Chasing clouds in West Africa
West Africa is changing. An explosively growing population, massive urbanisation, complex meteorological influences, unregulated deforestation and air pollution modify the composition of the atmosphere, not only impacting human health but also the weather and climate. How bad the problem actually is and how exactly these emissions are changing the region in the long-term is not yet clear. Researchers from the German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR) used the Falcon research aircraft to analyse the tropical air on the West African coast in order to determine its composition and its effect on the clouds’ climate-relevant properties. The measurement flights were part of the five-year EU project DACCIWA-Projekt (engl.) (Dynamics-Aerosol-Chemistry-Cloud Interactions in West Africa).
A cocktail of emissions
Monsoon winds with sea salt from the south, Sahara winds with dust from the north, charcoal fires and burning rubbish from cities as well as power plants, ship traffic, oil rigs and out-dated engines – the air over the coastal region of West Africa is a unique mixture of various gases, liquids and particles. At the same time, multi-layer cloud decks frequently form in the atmosphere that exert a large influence on the local weather and climate. The composition of the particles in the air – and what impact they have on the formation and breakup of clouds – has not been studied in detail, and this information is not included in the weather and climate models used to look to the future.
Aircraft, ground stations and weather balloons
The EU-funded project DACCIWA is investigating the relationship between weather, climate and air pollution in West Africa. It is coordinated by the Karlsruhe Institute of Technology (KIT) in Germany and consists of researchers from 16 international scientific organisations. For the first time, the entire chain of impacts of natural and manmade emissions on the West African atmosphere is investigated in a coordinated field campaign. As part of this campaign, three research aircraft based in Togo flew targeted missions over West Africa from June to July. In addition, DACCIWA scientists set up three highly instrumented measuring sites inland, launched weather balloons several times a day across the region, measured urban emissions and evaluated health data. This five-year project lays the foundation for new and more precise climate, weather and air quality models that support policies towards a more sustainable development for the region.
EU-Projekt DACCIWA: Klimaveränderungen in Westafrika
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DLR
Cloud layers under the microscope
The DLR researchers took off into the West African skies in the 40-year-old Falcon research aircraft from Lomé–Tokoin Airport, just five kilometres from the border with Ghana. The pilots from DLR’s Flight Experiments facilty in Oberpfaffenhofen steered the Falcon up to different altitudes through cloud layers and deliberately flew into exhaust gas plumes. Shipping traffic off the south coast of West Africa and the emissions of an oil platform off the coast of Ghana were also investigated. During the flights, the climate experts from the DLR Institute of Atmospheric Physics sweated it out at a cabin temperature of over 40 degrees and collected data inside and outside the clouds with the aid of trace gas, particle and cloud measurement instruments.
"Aerosols are particles in the atmosphere that originate from natural and anthropogenic sources," explains DLR project manager Hans Schlager. With the Falcon, we fly specifically inside clouds and investigate the aerosol load of air masses. This enables us to investigate the influence of the prevailing air pollution on the properties of the clouds.” Because an extensive stratus cloud layer forms over the coast of West Africa every day, the region is a perfect laboratory to study these interactions.
The three research aircraft flying coordinated missions across West Africa are DLR’s Falcon, the UK British Antarctic Survey Twin Otter and the ATR operated by the Service des Avions Français Instrumentés pour la Recherche en Environnement (SAFIRE), which is a joint entity of CNRS, Météo-France and the French Space Agency CNES. The aircraft were used in different ways based on their strengths, but all three had comparable instrumentation generating a rich dataset of atmospheric conditions across the region, which will be used to challenge our current understanding of the region.
Surprising results
Air pollution does not stay where it is produced, but runs up to 300 kilometres inland. The aircraft have been used to follow the air pollution from the big coastal cities (Accra, Abidjan, Lomé, Cotonou) as it streams inland reaching the inland forests and then heading towards the Sahara. First results surprisingly show that these plumes contain large fractions of organic material – a finding that points towards burning of charcoal, rubbish and agricultural waste at low temperature in the cities. The particles from these fires lead to a considerable haziness in the atmosphere. Less sunshine reaches the ground, thereby changing the daily pattern of temperature, wind and clouds. The measurements show for the first time an enormous complexity in the different cloud layers whose causes are still unclear.
Research up to 2018
DACCIWA scientists will investigate the influences of various emissions on cloud properties and air quality in West Africa until 2018. Looking ahead, Schlager comments: "Our results will be used to improve current climate and weather models. Together with our African partners, we will be able to issue more reliable forecasts for West Africa, one of the regions in the world that will feel the effects of climate change the most."
Read more about the campaign on DLR´s AeronauticsBlog: "A day in the tropical sky".