Stratospheric ozone climatology and variability over a southern subtropical site: Reunion Island (21° S; 55° E)

The study presents the climatological characteristics of stratospheric ozone observed over Reunion Island using in-situ (ozonesonde and SAOZ) and satellite (UARS-HALOE, SAGE-II and TOMS) measurements. It uses co-localised ozonesondes (from September 1992 to February 2005) and SAOZ measurements (from January 1993 to December 2004), SAGE-II data from October 1984 to February 1999 (similar to 15 years), HALOE data from January 1991 to February 2005 (similar to 15 years), and NIMBUS/TOMS data from January 1978 to December 2004 (27 years). The satellite measurements correspond to overpasses located nearby Reunion Island (21 degrees S; 55 degrees E). The height profiles of ozone concentration obtained from ozonesonde (0.5-29.5 km) show less bias in comparison with the HALOE and SAGE-II measurements. Though, the satellite (HALOE and SAGE-II) measurements underestimate the tropospheric ozone, they are in good agreement for the heights above 15 km. The bias between the measurements and the normalized ozone profile constructed from the ozonesonde and SAGE-II satellite measurement shows that the SAGE-II measurements are more accurate than the HALOE measurements in the lower stratosphere. The monthly variation of ozone concentration derived from ozonesonde and HALOE shows a nearly annual cycle with a maximum concentration during winter/spring and minimum concentration during summer/autumn months. The time evolution of total column ozone obtained from TOMS, SAOZ and the one computed from ozonesonde and SAGE-II, exhibits similar behaviour with analogous trends as above. The TOMS variation displays a higher value of total column ozone of about 3-5 DU (10%) in comparison with the SAOZ and the integrated ozone from ozonesonde and SAGE-II.