Block Adaptive Tree Solar Wind Research Articles

A 3D MHD‐Particle Tracing Model of Na+ Energization on Mercury's Dayside

AbstractData collected by the Fast Imaging Plasma Spectrometer (FIPS) aboard the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft showed singly charged Na+‐group ions at energies of between 1 and 13 keV in Mercury's northern planetary cusp. Most of these ions are likely formed by either photoionization or charge exchange of exospheric Na atoms, with initial energies of approximately 1 eV or less. FIPS observations did not establish which acceleration mechanism most reasonably accounts for this energy gain. Using the Adaptive Mesh Particle Simulator (AMPS) model, we undertake kinetic simulations of 1 eV Na+ test particles through the electric and magnetic fields output from the Block Adaptive Tree Solar wind Roe‐type Upwind Scheme (BATSRUS) global magnetohydrodynamic (MHD) model of Mercury's magnetosphere, in search of plausible explanations for the source of this energization. We find that Na+ with initial energy of 1 eV are readily picked up by the Dungey cycle return flow in the dayside magnetosphere. In some cases, this flow provides the energy for the ions to escape into the magnetosheath, and in other cases it energizes the ions to hundreds of eV before they pass immediately into the cusp. Those that escape can be rapidly picked up into the magnetosheath flow, where they are accelerated by pickup again up to tens of keV. These one‐ and two‐stage pickup processes on Mercury's dayside can account for the energies of many of the Na+ ions observed in Mercury's northern magnetospheric cusp by MESSENGER.

Efficient OpenMP parallelization to a complex MPI parallel magnetohydrodynamics code

The state-of-the-art finite volume/difference magnetohydrodynamics (MHD) code Block Adaptive Tree Solarwind Roe Upwind Scheme (BATS-R-US) was originally designed with pure MPI parallelization. The maximum problem size achievable was limited by the storage requirements of the block tree structure. To mitigate this limitation, we have added multi-threaded OpenMP parallelization to the previous pure MPI implementation. We opted to use a coarse-grained approach by making the loops over grid blocks multi-threaded and have succeeded in making BATS-R-US an efficient hybrid parallel code with modest changes in the source code while preserving the performance. Good weak scalings up to hundreds of thousands of cores were achieved both for explicit and implicit time stepping schemes. This parallelization strategy greatly extended the possible simulation scale from 16,000 cores to more than 500,000 cores with 2GB/core memory on the Blue Waters supercomputer. Our work also revealed significant performance issues for some of the compilers when the code is compiled with the OpenMP library, probably related to the less efficient optimization of a complex multi-threaded region.

Steady State Characteristics of the Terrestrial Geopauses

AbstractThe boundary separating solar wind plasma from ionospheric plasma is typically thought to be the magnetopause. A generalization of the magnetopause concept called the geopause was developed by Moore and Delcourt (1995, https://doi.org/10.1029/95RG00872). The geopause is a surface defined where solar wind quantities equal the ionospheric quantities. Geopause studies have helped characterize magnetospheric systems. However, comparative studies between the geopauses to the magnetopause have not been conducted. In this paper, we analyze the influence of inner boundary composition and interplanetary magnetic field (IMF) orientation on the steady state terrestrial geopauses and the magnetopause. This study simulates the Earth's magnetosphere by using the multifluid capabilities of the Block Adaptive Tree Solar wind Roe‐type Upwind Scheme magnetohydrodynamics model within the Space Weather Modeling Framework. The simulations show that the dayside magnetopause was not influenced by the presence of oxygen in the outflow for both IMF orientations and was larger than the other geopauses. In contrast, the nightside magnetopause was sensitive to the conditions in the outflow. The nightside magnetopause was smaller than the other geopauses with southward IMF. With northward IMF, the nightside magnetopause was the largest structure in comparison with the plasma‐based geopauses. Our results indicate that no single boundary surface dictates the transition from a solar wind dominated plasma to ionosphere dominated plasma.

