Biennial Variations in Surface Temperature over the United States as Revealed by Singular Decomposition

Abstract

Surface temperature variations over the contiguous United States during the period 1931–75 are examined using mean monthly averages for the 344 climate divisions. This data matrix is decomposed into orthogonal components using the method of singular decomposition. The third empirical orthogonal function, which accounts for nine percent of the nonseasonal variance, exhibits a significant quasi-biennial oscillation (QBO). The phase and amplitude of the QBO implied by this analysis were further studied using an extension of the singular decomposition method which we call Hilbert Singular Decomposition (USD). HSD uses the Hilbert Transformer to augment the data matrix and transform the real elements into complex elements so that coherent “wavelike” variations can be represented in terms of a complex singular decomposition. Additional cross-spectral analyses were performed for selected climate division aggregates. Two areas of maximum QBO amplitude are indicated; one over the northeastern United States, and a less distinct area over the southwestern United States. Variations in the two areas appear to be almost 180° out of phase.