An Observational and Numerical Study of Blocking Episodes near South America

Abstract

European Centre for Medium-range Weather Forecasts analyses during June 1985 are used to characterize the flow in the South America sector during a typical blocking episode. Numerical experiments are performed using a hemispheric shallow-water model to test whether such blocking episodes can be a result of local resonance between forced Rossby waves generated by the Andes Mountains and by an upstream forcing. It appears that while blocks generated in the Atlantic Ocean may respond to this mechanism from the beginning, the more frequency ones that develop from a ridge that advances from the Pacific Ocean may also benefit from it in the intensification and maintenance stages.