WMO CIMO SurveyNational Summaries of Methods and Instruments for Solid Precipitation Measurement- Preliminary results -

R Nitu

Meteorological Service of Canada

AMS, Phoenix, AZ

12 Jan 2009

Page 2 DRAFT - DATE

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.

Page 3 DRAFT - DATE

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)

Page 4 DRAFT - DATE

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

Page 5 DRAFT - DATE

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?

Page 6 DRAFT - DATE

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.

Page 7 DRAFT - DATE

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.

Page 8 DRAFT - DATE

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.

Page 9 DRAFT - DATE

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 cm2

▪ 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 cm2.

Page 10 DRAFT - DATE

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

Page 11 DRAFT - DATE

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:

Page 12 DRAFT - DATE

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.

Page 13 DRAFT - DATE

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.

Page 14 DRAFT - DATE

Thank you!

Rodica Nitu

Meteorological Service of Canada

Rodica.nitu@eg.gc.ca