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Preferred structures in large‐scale circulation and the effect of doubling greenhouse gas concentration in HadCM3
Author(s) -
Hannachi A.,
Turner A. G.
Publication year - 2008
Publication title -
quarterly journal of the royal meteorological society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.744
H-Index - 143
eISSN - 1477-870X
pISSN - 0035-9009
DOI - 10.1002/qj.236
Subject(s) - hadcm3 , climatology , greenhouse gas , northern hemisphere , environmental science , carbon dioxide , atmospheric sciences , climate change , general circulation model , geology , chemistry , oceanography , gcm transcription factors , organic chemistry
Preferred structures in the surface pressure variability are investigated in and compared between two 100‐year simulations of the Hadley Centre climate model HadCM3. In the first (control) simulation, the model is forced with pre‐industrial carbon dioxide concentration (1 × CO 2 ) and in the second simulation the model is forced with doubled CO 2 concentration (2 × CO 2 ). Daily winter (December–January–February) surface pressures over the Northern Hemisphere are analysed. The identification of preferred patterns is addressed using multivariate mixture models. For the control simulation, two significant flow regimes are obtained at 5% and 2.5% significance levels within the state space spanned by the leading two principal components. They show a high pressure centre over the North Pacific/Aleutian Islands associated with a low pressure centre over the North Atlantic, and its reverse. For the 2 × CO 2 simulation, no such behaviour is obtained. At higher‐dimensional state space, flow patterns are obtained from both simulations. They are found to be significant at the 1% level for the control simulation and at the 2.5% level for the 2 × CO 2 simulation. Hence under CO 2 doubling, regime behaviour in the large‐scale wave dynamics weakens. Doubling greenhouse gas concentration affects both the frequency of occurrence of regimes and also the pattern structures. The less frequent regime becomes amplified and the more frequent regime weakens. The largest change is observed over the Pacific where a significant deepening of the Aleutian low is obtained under CO 2 doubling. Copyright © 2008 Royal Meteorological Society

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