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A method is given by means of which quasi-permanent “velocity” fields may be constructed in which absolute vorticity is conserved if the atmosphere is treated as barotropic. For vorticity displacements these fields may be considered as constant for time intervals of the order of magnitude 24 hrs. Some simple approximate integration formulae are given for the Poisson- and Helmholz-equations. A graphical procedure is introduced to derive the isolines of vorticity and to perform the integration work. DOI: 10.1111/j.2153-3490.1952.tb01003.x
Ragnar Fjørtoft (1952) studied this question.