Geostrophic flow and Rossby-number scope
For sufficiently slowly varying large-scale flow away from strong friction, horizontal pressure-gradient and Coriolis accelerations can approximately balance.
Key knowledge
For sufficiently slowly varying large-scale flow away from strong friction, horizontal pressure-gradient and Coriolis accelerations can approximately balance. With nonzero f, the geostrophic velocity follows isobars on a constant-height surface. Small Rossby number supports the approximation but does not remove boundary or transient effects.
Values and equations
f ẑ×ug = −∇hp/ρ; ug = ẑ×∇hp/(ρf); Ro=U/(|f|L)
- ug,U
- geostrophic velocity vector and characteristic speed m s⁻¹
- f
- Coriolis parameter s⁻¹
- p
- pressure Pa
- ρ
- mass density kg m⁻³
- L
- horizontal scale m
- ẑ
- upward unit vector 1
- ∇h
- horizontal gradient operator m⁻¹
- Ro
- Rossby number 1
Conditions and scope
- Use Ro=U/(|f|L)≪1 with stated speed/scale; the approximation is singular near f=0.
- Here ẑ points upward and the pressure gradient is horizontal; curved rapid flow or strong friction needs additional terms.
Sources · 1
References
Sources retain their recorded scope. A source link alone does not establish verification of every statement.
Evidence and review
Read small-Rossby-number momentum balance and Cartesian/vector forms; avoided universal isobar-following assertion.
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Entry details
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- uni-earth-geostrophic-balance
- Revision
- core.1
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