Mei-Yun Lin

Title: Do “hidden heavy ions” play an important role in the polar wind study?

Abstract: The source of magnetospheric H+ are both the solar wind the ionosphere, while the low charge state heavy ions, including N+, O+, N2+, NO+ and O2+, can only come from the ionosphere. Albeit limited, several observations show the importance of ionospheric N+ and molecular ions, including NO+, N2+ and O2+, in the high-altitude ionosphere and magnetosphere, opening up the question of the composition of ion outflow. However, the mechanisms responsible for accelerating the ionospheric heavy ions from eV to keV energies are still largely unknown. The abundances of these “hidden heavy ions” and how they change the polar wind solution help understand the energization of these cold ions and reveal the link between lower thermosphere and the ionosphere. Developed from the Polar Wind Outflow Model (PWOM), the Seven Ion Polar Wind Outflow Model (7iPWOM) solves the gyrotropic transport equations for all the relevant ion species (e-, H+, He+, N+, O+, N2+, NO+ and O2+) along open magnetic field lines. However, such a hydrodynamic approach is limited to the region where collisions are important. For the altitudes above the collision-dominated region, the hydrodynamic solution becomes increasingly inadequate, and thus, the 7iPWOM applies a kinetic particle-in-cell (PIC) solution that enables the inclusion of wave-particle interactions (WPI) and Coulomb collision. Preliminary simulations using the 7iPWOM suggest that the N+ ions play a key role in the polar wind solution under all conditions both in the hydrodynamic and kinetic solutions. On the other hand, the difference of the ion density altitude profile of N+ and O+implies the impacts of mechanisms responsible for energization of N+ in the polar wind are different from it of O+, not only in the collision-dominated region but also in the high-altitude region. This means that the local heating sources to O+and N+ in the polar wind, even small amount of it, can induce the plasma instability and then possibly affect the large-scale transport properties. Overall, the inclusion of the hidden heavy ions, including N+ and molecular ions, lead to the improvement of the polar wind solution, strongly suggesting the necessary to consider these “hidden heavy ions” for future ionospheric outflow studies.

Bio: Mei-Yun is a Ph.D. candidate in HeRA group within the Department of Electrical and Computer Engineering in University of Illinois at Urbana-Champaign, advised by Prof. Raluca Ilie. Her primary research focus is understanding the acceleration mechanisms responsible for ionospheric outflow, and its impacts on the magnetospheric dynamics.

 Before coming to the United State for graduate school, Mei-Yun obtained the bachelor’s degree in the Department of Electrical Engineering from the National Taiwan Universit, in Taiwan, where she is originally from. She joined the group with almost zero knowledge about the Space Science. However, through her rigorous training at UIUC she quickly developed the skills to become an expert in modeling the ionospheric outflow. Mei-Yun’s woks has been recognized by the American Geophysical Union, where she was awarded the Outstanding Student Presentation Award in 2019. In 2020, Mei-Yun has been elected as the Student Representative of the NSF Geospace Environment Modeling Program, where she will serve for the next two years.