chuixiang (tree) yi school of earth and environmental sciences queens college, city university of...
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Chuixiang (Tree) YiChuixiang (Tree) Yi
School of Earth and Environmental SciencesSchool of Earth and Environmental SciencesQueens College, City University of New YorkQueens College, City University of New York
Acknowledgements to
Russ Monson, University of ColoradoDean Anderson, USGS
Brian Lamb, Washington State UniversityJohn Zhai, University of Colorado
Andrew Turnipseed, NCARSean Burn, University of Colorado
3
5
0 0 0
r r r
r
Z Z Z
Z
S T HA VA
c c cNEE dz w c u dz w dz
t x zF F F F
Eddy Flux TowerEddy Flux Tower
COCO22 HH22OO
CHCH44 T T
COCO22 HH22OO
CHCH44 T TCOCO22 HH22OO
CHCH44 T T
Super-stable layer, flow separation (Yi et al., 2005)
Courtesy of Jielun Sun Canopy flows are separated by a
superstable layer in calm nights.
Davis et al. 2004
West West towertower
South South towertower
North North towertower
East East towertower
Vertical advectionVertical advection
0 0
r s r
s
Z Z Z
vadv Z
c c cF w dz w dz w dz
z z z
00
hWind SpeedWind Speed Air TemperatureAir Temperature
Super-stable layerSuper-stable layer
ZZss
ZZrr
w++
--
Nighttime dc/dz is always negativeNighttime dc/dz is always negative
Vertical exchange zoneVertical exchange zone
Horizontal exchange zoneHorizontal exchange zone
Yi et al., 2008Yi et al., 2008
sZ
rr s
r r s s
ZZ Zvadv Z Z Z Z
r s
w wF w c w c cdz
Z Z
Vertical advectionVertical advection
s sZ Z =
r r r
s
Z Z Z
vadv Z
c wc wF w dz dz c dz
z z z
=
=
= ( )
rr
r rs
r r r
r r
ZZvadv Z Z Z
r s
Z Z Z
Z Z
wF w c cdz
Z Z
w c w c
w c c
Lee’s assumptionLee’s assumption
r sZ Z
r s
w ww
z Z Z
0 at super-stable layersZ
w ,r rZ Zw c
0sZw
ZZss
ZZrr
Super-stable Super-stable layerlayer
1 r
s
Z
Zr s
c cdzZ Z
Yi et al., 2008Yi et al., 2008
sZ
rr s
r r s s
ZZ Zvadv Z Z Z Z
r s
w wF w c w c cdz
Z Z
Vertical advectionVertical advection
s sZ Z =
r r r
s
Z Z Z
vadv Z
c wc wF w dz dz c dz
z z z
=
=
= ( )
rr
r rs
r r r
r r
ZZvadv Z Z Z
r s
Z Z Z
Z Z
wF w c cdz
Z Z
w c w c
w c c
Lee’s assumptionLee’s assumption
r sZ Z
r s
w ww
z Z Z
0 at super-stable layersZ
w ,r rZ Zw c
0sZw
ZZss
ZZrr
Super-stable Super-stable layerlayer
1 r
s
Z
Zr s
c cdzZ Z
Yi et al., 2008Yi et al., 2008
Longitude (degree)
-105.5485 -105.5475 -105.5465
Latit
ude
(deg
ree)
40.0315
40.0320
40.0325
40.0330
40.0335
WT
NT
ET
ST
136
10
21.5
136
10
31
1
6
1
6
wind direction
NT
ET
ST
Longitude (degree)
-105.5485 -105.5475 -105.5465
Latit
ude
(deg
ree)
40.0315
40.0320
40.0325
40.0330
40.0335
WT
NT
ET
ST
136
10
21.5
136
10
21.5
136
10
31
1
6
1
6
wind directionwind direction
NT
ET
ST
Horizontal advection calculationHorizontal advection calculation
0
rZ
hadv
cF u dz
x
0cos
rZ
iT
cu dz
r
WT ET
height
c
r
Horizontal CO2 gradient
Horizontal CO2 gradient
Ho
rizo
nta
l CO
2 g
rad
ien
t
Ho
rizo
nta
l CO
2 g
rad
ien
tWT NT
height
c
r
u
WT ST
height
c
r
Horizontal CO2 gradient
Horizontal CO2 gradientYi et al., 2008Yi et al., 2008
Horizontal advection calculationHorizontal advection calculation
Longitude (degree)
-105.5485 -105.5475 -105.5465
La
titu
de
(d
eg
ree
)
40.0315
40.0320
40.0325
40.0330
40.0335
WT
NT
ET
ST
136
10
21.5
136
10
31
1
6
1
6
wind direction
NT
ET
ST
Longitude (degree)
-105.5485 -105.5475 -105.5465
La
titu
de
(d
eg
ree
)
40.0315
40.0320
40.0325
40.0330
40.0335
WT
NT
ET
ST
136
10
21.5
136
10
21.5
136
10
31
1
6
1
6
wind directionwind direction
NT
ET
ST
WT ET
height
c
r
Horizontal CO2 gradient
Horizontal CO2 gradient
WT NT
height
c
r
u
WT ST
height
c
r
12
iTiT0
1 31 3
6 106 10
cos
cos *2 cos *2
cos *4 cos *4,
hadv
WT iT WT ET
m iT m ETm m
