1. WMO CIMO Survey National Summaries of Methods and Instruments for Solid Precipitation Measurement - Preliminary results - R Nitu Meteorological Service of Canada AMS, Phoenix, AZ 12 Jan 2009

2. DRAFT - DATE Page 2 Scope The WMO CIMO-XIV, has tasked the Expert Team on Surface-Based Instrument Intercomparisons and Calibration Methods to: – assess the methods of measurement and observation of solid precipitation at automatic stations: –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. Goals of the survey: –The extent of using automatic instruments for measuring precipitation (liquid and solid); –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 Questions: How many stations use automatic precipitation gauges? How many stations use shields with such gauges as recommended by WMO? If so what type of shielding? How many stations use heated gauges? How many stations use other type of electronic sensors to measure precipitation, e.g. distrometers, snow pillows, etc?

6. DRAFT - DATE Page 6 Survey Results By Dec 2008: –53 Member countries responded to the 2008 CIMO Questionnaire (46% of the global landmass) operate precipitation measurement programs using a combination of manual observations and automatic instruments: ▪41,187 stations, ▪Average density: 1 station/1100 sq Km. –34 of the respondents (28% of the land mass) measure solid precipitation: ▪17,242 stations, ▪Average density: 1 station/2200 sq Km.

7. DRAFT - DATE Page 7 How many stations use automatic precipitation gauges? Measuring the amount of precipitation (41,187 stations, 53 countries): –82% of stations use manual means of observation; –18% of stations use automatic instruments in 33 participating Member countries. Measuring snow on the ground and snowfall (17,242 stations, 34 countries): –93% of stations use manual means of observation; –7% of stations use automatic sensors.

8. DRAFT - DATE Page 8 Automatic instruments in use Amount of precipitation: Weighing type gauges: measuring the mass accumulated in its bucket over a given period. Tipping bucket type gauges: integrating over time the mass falling onto one of two small buckets in a tipping balance.

9. DRAFT - DATE Page 9 Automatic instruments in use Weighing Type Gauges: ▪used in 18 NMHSs, ▪Six manufacturers (Geonor, OTT, Vaisala, MPS Systems, Meteoservis, and Belfort); ▪Collecting area: 200, 400, 500 cm 2 ▪Collecting capacity: 250 to 1000 mm ▪Heating: optional (Geonor, OTT, Vaisala), standards feature (MPS Systems, Meteoservis) Tipping Bucket Type Gauges: ▪Used in 22 countries; ▪28 different types of instruments from 21 manufacturers; ▪The majority have heating circuits (funnel, collecting ring); ▪Sensitivity: 0.1;0.2;0.25;0.5 mm of precipitation; ▪Collecting area: 200 to 1000 cm 2.

10. DRAFT - DATE Page 10 How many stations use shields with gauges, as recommended by WMO? If so, what type of shielding? Overall, the automatic gauges: –28% used with windshields –72% do not have windshields Weighing type gauges (WG): –78% of WG use single wind shields (Alter, Tretyakov, Nipher); –22% of WG do not have wind shields; Tipping Bucket type Gauges: –30% configured with wind shields (Japan, USA) –1% configured with windshields in 6 other countries; –69% do not have windshields

11. DRAFT - DATE Page 11 Automatic Instruments for Solid Precipitation 13 participating countries use automatic instruments for snow on the ground and snowfall; 7% of sites reporting solid precipitation; Types of instruments: –sonic ranging sensors, –optical forward scatter sensors; –snow pillow sensors. Sensors per site: 1-3; SR-50:

12. DRAFT - DATE Page 12 Next steps 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 for precipitation measurement of WMO Technical Commissions and Programs. Assess the need for an intercomparison of methods and equipment for automatic snowfall, snow depth, precipitation measurements.

13. DRAFT - DATE Page 13 Intercomparison? Potential Outcomes: Relative performance of measurement of gauges in use. Efficiency and configuration 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.

14. DRAFT - DATE Page 14 Thank you! Rodica Nitu Meteorological Service of Canada Rodica.nitu@eg.gc.ca