Magnetic Carpet on the Sun

Overview

Solar variability is a leading factor in determining space weather, which has a great impact on Earth's environment. Increased understanding and realistic modeling of the Sun in different states of activity are critical for accurately predicting large space weather events. Observations from NASA's space- and ground-based telescopes have revealed ubiquitous, small-scale magnetic fields carpeting the entire surface of the Sun. The fields are observed as “salt and pepper” on magnetograms, displaying fascinating patterns in the Sun's “magnetic carpet.” These magnetic fields are an important ingredient of solar magnetoconvection turbulence. The origin of magnetic fields on the Sun is explained as a dynamo process, in which highly turbulent hot plasma flows stretch, twist, and fold magnetic field lines and greatly amplify the field strength.

Project Details

Our simulation domain includes the upper convective layer of the Sun, photosphere, and chromosphere. The mathematical model used is based on first physical principles. It employs state-of-the-art models of Large-Eddy Simulations (LES) of magnetohydrodynamic (MHD) turbulence, as well as the capability to perform multi-group modeling of radiation transfer. The simulations utilize the parallel SolarBox code developed at NASA Ames Research Center.

Results and Impact

The realistic simulations of the solar interior and atmosphere reproduce and explain the small-scale dynamo process on the Sun, and help us understand the problem of magnetic field generation, the effects of back-reaction of magnetic patches on surrounding flows, the formation and evolution of the “magnetic carpet,” and its energetic and dynamical links with the turbulent environment of the solar surface and atmosphere. Likewise, realistic computer models of the structure and dynamics of the small-scale magnetic fields allow us to better understand the dramatic changes of near-surface magnetoconvection during the processes of magnetic flux emergence and mass eruptions. We also use this knowledge to interpret data from NASA's Solar Dynamics Observatory, Hinode, and IRIS missions.

Our simulations clearly demonstrate:

• The small-scale dynamo process on the Sun is turbulent in nature.
• The local dynamo process has the strongest efficiency in subsurface layers of the convective zone, just beneath the visible surface.
• Small-scale dynamo action results in the amplification of magnetic fields from an extremely weak initial strength of
  10^-2 – 10^-6 Gauss to stronger than 1,000 Gauss.
• Realistic modeling of the magnetic carpet's small-scale dynamics allows us to better understand the dramatic changes of the near-surface magnetoconvection, associated with solar eruptions.

Role of High-End Computing Resources

The 3D, radiative MHD numerical simulations require massive computational resources. These simulations were accomplished using the Pleiades supercomputer at the NASA Advanced Supercomputing (NAS) facility, which delivered highly efficient performance running SolarBox on 4,000 - 8,000 processors. NAS experts provided 3D visualization support, which greatly contributed to the success of this project.