACT FROM AUTHOR]

Cross‐track ion drifts measured by the Swarm A satellite are compared with colocated line‐of‐sight Super Dual Auroral Radar Network (SuperDARN) velocities in approximately the same directions. More than 200 Swarm A passes over four polar cap SuperDARN radars in the Northern and Southern Hemispheres are considered. Overall, the Swarm‐based velocities are larger than the SuperDARN velocities; the slope of the best fit line to the data is ~0.67. Somewhat stronger differences are found when Swarm A measurements for the entire year 2016 are compared with SuperDARN vector data from global‐scale convection maps. Swarm ion drift data demonstrate known features of the high‐latitude convection patterns, for example, reverse convection cells at interplanetary magnetic field Βz > 0. The latitudes of the convection reversal boundary inferred from SuperDARN are found to be in reasonable agreement with those determined from Swarm A and Swarm B, with Swarm‐based latitudes occurring roughly 1° more equatorward, typically. Key Points: Swarm cross‐track ion drifts are smaller than SuperDARN radar velocitiesOverall Swarm‐SuperDARN differences are by a factor of 1.5 but smaller in many instancesSwarm shows major features of plasma flow patterns and superior in monitoring flow reversals [ABSTRACT FROM AUTHOR]