Quantifying the Energy Input into the Ocean due to Tropical Cyclones in the North Atlantic from 1994-2015

• Main Author: Finlay, Belinda
• Format: Master Thesis
• Language: English
• Published: UNSW, Sydney 2021
• Subjects: tropical cyclone; hurricane; Ocean Heat Content; Mixed Layer; anzsrc-for: 3708 Oceanography; North Atlantic
• Online Access: http://hdl.handle.net/1959.4/100473; https://unsworks.unsw.edu.au/bitstreams/b370152c-9288-4ff7-8233-060f6d89b843/download; https://doi.org/10.26190/unsworks/24180

Tropical cyclones are the most destructive synoptic-scale weather systems globally. Their strong surface winds and heavy rainfall significantly affect the tropical and extratropical regions they pass through. Tropical cyclones also affect the ocean, driving high waves and storm surge, and impact the underlying ocean structure through ocean heat changes potentially increasing the ocean heat content over the months following their passage. In this study, the impact of tropical cyclones on the ocean surface and subsurface structure in the North Atlantic Ocean is characterised using the Hybrid Coordinate Ocean Model (HYCOM) reanalysis between 1994 and 2015. Composites of 207 tropical cyclones from the National Hurricane Centre (NHC) besttrack data (HURDAT2) provide a broad representation of how North Atlantic tropical cyclones affect the ocean. The composites show the development of a cold wake and the associated subsurface warm anomaly, leading to overall increased ocean energy which supports previous studies. These features develop through three main physical processes: surface heat fluxes, vertical mixing, and deep upwelling forced beneath the tropical cyclone core. Changes in the formation of the cold wake and warm subsurface anomaly vary depending on tropical cyclone intensity, translation speed and ocean stratification. Changes in these drivers determine whether sensible and latent heat loss or vertical mixing dominate the cold wake and subsurface warm anomaly formation. Upwelling beneath the tropical cyclone core impacts the warm anomaly, resulting in category three tropical cyclones developing the most significant subsurface warming. The temperature changes induced by tropical cyclones are evident up to 150 days after the passage of the tropical cyclone. Energy can be found in both the thermocline and the mixed layer. The movement of energy into the mixed layer, caused by seasonal deepening of the mixed layer, was previously assumed to be released into the atmosphere; however, the HYCOM reanalysis shows ...