Linking horizontal and vertical transports of biomass fire emissionsto the tropical Atlantic ozone paradox during the Northern Hemisphere winter season: climatology

[摘要] During the Northern hemisphere winter season, biomass burning is widespreadin West Africa, yet the total tropospheric column ozone values (<30DU)over much of the Tropical Atlantic Ocean (15°N-5°S) are relativelylow. At the same time, the tropospheric column ozone values in the SouthernTropical Atlantic are higher than those in the Northern Hemisphere (ozoneparadox). We examine the causes for low tropospheric column ozone values byconsidering the horizontal and vertical transport of biomass fire emissionsin West Africa during November through March, using observed data whichcharacterizes fires, aerosols, horizontal winds, precipitation, lightningand outgoing longwave radiation. We have found that easterly winds prevailin the lower troposphere but transition to westerly winds at pressure levelslower than 500hPa. A persistent anticyclone over West Africa at 700hPa isresponsible for strong easterly winds, which causes a net outflow ofozone/ozone precursors from biomass burning in West Africa across theAtlantic Ocean towards South America. The lowest outgoing longwave radiation(OLR) and highest precipitation rates are generally found over the centralAtlantic, some distance downstream of fires in West Africa making thevertical transport of ozone and ozone precursors less likely and ozonedestruction more likely. However, lightning over land areas in CentralAfrica and South America can lead to enhanced ozone levels in the uppertroposphere especially over the Southern tropical Atlantic during theNorthern Hemisphere winter season.

[学科分类] 大气科学