I've done a PCA and varimax-rotated the EOF loadings (i.e. eigenvectors of the covariance matrix scaled by the square roots of the respective eigenvalues) and calculated the rotated PCs by multiplying the rotated EOFs with the original dataset. Now I'd like to estimate the variance explained by each rotated EOF, but I can't find any information on how to do this, despite many textbooks and papers showing explained variance of rotated EOFs.
Take for example this paper which is demonstrated in Statistical Methods in the Atmospheric Sciences by D. S. Wilks, but not fully explained.
How do I compute explained variances of varimax-rotated PCs?