Downdraft Impacts on Tropical Convection

January 25, 2013

Katherine Thayer-Calder

Committee: Dave Randall (advisor), Eric Maloney, Dick Johnson, Michelle Strout (Computer Science)

Abstract

Downdrafts are an integral part of the convective cycle, and have been observed and documented for more than a hundred years. But many questions still surround convective downdrafts and their most difficult to observe properties. These questions have made the parameterization of convective downdrafts in global climate models (GCMs) very difficult. Designers of parameterizations have resorted to a wide range of assumptions and unverified hypotheses in their models of convective downdrafts.

In the last ten years, computing resources have advanced to a point where large domain, high resolution cloud resolving models (CRMs) can easily be run for long simulations. This study uses 1 km horizontal resolution simulations from the System for Atmospheric Modeling (SAM) v6.8.2 to examine convective downdrafts. We consider a variety of assumptions and questions that arise in the development of convective parameterizations. This study explores convective mass budgets, boundary layer variability and quasi- equilibrium, and buoyancy sources and magnitudes within downdrafts.