Validation of Landau-Fluid Closures for Kinetic-Scale Plasma Turbulence: A Comparison with Fully Kinetic Simulations

Understanding energy cascades across multiple scales remains challenging in magnetospheric physics, where processes span from large fluid scales down to kinetic scales. Two-fluid simulations employing local Landau-fluid closures offer a computationally efficient alternative to kinetic simulations for modeling the multiscale plasma dynamics. These closures, derived from linear kinetic theory, approximate kinetic effects while maintaining the computational advantages of fluid descriptions. However, their theoretical validity requires the plasma to remain close to local thermodynamic equilibrium (LTE), a condition frequently violated in magnetospheric phenomena such as turbulence in the magnetosheath and reconnection outflows.

We investigate the performance of two-fluid Landau-fluid models in regimes far from LTE through comparison against benchmark Vlasov simulations. Our results demonstrate that despite operating outside their formal regime of applicability, Landau-fluid closures can accurately reproduce kinetic-scale physics (with some limitations that we will highlight) when the local closure parameter is appropriately chosen. The agreement of energy spectra extends across the kinetic range, capturing the essential energy cascade and dissipation mechanisms.

These findings validate Landau-fluid approaches as a robust tool for large-scale magnetospheric simulations where computational constraints prohibit kinetic treatments. This is particularly relevant for interpreting multiscale observations and resolve scale coupling in key magnetospheric regions.