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R. Van Malderen 1,5 , E. Pottiaux 2,5 , H. Brenot 3 and S. Beirle 4

Max Planck Institute for Chemistry. Royal Meteorological Institute of Belgium. Belgian Institute for Space Aeronomy. Solar-Terrestrial Centre of Excellence. Royal Observatory of Belgium. 1. 2. 3. 4. 5. R. Van Malderen 1,5 , E. Pottiaux 2,5 , H. Brenot 3 and S. Beirle 4.

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R. Van Malderen 1,5 , E. Pottiaux 2,5 , H. Brenot 3 and S. Beirle 4

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  1. Max Planck Institute for Chemistry Royal Meteorological Institute of Belgium Belgian Institute for Space Aeronomy Solar-Terrestrial Centre of Excellence Royal Observatory of Belgium 1 2 3 4 5 R. Van Malderen1,5, E. Pottiaux2,5, H. Brenot3 and S. Beirle4

  2. Introduction ROB What?inter-technique comparison between 4 different instruments measuring the same atmospheric variable Which variable? integrated water vapour (IWV) Where? world-wide, but first focus on Brussels, (50°48'N, 4°21'E, 100 m asl) as case study When? The different instruments cover different observation periods. Aims? • assess the quality of the different measurements: the precision - accuracy - performance of the instruments • obtain a better monitoring and understanding of the changing water vapourcontent in the atmosphere WMO CIMO TECO, Brussels, 16-18 Oct. 2012

  3. Outline ROB • Instruments and datasets • Case study: Brussels • Data overview • Scatter plots • Impact of cloudcover • World-wide data exploitation • Site selection • Scatter plot properties • Conclusions & Perspectives WMO CIMO TECO, Brussels, 16-18 Oct. 2012

  4. Instruments & datasets Case study: Brussels World-wide exploitation Conclusions & perspectives ROB • CIMEL sun photometer • direct sun measurements @ 940nm (and @ 675 and 870 nm for aerosol correction) • clear sky only • level 2 data from the AERONET website • GOME/SCIAMACHY/GOME-2 • air mass corrected differential optical absorption spectroscopy method applied to nadir measurements around 700 nm. • cloud cover is an issue • GNSS/GPS • International GNSS Service (IGS) database (homog. reprocessing) • at all weather conditions, always • Tsurf and psurf are needed: ZTD  IWV • Radiosondes(RS) • different types • launched at all weather conditions WMO CIMO TECO, Brussels, 16-18 Oct. 2012

  5. Instruments & datasets Case study: Brussels World-wide exploitation Conclusions & perspectives ROB • different instruments = different observation periods • scatterplots of simultaneous IWV measurementswithrespect to the GNSS device as reference WMO CIMO TECO, Brussels, 16-18 Oct. 2012

  6. Instruments & datasets Case study: Brussels World-wide exploitation Conclusions & perspectives ROB • biaswith GPS ranges between -0.6 mm and +0.6 mm • best overall agreement between GPS and CIMEL sunphotometer • regressionslopeclosest to 1 for all-weatherdevicesscatter plot  influence of cloudcover? GPS-CIMEL GPS-RS9x GPS-GOME(2)/SCIA WMO CIMO TECO, Brussels, 16-18 Oct. 2012

  7. Instruments & datasets Case study: Brussels World-wide exploitation Conclusions & perspectives ROB GPS-CIMEL • cloudcover↗ regressionslopes↘ and correlation coefficients ↘ • GPS measurementsincorporate contribution fromclouds in directions towards satellites WMO CIMO TECO, Brussels, 16-18 Oct. 2012

  8. Instruments & datasets Case study: Brussels World-wide exploitation Conclusions & perspectives ROB • selection of 28 sites world-wide (NH), with focus on CIMEL-GPS co-location and based on meteo data availability (GPS)! WMO CIMO TECO, Brussels, 16-18 Oct. 2012

  9. Instruments & datasets Case study: Brussels World-wide exploitation Conclusions & perspectives ROB • scatter plot propertiesfor the 28 co-locations, orderedwithincreasinglatitutefromleft to right • geographicaldependency? WMO CIMO TECO, Brussels, 16-18 Oct. 2012

  10. Instruments & datasets Case study: Brussels World-wide exploitation Conclusions & perspectives ROB • similarinter-technique conclusions as for the Brussels case study! WMO CIMO TECO, Brussels, 16-18 Oct. 2012

  11. Instruments & datasets Case study: Brussels World-wide exploitation Conclusions & perspectives ROB • althoughoriginally tracing other slants/directions, very good agreement between the ground-based (2) and in-situ (1) devices • The IGS database of GPS measurements and the AERONET sunphotometermeasurements are verypromising to beused for IWV trend analysis due to theirhomogeneous data reprocessing (IGS) and theirregular instrument calibration (AERONET). • The weather observations bias (partlyclearskyneeded) in the sunphotometer and GOME(2)/SCIAMACHY data series affects the comparisonwith all-weatherdevices, but whatis the impact on the trends?  subject of a subsequentstudy WMO CIMO TECO, Brussels, 16-18 Oct. 2012

  12. Instruments & datasets Case study: Brussels World-wide exploitation Conclusions & perspectives ROB Brussels (Belgium) Calgary (Italy) monthlymeans monthlymeans • althoughoverall good agreement, small difference in trend slope between GPS and radiosonde time series (-0.15 vs. -0.45 mm/decade) • RS IWV < IGS IWV in earlyyears: instrumentation change for RS? • Large difference in IWV trends (0.16 vs. 1.29 mm/decade) WMO CIMO TECO, Brussels, 16-18 Oct. 2012

  13. Instruments & datasets Case study: Brussels World-wide exploitation Conclusions & perspectives ROB Summary: all European IGS stations starting in 1995/1996 • ratherconsistent picture: IWV ↑ , mostsignificantly (> 0.5 mm/dec) in central Europe • trend difference in ZTD between 2 IGS stations (MADR, VILL) nearMadrid (both use the samemeteo station data) • Brussels? WMO CIMO TECO, Brussels, 16-18 Oct. 2012

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