May 20, 2022

Langmuir wave motion observed in the most intense radio sources in the sky by H. Reid and E. Kontar

The LOFAR contours are at 75% of the peak flux of the type III bursts going from 40 MHz to 30 MHz in the colour sequence white-blue-green-yellow-red. The LOFAR beam shape at 75% for 30 MHz is shown in the leading left corner in white.
This new method increases the scope of solar radio bursts to be used as a remote plasma temperature level diagnostic. The radio fine structure also provides an extra method to estimate the electron beam bulk speed, which is mainly controlled by the beam energy density.

Figure 2– Magnification of one type III fine structure from the LOFAR information (left) and the simulations (right). The black dashed lines show a linear fit to the drift, approximating a continuous velocity of 0.69 Mm/s for the observed type III burst and 0.6 Mm/s for the simulated type III burst. Image from Reid & & Kontar, Nature Astronomy, 2021.
Type III radio emission varies because the background electron density turbulence regulates the development of Langmuir waves from the electron beam. The characteristic strength of density turbulence parallel to the electromagnetic field, $Delta n/n$ and the particular intensity of radio fine structure $Delta I/I$ are analytically related through
for the thermal velocity $v _ $ and the beam speed $v_b$. The simulations also find the same relation (Figure 3). This new strategy additional boosts the scope of radio fine structure to from another location determine the level of density turbulence, with the observations finding a level of 0.003.

These solar radio bursts also provide a distinct chance to understand particle acceleration and transport which is important for our forecast of severe space weather events near the Earth. The radio great structure also supplies an extra method to approximate the electron beam bulk speed, which is primarily controlled by the beam energy density.

Figure 3– The relation between the radio great structure $Delta I/I$ and the level of density fluctuations $Delta n/n$ discovered from different simulations. The black triangle shows the predicted level of turbulence from observations and the black dashed line shows the analytical relation in between $Delta I/I$ and $Delta n/n$ from observations. Image from Reid & & Kontar, Nature Astronomy, 2021.
In summary, the results produce a framework for making use of the diagnostic capacity of radio burst fine structure to approximate plasma temperatures and density turbulence. This new potential is especially relevant provided the boosted resolution of new-age ground-based radio telescopes that are resolving much more fine structure stemming from the solar corona. Furthermore, the closer proximity of Parker Solar Probe and Solar Orbiter to radio emission coming from the very high corona or solar wind, and hence greater level of sensitivity, allows fine structures to be discovered in situ.
Based on a recent paper: Reid, H.A.S., Kontar, E.P. Fine structure of type III solar radio bursts from Langmuir wave movement in unstable plasma, Nature Astronomy (2021 ). DOI: 10.1038/ s41550-021-01370-8.
References:.
Suzuki, S. & & Dulk, G. A. Bursts of Type III and Type V 289– 332 (Cambridge Univ.
Press, 1985). Reid, & H.A.S., & Kontar, E.P., Nature Astronomy, 2021.

The Sun consistently produces energetic electrons in its external atmosphere that consequently travel through interplanetary space. These electron beams generate Langmuir waves in the background plasma, producing type III radio bursts that are the brightest radio sources in the sky (Suzuki & & Dulk, 1985). These solar radio bursts likewise supply a special chance to understand particle velocity and transport which is necessary for our prediction of severe space weather condition events near the Earth. However, the formation and movement of type III fine frequency structures (see Figure 1) is a puzzle but is frequently believed to be connected to plasma turbulence in the solar corona and solar wind.
A Recent work by Reid & & Kontar, Nat Astro, 2021, integrates a theoretical structure with kinetic simulations and high-resolution radio type III observations utilizing the Low Frequency Array (LOFAR) and quantitatively demonstrates that the great structures are caused by the moving extreme clumps of Langmuir waves in a rough medium. These results reveal how type III great structure can be used to remotely analyse the intensity and spectrum of compressive density fluctuations, and can infer ambient temperature levels in astrophysical plasma, both significantly broadening the existing diagnostic capacity of solar radio emission.

In summary, the outcomes create a structure for exploiting the diagnostic capacity of radio burst fine structure to estimate plasma temperature levels and density turbulence. This new potential is particularly relevant provided the enhanced resolution of new-age ground-based radio telescopes that are dealing with much more fine structure originating from the solar corona. The closer distance of Parker Solar Probe and Solar Orbiter to radio emission originating in the really high corona or solar wind, and thus greater level of sensitivity, allows fine structures to be identified in situ.

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