Abstract
Abstract. The MetOp/Infrared Atmospheric Sounding Interferometer (IASI) instruments have provided data for operational meteorology and document atmospheric composition since 2007. IASI ozone (O3) data have been used extensively to characterize the seasonal and interannual variabilities and the evolution of tropospheric O3 at the global scale. SOftware for a Fast Retrieval of IASI Data (SOFRID) is a fast retrieval algorithm that provides IASI O3 profiles for the whole IASI period. Until now, SOFRID O3 retrievals (v1.5 and v1.6) were performed with a single a priori profile, which resulted in important biases and probably a too-low variability. For the first time, we have implemented a comprehensive dynamical a priori profile for spaceborne O3 retrievals which takes the pixel location, time and tropopause height into account for SOFRID-O3 v3.5 retrievals. In the present study, we validate SOFRID-O3 v1.6 and v3.5 with electrochemical concentration cell (ECC) ozonesonde profiles from the global World Ozone and Ultraviolet Radiation Data Centre (WOUDC) database for the 2008–2017 period. Our validation is based on a thorough statistical analysis using Taylor diagrams. Furthermore, we compare our retrievals with ozonesonde profiles both smoothed by the IASI averaging kernels and raw. This methodology is essential to evaluate the inherent usefulness of the retrievals to assess O3 variability and trends. The use of a dynamical a priori profile largely improves the retrievals concerning two main aspects: (i) it corrects high biases for low-tropospheric O3 regions such as the Southern Hemisphere, and (ii) it increases the retrieved O3 variability, leading to a better agreement with ozonesonde data. Concerning upper troposphere–lower stratosphere (UTLS) and stratospheric O3, the improvements are less important and the biases are very similar for both versions. The SOFRID tropospheric ozone columns (TOCs) display no significant drifts (<2.5 %) for the Northern Hemisphere and significant negative ones (9.5 % for v1.6 and 4.3 % for v3.5) for the Southern Hemisphere. We have compared our validation results to those of the Fast Optimal Retrievals on Layers for IASI (FORLI) retrieval software from the literature for smoothed ozonesonde data only. This comparison highlights three main differences: (i) FORLI retrievals contain more theoretical information about tropospheric O3 than SOFRID; (ii) root mean square differences (RMSDs) are smaller and correlation coefficients are higher for SOFRID than for FORLI; (iii) in the Northern Hemisphere, the 2010 jump detected in FORLI TOCs is not present in SOFRID.
Highlights
Ozone (O3) in the stratosphere protects life from solar UV radiation
This study aimed at assessing the quality of two different versions of SOFRID-O3 at the global scale and over the 10-year Infrared Atmospheric Sounding Interferometer (IASI) period using ozonesondes from the World Ozone and Ultraviolet Radiation Data Centre (WOUDC)
SOFRIDO3 v1.6 retrievals are based on a single a priori profile like most other global IASI O3 retrievals (Barret et al, 2011; Dufour et al, 2012; Boynard et al, 2016, 2018)
Summary
Ozone (O3) in the stratosphere protects life from solar UV radiation. O3 is an oxidative pollutant harmful for human health through irritation of respiratory tracts (Brunekreef and Holgate, 2002) and for vegetation through deposition on leaves that leads to the reduction of plant growth (Ainsworth et al, 2012). Tropospheric O3 is a powerful greenhouse gas whose increase during the 20th century has significantly contributed to global warming (Shindell et al, 2006). The radiative forcing of O3 is important in the tropical upper troposphere–lower stratosphere (UTLS) (Chen et al, 2007). It is important to document the evolution of O3 in these different layers independently. There is clear evidence from satellite databases that upper stratospheric O3 has in-
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