Issue |
A&A
Volume 690, October 2024
|
|
---|---|---|
Article Number | L6 | |
Number of page(s) | 8 | |
Section | Letters to the Editor | |
DOI | https://doi.org/10.1051/0004-6361/202451134 | |
Published online | 09 October 2024 |
Letter to the Editor
Origin of the type III radiation observed near the Sun
1
Space Sciences Laboratory, University of California, Berkeley, California, USA
2
Physics Department, University of California, Berkeley, California, USA
3
University of Minnesota, Minneapolis, Minnesota, USA
4
LPC2E, CNRS-University of Orléans-CNES, 45071 Orléans, France
5
Max-Planck Institute of Solar System Research, Göttingen, Germany
6
Uzhhorod National University, Uzhhorod, Ukraine
Received:
15
June
2024
Accepted:
6
September
2024
Aims. We investigate processes associated with the generation of type III radiation using Parker Solar Probe measurements.
Methods. We measured the amplitudes and phase velocities of electric and magnetic fields and their associated plasma density fluctuations.
Results. 1. There are slow electrostatic waves near the Langmuir frequency and at as many as six harmonics, the number of which increases with the amplitude of the Langmuir wave. Their electrostatic nature is shown by measurements of the plasma density fluctuations. From these density fluctuations and the electric field magnitude, the k-value of the Langmuir wave is estimated to be 0.14 and kλd = 0.4. Even with the large uncertainty in this quantity (more than a factor of two), the phase velocity of the Langmuir wave was < 10 000 km/s. 2. The electromagnetic wave near the Langmuir frequency has a phase velocity lower than 50 000 km/s. 3. We cannot determine whether there are electromagnetic waves at the harmonics of the Langmuir frequency. If they existed, their magnetic field components would be below the noise level of the measurement. 4. The rapid (less than one millisecond) amplitude variations typical of the Langmuir wave and its harmonics are artifacts resulting from the addition of two waves, one of which has small frequency variations that arise because the wave travels through density irregularities. None of these results are expected in or consistent with the conventional model of the three-wave interaction of two counter-streaming Langmuir waves that coalesce to produce the type III wave. They are consistent with a new model in which electrostatic antenna waves are produced at the harmonics by radiation of the Langmuir wave, after which at least the first harmonic wave evolved through density irregularities such that its wave number decreased and it became the type III radiation.
Key words: Sun: radio radiation / solar wind
© The Authors 2024
Open Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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