Compression wave Longitudinal density oscillation in the substrate propagation c_s = √(dP/dρ) = c Modon soliton Counter-rotating vortex dipole self-advecting on background CW CCW c_modon = n₁ω₀λ³ / K Vortex lattice shear wave Tkachenko wave — transverse oscillation of vortex array c_T = √(κ_q Ω_v / 4π) c c_s c_modon c_T Lorentz invariance requires all three equal λ³ = ℏK α_mf / (2m_e c) λ = 96.9 μm</