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

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.

Consistency of total column ozone measurements between the Brewer and Dobson spectroradiometers of the LKO Arosa and PMOD/WRC Davos

“…The spectroradiometers operating at Davos and Arosa belong respectively to the global Brewer and Dobson networks and are traceable to their respective network reference instruments, Dobson D083 via the RVI regional Dobson D064 from Hohenpeissenerg, Germany, and the Brewer Triad maintained by the Regional Brewer calibration center -Europe (RBCC-E), at the Izaña Atmospheric Research Center, Tenerife, Canary Islands, Spain (León-Luis et al , 2018). For details on the maintenance and calibration schedules we refer to the publications of Scarnato et al (2010), and .…”

The world Brewer reference triad – updated performance assessment and new double triad

“…The performance of the European regional reference instruments (i.e., RBCC-E triad) was reported by León-Luis et al, (2018) and compared with the world reference instruments, specifically the BrT. León-Luis et al, (2018) reported that RBCC-E instruments have a mean 3-month standard deviation (δ3month) of 0.27 %, and concluded that the RBCC-E instruments have 36 % lower δ3month when comparing to the world reference instruments (i.e., BrT, 1984BrT, -2004. However, the comparison was not straightforward.…”

“…However, this approach is not possible in reality. Several other means to form these (daily or time-resolved) baseline ozone values were used in the past: 1) the average of all satisfactory measurements for each instrument (Kerr et al, 1998), 2) a second-order time-resolved statistical model (Fioletov et al, 2005), 3) a third-order simple polynomial fit (Stübi et al, 2017), and 4) a fourth-order time-resolved statistical model (León-Luis et al, 2018). In general, these approaches aim to define the best baseline total column ozone values for each day, which are as close to true ozone values as possible.…”

“…The Arosa triad (Staehelin et al, 1998;Stübi et al, 2017), formed in 1998, was the second Brewer triad worldwide (composed of two Mark II and one Mark III instruments). To better coordinate the Brewer network at the regional scale (León-Luis et al, 2018;Redondas et al, 2018), the RBCC-E triad was formed in 2003 (composed of three Mark III instruments). The regional reference instruments are regularly compared to the world reference instruments via a travelling standard.…”

Description of the Baseline Surface Radiation Network (BSRN) station at the Izaña Observatory (2009–2017): measurements and quality control/assurance procedures

“…The study of these historic datasets reveals an increase in the surface solar radiation until the 1950s, known as "early brightening" (Ohmura, 2009;Wild, 2009), but only observed in Europe due to the scarcity of available data. The study of surface solar radiation longterm records shows decadal changes with a decline of surface solar radiation from the first available records, around 1950, until the middle of the 1980s (Stanhill and Cohen, 2001;Liepert, 2002), a period known as "global dimming", and an increment in the surface solar radiation since the middle of 1980s, a period known as "global brightening" (Wild et al, 2005).…”