The Tropical Precipitation Response to Andes Topography and Ocean Heat Fluxes in an Aquaplanet Model

Abstract

his aquaplanet modeling study using the Geophysical Fluid Dynamics Laboratory Atmospheric Model, version 2.1 (GFDL AM2.1), examines how ocean energy transport and topography influence the location of tropical precipitation. Adding realistic Andes topography regionally displaces tropical rainfall from the equator into the Northern Hemisphere, even when the wind?evaporation feedback is disabled. The relative importance of the Andes compared to the asymmetric hemispheric heating of the atmosphere by ocean transport is examined by including idealized and realistic zonally averaged surface heat fluxes (also known as q fluxes) in the slab ocean. A hemispherically asymmetric q flux displaces the tropical rainfall toward the hemisphere receiving the greatest heating by the ocean. The zonal-mean displacement of rainfall is greater in simulations with a realistic q flux than with a realistic Andes topography. Simulations that add both a q flux and topography displace rainfall farther to the north in the region 120° to the west of the Andes than in simulations that only have a q flux. Cloud and clear-sky radiative feedbacks in the tropics and subtropics of this model both act to amplify the energy flux and the precipitation response to a given hemispheric asymmetry in oceanic forcing.