orographic processes andrew orr

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Orographic Processes Andrew Orr

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Orographic Processes Andrew Orr. Large scale flow response Antarctica. Experiment simulating westerly flow. Baines and Fraedrich, 1989. Turner et al., 2009. Mean JJA 700hPa height. Large scale flow response Greenland. Surface wind speed. Mean sea level pressure. Petersen et al., 2003. - PowerPoint PPT Presentation

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Page 1: Orographic Processes Andrew Orr

Orographic Processes

Andrew Orr

Page 2: Orographic Processes Andrew Orr

Turner et al., 2009 Baines and Fraedrich, 1989 Mean JJA 700hPa height

Experiment simulating westerly flow

Large scale flow responseAntarctica

Page 3: Orographic Processes Andrew Orr

Orr et al., 2005 Petersen et al., 2003

Large scale flow responseGreenland

Surface wind speed Mean sea level pressure

Page 4: Orographic Processes Andrew Orr

Powers et al., 2003

High horizontal resolution required to represent complex orography and associated processes

Complex orography

Spiers et al., 2010

Page 5: Orographic Processes Andrew Orr

Smith et al., 2006

Mean orography UK Met Office Unified Model (UM)

Page 6: Orographic Processes Andrew Orr

Rontu, 2007

Topographic map of Carpathian mountains

Sensitivity to resolution

Streamlines over the Carpathian profile with different resolutions:

orography smoothed to 32, 10, and 3.3 km

Page 7: Orographic Processes Andrew Orr

Nh/U=0.5 Nh/U=1

Olafsson and Bougeault, 1996

Nh/U=1.4 Nh/U=2.2

1 number, Froude U

NhF

Basic flow response to isolated mountain

Page 8: Orographic Processes Andrew Orr

Petersen et al, 2003 parameter Coriolis:

,numberRossby o

f

fL

UR

x

RoF ;5.1 42.0;5.1 RoF

Sensitivity to the Coriolis force

km100~ radius,n deformatioRossby Rf

NhL

Page 9: Orographic Processes Andrew Orr

Horizontal and vertical windUnified Model, 12km res

Blocking conditions, 29 Jan 2002 Flow-over conditions, 21 Feb 2002

Orr et al., 2007

Antarctic Peninsula

Page 10: Orographic Processes Andrew Orr

Potential temperatureUnified Model, 12km res

Blocking conditions, 29 Jan 2002 Flow-over conditions, 21 Feb 2002

Page 11: Orographic Processes Andrew Orr

Aircraft observationsFlight 19: Jan 2006, ascent from Rothera

and descent over the Larsen Ice Shelf

Page 12: Orographic Processes Andrew Orr

Marshall et al., 2006

Eastern Peninsula summer warming of 2oC over 40 yearsDifference in ERA40 10 m winds and surface temperature between years with strongly positive and strongly negative summer Southern Annular Model (SAM)

Page 13: Orographic Processes Andrew Orr

Comparison of observations and AMPSFlight 19: Jan 2006, perturbations in vertical velocity and temperature, ascent from Rothera and descent over the

Larsen Ice Shelf against Polar MM5, 10 km res

Page 14: Orographic Processes Andrew Orr

1)Modified parametrization for the prediction of ice cloud fraction

2)Improved cloud-radiation interactions

3)An optimal stable boundary layer treatment

4)Improved calculation of heat transfer through snow and ice surfaces

5)The addition of fractional sea ice surface type

Polar MM5

Is further optimization required?

Is higher horizontal or vertical resolution required?

Bromwich et al., 2001

Page 15: Orographic Processes Andrew Orr

Is a higher resolution required?Comparison of observations and COAMPS 1.7 km resolution simulation on 29 Jan 1997 over Greenland

Doyle et al., 2005

Page 16: Orographic Processes Andrew Orr

Comparison of observations and AMPS:

impact of cold pool

Spiers et al., 2010

Polar MM5 at 2.2km resolution on a grid encompassing the Ross Island Area

Page 17: Orographic Processes Andrew Orr

Lilly and Kennedy, 1973

Down-slope wind stormsObservations over Rocky mountainsWave reflection, hydraulic jump, trapped lee waves

Page 18: Orographic Processes Andrew Orr

Evaluation of AMPS15-16 May Ross Island severe wind storm case study simulated by AMPS (Polar MM5) at 3.3 km, res

