Solar Chromospheric Plasma Turbulence and Heating Driven by Neutral-Plasma Coupling

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Most of the light reaching Earth originates at the "surface" of the sun, a region called the photosphere. The regions immediately above this surface, the solar chromosphere and corona, create most of the dangerous Ultraviolet (UV) and X-ray radiation. These regions also generate the solar wind, a stream of charged particles, a plasma, that reach the Earth at speeds in excess of 400km/s. Both the rapidly changing radiation and the solar wind create space weather that results in hazards for spacecraft, astronauts, and also have a number of important impacts on Earth by inducing current surges and disrupting communication. A long-standing mystery has prevented scientists from understanding and accurately modeling the solar atmosphere: a short distance above the photosphere, the chromosphere's temperature jumps up by almost a factor of two, providing some of the energy that creates the even hotter corona and solar wind. This project will investigate previously unexplored physical processes in the solar chromosphere and develop a more complete physics-based explanation of the origin of the heating. This project will examine whether neutral solar fluid flows, emerging from the photosphere, can transfer sufficient energy into plasma turbulence to heat the chromosphere in order to account for the observed UV spectra. This requires five linked research tasks: (1) solving for plasma drifts and fields when a convecting neutral gas pushes it across magnetic field lines; (2) analyzing the theory of streaming instabilities applicable to the collisional plasma found there; (3) performing a series of kinetic simulations to explore the nonlinear and thermal properties of the resulting turbulence; (4) incorporating the resulting electron heating into a radiative transport code in order to evaluate its impact on chromospheric radiance; and (5) comparing the resulting predictions with observations. This grant will provide opportunities to recruit and train student researchers in plasma and solar physics, simulations, and modeling. This research, the sophisticated simulators, and these students will have an impact far beyond the duration of this grant.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.