Download - Data quality control for the ENSEMBLES grid
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Data quality control for the ENSEMBLES grid
Evelyn ZenklusenMichael Begert
Christof Appenzeller Christian HäberliMark LinigerThomas Schlegel
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ECSN Datamanagement Workshop 2005, E. Zenklusen
Data Collation (KNMI)
Gridding (UEA, UOXFDC)
Tmean
Quality control (KNMI, MeteoSwiss)
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ECSN Datamanagement Workshop 2005, E. Zenklusen
What we have and what we aim at …
Methods based on ECA&D experience:
implemented statement if series are
homogeneous or not for a given period (e.g.1946-1999)
Additional goals: date the breakpoints homogeneous subperiods separate information for each
climate variable
useful (), doubtful (), suspect ()
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ECSN Datamanagement Workshop 2005, E. Zenklusen
THOMAS(Tool for Homogenization of Monthly Data Series at MeteoSwiss)
Pro: Twelve different homogeneity tests implemented Includes full station history Based on monthly time series but daily output resolution possible
Contra: Includes a lot of manual work (construction of reference series,
interpretation of test results) not suited for large datasets (ENSEMBLES)
But: the Swiss series homogenized by THOMAS provide a highly valuable
core dataset for the testing in ENSEMBLES
Reference and details:Begert Michael, Schlegel Thomas and Kirchhofer Walther, 2005: “Homogenous temperature and precipitation series of Switzerland from 1864 to 2000”, Int. J. Climatol. 25: 65-80.
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ECSN Datamanagement Workshop 2005, E. Zenklusen
VERAQC (Vienna Enhanced Resolution Analysis Quality Control at Univ. Vienna)
Pro: based on objective spatial interpolation designed for quality control applied at MeteoSwiss on daily data idea: use VERAQC-output for
homogenization
Contra: Not yet tested. - Does it work??
References and details:Steinacker Reinhold, Christian Häberli and WolfgangPöttschacher, 2000: "A transparent method for the analysis and quality evaluation of irregularly distributedand noisy observational data", Monthly Weather Review, Vol. 128, No. 7, pp. 2303-2316.
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Deviation
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ECSN Datamanagement Workshop 2005, E. Zenklusen
European monthly data
VERAQC for homogenizing the ENSEMBLES dataset
Significantbreakpoints
“Deviations”
Homogeneity test(Easterling&Peterson two-phase
Regression homogeneity test
Alexandersson’s standard normalhomogeneity test)
VERAQC
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ECSN Datamanagement Workshop 2005, E. Zenklusen
number of breakpoints detected: 0(), 1(), 2(), 3(), 4(), >5()
Precipitation
1960-2004
VERAQCAlexandersson
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ECSN Datamanagement Workshop 2005, E. Zenklusen
number of breakpoints detected: 0(), 1(), 2(), 3(), 4(), >5()
Tmin
1960-2004
VERAQCAlexandersson
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ECSN Datamanagement Workshop 2005, E. Zenklusen
Example series: precipitation Beesel 1960-2004
Breakpoints detected by Easterling & Peterson
Deviation series
Breakpoints detected by Alexandersson
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ECSN Datamanagement Workshop 2005, E. Zenklusen
Discovered limitations of VERAQC
sensitivity to changes in network density incomplete deviation series for some stations (example Amiandos)
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ECSN Datamanagement Workshop 2005, E. Zenklusen
Changes in the station network:Example Amiandos precipitation 1960 - 2004
Observation series:
Deviation series:
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ECSN Datamanagement Workshop 2005, E. Zenklusen
Discovered limitations of VERAQC
sensitivity to changes in network density incomplete deviation series for some stations (example Amiandos) artificial breakpoints (example Andermatt)
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ECSN Datamanagement Workshop 2005, E. Zenklusen
Changes in the station network:Example Andermatt maximum temperature 1960-2004
Deviations Andermatt Tmax
Deviations Locarno Tmax
Deviations Engelberg Tmax
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ECSN Datamanagement Workshop 2005, E. Zenklusen
Discovered limitations of VERAQC
sensitivity to changes in network density incomplete deviation series for some stations (example Amiandos) artificial breakpoints (example Andermatt)
One step further to test the process… analyse only complete station series of a desired period
e.g. 1960-2000 (network density of complete climate series is high) Precipitation: 795 stations (~55%) Tmin: 527 stations (~60%)
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ECSN Datamanagement Workshop 2005, E. Zenklusen
number of breakpoints detected: 0(), 1(), 2(), 3(), 4(), >5()
Precipitationonly complete series
1960-2000
VERAQCAlexandersson
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ECSN Datamanagement Workshop 2005, E. Zenklusen
number of breakpoints detected: 0(), 1(), 2(), 3(), 4(), >5()
Tminonly complete series
1960-2000
VERAQCAlexandersson
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ECSN Datamanagement Workshop 2005, E. Zenklusen
Lower(), equal() or higher () number of breakpoints if only complete series are tested
Tmin
Difference breakpointsall
- breakpointscomplete
1960-2000
VERAQCAlexandersson
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ECSN Datamanagement Workshop 2005, E. Zenklusen
Skill of VERAQC:CH-stations comparison with THOMAS
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VERAQC_epVERAQC_alex
0-3 m 3-6 m 6-12 m false alarms missed
Precipitation 1960-2000, only complete series
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Total amount of breakpointsdetected:VERAQC_ep: 79VERAQC_alex: 52
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ECSN Datamanagement Workshop 2005, E. Zenklusen
Skill of VERAQC:CH-stations comparison with THOMAS
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VERAQC_epVERAQC_alex
0-3 m 3-6 m 6-12 m false alarms missed
Tmin 1960-2000, only complete series
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Total amount of breakpointsdetected:VERAQC_ep: 197VERAQC_alex: 110
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ECSN Datamanagement Workshop 2005, E. Zenklusen
Has VERAQC detected the large adjustments and missed the small ones?
Precipitation(mean adjustment factors
of THOMAS)
Minimum temperature(mean adjustment amounts
of THOMAS)
detected missed detected missed
EP 21.0%(± 10.5)
14.0%(± 7.8)
0.81°C(± 0.46)
0.62°C(± 0.39)
SNHT 24.0%(± 13.9)
14.7%(± 7.3)
0.89°C(± 0.46)
0.61°C(± 0.38)
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ECSN Datamanagement Workshop 2005, E. Zenklusen
Summary and conclusions
ECA&D procedure is implemented and works With VERAQC an automated homogeneity test procedure
has been implemented and tested method shows unsatisfying results
significant loss of stations at the edge of investigated area sensitive to changes in the network density high number of undetected inhomogeneities and false alarms sensitive to inhomogeneities in “reference series”
(dispersion of inhomogeneities)
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ECSN Datamanagement Workshop 2005, E. Zenklusen
Outlook
Two ways to proceed: Improvement of VERAQC test procedure
reduce influences of the varying network density(anomalies as inputdata, flag breakpoints generated by network changes)
reduce false alarm rate(combination of test results, test tuning)
Calculation of deviation series according to THOMAS procedure
selection of reference stations due to correlation analysis use a mean of chosen reference series to calculate the deviations
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ECSN Datamanagement Workshop 2005, E. Zenklusen
Thank you for your attention
questions …?