Normalized growth rate of O⁺ cyclotron harmonics plotted against normalized real frequency for different wave propagation angles, as indicated in the legends. Panels (a) and (b), show results for the magnetosheath (25 cm⁻³) and the IMB region (100 cm⁻³), respectively, while panel (c) shows the results for the IMB region with reduced plasma density (50 cm⁻³).