Substorm Onset from Sheared Zonal Flow Vortices and Interchange Dynamics*

Kalmoni et al.[JGR 2016 and Substorm Conference 2017] propose a theoretical model to interprete their extensive statistical analysis of early phase of substorm onsets. The analysis shows that a chain of small size (<100km) weak auroral brigthenings called “beads” develops along the latitude of the magnetic field foot points that defined by early auroral brightening and subsequent substorm auroral arcs. We study and extent 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 resulting 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 extent conditions for the onset of the beads and the substorm dynamics.