Impacts of the Three-Dimensional Oceanic Thermal Structure and Translation Speed on Tropical Cyclogenesis and Intensity Fluctuations during the 2005 North Atlantic Hurricane Season

• Main Author: Pino, Jordan Vick
• Other Authors: Trepanier, Jill C.
• Format: Others
• Language: en
• Published: LSU 2015
• Subjects: Geography & Anthropology
• Online Access: http://etd.lsu.edu/docs/available/etd-09222015-180348/

Tropical cyclones are some of the most devastating natural phenomena on the planet. While it has long been recognized that sea surface temperature is an important factor in the evolution of tropical cyclones, it is limited due to its two-dimensional nature. This research seeks to investigate the role of the three-dimensional oceanic thermal structure and translation speed (U_h) on the cyclogenesis and intensity fluctuations of these powerful storm systems. This investigation utilized two main data sets: (1) depth of the 26°C isotherm (D26) which indicates the depth (or volume) of the warm water layer, and (2) hourly-interpolated wind speed (U₁₀) and translation speed (U_h). These two data sets were used to complete an along-track analysis of 23 named tropical systems during the 2005 North Atlantic basin hurricane season. A more detailed analysis of five of the seasons major storms (U₁₀ <u>></u> 50 m s^-1; Dennis, Emily, Katrina, Rita, and Wilma) was undertaken to determine whether D26 and U_h for these major storms played a role in their attainment of major status.<br/><br/><br/> Results suggest that the condition of the underlying three-dimensional oceanic thermal structure played a role in the cyclogenesis and intensity fluctuations. U_h was also found to be a likely factor in the intensification and weakening processes by affecting the amount of time a storm spent over the ocean. Oceanic mesoscale features such as warm- and cold-core eddies, coupled with U_h, are likely to influence storm intensity by providing either abundant or insufficient oceanic heat content. Specifically, warm-core eddies were found to be especially important for the rapid intensification of major storms. These storms were found to pass either in close proximity or directly over these eddies, triggering intensification. The minimum D26 value for tropical storm cyclogenesis was found to be 23.5 m, and for hurricanes (category 1) it was 36.8 m. The surface area of the North Atlantic basin over which these minimum thicknesses of the surface warm layer occur was found to expand and then contract over the season (1 June 30 November), reaching a peak in August and September. Linear regression models suggest that major storms, most notably category 5, appear to be influenced more by along-track D26 and U_h than weaker storms.