This Principal Investigator (PI) will use computational methods to address the problem of imbalanced magnetohydrodynamic (MHD) turbulence in the solar wind, particularly near the Sun. The PI's team will develop a new computer code to solve the 'reduced MHD' (RMHD) equations for incompressible turbulence, taking account of the inhomogeneous density and background flow characteristics of the solar wind. These fundamental equations will be solved under a variety of conditions and the solutions will be used to examine plasma density effects and the heating of test-particle ions propagating within the computed electromagnetic fields. The PI's approach is novel because of its inclusion of reflected waves in his turbulence model. His numerical results will be used to test several existing theories of turbulence and to revise these theories as needed to account for wave reflection.

Based on this work, the PI will deliver targeted lectures in plasma physics short courses developed for graduate students, postdoctoral researchers, and advanced undergraduate students. By providing these young scientists with specialized training and exposure to ongoing research developments, these short courses will promote the integration of research and education. The PI is also a Working Group Leader in the Solar, Heliospheric, and Interplanetary Environment (SHINE) research community, as well as a member of the SHINE Steering Committee. In this capacity, the PI will actively contribute to organizing the annual SHINE Workshop, which provides student participants with special tutorial sessions and opportunities to present their own research. By placing a high priority on student involvement, the SHINE Workshop has been an effective means of integrating research and education.

Project Report

The solar wind is a quasi-steady outflow of particles from the Sun. These particles pervade interplanetary space and provide the backdrop for many of the important physical processes that occur in the interplanetary medium. For example, shock waves in the interplanetary medium can accelerate particles to very high energies. When such high-energy particles reach Earth, they pose a direct hazard to astronauts and cause secondary effects that can damage satellites and electrical power grids on the ground. The origin of the solar wind is a longstanding problem. One of the leading theories is that the solar wind is heated and accelerated by a type of wave that is launched by the Sun --- the Alfven wave. Alfven waves differ from electromagnetic waves such as radio waves, microwaves, and visible light. Such electromagnetic waves can propagate in a vacuum. In contrast, the Alfven wave only propagates in plasmas, which are gases whose temperatures are so high that electrons are stripped out of the atoms that normally hold them, leading to an admixture of positively charged ions and negatively charged free electrons. The goal of this project was to understand the evolution of Alfven waves that are launched from the Sun and gain further insights into the hypothesis that such waves generate the solar wind. Our approach was to develop a computer code that can simulate the propagation and reflection of Alfven waves that are launched by the Sun into the plasma that surrounds the Sun. This computer code can also simulate the development of Alfven wave turbulence. In particular, after some of the Alfven waves launched by the Sun are reflected back towards the Sun, interactions between counter-propagating waves lead to turbulence (random, broad-band fluctuations in the magnetic field, electric field, and average plasma velocity). This turbulence may play an important role in heating the solar wind, because it transfers energy from large-wavelength Alfven waves to small-wavelength Alfven waves, which then dissipate. We successfully developed and tested this new computer code, and have carried out a large series of numerical simulations of Alfven wave turbulence near the Sun. Our code is the first code that can simulate Alfven-wave propagation, reflection, and turbulence taking into account the inhomogeneities in the velocity, magnetic field, and density of the background plasma without approximating the nonlinear terms in the governing equations. Our simulations extend from the solar surface out to a distance of over ten solar radii from the Sun, covering the range of radii in which most of the heating and acceleration of the solar wind take place. Our work has led to new insights into the nature of reflection-driven Alfven-wave turbulence and its possible role in the solar wind's origin and will help lead to more accurate modeling of the solar wind in the future.

Agency
National Science Foundation (NSF)
Institute
Division of Atmospheric and Geospace Sciences (AGS)
Application #
1003451
Program Officer
Ilia Roussev
Project Start
Project End
Budget Start
2010-07-01
Budget End
2013-06-30
Support Year
Fiscal Year
2010
Total Cost
$466,005
Indirect Cost
Name
University of New Hampshire
Department
Type
DUNS #
City
Durham
State
NH
Country
United States
Zip Code
03824