The current system of dipolarizing flux bundles and their role as wedgelets in the substorm current wedge

Abstract

In this chapter, we review recent observations of the current system of dipolarizing flux bundles (DFBs), small magnetotail flux tubes (typically < ~3 RE in XGSM and YGSM) with a significantly more dipolar magnetic field than their background. When propagating, a DFB or a group of several consecutive DFBs is known as a bursty bulk flow. A DFB's current system consists of a duskward current at the dipolarization front (DF, the leading edge of a DFB), a dawnward current immediately earthward of the DFB, field-aligned currents (FACs) at the DF and earthward of the DFB, and cross-tail current reduction inside the DFB. The FACs and cross-tail current reduction resemble a substorm current wedge (SCW), but are of much smaller scale. Therefore, each DFB possibly serves as a wedgelet, the building block of an SCW. We review a suggested way in which many wedgelets may collectively form a large-scale SCW. We also present some new results that help us to understand the DFB current system.