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Annular modes in global daily surface pressure
Author(s) -
Baldwin Mark P.
Publication year - 2001
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/2001gl013564
Subject(s) - empirical orthogonal functions , surface pressure , anomaly (physics) , climatology , sign (mathematics) , arctic oscillation , geology , mode (computer interface) , polar , oscillation (cell signaling) , sea surface temperature , physics , atmospheric sciences , northern hemisphere , mathematics , chemistry , oceanography , mathematical analysis , biochemistry , astronomy , computer science , condensed matter physics , operating system
Annular modes are patterns characterized by synchronous fluctuations in surface pressure of one sign over the polar caps and the opposite sign at lower latitudes. The Southern Annular Mode (SAM) and Northern Annular Mode (NAM, also called the Arctic Oscillation) patterns are the leading empirical orthogonal functions (EOFs) of slowly‐varying, hemispheric, cold‐season, sea‐level pressure anomalies (deviations from climatology). Daily indices of the SAM and NAM are a measure of the similarity between surface pressure anomaly patterns and the annular modes. Here it is shown that the first two EOF time series of daily, global, year‐round, zonally‐averaged surface pressure are nearly identical to the SAM and NAM indices. Together they account for more than 57% of the daily variance of zonally‐averaged surface pressure. The SAM and NAM patterns extend through the tropics, well into the opposite hemispheres. Fluctuations of the SAM and NAM indices are accompanied by interhemispheric transfer of mass.