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IntroductionIntroduction• IsoTrans (Isotopic Tracers in Atmospheric Transport):
ANSTO “mother” Project for IPILPSBroader scope
•Purpose of presentation: Introduction to IsoTrans (very short)How is IsoTrans contributing to the improvement of
surface and boundary layer representations in models?Evaluation and development of LSSs in isotope-enabled
hydroclimate models (main subject of current workshop)How can SWI obs “add value” to our understanding of moisture
exchange in plant canopies, particularly ET partitioning?Natural radionuclides and turbulent mixing in the lower
atmosphere
Modelling
Process
studies
Sources & sinks
Physical processes
Predictive modelling
Current models do not reproduce well the complex cycles of exchange, mixing and
transport in the lower atmosphere
Problem
IsoTrans: DriversIsoTrans: DriversEffective Environmental Management Strategies need …
Informed predictions of mixing and movement
Sources & sinks
Physical processes
Predictive modelling
IsoTrans: DriversIsoTrans: DriversEffective Environmental Management Strategies need …
Informed predictions of mixing and movement
• International scientific community (1) Inability to accurately reproduce diurnal cycle a
severe limiting factor for weather and climate models (2) Need new methods to accurately track down the
origins and dynamics of atmospheric pollution (3) Lack of independent methods for evaluation of
numerical weather and climate prediction models
Modelling & Prediction Panel
IAEA
Nuclear tools applied to contemporary atmospheric issues
0 200kmMelbourne
Sydney
Brisbane
1000km
100km
IsoTrans: 3 Foci, 3 ScalesIsoTrans: 3 Foci, 3 Scales
(3) Isotopes at the land surface• Stable water isotopes• Land surface processes• Diurnal observations• Model evaluations• Major river basins,
including the MDB
(1) Local mixing• Vertical mixing processes in the
lower atmosphere• Towers and aircraft• Sydney area
(2) Regional transport• Wider Sydney region /
Eastern Sea Board• Pollution sources & dynamics• Horizontal array of surface
measurements
IsoTrans Process StudiesIsoTrans Process Studies• IsoTrans Task 3 (IPILPS)• How can SWI observations “add value” to our understanding
of moisture exchange in plant canopies, particularly evapo-transpiration partitioning?Discuss the Keeling approach for estimating the
transpired component of ET in vegetation canopiesExamine turbulent transport within vegetation canopiesAnalyze SWI behaviour in Tumbarumba air spacePresent first guess at ET partition for Tumbarumba
• Thanks to David Griffith (Wollongong Uni) for providing the vertical D data, and Helen Cleugh / Ray Leuning for providing the met data
Use of SWIs to Partition ETUse of SWIs to Partition ET
1000*;where
:""isotopeofFlux
:fluxTotal
000
xs
xs
xx
xx
xE
xT
xE
xET
xE
xT
xE
xET
ET
TT
TxTE
xEET
xET
xT
xE
xET
ixi
xi
xi
TEET
R
RR
c
cR
RR
RR
F
Ff
FRFRFRFFF
FRwcFx
FFF
Concept: simple mix of 2 fluxes with distinct isotopic signatures (): evap (frac) and transp (non-frac)
T, E: composition of contributing sources (measured / calculated)
ET: “effective” combined source
FET: from EC FT
How to estimate ET?
Keeling (1958)Keeling (1958)• Carbon isotope ratio closely follows concn in diurnal
time series over different vegetated surfaces• Mutual variation suggests simple 2-part mixing
(air and plants)
““Keeling” Analysis (1)Keeling” Analysis (1)
xET
m
xET
xaa
xm
ETxETa
xam
xm
ETxETa
xam
xmi
xi
xi
xET
xa
xm
ETam
CC
CCC
CRCRCRCRC
CCCx
CCC
1
:""isotopeWater
: waterTotal
2-part mixing model (ambient + combined ET)
Cm, mx: measured
Ca, ax: background
component from atmosphere
CET, ETx: combined
component from evap and transp
Linear relation if Ca, ax and ET
x constant, with intercept ETx
““Keeling” Analysis (2)Keeling” Analysis (2)• Versatile (temporal
& vertical gradients)• Problems:
Extrapolated intercept susceptible to large errors
Breakdown of assumptions
Yakir and Sternberg (2000)
1. Simple mixing of two major sources/sinks (atmos & ET)
2. No sources/sinks other than evap & transp (eg. dew, fog)
3. Relative contribution of all subsources remains fixed (eg. “non-fractionating” transpiration assumption true only when averaged over whole day: Harwood et al. 1998)
Diurnal variation of 18O of transpired water vapour for leaves on day 1 () and day 2 ( ,,) indicating the vapour pressure deficit (VPD) status and general trend over the day (solid line).
