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Similarity‐based approximations for the evolution of a gravity current

Approximations to similarity solutions for two‐dimensional and axisymmetric gravity currents are described. These are based on the entrainment behaviour and its implication for the evolution of gravity‐current height and reduced gravity. It is shown how this approach permits the approximation of gravity‐current behaviour without the need for information about the buoyancy or, equivalently, distance from the point of origin. It is also shown that the usual front‐speed scaling may be derived from consideration of baroclinic vorticity generation at the front in both two‐dimensional and axisymmetric configurations. The importance of vorticity in defining the flow direction is also discussed.