NSWP: Formation and Characteristics of the Harang Reversal and Relations to Substorms: Simulations with the Rice Convection Model

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The reversal in the direction of the ionospheric electric field in the region known as the Harang discontinuity is known to play an important role in the large-scale dynamics of the ionosphere and magnetosphere. This project uses the Rice Convection Model (RCM) to simulate the Harang reversal in order to evaluate the physical processes responsible for its formation and characteristics, as well as its evolution during substorms. The RCM can appropriately take into account the physics of the plasma drift transport within the plasma sheet, and it solves for the ionospheric electric potential self-consistently with the plasma sheet dynamics through their coupling by field-aligned currents. This project will further develop simulations to be more realistic. A magnetic field solver will provide magnetic fields that are in force balance with the RCM plasma pressures. Particle boundary conditions will be established using observations from the Geotail satellite. This combined model will be used to provide quantitative evaluation of the physical processes believed to govern the Harang reversal. The quantitative results from the simulations will be compared with ground-based radar observations. To evaluate the underlying physical processes, individual physical parameters in the model will be varied to see how the variations effect the Harang reversal. By varying a single paramter while keeping others fixed it will be possible to determine the effect of each parameter on the formation and characteristics of the Harang reversal. To understand the relationship between the Harang reversal and magnetic substorms and to test a substorm theory, this project will evaluate the evolution of the Harang reversal and its correlations to the plasma sheet during the substorm growth phase and during the initial stage after a strong decrease in plasma sheet convection. The project will examine whether or not a decrease in the convective electric field leads towards increasingly rapid changes and instability as predicted by the theory. The simulations will be the first to provide quantitative assessment of the Harang reversal, its correlations with the plasma sheet, its evolution and response to variations of interplanetary conditions during substorms, and its potential use to predict substorms, which will be crucial to understanding magnetosphere-ionosphere coupling within the plasma sheet and substorm triggering.