1. Impact of a Hybrid Ensemble-Variational Data Assimilation System on the Performance of an ETKF-based EPS System Åke Johansson, Jelena Bojarova and Nils Gustafsson

2. Data Assimilation Ensemble System Marriage

3. Time Period 17 JAN – 5 MAR 2008 ↓ 25 JAN – 6 FEB 2008 17 5 JAN MAR t O 24 6 JAN FEB t O

4. Time Period 17 JAN – 5 MAR 2008 ↓ 25 JAN – 6 FEB 2008 17 5 JAN MAR t O 24 6 JAN FEB t O

5. 48 42 36 30 24 18 12 06 00 t O t F 00 06 12 18 00 06 12 18 00 06 12 00 06 12 18 00 12 06 18 48 42 36 30 24 18 12 06 00 Time Forecast Lead Time Forecast Lead Time

6. Horizontal Domain

7. Vertical Domain 40 Levels

8. Boundary Conditions EuroTEPS Zone at the Horizontal Boundaries Layer at the top of the Model

9. Boundary Conditions EuroTEPS Zone at the Horizontal Boundaries Layer at the top of the Model

10. Ensemble Characteristics Size: 12 Members Centering: Spherical Simplex Inconsistent with the BC from EuroTEPS which are Paired

11. Ensemble Characteristics Size: 12 Members Centering: Spherical Simplex Inconsistent with the BC from EuroTEPS which are Paired

12. Ensemble Characteristics Size: 12 Members Centering: Spherical Simplex Inconsistent with the BC from EuroTEPS which are Paired

14. EXPERIMENT COMPARISON - 1 ETKF vs EuroTEPS

15. MODEL HIRLAM Trunk APR 2010

16. Boundary Conditions EuroTEPS ETKF 20% EuroTEPS 80% ETKF EuroTEPS 100% EuroTEPS

17. DATA and DA ONLY Conventional Data 3D-VAR

18. Error growth

28. Vertical structure and Amount of Observations

29. Total amount of assimilated observations Large variations with cycle

34. Spectra

35. EuroTEPS

50. Spectra ETKF

56. EXPERIMENT COMPARISON - 2 ETKF vs ETKF Hybrid

57. MODEL HIRLAM Trunk NOV 2010

58. Boundary Conditions EuroTEPS ETKF 20% EuroTEPS 80% ETKF ETKF Hybrid 20 % EuroTEPS 80% ETKF

59. DATA and DA Conventional Data + ATOVS 3D-VAR ± HYBRID

60. CAVEAT Localization scale of implicit Schur product 200 km  500 km Localization Function Compact support  Exponential Decay

61. Error growth

62. From EXP 1

83. Spectra

92. Vertical structure and Amount of Observations

102. Conclusions ● The Hybrid System improves some aspects of the ETKF performance ● ATOVS data has a beneficial impact on the ETKF performance

103. Conclusions ● The Hybrid System improves some aspects of the ETKF performance ● ATOVS data has a beneficial impact on the ETKF performance

104. CAVEAT ● Only 2 weeks diagnosed

105. CAVEAT ● Only 2 weeks diagnosed ● Only 12 members

106. CAVEAT ● Only 2 weeks diagnosed ● Only 12 members ● Climatological SST and Sea Ice

107. CAVEAT ● Only 2 weeks diagnosed ● Only 12 members ● Climatological SST and Sea Ice ● Only 1 ATOVS Channel

108. CAVEAT ● Only 2 weeks diagnosed ● Only 12 members ● Climatological SST and Sea Ice ● Only 1 ATOVS Channel ● Too strong localization