wind science 101: i. overview of wind patterns
DESCRIPTION
Wind Science 101: I. Overview of Wind Patterns. Eugene S. Takle Professor Department of Agronomy Department of Geological and Atmospheric Science Director, Climate Science Program Iowa State University Ames, IA 50011. WESEP REU Short Course Iowa State University Spring 2011. Outline. - PowerPoint PPT PresentationTRANSCRIPT
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Wind Science 101:I. Overview of Wind Patterns
Eugene S. TakleProfessor
Department of AgronomyDepartment of Geological and Atmospheric Science
Director, Climate Science ProgramIowa State University
Ames, IA 50011
WESEP REU Short CourseIowa State University
Spring 2011
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Outline Global scale 3-D global circulation patterns and wind energy Surface and upper-air tropical and mid-latitude weather systems, including
prevailing westerlies Mesoscale Great Plains Low-Level Jet and nocturnal LLJs Sea-breeze Monsoon circulation Off-shore resources US wind resource maps Forecasting wind resources Atmospheric boundary layer Structure and diurnal/seasonal evolution Impact of static and dynamic stability on horizontal wind speeds and vertical
profiles Turbulent flows and interactive wakes
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http://eesc.columbia.edu/courses/ees/climate/lectures/gen_circ/index.html
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Not to scale!
Mean radius of the earth:
6371 kmHeight of the troposphere:
0-7 km at poles20 km at
Equator
90% of atmosphere is in the lowest 15 miles (24 km)99% in lowest 30 miles (48 km)
Non-rotating Earth heated at its Equator
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Global Precipitation Patterns
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NOAA NCEP-NCAR CDAS-1 MONTHLY 300 mb [ u , v ] climatology
January
Wind speed at 12 km
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NOAA NCEP-NCAR CDAS-1 MONTHLY 300 mb [ u , v ] climatology
July
http://eesc.columbia.edu/courses/ees/climate/lectures/gen_circ/300mbWinds.html
Wind speed at 12 km
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NOAA NCEP-NCAR CDAS-1 MONTHLY Diagnostic above_ground [ u , v ] climatology (m/s)
January
http://eesc.columbia.edu/courses/ees/climate/lectures/gen_circ/300mbWinds.html
Wind speed near surface
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NOAA NCEP-NCAR CDAS-1 MONTHLY Diagnostic above_ground [ u , v ] climatology (m/s)
July
http://eesc.columbia.edu/courses/ees/climate/lectures/gen_circ/300mbWinds.html
Wind speed near surface
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NOAA NCEP-NCAR CDAS-1 DAILY300 mb height (m) and winds (m/s)1 Apr 1997
http://eesc.columbia.edu/courses/ees/climate/lectures/gen_circ/300mbWinds.html
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Continental and Regional influences Continental scale circulation, jet streamsGreat Plains Low-Level JetNocturnal LLJCoastal JetsSea breezesMountain-valley flowsMountain compression of stream linesOff-shore wind
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Mechanism of Low-Level Jets:
General PrinciplesGreat Plains Low-Level Jet (GPLLJ)
Nocturnal Low-Level Jet (LLJ)Coastal Jet (CJ)
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Mechanism of Low-Level Jets:
General PrinciplesGreat Plains Low-Level Jet (GPLLJ)
Nocturnal Low-Level Jet (LLJ)Coastal Jet (CJ)
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HLPressure Gradient
Fp
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HLPressure Gradient
V Fc
Fp
Fc = -2ΩxV
Coriolis Force
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HLPressure Gradient
VFc
Fp
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HLFp Fc
Vg
Geostrophic Balance
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HLFp
Fc
V
FfFrictional Force
Ff = -CdvV
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HLFp
Fc
V
At night, friction is eliminated, flow is accelerated, V increases
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HLFp
Fc
V
Coriolis force increase, wind vector rotates and speed continues to increase
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HLFp
Fc
VVg
Wind vector rotates and speed continues to increase and exceeds geostrophic wind
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Mechanism of the Nocturnal Low-Level Jet:
General PrinciplesGreat Plains Low-Level Jet (GPLLJ)
Nocturnal Low-Level Jet (LLJ)Coastal Jet (CJ)
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Rocky Mountains
Missouri River
High Temp Low TempLow Press High Press
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H
