The relationship between tropical cyclones and the upper ocean: Investigating possible climate feedbacks
Abstract
The climate system is very sensitive to vertical mixing in the upper tropical oceans, which affects the surface energy budget, triggers primary productivity, and contributes to sustaining and regulating the meridional overturning circulation and heat transport. Understanding sources of this mixing is critical for explaining the nature of climate variability. This thesis examines the role of tropical cyclones within Earth's climate system by investigating these events as an important source of upper ocean vertical mixing in the tropics. Utilizing observation-based data platforms, I investigate the potential for feedbacks between extreme winds, surface temperature, and ocean mixing that may fundamentally impact the climate system. Using reanalyzed winds, I estimate low frequency variations in globally integrated tropical cyclone intensity from 1958 to 2004. Trends in integrated intensity were found to be consistent with previous, independent analyses, and globally integrated intensity correlated with trends in tropical sea surface temperature. I employ sea surface temperature records to estimate the annually accumulated downward heat pumping by tropical cyclone mixing. Consistent with Kerry Emanuel's 2001 hypothesis, results show that tropical cyclone-induced mixing generally leads to cooling of the surface oceans, likely corresponding to warming beneath the mixed layer. This mixing is extremely sensitive to sea surface temperature, and the magnitude is sufficient to account for the majority of the mixing currently represented as "background" diffusivity in ocean models. This work suggests that tropical cyclones are an active component of Earth's climate system. Results provide evidence that tropical cyclone-induced ocean mixing is a fundamental physical mechanism that may act to stabilize tropical temperature and mix the upper ocean. This mixing is sensitive to surface temperature, and increased tropical temperatures may diminish the equator-to-pole surface gradients by amplifying climate change at high latitudes while buffering the tropics to warming. Better representation of tropical cyclones in conceptual and numerical models may help to explain unresolved questions about past warm climates as well as provide a better understanding about the nature of climate change for the future.
Degree
Ph.D.
Advisors
Huber, Purdue University.
Subject Area
Physical oceanography|Atmospheric sciences
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