dc.description.abstract | Up until now, the mechanisms behind tropical cyclogenesis is still not fully understood. Thus, this study seeks to find the primary air-sea environmental parameters of tropical cloud clusters (TCC) that may eventually lead to the development of a typhoon. First, this study collected data related to developing and nondeveloping TCCs, and applied the linear discriminant analysis (LDA) to analyze the air-sea parameters differences between developing and nondeveloping TCC sets. The thresholds from the differences can thus be used to establish the tropical cyclogenesis potential index (TCPI) for early typhoon formation detection.
LDA is usually used to classify unknown cases to different groups according to discriminant functions. In this study, the Western Pacific JTWC best tracks, global tropical cloud cluster dataset, and NCEP FNL Analyses data are collected and used to establish a comprehensive environmental LDA discriminant function with seven air-sea parameters: 1) 850hPa relative vorticity, 2) 850hPa-200hPa vertical wind shear, 3) 925hPa divergence, 4) latitude, 5) 850hPa relative humidity, 6) SSM/I composite heat energy, and 7) sea surface temperature. Eventually, we can apply the discriminant function established by the historical cases to classify future unknown cases.
Meanwhile, the air-sea environmental thresholds for cyclonegensis from the LDA method are verified by 83 independent typhoon cases that occurred during 2010 to 2013. The discriminant functions are then converted into tropical cyclogenesis probability (TCP) maps. Results show that if the threshold for tropical cyclogenesis probability is set to 60%, the average hit rate of the method is 96.4%, and the average forecast time is roughly 53.1 hours ahead of JTWC’s official tropical cyclone warning.
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