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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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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
Contents
  • Introduction
    • Background
    • Objectives
  • Methods
    • Site
    • Instruments
    • Calibration
    • QA/QC
  • Results
  • Conclusions
introduction
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
methods 1
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
methods 2
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
results
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
choice of the references
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
results for screens 1
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
results for screens 2
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
results for screens 3
Results for screens - 3
  • Combined effect of wind and radiation
results for hygrometers 1
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
results for hygrometers 2
Results for hygrometers – 2
  • Periods with relative humidity lower than 20%
conclusions what is next
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
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