On the comparison between two sets of 500 mb geopotential height eigenfunctions

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Abstract
When the largest eigenvalues of an Empirical Orthogonal Function (EOF) analysis are of similar magnitude, the corresponding EOFs do not hold great interest when they are considered one at a time; only the vector subspace generated by the first EOFs is significant. In this case, the comparison between two EOF analyses may be summarized by a distance index between the two subspaces. Such a method is applied to EOF analyses over the northern hemisphere of the 500 mb geopotential height from 10 winters of simulation (using a version of the ECMWF spectral model) and 13 observed winters. For more than the first three low-order EOFs, the agreement between simulation and observation is statistically significant. DOI: 10.1111/j.1600-0870.1986.tb00477.x