Global Teleconnections in the 250-mb Streamfunction Field during the Northern Hemisphere Winter

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Abstract
Teleconnections of the streamfunction in the global domain based on ECMWF 250-mb winds for the 11 northern winters from 1978/79 through 1988/89 are documented in this study. A zonal structure with a node near the equator, indicating an out-of-phase relationship between the streamfunctions in the Northern and Southern hemisphere, appears to mask the fluctuations of the asymmetric components of streamfunction. After removing zonal means, a global pattern emerges as the dominant structure in the low-frequency band. This pattern consists of several dipoles straddling either the exit region of midlatitude jets or the equator, indicating the existence of teleconnections not only between the midlatitudes and the tropics but also between the Northern and Southern hemispheres. Teleconnection patterns in the intermediate-frequency band are predominantly wavelike. Seven waveguides are identified based on the one-point lag-correlation maps for base points near the maximum teleconnectivity. Among them are three waveguides that have not been identified in previous studies. One originates in Europe, skirts the southern Eurasian continent, and spreads into the western Pacific. The other two originate in the northern central Pacific and the North American continent, respectively, and cross the equatorial regions of the westerlies into the Southern Hemisphere. The existence of cross-equatorial waveguides indicates the possibility of interhemispheric interaction and is in agreement with the hypothesis of Webster and Holton. Squared refractive indices are calculated based on the climatological flow and are found to be consistent with the existence of waveguides.

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