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

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 the WRF 3DVAR System in a Rapid Update Cycle Configuration.

13th WRF Users Workshop 2012


Outline
Outline the WRF 3DVAR System in a Rapid Update Cycle Configuration.

  • 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 the WRF 3DVAR System in a Rapid Update Cycle Configuration.

  • 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

13th WRF Users Workshop 2012


Thomas schwitalla institute of physics and meteorology university of hohenheim

29.07.2012 the WRF 3DVAR System in a Rapid Update Cycle Configuration.

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 the WRF 3DVAR System in a Rapid Update Cycle Configuration.

  • 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 the WRF 3DVAR System in a Rapid Update Cycle Configuration.

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 the WRF 3DVAR System in a Rapid Update Cycle Configuration.

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 the WRF 3DVAR System in a Rapid Update Cycle Configuration.

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 the WRF 3DVAR System in a Rapid Update Cycle Configuration.

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…. the WRF 3DVAR System in a Rapid Update Cycle Configuration.

Assimilation of radial velocities only

Last RUC step at 06UTC

13th WRF Users Workshop 2012


Looks promising but1
Looks promising, but…. the WRF 3DVAR System in a Rapid Update Cycle Configuration.

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…. the WRF 3DVAR System in a Rapid Update Cycle Configuration.

Horizontal distribution of ZTD O-A

No reflectivities

13th WRF Users Workshop 2012


Looks promising but3
Looks promising, but…. the WRF 3DVAR System in a Rapid Update Cycle Configuration.

Horizontal distribution of ZTD O-A

With reflectivities

13th WRF Users Workshop 2012


Looks promising but4
Looks promising, but…. the WRF 3DVAR System in a Rapid Update Cycle Configuration.

  • 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…. the WRF 3DVAR System in a Rapid Update Cycle Configuration.

  • Overestimation of IWV

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

13th WRF Users Workshop 2012


Summary
Summary the WRF 3DVAR System in a Rapid Update Cycle Configuration.

  • 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 the WRF 3DVAR System in a Rapid Update Cycle Configuration.

  • 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 the WRF 3DVAR System in a Rapid Update Cycle Configuration.

  • 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! the WRF 3DVAR System in a Rapid Update Cycle Configuration.

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 starting at 12Z, July 22, 2007

13th WRF Users Workshop 2012


Looks promising but6
Looks promising, but…. starting at 12Z, July 22, 2007

16.04.2012

13th WRF Users Workshop 2012

Institut für Physik und Meteorologie