Response of the Geospace System to the Solar Wind Dynamic Pressure Decrease on 11 June 2017: Numerical Models and Observations

AbstractOn 11 June 2017, a sudden solar wind dynamic pressure decrease occurred at 1437 UT according to the OMNI solar wind data. The solar wind velocity did not change significantly, while the density dropped from 42 to 10 cm−3 in a minute. The interplanetary magnetic field BZ was weakly northward during the event, while the BY changed from positive to negative. Using the University of Michigan Block Adaptive Tree Solarwind Roe Upwind Scheme global magnetohydrodynamic code, the global responses to the decrease in the solar wind dynamic pressure were studied. The simulation revealed that the magnetospheric expansion consisted of two phases similar to the responses during magnetospheric compression, namely, a negative preliminary impulse and a negative main impulse phase. The simulated plasma flow and magnetic fields reasonably reproduced the Time History of Events and Macroscale Interactions during Substorms and Magnetospheric Multiscale spacecraft in situ observations. Two separate pairs of dawn‐dusk vortices formed during the expansion of the magnetosphere, leading to two separate pairs of field‐aligned current cells. The effects of the flow and auroral precipitation on the ionosphere‐thermosphere (I‐T) system were investigated using the Global Ionosphere Thermosphere Model driven by simulated ionospheric electrodynamics. The perturbations in the convection electric fields caused enhancements in the ion and electron temperatures. This study shows that, like the well‐studied sudden solar wind pressure increases, sudden pressure decreases can have large impacts in the coupled I‐T system. In addition, the responses of the I‐T system depend on the initial convection flows and field‐aligned current profiles before the solar wind pressure perturbations.

Synthetic Radio Imaging for Quiescent and CME-flare Scenarios

Abstract Radio observations grant access to a wide range of physical processes through different emission mechanisms. These processes range from thermal and quiescent to eruptive phenomena, such as shock waves and particle beams. We present a new synthetic radio imaging tool that calculates and visualizes the bremsstrahlung radio emission. This tool works concurrently with state-of-the-art magnetohydrodynamic simulations of the solar corona using the code Block-Adaptive Tree Solarwind Roe Upwind Scheme (BATS-R-US). Our model produces results that are in good agreement with both high- and low-frequency observations of the solar disk. In this study, a ray-tracing algorithm is used, and the radio intensity is computed along the actual curved ray trajectories. We illustrate the importance of refraction in locating the radio-emitting source by comparison of the radio imaging illustrations when the line of sight is considered instead of the refracted paths. We are planning to incorporate nonthermal radio emission mechanisms in a future version of the radio imaging tool.

Electron Drift Resonance in the MHD‐Coupled Comprehensive Inner Magnetosphere‐Ionosphere Model

AbstractRelativistic electrons in the outer radiation belt are highly dynamic and respond to interplanetary solar wind structures interacting with the Earth's magnetic field. A known mechanism dictating electron dynamics is the drift‐resonant interaction with ultralow frequency (ULF) waves. The present work simulates the ring current and radiation belt electron populations in the bounce‐averaged, kinetic Comprehensive Inner Magnetosphere‐Ionosphere model coupled with the Block Adaptive Tree Solar Wind Roe‐type Upwind Scheme global magnetospheric magnetohydrodynamic (MHD) code using an idealized ULF wave solar wind density driver. ULF waves generated with 10 min periods (at 1.67 mHz frequencies) in the MHD model are characterized and the corresponding energization of electrons and radial transport of electron phase space density is presented. The drift‐resonant electron energy is determined in the simulation and is consistent with the electron resonance conditions in dipolar magnetic fields. The present results will be an important component of understanding inner magnetospheric dynamics and how these inner magnetospheric populations interact with ULF waves resulting from interplanetary solar wind structures.

