Evaluation of the use of five laboratory determined ozone absorption cross sections in brewer and dobson retrieval algorithms

Abstract

The primary ground-based instruments used to report total column ozone (TOC) are Brewer and Dobson Spectrophotometers, in separate networks. These instruments make measurements of the UV irradiances, and through a well-defined process a TOC value is produced. Inherent in the algorithm is the use of a laboratory determined cross-section data set. We used five ozone cross section data sets: three Bass and Paur, Daumont, Malicet and Brion (DMB) and a new Institute of Environmental Physics (IUP), University of Bremen, set. The three Bass and Paur (1985) sets are: quadratic temperature coefficients from IGACO web page (IGQ4), the Brewer network operational calibration set (BOp), and the set used by Bernhard et al. (2005), in the reanalysis of the Dobson absorption coefficient values (B05). The ozone absorption coefficients for Brewer and Dobson are then calculated using the normal Brewer operative method which is essentially the same as used on Dobson. <br><br> Considering the standard TOC algorithm for the Brewer instruments and comparing to the Brewer standard operational calibration data set, using the slit functions for the individual instruments: we find the UIP data set changes the calculated TOC by −0.5%, the DBM data set changes the calculate TOC by −3.2%, and the IGQ4 data set at −45 &deg;C changes the calculated TOC by +1.3%. <br><br> Considering the standard algorithm for the Dobson instruments, and comparing to results using the official 1992 ozone absorption coefficients values and the single set of slit functions defined for all Dobson instruments, the calculated TOC changes by +1%, with little variation depending on which data set is used <br><br> We applied the changes to the European Dobson and Brewer reference instruments during the Izaña 2012 Absolute Calibration Campaign. The application of a common Langley calibration and the IUP cross section the differences between Brewer and Dobson vanish whereas using Bass and Paur and DBM produce differences of 1.5% and 2% respectively. A study of temperature dependence of these cross section (XS) data sets is presented using the Arosa, Switzerland total ozone record of 2003–2006, obtained from two Brewer instrument types and a Dobson instrument, combined with the stratospheric ozone and temperature profiles from the Payerne soundings in the same period. The seasonal dependence of the differences between the results from the various instruments is greatly reduced with the application of temperature dependent absorption coefficients, with the greatest reduction obtained using the IUP data set

The Effect of Three Different Absorption Cross-Sections and their Temperature Dependence on Total Ozone Measured by a Mid-Latitude Brewer Spectrophotometer

“…The value of the gradient at the effective temperature of −45°C, 0.0967% per degree Celsius, is comparable with other estimates summarized in Table 4 of Scarnato et al (2009), as well as with the value of 0.09% per degree Celsius calculated by Redondas et al (2013) (see also Table 1). These differences are mainly a result of the different characteristics (slit function and operational wavelengths) of the instruments considered.…”

“…In the latter study the temperature dependence of the cross-sections was calculated from data at five temperatures, while in our study the calculation was carried out at only four. When we used data at five temperatures in our parameterization, the calculated gradient at −45°C was almost halved, resulting in a value similar to the one reported by Redondas et al (2013). Hence, it appears that the parameterization used to derive the cross-sections at any temperature is very sensitive to the number of data points considered, as also discussed in Scarnato et al (2009) for the BP crosssections.…”

“…The filled circles correspond to the gradient at −45°C calculated for each crosssection dataset. (2009) and close to two times higher than in Redondas et al (2013). In the latter study the temperature dependence of the cross-sections was calculated from data at five temperatures, while in our study the calculation was carried out at only four.…”

“…In earlier studies the temperature sensitivity of the BP ozone absorption coefficient was estimated to be in the range of 0.001 to 0.11% per degree Celsius (Kerr, 2002;Kerr, Asbridge, & Evans, 1988;Scarnato, Staehelin, Peter, Grobner, & Stubi, 2009;Van Roozendael et al, 1998), depending strongly on the characteristics of each instrument (operating wavelengths, slit function shape, and width). During the Sodankylä Total Column Ozone Intercomparison (SAUNA; http:// fmiarc.fmi.fi/SAUNA/) campaign Redondas, Evans, Stuebi, Köhler, and Weber (2013) calculated the temperature sensitivity of the BDM ozone absorption coefficient for temperatures of −45°C to be −0.044% per degree Celsius, whereas Scarnato et al (2009) estimated the temperature sensitivity of three different Brewer spectrophotometers in Arosa, Switzerland, to be in the range of −0.131 to −0.128% per degree Celsius.…”

Evaluating a new homogeneous total ozone climate data record from GOME/ERS‐2, SCIAMACHY/Envisat, and GOME‐2/MetOp‐A

“…Despite the similar performance of the Brewer and Dobson instruments, small differences in the range of ±0.6% are introduced due to the use of different wavelengths and different temperature dependence for the ozone absorption coefficients [ Staehelin et al, ]. Very recent studies have evaluated the effects of using different ozone absorption cross sections as well as correcting for the Brewer temperature dependence on the total ozone columns and their interconsistency with the Dobson total ozone columns [ Fragkos et al, ; Redondas et al, ]. Correcting for the difference between the real stratospheric temperature and the temperature at −45 °C and −46.3 °C assumed by the operational Brewer and Dobson algorithms, respectively, for middle latitude stations results in a TOC difference ranging between around 0% for the summer months and 1.5–2% for the winter months.…”