Abstract
Abstract. This paper presents comparison results of the total column ozone (TCO) data product over 13 southern tropical and subtropical sites recorded from the Infrared Atmospheric Sounder Interferometer (IASI) onboard the EUMETSAT (European organization for the exploitation of METeorological SATellite) MetOp (Meteorological Operational satellite program) satellite. TCO monthly averages obtained from IASI between June 2008 and December 2012 are compared with collocated TCO measurements from the Ozone Monitoring Instrument (OMI) on the OMI/Aura satellite and the Dobson and SAOZ (Système d'Analyse par Observation Zénithale) ground-based instruments. The results show that IASI displays a positive bias with an average less than 2 % with respect to OMI and Dobson observations, but exhibits a negative bias compared to SAOZ over Bauru with a bias around 2.63 %. There is a good agreement between IASI and the other instruments, especially from 15° S southward where a correlation coefficient higher than 0.87 is found. IASI exhibits a seasonal dependence, with an upward trend in autumn and a downward trend during spring, especially before September 2010. After September 2010, the autumn seasonal bias is considerably reduced due to changes made to the retrieval algorithm of the IASI level 2 (L2) product. The L2 product released after August (L2 O3 version 5 (v5)) matches TCO from the other instruments better compared to version 4 (v4), which was released between June 2008 and August 2010. IASI bias error recorded from September 2010 is estimated to be at 1.5 % with respect to OMI and less than ±1 % with respect to the other ground-based instruments. Thus, the improvement made by O3 L2 version 5 (v5) product compared with version 4 (v4), allows IASI TCO products to be used with confidence to study the distribution and interannual variability of total ozone in the southern tropics and subtropics.
Highlights
Atmospheric ozone plays a key role since it protects the biosphere from harmful ultraviolet radiation
Otherwise the bias between Ozone Monitoring Instrument (OMI) and Infrared Atmospheric Sounder Interferometer (IASI) is basically due in part to the different characteristics according to the vertical and horizontal resolution of each instrument, and the bias which can be associated with the existing differences between UVvisible and infrared spectroscopy used in the retrieval processes
It is worth noting that the examined data product in this work is the IASI level 2 PPF developed by the IASI Sounding Science Working Group (ISSWG) under EUMETSAT supervision
Summary
Atmospheric ozone plays a key role since it protects the biosphere from harmful ultraviolet radiation. About 90 % of its mass is found in the stratosphere where ozone is formed through photochemical reactions. Most ozone is formed in the tropics but is rapidly transported to higher latitudes by Brewer–Dobson large-scale circulation (Weber et al, 2011). Global total column ozone (TCO) has depleted gradually since 1980 with an increase of chlorofluorocarbon concentrations in the stratosphere due to anthropogenic activities. Ozone is under high surveillance, especially since the discovery of the Antarctic ozone hole (Farman et al, 1985; Krueger et al, 1992; Stolarski et al, 1990). In 1987, the Montreal protocol was formulated in order to regulate the emissions of substances that deplete ozone (United Nations Environment Programme UNEP, 2009); we have been expecting an increase in ozone . Different observations and studies have shown that subtropical
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