Steinhoff et al., 2008

+ Formation of barrier jet + Interacts with pre-existing near-surface radiation inversion over Ross Ice Shelf +Resulting conditions favourable for development of large-amplitude mountain waves + Leads to down slope windstorm in Ross Island Area+ Underestimation of wind speed due to misplacement of hydraulic jump + Originates from inaccuracies in storm track+ Migration to WRF and 3dVar assimilation might lead to improvement

Page 19: Orographic Processes Andrew Orr

Mobbs et al., 2005

Rotors

Sheridan and Vosper, 2006

Wind component simulated by Met Office model BLASIUS at 200 m resolution

Page 20: Orographic Processes Andrew Orr

Barrier jet

Olson et al., 2007

Comparison of winds and temperatures (dashed) at 150 m from observations and 4km MM5 simulation on 26 Sep 2004

Page 21: Orographic Processes Andrew Orr

Cross section: winds, terrain-parallel wind (solid line), potential temperature (dashed line)

Page 22: Orographic Processes Andrew Orr

Hybrid gap-barrier jet13 Oct 2003

Page 23: Orographic Processes Andrew Orr

Doyle and Shapiro, 1999

Tip-jetsComparison of observations and COAMPS simulated surface wind greater than 30 m/s on 18 Feb 1997

Page 24: Orographic Processes Andrew Orr

Parish and Bromwich, 2007

Katabatic windsMean wintertime streamlines over the surface of the Antarctic

Page 25: Orographic Processes Andrew Orr

Mean AMPS surface wind speed from June 2003 – May 2004

Page 26: Orographic Processes Andrew Orr

Comparison of observations and forecast over Greenland

Brmowich et al., 2001

Polar MM5, 40 km res

‘reproduce the observed atmospheric state with a high degree of realism’

Page 27: Orographic Processes Andrew Orr

Strong wind events

Turner et al, 2009

Page 28: Orographic Processes Andrew Orr

Case study: ERA40 MSLP at 0600 GMT 25 July 2004 when Mawson experienced a hurricane force wind of 37.5 m/s

Interaction between katabtic pressure gradient force and synoptic pressure gradient force

Page 29: Orographic Processes Andrew Orr

ERA40 UM 12 km

Wind speed at MawsonObserved: 37 m/sERA40: 20 m/sUM 12 km: 22 m/s

Comparison of ERA40 and UM 12 km simulation10 m winds and MSLP

Minimum MSLPERA40: 944 hPaUM 12km: 936 hPa

UM captures synoptic forcing and simulates stronger katabatic winds

Page 30: Orographic Processes Andrew Orr

Observed: 37 m/sUM 12 km: 22 m/sUM 4 km: 24 m/s

Comparison of UM 12 and 4 km simulations

Is higher resolution required to capture local topographical conditions?

Is optimization of model required ?

Page 31: Orographic Processes Andrew Orr

Bromwich et al., 2005

Evaluation of AMPSPolar MM5 at 30 km resolution from Sep 2001 to Aug 2003, 12-36 h

Reduced surface wind speed correlation at coast line reflecting complex topography

Page 32: Orographic Processes Andrew Orr

Coastal jets (4 km res)Very sharp gradients in velocity across coastline

~30 m/s

~20 m/s

Page 33: Orographic Processes Andrew Orr

Mechanism

1) Offshore winds cross coastline2) Accelerate due to reduced drag3) Turn to the left in the Southern

Hemisphere4) If coast is on the left of the wind results in

horizontal convergence5) Associated with this is the inversion height

rising offshore, due to conservation of mass

6) Coriolis force induces a wind jet parallel to coastline (see Hunt et al., 2004)

7) Temperature falls offshore encouraging condensation and more cloud

Land

Sea

convergence

Orr et al., 2005

sfun

h

~

Page 34: Orographic Processes Andrew Orr

Laboratory investigation

Page 35: Orographic Processes Andrew Orr

UM simulation at 12 and 2 km

Page 36: Orographic Processes Andrew Orr

Orographic rain

Smith

Page 37: Orographic Processes Andrew Orr

Webster et al., 2008

Case study over New ZealandQualitative agreement at 12km resolution and quantitative agreement at <4 km resolution

Page 38: Orographic Processes Andrew Orr

Summary

+ Polar regions marked by complex orography. Requires a high resolution to resolve.

+ Some processes forecast well at medium resolution, such as barrier jets, katabatic winds

+ Some processes dependent on resolution (for example, gravity waves, rotors, precipitation, coastal jets)

+ Some processes dependent on boundary layer, etc, and complex interactions (for example, fohn winds)

+ Initial conditions important, both upstream and downstream