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Electric charging in the comma-head regions of continental winter cyclones

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Title: Electric charging in the comma-head regions of continental winter cyclones
Author(s): Wegman, Joseph
Advisor(s): Rauber, Robert M.
Department / Program: Atmospheric Sciences
Discipline: Atmospheric Sciences
Degree Granting Institution: University of Illinois at Urbana-Champaign
Degree: M.S.
Genre: Thesis
Subject(s): Winter Charging Lightning Continental Comma-head Electric Wraparound Region Profiler Electric Field Mill Climatology
Abstract: Lightning in the comma-head region of winter cyclones is a relatively rare phenomenon. The nature of the electric charging in wintertime precipitation bands is unknown. During the ProfiLing Of Winter Storms (PLOWS) project, the surface electric field was measured using an electric field mill (EFM) during band passages during two cyclones on 24 November 2009 and 9 December 2009. The EFM was collocated with the University of Alabama Huntsville Mobile Integrated Profiling System (MIPS) and was typically deployed under the comma-head. Included with the MIPS was a vertically pointed profiling radar that was used to derive signal-to-noise ratio, vertical radial velocity, and spectral width of the bands passing overhead. The 24 November 2009 cyclone featured a band around 1400 UTC that produced 4 lightning strokes near the EFM. Each lightning stroke resulted in an instantaneous jump in the surface electric field, the magnitude of which diminished with increasing distance from the EFM. The profiler during the lightning indicated vertical radial velocity (W) values with the band approaching 4 m/s near cloud top and spectral widths (SW) exceeding 6 m/s in the same region. For the other bands and cells analyzed during the two cyclones when no lightning occurred, values of W and SW concurrently never reached these thresholds. The 9 December 2009 cyclone did not produce any lightning near the PLOWS equipment. However, bands in the convective region passing overhead resulted in fluctuations in the surface electric field when values of W and SW were both greater than 2 m/s in updrafts near cloud top. The magnitude of the fluctuations increased with increasing values of W and SW. A climatology of 22 storms over 4 winter seasons was developed looking at lightning stroke locations in the comma-head. The ratio of distance from the comma-head/dry slot interface divided by the total width of the comma-head was calculated for each lightning stroke. The storms were then grouped based on the mean location within the comma-head of most of the lightning. The climatology showed that 16 out of 22 cyclones had most of their lightning in the equatorial/southern region of the comma-head, with most of the lightning occurring with dry slot convection, or along the interface between the dry slot and the comma-head. When lightning occurred further north, it was comparatively infrequent and isolated.
Issue Date: 2012-09-18
URI: http://hdl.handle.net/2142/34360
Rights Information: Copyright 2012 Joseph Wegman
Date Available in IDEALS: 2012-09-18
Date Deposited: 2012-08
 

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