A Comparison of Intermonthly and Interannual Teleconnections in the 700 mb Geopotential Height Field during the Northern Hemisphere Winter

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Abstract
Intermonthly and interannual teleconnection patterns in the 700 mb geopotential height field during the Northern Hemisphere winter are computed by the method of digital filtering and spatial correlation analysis. A comparison of the teleconnection patterns of the intermonthly signal with the patterns described by Wallace and Gutzler shows that the western Pacific, western Atlantic and Pacific-North American patterns are clearly defined by the intermonthly signal; weak evidence for the eastern Atlantic pattern is also found. A northern Asian pattern, having one center over Mongolia and another over the Kara Sea near 70°N, 70°E, is also found to be a prominent feature of the intermonthly signal. The one-point correlation maps show that the spatial correlation function is dominated by the intermonthly band. The Pacific-North American pattern is well-defined in both the intermonthly and interannual bands. Three additional patterns—the North Pacific, the Eurasian and the zonally-symmetric seesaw—appear in the interannual band. The North Pacific and Pacific-North American patterns qualitatively resemble patterns obtained by Horel and Wallace and by Chen in their studies of interannual teleconnections with the equatorial Pacific, while the, zonally-symmetric seesaw resembles the pattern identified by van Loon and Rogers. However the North Pacific, Pacific-North American and zonally-symmetric seesaw patterns are correlated with each other and with an index of the Southern Oscillation, suggesting that they are not independent modes of atmospheric variability. The fact that some teleconnection patterns can be separated into either the intermonthly band or the interannual band suggests that there may be some important differences in the dynamical mechanisms responsible for the variability. The results also suggest that digital filtering may be a useful method for isolating the low-frequency disturbances in observed data or in the mutts of climate change simulations.

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