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Signals in atmospheric pressure variations from 2 to ca . 70 months: Part I, simulations by two coupled ocean—atmosphere GCMs
Author(s) -
Hameed Sultan,
Currie Robert G.,
Lagrone Howard
Publication year - 1995
Publication title -
international journal of climatology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.58
H-Index - 166
eISSN - 1097-0088
pISSN - 0899-8418
DOI - 10.1002/joc.3370150803
Subject(s) - atmosphere (unit) , atmospheric sciences , climatology , gcm transcription factors , flux (metallurgy) , atmospheric pressure , spectral line , latitude , harmonics , environmental science , physics , mathematics , meteorology , general circulation model , geology , climate change , chemistry , oceanography , organic chemistry , quantum mechanics , astronomy , voltage
The Fourier transform of daily averaged solar flux at the top of the atmosphere shows that the spectrum is discrete at all latitudes with lines at 12, 6, 4, 3, 2·4, 2 months, etc., which follows from the orbital characteristics of the Earth. Application of the Fourier transform to over 6000 monthly air pressure series simulated by two different versions of the Oregon State University (OSU) general circulation model (OSU‐GCM) shows the same structure, and world‐wide the mean contributions of 12, 6, and 4·2 month signals to total variance are 40, 10, and 4 percent, respectively. The Fourier spectra also yield significant subharmonic peaks, with periods T 1 ≃ 40 and T 2 ≃ 26 months, the quasi‐triennial (QTO) and quasi‐ biennial (QBO) oscillations, and with a period T 3 ≃ 14 months, the atmospheric pole tide (APT). The spectra also yield evidence for a further 33 significant peaks, which can be explained as summation and difference tones caused by interaction of the annual and its five harmonics (first set of parents) with the subharmonics T i , i = 1 to 3 (second parents), and the expression for the tones is\documentclass{article}\pagestyle{empty}\begin{document}$$ f_{i \pm j} = 1/T_i \pm (j + 1)/12 $$\end{document}cycles per month (cpm), where j = 0,…5. The only requirement physically for these interactions is that the atmosphere be weakly non‐linear, a requirement now obviated by a simplified atmospheric model of O'Brien and Currie. World‐wide, the contribution to total variance of the 33 tones and three subharmonics is 26·8 per cent, whereas the contribution of noise is 19·4 per cent. The root‐mean‐square (RMS) errors between observations of the 33 frequencies, and between those predicted by the above equation, in the two OSU‐GCM simulations are 0·0015 and 0·0010 cpm, respectively. The two sets of parents and 33 tones vary in period from 2 to ca. 70 months and demonstrate that the spectrum of climate on these time‐scales is ‘signal‐like’ rather than ‘noise‐like’ as traditionally believed.