ESS228
Prof. Jin-Yi Yu
Brunt–Väisälä
Frequency (N)
•A fluid
parcel in the presence of stable stratification (N2 >0) will oscillate vertically if perturbed vertically from its starting position.
•In atmospheric dynamics, oceanography, and geophysics, the Brunt-Vaisala frequency, or buoyancy frequency, is the angular frequency at which a vertically displaced parcel will oscillate within statically stable environment.
•The Brunt–Väisälä frequency relates to internal gravity waves and provides a useful description of atmospheric and oceanic stability.
q Consider a parcel of (water or gas) that has
density of ρ0 and
the environment with a density that is a function of height: ρ =
ρ(z). If the parcel
is displaced by a small vertical increment z', it will subject to an extra gravitational force against
its surroundings of:
where
è
è
for the atmosphere
for oceans