INTERCOMPARISON OF WINTER PERFORMANCE OF RAIN GAUGESINTERCOMPARISON OF WINTER PERFORMANCE OF RAIN GAUGES

The network of Automatic Weather Stations (AWS) operated by the Austrian Central Institute for Meteorology and Geodynamics (ZAMG) will be extended with 50 new AWS in near future. For the selection of a reliable rain gauge, after preliminary field tests in Vienna, an intercomparison of tipping bucket and weighing gauges at a mountain test site was performed during the time period ranging form November 2005 to March 2006.

� Collecting orifice of 500cm2 for for compatibility with the existing network equipped with tipping bucket gauge PAAR AP23 (now out of production)

� Minimum measurement resolution of 0,1mm/minute. Maximum delay ofmeasurement less or equal 1 minute

� Reduced maintenance, easy operation and cleaning� Sufficient and reliable heating for winter operation� Availability of spare parts� Maintenance, repairing and calibration with the available laboratory facilities

of ZAMG� Availability of 40-50 instruments within the end of year 2006

Tested instruments

Requirements for precipitation measurement instruments

ring 10W, funnel 50Woutflow, interior 20W0,1mm500 cm2tipping bucketAP23Paar

ring 56W, funnel 48Woutflow, interior 31W 0,1mm500 cm2tipping bucketMR3H-FMeteoservis

funnel 70W0,1mm500 cm2tipping bucketMR3HMeteoservis/Kroneis

ring 30W0,01mm500 cm2weighingTRWsMPS System

ring 50W0,1mm500 cm2weighingNIWA MED K505

Sommer

heatingreso-lutionorifice measuring

principletypemanufacturer

Martin MairCentral Institute for Meteorology and Geodynamics, Technical Department, Hohe Warte 38, Vienna, Austria, martin.mair@zamg.ac.at

The site is situated in Western Austria at 2085 m above sea-level in the Arlbergregion, where we often have severe weather conditions with low temperature rime and frost accretion in combination with high wind speed.

Test site

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Nov 2005 Dez 2005 Jan 2006 Feb 2006 March 2006 Totalprecipitation

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Sommer

MPS

Paar

MR3H

MR3H-F

Measurement results

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Sommer

MPS

Paar

MR3H

MR3H-F

Introduction

Weighing gauges

• Sum of precipitation quantity close to standard rain gauge

• Delay of data output up to 30min

• Overestimation of precipitation intensities up to factor 4

• Non compensated temperature effects

MPS TRWs

• Average overestimation of precipitation up to 50%, several days more than +300%

• Correlation of non real precipitation with temperature variation (e.g. sunrise)

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p re c ip .d e te c to r

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Tipping bucket gauges

• No reliable operation at temperatures below –5°C

• Snow accumulation in the funnel due to inadequate heating

Meteoservis/Kroneis MR3H

• In the standard version the outflow is blocked by ice accretion

• Improved version shows reliable operation

Meteoservis MR3H-F

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M R 3 H -F

p re c ip .D e te c tor

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Pa a r

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M R 3 H -Fne wprec ip .de tec tor

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air te m p e ra tu resun sh in e

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Monthly sum of precipitation reported by the rain gauges under test in relation to Paar(standard rain gauge).

Definition of instrument failure� Deviation of daily precipitation quantity >±300% from mean

precipitation of all instruments�Precipitation reported without signal from precipitation

detector >1h� Delayed output (software filter or insufficient heating)

� Omission of precipitation > 20min (blockage of instrument)

17.01.2006 15:00 to 18.01.2006 15:00. 10.04.2006 15:00 to 11.04.2006 15:00.

Percentage of days with more than one failure of operation for different instruments

08.02.2006. 13.02.2006.

NIWA MED K505