Meteorological Observatory Lindenberg Results of the Measurement Strategy of the GCOS Reference Upper Air Network (GRUAN) Holger Vömel, GRUAN Lead Center DWD Meteorological Observatory Lindenberg CIMO TECO 2012

Meteorological Observatory Lindenberg Water vapor trends in the troposphere? Motivation 1: Long term „trend“ humidity

Meteorological Observatory Lindenberg Water vapor trends in the troposphere? Dessler and Davis, JGR 2010 Specific humidity at 300 hPa

Meteorological Observatory Lindenberg Water vapor trends in the upper troposphere? e.g.: Lindenberg 8km (0:00 UT)

Meteorological Observatory Lindenberg Freiberg RKS-2 RKS-5 MARZ RS80 RS92 Water vapor trends in the upper troposphere? e.g.: Lindenberg 8km (0:00 UT)

Meteorological Observatory Lindenberg  No trend estimate possible: Trend signals dominated by instrumental change  Observations have been done for numerical weather prediction, not for long term climate  Measurements are not traceable (Instrumental uncertainties not well characterized and systematic errors disregarded )  Instrumental change instantaneous not managed  Meta data are incomplete  Note: Even the Vaisala RS92 data record is inconsistent Water vapor trends in the upper troposphere? e.g.: Lindenberg 8km (0:00 UT)

Meteorological Observatory Lindenberg GCOS Reference Upper Air Network  GRUAN in response to the need of WMO and the Global Climate Observing System for highest accuracy data possible  Ground based network for reference upper air observations for climate under GCOS and integrated into WIGOS  Currently 16 sites, with aim to expand to 30 to 40 sites worldwide Check out

Meteorological Observatory Lindenberg GRUAN goals  Maintain observations over decades  Validation of satellite systems  Characterize observational uncertainties  Traceability to SI units or accepted standards  Comprehensive metadata collection and documentation  Validate observations through deliberate measurement redundancy  Long-term stability through managed change Priority 1: Water vapor, temperature, (pressure and wind) Priority 2: Ozone, …

Meteorological Observatory Lindenberg The GCOS Reference Upper-Air Network: What constitutes a “reference” observation?

Meteorological Observatory Lindenberg Reference observation A GRUAN reference observation: Is traceable to an SI unit or an accepted standard Provides a comprehensive uncertainty analysis Maintains all raw data Is documented in accessible literature Is validated (e.g. by intercomparison or redundant observations) Includes complete meta data description

Meteorological Observatory Lindenberg Establishing reference quality Best estimate +Uncertainty Uncertainty of input data Traceable sensor calibration Transparent processing algorithm Disregarded systematic effects Black box software Proprietary methods

Meteorological Observatory Lindenberg Establishing Uncertainty Error is replaced by uncertainty  Important to distinguish contributions from systematic error and random error A measurement is described by a range of values A measurement is expressed as m ± u  m is corrected for systematic errors  u is random uncertainty Literature:  Guide to the expression of uncertainty in measurement (GUM, 1980)  Guide to Meteorological Instruments and Methods of Observation, WMO 2006, (CIMO Guide)  Reference Quality Upper-Air Measurements: Guidance for developing GRUAN data products, Immler et al. (2010), Atmos. Meas. Techn.

Meteorological Observatory Lindenberg Uncertainty, Redundancy and Consistency  GRUAN stations provide redundant measurements  Redundant measurements should be consistent: No meaningful consistency analysis possible without uncertainties if m 2 has no uncertainties use only u 1 (“agreement within errorbars”)

Meteorological Observatory Lindenberg Uncertainty and Raw Data Analyze sources of uncertainty: systematic: calibration, radiation errors, … random: noise, production variability, … Document this!  Synthesize best uncertainty estimate: Uncertainties for every data point, i.e. vertically resolved  Raw data: Store all raw and all meta data to allow future reprocessing

Meteorological Observatory Lindenberg Determining the Uncertainty: Daytime temperature Vaisala RS92

Meteorological Observatory Lindenberg Uncertainty example: Daytime temperature Vaisala RS92

Meteorological Observatory Lindenberg Uncertainty example: Daytime temperature Vaisala RS92

Meteorological Observatory Lindenberg Uncertainty example: Daytime temperature Vaisala RS92 Assumptions:  On average 50% of maximum insolation  Downward direct, downward and upward diffuse radiation  Radiative streamer model for radiation field, with climatological clouds

Meteorological Observatory Lindenberg Uncertainty example: Daytime temperature Vaisala RS92 Sources of measurement uncertainty (in order of importance):  Sensor orientation  Ventilation  Unknown radiation field  Lab measurements of the radiative heating  Ground check  Calibration

Meteorological Observatory Lindenberg GRUAN Data Product: RH uncertainty RH Uncertainty:

Meteorological Observatory Lindenberg GRUAN Data Product: RH uncertainty Good example: 28 Mar 2012:

Meteorological Observatory Lindenberg GRUAN Data Product: RH uncertainty Good example: 28 Mar 2012:

Meteorological Observatory Lindenberg GRUAN Data Product: RH uncertainty Good example: 28 Mar 2012:

Meteorological Observatory Lindenberg Redundant Observations: CFH and GRUAN RS92

Meteorological Observatory Lindenberg GRUAN Data Product: RH uncertainty Cooperation with manufacturers needed to address these issues Bad example: 15 Mar 2012:

Meteorological Observatory Lindenberg Traceability Manufacturer Independent Ground Checks

Meteorological Observatory Lindenberg Additional ground checks

Meteorological Observatory Lindenberg Additional ground checks Production Year:

Meteorological Observatory Lindenberg Additional ground checks Lindenberg Ground Check 30 May 2012, 0:00 GC25 (0%)SHC (100%) U U

Meteorological Observatory Lindenberg U1 switched on U2 switched on

Meteorological Observatory Lindenberg Change Management

Meteorological Observatory Lindenberg Change Management Change management is mandatory to maintain traceability, homogeneity in a time series and consistency within a network A new system, software, or procedure must be evaluated prior to implementation Systematic and random errors must be quantified for the new system in the same manner as for the old system  Redundant observations verify that the new system are of equal quality as the old system.  If transfer functions are required, old data will be reprocessed based on the stored raw data

Meteorological Observatory Lindenberg Summary  GRUAN is an approach to long term observations of upper air essential climate variables  Focus on priority 1 variables to start: Water vapor and temperature (starting to bring in other variables)  Reference observation means: quantified uncertainties traceable well documented  Understand the uncertainties: analyze sources synthesize best estimate verify in redundant observations  Management of change utilizes measurement uncertainty