Fig. 4

Source emission locations inferred by correcting for radio wave transport for the type III burst on 2020 July 21, assuming (a) fundamental and (b) harmonic sources. The source positions of the fundamental (\(r=[9.6, 17.7, 22.2, 31.4] \, R_\odot\) and \(\theta =-[155.1, 154.9, 154.7, 154.2]\) degrees) and harmonic (\(r=[15.8, 29.7, 37.2, 52.6] \, R_\odot\) and \(\theta =-\left[ 155.0, 154.3, 153.7, 151.8\right]\) degrees) are shown by the stars at radial distances inferred from the nominal simulations to the field line that is rooted at the Sun in alignment with the fitted longitude at 0.9 MHz. The uncertainty in this fitted longitude of \(\pm 2.7\) degrees is also shown on the source positions. The average 1 au scaled solar wind speed measured across all spacecraft of \(v_{\textrm{sw}}=310\) km \(\hbox {s}^{-1}\) has been used, as best inferred from Solar Orbiter (Fig. 1). Varying \(v_{\textrm{sw}}\) weakly affects the source angles: for instance, using \(v_{\textrm{sw}}=380\) km \(\hbox {s}^{-1}\) instead of \(v_{\textrm{sw}}=310\) km \(\hbox {s}^{-1}\) shifts the 0.2 MHz sources by \(-0.2\) degrees (fundamental) and \(-0.6\) degrees (harmonic). The inset shows a zoomed out region of the heliosphere with the fitted longitudes \(\theta _0\) depicted at 1 au as described in Fig. 1. The lower left square in the inset represents the region shown in the main panels.