On spectra and coherence of tropical climate anomalies

Abstract

Time series of hydrometeorological indices from key tropical land areas, of sea surface temperature (SST), and of sea level pressure (SLP) for various latitude zones of the Atlantic, as compiled from ship observations, form the major basis for a study of variance and coherence characteristics of tropical circulation and climate. The novel non-integer technique of Schickedanz-Bowen is used.

SLP in the Eastern Equatorial Pacific and SLP and SST in the Atlantic show large variance in the long end of the spectrum, thus reflecting the inertia and trend of atmosphere and hydrosphere. However, a marked preference for SLP variations is apparent around 2.5 years in the Equatorial Atlantic, and around 6 and 20 years in the North Australian region. The behavior of SST in the El Niño region off the Ecuador/Peru coast differs from other parts of the World oceans, in that variance is concentrated at 2–8 and around 15 years, rather than the long end of the spectrum. Variance in regional hydrometeorological series is concentrated around 2–2.5, 10, and 13–21 years. Spatial linkages are most prominent around 2.3, 5, 8, and 14 years, and appear related to preferred modes of circulation and climate anomalies identified by earlier stratification and principal component studies.