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. During austral winter, a compact low cloud deck over the South Atlanticcontrasts with clear sky over southern Africa, where forest fires triggeredby dry conditions emit large amounts of biomass burning aerosols (BBAs) in thefree troposphere. Most of the BBA burden crosses the South Atlantic embeddedin the tropical easterly flow. However, midlatitude synoptic disturbancescan deflect part of the aerosol from the main transport path towardssouthern extratropics. In this study, the first objective classification of the synopticvariability controlling the spatial distribution of BBA in southern Africaand the South Atlantic during austral winter (August to October) ispresented. By analysing atmospheric circulation data from reanalysisproducts, a six-class weather regime (WR) classification of the region isconstructed. The classification reveals that the synoptic variability iscomposed of four WRs, representing disturbances travelling at midlatitudes,and two WRs accounting for pressure anomalies in the South Atlantic. The WRclassification is then successfully used to characterise the aerosol spatialdistribution in the region in the period 2003–2017, in both reanalysisproducts and station data. Results show that the BBA transport towardssouthern extratropics is controlled by weather regimes associated withmidlatitude synoptic disturbances. In particular, depending on the relativeposition of the pressure anomalies along the midlatitude westerly flow, theBBA transport is deflected from the main tropical route towards southernAfrica or the South Atlantic. Moreover, the WRs accounting for midlatitudedisturbances show organised transition sequences, which allow one to illustratethe evolution of the BBA northerly transport across the region in thecontext of a wave pattern. The skill in characterising the BBA transport shown by the WR classificationindicates the potential for using it as a diagnostic/predictive tool for theaerosol dynamics, which is a key component for the full understanding andmodelling of the complex radiation–aerosol–cloud interactions controllingthe atmospheric radiative budget in the region.

A weather regime characterisation of winter biomass aerosol transport from southern Africa