The dynamic effects of the Andes Cordillera on the atmospheric flow: A channel model study

Date of Award




Degree Name

Doctor of Philosophy (Ph.D.)


Meteorology and Physical Oceanography

First Committee Member

Lee E. Branscome - Committee Chair

Second Committee Member

Rainer Bleck - Committee Member


The influence of the Andes Cordillera upon the stationary, standing and transient aspects of the atmospheric flow is studied. A 7-layer dry primitive equation channel model is Mercator geometry is used. The model employs a sigma-modified vertical coordinate in which the coordinate surfaces do not follow the terrain but rather intersect it.Two sets of experiments with and without topography are performed. A Newtonian forcing term in the thermodynamic equation allows long term integrations which are carried out for more than 500 days in this study. The two sets of experiments differ in the initial conditions and forcing potential temperature fields used. They have a frontal zone which is either located to the north (the northern set) or to the south (the southern set) of 29$\sp\circ$S.The experiments go through two distinct phases. The adjustment period spans the first 5 months of the integrations approximately, and is characterized by the southward displacement of the mean-zonal jet. The post-adjustment period is distinguished by the enduring presence of the jet in its equilibrium position.Eliassen-Palm cross sections drawn for the adjustment period suggest a direct link between the southward movement of the mean-zonal jet and the direction of the eddy momentum fluxes. Their orientation changes from equatorward to poleward as the mean-zonal jet starts to move southward.A realistic mean meridional circulation is seen during the post-adjustment phase in the southern experiments and the northern experiment with orography. Convergence of transient meridional heat and momentum fluxes plays a major role on the maintenance of the mean-zonal jet in its latitudinal position of equilibrium.The mountain experiments are dominated by synoptic time scales (4-5 days) while longer periods (30-60 days) predominate in the no-mountain integrations.The presence of the Andes Cordillera favors (a) cyclone deepening near 50$\sp\circ$S in Patagonia, Argentina, due to mountain-induced release of baroclinic instability; (b) small amplitude but statistically significant standing waves in the 500 mb geopotential field; (c) enhanced convergence of transient meridional momentum flux near (45$\sp\circ$S, 70$\sp\circ$W); (d) a significant increase in the value of poleward transient heat fluxes and their convergence in the vicinity of the orography.


Physics, Atmospheric Science

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