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School of Earth and Environment ICAS. Observations and modelling of severe windstorms during T-REX: importance of the upstream profile. Ralph Burton 1 , Simon Vosper 2 , Peter Sheridan 2 , Stephen Mobbs 1. 1 Institute for Climate and Atmospheric Science, School of Earth and Environment,

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School of Earth and Environment

ICAS

Observations and modelling of severe windstorms

during T-REX:

importance of the upstream profile

Ralph Burton1, Simon Vosper2, Peter Sheridan2, Stephen Mobbs1

  • 1 Institute for Climate and Atmospheric Science, School of Earth and Environment,

  • University of Leeds, U.K.

  • Met Office, Exeter, U.K.

Leeds T-REX team:

Barbara Brooks, Ian Brooks, Rosey Grant, James Groves, Martin Hill,

Matt Hobby, Felicity Perry, Victoria Smith, Will Thurston


School of Earth and Environment

ICAS

Introduction: T-REX

Comparing models and observations:

Relating the winds in the valley to the upstream flow

Summary


T-REX: March – April 2006

The biggest field campaign ever mounted to study

rotors/gravity waves

ARL White Sands Missile Range

Scripps Institute of Oceanography

Colorado Research Associates

Cooperative Research in Environmental Science

Desert Research Institute

DLR

Lawrence Livermore National Laboratory

UK Met Office

NASA

NCAR

Naval Research Laboratory

NOAA

Arizona State University

Colorado State University

Harvard University

University of Houston

University of Innsbruck

University of Leeds

University of New Hampshire

North Carolina State University

Stanford University

University of Utah

Yale University


From “Hazardous Mountain Winds

and their Visual Indicators”,

1988

Accident rate 40% higher

in the 11 mountain

states

Accident rate less than 3 per 100,000

Accident rate greater than 3 per 100,000


DEM of the U.S. showing regions

of elevated terrain



Inyo Register,

March 2006




T-REX IOP6: 25th – 26th March 2006

Kuettner 1959

“A full temporal evolution of a trapped-lee-wave rotor event

was captured in this IOP. There was a strong and well defined

wave/rotor event with wave clouds, roll clouds,

cap cloud over the Sierra, and a dust storm in Owens Valley.”

(Mission Summary)

Photo: A. Doernbrack


26th March 2006 6:39PM LT

Height (m)

w (m/s)


What we want to do, in a nutshell:

Take an upstream profile, and attach a number N1 to it

15

Height (km)

10

5

Θ (K)


What we want to do, in a nutshell:

Take an upstream profile at time T, and attach a number N1 to it

15

Height (km)

10

5

Θ (K)

Look at the downstream winds at time T: attach a number N2 to them

Look at lots of cases (different T).

Are N1 and N2 related? - Predictability


For the downstream winds.

We seek a statistical parameter to describe

the effect of severe winds.

From Mobbs et al. 2005 (“Observations of downslope winds and rotors

in the Falkland Islands”, QJRMS, 131, 2839-2860

σ2 =σu2 ++ σv2

|U| = average wind speed

Produce a time series of σ|U|


Locations of the AWS: DRI Leeds

Produce a time series of σ|U|


For the upstream profiles.

It is thought that the stratification and the shear

of the upstream profile are important parameters

in determining the nature of the downstream response.

From Hertenstein and Kuettner, “Rotor types associated

with steep lee topography: influence of the wind profile”,

Tellus A, 57, 117-135



Principal Components Analysis (PCA) of the upstream profiles

Take time series of upstream profiles; UM output every 10 seconds

Perform PCA: extracts two features:

EOFs (Empirical Orthogonal Functions)

Describe the dominant structures in the profiles (inversions etc)

PC Scores (Principal Component Scores)

A numerical value: a measure of how

similar the profile is to the dominant structures

at each point in time;

PCA is an objective method

Produce a time series of the principal component scores


UM: Principal components analysis of the upstream profile

between 3 and 5 km

dU/dz

N

These are the dominant structures in the N and dU/dz profiles

for all upstream profiles (sample size: 6840)

Maximum in both shear and stability at 4250m




Correlations: UM wind effect parameter σ |U|

with upstream profile structure

UM winds


Correlations: AWS wind effect parameter σ |U|

with upstream profile structure

Insert pic here

AWS winds


School of Earth and Environment

ICAS

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 between

the UM winds in the valley and the upstream N and dU/dz profiles for all of IOP6 (19 hours);

The correlation is not as strong for the observed winds. But then

the 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.



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