Vertical distribution of propane and ethane in the UTLS from MIPAS observations using new spectroscopic data

The Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) measured the atmospheric limb emission in the thermal-infrared spectral region on board the ENVISAT satellite in the time span from June 2002 to April 2012. We used MIPAS data to study seasonal and latitudinal variations of propane (C3H8) and ethane (C2H6) in the upper troposphere lower stratosphere (UTLS) region. Retrievals were made using the 700-800 cm-1 spectral region, where new spectroscopic data of ethane had become available. To make feasible the joint retrieval of propane and ethane from their extremely weak spectral features, we used the Optimized Retrieval Model (ORM), the scientific prototype of the ESA level 2 processor for MIPAS, upgraded with the Multi-Target Retrieval (MTR) functionality and with the possibility to use Optimal Estimation (OE) to apply external constraints to the state vector. In order to evaluate the sensitivity of MIPAS measurements to seasonal and latitudinal distribution of C3H8 and C2H6 we analysed a dataset containing measurements in nominal observation mode acquired in selected dates of each month of the year 2008. Preliminary results on propane and ethane global UTLS distribution and on their seasonal behaviour will be presented.