Secular changes of annual and interannual variability in the tropics during the past century

Wavelet transforms, which can unfold signals in both time and frequency domains, are used to analyze the Comprehensive Ocean and Atmospheric Data Sets for the period 1870-1988. The focus is on secular changes in the interannual variability and the annual cycle of selected equatorial regions. The amplitude of El Nino/Southern Oscillation (ENSO) is found to be large from 1885 to 1915, to be small during the period 1915-1950, and to increase rapidly after about 1960. Surprisingly, the decadal variations in the amplitude of ENSO are not matched by similar decadal variations in the amplitude of the annual cycle. -from Authors