Substorm-time ionospheric trough dynamics: Its evolution and relationship with FACs and convection flows

Dynamics of the ionospheric mid-latitude and high-latitude troughs during substorms are investigated using multiple instruments, including GPS TEC and PFISR, with focus on the evolution of the troughs and their relationship with field-aligned currents (FACs) and convection flows. We describe the evolution of the mid-latitude trough during substorms. Its poleward wall shifts equatorward rapidly after substorm onset due to enhanced energetic electron precipitation. The mid-latitude trough narrows or even disappears during the expansion phase and can reappear during the recovery phase as auroral activity retreats poleward. This study demonstrates the potential of GPS TEC in detecting substorm related auroral activity and energetic particle precipitation on a regular basis. In addition, we find that the high-latitude trough can occur right after substorm onset east of the Harang reversal and that it can last for more than an hour. The termination of the high-latitude trough is usually associated with intrusion of auroral forms and accompanied by intensification of negative H perturbations. It has been a puzzle for a long time why high-latitude troughs predominantly occur just east of the Harang reversal in the post-midnight sector. We suggest that the high-latitude trough is associated with the formation of downward FACs of the substorm current system, which usually occur just east of the Harang reversal. We further discuss the effects of substorm related convection pattern, structured FACs, and precipitating particle species on creating the complex electron density variations in the subauroral and auroral regions.