joint Spatiotemporal Modes of Surface Temperature and Sea Level Pressure Variability in the Northern Hemisphere during the Last Century

Abstract

Coherent spatiotemporal modes of climatic variability are isolated based on a multivariate frequency domain singular value decomposition (SVD) of nearly a century of monthly Northern Hemisphere sea level pressure (SLP) and surface temperature data. Insight into the underlying physical processes associated with potential climatic signals is obtained by examining the relationship between surface temperature and inferred atmospheric circulation patterns as they evolve over the a typical cycle, taking potential seasonal distinctions into account. Our analysis provides evidence for two significant independent secular variations describing a secular warming trend (and accompanying changes in circulation patterns) and a century timescale ?oscillation? marked by high-amplitude variations in temperature and SLP in the North Atlantic that are similar to those observed in recent model simulations. Quasi-oscillatory interdecadal (16?18 yr timescale) variability also displays a pattern similar to those predicted in recent model experiments, with an apparent origin in the North Pacific. Weaker quasi-decadal (10?11-yr timescale), largely cold-season oscillatory behavior is more closely tied to the North Atlantic and may involve analogous mechanisms. Interannual variability is examined with an ?evolutive? generalization of our procedure to captures the time-evolving frequency and amplitude characteristics of the associated climate signal. Variability exhibiting the characteristic climatic patterns of the global El Niño-Southern Oscillation (ENSO) phenomenon is described by two largely distinct frequency bands within the broader 3?7-yr ENSO band. The drifting central frequencies of these two dominant bands is suggestive of nonstationary behavior in ENSO. A quasibiennial signal exhibits a gradual trend toward increasing frequency. Prospects for improved long-range climate forecasting are discussed.