1. Slide 1 October 2011 Verification for polar regions  Scores computed for polewards of 65°  NB proposed for CBS is polewards of 60°  Verification at ECMWF using available fields from other centres  Done for Z500 only  All verification against analysis (each centre against own analysis)  ERA-Interim scores shown as reference (ERA is fixed model and assimilation system) Slide 1

2. Slide 2 ECMWF operational and ERA-Interim (1990-2011)  Z500 ACC=80%, 12-month moving average  N Pole: clear improvement in system around 2000, and consistently better than ERA beyond 2002. But the apparent change 2001-2002 and 2008-09 are matched in ERA  S Pole: clear sustained improvement in 1990s; still positive trend  ERA changes: either atmospheric variability or changes to observing system October 2011 Slide 2 N Pole S Pole

3. Slide 3 Comparison with other centres (2000-2011) N pole  Day 3 forecasts (T+72)  Z500, 12-month moving average  Each centre verified against own analysis  ERA-I shown for reference October 2011 Slide 3 rms error ACC

4. Slide 4 Comparison with other centres (2000-2011) S pole  Day 3 forecasts (T+72)  Z500, 12-month moving average  Each centre verified against own analysis  ERA-I shown for reference October 2011 Slide 4 rms error ACC

5. Slide 5 Comparison with other centres (2000-2011) N pole  Day 5 forecasts (T+120)  Z500, 12-month moving average  Each centre verified against own analysis  ERA-I shown for reference October 2011 Slide 5 rms error ACC

6. Slide 6 Comparison with other centres (2000-2011) S pole  Day 5 forecasts (T+120)  Z500, 12-month moving average  Each centre verified against own analysis  ERA-I shown for reference  NB some dates missing for CMC in 2009 – affects these scores for 2009 (other years OK) October 2011 Slide 6 rms error ACC

7. Slide 7 Comparison with other centres (2000-2011) N pole  Variability (activity) of forecast and analysis fields: standard deviation of anomalies  Day 5 forecasts (T+120)  Z500, 12-month moving average  ERA-I shown for reference  Compared to the analysis, Met Office forecast now rather underactive; CMC overactive (this can affect the rms errors)  NB some dates missing for CMC in 2009 – affects these scores for 2009 (other years OK) October 2011 Slide 7 analysis forecast

8. Slide 8 Comparison between analyses (N Pole)  Differences between the analyses of different centres  Z500 30 day moving average  Decrease over last decade in the difference between the analyses of different centres October 2011 Slide 8 rms difference mean difference

9. Slide 9 Comparison between analyses (S Pole)  Differences between the analyses of different centres  Z500 30 day moving average  Decrease over last decade in the difference between the analyses of different centres October 2011 Slide 9 rms difference mean difference

10. Slide 10 Comparison with other centres (JJA 2011) arctic  Mean scores over 3 months (June, July, August 2011)  Includes JMA  This for polewards of 60° (the new proposed CBS area)  All centres have slightly lower rmse and higher ACC for this larger area  In winter (DJF) it is opposite (error larger in the larger area, consistent with higher average activity towards mid-latitudes)  The definition of the area does not affect the relative performance of the different models October 2011 Slide 10

11. Slide 11 Comparison with other centres (JJA 2011) N pole  Mean scores over 3 months (June, July, August 2011)  Includes JMA  This for polewards of 65° (for comparison with previous slide) October 2011 Slide 11

12. Slide 12 Comparison with other centres (JJA 2011) antarctic  Mean scores over 3 months (June, July, August 2011)  Includes JMA  This for polewards of 60° (the new proposed CBS area) October 2011 Slide 12