1. CIMO Survey National Summaries of Methods and Instruments Related to Solid Precipitation Measurement at Automatic Weather Stations - Very Preliminary results - R Nitu, G Fournier WMO/CIMO - TECO St Petersburg, Nov 29, 2008

2. DRAFT - DATE Page 2 Scope The fourteenth session of the WMO CIMO (CIMO-XIV), has tasked the Expert Team on Surface-Based Instrument Intercomparisons and Calibration Methods, to assess the needs and methods of measurement and observation of solid precipitation at automatic stations: –Preparing national summaries of methods, issues and challenges; –Updating metadata related to precipitation measurement instrumentation at all NMHS AWS; –Documenting the needs of WMO Technical Commissions and Programs; –Compiling measurement standards and requirements of WMO Technical Commissions. –Assessing the need for an intercomparison of methods and equipment for automatic snowfall, snow depth, precipitation measurements, and develop an intercomparison plan.

3. DRAFT - DATE Page 3 1986-1993 WMO Solid Precipitation Measurement Intercomparison assessed national methods of measuring solid precipitation against methods of known accuracy and reliability (primarily manual); determined wind related errors in national methods of measuring solid precipitation; derived standard methods for adjusting solid precipitation measurements; introduced a reference method of solid precipitation measurement for general use to calibrate any type of precipitation gauge. Final report: WMO/TD- No. 872, 1998, WMO Solid Precipitation Measurement Intercomparison, by B.E. Goodison and P.Y.T. Louie (both Canada), and D. Yang (China)

4. DRAFT - DATE Page 4 2008 CIMO Survey on Methods and Instruments for Solid Precipitation Distributed July 2008, through CIMO Secretariat. Response deadline: Sept 15, 2008 Goals of the survey: –the extent of measuring solid precipitation using automatic instruments; –parameters measured, instruments used and their configuration; –Identify adjustments applied to precipitation measurements; –Summary of derived solid precipitation parameters from automatic stations measurements; –Summary of testing/developing new instruments and methods of measurement of solid precipitation parameters

5. DRAFT - DATE Page 5 Preliminary Results By mid October 2008: –51 Member countries responded to the 2008 CIMO Questionnaire (40% of the global landmass) –45 respondents provided detailed information on their precipitation measurement programs, a combination of manual observations and automatic instruments: ▪27,812 stations, ▪Average density 1 station/1280 sq Km). –32 of the respondents measure solid precipitation: ▪13,614 stations ▪Average density: 1 station/2097 sq Km. Additional responses are still encouraged.

6. DRAFT - DATE Page 6 Measurement synopsis Of the 45 Member countries providing detailed information on their measurement programs: –45, measure Accumulated Precipitation (100%); –27, measure Depth of snow on the ground (60%); –13, measure Snowfall amount (29%); –17, measure Snow water equivalent (38%). Note: various parameters are monitored in various countries.

7. DRAFT - DATE Page 7 Use of automatic instruments 30 responding Member countries operate automatic instruments at 6590 stations (24% of stations included in the survey). –Many of the automatic precipitation instruments operate in conjunction with a human observation program. Reporting of snow parameters, from 13,614 stations: –10% of stations use automatic sensors. –90% of stations use manual measurements 10 Member countries use automatic snow depth sensors 3 Member countries derive snowfall using data from automatic instruments (Canada, Germany, Japan).

8. DRAFT - DATE Page 8 Measuring total precipitation accumulation: instruments in use Of the 6590 stations using automatic instruments for measuring total precipitation accumulation: –14% use weighing type gauges: ▪used in 15 NMHSs, ▪from 5 different manufacturers (Geonor, OTT, Vaisala, MPS Systems, and Belfort); ▪All are used with shields (Alter, Tretyakov). –86% use tipping bucket type gauges, ▪Used in 18 countries ▪23 different types of instruments. ▪The majority have heating circuits.

9. DRAFT - DATE Page 9 Measuring snow on the ground: instruments in use Instruments in use: Sonic ranging sensors –SR-50 from Campbell Scientific, most widely used (488 stations) –Sommer Ultrasonic snow depth sensor USH-8, –MPS System SwS-3, –Ultrasonic snow level meter Ogasawara Keiki Seisakusho JMA-95-1, –Ultrasonic Kaijo Sonic JMA-89, JMA-93, JMA-04-1. SR-50:

10. DRAFT - DATE Page 10 Next steps Complete analysis of the results: first half of 2009 Final report on the Questionnaire results: mid 2009. Evaluation of results by the Expert team on Surface Instrument Intercomparison and Calibration Methods. In cooperation with their representatives, document the needs of WMO Technical Commissions and Programs, regarding precipitation measurement. Assess the need for an intercomparison of methods and equipment for automatic snowfall, snow depth, precipitation measurements.

11. DRAFT - DATE Page 11 Intercomparison? Potential Outcomes: Understand the performance of measurement of gauges in use. The efficiency of shields for precipitation gauges, in particular those measuring solid precipitation (snow). The re-evaluation of the Double Fence Intercomparison Reference (DFIR) using automatic gauges. Development of adjustment curves using hourly precipitation and 2- meter wind during the precipitation events.

12. DRAFT - DATE Page 12 Message Additional responses are still expected and encouraged. Thank you! Rodica Nitu Meteorological Service of Canada Rodica.nitu@eg.gc.ca