skyler goldman, meteorology, dmes
DESCRIPTION
RELATIONSHIP BETWEEN ROUGHNESS LENGTH, STATIC STABILITY, AND DRAG COEFFICIENT IN A DUNE ENVIRONMENT. Skyler Goldman, Meteorology, DMES. Introduction to the subject. Drag (Wind) coefficient- quantifies the drag or resistance of an object in a fluid environment such as air or water. - PowerPoint PPT PresentationTRANSCRIPT
![Page 1: Skyler Goldman, Meteorology, DMES](https://reader033.vdocuments.mx/reader033/viewer/2022061610/5681642e550346895dd5f53b/html5/thumbnails/1.jpg)
Skyler Goldman, Meteorology, DMES
RELATIONSHIP BETWEEN ROUGHNESS LENGTH, STATIC STABILITY, AND DRAG COEFFICIENT IN A DUNE ENVIRONMENT
![Page 2: Skyler Goldman, Meteorology, DMES](https://reader033.vdocuments.mx/reader033/viewer/2022061610/5681642e550346895dd5f53b/html5/thumbnails/2.jpg)
Introduction to the subject• Drag (Wind) coefficient- quantifies the drag or
resistance of an object in a fluid environment such as air or water. – A lower drag coefficient indicates the object will have
less aerodynamic or hydrodynamic drag. – Less Drag = Less Resistance!!
• For small scale flow (dune environment), a better characterization of the surface drag can go a long way towards understanding and modeling the air flow.
• Understanding what affects wind flow and magnitude is important to meteorology and engineering
![Page 3: Skyler Goldman, Meteorology, DMES](https://reader033.vdocuments.mx/reader033/viewer/2022061610/5681642e550346895dd5f53b/html5/thumbnails/3.jpg)
Data Collected• Temperature and wind
collected using anemometer attached to stadia rod and elevated from 6.5 ft to 25 ft over seven different stations (vegetated and non-vegetated) on six different days
Courtesy of Sarah Collins
![Page 4: Skyler Goldman, Meteorology, DMES](https://reader033.vdocuments.mx/reader033/viewer/2022061610/5681642e550346895dd5f53b/html5/thumbnails/4.jpg)
Neutral vs. Corrected Drag Coefficient
• Overall goal is to draw comparisons between drag coefficient and wind profiles.
• 1st Type of drag coefficient (Cd)– Neutral (dependent on roughness length (zo)
Increasing roughness length (zo)
(Figures from Beljaars, A. The Parameterization of the Boundary Layer, 5/1992. European Centre for Medium-Range European Weather Forecasts)
Height (m
)
Wind Speed (m/s)
The impact of surface friction on atmosphere extends upwardsas zo increases.
![Page 5: Skyler Goldman, Meteorology, DMES](https://reader033.vdocuments.mx/reader033/viewer/2022061610/5681642e550346895dd5f53b/html5/thumbnails/5.jpg)
Neutral Drag Coefficient
22 )][ln( o
rd z
zkC
K = von Karman constant (0.4)Zr = Reference height (6.5 ft)Zo = Roughness length
Higher the roughness length, higher the drag coefficient
![Page 6: Skyler Goldman, Meteorology, DMES](https://reader033.vdocuments.mx/reader033/viewer/2022061610/5681642e550346895dd5f53b/html5/thumbnails/6.jpg)
2nd Type of Drag Coefficient• Corrected
(dependent on stability factor and roughness)
MOMENTUM
• Momentum moves downward more easily in unstable air than stable. • Near surface, unstable regimeproduces steeper wind profiles
Diagram from: Air-sea Interaction: Laws and Mechanisms, CsanadyStructure of the Atmospheric Boundary Layer, Sorbjan
![Page 7: Skyler Goldman, Meteorology, DMES](https://reader033.vdocuments.mx/reader033/viewer/2022061610/5681642e550346895dd5f53b/html5/thumbnails/7.jpg)
Corrected Drag Coefficient
22 )]()[ln( Lz
zzkC r
mo
rd
22 )][ln( o
rd z
zkCNeutral =
Corrected =
Where is a stability function
But…how do we find this stability function???
