3D-VAR data assimilation experiments for the double-nested limited area model ALADIN/Hungary

1. Steluta Alexandru Supervisor: Andras Horanyi 3D-VAR data assimilation experiments for the double-nested limited area model ALADIN/Hungary EWGLAM meeting

2. Introduction • The aim:to get an idea about the best strategy of the 3D-VAR data assimilation scheme for a double nested-limited area model. • Variational assimilation consists in minimizing a cost function J(x). • The adjoint operator is used to compute the gradient of the cost function J(x). EWGLAM meeting

3. What does it mean a double-nested model? ARPEGE ALADIN/LACE ALADIN/Hungary boundary conditions EWGLAM meeting

4. What does it mean a double-nested model? 8 km resolution 12 km resolution EWGLAM meeting

5. The experiments performed (I) Different lateral boundary techniques: • Time-consistency • Space-consistency EWGLAM meeting

6. Results • Statistical measures • RMSE • BIAS • Diagnostic measures • Time evolution of the fields • Spectral energy on ellipses • Subjective evaluation • Maps with increments • Maps with meteorological fields EWGLAM meeting

7. RMSE oper RMSE time RMSE space Verification of the analysis The fields are closer to the observations using 3D-VAR scheme. Period 25.02 - 02.03.2002 00 UTC EWGLAM meeting

8. RMSE oper RMSE time RMSE space Verification of 6h forecast • The fields with 3D-VAR are keeping the initial improvement, but not for all levels. • The time-consistency is a better technique for the double-nested limited area model. EWGLAM meeting

9. The experiments performed (II) • Digital FiIter Initialization • Incremental Digital FiIter Initialization • no initialization Different initialization methods: EWGLAM meeting

10. time DFI time no DFI time IDFI Time evolution of the pressure in cycling 02.03.2002 00 UTC In 3D-VAR cycling, digital filter initialization has to be applied. EWGLAM meeting

11. time DFI cycling; DFI production time no DFI cycling; no DFI production time IDFI cycling; DFI production oper Time evolution of the pressure in production 02.03.2002 00 UTC In production, digital filter initialization is need. EWGLAM meeting

12. The experiments performed (III) Different lateral boundary conditions files: • ALADIN/LACE • ARPEGE EWGLAM meeting

13. RMSE oper RMSE ARPEGE RMSE LACE Verification of the analysis • The fields are closer to the observations using 3D-VAR scheme. • There is no signifficant difference for the analyses with 3D-VAR, when different LBC files were used. Period 25.02 - 25.03.2002 00 UTC EWGLAM meeting

14. RMSE oper RMSE ARPEGE RMSE LACE Verification of 6h forecast • The fields with 3D-VAR are keeping the initial improvement, but not for all levels. • The choice of the LBC files is not so important. EWGLAM meeting

15. Conclusions • The forecast with 3D-VAR keeps the improvement of the analysis. • Using time-consistency, a better forecast is obtained. • In 3D-VAR cycling and in production, digital filter initialization method is need. • The choice of the lateral boundary conditions files is not so important. EWGLAM meeting

16. Future plans • Case studies • More data to be used. • Tests with lagged statistics. • Use of the spectral blending procedure. EWGLAM meeting

17. THANK YOU FOR YOUR ATTENTION! EWGLAM meeting