Harwood et al. (1998)
Yepez et al. (2003)Yepez et al. (2003)• Vertically-distrib D and 18O in semi-arid savanna woodland• Upper/lower profiles: analysed total and understory flux• Post-monsoon: transp 85% total, grass 50% understorey ET• Total ET 3.5mm/d = 2.5 (70%) tree trans + 0.5 (15%) grass
Williams et al. (2004)Williams et al. (2004)• Vert distrib D Morocco olive orchard following 100mm irrig• Keeling vs sap flow (v. hard to get representative data)• Trans/soil evap by isotope method within 4%/15% sap flow• Transpiration: pre-irrig 100%, post-irrig 70-85%
Complex CanopiesComplex Canopies• How can use of isotopes “add value” to understanding of ET
from a complex canopy/ecosystem such as Tumbarumba?
Atmospheric Boundary LayerAtmospheric Boundary Layer• First need to understand turbulent mixing processes in the
canopy, and interactions with atmospheric boundary layer
(Stull, 1988)
ABL Structure and TurbulenceABL Structure and Turbulence
Day
Night
(Holtslag and Duynkerke, 1998)
(Wyngaard, 1990)
Vegetation CanopiesVegetation Canopies• “The essential differences
between turbulence in the canopy air space and that in the boundary layer above result from the sources and sinks of momentum and scalars that are spread through the canopy” (Kaimal and Finnigan, 1994)
• Canopy turbulence is dominated by the large eddies that form in the intense shear layer confined to the crown or upper part of the canopy
Wind in Vegetation CanopiesWind in Vegetation Canopies• Similar behaviour over large
range of obs/model canopies
• Wind-shear max canopy top
• Attenuation below, foliage density determines rate
• Canopy turbulence strongly inhomogeneous in vertical
• All momentum absorbed in upper part of canopy (c.f. constant stress layer above)
• Large momentum gradient required to sustain steady air flow against aerodynamic drag of foliage
7/3/05 Tumbarumba
0
10
20
30
40
50
60
70
0.00 1.00 2.00 3.00 4.00 5.00
Windpeed (m/s)
He
igh
t (m
)
0
3am
6am
9am
12
3pm
6pm
9pm
Night(calm)
Day (gradient + inflection)
Turbulence in Vegetation CanopiesTurbulence in Vegetation Canopies• Skewness
Measure of turbulent intermittencyZero in surface layerCanopy: SKu +ve & SKw=-veTurbulence is dominated by intermittent
downward moving gusts (large eddies)
• Spectral peaksCanopy: peak positions constant“Large eddies” extend through
whole depth of foliage and into the air above
(Kaimal and Finnigan, 1994)3 3
u uSK u
Turbulence in Vegetation CanopiesTurbulence in Vegetation Canopies• TKE budget
Shear prodn peaks near canopy topWake prodn high in upper thirdTurbulent transport: sink of TKE at
canopy top, source in lower canopyLower canopy TKE not locally produced:
imported from above by “large eddies”Dissipation much higher than free stream:
wake and waving terms convert dominant large scale motions to smaller eddies
• Canopy turbulence dominated by canopy-scale “large eddies” Cool dry gusts displacing warm moist canopy air at all levels Counter-grad fluxes; non-local mixing; turb transport; distributed sources Surface layer flux-profile mixing relationships (“K-theory”) are inapplicable
in vegetation canopies
(Kaimal and Finnigan, 1994)
Turbulence in TumbarumbaTurbulence in Tumbarumba
• Quiescent at night• Strong in daytime (9:00-15:00): ABL convective motions
7/3/05 Tumbarumba
0.00
5.00
10.00
15.00
20.00
25.00
30.00
35.00
40.00
0:00
3:00
6:00
9:00
12:00
15:00
18:00
21:00
0:00
Time
SD
Win
d d
irn
70
m
(de
g)
Temperature in Vegetation CanopiesTemperature in Vegetation Canopies• NightNight: :
lower canopy unstable strat - enhanced mixing
upper canopy stable strat (no turb - dew formation possible)
Tumbarumba: slightly stable (suppresses mixing)
• DaytimeDaytime::crown max (sun on foliage),
with stable strat below. But +ve (counter-grad) flux, so bimodal
Intermittent mixing by large eddies + quiescent periods
Tumbarumba: rapid increase of whole profile in morning; unstable for remainder of day
7/3/05 Tumbarumba
0
10
20
30
40
50
60
70
0.000 5.000 10.000 15.000 20.000
Potential Temp (Celsius)
