20 Apr 2021

20 Apr 2021

Review status: this preprint is currently under review for the journal ACP.

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

Marco Gaetani1,2, Benjamin Pohl3, Maria del Carmen Alvarez Castro4,5, Cyrille Flamant6, and Paola Formenti1 Marco Gaetani et al.
  • 1Institut Pierre Simon Laplace, Laboratoire Interuniversitaire des Systèmes Atmosphériques, UMR CNRS 7583, Université Paris-Est Créteil, Université de Paris, Institut Pierre Simon Laplace, Créteil, France
  • 2Scuola Universitaria Superiore IUSS, Pavia, Italia
  • 3CRC/Biogéosciences, UMR6282 CNRS / Université de Bourgogne Franche-Comté, Dijon, France
  • 4University Pablo de Olavide, Seville, Spain
  • 5CMCC, Bologna, Italy
  • 6Institut Pierre Simon Laplace, Laboratoire Atmosphères, Milieux, Observations Spatiales, UMR CNRS 8190, Sorbonne Université, Université Versailles Saint Quentin, Paris, France

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

In this study, a characterisation of the synoptic variability controlling the spatial distribution of BBA in southern Africa and South Atlantic during austral winter (August to October) is presented. By analysing atmospheric circulation data from reanalysis products, a 6-class weather regime (WR) classification of the region is constructed. The classification reveals that the synoptic variability is composed by four WRs representing disturbances travelling at midlatitudes, and two WRs accounting for pressure anomalies in the South Atlantic. The WR classification is then successfully used to characterise the aerosol spatial distribution in the region in the period 2003–2017, in both reanalysis products and station data. Results show that the BBA transport towards southern extratropics is controlled by weather regimes associated with midlatitude synoptic disturbances. In particular, depending on the relative position of the pressure anomalies along the midlatitude westerly flow, the BBA transport is deflected from the main tropical route towards southern Africa or the South Atlantic.

This paper presents the first objective classification of the winter synoptic circulation over South Atlantic and southern Africa. The classification shows skills in characterising the BBA transport, indicating the potential for using it as a diagnostic/predictive tool for aerosol dynamics, which is a key component for the full understanding and modelling of the complex radiation-aerosol-cloud interactions controlling the atmospheric radiative budget in the region.

Marco Gaetani et al.

Status: open (until 15 Jun 2021)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse

Marco Gaetani et al.

Marco Gaetani et al.


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Short summary
During the dry austral winter, forest fires in tropical Africa emit large amount of smoke in the atmosphere, with large impacts on climate and air quality. The study of the relationship between atmospheric circulation and smoke transport shows that midlatitude atmospheric disturbances may deflect the smoke from the Tropical Africa towards southern Africa. Understanding the distribution of the smoke in the region is very important for climate modelling and air quality monitoring.