The Substorm Current Wedge

 
 

Almost 40 years ago the concept of the substorm current wedge (SCW) was developed to explain the pattern of magnetic signatures observed on the ground and in geosynchronous orbit during the substorm expansion phase. The ensuing decades saw advancements in our understanding of this system from new observations, including radar and low-altitude spacecraft, theoretical considerations, and MHD simulations, and the SCW remains a guiding paradigm on the large scale to this day. Yet recent results from new radar instrumentation, Cluster, and the coordinated ground and in situ measurements of the THEMIS mission have identified key areas in which the SCW paradigm needs to be revised and extended. Specific questions include the role of current filamentation and other small-scale processes, how the current systems of multiple onsets are related, and how other processes that contribute to substorm currents fit within the SCW model. We propose to bring together an inter-disciplinary group of experts on the ionosphere, magnetosphere, modeling and theory to produce a comprehensive review paper with two primary goals. First, we will review the work of the past 40 years covering historical development, a thorough summary of the ground, ionospheric and magnetospheric observations that underpin the model, and an overview of the necessary theoretical frameworks. Second, we will pull together the wealth of recent advancements enabled by the THEMIS and Cluster missions, with an emphasis on how recent observations have expanded our knowledge beyond the simple conceptual model, and necessitated an extension of the phenomenological picture.

 

Abstract: