A MIPAS Cloud-Aerosol Index and Top height Product
Sembhi, Harjinder1; P. Moore, David2; Trent, Timothy2; Remedios, John1
1University of Leicester, UNITED KINGDOM; 2NCEO/University of Leicester, UNITED KINGDOM
Detection of the presence of clouds and aerosols is important for infra-red, limb-viewing instruments. This is evident from the spectra recorded by the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS). Initially, this interest was in the removal of cloud-affected data so that trace gas retrievals could be more accurate; work in this context has been performed in the frame of the MIPAS Quality working Group. However, it has also become clear that MIPAS cloud detection provides considerable sensitivity to clouds and aerosols which are important in their own right. This work was undertaken in the frame of the ESA MIPClouds project.
In this paper we describe a new cloud-aerosol index and top height (CATH) product derived from MIPAS emission spectra, resulting from our studies; the data product will be available online for the entire mission data set. Specifically, we present simulation results used to determine improved cloud and aerosol detection thresholds for the 12 µm spectral region. The new thresholds allow much more sensitive detection of particle distributions in the UTLS, with extinction detection limits above 13 km often better than 10−4 km−1, with values approaching 10−5 km−1 in some cases. Using these data, we also associate a cloud/aerosol top height with each MIPAS vertical profile (sweep) of the atmosphere.
In order to assess the accuracy of MIPAS CATH, we will present an inter-comparison of MIPAS CATH with cloud and aerosol top heights derived from HIRDLS and CALIOP and show that top height distributions and occurrence frequencies (between 12 km and 20 km) are in good agreement with these contemporaneous instruments. The results highlight that cloud and aerosol UTLS particle distributions derived from high-resolution limb sounders are strongly consistent with lidar observations. Furthermore, to assess the sensitivity of MIPAS CATH to monitor aerosol injections in the UTLS, the results for several pollution case studies including wildfire and volcanic events will be presented. Finally, we comment on the possibilities for discriminating types of aerosol/cloud in MIPAS data.