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

2021 ◽  
Author(s):  
Marco Gaetani ◽  
Benjamin Pohl ◽  
Maria del Carmen Alvarez Castro ◽  
Cyrille Flamant ◽  
Paola Formenti
Keyword(s):  
Spatial Distribution ◽  
Southern Africa ◽  
Forest Fires ◽  
South Atlantic ◽  
Austral Winter ◽  
The South ◽  
Predictive Tool ◽  
Weather Regime ◽  
Synoptic Variability

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.

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

2021 ◽  
Vol 21 (21) ◽  
pp. 16575-16591
Author(s):  
Marco Gaetani ◽  
Benjamin Pohl ◽  
Maria del Carmen Alvarez Castro ◽  
Cyrille Flamant ◽  
Paola Formenti
Keyword(s):  
Spatial Distribution ◽  
Southern Africa ◽  
Forest Fires ◽  
South Atlantic ◽  
Austral Winter ◽  
The South ◽  
Predictive Tool ◽  
Weather Regime ◽  
Synoptic Variability

Abstract. During austral winter, a compact low cloud deck over the South Atlantic contrasts with clear sky over southern Africa, where forest fires triggered by dry conditions emit large amounts of biomass burning aerosols (BBAs) in the free troposphere. Most of the BBA burden crosses the 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, the first objective classification of the synoptic variability controlling the spatial distribution of BBA in southern Africa and the South Atlantic during austral winter (August to October) is presented. By analysing atmospheric circulation data from reanalysis products, a six-class weather regime (WR) classification of the region is constructed. The classification reveals that the synoptic variability is composed of 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. Moreover, the WRs accounting for midlatitude disturbances show organised transition sequences, which allow one to illustrate the evolution of the BBA northerly transport across the region in the context of a wave pattern. The skill in characterising the BBA transport shown by the WR classification indicates the potential for using it as a diagnostic/predictive tool for the 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.

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

2020 ◽  
Author(s):  
Marco Gaetani ◽  
Maria del Carmen Alvarez Castro ◽  
Cyrille Flamant ◽  
Benjamin Pohl ◽  
Paola Formenti
Keyword(s):  
Biomass Burning ◽  
Southern Africa ◽  
Forest Fires ◽  
Reanalysis Data ◽  
South Atlantic ◽  
Austral Winter ◽  
Weather Regime ◽  
Low Cloud ◽  
Transport Path ◽  
Dry Conditions

<p>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.</p><p>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.</p><p>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.</p><p> </p>

scholarly journals Potential Sources of Decadal Climate Variability over Southern Africa

2015 ◽  
Vol 28 (22) ◽  
pp. 8695-8709 ◽  
Author(s):  
Yushi Morioka ◽  
Francois Engelbrecht ◽  
Swadhin K. Behera
Keyword(s):  
Indian Ocean ◽  
Climate Variability ◽  
Southern Africa ◽  
South Atlantic ◽  
Decadal Climate Variability ◽  
The South ◽  
Sst Anomaly ◽  
Decadal Climate ◽  
Southwestern Indian Ocean ◽  
Sst Anomalies

Abstract Potential sources of decadal climate variability over southern Africa are examined by conducting in-depth analysis of available datasets and coupled general circulation model (CGCM) experiments. The observational data in recent decades show a bidecadal variability noticeable in the southern African rainfall with its positive phase of peak during 1999/2000. It is found that the rainfall variability is related to anomalous moisture advection from the southwestern Indian Ocean, where the anomalous sea level pressure (SLP) develops. The SLP anomaly is accompanied by anomalous sea surface temperature (SST). Both SLP and SST anomalies slowly propagate eastward from the South Atlantic to the southwestern Indian Ocean. The analysis of mixed layer temperature tendency reveals that the SST anomaly in the southwestern Indian Ocean is mainly due to eastward advection of the SST anomaly by the Antarctic Circumpolar Current. The eastward propagation of SLP and SST anomalies are also confirmed in the 270-yr outputs of the CGCM control experiment. However, in a sensitivity experiment where the SST anomalies in the South Atlantic are suppressed by the model climatology, the eastward propagation of the SLP anomaly from the South Atlantic disappears. These results suggest that the local air–sea coupling in the South Atlantic may be important for the eastward propagation of the SLP anomaly from the South Atlantic to the southwestern Indian Ocean. Although remote influences from the tropical Pacific and Antarctica were widely discussed, this study provides new evidence for the potential role of local air–sea coupling in the South Atlantic for the decadal climate variability over southern Africa.

scholarly journals Relationship between spatial distribution of chaetognaths and hydrographic conditions around seamounts and islands of the tropical southwestern Atlantic

2014 ◽  
Vol 86 (3) ◽  
pp. 1151-1165 ◽  
Author(s):  
CHRISTIANE S. DE SOUZA ◽  
JOANA A.G. LUZ ◽  
PAULO O. MAFALDA JUNIOR
Keyword(s):  
Spatial Distribution ◽  
Water Column ◽  
Water Mass ◽  
South Atlantic ◽  
Northeastern Brazil ◽  
Southwestern Atlantic ◽  
The South ◽  
Water Column Stability ◽  
South Atlantic Central Water ◽  
Hydrographic Conditions

