Quality assessment of the Ozone_cci Climate Research Data Package (release 2017) – Part 1: Ground-based validation of total ozone column data products release_ijsqbtlrp5esnp3m5kydnl34ly

Abstract

<strong>Abstract.</strong> The GOME-type Total Ozone Essential Climate Variable (GTO-ECV) is a level-3 data record, which combines individual sensor products into one single cohesive record covering the 22-year period from 1995 to 2016, generated in the frame of the European Space Agency's Climate Change Initiative Phase II. It is based on level-2 total ozone data produced by the GODFIT (GOME-type Direct FITting) v4 algorithm as applied to the GOME/ERS-2, OMI/Aura, SCIAMACHY/Envisat and GOME-2/Metop-A and Metop-B observations. In this paper we examine whether GTO-ECV meets the specific requirements set by the international climate–chemistry modelling community for decadal stability long-term and short-term accuracy. In the following, we present the validation of the 2017 release of the Climate Research Data Package Total Ozone Column (CRDP TOC) at both level 2 and level 3. The inter-sensor consistency of the individual level-2 data sets has mean differences generally within 0.5<span class="thinspace"></span>% at moderate latitudes (±50°), whereas the level-3 data sets show mean differences with respect to the OMI reference data record that span between −0.2<span class="thinspace"></span>±<span class="thinspace"></span>0.9<span class="thinspace"></span>% (for GOME-2B) and 1.0<span class="thinspace"></span>±<span class="thinspace"></span>1.4<span class="thinspace"></span>% (for SCIAMACHY). Very similar findings are reported for the level-2 validation against independent ground-based TOC observations reported by Brewer, Dobson and SAOZ instruments: the mean bias between GODFIT v4 satellite TOC and the ground instrument is well within 1.0<span class="thinspace"></span>±<span class="thinspace"></span>1.0<span class="thinspace"></span>% for all sensors, the drift per decade spans between −0.5<span class="thinspace"></span>% and 1.0<span class="thinspace"></span>±<span class="thinspace"></span>1.0<span class="thinspace"></span>% depending on the sensor, and the peak-to-peak seasonality of the differences ranges from ∼ 1<span class="thinspace"></span>% for GOME and OMI to  ∼ 2<span class="thinspace"></span>% for SCIAMACHY. For the level-3 validation, our first goal was to show that the level-3 CRDP produces findings consistent with the level-2 individual sensor comparisons. We show a very good agreement with 0.5 to 2<span class="thinspace"></span>% peak-to-peak amplitude for the monthly mean difference time series and a negligible drift per decade of the differences in the Northern Hemisphere of −0.11<span class="thinspace"></span>±<span class="thinspace"></span>0.10<span class="thinspace"></span>%<span class="thinspace"></span>decade<sup>−1</sup> for Dobson and +0.22<span class="thinspace"></span>±<span class="thinspace"></span>0.08<span class="thinspace"></span>%<span class="thinspace"></span>decade<sup>−1</sup> for Brewer collocations. The exceptional quality of the level-3 GTO-ECV v3 TOC record temporal stability satisfies well the requirements for the total ozone measurement decadal stability of 1–3<span class="thinspace"></span>% and the short-term and long-term accuracy requirements of 2 and 3<span class="thinspace"></span>%, respectively, showing a remarkable inter-sensor consistency, both in the level-2 GODFIT v4 and in the level-3 GTO-ECV v3 datasets, and thus can be used for longer-term analysis of the ozone layer, such as decadal trend studies, chemistry–climate model evaluation and data assimilation applications.
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