wind science 101: i. overview of wind patterns
Post on 19-Mar-2016
34 Views
Preview:
DESCRIPTION
TRANSCRIPT
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
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
http://eesc.columbia.edu/courses/ees/climate/lectures/gen_circ/index.html
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
Global Precipitation Patterns
NOAA NCEP-NCAR CDAS-1 MONTHLY 300 mb [ u , v ] climatology
January
Wind speed at 12 km
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
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
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
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
Continental and Regional influences Continental scale circulation, jet streamsGreat Plains Low-Level JetNocturnal LLJCoastal JetsSea breezesMountain-valley flowsMountain compression of stream linesOff-shore wind
Mechanism of Low-Level Jets:
General PrinciplesGreat Plains Low-Level Jet (GPLLJ)
Nocturnal Low-Level Jet (LLJ)Coastal Jet (CJ)
Mechanism of Low-Level Jets:
General PrinciplesGreat Plains Low-Level Jet (GPLLJ)
Nocturnal Low-Level Jet (LLJ)Coastal Jet (CJ)
HLPressure Gradient
HLPressure Gradient
Fc
Fp
Fc = -2ΩxV
Coriolis Force
HLPressure Gradient
Fc
Fp
HLFp Fc
Vg
Geostrophic Balance
HLFp
Fc
V
FfFrictional Force
Ff = -CdvV
HLFp
Fc
V
At night, friction is eliminated, flow is accelerated, V increases
HLFp
Fc
V
Coriolis force increase, wind vector rotates and speed continues to increase
HLFp
Fc
VVg
Wind vector rotates and speed continues to increase and exceeds geostrophic wind
Mechanism of the Nocturnal Low-Level Jet:
General PrinciplesGreat Plains Low-Level Jet (GPLLJ)
Nocturnal Low-Level Jet (LLJ)Coastal Jet (CJ)
Rocky Mountains
Missouri River
High Temp Low TempLow Press High Press
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
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)
Heig
ht a
bove
gro
und
Horizontal wind speed
Great Plains Low-Level Jet Maximum (~1,000 m above ground)
~1 km
Mechanism of the Nocturnal Low-Level Jet:
Great Plains Low-Level Jet (GPLLJ)Nocturnal Low-Level Jet (LLJ)
Coastal Jet (CJ)
High Temp Low Temp
Low Press High Press
HLFp
Fc
VVg
Heig
ht a
bove
gro
und
Horizontal wind speed
Nocturnal Low-Level Jet Maximum (~400 m above ground)
~400 m
Mechanism of the Nocturnal Low-Level Jet:
Great Plains Low-Level Jet (GPLLJ)Nocturnal Low-Level Jet (LLJ)
Coastal Jet (CJ)
High Temp Low Temp
Low Press High Press
Coastal Mountains
High Temp Low Temp
Low Press High Press
HLFp
Fc
V
FfFrictional Force
Ff = -CdvV
Mountains producean additional pressure force
Heig
ht a
bove
gro
und
Horizontal wind speed
Coastal Jet Maximum (~50-400 m above ocean)
~50-400 m
Note high winds at mountain ridges
100 km
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]
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
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
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
1 knot= 1.151 mph= 0.514 m/s
Num
ber o
f Occ
urre
nces
Winspeed (m/s)
2 10864 12 14 16 18 20 22
Heig
ht (z
)
Windspeed
Power Law
Logarithmic Dependence
U* = friction velocityk = von Karman’s constant (0.40)zo= roughness length
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
Modeling the Atmospheric Boundary Layer
In Tensor Notation:
K = constant
One-and-a-half order:
Turbulence options:
ε = dissipation
Turbulence Kinetic Energy:
Third Order:
ε = q3/Λ
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)
top related