Purdue University Graduate School
Dissertation_ZDRarcsFINAL.pdf (7.68 MB)

ZDR Arc Area and Intensity as a Precursor to Low Level Rotation in Supercells

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posted on 2023-04-26, 00:20 authored by Allison LafleurAllison Lafleur

 It has been hypothesized that some measurable properties of $Z_{DR}$ arcs in supercells may change in the minutes prior to tornadogenesis and tornadogenesis failure, and that $Z_{DR}$ arc area will change with SRH and can be used as a real-time proxy to estimate SRH. Output form the Cloud Model 1 (CM1) along with a polarimetric emulator is used to simulate $Z_{DR}$ arcs in 9 tornadic and 9 non-tornadic supercells. A random forest algorithm is used to automatically identify the $Z_{DR}$ arcs. Finally the inflow sector SRH is calculated at times when $Z_{DR}$ arcs are identified. To analyze the change in intensity and area a comparison between the average $Z_{DR}$ value inside and outside of the arc, as well as the spatial size of the arc and storm was done. Model calculated SRH is then compared to these metrics.


 It has also been observed that hail fallout complicates the automatic identification of $Z_{DR}$ arcs. In this study, three experiments are run where the simulated $Z_{DR}$ arcs are produced. One using all categories of hydrometeors, one where wet growth and melting of hail is excluded, and one excluding the contribution to $Z_{DR}$ from the hail hydrometeor category. The same analysis as above is repeated for all three experiments. Finally observed $Z_{DR}$ arcs are analyzed to see if these results are applicable to the real world. 


Degree Type

  • Doctor of Philosophy


  • Earth, Atmospheric and Planetary Sciences

Campus location

  • West Lafayette

Advisor/Supervisor/Committee Chair

Robin Tanamachi

Advisor/Supervisor/Committee co-chair

Daniel Dawson

Additional Committee Member 2

Daniel Chavas

Additional Committee Member 3

Stephen Frasier

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