Spectral domains R1–R4, where the approximations given in Eqs. (12) and (13) of the modified plasma dispersion function (8) can be used. For a dominance of suprathermal populations, indices κ_a → 1/2, and α_κa → 0 increasing (m_eα_κeβ_e,∥/m_p)^−1/2 and (α_κpβ_p,∥)^−1/2 to very large values, and also enlarging the area where the arguments |g_a| > 1 are large enough to apply the approximation in Eq. (13) for both species a = e,p, (W_r,i = ω_r,i/Ω_p, K = kc/ω_p,p).