Figure 4– The visual speed of the source for the basic emission. The favorable value represents the external movement from the solar disk center, while the unfavorable value represents the inward motion in this figure.
Conclusion.
1. For the essential emission, both the source size and decay time boost with the scattering rate coefficient or the difference of density change. The isotropic fluctuation can produce a bigger decay time than a highly anisotropic change, while the source size is not sensitive to the level of anisotropy for α > > 0.2. For the harmonic emission, both the source size and decay time are largely identified by the difference of the density. The decay time of the harmonic emission is considerably smaller sized than that of the fundamental emission for the very same background criteria.
$ and$ alpha= 0.719$ near the source area of the fundamental emission at the frequency of 35 MHz.
3. The statistical results of the balanced out show that the source of the fundamental emission is more external moved than that of the harmonic emission by the proliferation result, which might account for the co-spatial positions of the harmonic and essential emission in some observations.
The observed source position and size can have considerable visual movement and growth due to the wave proliferation results. Both the visual speed and the expansion rate tend to be big for highly anisotropic medium.
Based on recent paper: Zhang P.J., Wang C.B., Kontar E.P. 2021, ApJ., 909, 195.
Referrals.
Arzner K., & & Magun A., 1999, A&A, 351, 1165.
Kontar E. P., Chen X., Chrysaphi N., et al. 2019, ApJ, 884( 2 ): 122.
Kuznetsov A. A., Chrysaphi N., Kontar E. P., & & Motorina G., 2020, ApJ, 898, 94.
Steinberg J., Aubier-Giraud M., Leblanc Y., & & Boischot A., 1971, A&A, 10, 362.
Zhang P., Zucca P., Sridhar S. S., et al., 2020, A&A, 639, A115.
* Full list of authors: PeiJing Zhang, ChuanBing Wang, Eduard P. Kontar.
The imaging and spectroscopy observations of solar radio bursts can provide details on the non-thermal electrons related to the transient energy release in the solar active region and the parameters of the background plasma. the corona plasma is an inhomogeneous refractive media for solar radio waves. Propagation results, namely the refraction and scattering of waves, can trigger the contortion of the observed radio source, consisting of the expansion of the source size, and the offset of the visual source position from the “real source” at the wave generation website.
Ray-tracing simulation is an efficient approach to investigate the wave proliferation effects, which can help us in interpreting the imaging and spectroscopy observation and in diagnosing the solar corona properties from the observation outcomes (Steinberg et al. 1971; Arzner & & Magun,1999; Kuznetsov et al., 2020). Figure 1 reveals an example of simulation results of a point pulse source produced at the limb with highly anisotropic fluctuation of the background plasma density, on the basis of the anisotropic radio-wave scattering model developed by Kontar et al. (2019 ). With this approach we can obtain the source size, position, period and visual speed.
Figure 1– [GIFmovie] Temporal variations of the 2D-flux circulation of the evident source in the sky aircraft (upper panel) and the total flux (lower panel) in a simulation with a point pulse source for basic emission at 35 MHz. The starting position angle of the source is 45 Degree. The specification set is $epsilon= 0.27$ and $alpha= 0.104$.
In this work, we perform ray-tracing simulations on radio wave transportation in the corona and interplanetary area, and compare the simulation results with previous observations to approximate the property of the background plasma.
Simulation Results
1. Source Size and Duration
The source size and period are the most typical details that can be drawn out from imaging and spectroscopy observations of solar radio bursts. Figure 2 reveals the source size and decay time of the simulation results for the basic emission. The simulation results in the parameter area can be utilized to constrain the background plasma residential or commercial properties near the wave generation site. By comparing the observed duration and source size with the simulation results, we can estimate the scattering coefficient and the anisotropic specification η= 8.9 × 10 − 5 km − 1 and α= 0.719 with a point pulse source assumption
.
Figure 3– The offset of the rebuilded source centroid from the beginning point of the essential emission (left panel) and the harmonic emission (ideal panel). The comparable scale length of density change $ h_0$ near the wave generation site are about 860 km and 1010 km for the harmonic emission and the essential emission respectively.
3. Visual speed of the source.
The propagation effects can likewise be (partially) responsible for the high speed movement of the observed source in the sky airplane at a given frequency (Zhang et al, 2020).
Proliferation results, particularly the refraction and scattering of waves, can cause the deformation of the observed radio source, including the expansion of the source size, and the balanced out of the visual source position from the “genuine source” at the wave generation website.
Temporal variations of the 2D-flux circulation of the evident source in the sky airplane (upper panel) and the total flux (lower panel) in a simulation with a point pulse source for essential emission at 35 MHz. Figure 2 shows the source size and decay time of the simulation results for the essential emission. By comparing the observed period and source size with the simulation results, we can estimate the scattering coefficient and the anisotropic parameter η= 8.9 × 10 − 5 km − 1 and α= 0.719 with a point pulse source presumption
.
Figure 2– The source size and decay time of the simulation results for the essential emission. Purple lines in the left panel reveal the shape of source size, and black lines in the right panel reveal the contour of the decay time for the simulation data. The green square marks the cross point of the strong shape lines at $ epsilon= 0.277$ and $alpha= 0.719$. The equivalent scale length of density change $h_0$ has to do with 860 km near the wave generation site.
2. Offset of Source Position.
Figure 3 reveals the offset of the reconstructed source centroid from the starting point. We can see that for the same frequency, the source of fundamental emission is more outside moved than that of the harmonic emission. This may produce the co-spatial positions of the essential and harmonic waves in the observation of some type III radio bursts.
We can see that for the very same frequency, the source of fundamental emission is more external moved than that of the harmonic emission.