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The potential for improved trace gas retrievals from MIPAS in the presence of clouds

Alison Waterfall(1), Richard Siddans(1), Brian Kerridge(1) and Jolyon Reburn(1)

(1) Rutherford Appleton Laboratory, Rutherford Appleton Laboratory, Didcot, OX11 0QX, United Kingdom


The Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) measures high resolution limb infrared emission spectra from the mesosphere down into the upper troposphere, allowing the concentrations of many trace gas species to be derived. However, in the lower part of this region, cloud contamination becomes a particular problem in producing consistently good quality retrievals of upper tropospheric trace gases in the scientifically interesting regions of the tropics. In the operational processor, a cloud index threshold is defined below which retrievals are rejected as too cloudy to be retrieved, and above which the spectra can be subject to the normal trace gas retrievals. However, for a range of cloud conditions corresponding to cloud index values around this threshold, cases will exist whereby the presence of cloud in the spectra would unduly influence the normal trace gas retrievals, but where sufficient information exists that if cloud were to be more explicitly included in the retrieval process then improved trace gas information may be obtainable, along with potentially useful information on the cloud.

In this presentation, we will present results investigating the potential for trace gas retrievals of water vapour and ozone in the presence of clouds, using a forward model capable of simulating multiple scattering in 3D cloudy atmospheres.