Results of an Adaptive Radiative Transfer Parameterisation for the Lokal-Modell
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Results of an Adaptive Radiative Transfer Parameterisation for the
Lokal-Modell
LM-User-Seminar
5th – 7th March 2007, Langen
Annika Schomburg1) , Victor Venema1), Felix Ament2), Clemens Simmer1)
1) Department of Meteorology, University of Bonn, Germany
2) MeteoSwiss, Switzerland
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Outline
• The idea and approach
• Results– Improvements in RMSE– Improvements in model consistency
• Summary
• Outlook
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The Idea: Adaptive parameterisation
calculate error-estimator based on
a simple radiation scheme for
each grid point
Grid points where…
…Δ ‘large‘
…Δ ‘small‘
Apply „perturbation method“
for surface fluxes
Recalculate radiation
fluxes with exactscheme
Perturbation method:
)()(
)()(
tFttFF
FtFttFsimplesimplesimple
simple
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Approach
• Simple radiation scheme:
→ Multivariate linear regression
• Predictands:
– longwave:
– shortwave: transmissivity:
• Distinction of 4 categories,
with different sets of predictors:
surL
ec
solarcloud free
infraredcloud free
solarcloudy
infraredcloudy
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Simple radiation scheme
Cloudfree Cloudy
Cosine of solar zenith angle LWP
IWV CLCL
Surface pressure CLCT
Continental aerosols Cosine of solar zenith angle
Cloud thickness
IWV
Temperature at cloud base
Predictors: SOLAR
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Simple radiation scheme:
Cloudfree Cloudy
IWV IWV
Surface temperature Temperature at cloud base
Cosine of zenith angle Surface temperature
CLCT
Cloud thickness
CLCL
Cosine of zenith angle
LWP
Predictors INFRARED
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Approach
Implementation of adaptive scheme into LM – First tests and configuration on PC
(small model domain) – After successfull implementation:
exemplary cases on LMK-domain on parallel machine at DWD
• Horizontal resolution: 2.8 km• Frequency of call to adaptive
scheme: 2.5 min
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Approach
• Problem: Radiation of 3 separate model runs not comparable due to different evolution of cloud field → Development of a model version „3 in 1“:– Calculation of the radiation fluxes
• hourly• adaptive• frequently (every 2.5 min)
... in the same model run– Dynamics only influenced by frequent radiation
• Test for 3 summer days characterised with much
convection
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Results: 21 June 2004, small model domain
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Example-error-fields for 15:30 UTC
Initialisation at 02:00 UTC
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Correlation lengths for error fields (15:30 UTC)
The covariance functions of the errors in the solar (a) and infrared (b) fluxes at the surface.
Hourly
Adaptive
Hourly
Adaptive
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Results for 13 August 2004 (LMK domain)
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Results for stratiform winter day: 22 December 2005
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Results: Improvements of model consistency
Total surface net flux: solar + IR [W/m²]
Total surface net flux: solar + IR [W/m²]
21 June 2004
Adaptive approach leads to a considerable reduction of unrealistic situations
1h-update
2.5 min- update
Adaptive
Median and 0.25 quantiles
Median and 0.25 quantiles
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Instantaneous RMSE
with adaptive scheme smoother error curves
21June 2004
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Smoother developing of model variables with time
Adaptive approach prevents „wavy“ structure of developing of variables with time
Surface temperature
21 June 2004
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Summary
• Improvements of RMSE: – 30% to 40% for SW, – 13% to 44% LW fluxes
• for one exemplary stratiform winter day – 40% improvement for solar fluxes– 4% detoriation for infrared fluxes
• Daily biases worse than in operational mode
• More self-consistent and smoother model runs
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Outlook: improvement opportunities
• Separate regressions for winter and for summer• „Online learning“ regression• Other simple radiation scheme instead of
regression :– very simple physical scheme– neural network
• Application to whole vertical column, not only on surface fluxes
• Comparison to LMK radiation update configuration
• Application to other parts of model physics
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Thank you for your attention!
For further information see also:
www.meteo.uni-bonn.de/venema/themes/adaptive_parameterisations/
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Motivation: Sensitivity Study
• Comparison:
LM withhourly radiation
LM withRadiation
every 2.5 min
Model domain:
Horizontal resolution: 2.8 km
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Motivation: Solar radiation flux vs. rainrate
13/08/2004 21/06/2004
Prognostic precipitation Diagnostic precipitation
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Cloud field 15:30 UTC
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Parallel Mode
• Number of allowed updates is prescribed, therefore computation of error estimator for whole model domain and recalculation of „worst“ gridpoints
• Communication between processors required• Processors have to wait for each other• Adaptive selection for whole model domain too
expensive!
• Adaptive selection related to subdomains
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Results for 19 September 2001, large model domain
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Adaptive RT parameterisation II: “Search Scheme”
• uses spatial correlations• update every 5 minutes one
out of 4x4 columns• for other 15 columns: search
for similar column in the vicinity (search region 7x7 pixels)
• similarity index to be minimised:
twwLWPwCCTwCCLw 43321
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Comparison of adaptive schemes for a case study
Persistence Perturbation Search
05
101520253035404550556065707580
SW
LW
RM
SE
[W
/m²]
19 September 2001, 12:30 UTC, offline versions
RM
SE
[W
/m²]
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(a) (b) (c)
(d) (e) (f)
(g)Bias: 5 W m-2RMS: 77 W m-2
(h)Bias: 6 W m-2RMS: 43 W m-2
(i)Bias: 2 W m-2RMS: 31 W m-2
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Errors in the solar heating rates (W m-2) in the LM at the surface for 12.30 h UTC. (a) The two-stream calculation of the solar surface flux is the reference field(b) Cloud cover of low clouds (c) Total cloud cover (d) the 1-h persistence assumption, (e) the adaptive perturbation scheme, (f) the adaptive search scheme. The corresponding errors are shown in the same order in the third row.