Abstract
Abstract. SCIAMACHY (SCanning Imaging Absorption spectroMeter for Atmospheric CHartographY) lunar occultation measurements have been used to derive vertical profiles of stratospheric water vapor for the Southern Hemisphere in the near infrared (NIR) spectral range of 1350–1420 nm. The focus of this study is to present the retrieval methodology including the sensitivity studies and optimizations for the implementation of the radiative transfer model on SCIAMACHY lunar occultation measurements. The study also includes the validation of the data product with the collocated measurements from two satellite occultation instruments and two instruments measuring in limb geometry. The SCIAMACHY lunar occultation water vapor measurement comparisons with the ACE-FTS (Atmospheric Chemistry Experiment Fourier Transform Spectrometer) instrument have shown an agreement of 5% on the average that is well within the reported biases of ACE in the stratosphere. The comparisons with HALOE (Halogen Occultation Experiment) have also shown good results where the agreement between the instruments is within 5%. The validations of the lunar occultation water vapor measurements with MLS (Microwave Limb Sounder) instrument are exceptionally good, varying between 1.5 to around 4%. The validations with MIPAS (Michelson Interferometer for Passive Atmospheric Sounding) are in the range of 10%. A validated dataset of water vapor vertical distributions from SCIAMACHY lunar occultation measurements is expected to facilitate the understanding of physical and chemical processes in the southern mid-latitudes and the dynamical processes related to the polar vortex.
Highlights
SCIAMACHY (SCanning Imaging Absorption spectroMeter for Atmospheric CHartographY) (Burrows et al, 1995) is a moderate resolution 8-channel grating spectrometer on-board Envisat, launched in 2002
Owing to its longer chemical lifetime with respect to the timescale of the stratospheric dynamical processes, water vapor is used as an excellent tracer of atmospheric circulations and waves, etc. (Pan et al, 2007)
It should be noted here that in its comparisons with other satellite instruments including Atmospheric Chemistry Experiment (ACE)-FTS, Halogen Occultation Experiment (HALOE) and MIPAS, the MLS water vapor version 2.2 is noted (Lambert et al, 2007) to exhibit sharp differences or kinks around 26.1–31.6 hPa, which is the region within a few kilometres from 25 km
Summary
SCIAMACHY (SCanning Imaging Absorption spectroMeter for Atmospheric CHartographY) (Burrows et al, 1995) is a moderate resolution 8-channel grating spectrometer on-board Envisat, launched in 2002. Since the launch of its host satellite, the instrument has provided total columns as well as vertical profiles of atmospheric parameters relevant to ozone chemistry, air pollution and global climate change issues, from the troposphere up to the mesosphere (Gottwald and Bovensmann, 2011). SCIAMACHY lunar occultation measurements have provided valuable datasets of atmospheric species, as ozone, nitrate radical and nitrogen dioxide (Amekudzi et al, 2005, 2009), which have been used for physical and chemical interpretations and analysis. Azam et al.: SCIAMACHY lunar occultation water vapor measurements tropopause This has to pass through the cold trap of the temperature minimum at the tropopause region; above this region the oxidation of methane and other hydrocarbons release hydrogen containing free radicals with H2O being formed by the reaction with OH. The measurements give localized coverage where the vertical profiles of stratospheric constituents are retrieved with a vertical resolution of 3–4 km
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