A new non-LTE retrieval method for atmospheric parameters from MIPAS-ENVISAT emission spectra

The Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) is a high-resolution limb emission sounder on board the European polar platform ENVISAT to be launched in 2001. A large number of trace gases relevant to stratospheric ozone chemistry and global change are expected to be retrieved from measured IR spectra. In this paper we present an innovative retrieval method accounting for non-local thermodynamic equilibrium (non-LTE) as part of the MIPAS semi-operational data processor developed at the Institut fur Meteorologie und Klimaforschung (IMK). The new approach enables the treatment of vibrational, rotational, and spin non-LTE as well as a dependence of the non-LTE state distribution on the retrieval target quantities. The method has been tested for its application to the non-LTE analysis of 5.3 mum daytime emissions of NO((II)-I-2). A conventional non-LTE retrieval approach using ab initio vibrational temperatures of NO cannot be applied due to rotational and spin non-LTE in the thermosphere, and the dependence of stratospheric vibrational temperatures on the NO abundance itself. The ability of the developed non-LTE inversion tool to retrieve stratospheric NO abundances, NO and kinetic temperature in the thermosphere, and important non-LTE process parameters has been investigated.