Heliophysics Research

Collaborative Space Weather Modeling

Project Participants (BAERI): Irina Kitiashvili, Bob Stein, Thomas Hartlep

Project Description

The goal of Collaborative Space Weather Modelling is to model the emergence of active regions and sunspots through the upper layers of the solar convection zone by numerically solving the magneto-hydrodynamic conservation equations of mass, momentum, energy, and magnetic field.  The results of global solar dynamo calculations are used to impose bottom boundary conditions on the vertical velocity and horizontal magnetic field.  The magnetic field entering the computational domain at the bottom is accelerated upward by buoyancy (due to lower density where the magnetic field is strong) and advected upward by rising convective motions.  These two processes bring the magnetic flux to the solar surface.  Convective motions not only carry the magnetic field toward the solar surface, but also shred the rising magnetic field into thin filaments which emerge as small mixed polarity magnetic bipoles at the surface, while at the same time the large-scale, supergranule, convective motions confine the filament bundles into omega-shaped loops that emerge as the active regions.  Modeling active region emergence process as realistically as possible provides a synthetic data set which can be used to compare with solar observations to develop techniques for predicting the emergence of active regions before they appear at the visible solar surface.  This is one step in the chain of understanding and being able to predict the impact on the Earth of events on the Sun.

Accomplishments

  • Enlarged 96 Mm wide by 20 Mm deep computational domain to 192 Mm wide and began the process of relaxing it to develop larger-scale convective cells near the bottom of the domain. This has run for a time slightly longer than the time for typical surface down flows to reach the bottom of the computational domain;
  • Developed and tested new bottom boundary conditions to incorporate spatially and temporally varying velocity and magnetic field values determined from global dynamo calculations;
  • Investigated a problem near the visible surface that inhibited running the simulation at very low resolution, needed in order to speed up the relaxation in deep levels; and
  • Continued small-scale (48 Mm wide) simulation of magnetic flux emergence, which resulted in merging of smaller magnetic flux concentrations into a small sunspot.  During the merger process, light bridges formed and disappeared and incipient penumbra appeared.

Selected Publications:

“Oscillations and Convection Simulations”, Robert Stein, SCORE16 (Stellar Convection and Oscillations and their Relationship) workshop, Aarhus University, Denmark, October 2016

“Active Region Formation and Subsurface Structure”, Robert Stein, SDO16, Burlington, VT, October 2016

“Sun’s Weather Controls Earth’s Space Weather”, Robert Stein, Supercomputing 2016, Salt Lake City, UT, November 2016

Heliophysics Modeling and Simulation

Project Participants (BAERI): Thomas Hartlep

Project Description

In this project, we study the structure and evolution of the solar interior and surface using numerical simulations.  There are two efforts in this project: One goal is the modeling of the magnetic field on the entire surface of the Sun.  This is challenging because only part of the Sun is visible at any given time. However, knowledge of the entire surface is crucial for space weather modeling and forecasting.  Using observational data and a surface flux transport model, we want to estimate the current state of the solar magnetic field on the entire solar surface and predict its state in the future.  Another effort in this project is aimed at improving our knowledge of the solar interior flows. Signatures of sound waves are visible on the solar surface and allow us to probe the interior similar to earth seismology. Using numerical simulations of wave progation in the solar interior, we aim to improve helioseismic measurement and inversion techniques.

Accomplishments

  • Wrote scripts for retrieving magnetic field data from the Helioseismic and Magnetic Imager (HMI)/Solar Dynamics Observatory (SDO) and prepared it for ingestion into the surface flux transport code;
  • Set-up and performed simulations of wave propagation through localized flow perturbations in the solar interior (ongoing) that are being used to derived numerical sensitivity kernels for flows in the solar interior;
  • Devised code for calculating 2-D sensitivity kernels given measurements of travel times of helioseismic wave in above simulations; and
  • Derived preliminary 2-D kernels for horizontal flows for select distances and single frequency

Selected Publications:

Roth, M.; Doerr, H.-P.; Hartlep, T. 2016. Verification of the helioseismic Fourier-Legendre analysis for meridional flow measurements. Astronomy & Astrophysics, Volume 592, id.A106. doi:10.1051/0004-6361/201526971.

Díaz Alfaro, M.; Pérez Hernández, F.; González Hernández, I.; Hartlep, T. 2016. Seismic Holography of the Solar Interior near the Maximum and Minimum of Solar Activity. Solar Physics, Volume 291, Issue 5, pp.1323-1340. doi: 10.1007/s11207-016-0912-3.

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