Paper 2, Section I, D

Fluid Dynamics
Part IB, 2018

The Euler equations for steady fluid flow u\mathbf{u} in a rapidly rotating system can be written

ρf×u=p+ρg,\rho \mathbf{f} \times \mathbf{u}=-\nabla p+\rho \mathbf{g},

where ρ\rho is the density of the fluid, pp is its pressure, g\mathbf{g} is the acceleration due to gravity and f=(0,0,f)\mathbf{f}=(0,0, f) is the constant Coriolis parameter in a Cartesian frame of reference (x,y,z)(x, y, z), with zz pointing vertically upwards.

Fluid occupies a layer of slowly-varying height h(x,y)h(x, y). Given that the pressure p=p0p=p_{0} is constant at z=hz=h and that the flow is approximately horizontal with components u=(u,v,0)\mathbf{u}=(u, v, 0), show that the contours of hh are streamlines of the horizontal flow. What is the leading-order horizontal volume flux of fluid between two locations at which h=h0h=h_{0} and h=h0+Δhh=h_{0}+\Delta h, where Δhh0\Delta h \ll h_{0} ?

Identify the dimensions of all the quantities involved in your expression for the volume flux and show that your expression is dimensionally consistent.