Adaptive numerical algorithms in space weather modeling

Abstract

Space weather describes the various processes in the Sun-Earth system that present danger to human health and technology. The goal of space weather forecasting is to provide an opportunity to mitigate these negative effects. Physics-based space weather modeling is characterized by disparate temporal and spatial scales as well as by di fferent physics in different domains. A multi-physics system can be modeled by a software framework comprising of several components. Each component corresponds to a physics domain, and each component is represented by one or more numerical models. The publicly available Space Weather Modeling Framework (SWMF) can execute and couple together several components distributed over a parallel machine in a flexible and e fficient manner. The framework also allows resolving disparate spatial and temporal scales with independent spatial and temporal discretizations in the various models. Several of the computationally most expensive domains of the framework are modeled by the Block-Adaptive Tree Solarwind Roe Upwind Scheme (BATS-R-US) code that can solve various forms of the magnetohydrodynamics (MHD) equations, including Hall, semi-relativistic, multi-species and multi-fluid MHD, anisotropic pressure, radiative transport and heat conduction. Modeling disparate scales within BATS-R-US is achieved by a blockadaptive mesh both in Cartesian and generalized coordinates. Most recently we have created a new core for BATS-R-US: the Block-Adaptive Tree Library (BATL) that provides a general toolkit for creating, load balancing and message passing in a 1, 2 or 3 dimensional blockadaptive grid. We describe the algorithms of BATL and demonstrate its e fficiency and scaling properties for various problems. BATS-R-US uses several time-integration schemes to address multiple time-scales: explicit time stepping with fixed or local time steps, partially steady-state evolution, point-implicit, semi-implicit, explicit/implicit, and fully implicit numerical schemes. Depending on the application, we find that di fferent time stepping methods are optimal. Several of the time integration schemes exploit the block-based granularity of the grid structure. The framework and the adaptive algorithms enable physics based space weather modeling and even forecasting.https://ntrs.nasa.gov/search.jsp?R=20110005631 2018-05-12T08:50:45+00:00Z

Comparison of 3D kinetic and hydrodynamic models to ROSINA-COPS measurements of the neutral coma of 67P/Churyumov-Gerasimenko

“…The hydrodynamic model is based on the BATS-R-US code (Powell et al 1999;Tóth et al 2012) that solves the Euler equations on a 3D block adaptive Cartesian grid. The molecular mass is M = 18 Da for the dominant H 2 O molecules, and the adiabatic index is γ = 4/3.…”

Constraining the pickup ion abundance and temperature through the multifluid reconstruction of the Voyager 2 termination shock crossing

“…We adapted the multifluid BATS-R-US MHD code [Tóth et al, 2012] for local shock tube simulations of the termination shock, where thermal solar wind ions, pickup ions, and electrons are treated as three separate fluids. Neutrals are not included in this model, because the charge exchange mean free path of neutrals (~50-100 AU) is much larger than the length scale of the termination shock.…”

“…These models do not yield a self-consistent description of the pickup ions; therefore, additional assumptions are needed to link the upstream pickup ion pressure with the downstream pickup ion pressure across the termination shock [Zank et al, 1996[Zank et al, , 2010Fahr and Chalov, 2008]. The truly self-consistent treatment of the thermodynamics of each ion species and electrons is implemented in multi-ion multifluid MHD models [Harnett and Winglee, 2006;Glocer et al, 2009;Najib et al, 2011;Tóth et al, 2012]. These models solve separate continuity, momentum, and energy equations for each ion species.…”

“…We adapted the multifluid Block-Adaptive-Tree Solar Wind Roe-Type Upwind Scheme (BATS-R-US) MHD code [Tóth et al, 2012] for local shock tube simulations of the termination shock, where thermal solar wind ions, pickup ions, and electrons are treated as separate fluids. This multifluid shock tube model is applied for the detailed reconstruction of the Voyager 2 termination shock crossing in order to pin down the unknown pickup ion parameters.…”

Adaptive kinetic-fluid solvers for heterogeneous computing architectures

“…Multi-scale kinetic-fluid models are being developed to enable using kinetic and fluid solvers in different parts of systems to achieve maximum fidelity and efficiency. 5,6,7,8,9,10 Adaptive kinetic-fluid models apply different solvers in dynamically selected regions of physical or phase space for efficient description of multi-scale phenomena in complex systems. Appropriate solvers are selected using sensors locally detecting phase space regions where kinetic approach is required and apply fluid models in other parts of the system.…”