observations and modelling of iop6: response of the valley winds to the upstream profile
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School of Earth and Environment INSTITUTE FOR ATMOSPHERIC SCIENCE. Observations and modelling of IOP6: response of the valley winds to the upstream profile. R. Burton 1 , S. Vosper 2 , P. Sheridan 2 , S. Mobbs 1. 1 Institute for Atmospheric Science, School of Earth and Environment, - PowerPoint PPT PresentationTRANSCRIPT
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Observations and modelling of IOP6: response of the valley windsto the upstream profile
R. Burton1, S. Vosper2, P. Sheridan2, S. Mobbs1
1 Institute for Atmospheric Science, School of Earth and Environment, University of Leeds, U.K.2 Met Office, Exeter, U.K.
School of Earth and EnvironmentINSTITUTE FOR ATMOSPHERIC SCIENCE
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Introduction
IOP6: severe winds in the valley
Relating the winds in the valley to the upstream flow
Further work
School of Earth and EnvironmentINSTITUTE FOR ATMOSPHERIC SCIENCE
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Photo: A. Doernbrack
T-REX IOP6: 24th – 26th March 2006
“A full temporal evolution of a trapped-lee-wave rotor eventwas captured in this IOP. There was a strong and well definedwave/rotor event with wave clouds, roll clouds, cap cloud over the Sierra, and a dust storm in Owens Valley.”
(Mission Summary)
Kuettner 1959
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Locations of the AWS: DRI Leeds
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Comparing winds from UM and AWS is difficult:instead we seek a statistical parameter to describethe effect of severe winds.
From Mobbs et al. 2005 (“Observations of downslope winds and rotorsin the Falkland Islands”, QJRMS, 131, 2839-2860
σ2 = σu2 ++ σv
2 |U| = average wind speed
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It is thought that the stratification and the shearof the upstream profile are important parametersin determining the nature of the downstream response.
From Hertenstein and Kuettner, “Rotor types associatedwith steep lee topogreaphy: influence of the wind profile”,Tellus A, 57, 117-135
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It is known that the stratification and the shearof the upstream profile are important parametersin determining the nature of the downstream response.
Can the wind effect parameter be linked to theupstream profile?
From Hertenstein and Kuettner, “Rotor types associatedwith steep lee topogreaphy: influence of the wind profile”,Tellus A, 57, 117-135
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UM configuration
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UM: Principal components analysis of the upstream profilebetween 3 and 5 km
These are the dominant structures in the N and dU/dz profilesfor all upstream profiles (sample size: 6840)Maximum in both shear and stability at 4250m
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Time series of principal components; wind effect parameter: UM
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Time series of principal components; wind effect parameter: UM
Wind starts to veer to the south:another mechanism?
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Time series of principal components; wind effect parameter: AWS
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Correlations: UM wind effect parameter with upstreamprofile structure
UM winds
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Correlations: AWS wind effect parameter with upstreamprofile structure
AWS winds
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Summary
The dominant structure in the UM profiles between 3km and 5km is a peak in shear and a peak in stability at z = 4250m
There is a very strong ( r = 0.95; r = 0.87) correlation betweenthe UM winds in the valley and the shape of the upstream N and dU/dz profiles for all of IOP6;
The correlation is not as strong for the observed winds. But thenthe model is reacting to the model profiles, which may differ slightly to the observed profiles.
Is this behaviour unique? Or does it apply to other IOPs?Ongoing.
School of Earth and EnvironmentINSTITUTE FOR ATMOSPHERIC SCIENCE
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Correlations between first PC score for N and dU/dz