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
1.
Introduction
•
•
2.
Methods
•
•
•
•
3.
4.
2
Background
Objectives
Site
Instruments
Calibration
QA/QC
Results
Conclusions
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
3
Methods - 1
Site
 Ghardaïa, in central Algeria
Instruments
 29 screens/shields
o artificially-ventilated: 7 different models
o 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
4
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
5
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
o More than 95% available valid data
 The analysis was made jointly by :
o Météo-France : Muriel Lacombe and Michel Leroy
o ONM: Djazia Bousri and Mohamed Mezred
 Final report : published soon
 A dedicated study for each model of instrument is available
6
Temperature during the intercomparison period
7
Relative humidity during the intercomparison period
8
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
9
Temperature differences with VEIG22 (°C)
10
Median
5% - 95% interval
345461
239793
SVAI1
SVAI2
25% - 75% interval
0.5% - 99.5% interval
11204
44570
44570
VYOU2
503124
VFIS2
VTHY2
503124
VFIS1
VYOU1
476818
VEIG21
9655
503124
VEIG12
499531
503116
VEIG11
VROT1
503124
VDAV2
VTHY1
503124
VDAV1
503124
503124
SSOC2
503124
503124
SSOC1
SYOU2
503124
SDAV2
SYOU1
503123
503124
503124
LSOC
SDAV1
503124
503124
SWIN2
503124
LLAN2
SWIN1
503124
LCAS
-1,5
LLAN1
-1
503124
-0,5
308333
0
LBOM
0,5
ATHI2
1
329206
1,5
ATHI1
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 the reference
Number of cases
Screen/Shield
Extrema
Results for screens - 2
During clear days and low wind speeds
 Some small naturally-ventilated screens are colder
 Artificially-ventilated screens are generally warmer
 Large Stevenson screens are very close to the reference
325
4720
4720
VTHY2
VYOU1
VYOU2
18006
VFIS2
247
18006
VFIS1
18005
17060
VEIG21
VROT1
18006
VEIG12
VTHY1
18006
VEIG11
8907
SVAI2
18006
14159
SVAI1
VDAV2
18006
SSOC2
18006
18006
SSOC1
18006
18006
SDAV2
SYOU2
18006
VDAV1
18006
LSOC
SDAV1
18006
18006
LLAN2
18006
18006
LLAN1
SWIN2
18006
LCAS
SYOU1
18006
LBOM
18006
12657
ATHI2
SWIN1
14214
ATHI1
Number of cases
5
Temperature differences with VEIG22 (°C)
4
3
2
1
0
-1
-2
-3
-4
-5
Screen/Shield
11
Median
5% - 95% interval
25% - 75% interval
0.5% - 99.5% interval
Extrema
Results for screens - 3
Combined effect of wind and radiation
12
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
UHMP11
UHMP12
UHMP21
464160
464159
464114
9600
11043
VTHY2
SVAI2
463970
VTHY1
SVAI1
464168
VROT1
464168
VFIS2
464077
VFIS1
464064
UTES2
241294
UHMP22
329350
LBOM
Relative humidity differences with UHMP2 (%)
Number of cases
464160
20
18
16
14
12
10
8
6
4
2
0
-2
-4
-6
-8
-10
-12
-14
-16
-18
-20
Sensor
13
Median
5% - 95% interval
25% - 75% interval
0.5% - 99.5% interval
Extrema
Results for hygrometers – 2
Periods with relative humidity lower than 20%
UHMP11
UHMP12
UHMP21
86305
86305
86304
0
0
VTHY2
SVAI2
86307
VTHY1
SVAI1
86308
VROT1
86308
VFIS2
86305
VFIS1
86305
UTES2
64156
UHMP22
68206
LBOM
Number of cases
86307
6
Relative humidity differences with UHMP2 (%)
5
4
3
2
1
0
-1
-2
-3
-4
-5
-6
Sensor
Median
14
5% - 95% interval
25% - 75% interval
0.5% - 99.5% interval
Extrema
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:
o To select references
o To study each sensor’s behaviour
 Experience and specific tools were developped
o Database systems, QC softwares, macros/codes for
plots…
 A similar comparison is planned in Canada
o for cold desert conditions
15
Thank you !