Solar coronal density turbulence and magnetic field strength at the source regions of two successive metric type II radio bursts

Abstract

We report spectral and polarimeter observations of two weak, low frequency ($\approx$85-60\,MHz) solar coronal type II radio bursts that occurred on 2020 May 29 within a time interval $\approx$2\,min. The bursts had fine structures, and were due to harmonic plasma emission. Our analysis indicates that the magnetohydrodynamic (MHD) shocks responsible for the 1st and 2nd type II bursts were generated by the leading edge (LE) of an extreme-ultraviolet (EUV) flux rope/coronal mass ejection (CME) and interaction of its flank with a neighbouring coronal structure, respectively. The CME deflected from the radial direction by ${\approx}25^{\arcdeg}$ during propagation in the near-Sun corona. The estimated power spectral density (PSD) and magnetic field strength ($B$) near the location of the 1st burst at heliocentric distance $r\approx 1.35R_{\odot }$ are $\approx 2\times 10^{-3}{\mathrm{W}}^2\mathrm{m}$ and $\approx$1.8\,G, respectively. The corresponding values for the 2nd burst at the same $r$ are $\approx 10^{-3}{\mathrm{W}}^2\mathrm{m}$ and $\approx$0.9\,G. The significant spatial scales of the coronal turbulence at the location of the two type II bursts are $\approx$62\,-\,1\,Mm. Our conclusions from the present work are that the turbulence and magnetic field strength in the coronal region near the CME LE are higher compared to the corresponding values close to its flank. The derived estimates of the two parameters correspond to the same $r$ for both the CME LE and its flank, with a delay of $\approx$2\,min for the latter.

11 Pages, 4 Figures, Published in The Astrophysical Journal

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