Teleconnections

Teleconnections are hemispheric-scale statistical relationships that result from the spatial interdependencies between the atmosphere and the ocean. In other words, teleconnections describe how atmospheric or oceanic circulation changes occurring at one location are linked to changes at other locations that are widely separated geographically. On the order of weeks to years, these global associations are recognized by an atmospheric circulation disturbance occurring at select locations or “centers of action,” thereby producing oscillations affecting weather patterns downstream. These action centers identify the climatological positions of low- and high-pressure areas associated with particular atmospheric teleconnection patterns or cold and warm sea surface temperature regions with oceanic teleconnection patterns. Frequently, atmospheric oscillations are strongly linked or coupled with oceanic changes. Locations in the vicinity of the action centers shift from characteristic climatologically normal conditions to distinct patterns of climate anomalies that [Page 2790]occur over a range of time periods. The climate anomalies produced by a teleconnection pattern depend on its phase, indicating the prevailing extremes in the action center variable. Teleconnection patterns represent a principal mode of annual large-scale atmospheric circulation variability that produces both short- and long-term regional climate effects.

Teleconnections are identified through statistical techniques demonstrating the degree to which fluctuations in a variable are related to two or more separate areas. Correlation analysis describes the strength and direction of association between paired variables, such as pressure changes in one location compared with all other locations. The El Niño Southern Oscillation (ENSO) is typically identified in this manner. ENSO is an interannual periodic abnormal warming or cooling of the eastern equatorial Pacific SSTs that is regularly accompanied by a shift in the typical surface pressure field between the Australian and Peruvian coasts, the primary action centers that are strongly negatively correlated. Eigenvector-based methods, such as principal component analysis, allow one to detect groups of interrelated variables, simplify the representation of the data field, and recognize similar regional modes of variability. The Pacific/North American pattern is often produced from eigenvector methods that distinguish three primary action centers across North America based on the cold season midtropospheric geopotential height field (i.e., the altitude of the 500- or 700-hectopascal pressure surface). Statistical methods such as these have been used to recognize sets of action centers unique to each teleconnection pattern.

The strength, phase, and location of the teleconnection pattern establish the geographical extent and severity of the climate impacts. For instance, strongly positive ENSO phases (or El Niño) during December to February are typically linked to increased precipitation in northwestern South America and the Southern United States, decreased precipitation in Northern Australia, and higher temperatures in northwestern Canada and South Asia; negative ENSO phases (or La Niña) usually have the reverse effects. The expected climate anomalies associated with a teleconnection phase suggests a potential for increased long-range climate forecasting. Consequently, teleconnections has been a major component of atmospheric research in recent decades.