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 - PowerPoint PPT Presentation
SADDU Meeting, IUP/IFE University of Bremen, SADDU Meeting, IUP/IFE University of Bremen, Bremen, Germany, 16 - 17 June, 2008 Bremen, Germany, 16 - 17 June, 2008 First retrievals of the water vapor First retrievals of the water vapor content in the upper troposphere content in the upper troposphere and lower stratosphere from and lower stratosphere from SCIAMACHY limb measurements 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 (2) Now at the School of Earth and Environment, University of Leeds, UK
Transcript
SADDU Meeting, IUP/IFE University of Bremen, Bremen, SADDU Meeting, IUP/IFE University of Bremen, Bremen, Germany, 16 - 17 June, 2008Germany, 16 - 17 June, 2008
First retrievals of the water vapor content in First retrievals of the water vapor content in the upper troposphere and lower the upper troposphere and lower
stratosphere from SCIAMACHY limb stratosphere from SCIAMACHY limb measurements 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
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MotivationMotivation
Dhomse et al., 2008
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?
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MotivationMotivation
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
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
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Retrieval methodRetrieval method
Forward modeling, SCIATRAN 3.0Fully spherical for SSApproximation for MS
Viewing geometry and geolocation from the measurements
Simulated limb spectraWeighting functions
Pre-processing (DOAS-type fit) at each tangent heightShift and squeeze correctionSpectral corrections
Main inversion procedureSolution: 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
Nex
t ite
ratio
n
Measured and simulated limb spectraVertically integrated WFs
Correction parameters
Measured and simulated limb spectra with all corrections from the pre-processing step appliedWeighting functionsA priori constraints
Vertical distributions of trace gas number densities
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Selection of spectral rangeSelection of spectral range
Selected spectral range: 1375 -1390 nm
Simulated limb spectrum at 12 km tangent height
“Stratospheric part”: altitude > 10km
“Tropospheric part”: altitude <= 10 km
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Example spectral fitsExample 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
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Sensitivity of SCIAMACHY limb measurementsSensitivity of SCIAMACHY limb measurements
Averaging kernels Theoretical precision
Dependence on a priori information
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Comparisons to independent measurements (1)Comparisons to independent measurements (1)
HALOE: space-borne solar occultation measurements at 6.6
February 6, 2003 (orbit 4905)SCIA: 18:12 UTC, HALOE: 14:40 UTC
February 10, 2003 (orbit 4957)SCIA: 9:28 UTC, HALOE: 6:32 UTC
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Comparisons to independent measurements (2)Comparisons to independent measurements (2)
HALOE: space-borne solar occultation measurements at 6.6
February 10, 2003 (orbit 4961)SCIA: 16:10 UTC, HALOE: 11:20 UTC
February 15, 2003 (orbit 5028)SCIA: 8:28 UTC, HALOE: 17:05 UTC
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Comparisons to independent measurements (3)Comparisons to independent measurements (3)
In situ measurements at Boulder station: balloon-borne frost point hygrometer
July 2, 2003 (orbit 6994)SCIA: 16:45 UTC, Balloon: 5:16 UTC
July 7/8, 2003 (orbit 7080)SCIA: 16:57 UTC, Balloon: 5:04 UTC
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Comparisons to independent measurements (4)Comparisons to independent measurements (4)
In situ measurements at Boulder station: balloon-borne frost point hygrometer
November 20, 2003 (orbit 9012)SCIA: 16:15 UTC, Balloon: 18:16 UTC
January 27, 2004 (orbit 9986)SCIA: 17:18 UTC, Balloon: 18:18 UTC
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ConclusionsConclusions
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.
