Investigating the Effect of Upper Tropospheric Cirrus Clouds on Tropical MIPAS Level 2 Water Vapour and Ozone Retrievals

In this paper, the performance of the operational Level 2 MIPAS processor for offline data (versions 4.61 and 4.62) in the presence of cloud is examined. Using simulations of typical cloud scenarios, based on MIPAS cloud statistics for the tropics, the impact of varying cloud influence at 12 km and the tangent altitude above (i.e. 15 km) is investigated. It is found that with increased cloud presence, water vapour (H2O) concentrations possess a positive bias at the cloud altitude with a simultaneous negative bias at 15 km. The effect on ozone (O3) concentrations is not as significant as for H2O. However, increasing cloud influence is found to increase the operational random retrieval error for both H2O and O3. Using these results, new recommendations for cloud flagging tropical H2O and O3 retrievals are made. It is important that cloud information from MIPAS is used in correspondence with H2O and O3 profiles in the tropics.