Wednesday, February 18, 2015

ATMOS 2015: Validation and Alternative Retrievals of GOMOS Ozone Profiles in the UTLS Altitude Region


submitted the abstract below to the The European Space Agency's ATMOS 2015 – Advances in Atmospheric Science and Applications conference. Let's hope it'll get accepted...

Validation and Alternative Retrievals of GOMOS Ozone Profiles in the UTLS Altitude Region 
Janne Hakkarainen, Iolanda Ialongo, Viktoria Sofieva, Marko Laine, Johanna Tamminen, Erkki Kyrölä 
Finnish Meteorological Institute, Finland 
Global Ozone Monitoring by Occultation of Stars (GOMOS) is a satellite instrument onboard the ENVISAT platform that was in operation during 2002–2012. During this period, GOMOS observed about 880 000 vertical profiles of ozone, NO2, NO3 and aerosols. About half of these measurements were made during nighttime. The GOMOS measurement principle is based on the stellar-occultation technique. 
In this paper, we present rigorous validation and characterization of operational GOMOS ozone profiles in the upper troposphere lower stratosphere (UTLS) altitude region. The GOMOS profiles are validated using ozone soundings from NDACC (Network for the Detection of Atmospheric Composition Change). The results show a strong ozone overestimation by GOMOS in the tropopause region and below. The median relative difference grows up to 100 % and is particularly large in the tropics. The influence of retrieval uncertainties and star properties on the high bias in the troposphere is also investigated. 
In addition to the validation and characterization of the operational data product, we also show recent advantages of alternative retrieval algorithms that are designed in particular for processing the GOMOS measurements for UTLS applications. The retrievals are performed using re-designed two-step algorithm and alternative one-step algorithm. In one-step retrieval, the spectral and the vertical inversions of the two-step algorithm are executed simultaneously. This approach allows a better use of the smoothness prior information and the prior given for example to aerosol parameters affects the other species too. This feature is critical when going near the detection limit. The preliminary results show drastic improvement of the quality of the GOMOS profiles in the UTLS altitude region when compared against NDACC ozone soundings. To further evaluate the novel UTLS dataset (consisting of 171 233 profiles form 49 brightest starts in full dark), we perform a comparison against OSIRIS ozone dataset, which has shown reliable results in the UTLS altitude region.

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