The Dawn‐Dusk Asymmetry of the Interaction Between Dipolarizing Flux Bundles and the Ambient Plasma: Implications for Asymmetric Wedgelets

Abstract

AbstractThe substorm current wedge (SCW), the characteristic current system of Earth's substorms, has been suggested to be a collective effect of many “wedgelets,” mesoscale currents carried by magnetotail flux tubes of strong magnetic fields called dipolarizing flux bundles (DFBs). Each wedgelet contains an asymmetric pair of field‐aligned currents (FACs) so the net FAC of many wedgelets can equal an SCW's FAC content. It is unclear, however, why a wedgelet's FAC is asymmetric. To explore the reason, we investigate how earthward‐traveling DFBs interact with ambient plasma because this interaction leads to their FACs. The interaction is manifested as the pressure and magnetic field distributions around DFBs, which we examine statistically using THEMIS data. The statistical distributions are consistent with an interplay between the DFB‐caused mesoscale perturbations and the global magnetotail configuration and favor the rise of wedgelets' asymmetric FACs. This result reveals the importance of cross‐scale coupling in SCW formation.