A direct method of stream-function computation

An iterative method is described that fits a stream function (Ψ) to wind observations. The technique was designed for use in tropical regions where errors in height data and other difficulties preclude use of the geostrophic or balance equations to obtain y; however, the technique is believed to be sufficiently general to have other applications. Since the calculations may be carried out rapidly by an electronic computer, the technique might serve as a replacement for the laborious streamline-isotach method of tropical analysis.

The equations basic to the computations are given. If the stream function is defined to have the units of height (i.e., meters), it is convenient to use observed heights as the initial-guess field. Several iterations are made until the computed values of Ψ stabilize within a pre-determined limit. Explicit calculations of vorticity and of boundary values of Ψ, as required in a stream function obtained by solution of a Poisson equation, are not needed. Analyses of computed values of Ψ in the Caribbean are compared with independent, subjective analyses of the same data, and show excellent agreement. Autocorrelations show that computed values of stream function were considerably more persistent than height data for the period studied.