Magnetosphere-Ionosphere Coupling During Negative Pressure Pulse and Formation of Ionospheric Overshielding Electric Field

Transient changes in solar wind dynamic pressure, such as positive and negative pressure pulses, can lead to magnetospheric compression or expansion and the formation of global current systems. These current systems, in turn, generate electric fields in the ionosphere, which can propagate to low geomagnetic latitudes. While the effects of positive pressure pulses have been studied relatively extensively, negative pressure pulses are less studied and understood. For this study, we examine in detail the negative pressure pulse event that occurred during the main phase of the recent geomagnetic storm on 22-23 March 2023 with Dst_min = -163 nT. For this event, a strong negative pressure pulse during the main phase imposed significant perturbations to the coupled ionosphere-magnetosphere system, as evidenced by observations from Swarm, AMPERE, and ground-based magnetometers. We use a global 3D MHD model SWMF BATS-R-US coupled to the ionospheric solver to track the chain of effects from solar wind drivers to the ionosphere, interpret multi-s/c observations, and understand the coupling mechanisms. The MMS mission was in the solar wind near the bow shock, which allowed the use of MMS data for the timing analysis. Based on model results and analysis of observations, we relate changes in solar wind drivers to changes in field-aligned currents observed by Swarm and AMPERE. We show that the pressure pulse is related to the formation of an additional pair of field-aligned currents at low geomagnetic latitudes, which creates the overshielding electric field. We relate the overshielding field to the dynamics of Region II currents in both observations and the model and discuss the role of the ring current in this process.