Multi‐platform observations of a springtime case of Bodélé and Sudan dust emission, transport and scavenging over West Africa

Abstract

ABSTRACT:The structure of the Saharan air layer over Niger and Benin during a major springtime dust event from the Bodélé region and Sudan is investigated using airborne lidar and dropsonde measurements. Aircraft operations were conducted on 13 and 14 June 2006, within the framework of the African Monsoon Multidisciplinary Analysis Special Observing Period. Complementary ground-based and satellite observations, as well as European Centre for Medium-range Weather Forecasts analyses are used to investigate the regional aspects of emission, transport and deposition in the period from 9 to 14 June 2006, to provide a framework for the interpretation of the airborne measurements. The study details the transport patterns of dust from eastern Saharan sources towards the southwest in the springtime, and highlights the role of the intertropical discontinuity and the Darfur mountains in injecting the aerosols from Bodélé and Sudan, respectively, over the monsoon flow, and in the African easterly jet (AEJ) region. It also illustrates the impact of the daily variability of the emissions in the source regions on the dust load advected westward by the AEJ and observed over Benin. The impact of a mesoscale convective system (MCS) on the dust load and vertical distribution observed over Benin and southern Niger was also investigated, nearly 12 hours after its passage over Benin. The only discernible impact on the dust distribution is observed to be associated with widespread subsidence in the wake of the MCS, over northern Benin and Niger. Wet scavenging related to convective or stratiform rain could not be observed, as processed air masses were replaced by fresh dust transported in the upper Saharan air layer by the AEJ. Over southern Benin, the dust distribution appeared to be mostly controlled by processes affecting the planetary boundary layer upstream, i.e. over Nigeria or Chad. Because springtime dust from remote eastern sources (such as observed in this case) is mainly transported into the AEJ, it could impact on the radiation budget in the AEJ region, thereby possibly modifying the West African weather at the synoptic scale. Copyright

Temporal variability of mineral dust concentrations over West Africa: analyses of a pluriannual monitoring from the AMMA Sahelian Dust Transect

“…Indeed, in addition to the continental dust storms identified in March 2004 (Knippertz and Fink, 2006) and March 2006(Slingo et al, 2006Tulet et al, 2007), several meso-scale patterns of Saharan dust emissions and redistribution have been recently identified based on observations from the AMMA program (e.g. Flamant et al, 2007Flamant et al, , 2009BouKaram et al, 2008), the SAMUM experiments (Saharan Mineral Dust Experiment; May 2006; Morocco) (e.g. Knippertz et al, 2007Knippertz et al, , 2009 (Marsham et al, 2008).…”

Mapping the physico-chemical properties of mineral dust in western Africa: mineralogical composition

“…This approach does not apply to samples collected in the boundary layer during the monsoon season south of the ITCZ. In this case, the dominant flow is from the south-west: dust is present in the boundary layer only as a result of erosion by organised convection or under particularly stable conditions when high temperatures are established and the top height of the thermal turbulence in the boundary layer rises to or above the shear level, bringing dust from the free troposphere to the surface level (Flamant et al, 2009;Formenti et al, 2011b).…”

“…In summertime, a mixture of Sudan and Chad sources, including Bodélé, may have been sampled (Flamant et al, 2009). Finally, a number of episodes of erosive emissions by convection in the Sahel were also sampled and characterised (referenced as Sahel).…”

Long‐range transport of Saharan dust and its radiative impact on precipitation forecast: a case study during the Convective and Orographically‐induced Precipitation Study (COPS)

“…This underestimation may be due to the lack of east African sources in the simulation domain. For example, Flamant et al (2009) identified dust sensed over Niger in summer 2006 as mobilized from eastern African remote sources (Bodélé and Sudan) three days earlier. Therefore, the evaluation of the model skill in predicting dust in this area would benefit from a simulation with a larger domain.…”