Spacecraft measurements constraining the spatial extent of a magnetopause reconnection X line

AbstractMultispacecraft measurements from the Time History of Events and Macroscale Interactions during Substorms (THEMIS) mission are used to probe the spatial extent of an X line at the dayside magnetopause. A case study from 21 April 2014 is presented where two THEMIS spacecraft have a near‐simultaneous encounter with the equatorial dayside magnetopause separated by 3.9 Earth radii. Both spacecraft observe similar steady inflow conditions with southward interplanetary magnetic field and a high magnetic shear angle at the magnetopause (133°) boundary. One spacecraft observes clear fluid and kinetic signatures of active magnetic reconnection, while the other spacecraft does not observe reconnection. The predicted location of reconnection across the magnetopause is found using several theoretical models and a Block Adaptive Tree Solarwind Roe‐type Upwind Scheme (BATS‐R‐US) MHD simulation. Each model predicts a continuous X line passing close to the two spacecraft, suggesting both would observe reconnection, if active. Using the constraints of the multipoint measurements, the extent or length L of the reconnection is estimated to be 2.4≤L < 5.2 h in local time or 6≤L< 14 RE.

The two‐way relationship between ionospheric outflow and the ring current

AbstractIt is now well established that the ionosphere, because it acts as a significant source of plasma, plays a critical role in ring current dynamics. However, because the ring current deposits energy into the ionosphere, the inverse may also be true: the ring current can play a critical role in the dynamics of ionospheric outflow. This study uses a set of coupled, first‐principles‐based numerical models to test the dependence of ionospheric outflow on ring current‐driven region 2 field‐aligned currents (FACs). A moderate magnetospheric storm event is modeled with the Space Weather Modeling Framework using a global MHD code (Block Adaptive Tree Solar wind Roe‐type Upwind Scheme, BATS‐R‐US), a polar wind model (Polar Wind Outflow Model), and a bounce‐averaged kinetic ring current model (ring current atmosphere interaction model with self‐consistent magnetic field, RAM‐SCB). Initially, each code is two‐way coupled to all others except for RAM‐SCB, which receives inputs from the other models but is not allowed to feed back pressure into the MHD model. The simulation is repeated with pressure coupling activated, which drives strong pressure gradients and region 2 FACs in BATS‐R‐US. It is found that the region 2 FACs increase heavy ion outflow by up to 6 times over the noncoupled results. The additional outflow further energizes the ring current, establishing an ionosphere‐magnetosphere mass feedback loop. This study further demonstrates that ionospheric outflow is not merely a plasma source for the magnetosphere but an integral part in the nonlinear ionosphere‐magnetosphere‐ring current system.

Comparative analysis of dayside magnetic reconnection models in global magnetosphere simulations

AbstractWe test and compare a number of existing models predicting the location of magnetic reconnection at Earth's dayside magnetopause for various solar wind conditions. We employ robust image processing techniques to determine the locations where each model predicts reconnection to occur. The predictions are then compared to the magnetic separators, the magnetic field lines separating different magnetic topologies. The predictions are tested in distinct high‐resolution simulations with interplanetary magnetic field (IMF) clock angles ranging from 30 to 165° in global magnetohydrodynamic simulations using the three‐dimensional Block Adaptive Tree Solarwind Roe‐type Upwind Scheme code with a uniform resistivity, although the described techniques can be generally applied to any self‐consistent magnetosphere code. Additional simulations are carried out to test location model dependence on IMF strength and dipole tilt. We find that most of the models match large portions of the magnetic separators when the IMF has a southward component, with the models saying reconnection occurs where the local reconnection rate and reconnection outflow speed are maximized performing best. When the IMF has a northward component, none of the models tested faithfully map the entire magnetic separator, but the maximum magnetic shear model is the best at mapping the separator in the cusp region where reconnection has been observed. Predictions for some models with northward IMF orientations improve after accounting for plasma flow shear parallel to the reconnecting components of the magnetic fields. Implications for observations are discussed.

