Internal consistency of the Regional Brewer Calibration Centre for Europe triad during the period 2005–2016

León-Luis, Sergio Fabián; Redondas, Alberto; Carreño, Virgilio; López-Solano, Javier; Berjón, Alberto; Hernández-Cruz, Bentorey; Santana-Díaz, Daniel

Total ozone column measurements can be made using Brewer spectrophotometers, which are calibrated periodically in intercomparison campaigns with respect to a reference instrument. In 2003, the Regional Brewer Calibration Centre for Europe (RBCC-E) was established at the Izaña Atmospheric Research Center (Canary Islands, Spain), and since 2011 the RBCC-E has transferred its calibration based on the Langley method using travelling standard(s) that are wholly and independently calibrated at Izaña. This work is focused on reporting the consistency of the measurements of the RBCC-E triad (Brewer instruments #157, #183 and #185) made at the Izaña Atmospheric Observatory during the period 2005–2016. In order to study the long-term precision of the RBCC-E triad, it must be taken into account that each Brewer takes a large number of measurements every day and, hence, it becomes necessary to calculate a representative value of all of them. This value was calculated from two different methods previously used to study the long-term behaviour of the world reference triad (Toronto triad) and Arosa triad. Applying their procedures to the data from the RBCC-E triad allows the comparison of the three instruments. In daily averages, applying the procedure used for the world reference triad, the RBCC-E triad presents a relative standard deviation equal to inline-formulaσinline-formula= 0.41 %, which is calculated as the mean of the individual values for each Brewer (inline-formulaσ157inline-formula= 0.362 %, inline-formulaσ183inline-formula= 0.453 % and inline-formulaσ185inline-formula= 0.428 %). Alternatively, using the procedure used to analyse the Arosa triad, the RBCC-E presents a relative standard deviation of about inline-formulaσinline-formula= 0.5 %. In monthly averages, the method used for the data from the world reference triad gives a relative standard deviation mean equal to inline-formulaσinline-formula= 0.3 % (inline-formulaσ157inline-formula= 0.33 %, inline-formulaσ183inline-formula= 0.34 % and inline-formulaσ185inline-formula= 0.23 %). However, the procedure of the Arosa triad gives monthly values of inline-formulaσinline-formula= 0.5 %. In this work, two ozone data sets are analysed: the first includes all the ozone measurements available, while the second only includes the simultaneous measurements of all three instruments. Furthermore, this paper also describes the Langley method used to determine the extraterrestrial constant (ETC) for the RBCC-E triad, the necessary first step toward accurate ozone calculation. Finally, the short-term or intraday consistency is also studied to identify the effect of the solar zenith angle on the precision of the RBCC-E triad.

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León-Luis, Sergio Fabián / Redondas, Alberto / Carreño, Virgilio / et al: Internal consistency of the Regional Brewer Calibration Centre for Europe triad during the period 2005–2016. 2018. Copernicus Publications.

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