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(1) Institute of Environmental Physics, University of Bremen, Germany

First retrievals of the water vapor content in the upper troposphere and lower stratosphere from SCIAMACHY limb measurements. A. Rozanov 1 , M. Weber 1 , S. Dhomse 1,2 , V. Rozanov 1 , H. Bovensmann 1 , and J.P. Burrows 1. (1) Institute of Environmental Physics, University of Bremen, Germany

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(1) Institute of Environmental Physics, University of Bremen, Germany

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  1. First retrievals of the water vapor content in the upper troposphere and lower stratosphere from SCIAMACHY limb measurements A. Rozanov1, M. Weber1, S. Dhomse1,2, V. Rozanov1, H. Bovensmann1, and J.P. Burrows1 (1) Institute of Environmental Physics, University of Bremen, Germany (2) Now at the School of Earth and Environment, University of Leeds, UK

  2. Motivation • Tropical lower stratospheric (LS) water vapor decrease after 2000 • Related to increase in tropical upwelling velocities (Randel et al. 2006) • Related to an increase in extratropical wave-forcing (Dhomse et al. 2008) • Is the lower stratosphere getting drier as a result of an enhanced Brewer-Dobson circulation? • Is this a result of climate change (trend) or part of decadal variability? • Are there long-term changes in tropical convection? Dhomse et al., 2008

  3. Motivation • HALOE, SAGE II, and POAM ceased operation in 2005/2006 • Need for continuous satellite observations (ACE-FTS, MLS, MIPAS, SCIAMACHY) • ENVISAT (MIPAS, SCIAMACHY) has sufficient overlap with HALOE/SAGE (2002-2005) for extending time series, the mission is planned to be extended to 2013 • MIPAS and SCIAMACHY as limb emission/scatter sounder have a better spatial sampling than occultation instruments

  4. Limb measurement sequence • Vertical resolution: ~ 2.5 km at tangent point • Typical horizontal resolution in azimuth: 240 km • Horizontal resolution in flight direction: ~ 400 km • Duration of limb sequence: 60 sec • Global coverage: 6 days at the equator

  5. Retrieval method Viewing geometry and geolocation from the measurements • Forward modeling, SCIATRAN 3.0 • Fully spherical for SS • Approximation for MS Simulated limb spectra Weighting functions Measured and simulated limb spectra Vertically integrated WFs • Pre-processing (DOAS-type fit) at each tangent height • Shift and squeeze correction • Spectral corrections Next iteration Correction parameters Measured and simulated limb spectra with all corrections from the pre-processing step applied Weighting functions A priori constraints • Main inversion procedure • Solution: Optimal Estimation type with additional smoothing • Measurement vector: differential spectral signal at all selected tangent heights(12 - 28 km) • State vector: trace gas number densities at al altitude levels Vertical distributions of trace gas number densities

  6. Selection of spectral range Simulated limb spectrum at 12 km tangent height “Stratospheric part”: altitude > 10km “Tropospheric part”: altitude <= 10 km Selected spectral range: 1375 -1390 nm

  7. Example spectral fits Example spectral fits for SCIAMACHY orbit 4905 on February 6th, 2003, 18:13 UTC at 49oN,120oW, SZA@TP = 69o Tangent height 12.6 km Tangent height 19.2 km

  8. Sensitivity of SCIAMACHY limb measurements Dependence on a priori information Averaging kernels Theoretical precision

  9. Comparisons to independent measurements (1) HALOE: space-borne solar occultation measurements at 6.6 m February 10, 2003 (orbit 4957) SCIA: 9:28 UTC, HALOE: 6:32 UTC February 6, 2003 (orbit 4905) SCIA: 18:12 UTC, HALOE: 14:40 UTC

  10. Comparisons to independent measurements (2) HALOE: space-borne solar occultation measurements at 6.6 m February 15, 2003 (orbit 5028) SCIA: 8:28 UTC, HALOE: 17:05 UTC February 10, 2003 (orbit 4961) SCIA: 16:10 UTC, HALOE: 11:20 UTC

  11. Comparisons to independent measurements (3) In situ measurements at Boulder station: balloon-borne frost point hygrometer July 7/8, 2003 (orbit 7080) SCIA: 16:57 UTC, Balloon: 5:04 UTC July 2, 2003 (orbit 6994) SCIA: 16:45 UTC, Balloon: 5:16 UTC

  12. Comparisons to independent measurements (4) In situ measurements at Boulder station: balloon-borne frost point hygrometer January 27, 2004 (orbit 9986) SCIA: 17:18 UTC, Balloon: 18:18 UTC November 20, 2003 (orbit 9012) SCIA: 16:15 UTC, Balloon: 18:16 UTC

  13. Conclusions • First retrievals of the vertical distributions of the water vapor in the lower stratosphere and upper troposphere from SCIAMACHY limb measurements in near infrared spectral range are successfully done. • The retrieval algorithm has a good sensitivity between 12 and 23 km allowing the retrieval precision of 20-30% to be achieved. • From the limited comparison of SCIAMACHY water vapor with HALOE and Boulder frost hygrometer data so far, good agreement is found between 14 and 21 km. • Below 14 km there appears to be a dry bias in the HALOE data. • A stronger scattering of retrieval results is observed above 21 km which is related to a decreased signal to noise ratio in the measured spectra • Additional investigations are needed to study the effect of clouds located immediately below the instrument field of view as well as of the stratospheric aerosols.

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