CIMO SurveyNational 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

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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.

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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)

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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

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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.

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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.

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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).

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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.

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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:

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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.

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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.

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Message

• Additional responses are still expected and encouraged.

• Thank you!

Rodica Nitu

Meteorological Service of Canada

Rodica.nitu@eg.gc.ca