Fluctuations in Northern Hemisphere 700 mb Height Field Associated with the Southern Oscillation

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  • 1 Climate Analysis Center, NMC, NWS, NOAA Washington, DC 20746
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Abstract

Variations in the mid-troposphere circulation associated with the Southern Oscillation (SO) are investigated and documented using mean monthly 700 mb height data for the period 1951–79. The SO was defined by a Southern Oscillation Index (SOI) consisting of the difference in normalized mean monthly sea-level pressures at Tahiti and Darwin. Results for all four seasons are presented in the form of lagged, as well as contemporaneous, correlations and composites of height anomalies obtained separately for high and low SOI values.

Different SO teleconnection patterns are observed for each season. Strongest SO signals appear in the winter with SOI leading the height field by one to two seasons. The time lead may he useful in prognostic applications. The correlation in the summer is negligible. The winter teleconnection pattern over the North Pacific-North America-North Atlantic sector is similar to that shown by Bjerknes and others. Patterns for other seasons are also presented. The statistical significance of the various teleconnections patterns is discussed.

Distinct features are observed for the high and low SOI composites, where low SOI's are closely related to above normal equatorial central Pacific sea-surface temperatures. The high SOI composite in winter shows a tendency for more pronounced North America negative anomalies and North Atlantic positive anomalies, suggesting an association with one of the two phases of the North Atlantic Oscillation. The high SOI composites of other seasons also show more pronounced anomalies in various regions.

Abstract

Variations in the mid-troposphere circulation associated with the Southern Oscillation (SO) are investigated and documented using mean monthly 700 mb height data for the period 1951–79. The SO was defined by a Southern Oscillation Index (SOI) consisting of the difference in normalized mean monthly sea-level pressures at Tahiti and Darwin. Results for all four seasons are presented in the form of lagged, as well as contemporaneous, correlations and composites of height anomalies obtained separately for high and low SOI values.

Different SO teleconnection patterns are observed for each season. Strongest SO signals appear in the winter with SOI leading the height field by one to two seasons. The time lead may he useful in prognostic applications. The correlation in the summer is negligible. The winter teleconnection pattern over the North Pacific-North America-North Atlantic sector is similar to that shown by Bjerknes and others. Patterns for other seasons are also presented. The statistical significance of the various teleconnections patterns is discussed.

Distinct features are observed for the high and low SOI composites, where low SOI's are closely related to above normal equatorial central Pacific sea-surface temperatures. The high SOI composite in winter shows a tendency for more pronounced North America negative anomalies and North Atlantic positive anomalies, suggesting an association with one of the two phases of the North Atlantic Oscillation. The high SOI composites of other seasons also show more pronounced anomalies in various regions.

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