Reid, H. A.S. and Kontar, E. P. (2015) Stopping frequency of type III solar radio bursts in expanding magnetic flux tubes. Astronomy and Astrophysics, 577, A124. (doi: 10.1051/0004-6361/201425309)
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Abstract
Aims. Understanding the properties of type III radio bursts in the solar corona and interplanetary space is one of the best ways to remotely deduce the characteristics of solar accelerated electron beams and the solar wind plasma. One feature of all type III bursts is the lowest frequency they reach (or stopping frequency). This feature reflects the distance from the Sun that an electron beam can drive the observable plasma emission mechanism. The stopping frequency has never been systematically studied before from a theoretical perspective.<p></p> Methods. Using numerical kinetic simulations, we explore the different parameters that dictate how far an electron beam can travel before it stops inducing a significant level of Langmuir waves, responsible for plasma radio emission. We use the quasilinear approach to model the resonant interaction between electrons and Langmuir waves self-consistently in inhomogeneous plasma, and take into consideration the expansion of the guiding magnetic flux tube and the turbulent density of the interplanetary medium.<p></p> Results. We find that the rate of radial expansion has a significant effect on the distance an electron beam travels before enhanced levels of Langmuir waves, hence radio waves, cease. Radial expansion of the guiding magnetic flux tube rarefies the electron stream to the extent that the density of non-thermal electrons is too low to drive Langmuir wave production. The initial conditions of the electron beam have a significant effect, where decreasing the beam density or increasing the spectral index of injected electrons would cause higher type III stopping frequencies. We also demonstrate how the intensity of large-scale density fluctuations increases the highest frequency to which Langmuir waves can be driven by the beam and how the magnetic field geometry can be the cause of type III bursts that are only observed at high coronal frequencies.<p></p>
| Item Type: | Articles |
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| Status: | Published |
| Refereed: | Yes |
| Glasgow Author(s) Enlighten ID: | Kontar, Professor Eduard and Reid, Dr Hamish |
| Authors: | Reid, H. A.S., and Kontar, E. P. |
| College/School: | College of Science and Engineering > School of Physics and Astronomy |
| Journal Name: | Astronomy and Astrophysics |
| Publisher: | EDP Sciences |
| ISSN: | 0004-6361 |
| ISSN (Online): | 1432-0746 |
| Copyright Holders: | Copyright © 2015 EDP Sciences |
| First Published: | First published in Astronomy and Astrophysics 577:A124 |
| Publisher Policy: | Reproduced in accordance with the copyright policy of the publisher. |
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