Dynamics of the Shallow Meridional Circulation in the Tropical Eastern Pacific

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The generally accepted view of the meridional circulation in the tropical Eastern Pacific is one of a deep overturning cell driven by deep convective heating in the inter-tropical convergence zone, similar to the zonal mean Hadley circulation. However, recent observations of the atmosphere from a field campaign have called this view into question. In several independent data sets, a significant meridional return flow out of the region of the inter-tropical convergence zone was observed, but not only at high altitudes, but at low altitudes just above the atmospheric boundary layer. The causes and dynamics of this shallow return flow will be investigated with theoretical models and high-resolution three-dimensional numerical modeling. The interaction of the shallow return flow with the atmospheric boundary layer through shear-driven entrainment will be explored. The project will lead to new insights into tropical circulation and climate, as observations and preliminary numerical modeling suggest that this shallow return flow is equal or greater than that at high altitude.