Heliophysics Modeling & Simulation Project (HMS)
HMS Research Areas
NASA’s Heliophysics Modeling and Simulation project supports research studies that can be applied to a wide range of interests, from the basic physics of stellar structure and dynamics, to the interaction of stellar activity with space weather and near-Earth environments.
One of the principal research interests of the HMS team is to clarify the physical mechanism of magnetic field production inside the Sun—the solar dynamo—which generates nearly all intense solar surface activity, the solar cycle, and the solar wind. Also of interest are the variety of complex processes that connect activity in the upper layers of the Sun to events in the solar atmosphere.
The team also performs simulations of stars more or less massive than the Sun, and those of differing compositions. Such simulations provide the only currently available means of visualizing events on the surface or in the interior of other stars. They also provide, for example, data on stellar brightness variability in space and time that can enhance stellar modeling work and extra-solar planetary detection efforts.
Stokes Profile Studies
Small-scale structures in the solar photosphere are produced by cellular turbulent convection and magnetic fields. Spacecraft measure the light intensity and circular and linear polarizations (Stokes vector) at different wavelengths.
Stokes profiles are computed by solving the radiative transfer equations for polarized light under the assumption of local thermodynamic equilibrium, thereby determining the vector magnetic field distribution and thermodynamic properties in the photosphere. Comparisons of observed and computed spectral lines are used to validate numerical solutions for the solar atmosphere.
Realistic Solar MHD Modeling
Realistic numerical magnetohydrodynamic (MHD) simulations have led to substantial progress toward quantitative understanding of the Sun, as well as interpretation of new observational data from NASA’s Solar Dynamics Observatory, Hinode, and IRIS missions and from new large, ground-based telescopes. Realistic models have become achievable due to the combined availability of powerful supercomputers, such as Pleiades, and the development of efficient parallel computer codes.
We are modeling the top layer of the convection zone and lower atmosphere of the Sun, which allows us to the study energy exchange between these two areas. To model solar magnetoconvection, we use the Stellarbox code, which solves radiative 3D hydrodynamic and MHD equations in realistic solar conditions, and takes into account all essential physical phenomena: compressible fluid flow in a highly stratified medium, radiative heat transfer between fluid elements, real-gas equation of state, and magnetic effects.
The ab initio simulation approach used to study solar magnetoconvection is extremely important for understanding solar phenomena, including: the complicated physics of the Sun’s turbulent convection zone; generation of magnetic fields at different scales; spontaneous flow eruptions; stochastic excitation of acoustic waves; interactions between turbulence and magnetic fields in different physical and topological conditions; and the phenomenon of magnetic self-organization leading to formation of sunspots and active regions, which are primary sources of solar storms.