Tropopause referenced ozone climatology and inter-annual variability (1994–2003) from the MOZAIC programme

[摘要] The MOZAIC programme collects ozone and water vapour data using automaticequipment installed on board five long-range Airbus A340 aircraft flyingregularly all over the world since August 1994. Those measurements madebetween September 1994 and August 1996 allowed the first accurate ozoneclimatology at 9–12 km altitude to be generated. The seasonal variability ofthe tropopause height has always provided a problem when constructingclimatologies in this region. To remove any signal from the seasonal andsynoptic scale variability in tropopause height we have chosen in thisfurther study of these and subsequent data to reference our climatology tothe altitude of the tropopause. We define the tropopause as a mixing zone 30 hPathick across the 2 pvu potential vorticity surface. A new ozoneclimatology is now available for levels characteristic of the uppertroposphere (UT) and the lower stratosphere (LS) regardless of the seasonalvariations of the tropopause over the period 1994–2003. Moreover, this newpresentation has allowed an estimation of the monthly mean climatologicalozone concentration at the tropopause showing a sine seasonal variation witha maximum in May (120 ppbv) and a minimum in November (65 ppbv). Besides, wepresent a first assessment of the inter-annual variability of ozone in thisparticular critical region. The overall increase in the UTLS is about1%/yr for the 9 years sampled. However, enhanced concentrations about10–15 % higher than the other years were recorded in 1998 and 1999 inboth the UT and the LS. This so-called "1998–1999 anomaly" may beattributed to a combination of different processes involving large scalemodes of atmospheric variability, circulation features and local or globalpollution, but the most dominant one seems to involve the variability of theNorth Atlantic Oscillation (NAO) as we find a strong positive correlation(above 0.60) between ozone recorded in the upper troposphere and the NAOindex. A strong anti-correlation is also found between ozone and theextremes of the Northern Annular Mode (NAM) index, attributing the lowerstratospheric variability to dynamical anomalies. Finally this analysishighlights the coupling between the troposphere, at least the upper one, andthe stratosphere, at least the lower one.

[学科分类] 大气科学