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Verification
Verification with SYNOP, TEMP,and GPS data
P. Kaufmann, M. Arpagaus, MeteoSwissP. Emiliani., E. Veccia., A. Galliani., UGM
U. Pflüger, DWD
Verification
Surface Verification with SYNOP
Verification scores neglecting a diurnal cycle
Verification
3
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Availability of SYNOP data on GTS
Red dots: all “main” SYNOPS (6-hourly) availableGB: Sea level pressure but no pressure at station heightSpain, Italy, Balkans: Many stations do not report during the night (not even the automatically measured parameters)
PMSL
PS
Verification
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SYNOP Pressure: Standard Deviation of Errors
Standard deviation of errors (STDE) is considerably larger in winter than in summerIn winter much larger in the north than in the south
Winter 2003/4, 42 – 48 h
Summer 2004, 42 – 48 h
Verification
5
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SYNOP Pressure
Dependence of mean error (ME) on forecast rangeWinter: IncreaseSummer: Decrease
Winter 2003/4
Summer 2003
but …
Verification
6
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SYNOP Pressure
… decrease in summer disappeared in summer 2004Effect of ECMWF-IFS boundary conditions?Supported by results of IFS test chain summer 2003
Summer 2004
Verification
7
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Model Grid Points over Water on Coasts and Lakes
Winter 2003/4, forecast range 42 – 48 hCoasts and lakes: Large bias if model grid points over water are used!but: small bias for small islands and oil platforms – not all water points need to be eliminated
Nearest grid point regardless of surface type
Land points preferred
Verification
8
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SYNOP Temperature
Strong cold bias in winter (see verification of daily cycle), pronounced in AlpsWeak cold bias in summerStandard deviation high in complex terrain
Winter 2003/4, 42 – 48 h
STDE
ME
Summer 2004, 42 – 48 h
ME
Verification
Verification with TEMPs
Vertical profiles
Verification
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TEMP Geopotential Summer 2004 (JJA)
Sharp increase of mean error in stratosphere, reason unclearStandard deviation largest around tropopause LM only: negative bias below 600 hPa at +48 h
LM ME aLMo ME STDE
Verification
11
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TEMP Geopotential aLMo – LAMI
“South of the Alps”aLMo 6 stationsLAMI 7 stations
LAMI only July, AugustBias differences to aLMo below 500 hPa:
Bias at +12 h more positiveNegative bias at +48 hLAMI and LM both driven by GME, aLMo by IFS
aLMo ME
aLMo ME
Verification
12
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TEMP Temperature Summer 2004 (JJA)
Cold bias up to 0.7 K between 1000 and 750 hPaWarm bias 750 – 500 hPa, increase with forecast time up to 0.6 KWeak cold (LM: no) bias 500 – 250 hPaaLMo only: Strong cold bias in the stratosphere (150 hPa)Analysis (+00) h far better than all others – effect of nudgingStandard deviation largest spread around tropopause (200 hPa)
LM ME aLMo ME STDE
Verification
13
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TEMP Temperature aLMo – LAMI
LAMI only July, AugustSmaller cold bias near surfaceWarm bias extends higher up, up to 200 hPa level
aLMo ME
Verification
14
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TEMP Relative humidity Summer 2004 (JJA)
Bias of varying sign, 5 – 8%, related to bias of temperature?Moist below 850 hPaDry between 850 hPa and 500 hPaMoist between 500 hPa and 200 hPaDry above 200 hPaClear distinction between analysis and forecastsStandard deviation nearly uniform over large part of troposphere
LM ME aLMo ME STDE
Verification
15
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TEMP Humidity aLMo – LAMI
Relative humidity and dew point temperature are not directly comparable
?
aLMo ME
Relative humidity bias Dew point bias
Verification
16
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Long term evolution of RH RMSE
Decrease of RMSE for LM in 2004Effect of prognostic ice scheme and assimilation of pseudo-TEMPS from ECMWF into GME
LM RMSE of relative humidity
Verification
17
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TEMP Wind speed aLMo Summer 2004 (JJA)
Mean error well below 1 m/sSlightly increasing with forecast time Largest in boundary layer and near or above tropopause
Boundary layer: Different sign of bias for LM and aLMoStandard deviation largest at tropopause, consistent with strongest winds
LM ME aLMo ME STDE
Verification
18
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TEMP Wind speed aLMo – LAMI
Only stations south of the AlpsLargest bias at 700 hPa
Verification
Verification with GPS
Vertically Integrated Water Vapour
Verification
20
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GPS Integrated Water Vapour
Path delay (W – W0) caused by refraction
Error for geodesySignal for meteorology
Refractivity index depends onDry-air density (hydrostatic delay)Humidity (wet delay)
Wet delay = total delay – hydrostatic delayIntegrated water vapour:
Need of surface pressure and temperature from nearby SYNOPCurrently calculated by KNMI
Verification
21
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GPS data availability
Three processing centers deemed most reliable
Each covers primarily its home countryTime series have many gapsProcessing centers are not WMO members
LPT Switzerland
GFZ Germany GOP Czechia
Verification
22
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GPS IWV BIAS
Weak dry bias outside complex topographyBias (or mean error) is largest
In summerIn the mountains
Possible explanationsLarger specific humidity contents in summer than in winterHeight differences GPS antenna – SYNOP station – model surface are largest in mountainous terrain Summer 2003
Winter 2002/3
Verification
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GPS IWV Standard Deviation
STDE largest in summerHomogeneous in whole model domain
Problem in mountains only affect bias, i. e. values are shifted by constant offset
Summer 2003
Winter 2002/3
Verification
24
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Summary and Outlook
Model verification often stops at national boundaries: Model comparison difficultSurface verification with SYNOP
Pressure increase/decrease with forecast rangeStrong cold bias in winterNeed for continuous, quality-controlled data for the whole of Europe!
Model comparison even for TEMP difficult. Differences:Set of stationsTime (definition of a season)Statistical measures used: Only two out of ME, MAE, STDE, RMSE
GPSData availability problem (currently only available through European project; each centre provides subset only )Zenith total delay (ZTD) verification in the future to avoid interpolation problems between SYNOP and GTS locations