Holmboe's instability in exchange flows

A laboratory study of the exchange of two fluids of different density throu gh a constant-width channel with an underwater sill has enabled us to study Holmboe's instability in greater detail than has been possible in mixing-l ayer experiments. The internal hydraulics of the exchange flow are such tha t we have been able to observe the initiation of instability, the developme nt and behaviour of both symmetric and asymmetric Holmboe instabilities, an d the suppression of the instability at bulk Richardson numbers above about 0.7. A number of stability criteria resulting from previous numerical inve stigations have been verified experimentally. Our laboratory measurements a re consistent with theoretical predictions of wave speed and wavenumber.