Spatio-temporal assessment of aerosol-induced atmospheric heating rates in Nigeria

Résumé

Understanding the dynamics of atmospheric heating rates (AHR) is crucial for assessing the impact of aerosols on Earth's energy balance and consequently, on climate dynamics. This study investigates the spatial and temporal patterns of AHR across Nigeria from 2000 to 2022, using a radiative transfer model. Detrended Fluctuation Analysis (DFA) and Ordinary Least Squares Regression (OLR) were employed to assess the persistence of AHR over time. The Mann-Kendall test was applied to identify trends in AHR and other related variables, while causal relationships between AHR and influencing aerosol variables were examined using Transfer Entropy (TE) analysis. The national average AHR was 0.77±0.15 K/day, with an insignificant decreasing trend from 2000 to 2022. The AHR distribution correlated with aerosol optical depth (AOD) in all climate zones except BSh and BWh. In zones with persistent substantial and marginal decreases in AHR, sea salt (SS) and desert dust (DU) were the dominant variables, with the highest TE values of 0.155 and 0.179, respectively. Findings show that monthly aerosol absorption (Single Scattering Albedo (SSA) <0.89) was prevalent only in the Csb climate zone between November and February, while other zones remained dominated by aerosol scattering (SSA > 0.89). This suggests the essential role of scattering aerosols in limiting AHR, especially during the rainy season. The aerosol absorption by coarse-mode aerosols was more dominant in northern Nigeria compared to mixed-mode aerosol absorption. Seasonally, the mixed-aerosol mode dominated in southern Nigeria during the December-January-February (DJF), June-July-August (JJA), and September-October-November (SON) seasons. This study provides insights into the complex dynamics of AHR, with important consequences for climate and atmospheric processes across different regions and seasons.

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