Multi-satellite Observations During Theta Aurora Evolution

As the interplanetary magnetic field (IMF) rotates northward the number of convection reversal boundaries (CRB's) in the high-latitude ionospheric plasma flow increases from two to four (or more). Regions of sunward plasma flow at highest latitudes are characteristic of most convection signatures observed when the IMF has a northward component. In addition, some of the CRB's located at highest latitudes may be associated with precipitating particles on closed field lines and transpolar arcs (theta aurora). We present two case studies encompassing detailed relationships between plasma convection, field-aligned current, auroral emission, and particle precipitation boundaries. Electric and magnetic field and precipitating particle data are provided by DMSP and Astrid-2, while the Polar UVI instrument provides measurements of auroral emissions. Ace, Wind, and IMP-8 provide solar wind velocity, density and IMF measurements. Utilizing satellite data, the KTH model provides the high-latitude global potential pattern. We illustrate the influence of the IMF By component on theta aurora development by showing two events during which the theta originates on both the dawn and dusk sides of the auroral oval. Both theta then move across the entire polar region and become part of the opposite side of the auroral oval. Motion of the TPA and changes in the plasma convection pattern are correlated with the magnetosphere topology.