Abstract
Abstract. This paper presents the operational retrieval of tropical tropospheric ozone columns (TOCs) from the Second Global Ozone Monitoring Experiment (GOME-2) instruments using the convective-cloud-differential (CCD) method. The retrieval is based on total ozone and cloud property data provided by the GOME Data Processor (GDP) 4.7, and uses above-cloud and clear-sky ozone column measurements to derive a monthly mean TOC between 20° N and 20° S. Validation of the GOME-2 TOC with several tropical ozonesonde sites shows good agreement, with a high correlation between the GOME-2 and sonde measurements, and small biases within ~ 3 DU. The TOC data have been used in combination with tropospheric NO2 measurements from GOME-2 to analyse the effect of the 2009–2010 El Niño–Southern Oscillation (ENSO) on the tropospheric ozone distribution in the tropics. El Niño induced dry conditions in September–October 2009 resulted in relatively high tropospheric ozone columns over the southern Indian Ocean and northern Australia, while La Niña conditions in September–October 2010 resulted in a strong increase in tropospheric NO2 in South America, and enhanced ozone in the eastern Pacific and South America. Comparisons of the GOME-2 tropospheric ozone data with simulations of the ECHAM/MESSy Atmospheric Chemistry (EMAC) model for 2009 El Niño conditions illustrate the usefulness of the GOME-2 TOC measurements in evaluating chemistry climate models (CCMs). Evaluation of CCMs with appropriate satellite observations helps to identify strengths and weaknesses of the model systems, providing a better understanding of driving mechanisms and adequate relations and feedbacks in the Earth atmosphere, and finally leading to improved models.
Highlights
Ozone in the tropical troposphere plays various important roles
We assess the accuracy of the GOME2 tropical tropospheric ozone columns (TOCs) with ozonesonde measurements from the Southern Hemisphere Additional Ozonesondes (SHADOZ) network (Thompson et al, 2003a), and we study the effect of the 2009–2010 El Niño–Southern Oscillation (ENSO) on the tropospheric ozone distribution
An important advantage of the CCD method is that it is insensitive to the GOME-2 instrument degradation
Summary
Ozone in the tropical troposphere plays various important roles. It plays a key role in the global oxidizing power of the atmosphere as the main source of OH, the most important oxidant in the troposphere (Thompson, 1992). We describe the retrieval of the tropospheric ozone column (TOC) from GOME-2 measurements for the tropical region using the convective-cloud-differential (CCD) method. The original CCD method developed by Ziemke et al (1998) uses TOMS (for the period 1979–2005) and OMI (for 2004 onwards) total ozone measurements over bright, high-altitude clouds in the tropical western Pacific to obtain an above-cloud stratospheric ozone amount. In this region, bright clouds are often associated with strong convective outflows and cloud tops in the upper troposphere.
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