Methodology for Using the MOZAIC Ozone Climatology in Future Comparisons with Data from SCIAMACHY Onboard ENVISAT

The MOZAIC program was designed to collect ozone and water vapour data, using automatic equipment installed on board five long-range Airbus A340 aircraft flying regularly all over the world since August 1994 (Marenco et al. 1998). From ozone data recorded at cruise levels during a 2-year period (September 1994 to August 1996), the first accurate ozone climatology at 9–12 km altitude has been generated (Thouret et al. 1998a). From now on, we are providing different “elaborated” products such as the tropospheric ozone columns and the horizontal climatology with data referred to the tropopause altitude. We have chosen to use the tropopause altitude as the reference to get rid of its seasonal variations. Thus, we have access to the upper tropospheric ozone and to the lower stratospheric ozone distributions. In this first approach, we have chosen only to represent and analyse the measurements recorded at mid northern latitudes. In this study, we defined the tropopause as a mixing zone 30 mb thick centred on the surface PV = 2 PVU. Another set of climatologies is now available for the levels “tropopause ±15 mb” and “tropopause ±45 mb”. In the frame of TROPOSAT, this new set of climatologies demonstrates that we have started a development for future comparisons with the SCIAMACHY instrument, for example. The 8 first years of the MOZAIC program has allowed a first assessment of the inter-annual variability of ozone both in the free troposphere and in the UT/LS to be made. The results are surprisingly high (about 2 %/year). The year 1998 appears as a positive anomaly. Further studies have started to explain such a high increase of ozone in the troposphere and the lower stratosphere at northern mid-latitudes.