energy balance closure at four forest sites in wisconsin
DESCRIPTION
Energy balance closure at four forest sites in Wisconsin. Nan Lu LEES Lab, University of Toledo. 10/27/06. Energy balance closure. Rn = LE+ Hs + G + Qs Qs = Q soil + Q air + Q biomass. Energy balance. Evaluation method: - PowerPoint PPT PresentationTRANSCRIPT
Energy balance closure at four forest sites in Wisconsin
Nan LuLEES Lab, University of Toledo
10/27/06
Energy balance closure
Rn = LE+ Hs + G +LE+ Hs + G + Qs
QsQs= Q= Qsoilsoil + Q + Qairair + Q + Qbiomassbiomass
Energy balance Evaluation method: 1. Linear regression coefficient
(slope & intercept) between (LE+Hs) and (Rn-G-Qs) (EBC)
2. Ratio (EBR)
Energy Imbalance! 55-99% at 50 site-years (Wilson
et al., 2002)
Oliphant et al.,2004. AFM
Is Qs important? Qs was typically 5% of Rn in a mature mixed
forest; and it could be up to 10% under some particular conditions, e.g. overcast days, during or immediately following rainfall (McCaughey and Saxton, 1985).
The assessment of the contribution of storage heat to the total energy balance is few for both forest and agricultural ecosystems (Oliphant, 2004; Mayer, 2004) .
What are the conditions under which energy balance is not closed?
The lacks of energy balance closure in the forest were usually identified at night with low friction velocity (u*) (Wilson et al., 2002).
Clouds could play an important role in regulating the energy balance closure by limiting radioactive energy input as well as evaporation (Eltahir and Humphries, 1998; Petrone et al., 2002) .
Effects of forest type? Physical properties of the land surface such as
albedo, roughness and root zone depth affect different components of the energy balance by Rn as well as its partition into Hs and LE (Eltahir and Humphries, 1998).
Objectives 1) Dose heat storage (including Qsoil and
Qair) significantly contribute to the energy balance?
2) Do friction velocity and clouds have effects on energy balance closure?
3) Is energy balance closure different among different forest types?
Study site
23m
26m
9m
3m
Methods
z
sszsoil dzdt
dTCQ
0
)(
Zr
apaa dzdt
dTCQ
0
Zr
paw dz
dt
deCQ
0
Qair=Qa+Qw
(Oliphant et al.,2004. AFM)
Methods: Definition of cloudiness
0
500
1000
1500
2000
2500
0:00 6:00 12:00 18:00 0:00
Time
Day 187
0
500
1000
1500
2000
2500
0:00 6:00 12:00 18:00 0:00
Time
Ph
oto
n d
ensi
ty (
um
ol m
-2 s
-1)
PARPext
Day 186
Comparison of a sunny day (Day 186) and a cloudy day (Day 187) (at IHW, 2003)
Cloudiness=Pext-PARRelative Cloudiness=(Pext-PAR)/Pext
Results
1. Measured energy fluxes (Rn, LE, Hs, G) and storage heat (Qs)
Seasonal variation of LE/Rn, Hs/Rn, G/Rn and Qs/Rn
0
0.03
0.06
0.09
0.12
0.15
May Jun Jul Aug Sep Oct Nov
G/R
n
MRP02 MRP03MHW02 IHW03PB02
0
0.02
0.04
0.06
0.08
May Jun Jul Aug Sep Oct NovMonth
Qs/
Rn
