Abstract
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 to the algorithm is the use of a laboratory-determined cross-section data set. We used five ozone cross-section data sets: three data sets that are based on measurements of Bass and Paur; one derived from Daumont, Brion and Malicet (DBM); and a new set determined by Institute of Experimental Physics (IUP), University of Bremen. The three Bass and Paur (1985) sets are as follows: quadratic temperature coefficients from the IGACO (a glossary is provided in Appendix A) 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 instruments are then calculated using the normal Brewer operative method, which is essentially the same as that used for Dobson instruments. 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 IUP data set changes the calculated TOC by −0.5%, the DBM data set changes the calculated TOC by −3.2%, and the IGQ4 data set at −45 °C changes the calculated TOC by +1.3%. 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. We applied the changes to the European Dobson and Brewer reference instruments during the Izaña 2012 Absolute Calibration Campaign. With the application of a common Langley calibration and the IUP cross section, the differences between Brewer and Dobson data sets vanish, whereas using those of Bass and Paur and DBM produces differences of 1.5 and 2%, respectively. A study of the temperature dependence of these cross-section data sets is presented using the Arosa, Switzerland, total ozone record of 2003–2006, obtained from two Brewer-type instruments and one Dobson-type 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.
Highlights
The routine measurement of total column ozone (TOC) started in the mid-1920s with a prototype of the Dobson instrument (Dobson, 1968b) as a part of studies of atmospheric circulation
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 Institute of Experimental Physics (IUP) data set changes the calculated TOC by −0.5 %, the DBM data set changes the calculated TOC by −3.2 %, and the IGQ4 data set at −45 ◦C changes the calculated TOC by +1.3 %
The routine measurement of TOC started in the mid-1920s with a prototype of the Dobson instrument (Dobson, 1968b) as a part of studies of atmospheric circulation
Summary
The routine measurement of TOC started in the mid-1920s with a prototype of the Dobson instrument (Dobson, 1968b) as a part of studies of atmospheric circulation. In 2009, the ozone community established the ACSO committee (“Absorption Cross Sections of Ozone”) to review the presently available cross-section databases and to determine the impact of a change of the reference cross section for the different instrument types (ground-based and satellite) used in the individual instrument retrieval algorithms. – Both instrument types have demonstrated levels of internal stray light (Dobson, 1968a; Bais et al, 1996). The effect of the stray light is such that TOC is underestimated at ozone high slant path values (μX is defined as the product of the optical path length through the atmosphere with the calculated ozone). Brewer instruments are either single or double monochromators, the latter having demonstrably lower levels of internal stray light. This study will concentrate on the results of combination AD
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