Boussinesq Approximation

The Boussinesq approximation treats density as constant in the momentum and continuity equations except where it multiplies gravity in the buoyancy term. It is valid because seawater density varies by under 5 percent (about 1020 to 1050 kg per cubic meter), so the inertial effect of density anomalies is small but their buoyancy effect drives the flow. The approximation makes the flow effectively incompressible (grad dot v = 0) and underlies most ocean general circulation models. It filters acoustic waves and slightly misrepresents the global pressure work, which non-Boussinesq or anelastic formulations correct.