Bermuda High creates flow from the south in summer over the central US, which is accelerated at night by a terrain-induced pressure gradient
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Wind speed as a function of height during the LLJ peak on March 24, 2009 at 1000 LST from the Lamont, OK wind profiler (Adam Deppe MS thesis, ISU, 2011)
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Heig
ht a
bove
gro
und
Horizontal wind speed
Great Plains Low-Level Jet Maximum (~1,000 m above ground)
~1 km
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Mechanism of the Nocturnal Low-Level Jet:
Great Plains Low-Level Jet (GPLLJ)Nocturnal Low-Level Jet (LLJ)
Coastal Jet (CJ)
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High Temp Low Temp
Low Press High Press
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HLFp
Fc
VVg
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Heig
ht a
bove
gro
und
Horizontal wind speed
Nocturnal Low-Level Jet Maximum (~400 m above ground)
~400 m
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Mechanism of the Nocturnal Low-Level Jet:
Great Plains Low-Level Jet (GPLLJ)Nocturnal Low-Level Jet (LLJ)
Coastal Jet (CJ)
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High Temp Low Temp
Low Press High Press
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Coastal Mountains
High Temp Low Temp
Low Press High Press
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HLFp
Fc
V
FfFrictional Force
Ff = -CdvV
Mountains producean additional pressure force
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Heig
ht a
bove
gro
und
Horizontal wind speed
Coastal Jet Maximum (~50-400 m above ocean)
~50-400 m
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Note high winds at mountain ridges
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100 km
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Musial, W., and B. Ram, 2010: Large-scale Offshore Wind Power in the United States. Assessment of Opportunities and Barriers. NREL/TP-500-40745. 240 pp. [Available online at http://www.osti.gov/bridge]
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Take Home MessagesWinds are created by horizontal temperature difference
(which create density differences and hence pressure differences)
Rotation of the Earth creates bands of high winds (prevailing westerlies) at mid-latitudes
Interactions with the day-night heating and cooling of the
earth’s surface create changes in the vertical structure of the horizontal wind
Orographic feature (coastal regions, mountains, etc) create local circulations that enhance or decrease wind speeds
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Wind Science 101II. Atmospheric Boundary Layer
Eugene S. TakleProfessor
Department of AgronomyDepartment of Geological and Atmospheric Science
Director, Climate Science ProgramIowa State University
Ames, IA 50011
Honors Wind SeminarIowa State University
Spring 2011
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High Interannual Variability:Number of Wind Speed Reports per Month
≤ 5 kts at Mason City, IA 1 Oct 2001 – 30 Sep 2002 1 Jan – 31 Dec 1998
Data by Adam Deppe
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1 knot= 1.151 mph= 0.514 m/s
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Num
ber o
f Occ
urre
nces
Winspeed (m/s)
2 10864 12 14 16 18 20 22
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Heig
ht (z
)
Windspeed
Power Law
Logarithmic Dependence
U* = friction velocityk = von Karman’s constant (0.40)zo= roughness length
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High Interannual Variability:Number of Wind Speed Reports per Month
≤ 5 kts at Mason City, IA 1 Oct 2001 – 30 Sep 2002 1 Jan – 31 Dec 1998
Data by Adam Deppe
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Modeling the Atmospheric Boundary Layer
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In Tensor Notation:
K = constant
One-and-a-half order:
Turbulence options:
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ε = dissipation
Turbulence Kinetic Energy:
Third Order:
ε = q3/Λ
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Conceptual Model of Turbine-Crop Interaction via Mean Wind and Turbulence Fields
__ ___________________________________
Speed recovery
CO2H2O
Heat
day
nightA conceptual model of turbulence generated by turbines suggests enhancement of near-surface mixing both day and night, which will…
reduce daytime maximum temperature in the crop (good)increase night-time temperature in the crop (???)reduce dew-duration in crops (good)enhance downward CO2 flux into the canopy during daytime photosynthesis (good)enhance CO2 flux out of the canopy at night (???)suppress early killing frost (good)help dry down the crop before harvest (good)