On the current of a free mode in an elongated basin

The current of a free mode included in a zonally elongated basin is zonal almost everywhere, with the exception of the westernmost and easternmost areas of the fluid domain. The main difference between different circulation fields basically concerns the latitudinal localisation of the maximum and minimum flow. This aspect is investigated by determining how total vorticity selects above localisations. The result is that the latter only depends on the value taken by the total vorticity at the points where the stream function is zero. A set of examples illustrates the results.