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

1. Types of surfaces

• Foam

• Stone

• Bare soil

• Grass

• Concrete

• Dark and light asphalt

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

3. Approach

• Rn = S(1 – a) + LW↓ - LW↑

• Rn – SH – LH – Fg = 0

RnSH

LH

Fg

Turbulent Heat Transfer

• Sensible Heat

SH = rCpCDHU(Ts – Ta)

• Latent Heat

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.

• 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

• 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.

• 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

• 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

• 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

• 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

• 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

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