The Australian bushfires of February 2009: MIPAS observations and GEM-AQ model results

摘要

Starting on 7 February 2009, southeast Australia was devastated by largebushfires, which burned an area of about 3000 km2 on this day alone. Thisevent was extraordinary, because a large number of combustion products weretransported into the uppermost troposphere and lower stratosphere within afew days. Various biomass burning products released by the fire were observedby the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) onthe Envisat satellite. We tracked the plume using MIPAS C₂H₂, HCN andHCOOH single-scan measurements on a day-to-day basis. The measurements werecompared with a high-resolution model run of the Global EnvironmentalMultiscale Air Quality (GEM-AQ) model. Generally there is good agreementbetween the spatial distribution of measured and modelled pollutants. BothMIPAS and GEM-AQ show a fast southeastward transport of the pollutants toNew Zealand within one day. During the following 3–4 days, the plume remainednortheastward of New Zealand and was located at altitudes of 15 to 18 km.Thereafter its lower part was transported eastward, followed by westwardtransport of its upper part. On 17 February the eastern part had reachedsouthern South America and on 20 February the central South Atlantic. Onthe latter day a second relic of the plume was observed moving eastward abovethe South Pacific. Between 20 February and the first week of March, theupper part of the plume was transported westward over Australia and theIndian Ocean towards southern Africa. First evidence for entry of thepollutants into the stratosphere was found in MIPAS data of 11 February,followed by larger amounts on 17 February and the days thereafter. From MIPASdata, C₂H₂/HCN and HCOOH/HCN enhancement ratios of 0.76 and 2.16 werecalculated for the first days after the outbreak of the fires, which areconsiderably higher than the emission ratios assumed for the model run and atthe upper end of values found in literature. From the temporal decrease ofthe enhancement ratios, mean lifetimes of 16–20 days and of 8–9 days werecalculated for measured C₂H₂ and HCOOH. The respective lifetimescalculated from the model data are 18 and 12 days.