Relationship between spatial distribution of chaetognaths and hydrographic conditions around seamounts and islands off Northeastern Brazil were analyzed from 133 oceanographic stations during the months of January – April of 1997 and April – July of 1998. Oblique zooplankton tows, using 50 cm diameter Bongo nets with 500µm mesh with a flowmeter to determine the filtered volume, were carried out to a maximum of 200m depth. The Superficial Equatorial Water, which had a salinity > 36 PSU and temperature > 20°C, occupied the top 80 to 200m depth. Below this water mass was the South Atlantic Central Water with salinity ranging from 34.5 to 36 PSU and temperature from 6 to 20°C. The community of chaetognaths showed six species: Pterosagitta draco, Flaccisagitta enflata, Flaccisagitta hexaptera, Pseudosagitta lyra, Serratosagitta serratodentata, and Sagitta helenae. Of these species, F. enflata was the most abundant (32.05% in 1997 and 42.18% in 1998) and the most frequent (87.88% in 1997 and 95% in 1998) during both periods. A mesopelagic specie was identified (P. lyra). This specie was more abundant in 1997 (3.42%), when the upwelling was more intense. P. lyra occurred in 22% of the samples during 1997. The abundance of F. enflata, an epiplanktonic species, increased, associated with greater water-column stability.

scholarly journals Memory Effect of the Southern Atlantic Subtropical Dipole

2020 ◽  
Vol 33 (17) ◽  
pp. 7679-7696
Author(s):  
Wlademir Santis ◽  
Paola Castellanos ◽  
Edmo Campos
Keyword(s):  
Memory Effect ◽  
Mixed Layer ◽  
Ocean Model ◽  
Dominant Mode ◽  
South Atlantic ◽  
Austral Winter ◽  
The South ◽  
Climate Conditions ◽  
Temperature Anomalies ◽  
Sst Anomalies

AbstractThe South Atlantic subtropical dipole is the dominant mode of coupled variability in the South Atlantic, connecting sea level pressure and sea surface temperature. Previous studies have shown its great relevance to the climate conditions over South America and West Africa. We have used several numerical experiments with the Hybrid Coordinate Ocean Model to investigate the effects that an austral winter–spring dipole asserts on the South Atlantic. We explore the interaction between SST anomalies and the formation of the fossilized mixing region, which preserve temperature anomalies underneath the summer mixed layer, until they feed back to SST after the next autumn. It was found that, through this process, there is a memory effect that restores temperature anomalies from an austral winter–spring dipole back to the austral winter of the following year. The dominant mechanisms are the contribution from entrainment and surface net heat flux (NHF). Entrainment is mostly controlled by vertical temperature gradient anomalies, while surface NHF is controlled by interactions of climatological ocean heat loss and anomalies of mixed layer thickness. Our results suggest that the combined effect of entrainment and surface NHF is different in the southwest and northeast dipole regions, leading to differences in both intensity and timing of SST anomalies. Turbulent and nonlinear processes are most important to reduce entrainment in the southwest dipole region and to increase the memory effect asymmetry.

scholarly journals New Archeomagnetic Directional Records From Iron Age Southern Africa (ca. 425–1550 CE) and Implications for the South Atlantic Anomaly

2018 ◽  
Vol 45 (3) ◽  
pp. 1361-1369 ◽  
Author(s):  
Vincent J. Hare ◽  
John A. Tarduno ◽  
Thomas Huffman ◽  
Michael Watkeys ◽  
Phenyo C. Thebe ◽  
...  
Keyword(s):  
Iron Age ◽  
Southern Africa ◽  
South Atlantic ◽  
The South ◽  
South Atlantic Anomaly

The African Slave Trade and the Construction of the Iberian Atlantic

2017 ◽  
Author(s):  
Luiz Felipe de Alencastro
Keyword(s):  
Eighteenth Century ◽  
Latin America ◽  
South America ◽  
Southern Africa ◽  
Slave Trade ◽  
South Atlantic ◽  
The South ◽  
African Slave ◽  
History Of

Scholarly studies of the colonization of the Americas—especially of Latin America—have tended to minimize the role played by Africans and the African slave trade, treating the history of conquest and colonialism as a story of inevitable European domination of the hemisphere. However, from the sixteenth through the eighteenth century, colonialism in the Americas depended upon the exportation of slaves from Africa, a massive undertaking that was supported not only by Iberian Royal families but also by convoluted ideological and theological justifications elaborated by legal and religious scholars. During this period, Portugal dominated the slave trade, raiding its colonies in Southern Africa to supply its plantations (many run by Jesuits) in South America. In this sense, the story of the South Atlantic is a story of encounters and exchanges between Africa and the Americas.

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