Solar Wind Models of Multi-scale Fluid-kinetic Simulation Suite (MS-FLUKSS)

The Earth is embedded in a dynamic environment permeated by particles of both solar and extrasolar origins. Changes in the solar wind conditions can generate disturbances in interplanetary space and contribute to geomagnetic... [ view full abstract ]

The Earth is embedded in a dynamic environment permeated by particles of both solar and extrasolar origins. Changes in the solar wind conditions can generate disturbances in interplanetary space and contribute to geomagnetic storms. Modeling and observations are essential, complementary components of space plasma research that help us identify and understand the physical processes governing the solar wind dynamics on different scales. Magnetic field and/or plasma measurements taken in situ by a fleet of spacecraft (e.g., Advanced Composition Explorer, Helios, New Horizons, Ulysses, Voyager, and Wind) have enlightened us on the temporal (both cyclical and transient) variation of the solar wind throughout interplanetary space. Furthermore, remote sensing observations (e.g., interplanetary scintillation, magnetograms, and white-light images) complement in situ measurements of the solar wind by providing wider spatial coverage, albeit with generally lower temporal resolution and line-of-sight complications. Modeling studies, on the other hand, can help interpret the observed phenomena by providing physical/empirical explanations. Numerical models have greatly improved in recent years with advances in computational infrastructure and by employing data-driven or data-assimilative approaches. Multi-scale Fluid-kinetic Simulation Suite (MS-FLUKSS) is arguably one of the most sophisticated numerical codes designed primarily for modeling the partially ionized plasma throughout and beyond the heliosphere using adaptive mesh refinement technique on Cartesian or spherical grids. While the flow of ions is described by the magnetohydrodynamics (MHD) equations, neutral particles can be treated either hydrodynamically by solving the Euler equations or kinetically by solving the Boltzmann equation. Pickup ions resulting from the charge exchange between the solar wind and interstellar neutral atoms can be either approximated as a single, isotopic mixture with the solar wind or treated as a separate fluid. In addition to the aforementioned MHD, Euler, kinetic-Boltzmann, and pickup ion modules, MS-FLUKSS includes turbulence modules that take into account heating of the core solar wind when pickup ions are specified separately. While MS-FLUKSS has been principally used to model the solar wind outflow from above the coronal region to the heliospheric boundary with the local interstellar medium and validated against various spacecraft data, data-driven coronal MHD models are also currently in development to enable simulation of the plasma flow from the solar surface. As a courtesy to potential users and interested members of the space community, we provide a general description of MS-FLUKSS and a comprehensive history of the solar wind models developed in its framework, with an emphasis on heliospheric models driven by spacecraft data or coupled with external coronal/heliospheric models. We also discuss potential scientific and operational applications of MS-FLUKSS on prediction of space weather events.