WT iT WT ET
m iT m ETm m
cF u dz
r
c cu u
r r
c cu u
r r
The CO2 gradient The CO2 gradient that is closer to that is closer to wind direction is wind direction is first choice to first choice to use. For example, use. For example, the angle can be the angle can be limited bylimited by
cos 0.8
Yi et al., 2008Yi et al., 2008
Another horizontal advection calculationAnother horizontal advection calculation
( ) ( )c c c c
c Ui Vj i j U Vx y x y
U
cos( )iTiT
cc u
r
U
Projection of CO2 gradient into wind directionProjection of CO2 gradient into wind direction
Projection of CO2 gradient into x and y directionsProjection of CO2 gradient into x and y directions
UU
VV
COCO 22 g
radient
gra
dientWind direction
Wind direction
UU
VV
/c x
/c y
/c r
dc/dr dc/dr is CO2 gradient along a pair towersis CO2 gradient along a pair towers
x-y coordinate system x-y coordinate system is fixed on an instrumentis fixed on an instrument
Yi et al., 2008Yi et al., 2008
udc/drudc/drcos(cos())
Udc
/dx+
Vdc
/dy
Udc
/dx+
Vdc
/dy
Comparison between two Comparison between two methods methods
Good agreement betweenGood agreement betweenTwo algorithmsTwo algorithms
Yi et al., 2008Yi et al., 2008
Yi et al., 2008Yi et al., 2008
Yi et al., 2008Yi et al., 2008
NEE+Fhadv
NEE+Ftadv
NEE+u*filter
NEE
NEE+Fvadv
0 0
rZ
cz
NEE s dz w c
Yi et al., 2008Yi et al., 2008
Vertical advection
Horizontal advection
u* correction
Soil temperature (Soil temperature (ooC)C)
Ad
vect
ion
flu
xA
dve
ctio
n fl
ux
Yi et al., 2008Yi et al., 2008
Advection Advection correctioncorrection
BiologicalBiologicalcorrectioncorrection
TurbulenceTurbulence
*u
BacterialBacterial
soilT
SummarySummary
Advection fluxes have no correlation to Advection fluxes have no correlation to drivers of biological activity. Conversely, drivers of biological activity. Conversely, the biological correction (u* filter) is the biological correction (u* filter) is based on climatic responses of based on climatic responses of organisms, and has no physical organisms, and has no physical connection to aerodynamic processes.connection to aerodynamic processes.
ConclusionConclusion
We must accept the fact that the We must accept the fact that the biological correction has no physical biological correction has no physical
basesbases
24
Super-stable layer, flow separation (Yi et al., 2005)
Courtesy of Jielun Sun Canopy flows are separated by a
superstable layer in calm nights.
hWind SpeedWind Speed Air TemperatureAir Temperature
2
g TT zRiuz
(1) Slow mean airflow;(1) Slow mean airflow; (2) Maximum drag elements;(2) Maximum drag elements;
(3) Minimum vertical exchange;(3) Minimum vertical exchange;
(4) Maximum horizontal CO2 (or other scalar) gradient;(4) Maximum horizontal CO2 (or other scalar) gradient;
(5) Maximum ratio of wake and shear production rate.(5) Maximum ratio of wake and shear production rate.
Vertical exchange zoneVertical exchange zone
Horizontal exchange zoneHorizontal exchange zone
X Distance (m)
Yi et al. 2005Yi et al. 2005
Yi et al. 2008Yi et al. 2008
Horizontal CO2 gradients are maximum at the super stable layer
VPD (kPa)0 1 2 3 4
-32
-30
-28
-26
-24
-22
Niwot RidgeBowling et al.
R (
‰)
0.05 0.1 0.15 0.2-27
-26
-25
-24
-23
(m3 m-3)
R (
‰)
Whole Whole canopy layercanopy layer
(Schaeffer et al., 2008)
0 1 2 3 4-32
-30
-28
-26
-24
-22
VPD (kPa)
NWR Canopy InletsBowling et al. R
-ca
no
py (
‰)
0.05 0.1 0.15 0.2-32
-30
-28
-26
-24
-22
NWR Ground Inlets R
-gro
un
d (
‰)
θ (m3 m-3)
Super-stable Super-stable layerlayer
After dividedAfter divided by by Super-stable layerSuper-stable layer
Above SSLAbove SSL
Below SSLBelow SSL
RemindingReminding