The principal investigator (PI) plans to investigate the detailed physics of the radio emission from solar Type II and Type III radio bursts. He hopes to advance the basic understanding of nonlinear plasma behavior by solving the complete set of electromagnetic weak turbulence kinetic equations for electrons, ions, Langmuir turbulence, ion-acoustic turbulence, and electromagnetic transverse radiation. Since such a complete solution has never before been obtained, the PI asserts that such a result will lead to fundamental breakthroughs in nonlinear plasma physics. The PI plans to study the time scale of the plasma emission, the intensities for fundamental and harmonic emissions, and the radiation beaming patterns for fundamental and harmonic emissions. He will focus on determining which of the two competing processes for fundamental emission (decay or scattering) is dominant.
Since Type II bursts can provide a view of coronal mass ejections (CMEs) that complements the traditional coronagraph, and Type III bursts are often associated with the CME lift-off, these two classes of solar radio emission are important for the space weather research. Both emission signatures can serve as early warnings for CMEs and also as diagnostic tools for space weather forecasts. The PI also states that the results of this project will aid space weather modelers and observers. This activity will provide for the education and training of a graduate student and promote international scientific collaboration with researcher collaborators in Brazil.
" involved a theoretical investigation of the radio waves emanating from the Sun. In order to study how the radio waves are generated on the surface of the Sun and the upper atmosphere of the Sun known as the Solar Corona, one must study how the energetic electrons interact with the radio waves and another type of electromagnetic wave called the Langmuir waves. The theory that describes how the radio waves are generated starts from the phenomena known as the solar flares. The solar flares are impulsive events that take place at the Sunspot. During such events energetic electrons are injected out into the solar atmosphere. These electrons travel otuward, and as they travel through the outer solar atmosphere, they excite the above-mentioned electromagnetic waves called the Langmuir waves. Complicated physical processes that involve interactions of the Langmuir waves with the electrons eventually lead to the radio waves. These radio waves can be detected from the Earth. The Principal Investigator of the project, P. H. Yoon, developed a sophisticated theory that describes the said interaction between the Langmuir waves and the electrons. The theory is known as the "Plasma kinetic turbulence theory." According to this theory, the complicated interaction between the electrons and Langmuir waves not only leads to the generation of radio waves but also the Langmuir waves must modify the characteristics of the electrons such that by the time the flare-generated electrons reach the Earth environment, the electron distribution function must have undergone various physical processes to produce certain features that can be detected by the artifical satellites. The PI made a specific prediction about the electron distribution, and his theory was compared against the satellite measurement. An excellent agreement between the theory and space observation was found. The findings were published in a number of papers: [1] P. H. Yoon, Asymptotic equilibrium between Langmuir turbulence and suprathermal electrons, Phys. Plasmas 18, 122303, doi: 10.1063/1.3662105 (2011). [2] P. H. Yoon, Asymptotic equilibrium between Langmuir turbulence and suprathermal electrons in three dimensions, Phys. Plasmas 19, 012304, doi:10.1063/1.3676159 (2012). [3] P. H. Yoon, Electron kappa distribution and steady-state Langmuir turbulence, Phys. Plasmas 19, 052301, http://dx.doi.org/10.1063/1.4710515 (2012). [4] L. Wang, R. P. Lin, C. Salem, M. Pulupa, D. E. Larson, P. H. Yoon, and J. G. Luhmann, Quiet-time interplanetary ~ 2-20 keV superhalo electrons at solar minimum, Astrophys. J. Lett. 753, L23, doi:10.1088/2041-8205/753/1/L23 (2012). To be specific, the PI's theory predicted that the electron distribution function must be characterized by the so-called power-law velocity tail that features the power-law index equal to minu 6.5. The observed power-law index determined on the basis of the satellite date (from WIND and STEREO satellites) was between minus 5 to minus 8, with the mean average value equal to minus 6.7. Considering uncertainties inherent in the observation, the small difference between minus 6.5 and minus 6.7 is within the error range, so the comparison between theory and observation can be said to be spectacular. This positive comparison implies that the PI's theory of how the electrons and Langmuir waves interact is valid, and based upon such a theory, the problem of how the radio waves are generated from Sun can be explained. Besides the above papers, the PI published 16 other papers (total publications that acknowledge the NSF support with the award ID 0940985 is 20 peer-reviewed papers).
