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Comparison of OMI-DOAS satellite total ozone column observations with ground-based data from direct and diffuse solar irradiance in the Southwest Iberian Peninsula

Manuel Anton(1), D. Bortoli(2), J.M. Vilaplana(3), M. Kroon(4), A.M Silva(2,5), A.F. Domingues(2), A. Serrano(1), M.L. Cancillo(1) and B. de la Morena(3)

(1) Universidad de Extremadura, Avd. de Elvas, s/n, 06071 Badajoz, Spain
(2) Évora Geophysics Centre (CGE), University of Évora, Évora, Portugal
(3) Estación de Sondeos Atmosférico “El Arenosillo”, INTA, Huelva, Spain
(4) Royal Netherlands Meteorological Institute, (KNMI), De Bilt, Netherlands
(5) Department of Physics, University of Évora, Évora, Portugal

Abstract

The long term continuous observation of total ozone columns (TOC) at mid-latitudes is of great importance since a quantitative explanation of the observed ozone changes at these latitudes has not yet been provided. In this framework, daily TOC measurements from the Brewer spectroradiometer #150 located at El Arenosillo, Spain (37.10º N, 6.73º W) and the Spectrometer for Atmospheric TRAcers Monitoring (SPATRAM) located at Évora, Portugal (38.60º N, 7.90º W) are analyzed for the period 2006 to 2008. The main goal of this study is to compare TOC measurements retrieved from differential absorption retrieval methodologies using different viewing geometries: backscattered solar radiation (satellite Ozone Monitoring Instrument (OMI)), diffuse zenith sky radiation at Earth surface (SPATRAM) and direct solar radiation at Earth surface (Brewer). We perform a comparison between a traditional and recognized Brewer system - with which OMI satellite ozone data has been validated - and a newly developed DOAS system taking a different measurement approach.

The two ground-based stations are separated spatially by approximately 160 km. Nevertheless, the different viewing geometries used by the Brewer and SPATRAM spectroradiometers causes the measurements by these spatially “co-located” instruments not to be coincident in the atmosphere. Satellite TOC data recorded by the OMI instrument on board the NASA EOS-Aura satellite by means of the OMI-DOAS algorithm have been compared with respect to the two ground-based spectroradiometers showing an excellent agreement for the Brewer spectroradiometer (R2~0.95) and a good agreement for the SPATRAM instrument (R2~0.89). In addition, the OMI-DOAS satellite observations have been employed to analyze the natural spatial variability of TOC measurements as a potential source of uncertainty in the SPATRAM-Brewer comparison. In this contribution we present the results of our analysis and consider plausible explanations for the observed differences.