To what extent the recent upward trend in hemispheric mean surface air temperature should be purely ascribed to persistent circulation-related anomalies, is still an open question. The purpose of this study is to clarify the role played by the internal atmospheric variability in generating hemispheric mean surface air temperature anomalies. To investigate this problem an analysis is performed on a basis of monthly mean values from a 1000-years integration of the ECHAM1-LSG coupled model in which only the cold season was considered. In order to isolate important coupled modes of variability between time series of 500 hPa geopotential height and two metres temperature, a Canonical Correlation Analysis (CCA) was carried out. The two fields were prefiltered by retaining only the projection of each field on a (particular) subset of its Empirical Orthogonal Functions (EOFs) then applying CCA. This analysis has identified fairly distinct patterns associated with positive and negative trends of the hemispheric-mean surface air temperature. It is found that fluctuations in hemispheric-mean surface air temperature in the model are correlated with the strength of the North Atlantic Oscillation. The model results are then compared with the available observations.
VARIATIONS IN HEMISPHERIC AIR-SURFACE TEMPERATURE ASSOCIATED WITH LARGE SCALE FLOW PATTERNS
1998
Abstract
To what extent the recent upward trend in hemispheric mean surface air temperature should be purely ascribed to persistent circulation-related anomalies, is still an open question. The purpose of this study is to clarify the role played by the internal atmospheric variability in generating hemispheric mean surface air temperature anomalies. To investigate this problem an analysis is performed on a basis of monthly mean values from a 1000-years integration of the ECHAM1-LSG coupled model in which only the cold season was considered. In order to isolate important coupled modes of variability between time series of 500 hPa geopotential height and two metres temperature, a Canonical Correlation Analysis (CCA) was carried out. The two fields were prefiltered by retaining only the projection of each field on a (particular) subset of its Empirical Orthogonal Functions (EOFs) then applying CCA. This analysis has identified fairly distinct patterns associated with positive and negative trends of the hemispheric-mean surface air temperature. It is found that fluctuations in hemispheric-mean surface air temperature in the model are correlated with the strength of the North Atlantic Oscillation. The model results are then compared with the available observations.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
