04/03/2024
By Lynne Schaufenbil
"Heavy Ions in Earth’s Magnetosphere: Where Are They From?" by Mei-Yun Lin.
Abstract:
The presence of heavy ions in Earth’s magnetosphere alters the mass loading of the plasma, affects wave generation and propagation, and impacts the formation and transport of other energetic ion populations. Identifying the processes responsible for particle energization is one of the open questions in Heliophysics research, whether it pertains to coronal heating, the pickup ion process, ionospheric outflow, or magnetospheric transport. Furthermore, it holds the key to understanding the response of the Earth’s terrestrial environment to solar wind driving. The discovery of magnetospheric heavy ions in the 1970s has led to widespread belief that low-charge state heavy ions in Earth’s magnetosphere must originate from the ionosphere. However, this could not be the case for all species. This talk compares the production and transport of molecular N2+, NO+, and O2+ with metallic Mg+ and Fe+ in Earth’s magnetosphere. While molecular ions are mainly produced from the ionospheric chemistry in the low-altitude region, metallic ions in the ionosphere are mostly deposited from the ablation of meteoroids. In addition to their ionospheric origin, metallic ions can be created from the ionization of the lunar exosphere and become a common species in the lunar pickup ions. Different strategies are developed to evaluate the upper-limit contributions of heavy ions from the ionosphere and the Moon across different solar and geomagnetic conditions. The Polar Wind Outflow Model (PWOM), a physics-based model solving the transport of ionospheric outflow, is adopted to estimate the ionospheric contribution. On the other hand, in-situ THEMIS-ARTEMIS observations of ion and electron fluxes are utilized to properly calculate the ionization rates of the lunar-origin ions when the Moon passes through the upstream solar wind, magnetosheath, and magnetotail. Due to the limited supply of heavy ions from the ionosphere, the abundance, and fluxes are regulated by the timescale of production and loss at lower altitudes as well as the composition of the ionospheric plasma. Therefore, the preliminary results suggest that metallic ions observed in the near-Earth environment are more likely from the Moon, and their abundances are highly associated with the geomagnetic activities and the locations of the Moon in the magnetosphere.
Bio:
Mei-Yun Lin is the NASA Jack Eddy Postdoc at Space Sciences Lab, University of California, Berkeley. She received her Ph.D. and M.S. degree from the Department of Electrical and Computer Engineering at the University of Illinois at Urbana-Champaign. Her primary research focus is understanding the underlying physics responsible for heavy ion outflow, through a combination of numerical modeling and data analysis. She was awarded the NASA Jack Eddy Postdoc Fellowship in 2023 and the NASA FINESST fellowship in 2021. Her works had also been recognized by the American Geophysical Union where she was awarded the Outstanding Student Presentation Award in both 2019 and 2020. Other than research, Lin is heavily involved in the scientific community, as she was elected and served as the Student Representative of the NSF Geospace Environment Modeling Program from 2020 to 2022 and the chair of the AGU SPA Student Leadership Advisory Committee in 2023.
If you would like to attend the seminar, please contact Lynne_Schaufenbil@uml.edu for the Zoom link.