Electron density and Alfvén speeds obtained from the MAST model. Iso-surfaces of the 228 MHz fundamental (a and c) and harmonic plasma level (b and d) with overlaid Alfvén speed values at that height obtained from the MAST model. The electron densities corresponding to this surface are 6.4 × 10⁸ for fundamental emission and 1.6 × 10⁸ cm⁻³ for harmonic emission. The surfaces show the relative height of this emission at various locations on the Sun. The surfaces are overlaid with Alfvén speed values at those heights. In the bottom panels, a sphere has been included as a visual guide at a distance of 1.1 R_⊙ for fundamental emission (c) and 1.2 R_⊙ for harmonic emission (d). The Alfvén speed is highly variable across these density surfaces.