Interaction of an upper-tropospheric jet with a squall line originating along a cold frontal boundary

Stechman, Daniel M

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https://hdl.handle.net/2142/89056 Copy

Description

Title

Interaction of an upper-tropospheric jet with a squall line originating along a cold frontal boundary

Author(s)

Stechman, Daniel M

Issue Date

2015-12-07

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

• Rauber, Robert M.
• McFarquhar, Greg M.
• Jewett, Brian F.

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)

• frontal squall line
• upper-tropospheric jet
• momentum
• Bow Echo and Mesoscale Convective Vortex Experiment (BAMEX)
• Weather Research and Forecasting (WRF)
• simulation
• vertical vorticity
• mesoscale

Abstract

On 8 June 2003, an expansive squall line along a surface cold frontal boundary was sampled during the Bow Echo and Mesoscale Convective Vortex Experiment. The Naval Research Laboratory P-3 aircraft and the National Oceanic and Atmospheric Administration P-3 aircraft simultaneously sampled the leading and trailing edge of this squall line, respectively, with X-band Doppler radars. Data from these two airborne radar systems have been synthesized to produce a quad-Doppler analysis of the squall line, yielding a detailed three-dimensional kinematic analysis of its structure. A simulation of the squall line was carried out using the Weather Research and Forecasting model to complement the quad-Doppler analysis. The simulation employed a 3 km, convection-allowing, nested domain centered over the quad-Doppler domain, along with a 9 km parent domain to capture the larger synoptic-scale cyclone. The quad-Doppler analysis reveals that the convective line was embedded within the upper-tropospheric jetstream, causing local decelerations and deviations in the jet-level flow. The vertical transport of low momentum air from the boundary layer via convective updrafts is shown to significantly decelerate jet-level flow. The convective updrafts are also found to tilt baroclinically generated horizontal shear into the vertical, contributing to the generation of counter rotating ribbons of vertical vorticity parallel to the squall line. The orientation of these ribbons parallel to the squall line was found to couple with vertical momentum transport to produce the observed decelerations within the jetstream. Obstacle-flow is considered as a possible factor in the observed flow pattern, though an analysis of pressure perturbations in the horizontal are used to show this is not an appropriate theory for this system.

Graduation Semester

2015-12

Type of Resource

text

Permalink

http://hdl.handle.net/2142/89056

Copyright and License Information

Copyright 2015 Daniel Stechman

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