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Deutscher WetterdienstDeutscher WetterdienstMeteorological Observatory Lindenberg Meteorological Observatory Lindenberg

Richard Assmann ObservatoryRichard Assmann Observatory

The GCOS Reference Upper Air NetworkThe GCOS Reference Upper Air Network

Holger Vömel

GRUAN Lead CenterMeteorological Observatory Lindenberg

German Weather Service

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GRUAN MandateGRUAN Mandate

The GCOS Reference Upper-Air Network is tasked to:

1. Provide long-term high quality climate records

2. Constrain and calibrate data from more spatially-comprehensive global observing systems (including satellites and current radiosonde networks)

3. Fully characterize the properties of the atmospheric column

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Measured quantitiesMeasured quantities

Focus on priority 1: Pressure, temperature, water vaporFocus on priority 1: Pressure, temperature, water vapor Focus on upper troposphere and stratosphereFocus on upper troposphere and stratosphere Focus on reference observations for climate researchFocus on reference observations for climate research

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Initial NetworkInitial Network

To be expanded to about 30 to 40 stations worldwide

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Initial NetworkInitial Network

To be expanded to about 30 to 40 stations worldwide

Tibetan Plateauis missing

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Reference observationsReference observations

To be a referenceTo be a referenceGRUAN observations must:GRUAN observations must:

• Specify measurement uncertainty for every data point

• Relate to the definition of a unit or a transfer standard

• Be traceable (meta-data, documentation)

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Establishing reference qualityEstablishing reference quality

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Establishing UncertaintyEstablishing Uncertainty

• Guide to the expression of uncertainty in measurement (GUM, 1980)Evaluation of measurement data – Guide to the expression of uncertainty in

measurement(http://www.bipm.org/utils/common/documents/jcgm/JCGM_100_2008_E.pdf)

• CIMO guide for observationsGuide to Meteorological Instruments and Methods of Observation, World

Meteorological Organization, 7th edn., 2006(http://www.wmo.int/pages/prog/www/IMOP/publications/CIMO-Guide/CIMO Guide-7th Edition-

2006.html)

• A guide for upper-air reference measurementsPaper by Immler et al. (2010) submitted to Atmos. Meas. Techn.

Open for public comments

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UncertaintyUncertainty

GUM concept:GUM concept:• The "true value" of a physical quantity is no longer used.

• Error is replaced by uncertainty

• Result of a measurement = a range of values

generally expressed by m ± u

m is corrected for systematic effects

u is (random) uncertainty

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Example: Vaisala RS92 temperature

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RS92 calibrationRS92 calibration

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Sources of uncertaintySources of uncertainty

• Sensor calibration:Sensor calibration:Accuracy of calibration referenceAccuracy of calibration referenceAccuracy of calibration modelAccuracy of calibration model

• Sensor integration:Sensor integration:Integration into radiosondeIntegration into radiosondeTelemetry limitationsTelemetry limitations

• Sensor characterization:Sensor characterization:Time lag variation of polymer sensorTime lag variation of polymer sensorController stability of frostpoint hygrometerController stability of frostpoint hygrometerProduction variability Production variability

• External influences:External influences:Radiation errorRadiation errorBalloon/payload contaminationBalloon/payload contaminationSensor icingSensor icing

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Sources of uncertaintySources of uncertaintyExample : TemperatureExample : Temperature

• Sensor calibration:Sensor calibration:Accuracy of calibration referenceAccuracy of calibration referenceAccuracy of calibration modelAccuracy of calibration model

• Sensor integration:Sensor integration:Integration into radiosondeIntegration into radiosondeTelemetry limitationsTelemetry limitations

• Sensor characterization:Sensor characterization:Time lag variation of polymer sensorTime lag variation of polymer sensorController stability of frostpoint hygrometerController stability of frostpoint hygrometerProduction variability Production variability

• External influences:External influences:Radiation errorRadiation errorBalloon/payload contaminationBalloon/payload contaminationSensor icingSensor icing

Vaisala RS92 daytimeVaisala RS92 daytime

0.01K (est.)0.01K (est.) 0.01K (est.)0.01K (est.)

? *? * - -

0.5 K * (strat.)0.5 K * (strat.) 0.5 K 0.5 K

(strat.)(strat.)>1.0K (temporarily)>1.0K (temporarily)

(* after correction is applied)(* after correction is applied)

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Ground check correctionGround check correction

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0.4

0.2

0.0

-0.2

-0.4 Sep 09 Oct 09 Nov 09 Dec 09 Jan 10 Feb 10

Lindenberg additional groundcheckLindenberg additional groundcheck

Mean = -0.11 +/- 0.06 K

ΔT

[K]

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Determination of radiation effectDetermination of radiation effect

Vacuum chamber used for measuring the radiation effect using direct sunlight.

Radiation data of BSRN station was used.

RS-92, DFM-06 and Imet1 sensors tested.

Ventilation measured and varied during measurement.

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Redundant observations Redundant observations to validate uncertainty estimateto validate uncertainty estimate

LUAMI radiosonde intercomparison 2008LUAMI radiosonde intercomparison 2008

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SummarySummary

GRUAN is a reference network for upper air essential climate variables

To start focus on temperature and water vapor

Network is world wide (but large regions missing)

Reference observation: TraceableDocumentedQuantified uncertainties

Uncertainties: Analyze sources, synthesize best estimate, verify in redundant observations

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Extras

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Metrological Metrological TraceabilityTraceability

The result of a measurement can be related to the definition of a unit by an unbroken document chain of calibrations, each of which contributes to the measurement uncertainty

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What is a reference measurement?What is a reference measurement?

A reference measurement gives: A reference measurement gives:

The best estimate for the quantity to be measured

The best estimate for the level of confidence for this measurement (i.e. uncertainty)

To be a referenceTo be a referenceGRUAN observations must includeGRUAN observations must include

the measurement uncertaintythe measurement uncertainty

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UncertaintyUncertainty

Type A evaluation: statistical analysis

Type B evaluation:

previous measurement data

experience with or general knowledge of the behavior and properties of relevant instruments

manufacturer's specifications

data provided in calibration and other certificates

uncertainties assigned to reference data taken from handbooks

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Redundancy and ConsistencyRedundancy and Consistency

GRUAN stations should provide redundant measurements ( → collocation issue)

Redundant measurements should be in agreement.

an essential part of operational quality assurance

Consistency:

No meaningful consistency analysis possible without uncertainties

22

2121 uukmm

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Consistency analysisConsistency analysis

sig. diff.

sig. diff.

agree

consistent

0

1

2

3

expanded errorbars ( k=2)

Measurement A

Measerument B

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2121 uukmm