The Characterization of Ionospheric Convection Reversal Boundaries in the High-Latitude Region Using DMSP Data
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The characteristics of the convection reversal boundary (CRB) in the high latitude ionosphere are investigated by using Defense Meteorological Satellite Program (DMSP) ion drift and particle precipitation measurements from 2000 to 2015. A statistical study shows that the CRB location is well organized by the magnitude and direction of the Interplanetary Magnetic Field (IMF) components Bz and By. Observation also suggests that the average latitudinal movement of the CRB associated with By changes is comparable to that associated with Bz changes. Inspection of the CRB locations as a function of magnetic local time (MLT) shows that the CRB has a general spiral shape with a latitudinal gap at the dayside boundary. An observed uneven boundary expansion between the dawn and dusk side reveals that an initial reconfiguration of the boundary near local noon is redistributed around the dawn or dusk side dependent on the direction of By. Two halves of ellipses with different lengths for the semi-major axes are produced to represent the boundary location. The properties of the plasma motion at the CRB and its dependence on the location of the CRB and the IMF orientation are then investigated. A smaller variability in plasma drifts across the CRB is seen over a 4 h segment in MLT around dawn and dusk for stable southward IMF compared to that for variable IMF. Across these segments, a total potential drop ~10 kV is found, suggesting that the CRB behaves much like an adiaroic line, for which the plasma and the boundary move together. Considering a full range of IMF orientations with no stability constraint, a relatively narrow distribution of plasma drifts across the CRB is seen only between the 6-7 h and between 17-18 h MLT, and equatorward/poleward motions of the CRB are observed when the CRB is located at the highest/lowest latitudes. The smaller local time extent of the adiaroic line for variable IMF (~1 h) may be associated with rotation of the dayside merging gap in local time or local contractions and expansions of the polar cap boundary. A systematic case study of the relationship between the motion of the convection reversal boundary and the plasma motion from multi-satellite samplings is performed. Focusing on the cases with continuous poleward and equatorward CRB motion sampled by three consecutive satellites, the CRB usually moves at approximately the same speed and in the same direction as the local plasma flow. Differences in the inferred CRB motion and the local plasma motion may arise from the presence of a viscous-like interaction across the boundary, apparent motion induced by the local time displacement of consecutive samples across the CRB that is tilted with respect to a line of constant latitude and the merging or reconnection processes. The observations also suggest that monotonic migrations of the CRB over time scales of a half hour take place episodically with time scales shorter than the typical sample time of 15 minutes available from sequential measurements.