mesoscale dynamical downscaling and climatology of low level jets

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Mesoscale Dynamical Downscalingand

Climatology of Low Level JetsDaran L. Rife

EWEA Wind Resource Assessment Technology Workshop

Brussels, Belgium09 May 2011

2© 2011 University Corporation for Atmospheric Research. All rights reserved.

Roadmap

• Climate downscaling: Brief review• Know thy model: Nature versus models• Know thy model: Effective resolution• Know thy model: Temporal and spatial variability• Global climatology of low-level jets

3© 2011 University Corporation for Atmospheric Research. All rights reserved.

Climate downscaling

Courtesy Cliff Mass, Univ. Washington

Global scale data mapped to local regionwhile adding small scale variability

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Roadmap

• Climate downscaling: Brief review• Know thy model: Nature versus models• Know thy model: Effective resolution• Know thy model: Temporal and spatial variability• Global climatology of low-level jets

5© 2011 University Corporation for Atmospheric Research. All rights reserved.

Nature vs. models

Nature Model

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1.33 km

Model NatureNature vs. models

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Typical thickness of vertical layers in mesoscale models.

The real atmosphere is afluid continuum!

Treatment of atmospheric vertical structure

Hub height

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Treatment of cloudsNature Model

Clouds and rain can stronglyimpact near surface wind field.

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Roadmap

• Climate downscaling: Brief review• Know thy model: Nature versus models• Know thy model: Effective resolution• Know thy model: Temporal and spatial variability• Global climatology of low-level jets

10© 2011 University Corporation for Atmospheric Research. All rights reserved.

The atmosphere: A range of motions

Skamarock (2004) technique

Spectrum of visible light Spectrum of wind velocity

Skamarock (2004)

The atmosphere operates on a broad ranges of scales!

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Effective spatial resolution

Skamarock (2004) technique

From Skamarock (2004)

The point where model spectrum falls off the true spectrum, marks the length scale beyond which themodel is unable to resolve motions or features.

Length scale Length scalesmalllarge smalllarge

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Effective resolution: A real example

Kinetic energy spectra for winds near the ground, averaged over the northern hemisphere.

From Rife et al. (2010)

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Resolution~60 m in x-dir ~40 m y-dir

0.025 m vertical

Vertical

From Haupt et al. (2010)

Even CFD models underrepresent the true range of motions!

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Effective resolution(~100 m)

Even CFD models underrepresent the true range of motions!

From Haupt et al. (2010)

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Effective resolution also depends on the type of model

Skamarock (2004) technique

Red curves = ObservedGreen/blue curves = model

From Knievel et al. (2010)

Gulf stream

Gemini

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Roadmap

• Climate downscaling: Brief review• Know thy model: Nature versus models• Know thy model: Effective resolution• Know thy model: Temporal and spatial variability• Global climatology of low-level jets

19© 2011 University Corporation for Atmospheric Research. All rights reserved.

Spatial and temporal variability• Even high

resolution models under represent the true amount of atmospheric variability!

Rife et al. (2004)

100 km

40 km

40 km

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Roadmap

• Climate downscaling: Brief review• Know thy model: Nature versus models• Know thy model: Effective resolution• Know thy model: Temporal and spatial variability• Global climatology of low-level jets

21© 2011 University Corporation for Atmospheric Research. All rights reserved.

Global corridorsof wind power

Arrows = Mean 500-m-AGL winds at local midnight, plotted every 20th grid point.

Colors = Locations of strong nocturnal low-level jets.

From Rife et al. (2010; Journal of Climate)

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NLLJs: A vast resource of windenergy

Vertical, dotted black lines mark Bonner (1968) wind speed classes.

1985-2005

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Summary

• Downscaling models are an indispensible tool for wind resource assessment.

• Know the limitations of your model!• NLLJs are ubiquitous within world’s land covered

areas— Mesoscale through synoptic-scale in extent.— Vast source of wind power that remains largely

untapped.

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Questions?