Date of Award
Doctor of Philosophy in Oceanography
Strong surface winds of a hurricane locally cool the surface and warm the subsurface waters via turbulent mixing processes. While the surface cool anomalies generally decay in roughly a month, the warm subsurface anomalies can persist over a seasonal cycle. We examine questions related to the magnitude and cumulative footprint of subsurface warm anomalies forced by tropical cyclones during the combined global tropical cyclone seasons, making use of a global ocean model forced by tropical cyclones.
Simulations of the 2004-2005 tropical cyclone season are conducted with and without tropical cyclone wind forcing, blended with the daily Coordinated Ocean-ice Reference Experiments (COREs) atmospheric state. Physical characteristics of cyclone-forced surface and subsurface anomalies are elucidated. In particular, we examine the spatial extent and magnitude of tropical cyclone forced subsurface warm anomalies over the course of an entire season. This analysis allows us to estimate the contribution of cyclone-induced anomalies to the ocean heat content and sea surface temperature, and to understand anomalous meridional heat transport.
Globally, there is a maximum accumulated heat uptake 4:1 1021J, with the greatest regional contributions in the North Atlantic (1:7⋅1021J), West Pacific (1:5 1021J), and East Pacific (1:7⋅1021J). We find an export of heat from the subtropics to the tropics via rapid advective pathways, most notably in the West Pacific. These warm anomalies tend to remain in the equatorial band, with potential implications for the tropical climate system.
Analysis of a 20-year simulation using a semi-idealized tropical cyclone distribution reveals much of how the ocean adjusts to tropical cyclone induced warming on interannual timescales. The apparent quasi-equilibrium that the global ocean reaches over the first several years masks a great deal of regional variability. The redistribution of heat by intense cyclone winds results in semi-permanent warming of the upper-thermocline in some regions by as much as ¼ °C.
While there is a minimal impact on the upper ocean meridional heat transport, regional variability in anomalous heat content reaches a significant percentage of warming attributed to climate change. Lateral transport of warm anomalies plays a key role in maintaining the ocean heat balance, with those remaining in the mid-latitudes being released to the atmosphere during the local winter, and those exported poleward by upwelling in the tropics.
Crucially, transport pathways and ventilation mechanisms are regulated by the large-scale intra-seasonal and inter-annual climate variability, specifically the North Atlantic Oscillation, Asian monsoon, and El Nino Southern Oscillation. These internal climate modes modulate the accumulation, release, and redistribution of tropical cyclone induced heating in a manner not addressed in globally focused analysis.
Bueti, Michael R., "Impact of Tropical Cyclones on Ocean Heat Content and Transport" (2014). Open Access Dissertations. Paper 285.