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

The 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. Plain Language Summary: The electric current system of one of the most important energy release events in Earth's near‐space provides valuable information on how such events proceed. Previous studies showed that the current system consists of small elements with unexpected but necessary asymmetries. To understand how such asymmetries are formed, we examine the space plasma environment related to them using spacecraft data. The plasma environment suggests that the asymmetries arise from an interaction between small and global‐scale phenomena, indicating the importance of cross‐scale coupling in understanding the geospace. Key Points: We examine the statistical distribution of pressure and magnetic field strength around dipolarizing flux bundles (DFBs) using THEMIS dataAround a DFB in the dusk (dawn) sector of the magnetotail, the quantities are larger on its morning (evening) sideThis asymmetric distribution suggests an interplay between meso and global scales and favors asymmetric wedgelets as previously found [ABSTRACT FROM AUTHOR]