Metrewave solar type-III radio bursts provide a special methods to study the residential or commercial properties of turbulence throughout coronal heights. The arrival of high cadence picture spectroscopic imaging capabilities in meter wavebands have made observations of turbulence-related effects practical across a range of coronal heights. By comparing observations with existing designs, it is now possible to study the spatio-temporal scales and strength of density variations ($ delta$ N/N) across corona.
Occasion & & Analysis.
The events that pleased the following requirements were selected: source is close to the disk centre; has a single pulse structure in time across the entire 80– 240 MHz band; there are no strong pre-existing close-by sources. The disk-centre requirement ensured that the open field lines along which the burst activating supra-thermal electrons took a trip are alone the line of sight. The observed unstable source scattering effects in the image plane mainly depend only the plane perpendicular to open magnetic field structures.
Figure 1. (a-b)– Integrated flux density and area development of the Gaussian burst source. Thick black lines separate the MWA 2 MHz bands.( c): Normalised light curves at mid-band frequencies.
Imaging of this dataset was done at 0.5 s and 160 kHz resolution using AIRCARS pipeline. $, across the observation band. Note that the MWA observations were in 12 different 2 MHz bands centred around the frequencies of the light curves in the Fig. 1c.
Results.
Figure 2.( a)–$ delta$ N/N and the theoretical situation scale throughout height (dotted). (b): Intrinsic source sizes and the typical open flux tube sizes throughout height. (c-d): Mean source sizes and decay times across frequency with best-fit power law models (black). Shaded regions mark the empirical designs by Kontar, E.P. et al., 2019.
The observed burst source area increase in tandem with its strength evolution is consistent with the model of radiowave propagation under a turbulence isotropic in the image plane. The $delta$ N/N increased with coronal height following a power law function with an index of 2.2$ pm$ 0.7. Deconvolving the effect of scattering, the real source sizes might be approximated (Fig. 2 b) which were compared versus the empirical design for closed coronal loop sizes by Aschwanden, M, 2003.
Conclusions.
This work extends the outcomes on coronal turbulence in 30– 80 MHz range approximately 200 MHz using data from MWA. The strength of density fluctuations ($ delta$ N/N) increases with height as a power-law with an index of ~ 2.2$ pm$ 0.7. Integrated with earlier outcomes, the worths of $delta$ N/N varies just within a few factors across ~ 1.5– 2.2 R$ _ odot$. The sizes and the decay time of the burst source approximately follow the empirical model obtained for radio frequency information. The intrinsic sizes of the burst source were derived, remedying for scatter broadening. The results follow the expectations from an open coronal flux tube..
Based onrecent paper: Atul Mohan, 2021, A&A, 655, 77.
Recommendations.
Coles, W. A. & & Harmon, J. K. 1989, ApJ, 337, 1023.
Arzner, K. & & Magun, A., 1999, A&A, 351, 1165.
Wohlmuth, R., Plettemeier, D., Edenhofer, P., et al. 2001, Space Sci. Rev., 97, 9.
Aschwanden, M. J. 2003, ArXiv e-prints, arXiv: astro-ph/0309505.
Kontar, E. P., Chen, X., Chrysaphi, N., et al., 2019, ApJ, 884, 122.
The events that pleased the following criteria were selected: source is close to the disk centre; has a single pulse structure in time across the entire 80– 240 MHz band; there are no strong pre-existing nearby sources. (b): Intrinsic source sizes and the normal open flux tube sizes throughout height. The observed burst source area rise in tandem with its strength evolution is constant with the design of radiowave propagation under a turbulence isotropic in the image airplane. Deconvolving the effect of scattering, the real source sizes could be approximated (Fig. 2 b) which were compared versus the empirical model for closed coronal loop sizes by Aschwanden, M, 2003. The sizes and the decay time of the burst source roughly follow the empirical design derived for low frequency information.