Abstract
Abstract. 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 σ = 0.41 %, which is calculated as the mean of the individual values for each Brewer (σ157 = 0.362 %, σ183 = 0.453 % and σ185 = 0.428 %). Alternatively, using the procedure used to analyse the Arosa triad, the RBCC-E presents a relative standard deviation of about σ = 0.5 %. In monthly averages, the method used for the data from the world reference triad gives a relative standard deviation mean equal to σ = 0.3 % (σ157 = 0.33 %, σ183 = 0.34 % and σ185 = 0.23 %). However, the procedure of the Arosa triad gives monthly values of σ = 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.
Highlights
The ozone layer is a region of the Earth’s stratosphere that absorbs most of the Sun’s ultraviolet (UV) radiation (Anwar et al, 2016)
In order to summarize the history of the Regional Brewer Calibration Centre for Europe (RBCC-E) Brewer instruments, Table 1 provides the total number of days and measurements taken by these instruments since they became operational at Izaña Atmospheric Observatory (IZO) and as long as the weather conditions allowed them to operate
After 2010, The RBCC-E started using the same synchronization schedule in their Brewer instruments. These schedules take into account the sunrise and sunset times of each day and the introduced routines are distributed as a function of the solar zenith angle (SZA)
Summary
The ozone layer is a region of the Earth’s stratosphere that absorbs most of the Sun’s ultraviolet (UV) radiation (Anwar et al, 2016). The RBCC-E participated in the ATMOZ project (Traceability for the total atmospheric ozone column, https: //projects.pmodwrc.ch/atmoz/, last access: 5 July 2018), for which it organized an absolute calibration campaign with the Brewer and Dobson reference instruments. Es/eubrewnet, last access: 5 July 2018) which will allow the calculation of the TOC in near real time (Rimmer et al, 2018) This completes the objectives of this COST action, which aims to establish a coherent network of Brewer monitoring stations in order to harmonise operations and develop approaches, practices and protocols to achieve consistency in quality control, quality assurance and coordinated operations. The RBCC-E measurements are evaluated from the methods described for the world reference and Arosa triads to study its consistency With this idea in mind, this work has been structured as follows: an approach to ozone retrieval and Langley method is presented in Sect.
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