This study characterizes changes to the ocean structure and ocean thermal energy budget produced by tropical cyclones (TCs) over the North West Shelf of Australia using a 20-year composite of cyclone data (1996-2016) created from Bluelink ReANalysis data (BRAN). Part 1 focuses on the general effects of the passage of a TC over the region and the effects of the location in respect to the shelf edge. Cold temperature anomalies develop at the ocean surface beneath the TC core in response to strong mixing and deep upwelling driven by surface divergence and Ekman pumping. In the TC outer circulation, surface cold anomalies also develop. However, warm temperature anomalies appear in the subsurface below the mixed layer due to wind-driven mixing across the mixed layer. In the month following the passage of the TC, the surface cold temperature anomalies recover relatively quickly due to air-sea fluxes, while the subsurface warm anomalies take longer to recover. Over the shelf, stronger cold anomalies develop at the surface, and the TC direction of motion can further impact the development of currents. TCs that move perpendicular to the shelf edge drive stronger vertical currents in a wide region around the track and stronger SST anomalies and TCs that move parallel to the coast drive colder temperature anomalies at depth and stronger upward currents beneath the track. The presence of the shelf can affect the development of downwelling currents along the coast for TCs that are further offshore but move parallel to the coast.

This study characterizes the changes produced by tropical cyclones (TCs) over the North West shelf of Australia on the ocean structure and ocean thermal energy budget using a 20-year composite of cyclone data (1996-2016) created from Bluelink ReANalysis data (BRAN). Part 2 focuses on assessing the effects of season and TC intensity and translation speed on the development of temperature anomalies and the associated ocean heat content (OHC) changes. Stronger cold anomalies develop at the surface over locations with a shallow barrier layer, for strong and slow-moving TCs. The period of the year influences the recovery of the surface anomalies, which happens faster between December and February. The warm anomalies in the subsurface are stronger for more intense TCs and over locations with a shallow barrier layer, as the vertical mixing processes are more efficient. During the passage of the TC the majority of the OHC losses are located beneath the TC core and in the surface layer, while the OHC increases in the subsurface layer between 500 and 1000 km from the TC centre. When the temperature anomalies start to recover, the OHC increases at a stronger rate in the surface layer due to the air-sea heat fluxes and in the TC core region where the strong upwelling relaxes to downwelling. A month after the TC passage there is an overall increase in the OHC of the region after strong TCs and TCs that happen later in the season, while weak TCs cause an overall decrease in the OHC.