THE EOFS OF THE GEOPOTENTIAL EDDIES AT 500 MB IN WINTER AND THEIR PROBABILITY DENSITY DISTRIBUTIONS

The first empirical orthogonal function (EOF) is representative of the wintertime stationary eddies: the second and the fourth show good similarity to the PNA and WA teleconnection patterns, respectively. The pattern of the fifth EOF resembles a zonal wavenumber-3 with a latitudinally confined amplitude. The probability density distributions, estimated by means of nonparametric statistical techniques, have been computed both for the time-dependent amplitudes of individual EOFs. The EOF-5 appeared to be particularly relevant in this analysis; its amplitude shows a bimodal distribution, and bimodality is also found in the distribution of the combined amplitude of the first few EOFs when the fifth is included. The difference between the composite map computed averaging the fields classified in the high-amplitude mode and the corresponding map for the low-amplitude mode shows a positive maxima in regions known to be preferred locations for blocking centers