1 / 17 Deutscher Wetterdienst Meteorological Observatory Lindenberg Richard Assmann Observatory The GCOS Reference Upper Air Network Holger Vömel GRUAN Lead Center Meteorological Observatory Lindenberg German Weather Service

2 / 17 GRUAN 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

3 / 17 Measured quantities  Focus on priority 1: Pressure, temperature, water vapor  Focus on upper troposphere and stratosphere  Focus on reference observations for climate research

4 / 17 Initial Network To be expanded to about 30 to 40 stations worldwide

5 / 17 Initial Network To be expanded to about 30 to 40 stations worldwide Tibetan Plateau is missing

6 / 17 Reference observations To be a reference 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)

7 / 17 Establishing reference quality

8 / 17 Establishing Uncertainty Guide to the expression of uncertainty in measurement (GUM, 1980) Evaluation of measurement data – Guide to the expression of uncertainty in measurement ( CIMO guide for observations Guide to Meteorological Instruments and Methods of Observation, World Meteorological Organization, 7th edn., 2006 ( Guide-7th Edition html) A guide for upper-air reference measurements Paper by Immler et al. (2010) submitted to Atmos. Meas. Techn. Open for public comments

9 / 17 Uncertainty 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

10 / 17 Example: Vaisala RS92 temperature

11 / 17 RS92 calibration

12 / 17 Sources of uncertainty Sensor calibration: Accuracy of calibration reference Accuracy of calibration modelSensor calibration: Accuracy of calibration reference Accuracy of calibration model Sensor integration: Integration into radiosonde Telemetry limitationsSensor integration: Integration into radiosonde Telemetry limitations Sensor characterization: Time lag variation of polymer sensor Controller stability of frostpoint hygrometer Production variabilitySensor characterization: Time lag variation of polymer sensor Controller stability of frostpoint hygrometer Production variability External influences: Radiation error Balloon/payload contamination Sensor icingExternal influences: Radiation error Balloon/payload contamination Sensor icing

13 / 17 Sources of uncertainty Example : Temperature Sensor calibration: Accuracy of calibration reference Accuracy of calibration modelSensor calibration: Accuracy of calibration reference Accuracy of calibration model Sensor integration: Integration into radiosonde Telemetry limitationsSensor integration: Integration into radiosonde Telemetry limitations Sensor characterization: Time lag variation of polymer sensor Controller stability of frostpoint hygrometer Production variabilitySensor characterization: Time lag variation of polymer sensor Controller stability of frostpoint hygrometer Production variability External influences: Radiation error Balloon/payload contamination Sensor icingExternal influences: Radiation error Balloon/payload contamination Sensor icing Vaisala RS92 daytime 0.01K (est.) 0.01K (est.) 0.01K (est.) 0.01K (est.) ? * K * (strat.) 0.5 K (strat.) >1.0K (temporarily) (* after correction is applied)

14 / 17 Ground check correction

15 / Sep 09 Oct 09 Nov 09 Dec 09 Jan 10 Feb 10 Lindenberg additional groundcheck Mean = / K ΔT [K]

16 / 17 Determination 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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18 / 17 Redundant observations to validate uncertainty estimate LUAMI radiosonde intercomparison 2008

19 / 17 Summary  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: Traceable Documented Quantified uncertainties  Uncertainties: Analyze sources, synthesize best estimate, verify in redundant observations

20 / 17 Extras

21 / 17 Metrological Traceability  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

22 / 17 What is a reference measurement? 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 reference GRUAN observations must include the measurement uncertainty

23 / 17 Uncertainty  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

24 / 17 Redundancy 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

25 / 17 Consistency analysis