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The Etosha pan in northeastern Namibia is known to be one of the main dust sources in Austral Africa. In addition, the pan area is characterized by a high surface albedo, yielding the deepest and most turbulent planetary boundary layer (PBL) over the elevated, arid Namibian plateau during the Austral summer.In early September 2017, the Etosha pan region (and most of Namibia) was under the influence of a massive biomass burning aerosol plume originating from nearby Angola. The presence of large quantities of absorbing aerosols in and above the PBL disrupted the radiative balance over Etosha pan and impacted the PBL dynamics and thermodynamics diurnal cycle.In this study, we use a combination of ground-based remote sensing observations acquired in Windpoort, airborne observations from 5 flights performed with the SAFIRE Falcon 20 during the AEROCLO-sA field campaign (August-September 2017) and high resolution numerical mesoscale simulations to investigate the evolution of the PBL dynamics and thermodynamics over the Etosha pan as a function of the aerosol direct radiative forcing. The features of the PBL in the Etosha pan are also compared to those of surrounding areas characterized by darker surfaces. The impact of the PBL dynamics on aerosol distribution (dust and biomass burning particles) is also investigated using ground-based and airborne lidars, together with dropsondes released from the Falcon 20. Complementary observations include the suite of advanced airborne radiometers, airborne optical sensors for cloud and aerosol microphysics and a ground-based sunphotometer. [ABSTRACT FROM AUTHOR]

A specific instrumental synergy, associating ground-based lidar, airborne and spaceborne remote sensing measurements, was set up as part of the field campaign of the AErosol, RadiatiOn and CLOuds in southern Africa (AEROCLO-sA) project. The overarching objective of AEROCLO-sA is to improve our knowledge about the role of atmospheric aerosols on the specific climate of southern Africa. For this reason, the Henties Bay experimental site of the Research Centre of the University of Namibia (22° 6' S, 14° 17' E) in the Orongo region has been selected to implement a ground-based lidar between 22 August and 12 September, 2017. The geographical position of the site is favorable for such a study, it is bounded on its western side by the Atlantic Ocean and by the Namibia desert (~800 m amsl) on its eastern side. A big part of the year, as the west coast of South Africa, Henties Bay is covered with low clouds of stratocumulus type with very frequent fogs, and often overflown by air masses loaded with aerosol of various origins: forest fires, pollution, desert and/or ocean. Strong contributors to the aerosol load are the forest fires occurring during the dry season between August and October. Biomass burning aerosols exert a strong influence on the Earth's radiation budget by scattering and absorbing solar radiation, and influence the cloud formation and life time. The vertical distribution of absorbing aerosols is of paramount importance as it significantly influences the vertical profile of radiative heating in the atmosphere and, by this way, the stability of the atmosphere, thereby modifying convective and turbulent motions and clouds. The main vertical aerosol structures observed by lidar will be present and discussed. Passive (MODIS) and active (CALIPSO, CATS) space-borne observations coupled with back trajectory studies will allow for regionalized the local lidar observations. [ABSTRACT FROM AUTHOR]

The Sahara is the world's largest source of mineral dust in the atmosphere, which is a key player of the Earth system. Desert dust layers impact the radiative budget, atmospheric stability, cloud properties, chemical balances and air quality depending on the altitude at which they are transported. Over the Sahara, the three-dimensional (3D) distribution of dust is closely linked to dust uplifting mechanisms and its redistribution in the vertical, driven by the main atmospheric dynamical actors in the region. A better understanding of these mechanisms is very important for assessing the 3D budget of Saharan dust, which is currently highly uncertain. However, observations of the 3D distribution of desert dust are highly scarce and particularly over the Sahara where they exclusively rely on satellite remote sensing. Indeed, the two-dimensional (2D) distribution of dust is standardly observed: either its horizontal distribution in terms of aerosol optical depth from e.g. MODIS, OMI, IASI measurements and also in this last case mean dust layer altitudes or latitudinal transects of vertical profiles of dust from the CALIOP lidar. In order to overcome this limitation, we have developed a so-called AEROIASI new satellite approach for retrieving the 3D distribution of desert dust from thermal infrared spectra measured by IASI. This method uses full radiative transfer calculations from the KOPRA model and an auto adaptive Tikhonov-Philips-type regularization for deriving vertical profiles of dust extinction coefficient at 10 μm for most cloud-free IASI pixels, both over land (including bright desert surfaces) and ocean. The dust vertical distribution derived from AEROIASI agrees remarkably well with along track transects of CALIOP space-borne lidar vertical profiles as well as with aerosol optical depth derived from AERONET sun photometer measurements over West Africa.We use AEROIASI to investigate the role of the main dynamic actors in the vertical redistribution of dust over the Sahara during June 2011. We find a major role of the African easterly waves and cold air intrusions as those from the West African monsoon, affecting directly or indirectly the vertical distribution and propagation of major dust plumes. Cold pools generated by mesoscale convective systems are as well a major mechanism for uplifting dust over the Sahel and Southern Sahara. In the present study, we will present the full 3D distribution of dust observed by AEROIASI and the link with these major dynamic actors of the region. [ABSTRACT FROM AUTHOR]