Atmosphere Monitoring

Quarterly Evaluation of the UV and Solar Radiation Products

Antti Arola, Mireille Lefèvre, Marion Schroedter-Homscheidt, Lucien Wald, William Wandji

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P R I N C I P L E S O F T H E V A L I D A T I O N

• Validation against ground-based measurements serving as reference

• Ground-based measurements must offer high quality. Quality control is applied

• Follow ISO standard for uncertainty assessment. Compute deviations: model – ground-based measurements. Compute bias, standard deviation and RMSE of deviations.

• Compute other quantities and draw other graphs on an ad hocbasis

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C O L L E C T I O N O F M E A S U R E M E N T S

• Selection of stations offering high quality measurements with some archives for further possible control.

• Measurements should be detailed enough. For example, for UV radiation preferably spectral measurements. For solar radiation, measurements of the global irradiation together with the diffuse and direct components.

• Measurements from stations should be made available for validation within 3 months approximately.

• Selected stations have shown signs of continuity in measurements. Hence, results may be compared from one validation report to another.

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C O L L E C T I O N O F M E A S U R E M E N T S

• ~ 15 stations for UV products• Locations: Europe, USA and Antarctic

NEUBrew NetworkFMI and European UV databases

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C O L L E C T I O N O F M E A S U R E M E N T S

• 6 stations for solar radiation products (BSRN, GAW)• Two more to come in Northern Africa (sun belt)

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R E S U L T S F O R U V R A D I A T I O N• 30-day running mean UV Index around the local noon

Nyalesund (Norway)

Bergen (Norway)

Florence (Italy)

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R E S U L T S F O R U V R A D I A T I O N

• new UV processor from September 2015 onwards• new spatial resolution from May 2016 onwards; 80 km to ~ 40 km

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R E S U L T S F O R U V R A D I A T I O N

• SZA effects• Significant effects by absorbing aerosols• Convective clouds: high variability of cloud propertiesbetween morning and afternoon

SZA

CAMS minus OMI, April 2005, all-sky conditions

• Satellite-based UV comparisons around local noon time

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C O N C L U S I O N S F O R U V R A D I A T I O N

• Conclusions and perspectives

1. In general, ground-based measurements and CAMS estimates are well correlated

2. From January 2016 onwards, acceptable level of accuracy ( |rBias| < 0.2 and rRMSE < 0.5)

3. Comparisons of input parameters (aerosol, ozone, UV albedo,…) will be included in order to better understand

some of the differences between measurements and CAMS estimates

4. Increasing the number of ground-based stations over the world especially to include lower latitudes

5. Satellite-based UV comparisons: overpass times comparisons are planned

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R E S U L T S F O R S O L A R R A D I A T I O N

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R E S U L T S F O R S O L A R R A D I A T I O N

• Ability to reproduce the day-to-day variability. Very large correlation coefficients for global

irradiation and the direct and diffuse components.

• Bias and standard deviation of errors.

• Bias is often noticeable

• Tendency to overestimation for the global radiation and the diffuse component

• Tendency to underestimation for the direct component.

• Standard deviation of errors.

Usually small: the scattering of the errors is small.

• First conclusion

Bias is noticeable for each component.

Large correlation coefficients and fairly low standard deviations demonstrate that the CAMS-RAD

products match fairly well the coincident measurements on a one-to-one basis.

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R E S U L T S F O R S O L A R R A D I A T I O N

• Ability to reproduce the frequency distributions of measurements.

The statistical distributions of the estimates are fairly similar to those of the measurements. .

• Ability to reproduce the monthly means and standard deviation within a month.

• Bias is noticeable in monthly means

• Variability within a month is well reproduced by the CAMS radiation products. .

• Does the CAMS radiation products fit WMO requirements for measurements of hourly

global irradiation made by ground-based pyranometers?

• As a whole, the quality is less than “moderate quality” pyranometer measurements.

• Main cause is the bias

• Estimates at Tamanrasset are often close to the “moderate quality”.

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C O N C L U S I O N S F O R S O L A R R A D I A T I O N

CAMS solar products offer the same performances that the best current solar products.

The bias is a major problem for users (see graph).An empirical correction to remove the bias has been designed and will be applied in September 2017.

Green circle: no biasUpward triangle: overestimationDownward triangle: underestimation

Relative bias for various sites from several publications and reports

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R E P O R T S A V A I L A B L E O N T H E W E B S I T E

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Thank you for your attention