the seasonal variability of ozone mixing ratios and budgets in the tropical southern

tropical southern Pacific Authors: Jennifer C. Wei, V. R. Kotamarthi, D. J. Wuebbles Abstract. Significant seasonal variations in the concentrations of ozone, NOx, nonmethane hydrocarbons and other trace gases were observed in the southern tropical Pacific during the PEM-TROPICS-A (PT-A, Sep/Oct 1996) and PEM-TROPICS-B (PT-B, Mar/Apr 1999). Making these data sets more useful would require development of the relationship of these limited data sets to the seasonal and climatic variability of the atmosphere. Here we employ a three-dimensional global scale chemical transport model to generate the chemical climatology of troposphere and then evaluate the ozone budget in the southern tropical Pacific Ocean. We also identify key control factors in the model and compare model results with measurements. This process evaluates the effectiveness of the model in representing transport barriers, such as the Inter-Tropical Convergence Zone (ITCZ) and South Pacific Convergence zone (SPCZ) and the effects of biomass burning in South America and Africa on ozone in the middle of the Pacific Ocean. The model has considerable skill in reproducing the observed ozone profiles, including the seasonal variability. Transport of ozone from the west to the model mid-troposphere in the central Pacific during the PT-A period caused a net increase in the ozone burden. A net outflow of ozone from the region to the east reduced the ozone burden during the PT-B period. For the upper troposphere the horizontal advective flux inputs into the central Pacific show a similar trend. The input from the north was found to be much larger during the PT-B period than during the PT-A period. The in situ production and loss calculated in the 3-D model were in approximate agreement with values derived from measurements. The gradients in the model across the ITCZ and SPCZ are also compared with the measurements.