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The analysis and use of charts of absolute vorticity are described. Measurements from a winter and a summer series of maps gave 608 and 641 mb, respectively, as the pressure at the mean equivalent barotropic surface. It is shown that, on charts near the equivalent barotropic surface, the absolute-vorticity patterns give indications useful in short-range forecasting, since the lines of constant absolute vorticity are advected with nearly the speed of the wind. Examples are presented, showing typical contour and vorticity patterns for a rapidly moving pattern, a stationary pattern, and a situation of rapid trough development.
George P. Cressman (Sun,) studied this question.