Quantification of QLCS tornadogenesis, associated characteristics, and environments across a large sample

Goodnight, James Seth

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https://hdl.handle.net/2142/115775 Copy

Description

Title

Quantification of QLCS tornadogenesis, associated characteristics, and environments across a large sample

Author(s)

Goodnight, James Seth

Issue Date

2022-04-26

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

Trapp, Robert J

Committee Member(s)

• Kosiba, Karen
• Klees, Alicia

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)

• QLCS
• tornadogenesis

Abstract

The skillful prediction of tornadoes produced by quasi-linear convective systems (QLCSs) is a well-known operational forecasting challenge. This study was motivated by the possibility that the tornado warning potential depends on the generalized mechanism of QLCS tornadogenesis, namely, horizontal shearing instability and stretching (H&S) and tilting and stretching (T&S). Thus motivated, the manual identification of the tornadogenesis mechanism of 530 QLCS tornadoes was performed using heuristic yet process-driven criteria based on single Doppler radar (WSR-88D) data. This included 214/213/103 tornadoes that occurred during 2019/2017/2016, respectively. As a function of genesis mechanism, 36% appear to have formed via H&S, and 60% appear to have formed via T&S; the mechanism of the remaining 4% could not be determined, based on our methodology. It was found that approximately 30% of the H&S cases were operationally warned before tornadogenesis compared to 44% of the T&S cases. This is believed to be related to the attributes of the associated tornadic vortices: T&S produced vortices that were stronger and had a larger vertical extent than those produced through H&S. It was also found that T&S tornadoes were more common during the warm season and displayed a diurnal, midafternoon peak in frequency. A complementary effort to explore the environmental characteristics of QLCS tornadogenesis revealed that both mechanisms were supported in similar environments. The exception was pre-tornadic frontogenesis, which was more prominent for cool-season H&S cases, and suggestive of a more significant role of the larger-scale meteorological forcing in the vertical vorticity that fosters the H&S tornadogenesis.

Graduation Semester

2022-05

Type of Resource

Thesis

Copyright and License Information

This Work has been submitted to Weather and Forecasting. Copyright in this Work may be transferred without further notice.

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