Department of Climate and Space Sciences and Engineering in the College of Engineering at the University of Michigan

Dissertation Defense - Greg Tierney

Date: July 21, 2017
Time: 1:00 pm - 3:00 pm
Location: SRB Auditorium, room 2246

Title: An Examination of Extratropical Cyclone Sensitivity to Environmental Variability

Abstract: As primary drivers of synoptic-scale midlatitude atmospheric variability, extratropical cyclones (ETCs) are an important influence on day-to-day weather in the most populated regions of the planet. Given their environmental connections at multiple length scales, the impacts of ETCs in a future climate are difficult to predict. Separating these effects is complicated by incomplete observational coverage and the nonlinear response of the system to environmental perturbations. Therefore, we use numerical modeling to systematically explore ETC response to changes in environmental characteristics.

Improving upon previous perturbation schemes, we develop a novel scheme for perturbing environmental temperature (as a proxy for moisture) and baroclinicity and run several suites of experiments focused on ETC sensitivity to each environmental characteristic individually. Additionally, we perform the first examination of a bivariate parameter space, combining simultaneous perturbations to environmental temperature and baroclinicity. Additional experiments are performed to test the sensitivity of ETCs to choices in Coriolis configuration and radiation, often neglected in idealized sensitivity literature. These experiments reveal that extratropical cyclone development can be divided into three regimes: baroclinic, diabatically-limited, and diabatically-driven. While not a complete examination of all environmental variables, this suite of simulations demonstrates the need to consider ETC sensitivity to multiple variables simultaneously, as there are a breadth of scales at which ETCs are affected by changes to the Earth’s climate system.

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