The problem of determining the absolute velocity of marine currents, including its barotropic component, is revisited. A generalization of the classical Needler’s formula is discussed for a Boussinesq fluid and it is shown that the steady flow solution can be deduced from a variational principle that uses the constants of motion existing in the problem. A simple model of a steady flow is considered when the Bernoulli function consists of two terms. The first term is proportional to the square of Ertel’s potential vorticity and the second term is a quadratic function of the fluid buoyancy. This model is applied to mimic the circulation in the western Mediterranean Sea near the African coast. Alternatively, “potential temperature – salinity” coordinates are applied to construct the stream-tubes and infer the steady flow velocity in the simplest case of the Bernoulli function being proportional to the product of the above two variables.

重新讨论了确定洋流绝对速度的问题，包括其正压分量。讨论了 Boussinesq 流体的经典 Needler 公式的推广，并表明可以从使用问题中存在的运动常数的变分原理推导出稳态流解。当伯努利函数由两项组成时，考虑一个简单的稳定流模型。第一项与 Ertel 位涡的平方成正比，第二项是流体浮力的二次函数。该模型用于模拟地中海西部靠近非洲海岸的环流。或者，