northwestern and southwestern North America38 are well correlated with this time series of the decadal ENSO-like climate phenomenon.

Other Patterns

The patterns described above, while prominent in the literature and displaying variability on decadal timescales, represent only a subset of the decadal- to century-scale patterns identified and may or may not be of any more value than patterns not discussed here. For example, a number of regional atmospheric patterns have been analyzed, such as the North Pacific Oscillation,39 West Pacific Oscillation,40 West Atlantic Pattern,41 and Pacific Decadal Oscillation.42 A completely different kind of pattern, involving sea ice, has been found in the Southern Ocean. The Antarctic Circumpolar Wave is characterized by deviations in the Antarctic sea ice extent from monthly climatological averages, although it is also apparent in surface wind, SST, and SLP anomalies along the Antarctic polar front, near the winter marginal ice zone.43 It is also highly coherent with temporal variations in ENSO44 and Indian Ocean monsoons.45 Other atmospheric patterns have been identified in the Southern Hemisphere,46 though the data are frequently too few to allow detailed analyses.

In addition, there are structures that might be considered climate patterns, although they are often related to the other patterns or presented in a similar manner. For example, the Asian monsoon, while predominantly a seasonal signal, is strongly correlated with ENSO and shows decadal variability as indexed by precipitation and wind speeds over India.47 Some investigators treat this monsoon pattern as a distinct, decadally varying pattern. Also, global thermohaline circulation has been tied to distinct changes in the ocean surface conditions and NAO in the North Atlantic Ocean. Extensive studies have shown the relationship between the NAO, ocean conditions, and thermohaline circulation, although no unique pattern has been defined.

Finally, the COWL pattern, while not a fundamental mode of climate variability, as defined by the decomposition of climatological variable fields, or a particular climate phenomenon, does appear to represent a distinct geographic distribution of near-surface temperature anomalies. Despite the apparent shortterm memory of the COWL pattern, it displays long-term variability, as discussed in the case study above of anthropogenic “greenhouse” warming. Thus, COWL does represent another pattern and is often cited as such.

Research Imperatives for Explaining Climate Patterns

The large heat capacity and slow changes of the ocean must play a considerable role in climate anomalies persisting or evolving over decade to century timescales. This role is directly realized through SST, which sets the thermal contrast between the atmosphere and ocean and thus controls (together with



The National Academies | 500 Fifth St. N.W. | Washington, D.C. 20001
Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement