Transcript Hindcast Experiments - Max-Planck

Initialization of a Global Climate
Model with Oceanic Reanalysis
Motivation:
The intention of this project is to improve the qualitative and quantitative
climate prediction capabilities. For this purpose the coupled model of the
Max Planck Institute for Meteorology consisting of the atmosphere
model ECHAM5 and the ocean model MPI-OM is initialized with oceanic
reanalysis data from the Estimating the Circulation and Climate of the
Ocean (ECCO, Stammer et al. 2002) project. The role of the initial
conditions for seasonal to decadal climate predictions is investigated in
hindcast experiments over the second half of the 20th century.
Method:
Model:
ECHAM5/MPIOM (version cosmos-1.0.0), atmosphere resolution T63
L31, ocean resolution 1.5º L40
Control Experiments:
Four IPCC 20th century simulations with greenhouse gas and
tropospheric aerosol forcing.
Assimilation Experiment:
Anomaly coupling scheme (Pierce et al. 2004): Monthly mean oceanic
temperature and salinity fields are relaxed to anomalies from the ECCO
project added to the mean model climate over the period 1952-2001
between 80ºN - 80ºS in all layers except the surface layer.
Hindcast Experiments:
Hindcast experiments of 10 years duration are started from the
assimilation experiment on the 1st of January every four years (1954,
1958, 1962, 1966, 1970, 1974, 1978, 1982, 1986, 1990, 1994, 1998).
Basic question:
Are the hindcast experiments closer to the observations (assimilation
experiment) than the control experiments?
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Fig. 1: (a) Time series of monthly mean SST anomalies averaged
over the NINO3 region from the assimilation (thick black) and the
hindcast experiments (colored) together with observations (thin
black). (b)
RMS error between hindcast and assimilation
experiments at different lead times (thick) and the 1 standard
deviation range of the assimilation experiment (thin).
Fig. 2: (a) Time series of annual and global mean surface
temperature from the assimilation (solid black), hindcast (colored)
and ensemble mean control (dashed black) experiments. (b) RMS
error between assimilation and hindcast experiments at different
lead times (solid thick) and mean RMS error over the whole period
between assimilation and control experiments (dashed) together
with the 1 standard deviation range of the assimilation experiment
(solid thin).
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Fig. 3: As in Fig. 2 but for the North Atlantic max. MOC at 46ºN.
Results:
•The results are preliminary since the ensemble size is very small.
•The ENSO predictability is poor (Fig. 1) due to the too big ENSO
variance in the model and the starting date (spring barrier).
•Global mean temperature, North Atlantic meridional overturning
circulation (MOC) and sea surface temperature (SST) gain from the
initialization with the oceanic reanalysis data for 4 to 5 years (Fig. 2,
3 and 4).
Fig. 4: As in Fig. 2 but for the North Atlantic SST (0-60ºN, 10º-50ºW).
Conclusions:
•The method of initializing a coupled climate model with oceanic
reanalysis data is applicable.
•The anomaly coupling scheme avoids drift in the hindcast
experiments.
•Correction methods could possibly improve the prediction skill.
•The system cannot be used for climate predictions since the data
from the ECCO reanalysis project are not available in real time.
Holger Pohlmann, Johann Jungclaus, Jochem Marotzke
Max Planck Institute for Meteorology, Hamburg, Germany
Email: [email protected]