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
May Jun Jul Aug Sep Oct Nov
LE/R
n
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
May Jun Jul Aug Sep Oct NovMonth
Hs/
Rn
0
0.03
0.06
0.09
0.12
0.15
May Jun Jul Aug Sep Oct Nov
G/R
n
MRP02 MRP03MHW02 IHW03PB02
0
0.02
0.04
0.06
0.08
May Jun Jul Aug Sep Oct NovMonth
Qs/
Rn
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
May Jun Jul Aug Sep Oct Nov
LE/R
n
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
May Jun Jul Aug Sep Oct NovMonth
Hs/
Rn
Rn, LE, Hs and G of growing season
-100
0
100
200
300
400
500
600
700
800
0:00 6:00 12:00 18:00 0:00
Time
Rn (
W m
-2)
MRP02MRP03MHW02IHW03PB02
-100
-50
0
50
100
150
200
250
300
0:00 6:00 12:00 18:00 0:00
Time
LE (
W m
-2)
-100
-50
0
50
100
150
200
250
300
0:00 6:00 12:00 18:00 0:00
Time
Hs
(W m
-2)
-30
-20
-10
0
10
20
30
40
50
0:00 6:00 12:00 18:00 0:00
Time
G (
W m
-2)
Comparison of daily variation of Rn, G, Hs, LE among sites, error bar – SE
Comparison of maximum of Rn, LE, Hs and G of growing season among sites
Repeated ANOVA
Site/Yr N Rn LE Hs G
MRP02 650 658.26±7.63 a 165.98±4.12 c 191.92±3.79 a 21.54±0.6 b
MRP03 630 677.69±7.75 a 167.38±4.18 c 201.08±3.85 a 18.02±0.61 c
MHW02 557 582.95±8.24 b 191.42±4.45 b 134.45±4.1 c 15.96±0.65 d
IHW03 578 590.16±8.09 b 234.82±4.37 a 162.11±4.02 b 7.94±0.63 e
PB02 624 527.02±7.79 c 183.99±4.2 b 131.24±3.87 c 35.13±0.61 a
Multiple comparisons of maximum (10:00~12:00 AM) Rn, LE, Hs and G among sites in the growing season
Qs in the growing season
No difference on the daily scale!
Comparison of daily variation of storage heat fluxes (Qs, Qsoil, Qair) among sites, error bar – SE
-40
-20
0
20
40
0:00 6:00 12:00 18:00 0:00
Time
Qair (
W m
-2)
-40
-20
0
20
40
0:00 6:00 12:00 18:00 0:00
Time
Qsoil
(W m
-2)
-40
-20
0
20
40
0:00 6:00 12:00 18:00 0:00
Time
Qs (
W m
-2)
MRP02MRP03MHW02IHW03PB02
Comparison of Qs in different time periods of a day among sites
5<hr<=11 Site/Yr
Qs N Qsoil N Qair N
MRP02 12.89±0.93 c 333 0.63±0.42 c 335 14±0.55 b 969
MRP03 16.2±1.48 b 131 0.79±0.68 c 131 16.04±0.56 a 933
MHW02 19.56±0.64 a 712 3.57±0.29 b 712 16.3±0.61 a 788
IHW03 8.23±0.64 d 694 1.25±0.29 c 698 7.14±0.6 c 823
PB02 10.26±0.67 d 642 7.91±0.3 a 642 2.37±0.59 d 864
17<hr<=23 Site/Yr
Qs N Qsoil N Qair N
MRP02 -13.79±0.87 b 391 -1.8±0.15 a 395 -11.3±0.58 c 980
MRP03 -18.69±1.54 c 124 -1.43±0.26 a 126 -12.56±0.6 c 918
MHW02 -15.53±0.62 bc 779 -3.27±0.11 c 787 -12.02±0.62 c 861
IHW03 -9.03±0.7 a 606 -2.72±0.11 b 702 -6.14±0.68 b 727
PB02 -9.3±0.62 a 781 -7.2±0.11 d 782 -2.03±0.62 a 884
Results
2. Energy balance closure
Contribution of Qs to the energy balance closure
Site/yr MRP02 MRP03 MHW02 IHW03 PB02 Site/yr MRP02 MRP03 MHW02 IHW03 PB02
Slope 0.59 0.65 0.51 0.66 0.68 Slope 0.56 0.55 0.56 0.69 0.65Offset -10.22 -26.86 -17.43 -18.25 -15.40 Offset -0.37 1.75 -0.61 -9.63 -8.75R-square 0.82 0.81 0.81 0.82 0.89 R-square 0.88 0.87 0.85 0.89 0.93
