Neutral line model of substorms: Past results and present view

TLDR

Substorms exhibit a growth, expansion, and recovery sequence driven by solar wind–magnetosphere coupling, with ionosphere–tail interactions influencing onset and timing. This review examines the near‑Earth neutral line (NENL) model of magnetospheric substorms, highlighting its limitations and the need for further development to integrate comprehensive ionospheric and tail dynamics. The review finds that the NENL model is evolving to incorporate new observations and theoretical insights, remaining the most effective framework for organizing substorm dynamics.

Abstract

The near‐Earth neutral line (NENL) model of magnetospheric substorms is reviewed. The observed phenomenology of substorms is discussed including the role of coupling with the solar wind and interplanetary magnetic field, the growth phase sequence, the expansion phase (and onset), and the recovery phase. New observations and modeling results are put into the context of the prior model framework. Significant issues and concerns about the shortcomings of the NENL model are addressed. Such issues as ionosphere‐tail coupling, large‐scale mapping, onset triggering, and observational timing are discussed. It is concluded that the NENL model is evolving and being improved so as to include new observations and theoretical insights. More work is clearly required in order to incorporate fully the complete set of ionospheric, near‐tail, midtail, and deep tail features of substorms. Nonetheless, the NENL model still seems to provide the best available framework for ordering the complex, global manifestations of substorms.