The Origins of Easterly Waves in the East Pacific (Invited Presentation)

One goal of the upcoming Organization of Tropical East Pacific Convection (OTREC) field program that is being led by David Raymond and Zeljka Fuchs is to characterize the interaction of convection with east Pacific easterly waves (EWs). Fundamental questions remain about the origins of east Pacific EWs, including whether they are primarily locally generated, or result from the reinvigoration of and seeding by African EWs. Recent work on the origins of east Pacific EWs will be briefly summarized, including work conducted by David Raymond and collaborators. Looking forward to OTREC, we will then describe some of our recent results on the genesis of east Pacific EWs derived from reanalysis, satellite, and regional modeling studies. Eddy kinetic energy and vorticity budget analysis shows that the east Pacific provides a favorable environment for local disturbances such as those generated in the Bight of Panama region to grow upscale into EWs. Convection is an important means of vorticity generation within developing EWs. A moisture budget is used to explain the spatial distribution of convection within growing EWs that imprints a tilted vorticity structure on the wave leading to barotropic growth. Variations in the Caribbean low-level jet and Madden-Julian oscillation importantly (but differently) modify the environment in which EWs exist and are responsible for a significant modulation of EW activity. A regional modeling study in which topography near the Bight of Panama is flattened to suppress local orographically-generated convective disturbances produces a substantial reduction in east Pacific EW activity. These results support a local generation mechanism for east Pacific EWs. OTREC promises to help answer many outstanding questions on these issues.