INTERANNUAL VARIABILITY OVER THE EASTERN NORTH-ATLANTIC OCEAN - CHEMICAL AND METEOROLOGICAL EVIDENCE FOR TROPICAL INFLUENCE ON REGIONAL-SCALE TRANSPORT IN THE EXTRATROPICS

Observed boreal fall season (September-November) 1991 surface CO data from Mace Head, Ireland,are characterized by particularly high mixing ratios, as evidenced by high means, medians, and maxima for those mont hs, relative to the same data for boreal fall 1992 Air parcels charact erized by elevated CO during fall 1991 are attributed to European sour ces on the basis of isentropic back trajectory analysis. histogram of the 1991 data shows a bimodal distribution representing two discrete s ource regions, North Atlantic and European, while the 1992 data show o nly one mode, representing primarily zonal westerly flow over the Nort h Atlantic Ocean. A similar distinction exists in O-3 data between the two years. Considerable interannual variability has important implica tions for observationalists and modelers alike; an inherent uncertaint y is introduced by basing any determination of trend from only a few y ears of data. An isentropic flow climatology for Mace Head illustrates significant differences in the regional-scale flow patterns to Mace H ead between the 1991 and the 1992 fall seasons. These differences have been examined in terms of general dynamical principles and tropical/e xtratropical coupling. There is evidence of the existence of Rossby wa ve links with the tropical upper troposphere over South America and th e central Pacific Ocean which are responsible for the climatic forcing giving rise to the observed interannual variation in large-scale flow patterns and influencing the chemical character of air parcels reachi ng Mace Head. Using CO as a tracer for short-lived continental anthrop ogenic O-3 precursors and calculating Delta O-3/Delta CO for air parce l trajectories following anticyclonic paths over western Europe during the late summer and fall season of 1991, we estimate O-3 production o ver western Europe at about 66 (40-96) billion moles of O-3 per summer (similar to 3 Tg O-3 per summer), based on 1985 CO emission inventory data (37 Tg CO yr(-1) for western Europe),