Mid-latitude Tropospheric Ozone Columns from the MOZAIC program: climatology and interannual variability

Abstract. Several thousands ozone vertical profiles collected in the course of the MOZAIC program (Measurements of Ozone, Water Vapour, Carbon Monoxide and Nitrogen Oxides by In-Service Airbus Aircraft) from August 1994 to February 2002 are investigated to bring out climatological and interannual variability aspects. The study is centred on the most frequently visited MOZAIC airports, i.e. Frankfurt (Germany), Paris (France), New York (USA) and the cluster of Tokyo, Nagoya and Osaka (Japan). The analysis focuses on the vertical integration of ozone from the ground to the dynamical tropopause and the vertical integration of stratospheric-origin ozone throughout the troposphere. The characteristics of the MOZAIC profiles, frequency of flights, accuracy, precision, and depth of the troposphere observed, are presented. The climatological analysis shows that the Tropospheric Ozone Column (TOC) seasonal cycle ranges from a minimum wintertime at all four stations to a spring-summer maximum in Frankfurt, Paris, and New York. Over Japan, the maximum occurs in spring because of the earlier springtime sun. The invasion of monsoon air masses in the boundary layer and in the mid-troposphere then steeply diminishes the summertime value. Boundary layer contributions to the TOC are 10% higher in New York compare to Frankfurt and Paris during spring and summer, and are 10% higher in Japan compare to New York, Frankfurt and Paris during autumn and early spring. Local and remote anthropogenic emissions as well as biomass burning over upstream regions of Asia may be responsible of larger low- and mid-tropospheric contributions to the tropospheric ozone column over Japan throughout the year except during the summer-monsoon season. A simple Lagrangian analysis has shown that a minimum range of 10% of the TOC is of stratospheric-origin throughout the year. The investigation on the short-term trends of the TOC over the period 1995–2001 shows a linear increase of 0.7%/year in Frankfurt, 0.8%/year in Japan, 0.9%/year in Paris, and 1.1%/year in New York. Essential ingredients to these positive short-term trends are the continuous increase of wintertime tropospheric ozone columns from 1996 to 1999 and the positive contributions of the mid-troposphere whatever the season.