Interannual Variability and Predictability of 500 mb Geopotential Heights over the Northern Hemisphere

Abstract

The interannual variability of monthly mean 500 mb heights in a 15-year sample of observed data is compared to the variance expected from sampling errors associated with high-frequency fluctuations using the analysis of variance approach. The monthly mean ?signal? stands out significantly from the ?noise? over a substantial fraction of the Northern Hemisphere during the winter. The expected spectrum of variance at very low frequencies is assumed to be white at frequencies lower than (30 days)?1 rather than the (96 days)?1 cutoff used by Madden. This difference is justified by observing that the effective time between independent samples T0 is relatively insensitive to changes in the maximum lag over which the local autocorrelation is integrated to calculate T0. Further non-randomness in the variance of 500 mb heights is evidenced by the correlation between monthly mean height and contemporaneous daily variability.