Part 4 — Stratified Flow & Waves
Vertical structure and internal waves. A continuously stratified fluid decomposes into normal modes, each an independent QG system with its own deformation radius — the two-layer model is the crudest possible truncation of this richer theory. Internal gravity waves carry energy perpendicular to their own phase propagation; and a wave’s presence leaves a permanent, measurable mark on the mean flow it rides, from Stokes drift to critical-layer absorption.