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Variability in the width of the tropics and the annular modes
Author(s) -
Kidston J.,
Cairns C. W.,
Paga P.
Publication year - 2013
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 - 10.1029/2012gl054165
Subject(s) - hadley cell , latitude , geology , climatology , atmospheric sciences , geodesy , climate change , general circulation model , oceanography
The correlation between unforced variability in the latitude of the edge of the Hadley cell (Φ HC ) and latitude of the surface westerlies (Φ EDJ ) is examined using a simplified moist general circulation model (GCM) and a suite of state of the art GCMs. The correlation can be determined by the time‐mean separation of the two features. When the separation is small, there is a positive correlation, and as the separation between them increases, the correlation reduces. In the simplified model, a weak negative correlation emerges at large separations. The location of the anomalous meridional mass flux associated with variations in the latitude of Φ EDJ , relative to the climatological Hadley cell position, determines the extent to which Φ HC is influenced by changes in Φ EDJ . Changes in the latitude of Φ EDJ are driven by anomalous eddy momentum flux convergence, and these are approximately balanced by the Coriolis torque on the meridional flow, as expected under quasi‐geostrophic scaling. Under changing time‐mean climates, the anomalous flow associated with Φ EDJ variability translates location so that it is approximately fixed relative to the time‐mean Φ EDJ . This means that the influence of Φ EDJ variability on Φ HC varies as a function of the time‐mean separation of the features. Initial indications are that the same causal relationship holds in a suite of state of the art GCMs and that this explains the seasonal variation in the correlation between Φ HC and Φ EDJ .