Slope 0.63 0.63 0.60 0.67 0.70 Slope 0.62 0.57 0.59 0.70 0.67Offset -3.26 -3.64 -11.10 -13.25 -13.38 Offset -4.72 4.83 -5.81 -16.07 -13.67R-square 0.86 0.83 0.84 0.82 0.89 R-square 0.90 0.85 0.86 0.90 0.93
Slope 0.46 0.39 0.55 0.79 0.51 slope 0.64 0.57 0.60 0.67 0.67Offset 4.52 6.69 5.60 -0.62 -6.54 offset -10.51 3.00 -11.81 0.85 -13.18R-square 0.55 0.40 0.63 0.63 0.46 R-square 0.82 0.80 0.72 0.77 0.87
Slope 0.44 0.60 0.56 0.81 0.53 slope 0.63 0.56 0.59 0.67 0.67Offset -1.47 2.52 -2.97 -10.23 -12.15 offset -9.56 10.83 -3.81 1.60 -11.45R-square 0.40 0.53 0.74 0.58 0.47 R-square 0.82 0.78 0.67 0.77 0.85
slope 0.61 0.55 0.61 0.71 0.68offset 18.19 25.78 -6.38 -28.16 -10.45R-square 0.75 0.75 0.67 0.66 0.78
Daytime
No Qs
Plus Qs
Site/yr MRP02 MRP03 MHW02 IHW03 PB02 Site/yr MRP02 MRP03 MHW02 IHW03 PB02
Slope 0.59 0.65 0.51 0.66 0.68 Slope 0.56 0.55 0.56 0.69 0.65Offset -10.22 -26.86 -17.43 -18.25 -15.40 Offset -0.37 1.75 -0.61 -9.63 -8.75R-square 0.82 0.81 0.81 0.82 0.89 R-square 0.88 0.87 0.85 0.89 0.93
Slope 0.63 0.63 0.60 0.67 0.70 Slope 0.62 0.57 0.59 0.70 0.67Offset -3.26 -3.64 -11.10 -13.25 -13.38 Offset -4.72 4.83 -5.81 -16.07 -13.67R-square 0.86 0.83 0.84 0.82 0.89 R-square 0.90 0.85 0.86 0.90 0.93
Slope 0.46 0.39 0.55 0.79 0.51 slope 0.64 0.57 0.60 0.67 0.67Offset 4.52 6.69 5.60 -0.62 -6.54 offset -10.51 3.00 -11.81 0.85 -13.18R-square 0.55 0.40 0.63 0.63 0.46 R-square 0.82 0.80 0.72 0.77 0.87
Slope 0.44 0.60 0.56 0.81 0.53 slope 0.63 0.56 0.59 0.67 0.67Offset -1.47 2.52 -2.97 -10.23 -12.15 offset -9.56 10.83 -3.81 1.60 -11.45R-square 0.40 0.53 0.74 0.58 0.47 R-square 0.82 0.78 0.67 0.77 0.85
slope 0.61 0.55 0.61 0.71 0.68offset 18.19 25.78 -6.38 -28.16 -10.45R-square 0.75 0.75 0.67 0.66 0.78
No Qs at 5<hour<=11
Plus Qs at 5<hour<=11
No Qs at 17<hour<=23
Plus Qs at 17<hour<=23
All day
Two particular time periods
Energy balance closure under different conditions
0.20
0.40
0.60
0.80CloudySunny
0.20
0.40
0.60
0.80u<u* u>u*
0.2
0.4
0.6
0.8
Slo
pe
NoctualDaytime
-35.00
-15.00
5.00
25.00
-35.00
-15.00
5.00
25.00
-35
-15
5
25
Off
set
0.000.20
0.400.60
0.801.00
MR
P02
MR
P03
MH
W02
IHW
03
PB
02
0.000.20
0.400.60
0.801.00
MR
P02
MR
P03
MH
W02
IHW
03
PB
020
0.2
0.40.6
0.81
MR
P02
MR
P03
MH
W02
IHW
03
PB
02
R-s
qu
are
Energy balance closure under different conditions
All data available
Site/yr MRP02 MRP03 MHW02 IHW03 PB02 Site/yr MRP02 MRP03 MHW02 IHW03 PB02
Slope 0.59 0.65 0.51 0.66 0.68 Slope 0.56 0.55 0.56 0.69 0.65Offset -10.22 -26.86 -17.43 -18.25 -15.40 Offset -0.37 1.75 -0.61 -9.63 -8.75R-square 0.82 0.81 0.81 0.82 0.89 R-square 0.88 0.87 0.85 0.89 0.93
Slope 0.63 0.63 0.60 0.67 0.70 Slope 0.62 0.57 0.59 0.70 0.67Offset -3.26 -3.64 -11.10 -13.25 -13.38 Offset -4.72 4.83 -5.81 -16.07 -13.67R-square 0.86 0.83 0.84 0.82 0.89 R-square 0.90 0.85 0.86 0.90 0.93
