The project will investigate the turbulent generation of the fast solar wind by using an existing numerical model that solves the coupled quasilinear equations of proton diffusion and resonant wave growth. During this project, the Principal Investigator (PI) will progressively add more physical processes to the numerical model and finally compare the simulation output with observations. At each step, the team will explore the consequences of expanding their model on the heating and acceleration of coronal hole protons and minor ions. The PI asserts that these investigations will lead to more detailed kinetic models of the generation of the solar wind in the corona, enabling improved understanding and predictions of the state of the heliospheric environment. This work will also provide new insights into self-consistent plasma kinetics and the dissipation of plasma turbulence.
Specifically, the team will add nonlinear wave effects, such as resonance broadening and turbulent transport, to their simulations in order to yield realistic Alfvén wave growth in the solar wind. They will also incorporate such nonlinear calculations into their inhomogeneous coronal hole model. The team plans to construct a detailed kinetic model for the radial evolution of coronal hole protons as heated by imbalanced wave fields, obtaining predictions for the kinetic particle and wave states. The PI will also compare his model's output with actual coronal hole observations taken by existing spacecraft instruments.
The modeling effort will yield predictions of particle and wave fluxes that will guide the development of, and be tested by, future NASA spacecraft missions, such as 'Solar Orbiter' and 'Solar Probe Plus.' The tasks will be performed within the theoretical turbulence and reconnection group at the University of New Hampshire, which will provide opportunities for graduate students and postdoctoral researchers to participate in this project.
The solar wind is the continuous supersonic stream of charged particles which flows away from the Sun in all directions and fills the space between the planets. This wind is the medium which carries all the phenomena of "space weather", determining how and when magnetic storms will occur at Earth and the other planets, as well as affecting the radiation levels at any spacecraft sent above the Earth's atmosphere. This wind results from the observed strong particle heating in the solar atmosphere, but the detailed processes which cause this heating are still not known. We have developed a computational model describing the particle behavior in the low solar atmosphere under conditions of heating by a resonant interaction with ion-cyclotron waves. The waves are taken as a by-product of the well-accepted turbulent cascade of fluctuations emanating from the Sun, and we have shown that only about 1% of the total turbulent power is needed in these resonant modes to generate the solar wind. Our analysis also predicts the shape of the proton velocity distribution that is expected from the combination of this heating with the large-scale forces (such as gravity) acting on the plasma as it streams from the Sun. As this gas of charged particles flows away with increasing average speed, we find that the protons which flow faster than the average become much hotter than those flowing slower than the average. This difference should be a distinct characteristic of the wind close to the Sun, and this expectation will inform the design of the particle instruments being built for the upcoming Solar Probe Plus mission.
