Water tracers and isotopic fractionation in CAM (challenges and opportunities) David Noone Program in Atmospheric and Oceanic Sciences, and Cooperative Center for Research in Environmental Sciences University of Colorado, Boulder, CO, USA Also, B. Riley, C. Still, S. Wong N. Mahowald, A. Gettelman, A. Dessler, J. Randerson, P. Rasch, P. Thornton, K Oleson, G.Bonan …
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Water tracers and isotopic fractionation in CAM (challenges and opportunities ) David Noone Program in Atmospheric and Oceanic Sciences, and Cooperative.
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Water tracers and isotopic fractionation in
CAM(challenges and opportunities)David Noone
Program in Atmospheric and Oceanic Sciences, and Cooperative Center for Research in Environmental SciencesUniversity of Colorado, Boulder, CO, USA
Also, B. Riley, C. Still, S. Wong N. Mahowald, A. Gettelman, A. Dessler, J. Randerson, P. Rasch, P. Thornton, K Oleson, G.Bonan …
Overview Nature of the problem Applications to science, physics and code
What can we learn with isotopes?
Current development status of isoCAM and isoCLM
Implementation features/facilities Few “heads up” conclusions
Isotopic fractionation
-30
-25
-20
-15
-10
-5
0
00.20.40.60.81
Fraction of vapour remaining
"del
ta"
valu
e (p
erm
il)
d = 1000(R/Rs -1)
Rayleigh model(condensate instantly removed) dRv = a Rv
Total equilibrium (system closed) Rc = a Rv
e.g. a = 1.01
The substituted molecule is slightly heavier, allowing a different partitioning of energy between translational, vibration and rotational states. Isotopic fractionation is a quantum mechanical effect.
Liquids (and solids) have additional vibration states due to intermolecular forces.
So, for the same energy more of the light isotopes can be liberated from a liquid surface.(as 25°C, 1 percent more). The liquid is enriched, the vapor is depleted.
Hydrologic cycle with isotopic exchange
International Atomic Energy Agency
“Delta values” = (R/Rstandard-1)x1000 R = moles of H218O/moles of H2
16O
Fate of water from South America
DJF JJA
18O content of rain with South American source (permil)
MUGCM (Noone 2001)
Science targets - isotope model requirements1. Paleoclimate applications
- improving cloud parameterizations, boundary layer interactions, microphysics- stratosphere troposphere exchange- water in the general circulation
3. Terrestrial hydrology - energy budgets, water budgets/resources - biogeochemistry
Also, sources and sinks of water- variability and changes in water budgets
Ability to completely check on model hydrology
2 and 3 are hardest problems from a numerical/physics standpoint
Very successful NCAR Isotope Meeting – all groups represented
CCM3 prototype
GNIPObs.
CAM2
• Reasonable first simulation of water isotopes in precipitation in CAM2.Jung-Eun Lee and Inez Fung
CAM2 - Precipitation Weighted Annual Mean 18O in Precipitation
Mean Annual D in vapor
CAM2
Observed • Nebraska, USA (Ehhalt, 1974)• Heidelberg, Germany (Taylor, 1972: only up to 5 km) • Stratosphere (Pollock, 1980)
From Araguas-Araguas et al., 2000
• CAM 2 captures general feature of the vertical profile of water isotopes in vapor.• But minimum value too low--first guess: need more condensate in CAM2 upper tropopause, oxidation of methane (?) Jung-Eun Lee and Inez Fung
Isotopic depletion in the region of the tropopause
Fig. 2. Observations in the TTL compared with model calculations that used dDice= –565 . The dashed box represents ATMOS data of Kuang et al. Mean tropopause level is 14.4 ± 0.5 km.
Webster and Heymsfield, Science, 2003
Analytic Model of Isotopes v. Alt
Rayleigh CurveRayleigh Curve
(Gettelman, in preparation, 2004)
CCM3 - Annual zonal mean 18O CONTROL NO DEEP PLUMES
Messages from CRYSTAL Lots more ice than we might expect from model Stark difference between conditions in plumes
versus large scale. Model probably OK on an “area average”, but
smaller scale variability is very large(e.g. data 100x10-6 of ice, while models have 20x10-6 of water)
While BULK is correct, processes not necessarily well enough represented (processes governing isotopes same as those of cirrus - thus insight to cloud forcing, etc)
Land model – H2180, HDO (and
CO18O)
LSMv1 migrating to CLM3
Julian Day, 2001 (d)
18O
(O/ O
O)
198 199 200 201 202-10
0
10
20
Measured Leaf WaterPredicted Leaf WaterMeasured Stem WaterPredicted Stem Water
Performs extraordinarily well when forced with observed meteorology
Land surface exchange model (LSM)
(Noone, Riley, et al., in preparation, 2004)
Implementation in CAM/CLM Water (and isotope) tracking in atmosphere (CAM3) Water (and isotope) tracking in land model (CLM3)
Provides generic framework for any “water/aqueous” speciesi.e. explicit form of wet deposition, dissolved species
Water isotopes: H2O, HDO, H218O (also HTO, H2
17O) Isotope physics done at smallest scale possible while sticking to
“bulk” assumptions Track (exactly!) every bit of water in CAM, so can use isotopes to
deduce problems in, e.g., microphysics, convective fluxes, …
What about ocean tracers?
Presently “working” code now, target for science start mid-2004
CAM3 isotopes will contribute to new isotopic intercomparison project (also GISS, MU, ECHAM, Hadley Center, Frontier…)
CAM synergistic developments WACCM
include stratospheric chemistry, O3 exchange New “Data” dynamic core and data assimilation Facilitate tracer assimilation, transport computations
“isotopic reanalysis” is of great value for proxy interpretation Mesoscale modeling
- MM5 nearly has isotopes with ISOLSM (LBL for ARM) - WRF code structure in place to more easily facilitate isotopes,
isotopic development at planning stage - Also, WRF at cloud resolving scales can match LES isotope simulations at CU.
.
Isotopes add rigor for new parameterization development Adds additional requirements of systems
(especially mass conservation/consistency issues) Exercise of adding water tracers useful as it finds
inconsistencies in mass budgets New parameterization schemes will need to be used
for various tracer studies Being mindful of applications when physics is build