Slope 0.46 0.39 0.55 0.79 0.51 slope 0.64 0.57 0.60 0.67 0.67Offset 4.52 6.69 5.60 -0.62 -6.54 offset -10.51 3.00 -11.81 0.85 -13.18R-square 0.55 0.40 0.63 0.63 0.46 R-square 0.82 0.80 0.72 0.77 0.87
Slope 0.44 0.60 0.56 0.81 0.53 slope 0.63 0.56 0.59 0.67 0.67Offset -1.47 2.52 -2.97 -10.23 -12.15 offset -9.56 10.83 -3.81 1.60 -11.45R-square 0.40 0.53 0.74 0.58 0.47 R-square 0.82 0.78 0.67 0.77 0.85
slope 0.61 0.55 0.61 0.71 0.68offset 18.19 25.78 -6.38 -28.16 -10.45R-square 0.75 0.75 0.67 0.66 0.78
No Qs
Site/yr MRP02 MRP03 MHW02 IHW03 PB02 Site/yr MRP02 MRP03 MHW02 IHW03 PB02
Slope 0.59 0.65 0.51 0.66 0.68 Slope 0.56 0.55 0.56 0.69 0.65Offset -10.22 -26.86 -17.43 -18.25 -15.40 Offset -0.37 1.75 -0.61 -9.63 -8.75R-square 0.82 0.81 0.81 0.82 0.89 R-square 0.88 0.87 0.85 0.89 0.93
Slope 0.63 0.63 0.60 0.67 0.70 Slope 0.62 0.57 0.59 0.70 0.67Offset -3.26 -3.64 -11.10 -13.25 -13.38 Offset -4.72 4.83 -5.81 -16.07 -13.67R-square 0.86 0.83 0.84 0.82 0.89 R-square 0.90 0.85 0.86 0.90 0.93
Slope 0.46 0.39 0.55 0.79 0.51 slope 0.64 0.57 0.60 0.67 0.67Offset 4.52 6.69 5.60 -0.62 -6.54 offset -10.51 3.00 -11.81 0.85 -13.18R-square 0.55 0.40 0.63 0.63 0.46 R-square 0.82 0.80 0.72 0.77 0.87
Slope 0.44 0.60 0.56 0.81 0.53 slope 0.63 0.56 0.59 0.67 0.67Offset -1.47 2.52 -2.97 -10.23 -12.15 offset -9.56 10.83 -3.81 1.60 -11.45R-square 0.40 0.53 0.74 0.58 0.47 R-square 0.82 0.78 0.67 0.77 0.85
slope 0.61 0.55 0.61 0.71 0.68offset 18.19 25.78 -6.38 -28.16 -10.45R-square 0.75 0.75 0.67 0.66 0.78
Daytime&u>u*&sunny
Daytime
Daytime&u>u*
Discussion
-100
100
300
500
700
900
-200 200 600 1000 1400 1800
Pext-PAR (umol m-2 s-1)
W m
-2
LE
Hs
-100
100
300
500
700
900
0 0.5 1 1.5 2 2.5 3 3.5
Log (Pext-PAR)
LE
+Hs
(W m
-2)
Discussion
-3
-2
-1
0
1
2
3
4
-200 0 200 400 600 800
LE+Hs (W m-2)
EB
R
Linear regression between EBC and the canopy height (account for Qs and not account for Qs)
y = -0.0049x + 0.6788R2 = 0.8379
y = -0.0042x + 0.6971R2 = 0.7576
0.5
0.55
0.6
0.65
0.7
0.75
0.8
0 5 10 15 20 25 30
Canopy height (m)
Slo
pe
No S Include SQs Qs
EB
C
Conclusions 1. Net radiation and its portioning to LE, Hs
and G were different at half-hourly scale among sites; largest difference occurred around noon. But there was not a difference in Qs among sites.
2. Qs was different among sites during the hours after dawn and around dusk when Qs was a larger proportion of Rn. Storage was greater in the taller than shorter canopies.
Conclusions 3. Storage energy improved the energy
balance closure by 1-6% at of our study sites; during the particular time periods of dawn and dusk, Qs could increased energy balance closure by 9-11% for tall canopies.
4. Energy balance closure was higher when friction velocity was greater and the sky was clearer.