Impact of Ionospheric Density Structures on Ion Upflow Flux during the April 2023 Geomagnetic Storm

We study the impact of evolving ionospheric high-density structures (e.g., storm enhanced density, SED plumes) on upward ion fluxes during the CME-driven geomagnetic storm of April 23-24, 2023. During this period, there are two significant southward turnings of the IMF Bz component after the storm start, which are also associated with two dips in the SYM-H index. The first of these reaches a minimum SYM-H of ~ -175 nT while the second reaches ~ -225 nT. With regards to the ionospheric density, we focus on answering two overarching questions:
1) How do ionospheric high-density structures evolve during the various storm phases?
2) How does the presence of these structures affect ion upflow events and upflow flux?
During the ionospheric positive storm phase, we see the SED forming in mid-latitude regions as well as the associated plumes extending into the polar cap in the afternoon sector. When these plumes encounter fast vertical flows, particularly over the open-closed field line boundary, we see large upward fluxes peaking at 2 x 10^14 m^-2 s^-1 . The negative storm phase first becomes
apparent in the morning sector then later has an impact in the afternoon and evening sectors. In general, during the negative phase, we see much reduced TEC in the SED and plume structures. As a result, the upward fluxes are also reduced in magnitude.