The short-lived and narrow frequency-band great structures observed at the very same time at F and H frequencies give a frequency ratio of 1.66 and 1.73, similar to previous observations. Frequency-time cross-correlations suggest a frequency ratio of 1.99 and 1.95 with a time delay between the F and H emissions of 1.00 and 1.67 s, respectively for type III and type J bursts.
Figure 1. A physical circumstance of 2 vibrant spectra showing the time hold-up in between the observed and intrinsic F parts of the normal type III burst (left panel) and the type III burst with striae structures (ideal panel).
Solar radio bursts generated through the plasma emission system produce radiation near the local plasma frequency (essential emission, hereafter, F) and double the plasma frequency (harmonic, hereafter, H). While the theoretical ratio of these 2 frequencies is close to 2, synchronised observations give ratios ranging from 1.6 to 2, suggesting either a ratio various from 2, a delay of the F emission, or both.
Observations recommend that a postponed F component leads to the derived H/F frequency ratio to be less than 2, as highlighted in Figure 1. The time delay in between F and H components can be described by a mix of various group speeds and scattering results, with the latter forming a larger contribution. As the F element is given off at the regional plasma frequency, it undergoes a more powerful scattering effect than the H part, which lengthens the proliferation course of the F emission and causes a delayed F band.
Observations recommend that a delayed F part leads to the obtained H/F frequency ratio to be less than 2, as illustrated in Figure 1. As the F part is released at the regional plasma frequency, it goes through a more powerful scattering effect than the H part, which lengthens the proliferation course of the F emission and leads to a postponed F band.
Figure 2. LOFAR observations and correlation results for type III (a, b) and type J (c, d) bursts.
The narrow and brief frequency-band great structures observed at the very same time at F and H frequencies offer a frequency ratio of 1.66 and 1.73, comparable to previous observations. Frequency-time cross-correlations recommend a frequency ratio of 1.99 and 1.95 with a time hold-up in between the F and H emissions of 1.00 and 1.67 s, respectively for type III and type J bursts.
We quantitatively approximate the hold-up times triggered by the different group speeds and proliferation impacts through ray-tracing simulations of radio wave propagation (Kontar et al. 2019). If we adopt the same characteristic criteria as in the ray tracing simulations that effectively recreated the observed residential or commercial properties of the same type IIIb burst evaluated in Chen et al. (2020 ), the simulated hold-up time is extremely close to the observed delay, supporting to resolve the enduring question of why different frequency ratios are typically observed.
The delay time depends on the anisotropic rough conditions that vary between occasions. Using these simulations we have the ability to, for the very first time, provide quantitative estimates of the hold-up time of the F emissions triggered by radio-wave propagation effects at numerous frequencies, which need to be thought about in future studies.
Based upon the current paper by Xingyao Chen, Eduard P. Kontar, Daniel L. Clarkson and Nicolina Chrysaphi, The frequency ratio and time delay of solar radio emissions with fundamental and harmonic elements, MNRAS 520, 3117– 3126 (2023 ), DOI: https://doi.org/10.1093/mnras/stad325.
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