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Earth and Space Sciences · 术语表

什么是 Buoyancy frequency？

Definition 19.11 University Earth and Space Sciences — Year 3 · 第 19 章 — Geophysical Fluid Dynamics

The buoyancy frequency $N$ of a fluid at rest is defined by

N^2 = \frac{g}{\theta}\frac{\mathrm d\theta}{\mathrm dz}\ \text{(air)}, \qquad N^2 = -\frac{g}{\rho_0}\frac{\mathrm d\rho_\theta}{\mathrm dz}\ \text{(seawater)},

where $\theta$ is the potential temperature of the air and $\rho_\theta$ the potential density of the water, the density it would have if brought adiabatically to a reference pressure.

Buoyancy frequency. Left, the standard atmosphere: nearly uniform in the troposphere, twice as large in the isothermal lower stratosphere, larger still above 25\, km where the temperature rises. Right, an annual-mean column of the North Atlantic (temperature and salinity from the World Ocean Atlas 2023, potential density from EOS-80): a sharp maximum in the seasonal pycnocline, weak stratification below. — Buoyancy frequency. Left, the standard atmosphere: nearly uniform in the troposphere, twice as large in the isothermal lower stratosphere, larger still above $25\,\mathrm{km}$ where the temperature rises. Right, an annual-mean column of the North Atlantic (temperature and salinity from the World Ocean Atlas 2023, potential density from EOS-80): a sharp maximum in the seasonal pycnocline, weak stratification below.

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