物理海洋学名词-B 73

Glossary of Physical Oceanography and Related Disciplines

Steven K. Baum Department of Oceanography Texas A&M University

May 26, 2004
 

buoyancy
buoyancy frequency The frequency with which a parcel or particle of fluid displaced a small vertical distance from its equilibrium position in a stable environment will oscillate. It will oscillate in simple harmonic motion with an angular frequency defined by:
N2 = g(α*∂z/∂θ - β*∂S/∂z)
where g is the gravitational acceleration, theta is the potential temperature, α is the thermal expansion coefficient, and β is the saline contraction coefficient. In practice, the equivalent formula:
N2 = (-g/ρ*∂ρ/∂z )^1/2
is often used, where c is the velocity of sound, although care must be taken to consistently evaluate ρ and c. See Turner [1973] and McDougall et al. [1987].
buoyancy scale An important length scale in stratified flow with internal waves. This is defined as:
LB = √w¯2/N
where ¯ w is the ratio of the vertical turbulent and internal wave fluctuations and N the buoyancy frequency. This is used instead of the Ozmidov scale if the vertical velocity fluctuations due to internal waves are small compared to those due to turbulence.
Burger number A dimensionless number indicative of the importance of baroclinicity in a flow field. It is the square of the ratio of the Rossby radius of deformation to the horizontal scale of the flow, and is given by:
Bu = NH/ fL
where N is the buoyancy frequency, H the vertical scale of the flow (i.e. the depth), f is the inertial frequency, and L the horizontal scale of the flow. A Burger number of zero indicates a rotation dominated flow, while large values indicate stratification dominated flows. This was named for the mathematician/meteorologist Alewyn Burger.
Burma Sea See Andaman Sea.
Buys Ballot’s law A synoptic meteorology rule stating that if, in the northern hemisphere, an observer stands with his back to the wind, pressure is lower on his left hand than on his right, while in the southern hemisphere the converse is true. This was enunciated by Buys Ballot of Utrecht in 1857 and is basically a restatement of the fact that winds blow clockwise around a depression in the northern hemisphere and anticlockwise in the southern hemisphere
 

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