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Investigating Global Long-term Data Sets of the Atmospheric H 2 O VCD and of Cloud Properties

Investigating Global Long-term Data Sets of the Atmospheric H 2 O VCD and of Cloud Properties T. Wagner 1 , S Beirle 1 , M. Grzegorski 1 , M. Penning de Vries 1 , U. Platt 2 MPI für Chemie, Mainz, Germany Institut für Umweltphysik, University of Heidelberg, Germany. MPI Mainz Germany.

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Investigating Global Long-term Data Sets of the Atmospheric H 2 O VCD and of Cloud Properties

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  1. Investigating Global Long-term Data Sets of the Atmospheric H2O VCD and of Cloud Properties • T. Wagner1, S Beirle1, M. Grzegorski1, M. Penning de Vries1, U. Platt2 • MPI für Chemie, Mainz, Germany • Institut für Umweltphysik, University of Heidelberg, Germany MPI Mainz Germany • What can new satellite observations offer? (spectral measurements) • Model results & measurements of O4 & O2 absorption and Ring effect • Case studies • Conclusions

  2. What additional information can be expected from spectral measurements? (e.g. GOME) GOME & SCIA spectral properties O4 Both, trace gas absorptions and Ring effect (Raman scattering) are affected by modifications of the atmospheric light path, especially due to clouds. => They can provide information about the internal cloud structure

  3. Ring effect: ‚Filling-in‘ of Fraunhofer lines due to rotational Raman-scattering Solar Fraunhofer line in direct and scattered light Ratio spectrum of scattered and direct solar light The Ring effect is strongest in the UV Optical depth  2% Optical depth  10% GOME red GOME UV

  4. Cloud effects Hurrican Fran, 04.09.1996: NOAA GOES-8 Satellite, 16:02 UTC

  5. Realistic modelling of microscopic and macroscopic cloud properties Green points indicate scattering points of photons => reception area of the detector Backward Monte Carlo (TRACY-II, T. Deutschmann) aerosol layer aerosol layer Moderate forward peak Instrument Instrument Tim Deutschmann, IUP Heidelberg Tim Deutschmann, IUP Heidelberg Suniti Sanghavi, IUP Heidelberg aerosol layer Strong forward peak Instrument

  6. Model results as function of cloud altitude: Different dependence for O2 and O4 • Absorption is expresses as air mass factor (AMF) • It is a measure of sensitivity • AMF = 1 indicates an absorption corresponding to the vertical atmospheric column

  7. Model results as function of cloud altitude: Different dependence for O2 and O4 Ring effect shows monotonous decrease -In general, clouds cause a decrease of the absorptions of O2 and O4 and of the strength of the Ring effect -the Ring effect hardly depends on the surface albedo

  8. Dependence of the O2 absorption on cloud fraction and cloud altitude (vertical thickness: 1km,OD: 50) Results for surface albedo of 2%

  9. Long time mean 1996-2003 from GOME Normalised O2 absorption Derived cloud top height [km] Wagner et al., 2008

  10. Spatial correlation analyses between the GOME and ISCCP data sets (annual average) of effective cloud fraction (red) and cloud amount (blue). After the ISCCP cloud amount is corrected for the effect of changing optical depth, improved agreement with the GOME data is found.

  11. Correlation analyses between the GOME and ISCCP data sets (spatial variation of the annual average) of cloud height (red: uncorrected ISCCP top height, blue corrected ISCCP effective cloud top height). After the ISCCP data is corrected for the effect of changing optical depth, improved agreement with the GOME data is found.

  12. Correlation between effective cloud top height from FRESCO and derived from our Ring analysis (GOME observations in November 2000 for SZA 19-23°, CF >50%). Depending on the assumed cloud properties in the forward model, different effective cloud top heights are derived from the Ring effect observations.

  13. Special cases: I) Separation of the effects of clouds and snow/ice Dundee Satellite Receiving Station, Dundee University, Scotland (http://www.sat.dundee.ac.uk/).

  14. Special cases: II) Increased absorptions of O2 and O4 Typically the shielding effect of clouds is dominant It can be caused by clouds or mountains

  15. Special cases: II) Increased absorptions of O2 and O4 Sometimes, strongly enhanced absorptions indicate long light paths inside clouds The Ring effect shows no enhancement

  16. The cloud is also seen by the microwave measurements (liquid water path)

  17. Additional examples of strongly enhanced absorptions (about 10 per month for GOME-1 observations)

  18. 3-D effects (TRACY-2) Modelled Radiance

  19. 3-D effects (TRACY-2) Modelled O4 AMF

  20. 3-D effects (TRACY-2) Modelled Ring effect

  21. 1 day of H2O from GOME-1

  22. 1 day of H2O from GOME-2 (similar results from S. Noel, IUP Bremen) H2O SCD derived from GOME-2 for 20.01.2008. Due to the high spatial resolution and almost daily global coverage many details of the atmospheric H2O circulation can be seen.

  23. H2O anomalies during ENSO

  24. Cloud fraction anomalies during ENSO

  25. No Cloud anomalies in time series!

  26. Conclusions • Spectral measurements (O2 & O4 absorption & Ring effect) are well suited for cloud retrievals • Monte-Carlo radiative transfer modelling provides optimum link between observations and macroscopic and microscopic cloud properties; 3-D effects should be considered • Ring effect and O2/O4 absorptions are affected by clouds and snow/ice differently • Strongly enhanced absorptions found in GOME data (about 10 times per month, especially frequent for narrow swath mode) • New H2O product from GOME-2 • Application to atmospheric studies, e.g. ENSO

  27. Global average distribution of the Ring effect for November and December 2000 (left: cloud fraction <5%, right: cloud fraction >20%). In areas with high clouds, especially over the continents, the weakest Ring effect is found.

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