WRFChem Simulation of Aerosol perturbation on Outgoing Longwave Radiation over West Africa's Heterogeneous Landscapes

Abstract

Outgoing Longwave Radiation (OLR) across West Africa is characterized by significant variability as a consequence of the region's diverse landscape or landuse/landcover and the influence of various climatic drivers. This study revealed spatiotemporal patterns of OLR over West Africa, aiming to enhance our understanding through the assessment of the WRF-Chem model's ability to accurately capture these dynamic processes. CAMS reanalysis dataset was used to scrutinizing the model's performance on a regional scale. Two experiments were also conducted to investigate non-aerosol and aerosol perturbation on OLR variability in the region.  Our findings revealed a distinctive spatial heterogeneity in OLR across West Africa, particularly during different seasons. Notably, during the June-July-August (JJA) period, the Guinea coast exhibited lower OLR values (160 – 195 W/m²) attributable to dense cloud cover, increased precipitation, and elevated water vapor content. In contrast, the Sahel and Sahara Desert regions displayed an average OLR value of 225 W/m², associated with lower humidity and precipitation levels. The December-January-February (DJF) and March-April-May (MAM) seasons revealed higher OLR values (255 W/m²) in the Sahel and Sahara Desert, attributed to clear skies and reduced humidity. The evaluation of the WRF-Chem model demonstrated its competency in reproducing observed data, evidenced by a positive correlation and relatively low Root Mean Square Error (RMSE). Variations in model performance across different data points and seasonal periods were indicated by the Standard Deviation. Trend analyses also indicated an increasing trend and variability in OLR values from February to August in the Guinea Coast and Sahara Desert, contrasting with a decreasing trend in the Sahel region. In a pristine atmosphere devoid of aerosol perturbation, OLR exhibited less variability and greater consistency from the Guinea coast to the Sahara Desert, with occasional extreme values noted in the latter. Conversely, periods of aerosol perturbation revealed a wider range of OLR values, signifying increased variability influenced by aerosol-induced alterations to the atmosphere's radiative balance and energy exchange. The study concludes that the influence of aerosol perturbations emerges as a key factor, introducing heightened variability in OLR values, which holds implications for our understanding of radiative processes in this region.