Outflow in global magnetohydrodynamics as a function of a passive inner boundary source

Numerous studies of the terrestrial magnetosphere that use global magnetohydrodynamic codes have found that the model's inner boundary can act as a significant source of plasma, even if the radial velocity about the boundary is held at zero. Though inherent in many models, this “de facto outflow” is poorly understood. This work uses the Block Adaptive Tree Solar Wind Roe‐type Upwind Scheme MHD model to investigate the behavior of this type of outflow as a function of boundary conditions and solar wind drivers. It is found that even for temporally and spatially constant boundary conditions, the mass is accelerated away from the body in a dynamic manner. Fluxes organize into cusp, polar cap, and auroral zone concentrations. Pressure gradient forces appear predominantly responsible for cusp and polar cap outflow, while the Lorentz force, resulting from field‐aligned current systems, is the strongest driver of outflow in other regions. Integrated fluxes probed just outside of the inner boundary vary linearly as a function of cross polar cap potential and solar wind dynamic pressure. The resulting dynamics strongly resemble patterns found in in situ measurements, while net fluences agree within an order of magnitude. Two free parameters, inner boundary mass density and composition, can strongly affect results. Accounting for these unknowns is likely best left to physics‐based or empirical specifications of outflow. Despite this, such outflow appears to be an acceptable proxy.

CRCM + BATS‒R‒US two‒way coupling

We present the coupling methodology and validation of a fully coupled inner and global magnetosphere code using the infrastructure provided by the Space Weather Modeling Framework (SWMF). In this model, the Comprehensive Ring Current Model (CRCM) represents the inner magnetosphere, while the Block‒Adaptive‒Tree Solar‒Wind Roe‒Type Upwind Scheme (BATS‒R‒US) represents the global magnetosphere. The combined model is a global magnetospheric code with a realistic ring current and consistent electric and magnetic fields. The computational performance of the model was improved to surpass real‒time execution by the use of the Message Passing Interface (MPI) to parallelize the CRCM. Initial simulations under steady driving found that the coupled model resulted in a higher pressure in the inner magnetosphere and an inflated closed field‒line region as compared to simulations without inner‒magnetosphere coupling. Our validation effort was split into two studies. The first study examined the ability of the model to reproduce Dst for a range of events from the Geospace Environment Modeling (GEM) Dst Challenge. It also investigated the possibility of a baseline shift and compared two approaches to calculating Dst from the model. We found that the model did a reasonable job predicting Dst and Sym‒H according to our two metrics of prediction efficiency and predicted yield. The second study focused on the specific case of the 22 July 2009 moderate geomagnetic storm. In this study, we directly compare model predictions and observations for Dst, THEMIS energy spectragrams, TWINS ENA images, and GOES 11 and 12 magnetometer data. The model did an adequate job reproducing trends in the data. Moreover, we found that composition can have a large effect on the result.

CRASH: A BLOCK-ADAPTIVE-MESH CODE FOR RADIATIVE SHOCK HYDRODYNAMICS—IMPLEMENTATION AND VERIFICATION

We describe the CRASH (Center for Radiative Shock Hydrodynamics) code, a block adaptive mesh code for multi-material radiation hydrodynamics. The implementation solves the radiation diffusion model with the gray or multigroup method and uses a flux limited diffusion approximation to recover the free-streaming limit. The electrons and ions are allowed to have different temperatures and we include a flux limited electron heat conduction. The radiation hydrodynamic equations are solved in the Eulerian frame by means of a conservative finite volume discretization in either one, two, or three-dimensional slab geometry or in two-dimensional cylindrical symmetry. An operator split method is used to solve these equations in three substeps: (1) solve the hydrodynamic equations with shock-capturing schemes, (2) a linear advection of the radiation in frequency-logarithm space, and (3) an implicit solve of the stiff radiation diffusion, heat conduction, and energy exchange. We present a suite of verification test problems to demonstrate the accuracy and performance of the algorithms. The CRASH code is an extension of the Block-Adaptive Tree Solarwind Roe Upwind Scheme (BATS-R-US) code with this new radiation transfer and heat conduction library and equation-of-state and multigroup opacity solvers. Both CRASH and BATS-R-US are part of the publicly available Space Weather Modeling Framework (SWMF).

Adaptive numerical algorithms in space weather modeling

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 different relevant physics in different domains. A multi-physics system can be modeled by a software framework comprising 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 efficient 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-type Upwind Scheme (BATS-R-US) code that can solve various forms of the magnetohydrodynamic (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 block-adaptive 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 block-adaptive grid. We describe the algorithms of BATL and demonstrate its efficiency 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 different 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 short-term forecasting.

