Retrievability of Upper Tropospheric Species and Parameters from MIPAS/ENVISAT Data

Abstract

ENVISAT with MIPAS (Michelson Interferometer for Passive Atmospheric Sounding) (Fischer and Oelhaf, 1996) on board was successfully launched on 1st March, 2002. Since 24th March 2002, MIPAS has been measuring high-quality mid-infrared limb emission spectra with 0.035 cm-1 spectral resolution. The non-operational scientific level-2 data analysis of MIPAS/ENVISAT data to be performed at IMK has been developed further. The work of this project was focussed on various retrieval aspects in the upper troposphere region. On the basis of synthetic spectra, the information content of the spectra was analysed with respect to about 45 trace species, temperature and microphysical properties of cirrus clouds. The retrieval strategy for more than 30 trace species was set up, verified, and fine-tuned within test retrievals. Up to 20 species in the upper troposphere region can be detected with total accuracy (including all relevant systematic error sources) better than ±100 %, many of them better than ±10 %. Among these species are constituents which are of utmost interest for the understanding of the global and regional ozone budget in the upper troposphere, like acetone, NMHCs, PAN, or HO2. For the first time the impact of scattering of mid-infrared tropospheric radiation into the line-of-sight by cirrus particles was modelled with high spectral resolution. Spectrally high resolved signatures from tropospheric radiation scattered into the line-of-sight allow an improvement in the retrievability of microphysical parameters of cirrus clouds. The observation and retrieval scenarios to be applied for the derivation of tropical water vapour volume mixing ratio (VMR) close to the tropical tropopause was optimised with respect to accuracy versus vertical resolution. The achievable accuracy and vertical resolution is high enough to contribute to questions referring to processes in the tropical tropopause layer. First available MIPAS spectra were inspected in order to verify the predictions achieved on the basis of simulated measurements.