Orthogonal Wavelet Analysis: Interannual Variability in the Sea Surface Temperature

Abstract

The unique capability of orthogonal wavelets, which have attractive time-frequency localization properties as exemplified by the Meyer wavelet, is demonstrated in a diagnosis of the interannual variability using a 44-year dataset of the sea surface temperature (SST). This wavelet analysis is performed in conjunction with an empirical orthogonal function analysis and a Fourier analysis to illustrate their complementary capability. The focus of this article is on the equatorial Pacific SST, which is known to have far-reaching impacts on short-term climate variability. The Meyer spectrum brings to light intriguing episodic characteristics of three separate sequences of El Niño (abnormally warm) and La Niña (abnormally cold) events during the past 42 years. It quantities the relative contributions to the variability associated with different frequency ranges at different times. Through a wavelet cross-spectral analysis with the SST at an equatorial location and at a midlatitude location in the Pacific Ocean, the planetary character of the SST field associated with such events is also illustrated.