Radar observations of misovortices within multiple long-lake-axis-parallel lake-effect bands during the OWLeS project

Miller, Cameron Jordan

Permalink

https://hdl.handle.net/2142/106248 Copy

Description

Title

Radar observations of misovortices within multiple long-lake-axis-parallel lake-effect bands during the OWLeS project

Author(s)

Miller, Cameron Jordan

Issue Date

2019-12-09

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

Frame, Jeffrey

Department of Study

Atmospheric Sciences

Discipline

Atmospheric Sciences

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

M.A.

Degree Level

Thesis

Keyword(s)

• Radar
• Remote Sensing
• Lake-effect snow
• Horizontal Shearing Instability
• LLAP bands
• OWLeS
• snow
• mesoscale meteorology
• atmospheric sciences
• DOW

Abstract

The Ontario Winter Lake-effect Systems (OWLeS) Project collected a wealth of data on several lake-effect storms in the vicinity of Lake Ontario during the winter of 2013-14. Of all lake-effect band archetypes, long- lake-axis-parallel (LLAP) bands are the most intense, bringing the highest snowfall rates and greatest snow totals. Numerous previous studies have revealed convergence zones owing to secondary circulations within these bands. Horizontal shear along these convergence zones yields vortex sheets that can break into discrete misovortices, likely through horizontal shearing instability (HSI). These misovortices then can strengthen or be maintained via stretching by the band updrafts. Recent analysis of a single case from OWLeS documented a string of misovortices within a LLAP band and determined that all of the misovortices and wind shifts were cyclonic and that HSI was likely the primary method of vortex formation in that particular band. Herein, we perform similar analyses on several additional LLAP bands that occurred during OWLeS to investigate the robustness of these conclusions. Our analyses, utilizing single-Doppler WSR-88D observations and dual-Doppler wind syntheses of mobile radar data reveal that most of the wind shifts within the LLAP bands were cyclonic, but that anticyclonic shear zones and misovortices also exist. It was found that anticyclonic shear zones only form owing to the ingestion of land breeze circulations from the southern shore of Lake Ontario, however. To evaluate the presence of HSI, Rayleigh's and Fjortoft's instability criterions were analyzed, and it was found that both criteria for HSI are satisfied along the wind shifts within the bands while vortices were present, meaning that HSI is likely the dominant mechanism of vortex formation in these bands as well. Instances of cyclonic-anticyclonic vortex couplets are also observed in some of the bands, but their orientation is not consistent with the tilting of horizontal vorticity in a westerly shear regime.

Graduation Semester

2019-12

Type of Resource

text

Permalink

http://hdl.handle.net/2142/106248

Copyright and License Information

2019 by Cameron Miller. All rights reserved.

Owning Collections