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Volume 17,     Number 1,     Spring 2009

 

POLEWARD EXPANSION OF HADLEY CELLS
WILLIAM F. LANGFORD AND GREGORY M. LEWIS

Abstract. Reanalyses of climate data for recent decades have indicated that the Hadley cells of the atmospheric circulation are expanding toward the poles as well as slowing in their circulation velocity. Similarly, recent meteorological data show a poleward movement of the jet streams that affect midlatitude weather. Although the precise mechanism of these changes in Hadley cells and jet streams is not fully understood, it is believed to be linked with global warming. In this paper we study a simple mathematical model to investigate whether such qualitative changes could be induced purely by the physics of rotating spherical convection. The model consists of the Navier-Stokes equations for a Boussinesq fluid, rotating in a spherical shell, differentially heated with a latitudinal surface temperature gradient. Many other factors that influence the atmospheric circulation are excluded from this model. A decrease in the pole-to-equator temperature gradient in the model leads to an expansion and slowing of the Hadley circulation as well as a poleward movement of jet streams, thus suggesting a simple mechanism for these observed climate changes.

 

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