Sensitivity of Dobson and Brewer Umkehr ozone profile retrievals to ozone cross-sections and stray light effects

Abstract

Abstract. Remote sounding methods are used to derive ozone profile and column information from various groundbased and satellite measurements. Vertical ozone profiles measured in Dobson units (DU) are currently retrieved based on laboratory measurements of the ozone absorption crosssection spectrum between 270 and 400 nm published in 1985 by Bass and Paur (BP). Recently, the US National Aeronautics and Space Administration (NASA) and the European Space Agency (ESA) proposed using the set of ozone crosssection measurements made at the Daumont laboratory in 1992 (BDM) for revising the Aura Ozone Monitoring Instrument (OMI) and Global Ozone Monitoring Experiment (GOME) satellite ozone profiles and total ozone column retrievals. Dobson Umkehr zenith sky data have been collected by NOAA ground-based stations at Boulder, CO (BDR) and Mauna Loa Observatory, HI (MLO) since the 1980s. The UMK04 algorithm is based on the BP ozone cross-section data. It is currently used for all Dobson Umkehr data processing submitted to the World Ozone and Ultraviolet radiation Data Centre (WOUDC) under the Global Atmosphere Watch (GAW) program of the World Meteorological Organization (WMO). Ozone profiles are also retrieved from measurements by the Mark IV Brewers operated by the NOAA-EPA Brewer Spectrophotometer UV and Ozone Network (NEUBrew) using a modified UMK04 algorithm (O3BUmkehr v.2.6, Martin Stanek). This paper describes the sensitivity of the Umkehr retrievals with respect to the proposed ozone cross-section changes. It is found that the Correspondence to: I. Petropavlovskikh (irina.petro@noaa.gov) ozone cross-section choice only minimally (within the retrieval accuracy) affects the Dobson and the Brewer Umkehr retrievals. On the other hand, significantly larger errors were found in the MLO and Boulder Umkehr ozone data (−8 and +5 % bias in stratosphere and troposphere respectively) when the out-of-band (OOB) stray light contribution to the Umkehr measurement is not taken into account (correction is currently not included in the UMK04). The vertical distribution of OOB effect in the retrieved profile can be related to the local ozone climatology, instrument degradation, and optical characteristics of the instrument. Nonetheless, recurring OOB errors do not contribute to the long-term ozone trends.

Validation of OMI total ozone retrievals from the SAO ozone profile algorithm and three operational algorithms with Brewer measurements

“…The Brewer can be operated in single or double monochromator configuration. The double monochromator (MK-III model) is known to better reduce the impact of stray light on the measurement than the single monochromator (MK-II or MK-IV) does (Kerr, 2002;Petropavlovskikh et al, 2011). Spectral irradiance measurements can be made by a well-maintained Brewer instrument with the precision of ∼ ± 0.1 % (Kerr, 2002).…”

Absolute ozone absorption cross section in the Huggins Chappuis minimum (350–470 nm) at 296 K

“…Weak spectral absorptions play an important role in the radiative transfer of the Earth's atmosphere and accurate measurements of these are necessary for satellite retrievals of atmospheric trace gases (Burrows et al, 1999a;Bogumil et al, 2003;Petropavlovskikh et al, 2011). It has recently been recognized that weak electronic features in the nearultraviolet (UV), which are not well known, can be important for tropospheric radical production (Waschewsky et al, 1996;Matthews et al, 2005;Vaida, 2009).…”

A new Dobson Umkehr ozone profile retrieval method optimising information content and resolution

“…Due to the combination of low intensities and large intensity ratios received at the detector for high SZAs near the turn-around point, errors can be introduced due to stray light effects, which are currently not taken into account. These errors have been shown to have minimal effect on C-pair Umkehr-derived, long-term ozone trends (Petropavlovskikh et al, 2011). Stray light effects on Umkehr-derived time series are likely to be consistent if the same instrument is in operation for the duration of the time series.…”

“…The model is set up to use the ozone cross-section as described by Bass and Paur (1985), but can also use the more recent ozone cross-section studies by Daumont et al (1992) and Gorshelev et al (2014). However, the effect of the ozone cross-section used in C-pair Umkehr retrieval algorithms was studied by Petropavlovskikh et al (2011) and found to have minimal effect. As the Umkehr method measures the sum of all radiation scattered downwards from the zenith, the intensity is calculated, such that…”

“…Errors due to aerosols have a larger impact and have previously been described extensively (Dave, 1972a, b;Mateer and DeLuisi, 1992;Petropavlovskikh et al, 2004). Instrumental stray light effects can also have a significant effect, with Petropavlovskikh et al (2011) reporting a negative stratospheric retrieval bias for C-pair Umkehr retrievals. Thus, due to these deficiencies, we caution the direct comparison of the algorithm presented here to other algorithms.…”