Eastern equatorial Pacific SST variability: ENSO and non-ENSO components and their climatic associations

Using an updated Kaplan et al. global SST anomaly (SSTA) dataset (1870-1999 ) a canonical representation of El Nino-Southern Oscillation (ENSO) is cons tructed. When this canonical ENSO is subtracted from the data, a residual ( non-ENSO) dataset for SSTA is left that includes interseasonal to multideca dal variability. Over the eastern equatorial Pacific (Nino-3) the canonical ENSO accounts for about 79% of the total SSTA variability, and the residua l, dominated by decadal timescales, accounts for the rest. In particular, a bout 40%-50% of the amplitudes of the strong 1982-83 and 1997-98 El Nino ev ents were accounted for by the residual variability. The non-ENSO variabili ty is characterized by the known shift from cold to warm eastern tropical P acific in the mid-to late 1970s as well as by a (nonstationary) interannual variance increase during the 1980s and 1990s. Composite maps of surface (SST, sea level pressure, and winds) and troposph eric (divergent winds, velocity potential, and vertical velocity) variables are used to compare the spatial patterns characterizing the canonical ENSO and the residual components of the Nino-3 variability. The residual compos ites are found to only share large-amplitude fluctuations of SST anomalies in the equatorial Pacific east of the date line. When these composites are separated into decadal and interannual components, the decadal part closely resembles the structure of the Pacific decadal oscillation. The major patt erns of tropospheric variability associated with the ENSO and decadal non-E NSO components are very different. At low latitudes, they imply nearly oppo site impacts on farfield regional climates, based on their respective warmi ng (or cooling) phases within the Nino-3 region. This unexpected result for low-latitude climate associations runs contrary to the naive expectation ( recently shown to be true for North America) that a decadally warm tropical east Pacific will reinforce the climate effects associated with ENSO alone . This indicates that, in the Tropics, climate outlooks may be more accurat e if based on separately analyzed relationships between these SSTA componen ts and their associated climate fluctuations.