On the origin of tropospheric O3 over the Indian Ocean during the winter monsoon: African biomass burning vs. stratosphere-troposphere exchange

[摘要] This study investigates the origin of a commonly observed feature in theO₃ profiles: mid tropospheric O₃ maxima (300--500 hPa) over the tropical Indian Ocean. Acomparison and analysis of model simulations, using a 3-D global climate-chemistrymodel, and measured O₃ profiles from the INDOEX campaign is presented. EuropeanCentre for Medium-Range Weather Forecast (ECMWF) meteorological analyses havebeen assimilated into the 3-D model to represent actual meteorology. The modelrealistically simulates the observed mid-tropospheric O₃ maxima. The analysis of themodel simulations shows that the major source of the mid-tropospheric O₃ maxima isadvection of polluted air masses from continental biomass burning areas over Africa,with generally only a small contribution of stratospheric O₃. Previous studies hinted atstratosphere-troposphere exchange (STE) along the subtropical jet (STJ) as theprimary source of the mid-tropospheric O₃maxima over the Indian Ocean. Analysis of the model simulations shows that the mechanism causing themid-tropospheric transport of African biomass burning pollution and stratospheric airmasses are frontal zones or waves passing along the subtropical jets, causingadvection of tropical air masses in the prefrontal (equatorward) zone. Furthermore, thefrontal zones or waves also cause STE at the poleward side of the STJ. The modelsimulations also indicate that the contribution of STE in general is minor compared toadvection and in situ tropospheric production of O₃for the mid-tropospheric O₃budget over the Indian Ocean region.

[学科分类] 大气科学