Collisionless shocks are ubiquitous in space and astrophysical plasmas, where they often provide one of the most efficient mechanisms for particle heating and acceleration. Furthermore, planetary…

This is a $459,214.00 grant for research awarded by the National Aeronautics and Space Administration's (NASA) Shared Services Center to the Space Science Institute (SSI), a nonprofit research organization based in Boulder, Colorado. The grant, which does not have a set-aside designation, will fund a research project focused on understanding the role of plasma waves and instabilities in collisionless shocks - a ubiquitous phenomenon in space and astrophysical plasmas that can influence particle heating and acceleration, as well as space weather events. The project will combine high-resolution kinetic simulations with spacecraft observations from missions like Wind, THEMIS, and MMS to investigate these critical plasma processes. This research is directly relevant to NASA's strategic objectives in heliophysics, including exploring the physical processes at work in the space environment and advancing the knowledge needed to detect and predict extreme space weather conditions.

Collisionless shocks are ubiquitous in space and astrophysical plasmas, where they often provide one of the most efficient mechanisms for particle heating and acceleration. Furthermore, planetary BOW shocks control the interaction of the solar wind with planetary magnetospheres (notably that of the earth), while the arrival of interplanetary (IP) shocks often triggers significant space weather events, such as geomagnetic storms. IT has long been recognized that in a collisionless plasma, where coulomb binary collisions are too infrequent to control energy dissipation around shocks, plasma waves and instabilities may play a crucial role in providing the energy dissipation necessary for the shock to exist. ION acoustic, lower-hybrid, whistler-branch, and other fast, short-wavelengths fluctuations are routinely observed in spacecraft measurements and have been identified in relevant numerical simulations. Yet, IT remains unclear currently if these fluctuations play an essential role or, alternatively, are a relatively benign accompaniment to the shock which is ultimately controlled by kinetic behavior of individual particles (such as electrostatic and magnetic particle reflection). The goal of the proposed investigation is to address this uncertainty using a combination of high-resolution kinetic simulations and spacecraft observations. Methodology: the center element of the proposed work will be high-resolution (including those with cells size at or below debye length), fully kinetic particle-and-cell (PIC) simulations. The simulations will be predominantly 2D. A small number of 3D targeting specific issues (such as determination of the spectra of excited instabilities) may be conducted as well. The simulations will use initial and boundary conditions corresponding to typical conditions observed at the earth s BOW shock and IP shocks. The properties of the short-wavelength fluctuations and global structure of the shock (e.g. profiles of flow, temperature, particle distributions functions when available) will be compared to spacecraft observations from wind, themis, and MMS. Electric and magnetic field data from both wind, themis, and MMS will be analyzed in combination with particle data from thermal to suprathermal energies. The electromagnetic and electrostatic fluctuations will be identified and then compared to the observed particle distributions looking for evidence of free energy and/or the predicted effect of the waves on the particle distributions. We will compare to simulation results as even with MMS, many of the interactions occur too quickly to directly observe the evolution of the particle distributions. We will determine the initial and final states of the particle distributions from simulations and use that knowledge to quantify the effect of the waves on the distributions in the observations. Relevance of the problem to the heliophysics overarching goal: the proposal is directly relevant to the strategic objective to understand the sun and its interactions with earth and the solar system, including space weather since shocks are widely recognized as a major player in these interactions. The proposal directly addresses all three overarching science goals: i) to explore the physical processes at work in the space environment from the sun to earth and throughout the solar system II) to advance our understanding of the connections between the sun, earth, the planetary space environments, and the outer reaches of our solar system and III) to develop the knowledge and capability to detect and predict extreme conditions in space to protect life and society and to safeguard exploration beyond earth.