Adam H. Sobel
Department of Applied Physics and Applied Mathematics,
Department of Earth and Environmental Sciences,
Lamont-Doherty Earth Observatory,
Understanding deep convection by parameterizing large-scale dynamics
Room 811 AOSS, May 2, 2016, 3:30 PM
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.