A river plume spreads as a layer of fresh water of thickness over a sea so much…

PHYSICS · Multi-part · Fermi University Physics · Fluids & Continuum Physics · Waves, acoustics and compressible flow · Waves, acoustics and compressible flow

Signal Speeds in Fluids, Ch Internal gravity waves in a stratified fluid

Problem

A river plume spreads as a layer of fresh water of thickness h1=1.5 mh_1 = 1.5\,\mathrm{m} over a sea so much deeper that the lower layer may be treated as effectively infinite in depth and at rest. The fractional density difference between the layers is Δρ/ρ=0.015\Delta\rho/\rho = 0.015. ((a)) Find the reduced gravity g′g' and the long-wave speed of interfacial waves on this front. ((b)) Express this speed in knots (1 knot=0.5144 m s−11\,\mathrm{knot} = 0.5144\,\mathrm{m\,s^{-1}}), and say why a small boat moving at about this speed experiences unusually strong resistance (dead water).

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