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Observations and Numerical Simulations of Subrotor Vortices during T-REX

Doyle, James D. and Grubišić, Vanda and Brown, William O. J. and De Wekker, Stephan F. J. and Dörnbrack, Andreas and Weissmann, Martin and Jiang, Qingfang and Mayor, Shane D. (2009) Observations and Numerical Simulations of Subrotor Vortices during T-REX. Journal of the Atmospheric Sciences, 66 (5), pp. 1229-1249. DOI: 10.1175/2008JAS2933.1.

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Official URL: http://ams.allenpress.com/perlserv/?request=get-document&doi=10.1175%2F2008JAS2933.1

Abstract

High-resolution observations from scanning Doppler and aerosol lidars, wind profiler radars, as well as surface and aircraft measurements during the Terrain-induced Rotor Experiment (T-REX) provide the first comprehensive documentation of small-scale intense vortices associated with atmospheric rotors that form in the lee of mountainous terrain. Although rotors are already recognized as potential hazards for aircraft, it is proposed that these small-scale vortices, or subrotors, are the most dangerous features because of strong wind shear and the transient nature of the vortices. A life cycle of a subrotor event is captured by scanning Doppler and aerosol lidars over a 5-min period. The lidars depict an amplifying vortex, with a characteristic length scale of ∼500–1000 m, that overturns and intensifies to a maximum spanwise vorticity greater than 0.2 s−1. Radar wind profiler observations document a series of vortices, characterized by updraft/downdraft couplets and regions of enhanced reversed flow, that are generated in a layer of strong vertical wind shear and subcritical Richardson number. The observations and numerical simulations reveal that turbulent subrotors occur most frequently along the leading edge of an elevated sheet of horizontal vorticity that is a manifestation of boundary layer shear and separation along the lee slopes. As the subrotors break from the vortex sheet, intensification occurs through vortex stretching and in some cases tilting processes related to three-dimensional turbulent mixing. The subrotors and ambient vortex sheet are shown to intensify through a modest increase in the upstream inversion strength, which illustrates the predictability challenges for the turbulent characterization of rotors.

Document Type:Article
Title:Observations and Numerical Simulations of Subrotor Vortices during T-REX
Authors:
AuthorsInstitution or Email of Authors
Doyle, James D.Naval Research Lab., Monterey, CA, USA
Grubišić, VandaDesert Research Inst., Reno, NE, USA
Brown, William O. J.NCAR, Boulder, CO, USA
De Wekker, Stephan F. J.Univ. of Virginia, Charlottesville, VA, USA
Dörnbrack, AndreasUNSPECIFIED
Weissmann, MartinUNSPECIFIED
Jiang, QingfangNaval Research Lab., Monterey, CA, USA
Mayor, Shane D.California State Univ., Chico, CA, USA
Date:2009
Journal or Publication Title:Journal of the Atmospheric Sciences
Refereed publication:Yes
In SCOPUS:Yes
In ISI Web of Science:Yes
Volume:66
DOI:10.1175/2008JAS2933.1
Page Range:pp. 1229-1249
Status:Published
Keywords:rotor, subrotor, downslope wind, lidar
HGF - Research field:Aeronautics, Space and Transport
HGF - Program:other
HGF - Program Themes:other
DLR - Research area:Aeronautics
DLR - Program:L - no assignement
DLR - Research theme (Project):L -- no assignement
Location: Oberpfaffenhofen
Institutes and Institutions:Institute of Atmospheric Physics > Lidar
Deposited By: Martin Weissmann
Deposited On:27 Aug 2009 14:48
Last Modified:12 Dec 2013 20:41

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