Timing and localization of reconnection signatures - Is there a substorm model problem?

Abstract

[1] Observations place ionospheric substorm onset signatures on field lines that map to the near-Earth plasma sheet, and field-aligned currents (FACs) are observed before dipolarization, equatorward of open field lines. The near-Earth neutral line (NENL) model, however, appears to suggest perturbations to originate from the x-line on newly reconnected field lines, which map to much higher latitudes. Its order of dipolarization, FACs, and subsequent ionospheric signatures contradicts the observations. Using large-scale kinetic simulations, we demonstrate that these “flaws” of the NENL model are misconceptions and that the timing and location of signatures in the model are indeed consistent with observations. In a thinned current sheet, energetic ions are virtually unmagnetized, get further energized when passing through the neutral sheet, and travel earthward quickly and close to the neutral sheet, thus providing a pathway for early substorm signatures at relatively low latitudes.