Self‐consistent inner magnetosphere simulation driven by a global MHD model

We present results from a one‐way coupling between the kinetic Ring Current Atmosphere Interactions Model with Self‐Consistent B field (RAM‐SCB) and the Space Weather Modeling Framework (SWMF). RAM‐SCB obtains plasma distribution and magnetic field at model boundaries from the Block Adaptive Tree Solar Wind Roe Upwind Scheme (BATS‐R‐US) magnetohydrodynamics (MHD) model and convection potentials from the Ridley Ionosphere Model within SWMF. We simulate the large geomagnetic storm of 31 August 2005 (minimum SYM‐H of −116 nT). Comparing SWMF output with Los Alamos National Laboratory geostationary satellite data, we find SWMF plasma to be too cold and dense if assumed to consist only of protons; this problem is alleviated if heavier ions are considered. With SWMF inputs, we find that RAM‐SCB reproduces well storm time magnetosphere features: ring current morphology, dusk side peak, pitch angle anisotropy, and total energy. The RAM‐SCB ring current and Dst are stronger than the SWMF ones and reproduce observations much better. The calculated field‐aligned currents (FAC) compare reasonably well with 2 h averaged pictures from Iridium satellite data. As the ring current peak rotates duskward in the storm main phase, the region 2 FACs rotate toward noon, a feature also seen in observations. Finally, the RAM‐SCB magnetic field outperforms both the dipole and the BATS‐R‐US field at Cluster and Polar spacecraft locations. This study shows the importance of a kinetic self‐consistent approach and the sensitive dependence of the storm time inner magnetosphere on plasma sheet conditions and the cross polar cap potential. The study showcases the RAM‐SCB capability as an inner magnetosphere module coupled with a global MHD model.

Exploring sources of magnetospheric plasma using multispecies MHD

A persistent, unresolved problem in terrestrial magnetospheric physics is determining the dominant source and associated entry mechanism for plasma in the Earth's magnetosphere. This study uses the multispecies MHD code, Block Adaptive Tree Solar Wind Roe‐Type Upwind Scheme (BATS‐R‐US), to investigate this issue. Two proton species, ionospheric origin and solar wind origin, are defined in the system and the evolution of each population is followed under different idealized solar wind conditions. It is found that during southward oriented interplanetary magnetic field (IMF), the dominant source is ionospheric plasma entering deep down tail through reconnecting field lines. During northward IMF, the dominant source is solar wind plasma entering through the flanks of the magnetosphere. This two‐mode behavior is tested through data‐model comparisons of real world simulations. Comparisons of model results against Los Alamos National Laboratory Magnetospheric Plasma Analyzer density, pressure, and inferred oxygen content support the conclusions of the idealized results.

Modeling the Sun-to-Earth propagation of a very fast CME

We present a three-dimensional (3-D) numerical ideal magnetohydrodynamics (MHD) model describing the time-dependent propagation of a CME from the solar corona to Earth in just 18 h. The simulations are performed using the BATS-R-US (Block Adaptive Tree Solarwind Roe Upwind Scheme) code. We begin by developing a global steady-state model of the corona that possesses high-latitude coronal holes and a helmet streamer structure with a current sheet at the equator. The Archimedian spiral topology of the interplanetary magnetic field is reproduced along with fast and slow speed solar wind. Within this model system, we drive a CME to erupt by the introduction of a Gibson–Low magnetic flux rope that is embedded in the helmet streamer in an initial state of force imbalance. The flux rope rapidly expands, driving a very fast CME with an initial speed of in excess of 4000 km/s and slowing to a speed of nearly 2000 km/s at Earth. We find our model predicts a thin sheath around the flux rope, passing the earth in only 2 h. Shocked solar wind temperatures at 1 astronomical unit (AU) are in excess of 10 million degrees. Physics based AMR allows us to capture the structure of the CME focused on a particular Sun–Earth line with high spatial resolution given to the bow shock ahead of the flux rope.