Initial Doppler analysis for burst data recorded near June 6, 2020, 12:09:54 UTC. Panel a: angle between the ambient magnetic field vector (B) and the proton flow vector (V_sw). Panel b: electric field spectrogram. The color scale is selected to highlight the type B wave power. Colored symbols indicate the peak type B frequency for each spectrum, plotted with an offset from the type B spectral line so that both are visible. Orange, red, and blue symbols correspond to three distinct slopes observed in panel c. The dashed black line indicates the local electron cyclotron frequency. Panel c: observed type B wave frequency (radians/s) as a function of the cosine of the angle shown in panel a.