Decadal variations in tropical Pacific climate are examined using a centennial record of SST and a five-decade long reanalysis of upper ocean temperature and surface meteorology. Indices are defined to reflect the decadal characteristics of the midlatitude and tropical ocean and much of the paper focuses on understanding the fluctuations of these indices.

In midlatitudes the analysis reveals structures reminiscent of the Latif-Barnett advective mode. However, in the tropics the climate variability takes on a rather different character. Along the equator upper ocean heat content anomalies appear first in the west. These anomalies appear slowly to propagate eastward. The arrival of these anomalies in the eastern basin 5-6 years later are accompanied by SST anomalies of the same sign and corresponding changes in low level winds. Examination of the off-equatorial expression of these anomalies, indeed, reveal that they have many characteristics of a decadal ENSO.