Buoyancy frequency and static stratification
In a small-displacement incompressible Boussinesq parcel model, N²=−(g/ρ₀)dρ_b/dz gives the vertical restoring acceleration ξ̈=−N²ξ when parcel density is conserved.
Key knowledge
In a small-displacement incompressible Boussinesq parcel model, N²=−(g/ρ₀)dρ_b/dz gives the vertical restoring acceleration ξ̈=−N²ξ when parcel density is conserved. Density increasing downward gives N²>0 and a stable oscillatory restoring tendency; N²<0 gives overturning instability in this restricted model. Temperature alone cannot determine the sign when composition also affects density.
Values and equations
N²=−(g/ρ₀)dρ_b/dz; ξ̈=−N²ξ
- N²
- squared buoyancy frequency in the stated model s⁻²
- g
- gravitational acceleration m s⁻²
- ρ_b,ρ₀
- background buoyancy density and reference density kg m⁻³
- z,ξ
- upward height and small parcel displacement m
Conditions and scope
- z increases upward,ρ_b is the smooth background buoyancy-density profile andρ₀ a positive constant reference. Neglect pressure-compression differences and mixing/diabatic change in the displayed parcel model.
- Compressible air and seawater require an adiabatic parcel-density comparison or appropriate potential-density/thermodynamic formulation. Positive N² alone does not rule out shear or double-diffusive instabilities.
Sources · 1
References
Sources retain their recorded scope. A source link alone does not establish verification of every statement.
Evidence and review
Read actual incompressible buoyancy-displacement explanation and continuous-stratification setup. The simple N² formula is explicitly derived by comparing a density-conserving parcel withρ_b(z+ξ),rather than claiming clean extraction of the scanned equation9.1. Excluded its blanket instability inference from a subcritical Richardson number and all historical universal-spectrum/numerical estimates.
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Entry details
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