Incorporation of Stable Water Isotopes in GSM and Spectrum-Nudged 28-year Simulation

1
Incorporation of Stable Water Isotopes in GSM and
Spectrum-Nudged 28-year Simulation
NOAA 32nd Annual Climate Diagnostics and
Prediction Workshop, October 22-26, 2007,
Tallahassee, FL, USA
Kei YOSHIMURA1,2 1 Scripps Institution of
Oceanography, University of California San
Diego2 Institute of Industrial Science, The
University of TokyoEmail k1yoshimura_at_ucsd.edu,
HP http//meteora.ucsd.edu/kyoshimura
Summary
2. Results of Global Isotope Simulation with
Spectral Nudging
3. Comparison with in-situ observations.
Stable water isotopes are incorporated into
NCEP/ECPCs global spectral model in a manner
similar to other isotope models. In addition, a
newly developed spectral nudging technique
(Yoshimura et al., 2007) is used, which allows to
reproduce the actual spatial and temporal
distribution of water and isotopes distributions.
Divergence, vorticity, and temperature in
NCEP/NCAR Reanalysis 2 data are the base fields
that are nudged for more than 1000 km scales.
Specific humidity remains unnudged in order to
close the water budget. A T62L28 large-scale
nudging simulation for 1979-2006 has now been
simulated and the results show much more
realistic precipitation isotope variations in
comparison to other free-forecast simulations.
a. Global Climatology of SWI in Precipitation
compared with GNIP data
a. Typhoon event (2006/09/14-16)
Right figure shows observation (GNIP), model
mean by SWING, and IsoGSM annual climatology and
seasonal departure (DFJ-JJA) of d18O and d-excess
(dD-8d18O) in precipitation. The model mean and
IsoGSM agree quite well with lower d18O values in
high latitudinal regions (latitude effect), in
high elevation regions (altitude effect) and in
inland region (continent effect). d-excess also
shows good correspondence with observations.
IsoGSM results
Cyclonic field emerges
1. Introduction
a. What are Stable Water Isotopes (SWI)?
Figures from left to right, annual climatology
of precipitation d18O, its seasonal differences,
annual climatology of d-excess, and its seasonal
differences. From top to bottom, GNIP, Model
mean, and IsoGSM results are shown.
b. Global Climatology of SWI in Vapor compared
with TES Observation.
Right figure? dD in column vapor and the
seasonal variation, and the same of d-excess.
Bottom figure? Wordens (2007) result showing
the isotopic evidence of evaporation from
raindrop. It is caused by kinetic fractionation
processes. Right figure shows simulated result
for same criteria.
b. Traverse Observation over Antarctic Sea
(2006/01)
b. Why should SWI incorporated into GCMs?
From Worden et al., 2007
c. Seasonality of SWI in Precipitation
In the table below, by taking simple average of
correlation coefficients of monthly d18O and its
anomalies over all available sites (about 200),
IsoGSM with nudging has the best number. All
other models are enable to simulate seasonality
of isotopic climatology, but they all failed to
produce accurate interannual variability, whereas
IsoGSM is capable to do so.
c. What is merit of using NCEP/ECPC G-RSM?
Top right figure? Correlation coefficient
distributions of all monthly precipitation d18O
compared with GNIP dataset for three SWING models
and IsoGSM. Closer to one (blue) is
better. Further right figure?? Climatologic
seasonality in selected GNIP observation sites
(only 12 are shown among 660 sites).
Precipitation of ECHAM4, IsoGSM, and observation
are also shown. Right figure? The anomaly of
d18O is shown. It is calculated by removing
climatologic seasonality. All free forecast
models have difficulty to simulate such second
order variations.
d. Isotopic and other physics in Iso-GSM
Physical processes
Isotopic Physical processes
References Majoube, J., Fractionation factor of
18O between water vapor and ice, Nature, 299,
1242, 1970. Merlivat, L., Molecular
diffusivities of H216O, HD16O, and H218O in
gases, J.Chim.Phys., 69, 2864-2871,
1978. Merlivat, L., and J. Jouzel, Global
climatic interpretation of the deuterium oxygen
18 relationship for precipitation,
J.Geophys.Res., 84, 5029-5033, 1979. Jouzel, J.,
and L. Merlivat, Deuterium and oxygen 18 in
precipitation modeling of the isotopic effects
during snow formation, J. Geophys.Res., 89,
11749-11757, 1984. Stewart, M.K., Stable isotope
fractionation due to evaporation and isotopic
exchange of falling waterdrops Applications to
atmospheric processes and evaporation of lakes,
J.Geophys.Res., 80, 1133-1146, 1975. Yoshimura,
K. and M. Kanamitsu, Dynamical global downscaling
of global reanalysis, submitted to Mon.Wea.Rev.
(In revision) Acknowledgment This research is
funded by JSPS and CEC.
Spectral Nudging Scheme