Solar Dynamo — Parker Wave

Parker (1955) dynamo wave:
∂B_φ/∂t = α·B_r + η·∇²B_φ
∂B_r/∂t = -∂(ΩB_φ)/∂θ + η·∇²B_r
Wave: B ~ e^{i(kθ-ωt)}
ω² = αΩ'k²/2 → equatorward drift
Period: T ~ 2π/Im(ω) ≈ 11 yr