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Substorm Onset from Sheared Zonal Flow Vortices and Interchange Dynamics
Kalmoni et al. [1,2] propose a theoretical model to interpret an extensive statistical analysis of the first phase of substorm onsets. The analysis shows that a chain of small size (<100km) weak auroral brightening called “beads” develops along the latitude defined by the early brightening auroral arcs proceeding the onset of substorm auroral arcs. We study and extend the wave equations that include the ion energy distribution functions with the lower and higher energy ion components in auroral flux tubes along with the horizontal sheared ExB flows. The stability wave equations are similar to that in the Kalmoni analysis with some apparent differences in the terms that combine the Kelvin-Helmholtz meridional sheared flows with interchange dynamics in the auroral magnetic fields. The model gives conditions for the growth of the auroral beads and the release of energy from the local pressure gradients. Comparisons are made between the dynamics driven by the interchange and sheared flow dynamics. The results extend conditions for the onset of the beads and the substorm dynamics. More work is needed to compare the extended models with the growth of the “beads” from shear flow and the energy release from local interchange motions.