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U.K. Ozone and UV Trends and Extreme Events

U.K. Ozone and UV Trends and Extreme Events. Andrew C. Moss, George O’Neill, Andrew R.D. Smedley and John S. Rimmer University of Manchester. Acknowledgements: UKMO, DEFRA. Introduction. Overview of Sites Long-term Trends in Ozone and UV Statistical Determination of Extreme Events

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U.K. Ozone and UV Trends and Extreme Events

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  1. U.K. Ozone and UV Trends and Extreme Events Andrew C. Moss, George O’Neill, Andrew R.D. Smedleyand John S. Rimmer University of Manchester Acknowledgements: UKMO, DEFRA NOG Annual Meeting 2012

  2. Introduction • Overview of Sites • Long-term Trends in Ozone and UV • Statistical Determination of Extreme Events • Extreme Events Determined for: • Lerwick • Manchester • Reading • Comparison with Satellite Records NOG Annual Meeting 2012

  3. Overview and Map of Sites • Lerwick: • Dobson since 1952 • Manchester: • Brewer Mk III since 2000 • Reading: • Brewer Mk IV since 2002 • Camborne: • Dobson 1989 – 2003 • Dobson 1952 – 1967 • Bracknell: • Dobson 1967 - 1989 NOG Annual Meeting 2012

  4. Ground Based TrendsA.R.D. Smedley et al. International Journal of Climatology DOI: 10.1002/joc.2275, 2010 NOG Annual Meeting 2012

  5. Satellite TrendsA.R.D. Smedley et al. International Journal of Climatology DOI: 10.1002/joc.2275, 2010 NOG Annual Meeting 2012

  6. 1979 – 1993: • Lerwick ozone: -5.8% per decade. • Southern England ozone: -4.8% per decade. • Decreases at upper end of range in comparison with other European stations. • 1993 – 2011: both sites show small increase NOG Annual Meeting 2012

  7. Mann-Kendal NOG Annual Meeting 2012

  8. UV Ratio Trends ReadingA.R.D. Smedley et al. International Journal of Climatology DOI: 10.1002/joc.2275, 2010 NOG Annual Meeting 2012

  9. Determination of Extreme Events NOG Annual Meeting 2012

  10. Gaussian Quantile-Quantile Plot: Case for Changing Statistical Analysis for Identification of Extreme Events NOG Annual Meeting 2012

  11. Extreme Value Theory – Generalized Pareto Distribution Extreme events in total ozone over Arosa: Part 1: Application of Extreme Value Theory. Rieder et al. AtmosChem Phys, 10, 10021, 2010 Extreme events in total ozone over Arosa: Part 2: Fingerprints of atmospheric dynamics and chemistry and effects on mean values and long-term change. Rieder et al. . AtmosChem Phys, 10, 10033, 2010 NOG Annual Meeting 2012

  12. Determination of Threshold • Fit the GPD model to the data for a range of thresholds. • Find the point where the shape parameter becomes constant. • Check that this threshold does actually provide the best fit. NOG Annual Meeting 2012

  13. Quantile-Quantile Comparison NOG Annual Meeting 2012

  14. Quantile-Quantile Comparison NOG Annual Meeting 2012

  15. Arosa Data Extreme events in total ozone over Arosa: Part 1: Application of Extreme Value Theory. Rieder et al. AtmosChem Phys, 10, 10021, 2010 NOG Annual Meeting 2012

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  24. Results: % Frequency trends NOG Annual Meeting 2012

  25. Results: % Frequency trends NOG Annual Meeting 2012

  26. Results: % frequency trends NOG Annual Meeting 2012

  27. Results: Seasonality NOG Annual Meeting 2012

  28. Results: Annual running means NOG Annual Meeting 2012

  29. Conclusions • Tentative signs of ozone recovery in ground based obs. • Ozone inadequately described by a Gaussian Distribution. • EVT fits the extreme tails much better and provides different thresholds. • Frequency of extreme events follows overall trend of data as you would expect. • Seasonal Frequency loosely follows the same trend generally, however, variations from season to season. • Frequency of extreme events shows no long term trend on de-trended TOC data. • Frequency of extreme events shows seasonal variation • The mean value of extreme events follows the mean in the overall data indicating that there is no overall trend in the extreme values other than that present in the overall ozone data. NOG Annual Meeting 2012

  30. Thank You! NOG Annual Meeting 2012

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