For Space Plasmas: Sun-to-earth Simulations

are increasingly essential to basic and applied space-physics research for two primary reasons. First, the heliosphere and magnetosphere are vast regions of space from which we have relatively few in situ measurements. Numerical simulations let us “stitch together” observations from different regions and provide data-interpretation insight to help us understand this complex system’s global behavior. Second, models have evolved to where their physical content and numerical robustness, flexibility, and improving ease of use inspire researchers to apply them to intriguing scenarios with new measures of confidence. Indeed, many shortcomings and questions remain for even the most advanced models in terms of inclusion of important physical mechanisms, the spatial and temporal domains they can address, and thorny technical numerical issues to be dispatched. Nonetheless, over the last several years, modeling has crossed a threshold, making the transition from the arcane preserves of specialists to practical tools with widespread applications. Global computational models based on firstprinciples mathematical physics descriptions are essential to understanding the solar system’s plasma phenomena, including the large-scale solar corona, the solar wind’s interaction with planetary magnetospheres, comets, and interstellar medium, and the initiation, structure, and evolution of solar eruptive events. Today, and for the foreseeable future, numerical models based on magnetohydrodynamics (MHD) equations are the only self-consistent mathematical descriptions that can span the enormous distances associated with large-scale space phenomena. Although providing only a relatively low-order approximation to actual plasma behavior, MHD models have successfully simulated many important space-plasma processes and provide a powerful means for significantly advancing process understanding. Space scientists have used global MHD simulations for over 25 years to simulate space plasmas. Early global-scale 3D MHD simulations focused on