Computing Empirical Orthogobal Functions (EOFs) corresponds to find a decomposition of a time-varying fields into a sum of maps (the EOFs) times time series (confusing referred to as Prinicpal Components, PCs):

E(x,t) = ∑_{i=1^N Ei(x) pi(t)}

The EOFs and PCs are chosen such that for small N the difference with the full field is as small as possible.

In this field you can choose how many EOFS (and PCs) you want to have computed, and how the difference should be evaluated.

More EOFs only take slightly more time to compute, so feel free to give a large number.

The EOF decomposition can be defined in two ways. The first is to minimise the difference in absolute units, for instance in mb or mm/dy. The second is to minimse the fraction of the variability at each point that is explained by the EOF decomposition. The first method emphasises the areas in which the variability is large, the second one treats all areas equally.