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 • Toolkit (example data + software):

www.cmsaf.eu/tools• CM SAF Community Site available via

EUMETSAT: training.eumetsat.int

Clouds Radiation Water Vapor

• EUMETSAT Satellite Application Facility on Climate Monitoring 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°

September 2012 2

Jörg Trentmann1, Richard Müller1,

Arturo Sanchez-Lorenzo2, Martin Wild2

1Deutscher Wetterdienst, EUMETSAT Satellite

Application Facility on Climate Monitoring (CM SAF)2Eidgenössische Technische Hochschule (ETH), Zürich

Analyzing the Stability of Gridded

Surface Radiation Data Sets

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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

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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?

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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

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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

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Results: Climatology

•Bias in the order of ± 5 W/m2

•Absolute bias: ~ 10 W/m2

•Correlation of anomalies

between 0.8 and 0.9

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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

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Positive trends in both time series: GEBA: +5.3 W/m2/decCM SAF: +2.3 W/m2/dec

• Trends agree within their level of significance

Warszawa: CM SAF Meteosat / GEBA

1. Compare Linear Trends

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Mean all stations: CM SAF Meteosat / GEBA

1. Compare Linear Trends

Positive trends in both time series: GEBA: +3.6 W/m2/decCM SAF: +1.8 W/m2/dec

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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

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Warszawa: CM SAF Meteosat GEBA

Significant negative trend of 3 W/m2/dec in the bias time series

2. Analyze Bias Time Series

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Mean all stations: CM SAF Meteosat GEBA

2. Analyze Bias Time Series

Significant negative trend of 1.76 W/m2/dec in the mean bias time series

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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

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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

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3. Homogeneity Test

• No clear shift detected in all time series

• Maximum of (negative) shifts in 1993-1995

• Very few shifts after 1995

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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

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1. Linear Trends (> 1994)

Compare CM SAF Meteosat / GEBA after 1994

•Consistent linear trends (~ 4.6 W/m2/dec) •Zero trend in the bias time series•High homogeneity of the CM SAF Meteosat data

set after 1994 in Europe

Trend

Bias

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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/m2/dec

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• 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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