The effect of considering polar vortex dynamics in the validation of satellite total ozone observations

• Published in: Atmospheric research Vol. 238; p. 104870
• Main Authors: Paschou, Peristera, Koukouli, Maria-Elissavet, Balis, Dimitrios, Lerot, Christophe, Van Roozendael, Michel
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.07.2020
• Subjects: GOME2; OMI; Potential vorticity; Total ozone column; Validation; Validation; Potential vorticity; OMI; Total ozone column; GOME2
• ISSN: 0169-8095; 1873-2895
• DOI: 10.1016/j.atmosres.2020.104870

The main aim of this paper is to demonstrate the magnitude in which validation results of space-based total ozone column, TOC, measurements are affected by the location of the polar vortex. Potential Vorticity is used as an indicator to determine the polar vortex's boundary and surface area, provided by ERA-Interim reanalysis datasets from the European Centre for Medium-Range Weather Forecasts (ECMWF). The total ozone measurements that were examined fall within the hemispherical winter-spring period, focusing on middle and high latitudes on both hemispheres. The space-based total ozone data produced by the GODFIT (GOME-type Direct FITting) v4 algorithm as applied to the OMI/Aura, GOME-2/Metop-A and Metop-B observations, part of the European Space Agency's Ozone Climate Change Initiative project, are compared to TOC measurements from Brewer and Dobson spectrophotometers archived at the World Ozone and Ultraviolet Radiation Data Centre (WOUDC) repository. The satellite-to-ground collocations were classified depending on whether both satellite and ground-based measurements are inside or outside the polar vortex (matched) or one measurement is inside whereas the other one is outside the polar vortex (mismatched). It is shown that the matched cases present an improved agreement between satellite and ground TOC measurements compared to the mismatched cases. Considering all examined stations for GOME2-A, GOME2-B, and OMI, the mean bias for the mismatched cases was found to be 2.22 ± 0.4%, 1.84 ± 0.57%, and 1.93 ± 0.39% respectively, while for the matched cases was found to be 1.46 ± 0.17%, 1.69 ± 0.22%, 1.7 ± 0.19% respectively. For the three satellite sensors, the mismatched cases do not exceed 3.3% of the total available collocations per station during the winter-spring period between years 2007 and 2017, where applicable. Hence, on a global scale, the exclusion of mismatched collocated measurements does not cause significant changes and the resulting impact on the validation of the satellite TOCs is small. However, when considering single stations consistently affected by the polar vortex, we conclude that mismatched cases should be excluded from the comparisons. •Satellite ozone validation efforts may depend on the location of the polar vortex.•Different columns may be observed by the satellite and the ground-based observations.•For ten years of collocations very few mismatched cases are found on a global scale.•For individual stations the mismatched cases could be excluded.