A convective windstorm in a future climate: A pseudo-global warming study of the 10 August 2020 Midwest derecho

Orendorf, Sophie A.

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https://hdl.handle.net/2142/116275 Copy

Description

Title

A convective windstorm in a future climate: A pseudo-global warming study of the 10 August 2020 Midwest derecho

Author(s)

Orendorf, Sophie A.

Issue Date

2022-07-20

Director of Research (if dissertation) or Advisor (if thesis)

• Lasher-Trapp, Sonia G
• Trapp, Robert J

Committee Member(s)

Dominguez, Francina

Department of Study

Atmospheric Sciences

Discipline

Atmospheric Sciences

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

M.S.

Degree Level

Thesis

Keyword(s)

• derecho
• PGW
• climate change
• global warming
• convective windstorm
• QLCS
• MCS

Abstract

Severe straight-line winds in convective windstorms can cause significant damage to houses, crops, and infrastructure over a large-scale region, and even human injury or loss. The 10 August 2020 Midwest derecho resulted in four deaths, hundreds of injuries, and was the costliest thunderstorm event in U.S. history. Although substantial knowledge has been acquired regarding how the mechanisms producing convective windstorms in such quasi-linear convective systems act, it is unknown how their productivity might differ in a future, warmer climate. The pseudo global warming (PGW) method is utilized in this study to evaluate potential differences in how this specific derecho event might differ if it instead had occurred in a warmer climate, and to understand why. The method includes first simulating the 10 Aug 2020 event in the observed environment, and then simulating the same event in environments altered according to the predictions from five different climate models from the CMIP5 data set. The simulation of the historical event suggests that its strong surface winds were mainly produced by the lowering of a strong rear inflow jet (RIJ) within the quasi-linear convective system, rather than from mesovortices or downbursts that can also be associated with such systems and enhance wind speeds near the ground. In the future warmer climate, for all but one of the PGW simulations, the area of extreme surface winds increases. The RIJ in these PGW convective storms is stronger and occupies a larger area than in the historical case, and again appears to be the dominant mechanism behind the swaths of strong surface winds in those simulations. The increase in RIJ area is attributed to an increase in cold pool area, resulting from an increase in low-level evaporation due to a drier boundary layer in the environments predicted by the climate models. The increased cold pool area extends the baroclinic zone that is responsible for the RIJ, and thus increases its total area as well. Downbursts and mesovortices also occasionally appear in the PGW simulations and are generally less frequent than in the historical simulation, with some exceptions, but their transience and smaller spatial scales suggest they are of lesser importance to the areal extent of the damaging winds near the ground, compared to the RIJ. This study suggests that while derechos in a future climate may not differ in intensity, there could be an increase in the area impacted by the intense surface winds.

Graduation Semester

2022-08

Type of Resource

Thesis

Copyright and License Information

Copyright 2022 Sophie Orendorf

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