mini heat budget experiment - yale university · •time and place: august 18, 2009; esc front yard...
TRANSCRIPT
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Mini Heat Budget Experiment
• Time and place: August 18, 2009; ESC front yard
• Goal: Measure/calculate energy fluxes over different surfaces
– Net radiation
– Sensible heat flux
– Latent heat flux
• Measurements taken every 3 hours
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1. Types of surfaces
• Foam
• Stone
• Bare soil
• Grass
• Concrete
• Dark and light asphalt
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2. Instruments
• Eppley Pyranometer – measure of incoming and outgoing shortwave radiation (given in mV)
• Raytek Infrared Gun – surface temperature
• Kestrel handheld weather meter– air temperature, wind speed, humidity
• Spectrometer – measure of incoming and outgoing radiation as a function of wavelength
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3. Approach
• Rn = S(1 – a) + LW↓ - LW↑
• Rn – SH – LH – Fg = 0
RnSH
LH
Fg
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Turbulent Heat Transfer
• Sensible Heat
SH = rCpCDHU(Ts – Ta)
• Latent Heat
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4. Results
• Insolation
0
100
200
300
400
500
600
700
800
900
1000
6:00 9:00 12:00 15:00 18:00 21:00
[W/m
^2]
Insolation (Eppley)
Foam
Stone
Concrete
Clovers
Soil
Light Asph.
Dark Asph.
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• Midday albedo
0.00
0.05
0.10
0.15
0.20
0.25
0.30
0.35
0.40
0 1 2 3 4 5 6 7 8
Midday albedo (eppley) 1 = Foam2 = Stone3 = Concrete4 = Grass5 = Soil6 = Light Asphalt7 = dark Asphalt
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• Air Temperature [C]
290
292
294
296
298
300
302
304
306
308
6:00 9:00 12:00 15:00 18:00 21:00
Air
Te
mp
era
ture
[K
]
Air temperature
Foam
Stone
Concrete
Clovers
Soil
Light Asphalt
Dark Asph.
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• Surface Temperature [K]
290
300
310
320
330
340
350
0.00 3.00 6.00 9.00 12.00 15.00 18.00 21.00 24.00
K
Surface Temperature
Foam
Stone
Concrete
Clovers
Soil
Light Asphalt
Dark Asphalt
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• Net Radiation [Wm-2]
-100.00
0.00
100.00
200.00
300.00
400.00
500.00
600.00
700.00
0.00 3.00 6.00 9.00 12.00 15.00 18.00 21.00 24.00
Ne
t R
adia
tio
n [
W/m
^2]
Net Radiation (RCR)
Foam
Stone
Concrete
Grass
Soil
Light Asphalt
Dark Asphalt
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• Sensible Heat Flux
-100.00
0.00
100.00
200.00
300.00
400.00
500.00
0.00 3.00 6.00 9.00 12.00 15.00 18.00 21.00 24.00
[W/m
^2]
Sensible Heat Flux
Foam
Stone
Concrete
Clovers
Soil
Light Asphalt
Dark Asphalt
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• Latent heat Flux
0
50
100
150
200
250
300
0.00 3.00 6.00 9.00 12.00 15.00 18.00 21.00 24.00
[W/m
^2]
Latent Heat
Grass
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• Ground Heat Flux (Imbalance) [Wm-2]
-200.00
-100.00
0.00
100.00
200.00
300.00
400.00
500.00
600.00
0.00 3.00 6.00 9.00 12.00 15.00 18.00 21.00 24.00
Imbalance (Ground flux) - Eppley
Foam
Stone
Concrete
Grass
Soil
Light Apshalt
Dark Asphalt
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4. Conclusions
• Albedo: visually brightest surface (concrete) had the highest albedo and consequently lower surface temperatures. Some inconsistencies: bare soil had lower albedo than grass, but that is probably due to a mixed signal coming from both grass and soil.
• Net energy flux changes sign in the evening after sunset (1800 – 2100) thus changing from downward flux (into the soil) to upward flux (from the ground to the atmosphere)
• Main source of inaccuracies: parameterization of sensible and latent heat