Radial profile of the cyclotron frequency (solid black line) and the upper hybrid plasma frequency (coloured lines) for different base plasma density values given in units of cm⁻³. The plasma has been assumed to follow a hydrostatic density structure along any given field line while taking centrifugal force into account (Havnes & Goertz 1984, their Eq. (3)). The broken lines denote regions where cyclotron absorption precludes radiation escape. The yellow band shows the observed frequency range.