Self-sustaining magnetic field generation by conducting fluid flow
Parker's αΩ-dynamo: differential rotation (Ω-effect) winds poloidal field into toroidal field, while helical convection (α-effect) regenerates poloidal field from toroidal. The dynamo operates when the dynamo number D = α·ΔΩ·R³/η² exceeds a critical value. Earth's geodynamo and solar dynamo both rely on this mechanism.