The Effect of Large-Scale 16-Day Free Rossby Waves on Tropical Convection.

The presence of External Rossby (ER) waves has been documented throughout the literature. Many studies have found that these phenomena can affect the large-scale flow, one of these ways includes the possibility of exiting stationary forcing by resonance. In recent studies, resonance from westward moving Rossby waves has been found to be a possible mechanism to explain the occasional formation of blocking ridges over the Northern Atlantic Ocean. Little has been done on the effect of these modes on the large-scale circulation of the tropics. An Empirical Orthogonal Function (EOF) analysis was performed on the 15-30 day filtered vertically average geopotential height anomalies to extract its spatial patterns. The second and third EOFs are in quadrature with each other, representing a westward moving signal with an average period of around 16 days and a phase velocity of, closely resembling the 16-day ER mode. The Principal Components (PCs) from these eigenvectors were used to construct an External Rossby Wave Index (ERWI), which was used as a tool to monitor and track this 16-day ER wave. A composite analysis of each phase was performed to analyze the spatial structure of this wave. 100-day running average Outgoing Longwave Radiation (OLR) composites showed a westward moving active convection anomalies initiating in phase 5 over the eastern Pacific, moving west though phases 6-8 to the Maritime continent. Further investigation is needed to find a possible mechanism for the formation of these anomalies.