Using Stable Water Isotopes to investigate the Structure of Vertical Motions in the Tropics.

Obtaining a complete understanding of the interaction between convection and the large-scale circulation in the tropics remains an outstanding problem. The vertical structure of convective heating has been shown to have great influence in the large-scale response, and evidence suggests that it also has considerable geographical variation. How the vertical structure of convective heating, or, equivalently, of vertical velocity, varies across the tropical Pacific is still a matter of debate. Here, we show how stable water isotopes could be used to shed some light on the topic. Because these isotopes tend to be progressively less abundant with increasing height, precipitation associated with top-heavy profiles should be expected to be more depleted than that associated with bottom-heavy profiles. We verify this claim using a variety of sources: first, using observations from IAEA/WMO Global Network of Isotopes in Precipitation stations; then, using a simple model based on the budget of water isotopes in precipitation; finally, using a more complex isotope-enabled general circulation model. Finally, we show that the data from the Pacific, although scarce, suggests that precipitation in the eastern part is more enriched—and thus associated with more bottom-heavy velocity profiles—than that in the western part of the basin.