Handbook onMeteorological Observations

Henk Benschop, Jitze van der Meulen

Royal Netherlands Meteorological Institute

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BackgroundThe National Meteorological Authority should provide a Manual (or Guide) with Standard procedures on:

definitions of the variables to be observed functional specifications of each variable Recommended observation technology (standards) Siting and exposure of instruments Station inspection Data acquisition and data processing

(computation) Data presentation (code formats) Data validation and archive

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Problem Many guides are available on instrument

measurement, data processing and presentation and on weather information services- e.g. CIMO Guide, Manuals on GOS, GDPS, Codes, etc.

But no integral standard manual in which the national standards are stated to provide the data service from OBS to INFO.

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Objectives Definitions, units, coding, derived variables Requirements on range, resolution, measurement

uncertainty, frequency of measurements, etc. Instruments and technical specifications, calibration

procedures Procedures in case of missing data, methods for data

validation, procedures on site inspection Calculation of parameters, formulae to reduce data;

encoding siting and exposure criteria Inspection criteria Considerations with respect to the surroundings

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Handbookon Observations

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Structure in line with CIMO Guide1. General2. Temperature3. Atmospheric pressure4. Humidity5. Wind6. Precipitation7. Radiation8. Sunshine duration 9. Visibility 10. Evaporation 11. Soil temperature

12. Upper air pressure, temperature, humidity

13. Upper air wind 14. Present weather,

past weather, state of the ground

15. Observation of clouds

16. Ozone measurement17. Atmospheric

composition18. Seawater temperature19. Ocean waves 20. Lightning

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1. Description1.1 name of variable (e.g.. wind, precipitation) 1.2 definitions 1.3 units: standard cf. SI (e.g. m/s), or non-standard (e.g kts.) 1.4 derived variables (e.g. wind speed, -direction) + definition 1.5 codes and explanations (synop, metar)

Contents

2. Operational requirements2.1 range, e.g. 0 - 50 m/s 2.2 resolution, e.g. 0.1 ° C 2.3 required accuracy, e.g. ± 0.5 hPa 2.4 required frequency of observations, e.g. every 12 s2.5 required availability per specific period, e.g. 50 %

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3. Instruments and techniques 3.1 technical specifications of the instruments 3.2 management, maintenance and calibration procedures

Contents (cont.)

4. Procedures4.1 procedures in case of missing data 4.2 procedures for data validation 4.3 procedures for  control of observation sites (inspection)

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Contents (cont.)

5. Calculation of other parameterse.g. formula for reduction to MSL pressure, formula for calculating dew point from U and air-t

6. Siting, requirements with respect to surroundings6.1 Specific conditions per instrument 6.2 Conditions with respect to the surroundings of the site

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A. Temperature_1.50m(C) B. Relative_humidity_1.50m(%) C. Global Radiation(Joule/cm2) D. Temperature 10cm(C) E. Visibility F. Sum of precipitation(mm) G. Duration of precipitation(hr) H. Wind speed(m/s) I. Wind direction(degrees) J. Atmospheric pressure (hectoPascal)

Station lay-out

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Instrument description• E.g. cup anemometer

steel-cup .

A sensor is built into the mechanism the reacts to a signal from the rotating spindle every revolution. Registration of the rotation rate, which is near enough proportional to the prevailing wind speed, is done using a pulse counter. The number of pulses per unit time (e.g. per second) is counted and the speed of rotation is derived from this.

drum with slots

optical sensor with photo cell

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Codes (SYNOP, METAR, CLIMAT) Full explanation of codes, e.g. code fxfx:

group 910ff: the maximum wind gust in m/s in the 10 minutes preceding the moment of observation {i.e. exactly 5 minutes before every whole hour (UTC)} where this is 5 m/s or more greater than the synchronous value of ff in section 1.

(etc.)

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Validation

E.g. FX FX must be FH, otherwise suspect; FX must be FF, otherwise suspect; abs[FXh - (-1/6 (FXh-2+FXh+2) + 2/3 (FXh-

1+FXh+1))] must be 8 knots, otherwise FX is suspect;

FX must be 80 knots, otherwise suspect;

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Station inspection procedures

Every wind measurement site that has an operational function within the KNMI observation network is inspected on average twice annually by an official from WM/OD/station management. Extra interim inspections can also be carried out on request

The inspection can cover the following checks (example):d) Comparison of the instantaneous (12") wind speed value measured by the sensor with the instantaneous wind speed value as read off from a reference ...(etc.)

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Publication

Strategy: all open to the public (through national meteor. library)

• hard copy book, with replaceable loose leaves, yearly updated

• electronic versions available on WWW

http://www.knmi.nl/onderzk/applied/ob/nl/ob_handboek.html (Dutch)

http://www.dwd.de/EUMETNET/Berichte/Handbuch_NL.doc (English)

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Version management

Yearly updates:• procedure for updating text, figures, formulas• list of recipients• chapter ‘ownership’

To keep it up-to-date

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