Part 2 — Balance & Adjustment
How a rotating, stratified fluid finds its balance. Thermal wind ties vertical shear directly to a horizontal temperature gradient; geostrophic adjustment shows how an unbalanced disturbance sheds fast gravity waves and settles into a balanced remnant, predictable in advance from potential vorticity alone. The two-step PV-inversion algorithm introduced here — invert for velocity, advect PV, invert again — drives nearly every simulation in the rest of the book.