Relation between tropical easterly wave convection and tropical cyclogenesis over the Atlantic and east Pacific
Date of Award
Doctor of Philosophy (PhD)
Sundar A. C.
Walter A. Petersen
John R. Mecikalski
Atmospheric thermodynamics., Convection--Meteorology., Cyclones--Tropics, Lightning.
The characteristics of tropical easterly wave convection and the possible implications of convective structure on tropical cyclogenesis and intensification over the Atlantic Ocean and East Pacific were investigated in this study. Easterly waves were partitioned into northerly, southerly, trough, and ridge phases based on 700-hPa meridional wind data. Waves were subsequently divided according to whether they did or did not develop tropical cyclones (i.e., developing waves [DWs] and non-developing waves [NDWs], respectively), and composites of synoptic-scale and convective-scale variables as a function of wave phase and category were created using Eulerian and Lagrangian frameworks. Results of both the Eulerian and Lagrangian composites indicate that the greatest difference between DWs and NDWs is observed for the fractional coverage by infrared brightness temperatures ≤240 K and ≤210 K. Indicators of convective intensity (e.g., lightning flash rates, mean convective reflectivity profiles) provide relatively few statistically significant differences between DWs and NDWs, except over the East Pacific. In addition, the Lagrangian composites suggest that as genesis is approached for DWs, the coverage by convection and cold cloudiness increases, while convective intensity decreases. In contrast, convective coverage and intensity both increase with time for NDWs. Thus, the results of both the Lagrangian and Eulerian frameworks suggest that the coverage by cold cloudiness/convection is generally more important than convective intensity for tropical cyclogenesis. In terms of large-scale variables, both types of composites suggest that enhanced upper-level (~200 hPa) divergence and deep-layer moisture are particularly important for cyclogenesis and for distinguishing DWs from NDWs. The Eulerian composites also suggest that favorable large-scale conditions for cyclogenesis (e.g., significantly greater low-level [~925 hPa] vorticity) occur for Atlantic DWs relative to NDWs over regions farther east away from where these DWs spawn cyclones. In contrast, favorable conditions for tropical cyclogenesis don't develop for waves that spawn tropical cyclones over the East Pacific until these waves move over the East Pacific. Results of this study contribute to a greater understanding of the processes involved in tropical cyclogenesis and may contribute to applications that help improve forecasts of cyclogenesis from easterly waves.
Leppert, Kenneth D. II, "Relation between tropical easterly wave convection and tropical cyclogenesis over the Atlantic and east Pacific" (2012). Dissertations. 1.