Growth rate of the two modes given by Eq. (47). The real part is denoted by a solid curve (positive means a growing mode, negative means a damped mode) and the complex part (frequency of the oscillating mode) by a dotted line. Colors are used to distinguish the two modes; red showing the most unstable one. The left panel corresponds to an unstable case for which criterion 16 is not met (q_v → 0 ⇒ α_μ = β_c = 0). The right panel shows a case where the effect of the mean molecular weight is sufficient to stabilize the medium (α_μγ_s = 2,β_cγ_s = 1.7). Only a damped oscillating mode remains. Other numerical values are and (N_q/N_T)² = 30 (see Sect. 4.2.3).