A Radar Data Assimilation Experiment for COPS IOP 10 with the WRF 3DVAR System in a Rapid Update Cyc...
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A Radar Data Assimilation Experiment for COPS IOP 10 with the WRF 3DVAR System in a Rapid Update Cycle Configuration. . Thomas Schwitalla Institute of Physics and Meteorology University of Hohenheim. Motivation. Outline. WRF model setup Radar data assimilation in the WRF model

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Thomas Schwitalla Institute of Physics and Meteorology University of Hohenheim

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Thomas schwitalla institute of physics and meteorology university of hohenheim

A Radar Data Assimilation Experiment for COPS IOP 10 with the WRF 3DVAR System in a Rapid Update Cycle Configuration.

Thomas Schwitalla

Institute of Physics and Meteorology

University of Hohenheim


Motivation

Motivation

13th WRF Users Workshop 2012


Outline

Outline

  • WRF model setup

  • Radar data assimilation in the WRF model

  • First radar assimilation experiment over France

  • Summary

  • Outlook

13th WRF Users Workshop 2012


Wrf model setup

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 fromin from the Western Europe

  • Direct initialization from ECMWF forecast or analysis on model levels

  • CV6 Background error Matrix

13th WRF Users Workshop 2012


Thomas schwitalla institute of physics and meteorology university of hohenheim

29.07.2012

Rapid Update Cycle approach with WRF

Lateral boundary conditions from ECMWF analyses/forecast

T

00Z

03Z

06Z

09Z

12Z

Forecast

Forecast

Forecast

Forecast

Obs

Obs

Obs

Obs

T+0h

T+3h

T+6h

T+9h

T+12h

T + xx hours

3DVAR

3DVAR

3DVAR

3DVAR

Free forecast

ECMWF analysis + DFI

Update lateral boundary conditions

Update low boundary

13th WRF Users Workshop 2012


Radar data coverage during cops

Radar data coverage during COPS

  • 15 Doppler radar in total

    • 10 from France

    • 5 from Germany

  • S- and C-Band radars

  • Scanning radius up to 250km

  • Range resolution 1km

  • Rumax= 60m/s and 32m/s

  • 3D volume data

13th WRF Users Workshop 2012


Assimilation of radar data in wrf

Assimilation of radar data in WRF

Radial velocity assimilation:

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:

Derived from a Marshall-Palmer distribution with N0 = 8*106m-4

13th WRF Users Workshop 2012


Quality control and data thinning

Quality control and data thinning

Raw observations amount is too large and data are noisy

Data thinning and filtering prior to its use in a data assimilation scheme

Applied filtering procedure for e.g. German radar data:

According to quality flags, the raw observation is set to missing value

Calculation of a 3x3 average value

Calculation of variance for every raw observation

Variance rejection threshold 50dBZ² for reflectivity and 60m²/s² for radial velocity (Xiao, WRF Workshop 2008)

Additional smoothing along the ray and azimuth

Radial wind observation error = f(range)

Reflectivity error set to 5dBZ

Reflectivities are discarded above 4000m AGL and below 0°C

13th WRF Users Workshop 2012


Thomas schwitalla institute of physics and meteorology university of hohenheim

Assimilation of radial velocities only

03Z (second last RUC step)

06Z, last RUC step

Good agreement throughout the complete RUC

13th WRF Users Workshop 2012


Thomas schwitalla institute of physics and meteorology university of hohenheim

Assimilation of radial velocities only

No radar

With radar winds

Observation

Small but positive influence on the 3h precipitation forecast

(Reduction of RMSE ~6%, correlation slightly improved)

13th WRF Users Workshop 2012


Looks promising but

Looks promising, but….

Assimilation of radial velocities only

Last RUC step at 06UTC

13th WRF Users Workshop 2012


Looks promising but1

Looks promising, but….

Assimilation of reflectivities in addition

Last RUC step at 06UTC

Can you spot the difference?

13th WRF Users Workshop 2012


Looks promising but2

Looks promising, but….

Horizontal distribution of ZTD O-A

No reflectivities

13th WRF Users Workshop 2012


Looks promising but3

Looks promising, but….

Horizontal distribution of ZTD O-A

With reflectivities

13th WRF Users Workshop 2012


Looks promising but4

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 2012


Looks promising but5

Looks promising, but….

  • Overestimation of IWV

  • Assimilation of reflectivities leads to larger errors in the first few hours

13th WRF Users Workshop 2012


Summary

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?

13th WRF Users Workshop 2012


Outlook

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

13th WRF Users Workshop 2012


Acknowledgements

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)

13th WRF Users Workshop 2012


Thomas schwitalla institute of physics and meteorology university of hohenheim

Thanks for your attention!

13th WRF Users Workshop 2012


Results for cops iop10 performing a 3h ruc for 18 hours starting at 12z july 22 2007

Results for COPS IOP10 performing a 3h RUC for 18 hours starting at 12Z, July 22, 2007

13th WRF Users Workshop 2012


Radar data assimilation experiment for cops iop 10

Radar data assimilation experiment for COPS IOP 10

13th WRF Users Workshop 2012


Looks promising but6

Looks promising, but….

16.04.2012

13th WRF Users Workshop 2012

Institut für Physik und Meteorologie


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