Stratospheric ozone climatology and variability from ground-based and satellite observations over Irene, South Africa (25.5°S; 28.1°E)

Abstract

The climatological characteristic of ozone over Irene (25.˚S, 28.1˚E) was assessed in this thesis using ground-based satellite observations. The aim of this was to examine the variability of both total and vertical ozone distribution over Irene. Ground based instruments were selected since they provide accurate measurement of ozone while satellite measurements were used for this study because they provide a wider coverage. Satellite data from Total Ozone Mapping Spectrometer (TOMS) from November 1978 to May 1993, Global Ozone Monitoring Experiment-1 (GOME-1) from August 1995 to June 2003, Earth Probe Total Ozone Monitoring Spectrometer (EP-TOMS) from January 1997 to December 2005, Microwave Limb Sounder (October 2004 to April 2013), Ozone Monitoring Interferometer (OMI) from October 2004 to December 2013, Global Ozone Monitoring Experiment-2 (GOME-2) from January 2007 to December 2013, and Infrared Atmospheric Sounding Interferometer (IASI) from June 2008 to December 2011 and ground-based measurements from Dobson Instrument (August 1989 to December 2011) as well as Ozonesondes (November 1978 to Decemeber 2007) were used. The seven satellites and two ground based instruments used for this study were selected as they provide long term ozone monitoring data. The above satellites measurements were collected when they overpass over Irene. The height profiles of ozone concentration obtained from ozonesondes and satellite (MLS) are in good in good agreement from 15 km and above. Maximum ozone concentration was found in the height region of 23 km to 27 km. Above this height, ozone concentration reduced with increasing height. The monthly variation of ozone concentration from ozonesondes and MLS showed maximum concentration during spring and minimum concentration during autumn. Maximum ozone concentration from ozonesonde corresponds to 4.5x10¹² molecules/cm³ while that from MLS satellite was ~ 4.1x10¹² molecules/cm³ during spring. A difference in the range of 4x10¹¹molecules/cm³ and 0.8x10¹² molecules/cm³ was obtained for all seasons except during winter when the difference was in the range of 0.6x10¹² molecules/cm³ and 0.9x10¹² molecules/cm³. Satellite measurements used to determine column ozone replicated spring maximum and autumn minimum. TOMS variation displayed higher value of total column ozone of about 7 DU when compared with other satellites but had good agreement with Dobson instrument. Combined satellite measurement of ozone was within 3 DU with Dobson mesurement. Satellite comparison with Dobson improved when both GOME measurements were not used to within 1 DU while GOME comparison with Dobson was within 5 DU. EPTOMS and GOME-1 showed gradual increase in column ozone between 1995 and 2005 by ~2 DU which has increased to ~7 DU in the last decade as measured by OMI, GOME-2 and IASI satellites. Ozone variability over South Africa was consistent with the seasonal variability of spring maximum and autumn minimum. The lower part of South Africa had more total ozone compared to the central part and lower part of South Africa attributed to maritime activities taking place in the region as well as the impact of wind from ozone rich regions in the high latitudes to mid-latitude regions. The north eastern part of South Africa had ~5 DU more than other northern part. This is atributed to the impact of biomass burning in the surrounding regions. This study has shown that there was ozone loss between 1978 and 1991 in Irene but there has been gradual recovery of ozone by ~ 7 DU per decade.