Revisiting the Stormtime Magnetosphere-Ionosphere Coupling: Enhancement of the Dawnside Auroral Electrojet

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The geomagnetic storm is the most intense class of disturbances in geospace, and the critical target of space weather. Space weather is a relatively new area of space science, which aims at understanding and predicting space-oriented events that impact societal infrastructures such as satellite operations in general, GPS system, and power grids, and sometimes they even risk human health (e.g., radiation exposure for aircraft and space crews). This study investigates the stormtime ionospheric current and its source in the magnetosphere. During geomagnetic storms, the ionospheric current intensifies especially in high latitudes, partly because the energy input from the solar wind to the magnetosphere increases, and partly because intense auroral precipitation enhances the ionospheric conductance. Moreover, during some severe storms, the ionospheric current moves equatorward down to the northern part of the continental US, and farther south during historically intense storms. Such events are widely known as a threat to US power networks. This study seeks to observationally characterize and understand a stormtime current system in the dawn local time sector, where ground magnetic disturbances very often become the largest in magnitude. It is expected that the successful achievement of this project brings new insights into stormtime electrodynamics in geospace and contributes to building models to predict hazardous events.The target of this research project, the enhancement of the dawnside auroral electrojet (AEJ), which was recently identified as a plausible cause of the dawn-dusk asymmetry of stormtime ground magnetic depression, a characteristic feature of the storm main phase. The confinement of this current system in the dawn sector suggests that this AEJ enhancement is an ionospheric segment of a 3D current system, the dawnside wedge current (DWC) system. However, its generation process is largely unknown. One hypothesis is that (A) the DWC system is an intense substorm current wedge skewed dawnward, and an alternative idea is that (B) it forms because the dawnside ionospheric conductance enhances in the presence of intense global convection. This project seeks to observationally examine the characteristics of the DCW development from five viewpoints: (1) internal and external conditions for its occurrence; (2) spatial and temporal scales; (3) time sequence of its development and preconditioning; (4) dipolarization and particle injection; (5) plasma sheet convection. The team will systematically select events with SuperMAG indices, and will address (1) with the probability density functions of various internal and external parameters, (2) and (3) with polar distributions of magnetic disturbances and aurora, (4) with magnetic field and energetic particle flux measurements in the near-Earth magnetosphere, and (5) with convection measurements in the plasma sheet. We critically evaluate the results in terms of the aforementioned two hypotheses, (A) and (B). By revealing the process responsible for the formation of the DWC system, the present project will advance our understanding of storm dynamics to a new level.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.