AerGOM, an improved algorithm for stratospheric aerosol extinction retrieval from GOMOS observations – Part 2: Intercomparisons

Autor: C. É. Robert, C. Bingen, F. Vanhellemont, N. Mateshvili, E. Dekemper, C. Tétard, D. Fussen, A. Bourassa, C. Zehner
Jazyk: angličtina
Rok vydání: 2016
Předmět:
Zdroj: Atmospheric Measurement Techniques, Vol 9, Iss 9, Pp 4701-4718 (2016)
Druh dokumentu: article
ISSN: 1867-1381
1867-8548
DOI: 10.5194/amt-9-4701-2016
Popis: AerGOM is a retrieval algorithm developed for the GOMOS instrument onboard Envisat as an alternative to the operational retrieval (IPF). AerGOM enhances the quality of the stratospheric aerosol extinction retrieval due to the extension of the spectral range used, refines the aerosol spectral parameterization, the simultaneous inversion of all atmospheric species as well as an improvement of the Rayleigh scattering correction. The retrieval algorithm allows for a good characterization of the stratospheric aerosol extinction for a wide range of wavelengths.In this work, we present the results of stratospheric aerosol extinction comparisons between AerGOM and various spaceborne instruments (SAGE II, SAGE III, POAM III, ACE-MAESTRO and OSIRIS) for different wavelengths. The aerosol extinction intercomparisons for λ λ λ > 700 nm.Due to the unique observational technique of GOMOS, some of the results appear to be dependent on the star occultation parameters such as star apparent temperature and magnitude, solar zenith angle and latitude of observation. A systematic analysis is carried out to identify biases in the dataset, using the various spaceborne instruments as references. The quality of the aerosol retrieval is mainly influenced by the star magnitude, as well as star temperature to a lesser degree. To ensure good-quality profiles, we suggest to select occultations performed with star magnitude M T > 6 × 103 K. Stray-light contamination is negligible for extinction coefficients below 700 nm using occultations performed with a solar zenith angle > 110° but becomes important at larger wavelengths. Comparison of AerGOM results in the tropics shows an enhanced bias below 20 km that seem to confirm cirrus clouds as its cause. There are also differences between mid-latitude and tropical observations that cannot yet be explained, with a bias difference of up to 25 %.This bias characterization is extremely important for data users and might prove valuable for the production of unbiased long-term merged dataset.
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