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RESULTS OF THE WMO INTERCOMPARISON OF THERMOMETER SCREENS/SHIELDS AND HYGROMETERS IN HOT DESERT CONDITIONS Muriel Lacombe WMO CIMO-TECO 2010, 31 August 2010. Contents. Introduction Background Objectives Methods Site Instruments Calibration QA/QC Results Conclusions. Introduction.

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  1. RESULTS OF THE WMO INTERCOMPARISON OF THERMOMETER SCREENS/SHIELDS AND HYGROMETERS IN HOT DESERT CONDITIONS Muriel Lacombe WMO CIMO-TECO 2010, 31 August 2010

  2. Contents • Introduction • Background • Objectives • Methods • Site • Instruments • Calibration • QA/QC • Results • Conclusions

  3. Introduction • Background • Several intercomparisons of screens and hygrometers, all in temperate conditions • None in hot or cold desert conditions • Importance for climatology • Objectives • Performance of screens/shields for high radiations • Performance of hygrometers in high temperatures and very low humidity conditions • Evaluate the impact of ancillary factors on the sensors • Draft recommandations to CIMO

  4. Methods - 1 • Site • Ghardaïa, in central Algeria • Instruments • 29 screens/shields • artificially-ventilated: 7 different models • naturally-ventilated: 9 different models • 17 humidity sensors (8 different models) • 2 extra Thies ultrasonic wind sensors Most of sensors were installed in pairs. • Intercomparison period • From the 1st of Nov., 2008 to the 1st of Nov., 2009

  5. Methods - 2 • Calibration • Temperature measurements: calibrated Pt100 • Before the intercomparion, in the RIC of Trappes • On-site calibration • No calibration after the intercomparison for the moment • QA/QC • Daily check by local staff • Pictures taken once per month • Specific software to flag data according CBS recommendations

  6. Results • One full year of measurements • A large dataset although some gaps in the data • More than 500 000 minutes available for most of sensors • More than 95% available valid data • The analysis was made jointly by : • Météo-France : Muriel Lacombe and Michel Leroy • ONM: Djazia Bousri and Mohamed Mezred • Final report : published soon • A dedicated study for each model of instrument is available

  7. Temperature during the intercomparison period

  8. Relative humidity during the intercomparison period

  9. Choice of the references • Screens • Artificially-ventilated screen • The coldest during daytime • Choice: Eigenbrodt screen • Hygrometers • Thygan as first reference • Communication problems with Thygan, during the last 6 monthes • Another reference, the closest to Thygan • Choices: Thygan and Vaisala HMP45D

  10. Results for screens - 1 • General results • Nearly all small naturally-ventilated screens are warmer • Artificially-ventilated screens are not significantly colder • Large Stevenson screens are very close to thereference

  11. Results for screens - 2 • During cleardays and low wind speeds • Some small naturally-ventilated screens arecolder • Artificially-ventilated screens are generally warmer • Large Stevenson screens are very close to thereference

  12. Results for screens - 3 • Combined effect of wind and radiation

  13. Results for hygrometers - 1 • General results • 5 models gave very good results: 98% differences are within ± 3% • 2 models stayed within 4% of the reference • 1 model showed larger deviations

  14. Results for hygrometers – 2 • Periods with relative humidity lower than 20%

  15. Conclusions – What is next? • Final report : published soon • It is the first WMO intercomparison of screens/shields and hygrometers in hot desert conditions • Despite some gaps, a large dataset was collected during this intercomparison • A deep analysis was conducted: • To select references • To study each sensor’s behaviour • Experience and specific tools were developped • Database systems, QC softwares, macros/codes for plots… • A similar comparison is planned in Canada • for cold desert conditions

  16. Thank you !

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