Two EUFAR-funded research flight campaigns took place in Namibia in August and September 2017, namely EriSMA (investigating the Effects of Satellite assimilation of dust in NMM-DREAM Model over SW Africa) and ALLDUST-SA (The Etosha Pan as an Alluvial Dust Source – A Sub-basin Analysis). These projects were clustered with the AEROCLO-sA flight campaign (Aerosol RadiatiOn and CLOuds in southern Africa), headed by lead scientists Paola Formenti (LISA) and Cyrille Flamant who headed the flight campaign. AEROCLO-sA project is a French national research initiative led by six French laboratories consisting of Météo-France, the CNRS and various universities. Although the two EUFAR flight campaigns had their own specific research objectives, they were however organised under the umbrella of the AEROCLO-sA consortium, and hence could benefit from the spirit of the project and the scientific and technical expertise involved. Measurements were performed with the French FALCON F20 aircraft operated by SAFIRE, and equipped with a set of different instruments, in particular the high spectral resolution LIDAR LNG, the infra-red radiometer CLIMAT, the solar sun-photometer PLASMA, the OSIRIS radiometer, up- and down-welling pyranometers and pyrgeometers and in-situ instruments, and a releasing device for dropsondes as well as optical sensors for aerosol and cloud particle properties. Altogether, the measurements offered the possibility to profile and sample the aerosol load of the atmospheric column at high vertical resolution.
The ALLDUST-SA project aims for the sub-basin scale characterization of dust emission from the Etosha Pan, one of the most active dust sources in southern Africa. This salt pan located in northern Namibia is particularly interesting as it forms the endpoint of an ephemeral drainage system, which suggests a strong connection between annual precipitation pattern and dust activity. A strong variation in the dust activity from year to year is evident and documented by recent satellite-based studies - a significant feature that is essential to understand and hard to predict. Due to stronger than usual inundations of the pan during the first half of 2017 caused by above average rainfall amounts, the pan showed lower than usual dust emissions during this year’s dry season. However, an Etosha survey overflight was performed on 5 Sept 2017 (flight # fs20170006) aiming to assess the dust source activity and the contribution of dust originating from Etosha to the general aerosol burden over northern Namibia.
Indeed, several other hydrologically influenced dust source regions were within the range of the aircraft. Henceforth, due to the low dust activity in the Etosha pan during the flight campaign, the study area was broadened to other hydrologically-influenced dust sources along the Namibian coast. Fortunately, we were able to obtain LIDAR measurements showing airborne dust above the coastal dust sources during two flights in the morning and afternoon of 8 Sept 2017 (flight # fs20170011 and fs20170012). These measurements allow us to examine the precise location of the overflown Namibian coastal dust sources and the near-source transport of dust in the vicinity of the Atlantic Ocean.
The EriSMA project on the other hand aimed to improve the description of the dust plumes in the area provided by the NMM-DREAM model, by assimilating satellite dust retrievals within it, such as the MSG-SEVIRI dust optical depth and the CALIPSO and CATS dust vertical profiling. The results would be compared with dust microphysical and optical property retrievals, utilizing the airborne LIDAR profiles and the airborne in situ observations. The focus of the analysis has changed due to the low dust occurrence in the area during the research campaign. The interest has been shifted to the high-AOD smoke transport from the North of Namibia. This impressive smoke plume almost persisted during the whole period of the airborne measurements. The first analysis revealed some very interesting cases of smoke hydration above the ocean (flight on 7 September 2017, at 9 UTC) and/or land (flight on 8 September 2017, at 11 UTC, Fig. 4), as well as above the Etosha pan (flight on 6 September 2017, at 11 UTC). These cases will be analyzed with the In situ/Remote sensing aerosol Retrieval Algorithm (IRRA) (Tsekeri et al., 2017). IRRA combines airborne in situ with remote sensing measurements and provides the optical, microphysical and hygroscopic properties of the atmospheric aerosols.
For more information, contact Stefanie Feuerstein.
Figure 1: Dust emission from Namibian dust sources seen from MODIS Terra, acquired on 9 June 2004 (Image courtesy Jacques Descloitres, NASA-Goddard Space Flight Center)
Figure 2: Scientist team in front of SAFIRE’s F20 aircraft for the airborne campaign at Walvis Bay airport, Namibia (Image courtesy Laurent Labbouz)
Figure 3: Namibia from above: a glance out of the Falcon’s window reveals the aridity of the country (image courtesy Dominique Duchanoy)
Figure 4: Flight overview on 8 September 2017, at 11 UTC. Data shown are from the ocean-land transect part of the flight, during which we acquired possible interesting smoke particle hydration profiles for ERiSMA project