Distinguishing Subauroral Ion Drifts From Birkeland Current Boundary Flows

作者：Archer W E^*; Knudsen D J

来源：JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS, 2018, 123(1): 819-826.

DOI：10.1002/2017JA024577

The Swarm satellites regularly observe latitudinally narrow ion velocity jets exceeding 1 km/s relative to the surrounding plasma at high latitude. Two distinct categories of duskward directed flow channels are observed. The most common are situated between the Region 1 and Region 2 currents, are observed primarily during quiet geomagnetic conditions, and are called Birkeland current boundary flows. During active conditions, a second type of duskward directed ion velocity jet is observed at the equatorward edge of the Region 2 currents, colocated with a sharp poleward directed plasma density gradient, consistent with subauroral ion drifts. Pedersen current and electric field estimates from the Swarm satellites show both types of flow channel to be associated with low height-integrated Pedersen conductivity relative to the surrounding plasma. In this study we show two cases in which the Swarm satellites passed through both types of event on the same orbit, as well as the average ion velocity, field-aligned current, and plasma density surrounding 57 of these events. Some field-aligned current morphologies previously associated with subauroral ion drifts suggest that they may have instead been Birkeland current boundary flows. In this study we provide a comparative description of both phenomena to facilitate their distinction in future studies.
Plain Language Summary Subauroral ion drifts are intense, latitudinally narrow regions of westward flow known to occur premidnight at subauroral latitudes, often during active geomagnetic conditions. Recent studies have shown that during quiet geomagnetic conditions, narrow and intense plasma jets can form at the boundary between upward and downward field-aligned current in the auroral zone; these plasma jets are known as Birkeland current boundary flows. In this study we show measurements from Swarm satellites passing through both of these types of events during the same crossing of the northern auroral oval. We then compare and contrast the average plasma parameters surrounding these two types of events to facilitate distinction between subauroral ion drifts and Birkeland current boundary flows.

• 出版日期2018-1
• 单位Saskatoon; Saskatchewan