Model setup and Z-mode (UH) wave analysis. (a) Temporal evolution of the plasma density n₀ (red) and magnetic field strength B₀ (blue) in the radio source region. (b) Profiles of plasma frequency ω_pe, electron cyclotron frequency Ω_ce, and their ratio ω_pe/Ω_ce (red, blue, and black lines, respectively). (c) Electron distribution adopted for the linear growth rate calculation: background Maxwellian (T₀ = 2 MK) and energetic electrons with a loss-cone distribution (average velocity v_e = 0.3c). (d) Dispersion relations of Z-mode waves in warm plasmas with ω_pe/Ω_ce = 80 for perpendicular propagation, calculated using fluid approximation (red circles) and kinetic theory (black plus signs). The blue line corresponds to the dispersion curve of UH mode, ﹩{\omega }^{2}={\omega }_{p}^{2}+{{\rm{\Omega }}}_{\mathrm{ce}}^{2}+3{k}_{\perp }^{2}{v}_{0}^{2}﹩, and the black dashed line indicates the UH frequency (﹩{\omega }_{\mathrm{UH}}^{2}={\omega }_{\mathrm{pe}}^{2}+{{\rm{\Omega }}}_{\mathrm{ce}}^{2}﹩). (e) Growth rate distribution of Z-mode waves in (ω, θ) space; positive values indicate growth and negative values damping. (f) Growth rate of Z-mode waves at fixed propagation angle θ = 89 ﹩\mathop{.}\limits^{\unicode{x000b0}}﹩5.