Collaborative Research: Heating the Solar Chromosphere Through Plasma Turbulence

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The goal of this project is to provide a detailed verifiable explanation of the origin of the heating of the solar atmosphere. Most of the light reaching Earth originates at the 'surface' of the sun, a region called the photosphere. However, the regions of the solar atmosphere 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 that pass the Earth at speeds in excess of 400km/s. Both the rapidly changing radiation and the solar wind create hazards for spacecraft, astronauts, and have a number of important terrestrial impacts. A long-standing mystery has prevented scientists from understanding and accurately modeling the chromosphere and corona. A short distance above the 'surface' of the sun, the solar atmosphere's temperature jumps up by a factor of two to three. The goal of this project is to provide an explanation of the origin of this heating. The project will also provide opportunities to recruit and train student researchers in plasma and solar physics, simulations, and modeling at the Boston University. Many of the Boston University PI's undergraduate research advisees, about half of whom are women, have continued on to graduate school. This research will examine whether solar plasma flows emerging from the photosphere can transfer sufficient energy into turbulent plasma of the solar atmosphere, which, in turn, will heat the chromosphere sufficiently to explain whether the observed UV spectra originate there. It will also evaluate whether this mechanism can account for chromospheric spectral observations. This requires four 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; and (4) incorporating the resulting electron heating into a radiative transport code in order to evaluate its impact on chromospheric radiance. This research combines several research areas encompassed by the NSF/DOE Partnership in Basic Science and Engineering.