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Title:Radar observations of misovortices within multiple long-lake-axis-parallel lake-effect bands during the OWLeS project
Author(s):Miller, Cameron Jordan
Advisor(s):Frame, Jeffrey
Department / Program:Atmospheric Sciences
Discipline:Atmospheric Sciences
Degree Granting Institution:University of Illinois at Urbana-Champaign
Remote Sensing
Lake-effect snow
Horizontal Shearing Instability
LLAP bands
mesoscale meteorology
atmospheric sciences
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.
Issue Date:2019-12-09
Rights Information:2019 by Cameron Miller. All rights reserved.
Date Available in IDEALS:2020-03-02
Date Deposited:2019-12

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