Abstract
Abstract. The availability of long-term records of the total ozone content (TOC) represents a valuable source of information for studies on the assessment of short- and long-term atmospheric changes and their impact on the terrestrial ecosystem. In particular, ground-based observations represent a valuable tool for validating satellite-derived products. To our knowledge, details about software packages for processing Brewer spectrophotometer measurements and for retrieving the TOC are seldom specified in studies using such datasets. The sources of the differences among retrieved TOCs from the Brewer instruments located at the Italian stations of Rome and Aosta, using three freely available codes (Brewer Processing Software, BPS; O3Brewer software; and European Brewer Network (EUBREWNET) level 1.5 products) are investigated here. Ground-based TOCs are also compared with Ozone Monitoring Instrument (OMI) TOC retrievals used as an independent dataset since no other instruments near the Brewer sites are available. The overall agreement of the BPS and O3Brewer TOC data with EUBREWNET data is within the estimated total uncertainty in the retrieval of total ozone from a Brewer spectrophotometer (1 %). However, differences can be found depending on the software in use. Such differences become larger when the instrumental sensitivity exhibits a fast and dramatic drift which can affect the ozone retrievals significantly. Moreover, if daily mean values are directly generated by the software, differences can be observed due to the configuration set by the users to process single ozone measurement and the rejection rules applied to data to calculate the daily value. This work aims to provide useful information both for scientists engaged in ozone measurements with Brewer spectrophotometers and for stakeholders of the Brewer data products available on Web-based platforms.
Highlights
Ozone (O3) is present in small amounts in the terrestrial atmosphere, it plays a crucial role in the attenuation of solar ultraviolet (UV) radiation (200–400 nm) reaching the surface and in radiative processes controlling the energy balance on the Earth (Ramanathan and Dickinson, 1979; Dessler, 2000; Bordi et al, 2012; WMO, 2015).The cumulative amount of stratospheric and tropospheric ozone represents the total ozone column (TOC)
A growing number of sites have been equipped with Dobson spectrophotometers, and in the 1980s they began to be equipped with automated Brewer spectrophotometers (Brewer, 1973)
The time series of TOC daily means generated by BPS and O3Brewer and calculated from individual EUBREWNET ozone values are presented in Fig. 1
Summary
Ozone (O3) is present in small amounts in the terrestrial atmosphere, it plays a crucial role in the attenuation of solar ultraviolet (UV) radiation (200–400 nm) reaching the surface and in radiative processes controlling the energy balance on the Earth (Ramanathan and Dickinson, 1979; Dessler, 2000; Bordi et al, 2012; WMO, 2015).The cumulative amount of stratospheric and tropospheric ozone represents the total ozone column (TOC). The most common ground-based instruments for measuring TOC are spectrophotometers which are designed to measure ground level spectral intensities of solar ultraviolet radiation attenuated by the ozone absorption. From these spectra, it is possible to retrieve the TOCs. The first TOC observations were recorded using a Dobson spectrophotometer in the late 1920s. A growing number of sites have been equipped with Dobson spectrophotometers, and in the 1980s they began to be equipped with automated Brewer spectrophotometers (Brewer, 1973). Both Dobson and Brewer spectrophotometers are used all over the world, and the accuracy of measurements taken with a well-maintained Brewer spectrophotometer is 1 % in the direct-sun (DS) mode (Vanicek, 2006)
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