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

Atmospheric dynamics over southern Africa and South Atlantic is dominated by complex aerosol-radiation-cloud interactions, and the characterisation of the tropospheric distribution of aerosols is essential for the full understanding of these interactions.

During austral winter, a compact low cloud deck over South Atlantic contrasts clear sky over southern Africa, where forest fires triggered by dry conditions emit large amount of biomass burning aerosols in the free troposphere. Most of the aerosol burden crosses the Tropical Atlantic embedded in the tropical easterly flow. However, mid-latitude synoptic disturbances can deflect part of the aerosols from the main transport path towards southern extra-tropics.

In this study, a characterisation of the synoptic variability controlling biomass burning aerosols in southern Africa and South Atlantic during austral winter is presented. By analysing ECMWF reanalysis data, a weather regime classification of the region is constructed and used to characterise the aerosol distribution in the period 2003-2017. Results show three southward transport paths, each associated with a specific circulation regime.