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Dr. Bodo AhrensInstitut für Meteorologie und Geophysik derUniversität Wien
ERA40 Dynamical Downscaling
Bodo Ahrens, Alexander BeckInstitut für Meteorologie und Geophysik, Universität Wien
e-mail: [email protected]
Dr. Bodo AhrensInstitut für Meteorologie und Geophysik derUniversität Wien
Motivation
● High-resolution Alpine climate description (daily, Dx ~ 10km)● Training input for climate impact models● Test-bed for ECHAM DDS
Dr. Bodo AhrensInstitut für Meteorologie und Geophysik derUniversität Wien
Mesoscale Alpine Programme SOP: Sept. 7 to Nov. 15, 1999 \Bougeault et al 2001
FH analysis: ~6500 rain stations, no bias correction, daily/25km mesh size -> all data is interpolated to this mesh size
ERA40 (mesh size ~120km)
ALADIN (50km) ALADIN (12km)
MAP SOP precipitationFrei & Haeller (2001) analysis
Dr. Bodo AhrensInstitut für Meteorologie und Geophysik derUniversität Wien
Sequence of hindcasts
• 30h hindcasts, 6h coupling time step• discarding the first 6h (model spin up)• one-way nesting e.g. 12km nest directly in 120km ERA40 => a scale jump of a factor of 10
Dr. Bodo AhrensInstitut für Meteorologie und Geophysik derUniversität Wien
The problem: Optimal nesting strategy?
Dr. Bodo AhrensInstitut für Meteorologie und Geophysik derUniversität Wien
Nesting StrategiesERA40 (~120km)
LACE (12km)8pt buffer(op. in ARP)
direct
LACE (12km)32pt buffer
dire
ct32
LACE (12km)8pt buffer,blending(climate mode for small scales)
blen
ding
LACE (12km)8pt buffer
50km nest8pt buffer
double
Dr. Bodo AhrensInstitut für Meteorologie und Geophysik derUniversität Wien
Impact of Nesting ConfigurationFrei & Haeller (2001) analysis
direct double
bias:(mm/d)
doubleblendingdirect32directERA40
0.19 0.26 0.06 0.22
-1.03
Dr. Bodo AhrensInstitut für Meteorologie und Geophysik derUniversität Wien
Resolution Effects
50km
direct (12km), but 50km orography
direct (12km)
26 Sep. 1999 precipitation
Dr. Bodo AhrensInstitut für Meteorologie und Geophysik derUniversität Wien
12 km Nests
blendingdouble
direct direct32
Dr. Bodo AhrensInstitut für Meteorologie und Geophysik derUniversität Wien
Statistics
SPREX: temporal mean of ratios of spatial field variancesSPRET: spatial mean of ratios of pixel time series variancesR^2_X: temporal mean of squared spatial field correlationsR^2_T: spatial mean of squared time series correlations
1day
⇒ other errors are more important than differences due to nesting strategy
Dr. Bodo AhrensInstitut für Meteorologie und Geophysik derUniversität Wien
Pattern of R^2_X
Pattern of R^2_T
Dr. Bodo AhrensInstitut für Meteorologie und Geophysik derUniversität Wien
Statistics
Performance or evaluation problem below 100km?
Dr. Bodo AhrensInstitut für Meteorologie und Geophysik derUniversität Wien
Conclusions ● Precipitation patterns at 1d/100km scale are bet-
ter represented in ALADIN-12km than in ERA40-120km simulations.
● Nesting configuration not crucial despite the large resolution jump (factor 10), especially double nest-ing not necessary – “There are other problems!”
● Continuous blending (= spectral nudging) seems to be promising, but expensive!?
Dr. Bodo AhrensInstitut für Meteorologie und Geophysik derUniversität Wien
OutlookDirect nesting => DDS, but no regional climate due to lack of memory!
0.5 step into “climate simulation”: Surface blending, i.e.relaxation of ISBA sfc. to TESSEL sfc.
Implementation and test by Jure C. (for MAP SOP):- 90% blending better than 97% or no blending (-> memory is good & ERA40 sfc assimilation too!)- 100% blending (no reinitialization) worst (died in a 1999 sim. -> climate ISBA, improved radiation scheme)
Dr. Bodo AhrensInstitut für Meteorologie und Geophysik derUniversität Wien
NO vs 97% blending
Hydrol. Sim with WaSiM (500m,1h) in an Alpine watershed(2600km^2)
1999
Dr. Bodo AhrensInstitut für Meteorologie und Geophysik derUniversität Wien
Why with ALADIN?
● Operational in Austria and most neighbors● Packaged and phased with ARPEGE/IFS and closely related with ARPEGE-CLIMATE – Will this prevail??