Successive Westward Traveling Surges Driven by Sequential Plasma‐Sheet Bubble Injections

Abstract

The westward traveling surge (WTS) is one of the most prominent phenomena of auroral substorms (Akasofu, 1964). Following substorm onset, a WTS forms rapidly as an expanding bulge structure propagating westward (Akasofu et al., 1965). The generation mechanism and mapping of WTS are complicated and still not fully understood. The WTS is generally accompanied by intense localized upward field-aligned currents (FACs) (Marklund et al., 1998;Opgenoorth et al., 1983;Tighe & Rostoker, 1981) marking the western edge of the substorm current wedge (SCW) (McPherron et al., 1973). The SCW consists of Region-1 (R1) sense flowing downward into the ionosphere at the eastern side of the wedge and upward at the western side of the wedge, connected by a westward electrojet in the ionosphere. In the Cowling channel model (Boström, 1975), enhanced conductivity gradients lead to the strong westward current and polarization electric field, which is connected at its western edge via very localized intense upward FACs (where the WTS is observed) (