Energy balance closure at Wisconsin sites

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Energy balance closure at Wisconsin sites

• Nan Lu
• Lees Lab, EEES, University of Toledo
• March 24, 2006

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Energy balance closure
Hs LE Rn - G
- S

• Rn net radiation
• Hs sensible heat flux
• LE latent heat flux
• G soil heat flux

S storage heat flux between the soil heat plate
surface and the level of the eddy covariance
instruments
Energy balance ratio1
3
Storage heat flux subcomponents
S Qg Qa Qv Qp

• Qg soil heat storage between soil heat plate and
  soil surface
• Qa air column heat storage
• Qv biomass heat storage
• Qp photosynthetic heat component

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Objectives

• 1 To evaluate the potential source of
  differences in the energy balance within and
  among sites.

2 To examine how much of the energy balance
closure is improved by adding each of the
subcomponent of storage heat flux.
3 To evaluate the quality of energy balance
closure under a range of conditions in order to
identify possible causes for lack of closure in
the forest.
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Study site

• Northern part of Chequamegon - Nicolet
  National Forest in Wisconsin, USA

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Site information
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Methods
Directly-measured components Rn, Hs and LE, G

• Estimated components
• Qg Qa Qv

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Definition of conditions

• Initial data (data during rain time are removed)
• Different months in A year
• Different times in A day
• Morning 700 am
• Afternoon 100 pm
• Evening 1900 pm
• Midnight 100 am
• The data where fraction velocity (u)included and excluded.
• Values of ucrit are different for different sites
• Clear sky and cloudy sky daytime
• Rn - meanRn 0 when 700 amsky day time

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Preliminary results
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Energy fluxes differences among sites in 2002
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IHW_2003
Energy balance closure through a year
MHW_2003
HsLE(W/m2)
R-Square 0.8060 Slope 0.6673 Inter
-8.9054
R-Square 0.6380 Slope 0.5309 Intercept
-1.1968
Rn-G(W/m2)
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Comparison of energy closure among sites using
initial data
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Breaking data into months (IHW2003)
Mar R2 0.1998 S 0.4673 Int -6.8146
Sep R2 0.7537 S 0.7099 Int -10.0250
Jun R2 0.9015 S 0.6708 Int -3.4106
HsLE
Apr R2 0.7673 S 0.5059 Int -3.0066
Jul R2 0.8438 S 0.7017 Int -9.6442
Oct R2 0.8932 S 0.7323 Int -18.6266
May R2 0.8657 S 0.6555 Int 3.6799
Aug R2 0.8986 S 0.6703 Int -11.7049
Dec R2 0.5242 S 0.5815 Int -0.8381
Rn_G
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Breaking A day by time (IHW2003)
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Breaking A day by time (Mhw2003)
R-Square 0.3720 Slope 0.4000 Intercept
78.4817
R-Square 0.6525 Slope 0.5154 Intercept
-4.9549
R-Square 0.0023 Slope 0.0534 Intercept
-25.0351
R-Square 0.0425 Slope 0.3238 Intercept
-7.7102
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Ihw2003
Comparison of energy closure with uincluded and excluded
R2, Slope, Intercept

• mhw2003
• 0.6864, 0.52639, -4.42957
• 0.6678 0.53572 -2.92671
• mhw2002
• 0.7400 0.55027 0.57966
• 0.7171 0.55533 0.92489
• Mhw2004
• 0.6826 0.62029 -8.83475
• 0.6773 0.62829 -8.46399
• irp2003
• 0.7691 0.61747 -1.41003
• 0.7405 0.61868 -0.16168

• mrp2002
• 0.8157 0.56418 1.01026
• 0.7861 0.56876 0.69437
• Mrp2003
• 0.8719 0.55328 1.03014
• 0.8555 0.55954 -1.29397
• Mrp2004
• 0.8493 0.61163 -4.40165
• 0.8387 0.61772 -7.33496
• Mrp2005
• 0.8294 0.54967 3.38856
• 0.8111 0.55669 0.20877

R-Square 0.8783 Slope
0.6820 Intercept -8.0230
R-Square 0.8750 Slope
0.6852 Intercept -8.7129
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Clear sky vs. cloudy sky time
Ihw2003
R-Square 0.7601 Slope
0.6550 Intercept 5.0714
Cloudy sky
R-Square 0.7839 Slope
0.6783 Intercept -1.9221
Clear sky
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Comparison of energy closure in cloudy-sky and
clear-sky daytime
ClearR2 Slope Intcpt
Cloudy R2 Slope Intcpt
mhw2003 0.4583 0.4478 34.1210 mhw2002
0.5791 0.5692 -8.3515 Mhw2004 0.6347
0.6372 -11.5435 irp2003 0.6885 0.6616
-27.7009 mrp2002 0.6704 0.5689
2.7484 Mrp2003 0.7820 0.5593
-3.4809 Mrp2004 0.7303 0.6455
-21.7825 Mrp2005 0.7199 0.5673 -13.3668
0.5141 0.4918 31.9535 0.6118 0.5695
-6.0921 0.3886 0.5926 -4.9742 0.6285
0.6234 -2.3322 0.6602 0.5724
-3.0070 0.7412 0.5858 -15.6822 0.6737
0.6145 -11.3552 0.6484 0.5876 -9.9027
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Preliminary conclusion

• Rn, HS, LE and G are different among sites in the
  same year, and within sites through years.
• Energy balance closures are different among sites
  in the same year, and within sites through years.
• Energy balance closure is better in the morning
  of a day, and in the summer months of a year.
• Energy balance closure is better where uucrit,
  but the difference is not much.
• Energy balance closure is better when the sky is
  clear in the daytime, but the difference is not
  much.

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Further analysis
Directly-measured components Rn, Hs and LE, G

• Estimated components

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Estimate soil temperature

• Ts exp (kdepth)
• K f (soil water content, thickness of forest
  duff, accumulative vegetation cover)
• To estimate the soil temperature of the surface
  of soil heat plate by using the measurements at
  10cm and 30cm depths.

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Thank you!