)(Lzr
m
![Page 8: Skyler Goldman, Meteorology, DMES](https://reader033.vdocuments.mx/reader033/viewer/2022061610/5681642e550346895dd5f53b/html5/thumbnails/8.jpg)
Correcting for Stability…• According to theory, the [drag]
coefficients are a function of buoyancy and wind shear.
• The exact relationship is not known but is approximated using observed wind, temperature and moisture profiles near the surface.
- (Arya 2001)
![Page 9: Skyler Goldman, Meteorology, DMES](https://reader033.vdocuments.mx/reader033/viewer/2022061610/5681642e550346895dd5f53b/html5/thumbnails/9.jpg)
Courtesy of Cory Hodes
Profiles vary spatially and temporally
BEACH DUNE CREST WEST OF DUNE
![Page 10: Skyler Goldman, Meteorology, DMES](https://reader033.vdocuments.mx/reader033/viewer/2022061610/5681642e550346895dd5f53b/html5/thumbnails/10.jpg)
Finding Stability• To find stability function, a series of equations
are used– 1st – Find static stability using temperature,
pressure, and humidity data– 2nd – Determine Richardson Number
• Ri Number = static stability / windshear– Richardson Number is then related to a buoyancy
parameter– 3rd – Use buoyancy parameter to correct neutral
drag coefficient m
![Page 11: Skyler Goldman, Meteorology, DMES](https://reader033.vdocuments.mx/reader033/viewer/2022061610/5681642e550346895dd5f53b/html5/thumbnails/11.jpg)
What is Expected?• Neutral
– Higher the roughness length, higher the drag coefficient
– Roughness Lengths:
• Vegetated (Ponce)– Station 1: 0.17 ft– Station 2: 0.21 ft– Station 3: 2.44 ft– Station 4: 0.59 ft
• Non Vegetated (Denuded):– Station1: 0.45 ft– Station 2: 2.5 10^-3
ft– Station 3: 1.11 ft
22 )][ln( o
rd z
zkC
Roughness lengths from Sarah CollinsBeach profile map from John Hearin
Wind Flow Survey Profile 6/9/10
-5.0
0.0
5.0
10.0
15.0
20.0
25.0
0 50 100 150 200 250 300 350 400
Horizontal Station from Monument (ft)
Elev
atio
n (ft
) NA
VD88
MHHW
R-155T Out
R-155T ReturnStation 2
WATER
Station 1
Station 3
![Page 12: Skyler Goldman, Meteorology, DMES](https://reader033.vdocuments.mx/reader033/viewer/2022061610/5681642e550346895dd5f53b/html5/thumbnails/12.jpg)
Roughness Length vs. Drag Coefficient
0
0.02
0.04
0.06
0.08
0.1
0.12
0.14
0.16
0.18
0 0.5 1 1.5 2 2.5 3Roughness
Length (Zo, ft)
Station 1, Denuded DuneStation 2, Denuded DuneStation 3, Denuded DuneStation 1, Ponce ParkStation 2, Ponce ParkStation 3, Ponce ParkStation 4, Ponce Park
Dra
g C
oeff
icie
nt (C
d)
22 )][ln( o
rd z
zkC
![Page 13: Skyler Goldman, Meteorology, DMES](https://reader033.vdocuments.mx/reader033/viewer/2022061610/5681642e550346895dd5f53b/html5/thumbnails/13.jpg)
What is Expected?• Corrected for Stability
22 )]()[ln( Lz
zzkC r
mo
rd
Our data
(Arya 2001)
![Page 14: Skyler Goldman, Meteorology, DMES](https://reader033.vdocuments.mx/reader033/viewer/2022061610/5681642e550346895dd5f53b/html5/thumbnails/14.jpg)
Richardson Number vs. Drag Coefficient
0.0001
0.001
0.01
0.1
1
10
-10 -9 -8 -7 -6 -5 -4 -3 -2 -1 0 1
Richardson Number
Dra
g C
oeffi
cien
t
Station 1: Denuded z_o = 0.45
Station 2: Denuded z_o = 0.0025
Station 3: Denuded z_o = 1.11
Station 1: Ponce z_o = 0.17
Station 2: Ponce z_o = 0.21
Station 3: Ponce z_o = 2.44
Station 4: Ponce z_o = 0.59
![Page 15: Skyler Goldman, Meteorology, DMES](https://reader033.vdocuments.mx/reader033/viewer/2022061610/5681642e550346895dd5f53b/html5/thumbnails/15.jpg)
Putting it all together…• Based on formulas…
– High stability = low drag– Low stability = high drag
– High roughness length = high drag– Low roughness length = low drag
• Yet…how does this affect the wind profile?
