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PBLs, TURBULENCE AND TROPICAL CYCLONES

Courtesy NOAA

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CD Donelan etal, 2004

Maximum azimuthal wind speed (Emanuel, 2004)

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PBLs, TURBULENCE AND CLIMATE

Stratocumulus cloud deck off the California coast Courtesy Bjorn Stevens (UCLA) from DYCOMS II 1-5

ENTRAINMENT AND STRATOCUMULUS

DILUTION OF STRATUS BY ENTRAINMENT OF DRY WARM AIR ABOVE THE CLOUD DECK IS DETERMINED BY COMPLEX COUPLINGS OF TURBULENCE, RADIATION, AND CLOUD MICROPHYSICS. LARGE ENTRAINMENT RATES THIN THE CLOUD DECK WHICH RADICALLY ALTER THE RADIATIVE FORCING AT THE WATER SURFACE. THESE CHANGES IN SOLAR HEATING EXCEED EFFECTS ASSOCIATED WITH RELEASE OF GREENHOUSE GASES. STRATUS ACCOUNT FOR 1/3 OF THE CLOUDS OVER THE OCEAN.

Z

warm

cool

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Before Bonnie

After Bonnie... .

.....

SST Variations, Ocean Mixing and Biology

Shuyi Chen, RSMAS

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Urban smog from the Washington, D.C.-Baltimore metropolitan area contained by the summit ridgeline of South Mountain on the western side of the Shenandoah Valley. (Photo:J.Van Gundy)

PBLs, TURBULENCE AND DISPERSION

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PBLs, TURBULENCE AND WIND POWER

Power generation from large wind turbines is a growing industry. Machines are often located in heterogeneous locations that induce complex surface layer turbulence. The machines shown in these photographs are sited off the Australian coast to take advantage of persistent sea breezes. They are frequently buffeted by separated turbulent flow that develops over the sea cliff which impacts their performance.

Courtesy Keith Ayotte, Wind Lab Systems, Australia 1-9

BULK STRUCTURE OF THE ATMOSPHERIC PBL

`` We define the boundary layer as that part of the troposphere that is directly influenced by the presence of the Earth’s surface, and responds to surface forcings with a timescale of about an hour or less …” [Stull(1998)]

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LIDAR OBSERVATIONS OF PBL DIURNAL EVOLUTION

Local Time

Courtesy Shane Mayor NCAR 1-12

Local Time 1-13

“VIRTUAL” TURBULENCE

EVIDENCE FROM NUMERICAL EXPERIMENTS

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X

ZY

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X

ZY

hot

cool

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XY

EVOLUTION OF ENSTROPHY IN AN X-Y PLANE

steady periodic quasi-periodic turbulent

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T (min)

Average of the turbulent flow in time

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0

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0 0

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0

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Hot summer day Stratus Day after rainfall Pollutant advection

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MEAN AND TURBULENT FLUX PROFILES FOR PBLS WITH VARYING STRATIFICATION

LES RESULTS MOENG & SULLIVAN (1994)1-28

00

Idealized wind and turbulent flux profiles

Surface layer

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(x,y) usually aligned with the mean wind

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Neutral

0

Unstable Stable

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You are a fluid dynamicist visiting the Louvre in Paris and are asked by the curator to comment on the above paintings. What do you say?

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