Elijah Adesanya Adefisan and Amarachi Jovita Oghaego
In this study, we investigated the ability of Weather Research and Forecasting model coupled with the Chemistry option (WRF-Chem) using the GOCART dust scheme in capturing the spatial and temporal distribution of a severe dust storm which occurred in March 2006 over West Africa. The period (5th - 14th March, 2006) also coincided with the African Monsoon Multidisciplinary Analysis (AMMA) Special Observing Period (SOP) and some observed datasets from other platforms were also used. The WRF-Chem simulation was performed on a two-way nested domain in order to resolve the dust episode on high horizontal resolution dataset. From the 5th March, a dust storm raised in northern Algeria, which propagated southward spreading to the west and east on the subsequent days. Over the Gulf of Guinea, an intense dust haze was transported southward thereby generating an aerosol optical thickness (AOT) greater than 4 over Nigeria. Qualitative and quantitative characterizations between observations and WRF-Chem simulations demonstrated that the WRF-Chem model is highly efficient and can be recommended to simulate the spatial and temporal distribution of harmattan dust over West Africa. We discovered that the WRFChem modelled Aerosol Optical Depth (AOD) underestimated the AOD from AERONET as a result of all other aerosols like black carbon integrated into the observed which is not yet captured by model. The quantitative and qualitative analysis of the model output ascertain the capability of WRF-Chem to reasonably reproduce West African harmattan dust haze from the time and location of being raised to its transportation and propagation and hence its final settling or disappearance over the continental area of West Africa. Model simulation was able to partition the dust particles into five different sizes. It was discovered that dust particles of sizes 1.4 μm, 2.4 μm and 4.5 μm are more prevalent among other sizes from the raised and transported dust over West Africa.
