A Radar Data Assimilation Experiment for COPS IOP 10 with the WRF 3DVAR
System in a Rapid Update Cycle Configuration.
Thomas SchwitallaInstitute of Physics and Meteorology
University of Hohenheim
13th WRF Users Workshop 2012
Motivation
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13th WRF Users Workshop 2012
Outline
• WRF model setup• Radar data assimilation in the WRF model• First radar assimilation experiment over France• Summary• Outlook
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13th WRF Users Workshop 2012
WRF model setup
• Convection permitting resolution of 3.6km– No cumulus scheme applied!
• 550*550*50 grid boxes• Two-Moment microphysics• DFI initialization• Focus is set on events coming from in from
the Western Europe• Direct initialization from ECMWF forecast
or analysis on model levels• CV6 Background error Matrix
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13th WRF Users Workshop 201229.07.2012
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Rapid Update Cycle approach with WRF
Lateral boundary conditions from ECMWF analyses/forecastT
T+0h
ECMWF analysis + DFI
T+3h T+6h T+9h T+12h
3DVAR 3DVAR 3DVAR 3DVAR
Obs Obs Obs Obs
T + xx hours
Free forecast
Update low boundary Update lateral boundary conditions
Forecast Forecast Forecast Forecast
00Z 03Z 06Z 09Z 12Z
13th WRF Users Workshop 2012
Radar data coverage during COPS
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15 Doppler radar in total10 from France5 from Germany
S- and C-Band radarsScanning radius up to 250kmRange resolution 1kmRu
max= 60m/s and 32m/s3D volume data
13th WRF Users Workshop 2012
Assimilation of radar data in WRF
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Radial velocity assimilation:
)( Ti
i
i
i
i
ir vw
rzzv
ryyu
rxxv
Terminal velocity vT represents the fall speed of rain. It depends on the rain water mixing ratio qr under the assumption of a laminar flow (Re ≈ 300).
Reflectivities (dBZ) are assimilated applying the following operator:
3/1
log5.171.43mkgqZ rair
Derived from a Marshall-Palmer distribution with N0 = 8*106m-4
13th WRF Users Workshop 2012
Quality control and data thinning
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Raw observations amount is too large and data are noisy
1) According to quality flags, the raw observation is set to missing value2) Calculation of a 3x3 average value3) Calculation of variance for every raw observation4) Variance rejection threshold 50dBZ² for reflectivity and 60m²/s² for
radial velocity (Xiao, WRF Workshop 2008)5) Additional smoothing along the ray and azimuth
Applied filtering procedure for e.g. German radar data:
Radial wind observation error = f(range)Reflectivity error set to 5dBZReflectivities are discarded above 4000m AGL and below 0°C
Data thinning and filtering prior to its use in a data assimilation scheme
13th WRF Users Workshop 201229.07.2012
Assimilation of radial velocities only
Good agreement throughout the complete RUC
03Z (second last RUC step)06Z, last RUC step
13th WRF Users Workshop 201229.07.2012
Assimilation of radial velocities onlyObservationWith radar windsNo radar
Small but positive influence on the 3h precipitation forecast(Reduction of RMSE ~6%, correlation slightly improved)
13th WRF Users Workshop 201229.07.2012
Looks promising, but….Assimilation of radial velocities only
Last RUC step at 06UTC
13th WRF Users Workshop 201229.07.2012
Looks promising, but….Assimilation of reflectivities in addition
Can you spot the difference?
Last RUC step at 06UTC
13th WRF Users Workshop 201229.07.2012
Looks promising, but….Horizontal distribution of ZTD O-A
No reflectivities
13th WRF Users Workshop 201229.07.2012
Looks promising, but….Horizontal distribution of ZTD O-A
With reflectivities
13th WRF Users Workshop 201229.07.2012
Looks promising, but….
• Model imbalances despite DFI? - Hopefully not!• Relative humidity set to 100% in the model? – Yes, set to 100%• Deficits in cloud microphysics in 3DVAR scheme? – possible• Too many observations used (approx. 5000)?
13th WRF Users Workshop 201229.07.2012
Overestimation of IWV Assimilation of reflectivities leads
to larger errors in the first few hours
Looks promising, but….
13th WRF Users Workshop 2012
Summary
Setup of a unique WRF Rapid Update Cycle over central Europe applying a convection permitting resolution
First steps to assimilate 3D volume radar data from two different networks with WRF over Europe
Results are promising, but still deficiencies due to model imbalances, deficits in clear air dynamics
Quality issues of reflectivities – bias correction required? Problems with the humidity control variable qt in
combination with the applied microphysics schemes?
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13th WRF Users Workshop 2012
Outlook
Harmonize radar data quality and interpolation procedures OPERA European radar data base
Statistical evaluation of assimilating radar reflectivities Check short-term forecasts inside RUC Utilize polarization radar data ( CAOS) Comparison of 3DVAR-RUC and 4DVAR (challenging….) Testing (hybrid) ensemble data assimilation methods (EnKF,
3DVAR-ETKF, Ensemble-3DVAR) Incorporate GPS slant total delays and/or more ZTD data if
available to further improve the water vapor fields
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13th WRF Users Workshop 2012
Acknowledgements
• WRF team (especially Wei, Cindy, Xin and John)• Galina Dick from GFZ Potsdam• Klaus Stephan from the German Meteorological Service• Olivier Caumont from Météo France• ECMWF• High Performance Computing Center Stuttgart (HLRS)
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13th WRF Users Workshop 201229.07.2012
Thanks for your attention!
13th WRF Users Workshop 201229.07.2012
Results for COPS IOP10 performing a 3h RUC for 18 hours starting at 12Z, July 22, 2007
13th WRF Users Workshop 201229.07.2012
Radar data assimilation experiment for COPS IOP 10
13th WRF Users Workshop 2012
Looks promising, but….
29.07.2012 16.04.2012 Institut für Physik und Meteorologie