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Verification of Atmospheric Scores in Polar Regions: Analysis from ECMWF and Other Centers

This document provides an extensive verification of atmospheric scores computed for regions poleward of 60°, focusing on the ECMWF analysis of Z500. Key findings include significant improvements in forecast accuracy, particularly at the North Pole after 2000, and consistent positive trends at the South Pole during the 1990s. Day 3 and Day 5 forecast comparisons reveal variabilities in forecast accuracy amongst different meteorological centers, with detailed insights into mean scores over specific periods and their error metrics. The impact of atmospheric variability and observational changes is also discussed.

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Verification of Atmospheric Scores in Polar Regions: Analysis from ECMWF and Other Centers

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  1. 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) October 2011

  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 N Pole S Pole October 2011

  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 rms error ACC October 2011

  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 rms error ACC October 2011

  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 rms error ACC October 2011

  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) rms error ACC October 2011

  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) analysis forecast October 2011

  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 rms difference mean difference October 2011

  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 rms difference mean difference October 2011

  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

  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

  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

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