RESULTS OF THE WMO INTERCOMPARISON OF THERMOMETER SCREENS/SHIELDS AND HYGROMETERS IN HOT DESERT COND...
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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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Contents

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 SCREENS/SHIELDS AND HYGROMETERS IN HOT DESERT CONDITIONS

  • Introduction

    • Background

    • Objectives

  • Methods

    • Site

    • Instruments

    • Calibration

    • QA/QC

  • Results

  • Conclusions


Introduction
Introduction SCREENS/SHIELDS AND HYGROMETERS IN HOT DESERT CONDITIONS

  • 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 SCREENS/SHIELDS AND HYGROMETERS IN HOT DESERT CONDITIONS

  • 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 SCREENS/SHIELDS AND HYGROMETERS IN HOT DESERT CONDITIONS

  • 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 SCREENS/SHIELDS AND HYGROMETERS IN HOT DESERT CONDITIONS

  • 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


Temperature during the intercomparison period
Temperature during the intercomparison period SCREENS/SHIELDS AND HYGROMETERS IN HOT DESERT CONDITIONS


Relative humidity during the intercomparison period
Relative humidity during the intercomparison period SCREENS/SHIELDS AND HYGROMETERS IN HOT DESERT CONDITIONS


Choice of the references
Choice of the references SCREENS/SHIELDS AND HYGROMETERS IN HOT DESERT CONDITIONS

  • 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 SCREENS/SHIELDS AND HYGROMETERS IN HOT DESERT CONDITIONS

  • 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 SCREENS/SHIELDS AND HYGROMETERS IN HOT DESERT CONDITIONS

  • 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 SCREENS/SHIELDS AND HYGROMETERS IN HOT DESERT CONDITIONS

  • Combined effect of wind and radiation


Results for hygrometers 1
Results for hygrometers - 1 SCREENS/SHIELDS AND HYGROMETERS IN HOT DESERT CONDITIONS

  • 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 SCREENS/SHIELDS AND HYGROMETERS IN HOT DESERT CONDITIONS

  • Periods with relative humidity lower than 20%


Conclusions what is next
Conclusions – What is next? SCREENS/SHIELDS AND HYGROMETERS IN HOT DESERT CONDITIONS

  • 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


Contents

Thank you ! SCREENS/SHIELDS AND HYGROMETERS IN HOT DESERT CONDITIONS