He
igh
t (m
)
midnight
3am
6am
9am
noon
3pm
6pm
9pm
Humidity in Vegetation CanopiesHumidity in Vegetation Canopies• Night:Night:
Tumbarumba. Saturated (>80% at 70m, colder below), with slow decrease of whole profile: dew/fog
• Morning:Morning:Tumbarumba. Rapid increase of
whole profile: dew/fog re-evap as temp incr + transpiration “kicks in”
• Day:Day:Negative gradient + progressive
decrease of whole profile: dry air intrusion
Transpiration (secondary maximum in crown)
Large values near ground: surface moisture in leaf litter after rain
7-3-05 Tumbarumba
0
10
20
30
40
50
60
70
0.5 0.7 0.9 1.1 1.3 1.5
[H2O] (%)
He
igh
t (m
)
0-3am
3-6am
6-9am
9am-12
12-3pm
3-6pm
6-9pm
9pm-0
Moisture in air (%) v Time of day (Tumbarumba - 7 Mar 05)
0.200
0.400
0.600
0.800
1.000
1.200
1.400
1.600
1.800
2.000
H2O
%
0.4
4
10
26
34
42
70
Humidity in Vegetation CanopiesHumidity in Vegetation Canopies
Night: saturated (fog/dew dries air)
Morning warming: fog/dew re-evaporates + transpiration “kicks in”
Spread: fog/dew re-evaporates from top down
Afternoon: dry air intrusion + transpiration
Evening: mixing stops, temperature drops
Surface moisture in leaf litter after rain
07/03/2005Profile
0.5
0.7
0.9
1.1
1.3
1.5
1.7
1.9
2.1
2.3
2.5
00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 19 20 21 22 23 00
Hour of day
H2
O %
-180
-170
-160
-150
-140
-130
-120
-110
-100
-90
-80
de
l-D
p
er
mil
H2O
del-D
Isotopes in Vegetation CanopiesIsotopes in Vegetation Canopies
Humidity gradients only in afternoon
Isotope gradients all day
Isotopes in Vegetation CanopiesIsotopes in Vegetation Canopies
• NightNight. +ve grad: condensation onto surface/plants (temp dep). +ve grad: condensation onto surface/plants (temp dep)• MorningMorning. Re-evap of (heavy) dew/fog + transp + soil evap. Re-evap of (heavy) dew/fog + transp + soil evap• AfternoonAfternoon. -ve grad: transp + soil evap + mixing from above. -ve grad: transp + soil evap + mixing from above
7-3-05 Tumbarumba
0
20
40
60
-140 -130 -120 -110 -100 -90 -80del-D
He
igh
t (m
)0-3am
3-6am
6-9am
9am-12
12-3pm
3-6pm
6-9pm
9pm-0
Night Afternoon
Morning
Transp. ~ -40 o/ooSoil evap. ~ -95 o/ooAtmos. ~ -150 o/oo
Vertical Keeling AnalysisVertical Keeling AnalysisTumbarumba 7/3/05
-160.0
-140.0
-120.0
-100.0
-80.0
-60.0
-40.0
-20.0
0.0
0.000 0.200 0.400 0.600 0.800 1.000 1.200 1.400 1.600 1.800
1/[H2O]
del
D
0-3am
3-6am
6-9am
9am-12
12-3pm
3-6pm
6-9pm
9pm-0
Transp. ~ -40 o/oo
Soil evap. ~ -95 o/oo
Atmos. ~ -150 o/oo
Tumbarumba 7/3/2005
-120
-100
-80
-60
-40
-20
0
20
0:00
6:00
12:00
18:00
0:00
time
de
l-D
in
terc
ep
t
total understory • Intercept from Keeling plots: D
ET
• Guesses for D source values:Soil evap -950Transpiration -40
• Total FT(%):n/a at night20% morning (dodgy)80% afternoon
• Understorey60% at night (no!)20% morning (dodgy)50% afternoon
Tumbarumba Keeling AnalysisTumbarumba Keeling Analysis
Tumbarumba 7/3/05
-200
20406080
100120
0:00
6:00
12:00
18:00
0:00
time
FT
(%
)
total understorey
• r2 values: only high in afternoon
Tumbarumba 7/3/05
0
0.2
0.4
0.6
0.8
1
0:00
6:00
12:00
18:00
0:00
time
r2
total understorey
Tumbarumba Keeling AnalysisTumbarumba Keeling Analysis
7/3/05 Tumbarumba: all 70m data
-140.0
-120.0
-100.0
-80.0
-60.0
-40.0
-20.0
0.0
0.000 0.200 0.400 0.600 0.800 1.000 1.200 1.400 1.600 1.800
1/[H2O]
Time-varying Keeling AnalysisTime-varying Keeling Analysis
Transp. ~ -40 o/oo
Soil evap. ~ -95 o/oo
Atmos. ~ -150 o/oo
Intercept -66.6
R2=0.762
ConclusionsConclusions
• Vertically varying SWI data can be used to “add value” to our understanding of moisture exchange in plant canopies, particularly the partitioning of evapotranspiration
• The combination of time-varying and vertically-varying mixing analyses (Keeling+better?) of both D and 18O promises to be a very powerful tool for analysing ET in complex ecosystems such as Tumbarumba
• But …• Need to understand the “whole picture” in terms of the
airflow/turbulence regime within and above the canopy, so supporting meteorological data is essential.