Handbook on Meteorological Observations

1. Handbook onMeteorological Observations Henk Benschop, Jitze van der Meulen Royal Netherlands Meteorological Institute

2. Background The 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 TECO 2005

3. 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. TECO 2005

4. 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 TECO 2005

5. Handbookon Observations TECO 2005

6. 1. General 2. Temperature 3. Atmospheric pressure 4. Humidity 5. Wind 6. Precipitation 7. Radiation 8. 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 measurement 17. Atmospheric composition 18. Seawater temperature 19. Ocean waves 20. Lightning Structure in line with CIMO Guide TECO 2005

7. 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 % TECO 2005

8. 3. Instruments and techniques 3.1 technical specifications of the instruments 3.2 management, maintenance and calibration procedures Contents (cont.) 4. Procedures 4.1 procedures in case of missing data 4.2 procedures for data validation 4.3 procedures for  control of observation sites (inspection) TECO 2005

9. 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 TECO 2005

10. Station lay-out TECO 2005

11. 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 TECO 2005

12. 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.) TECO 2005

13. 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; TECO 2005

14. 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.) TECO 2005

15. 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) TECO 2005

16. Version management To keep it up-to-date • Yearly updates: • procedure for updating text, figures, formulas • list of recipients • chapter ‘ownership’ TECO 2005

17. TECO 2005