OZONE CLIMATOLOGIES AT 9-12 KM ALTITUDE AS SEEN BY THE MOZAIC AIRBORNE PROGRAM BETWEEN SEPTEMBER 1994 AND AUGUST 1996

From data collected at cruise levels by the five aircraft of the Measu rement of Ozone and Water Vapor by Airbus In-Service Aircraft (MOZAIC) program during a 2-year period (September 1994 to August 1996), an ac curate ozone climatology at 9-12 km altitude has been generated over t he northern hemisphere (130 degrees W-140 degrees E; 0 degrees-80 degr ees N), and down to 30 degrees S over South America and Africa. North of 35 degrees N, the distribution is dominated by the influence of ozo ne-rich air of stratospheric origin; farther south, ozone-poor air fro m the troposphere prevails. A classification based on a threshold of 1 00 ppbv of ozone is used to distinguish between the stratospheric and tropospheric components and to help in interpreting the data. Seasonal variations of ozone are observed in stratospheric air (maximum in spr ing, minimum in winter) and in tropospheric air (maximum in summer, mi nimum in autumn), related to the intensities of dynamic (tropopause va riations; stratosphere/troposphere exchanges) and chemical (photochemi stry) processes. The tropics exhibit variations that are heterogeneous in time and space, and reflect the influences of active photochemical processes, deep convection and biomass burning emissions. Ozone conce ntrations decrease with latitude in both the stratosphere and troposph ere. A strong vertical gradient is found in stratospheric air but not in tropospheric air, which is much more homogeneous. The integration o f data over characteristic geographical areas shows smaller concentrat ions over the Atlantic Ocean compared to the continents; this is relat ed to the zonal variation of the polar front and the position of ridge /trough pressure systems.