Atomic and Molecular Nitrogen Ions at the Dayside Magnetopause During the 2024 Mother's Day Storm

Ion measurements made with the Hot Plasma Composition Analyzers of the Magnetospheric Multiscale Mission (MMS-HPCAs) during the Mother's Day Storm (Gannon Storm) of 10-13 May 2024 yield the first observations of atomic and molecular nitrogen ions in the Earth's dayside outer magnetosphere. A population of ions identified as doubly charged nitrogen and oxygen was also measured. These observations were made within a highly compressed magnetosphere at a geocentric distance of ~6 Earth Radii during the early recovery phase of the storm. From the ion composition measurements and accompanying magnetic field data, we determine the reconnection rate at the magnetopause; we compare this result to a model reconnection rate that assumes the presence of only atomic oxygen and hydrogen. The heavy ion-laden-mass density in the magnetosphere was greater than the shocked solar wind mass density in the magnetosheath. Despite these conditions, magnetic reconnection still occurred at the magnetopause.