![Page 16: Skyler Goldman, Meteorology, DMES](https://reader033.vdocuments.mx/reader033/viewer/2022061610/5681642e550346895dd5f53b/html5/thumbnails/16.jpg)
LOWDRAG
HIGH DRAG
Wind Vectors Wind Vectors
decreaseWhen subjected to moredrag
Z Z
Wind Speed Wind Speed
GREATER CHANGE IN WIND SPEED OVER
HEIGHT
LITTLE CHANGEIN WIND SPEED OVER HEIGHT
![Page 17: Skyler Goldman, Meteorology, DMES](https://reader033.vdocuments.mx/reader033/viewer/2022061610/5681642e550346895dd5f53b/html5/thumbnails/17.jpg)
Final Question…• Evidence of direct relationship between
roughness and stability• Evidence of indirect relationship
between drag and stability• Wind profiles = little wind changes over
height with low drag• Wind profiles = large wind changes over
height with high drag• BUT…do these statements hold with
actual data….
![Page 18: Skyler Goldman, Meteorology, DMES](https://reader033.vdocuments.mx/reader033/viewer/2022061610/5681642e550346895dd5f53b/html5/thumbnails/18.jpg)
5/26/2010
-0.3
-0.1
0.1
0.3
0.5
0.7
0.9
Station 1, Mean HighWater
Station 2, Base of Dune Station 3, Top of Dune Station 4, A1A
Stat
ic S
tabi
lity/
Dra
g C
oeff
icie
nt
Drag Coeff icient
Station 2
0102030
0 5 10 15
Wind Speed (m/s)
Hei
ght (
ft)
Station 4
0102030
0 5 10 15
Wind Speed (m/s)
Hei
ght (
ft)
Station 3
0102030
0 5 10 15
Wind Speed (m/s)
Hei
ght (
ft)
Station 1
0102030
0 5 10 15
Wind Speed (m/s)
Hei
ght (
ft)
![Page 19: Skyler Goldman, Meteorology, DMES](https://reader033.vdocuments.mx/reader033/viewer/2022061610/5681642e550346895dd5f53b/html5/thumbnails/19.jpg)
6/9/2010
0
0.05
0.1
0.15
0.2
0.25
0.3
Station 1: Mean High Water Station 2: Top of Dune Station 3: Between Dune andA1A
Stat
ic S
tabi
lity/
Dra
g Co
effic
ient
Drag Coeff icient
Station 1
0
20
40
2 4 6 8Wind Speed (m/s)
Hei
ght (
ft)
Station 2
02040
2 4 6 8
Wind Speed (m/s)
Hei
ght (
ft) Station 3
02040
2 4 6 8
Wind Speed (m/s)
Hei
ght (
ft)
![Page 20: Skyler Goldman, Meteorology, DMES](https://reader033.vdocuments.mx/reader033/viewer/2022061610/5681642e550346895dd5f53b/html5/thumbnails/20.jpg)
Conclusions• Wind profiles on 26 May 2010
appear to be consistent with corrected drag estimates
• This is not true of all sampled days as estimates of zo can vary due to:– wind speed– fetch– wave height for station 1 which is
located near the high tide line.
![Page 21: Skyler Goldman, Meteorology, DMES](https://reader033.vdocuments.mx/reader033/viewer/2022061610/5681642e550346895dd5f53b/html5/thumbnails/21.jpg)
Questions…
Break is next, followed by:Emily Teske!