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

Abstract

Abstract. Total column ozone measured by Brewer and Dobson spectroradiometers at Arosa and Davos, Switzerland, have systematic seasonal variations of around 1.5 % using the standard operational data processing. Most of this variability can be attributed to the temperature sensitivity of approx. +0.1 %/K of the ozone absorption coefficient of the Dobson spectroradiometer (in this study D101). While the currently used Bass&Paur ozone absorption cross-sections produce inconsistent results for Dobson and Brewer, the use of the ozone absorption cross-sections from Serdyuchenko et al. (2013) in conjunction with an effective ozone temperature dataset produces excellent agreement between the investigated four Brewers (of which two double Brewers), and Dobson D101. Even though other ozone absorption cross-sections available in the literature are able to reduce the seasonal variability, all of those investigated produce systematic biases in total column ozone between Brewer and Dobson of 1.1 % to 3.1 %. The highest consistency of total column ozone from Brewers and Dobson D101 at Arosa/Davos of 0.1 % is obtained by applying the Rayleigh scattering cross-sections from Bodhaine et al. (1999), the ozone absorption cross-sections from Serdyuchenko et al. (2013), the effective ozone temperature from either ozonesondes or ECMWF, and the measured line-spread functions of Brewer and Dobson. The variability between Brewer and Dobson for single measurements of 0.9 % can be reduced to less than 0.5 % for monthly means and 0.3 % on yearly means. As show here, the proposed methodology produces consistent total column ozone datasets between Brewer and Dobson spectroradiometers of better than 1 %. For colocated Brewer and Dobson spectroradiometers, as is the case for the Arosa/Davos total column ozone times series, this allows the merging of these two distinct datasets to produce a homogeneous time series of total column ozone measurements. Furthermore, it guarantees the long-term future of this longest total column ozone time-series, by proposing a methodology how to eventually replace the ageing Dobson spectroradiometer with the state-of-the art Brewer spectroradiometer.

TOC intercomparison of Brewer, Dobson and BTS Solar at Hohenpeißenberg and Davos 2019/2020

“…In the following Figure 5 the seasonal course of all TOC data of the complete measurement campaign is illustrated. This explains the larger deviation of the Dobson 104 due to the seasonal dependency (Gröbner J., 2021;Kerr et al, 1988;Scarnato et al, 2010;Staehelin et al, 2003;Vanicek, 2006). The plot also shows the comparable trend of the Brewers and BTS Solar, since the least square fit is within ±1% over the whole measurement campaign.…”

“…The paper of Redondas et al (2014) describes the effects of the planned 55 introduction of new ozone absorption cross sections (Gorshelev et al, 2013;Serdyuchenko et al, 2013) on the Brewer and Dobson ozone retrievals. The comparison of Dobsons and Brewers with different cross-sections is newly performed at PMOD/WRC (Gröbner J., 2021). Both systems are still in use, even though Dobson spectrophotometers are no longer being manufactured.…”

The design and development of a tuneable and portable radiation source for in situ spectrometer characterisation

“…tency in the ozone absorption cross-sections used up to now (Bass and Paur, 1985). As shown in Gröbner et al (2021), the consistency can be significantly improved from 3 % to better than 1 % when using the actually measured line spread functions of a Dobson spectrophotometer, in conjunction with the cross-sections from IUP (Serdyuchenko et al, 2014).…”

“…This large discrepancy currently precludes a merging of both datasets and an eventual replacement of one instrument with another type. As shown in Gröbner et al (2021), the consistency can be significantly improved when using the actually measured line spread functions of a Dobson spectrophotometer, in conjunction with the cross-sections from IUP (Serdyuchenko et al, 2014). There is therefore a need for an improved characterisation and calibration of the Dobson and Brewer instruments, particularly by involving the reference instruments of each network.…”

Representativeness of the Arosa/Davos Measurements for the Analysis of the Global Total Column Ozone Behavior

“…Stratospheric ozone depletion over midlatitudes was first observed using the total column ozone time series over Arosa due to its long measurement period extending back to pre-ozone depletion conditions, its high intrinsic homogeneity, and quality (Staehelin, 1998a;Staehelin, 1998b;Staehelin et al, 2018). As discussed by Staehelin et al (2018) and Gröbner et al (2021), the Arosa/Davos total ozone time series requires continuous efforts to homogenize the measurements across different instruments and periods to produce the required level of uncertainty to be used for the assessment of ozone changes and observe the eventual recovery of the ozone layer.…”