AGS-PRF: A Continuum Kinetic Study of Heliospheric Collisionless Shocks

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Collisionless shocks are ubiquitous in space and astrophysical plasmas, and the heliosphere is no exception. The 2013 National Research Council Decadal Survey for Solar and Space Physics identifies collisionless shocks as a universal process that facilitates the transition from supersonic to subsonic flow, heats the plasma, and accelerates energetic particles. Planetary bow shocks provide a route to converting the supersonic and super-Alfvenic solar wind bulk kinetic energy into other forms of energy: plasma heat, particle acceleration, and electromagnetic energy. The Earth’s bow shock in particular has been a treasure trove of data on the means by which collisionless shocks energize the plasma, with an increased flurry of study in recent years due to the Magnetospheric Multiscale (MMS) Mission. During this 2-year Postdoctoral Research Fellowship (PRF) project, the PI will utilize in-situ data of bow shock crossings from the MMS to study collisionless shocks. Recently developed diagnostics, such as the field-particle correlation, when applied to the distribution function data from MMS, will allow the PI to confirm directly the presence of resonant energization processes in magnetosheath turbulence. He will deploy the field-particle correlation on simulations inspired by recent MMS bow-shock crossings. The PI will determine the energization processes present in these collisionless shocks by utilizing the continuum Vlasov-Maxwell solver developed by him, which provides a much higher fidelity representation of the distribution function compared to traditional particle-based methods. The research work will comprise continuum kinetic simulations, which would provide unprecedented resolution of the particle distribution function, thus allowing careful diagnosis of the kinetic processes present in the collisionless shocks. Using the results of the simulations as a “Rosetta Stone,” the PI will apply the field-particle correlation to the corresponding MMS data, and completely characterize the energetics of the plasma in these bow-shock crossings. During the project, alongside the research investigations, the PI will continue to serve as a steward of science, using his previous outreach and leadership experience. He will volunteer for the Hawkeyes in Space and Science programs at the University of Iowa and participate in the public outreach events organized by the programs. Likewise, he will work with fellow junior scientists in the American Physical Society’s Division of Plasma Physics (APS DPP) to grow and develop new programs aimed at students and early career scientists, such as the Student Day and Dissertation Talks. Despite the large volume of data coming out of space missions like the MMS, and complementary kinetic simulations, our understanding of the evolution of a collisionless shock as a function of Mach number and shock geometry, i.e., the angle between the shock normal and upstream magnetic field, remains incomplete. Kinetic instabilities upstream of the shock launched by reflected particles and wave-particle interactions in the plane perpendicular to the shock significantly complicate the energy transfer. The primary aim of this 2-year PRF project is to leverage cutting edge techniques for numerically integrating the kinetic equation, as well as novel diagnostics, to illuminate the energy conversion mechanisms of a collisionless shock. The project addresses questions of fundamental importance to the Solar-Terrestrial Research program, such as “processes by which energy is generated by the Sun, transported to the Earth, and ultimately deposited in the terrestrial environment.” The research and EPO agenda of this PRF project supports the Strategic Goals of the AGS Division in discovery, learning, diversity, and interdisciplinary research.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.