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Understanding deep convection by parameterizing large-scale dynamics

By: Adam Sobel, Professor, Columbia University

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Tight coupling between deep convection and larger-scale circulations in the atmosphere makes it difficult to understand the causal factors which control variations in precipitation on a range of space and time scales. One approach to untangling these factors involves simulating the convection in a small domain and parameterizing the large scale circulations which connect that domain to the rest of the atmosphere. The weak temperature gradient approximation is one such large-scale parameterization, based on well-understood aspects of geophysical fluid dynamics near the equator and thus appropriate for the study of tropical convection. I will review application of the weak temperature gradient approach to a range of specific observed phenomena in the tropics, including El Nino, the Madden-Julian oscillation, and tropical cyclones. I will then present a new large-scale parameterization appropriate outside the deep tropics, using the quasi-geostrophic omega equation. A motivation for this latter work is to understand the dynamics behind extreme precipitation events in the subtropics and midlatitudes, and I will show results from its application to the events leading to the 2010 floods in Pakistan.

Host: Charles Jackson, UTIG

When: Fri Jan 27, 2017 11:30am – 12:30pm Central Time