Top: Fundamental (i.e. ZKBP) and first four symmetric harmonics as functions of the stretched coordinate $\widehat{\xi }=H^{1/2}\xi$. The eigenvalues $\widehat{K}=K/H$ are indicated. Bottom: Spatial profile of the dimensionless ambipolar diffusive flux for the eigenfunctions shown in the top panel. The locations of the null crossings of the solution are marked with vertical dashed lines.