1. Surface-Based Instrument Intercomparisons and Calibration Methods Activity Report Draft recommendations Michel Leroy Chair of the ET-SBII&CM Commission for Instruments and Methods of Observation Fourteenth Session Geneva, 7 – 14 December 2006

2. Organization and Preparation of surface-based intercomparisons Terms of reference : Laboratory intercomparison of rainfall intensity (RI) measuring instruments. Combined intercomparison of thermometer screens/shields, in conjunction with humidity measurements, in various climatic regions

3. Laboratory intercomparison of RI instruments Following recommendations of an expert meeting in Bratislava (2001) and CIMO XIII, first step before a field intercomparison. International Organizing Committee established. Three laboratories : –DIAM, University of Genoa, Italy; De Bilt, KNMI, the Netherlands; Trappes, Météo-France. 4 meetings for the laboratory intercomparison: –Trappes (2003), Genoa (2005), De Bilt (2005), Geneva (2005)

4. Laboratory Intercomparison Project Manager : Prof. Luca Lanza. 15-Sept-2004  15-Sept-2005 Catching type instruments. 19 (pairs) of instruments, divided in 3 groups. Shift of instruments between laboratories. Final Report available from the CIMO/IMOP Website since January 2006.

6. Outcomes of laboratory intercomparison Each laboratory used its own testing device, based on constant flow and weighing. Proposal of a standardized procedure for laboratory calibration of catchment type rainfall intensity gauges. Draft Rec. 4.2/1 To be included in CIMO guide. Some tipping-bucket rain gauges with proper correction software and some weighing gauges satisfy the WMO RI requirement over limited RI ranges (±5% 2 – 2000 mm/h)

7. WMO Field Intercomparison of Rainfall Intensity Instruments The laboratory Intercomparison was a first step, easier to handle than a field test. Not all instrument types available on the market were tested in laboratory. Looking for a possible site, Vigna di Valle, Italy (Italian Meteorological Service, ReSMA) was selected. August 2007  August 2008

10. Field Intercomparison Call for instruments (March 2006) 24 instruments of different measuring principles were selected (54 proposed !). Reference based on a set of high quality devices, inserted in a pit gauge. Draft Rec. 4.2/2 : Procedure and reference instruments for field rainfall intensity intercomparisons

11. WMO Combined Intercomparison of Thermometer Screens/Shields, in conjunction with Humidity Measuring Instruments Looking for a possible site in harsh conditions, Ghardaïa, Algeria was selected. Desert region Jan. 2007  Jan. 2008 Instruments’ calibration before and after

13. Screens & Hygrometers Intercomparison Call for instruments (March 2006) 16 screens/shields’ types (29 proposed) and 11 hygrometers’ types(17 proposed) were selected. Reference : Thygan Data analysis : –International Organizing Committee –ISO standard 17714 (draft)

14. Intercomparisons Heavy load for the organizing country Heavy load for the ET and IOC members That explains the possible time delays in organizing an Intercomparison. Successful participation of HMEI, in proposing instruments to be tested (directly or in conjunction with a WMO member). Any help for intercomparisons ?

15. Future Intercomparisons Field RI Vigna di Valle, Italy : 2007-2008 Screens/humidity Ghardaïa, Algeria : 2007-2008 Intercomparisons in harsh climate conditions : artic, desert, tropical, marine, urban ? Intercomparison of Present Weather Sensors ?