title: The tracking, power trends and wave climate of tropical cyclones in the Coral Sea
Creators: name: Miller, John G
Publisher: name: Griffith University
Year: 2024
Subjects: subject: tropical cyclones
subject: Australia
subject: Coral Sea
subject: West Pacific Ocean

description: Tropical cyclones (TCs) originating in the Coral Sea present significant hazards to coastal regions in their surroundings. This research is aimed at understanding the tracking and power characteristics of these TCs in our region - it specifically investigates the spatial and temporal variabilities in wind-power and swell generated by tropical cyclones in the Coral Sea, over 50 years (1970 -2020) and has three objectives: 1) To group TCs with genesis in the Coral Sea and investigate and trend selected TC climatological metrics at a group level; 2) To determine which (if any) climatological indexes highly correlate (above 0.7) to TC intensity in the Coral Sea, using PDI and latitude of maximum intensity (LMI) as metrics, over 50 years(1970 -2020); 3) To determine the wave climate statistics of the waves in the Coral Sea, co-incident with TC activity, 1979 - 2020 and to spatially and temporally trend these statistics. The results of the first objective indicated that TC tracks over 50 years were statistically clustered in space based on maximum wind-weighted centroids. Track variance and curvature were assessed. Three clusters of tracks were identified, with differing predominant directions of movement, power dissipation index (PDI), locations of maximum intensity and frequency. Each cluster therefore had a different associated hazard. TCs that track in the area defined by the centrally located cluster demonstrated an increase in hazard, compared to the other two clusters and when comparing PDI, sinuosity, location of lowest central pressure and frequency of occurrence trends by cluster. Chapter 4 tackled objective 2 and showed three dominating indices for PDI: Niño 4 Sea Surface Temperature, the Dipole Mode Index (DMI) and the Madden Julian Oscillation (MJO). Examination of the correlation coefficients of a multiple linear regression (MLR) indicated that PDI in the Coral Sea is significantly raised during the co-incidence of warm pool El Niño, a negative DMI index and weak MJO events. For the most southerly located cluster of the three, the inclusion of the monthly SAM index raised the correlation. MLR results for LMI suggested a combined index comprised of the DMI East and the Southern Oscillation (SO), and denoted as DMI(E)SO, equivalent to the El Niño Southern Oscillation (ENSO), could be said to be a strong correlate of TC LMI in the Coral Sea. Results also indicated that DMI(E)SO is moderated by SAM and MJO in the more northerly located cluster 2; The third objective was fulfilled in chapter 5 in whichA TC wave hindcast, using WAVEWATCH III® with wind forcing from National Centres for Environmental Prediction Climate Forecasts System Version 2 (CFSv2) was used for this. Documented limitations in the wind-forcing of this hindcast with respect to TCs are discussed. Considering these limitations, the wave buoy validation results were surprisingly consistent, when comparing TC days to ambient conditions, and provide strong validation evidence for the wave climate results. The mean and extreme significant wave height profile for TCs were derived from the hindcast over the entire Coral Sea. Highest TC wave heights for the Coral Sea, averaged over 40 years (1979 -2020), were centred around 15°S, 155°E (centred in the Coral Sea Marine Park). An interdecadal increase (decrease) in TC significant wave height with positive (negative) IPO phase was evident in three of the four decades under study. The extreme wave distributions showed an eastwards displacement of TC generated extreme waves, compared to the mean wave climate and for the 50 and 100-year return levels. The highest extreme waves were evident near the northeastern tip of Australia and northwest of New Caledonia. An analysis of TC waves at three chosen locations along the Australian east coast was also produced from the hindcast. A major finding was that, for the Coral Sea, TC extreme wave heights were decreasing at the southerly located Brisbane wave buoy but increasing at the other two Australian east coast wave buoys selected for the study (not tested for statistical significance in both cases).