860 research outputs found
Studying dawn-dusk asymmetries of Mercury's magnetotail using MHD-EPIC simulations
MESSENGER has observed a lot of dawn-dusk asymmetries in Mercury's
magnetotail, such as the asymmetries of the cross-tail current sheet thickness
and the occurrence of flux ropes, dipolarization events and energetic electron
injections. In order to obtain a global pictures of Mercury's magnetotail
dynamics and the relationship between these asymmetries, we perform global
simulations with the magnetohydrodynamics with embedded particle-in-cell
(MHD-EPIC) model, where Mercury's magnetotail region is covered by a PIC code.
Our simulations show that the dawnside current sheet is thicker, the plasma
density is larger, and the electron pressure is higher than the duskside. Under
a strong IMF driver, the simulated reconnection sites prefer the dawnside. We
also found the dipolarization events and the planetward electron jets are
moving dawnward while they are moving towards the planet, so that almost all
dipolarization events and high-speed plasma flows concentrate in the dawn
sector. The simulation results are consistent with MESSENGER observations
Multi-GPU Acceleration of the iPIC3D Implicit Particle-in-Cell Code
iPIC3D is a widely used massively parallel Particle-in-Cell code for the
simulation of space plasmas. However, its current implementation does not
support execution on multiple GPUs. In this paper, we describe the porting of
iPIC3D particle mover to GPUs and the optimization steps to increase the
performance and parallel scaling on multiple GPUs. We analyze the strong
scaling of the mover on two GPU clusters and evaluate its performance and
acceleration. The optimized GPU version which uses pinned memory and
asynchronous data prefetching outperform their corresponding CPU versions by
5-10x on two different systems equipped with NVIDIA K80 and V100 GPUs.Comment: Accepted for publication in ICCS 201
Global Ten-Moment Multifluid Simulations of the Solar Wind Interaction with Mercury: From the Planetary Conducting Core to the Dynamic Magnetosphere
For the first time, we explore the tightly coupled interior-magnetosphere
system of Mercury by employing a three-dimensional ten-moment multifluid model.
This novel fluid model incorporates the non-ideal effects including the Hall
effect, inertia, and tensorial pressures that are critical for collisionless
magnetic reconnection; therefore, it is particularly well suited for
investigating magnetic reconnection in Mercury's magnetotail
and at the planet's magnetopause. The model is able to reproduce the observed
magnetic field vectors, field-aligned currents, and cross-tail current sheet
asymmetry (beyond the MHD approach) and the simulation results are in good
agreement with spacecraft observations. We also study the magnetospheric
response of Mercury to a hypothetical extreme event with an enhanced solar wind
dynamic pressure, which demonstrates the significance of induction effects
resulting from the electromagnetically-coupled interior. More interestingly,
plasmoids (or flux ropes) are formed in Mercury's magnetotail during the event,
indicating the highly dynamic nature of Mercury's magnetosphere.Comment: Geophysical Research Letters, in press, 17 pages, 4 (fancy) figure
The flow of plasma in the solar terrestrial environment
The overall goal of our NASA Theory Program is to study the coupling, time delays, and feedback mechanisms between the various regions of the solar-terrestrial system in a self-consistent, quantitative, manner. To accomplish this goal, it will eventually be necessary to have time-dependent macroscopic models of the different regions of the solar-terrestrial system and we are continually working toward this goal. However, our immediate emphasis is on the near-earth plasma environment, including the ionosphere, the plasmasphere, and the polar wind. In this area, we have developed unique global models that allow us to study the coupling between the different regions. These results are highlighted. Another important aspect of our NASA Theory Program concerns the effect that localized structure has on the macroscopic flow in the ionosphere, plasmasphere, thermosphere and polar wind. The localized structure can be created by structured magnetospheric inputs (i.e., structured plasma convection, particle precipitation or Birkeland current patterns) or time variations in these inputs due to storms and substorms. Also, some of the plasma flows that we predict with our macroscopic models may be unstable. Another one of our goals is to examine the stability of our predicted flows. Because time-dependent three-dimensional numerical models of the solar-terrestrial environment generally require extensive computer resources, they are usually based on relatively simple mathematical formulations (i.e., simple MHD or hydrodynamic formulations). Therefore, another long-range goal of our NASA Theory Program is to study the conditions under which various mathematical formulations can be applied to specific solar-terrestrial regions. This may involve a detailed comparison of kinetic, semikinetic, and hydrodynamic predictions for a given polar wind scenario or it may involve the comparison of a small-scale particle-in-cell (PIC) simulation of a plasma expansion event with a similar macroscopic expansion event. The different mathematical formulations have different strengths and weaknesses and a careful comparison of model predictions for similar geophysical situations will provide insight into when the various models can be used with confidence
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