Stokes parameters I, V, Q, and U (a–d) of the escaping radiation captured in a plane at a height H ≈ 2150 m, averaged over the time interval T ∈ [34.7, 43.4] μs, and normalized to the maximum value of the Stokes I value. The dashed magenta line denotes the last open field line, and the magenta plus shows the dipole axis. The black plus denotes the maximum of the average plasma density. The black squares in (a) denote regions for which the spectra are analyzed below. The color scales differ between figures.