1. September 2012 1 Advertisement: CM SAF Data freely available in netcdf-format User-friendly data access via the Web User Interface: www.cmsaf.eu/wui www.cmsaf.eu/wui Toolkit (example data + software): www.cmsaf.eu/tools www.cmsaf.eu/tools CM SAF Community Site available via EUMETSAT: training.eumetsat.inttraining.eumetsat.int Clouds RadiationWater Vapor EUMETSAT Satellite Application Facility on Climate Monitoring www.cmsaf.eu www.cmsaf.eu Provides satellite-derived climate data of geophysical variables Regional, up to global coverage Currently, data available from Jan 1982 to Feb 2012 Spatial resolution from 0.03° to approx. 1°

2. September 2012 2 Jörg Trentmann 1, Richard Müller 1, Arturo Sanchez-Lorenzo 2, Martin Wild 2 1 Deutscher Wetterdienst, EUMETSAT Satellite Application Facility on Climate Monitoring (CM SAF) 2 Eidgenössische Technische Hochschule (ETH), Zürich Analyzing the Stability of Gridded Surface Radiation Data Sets

3. September 2012 3 Motivation Gridded Climate Data Sets (e.g., satellite, reanalysis, surface obs) become increasingly available Three aspects of Climate Data Records should be evaluated:  Climatology (mean)  Temporal Variability (anomalies)  Temporal Stability (trend) Validation of gridded data sets often does not assess the temporal stability / homogeneity  Validation of a satellite-derived climate data set of solar irradiance using surface measurements

4. September 2012 4 Data Set CM SAF Meteosat (Posselt et al., 2012) 1983 – 2005; 0.03 deg; Meteosat Full Disk, monthly/daily/hourly 6 different satellite instruments (of the same type) used! Does this data set fulfill the requirements for climate quality?

5. September 2012 5 Reference Data Set GEBA: Global Energy Balance Archive, hosted at ETH Zürich > 200 surface stations globally starting 1930s Here: ca. 50 European stations starting 1983

6. September 2012 6 Data Set Validation Validation Strategy: Climatological measures (mean, variability) Evaluation of the stability 1.Comparison of linear trends 2.Temporal evolution of the bias 3.Application of homogeneity test

7. September 2012 7 Results: Climatology Bias in the order of ± 5 W/m 2 Absolute bias: ~ 10 W/m 2 Correlation of anomalies between 0.8 and 0.9

8. September 2012 8 Data Set Evaluation Evaluation Strategy: Climatological measures (mean, variability) Evaluation of the stability 1.Comparison of linear trends 2.Temporal evolution of the bias 3.Application of homogeneity test

9. September 2012 9 Positive trends in both time series: GEBA: +5.3 W/m 2 /dec CM SAF: +2.3 W/m 2 /dec Trends agree within their level of significance Warszawa: CM SAF Meteosat / GEBA 1. Compare Linear Trends

10. September 2012 10 Mean all stations: CM SAF Meteosat / GEBA 1. Compare Linear Trends Positive trends in both time series: GEBA:+3.6 W/m 2 /dec CM SAF: +1.8 W/m 2 /dec

11. September 2012 11 Data Set Evaluation Evaluation Strategy: Climatological measures (mean, variability) Evaluation of the stability 1.Comparison of linear trends 2.Temporal evolution of the bias 3.Application of homogeneity test

12. September 2012 12 Warszawa: CM SAF Meteosat  GEBA Significant negative trend of 3 W/m 2 /dec in the bias time series 2. Analyze Bias Time Series

13. September 2012 13 Mean all stations: CM SAF Meteosat  GEBA 2. Analyze Bias Time Series Significant negative trend of 1.76 W/m 2 /dec in the mean bias time series

14. September 2012 14 Data Set Evaluation Evaluation Strategy: Climatological measures (mean, variability) Evaluation of the stability 1.Comparison of linear trends 2.Temporal evolution of the bias 3.Application of homogeneity tests

15. September 2012 15 Warszawa: CM SAF Meteosat  GEBA 3. Homogeneity Test Penalized Maximum T test (PMT, Wang et al., 2008): Detects changes of the mean Model assuming constant values and (multiple) shifts Software and documentation readily available

16. September 2012 16 3. Homogeneity Test No clear shift detected in all time series Maximum of (negative) shifts in 1993-1995 Very few shifts after 1995

17. September 2012 17 3. Homogeneity Tests Homogeneity Test (SNHT) Shifts detected in 1987 and 1994 (corresponding to changes in satellite) No shift detected after 1994, data set is homogeneous between 1994 and 2005

18. September 2012 18 1. Linear Trends (> 1994) Compare CM SAF Meteosat / GEBA after 1994 Consistent linear trends (~ 4.6 W/m 2 /dec) Zero trend in the bias time series High homogeneity of the CM SAF Meteosat data set after 1994 in Europe Trend Bias

19. September 2012 19 Trend in Surface Radiation Spatial distribution of linear trend (1994 – 2005) based on CM SAF Meteosat Substantial variability (decrease in Mediterranean!) Mean Trend: 3.1 W/m 2 /dec

20. September 2012 20 Temporal stability of gridded climate data sets need to be evaluated Linear trends in surface irradiance in Europe tend to be reproduced by CM SAF data set Inhomogeneities have been detected in the CM SAF data set before 1994 The trend in surface irradiance in Europe between 1994 and 2005 is spatially inhomogeneous Outlook:  Compare with independently-derived gridded data sets (e.g., surface obs, reanalysis)  Evaluate the homogeneity of the surface data using multiple gridded data sets Conclusions

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