Twenty Years of Satellite Observations Reveal a Shift in the Diurnal Trend of Dust Optical Depth Over West Africa

Abstract West Africa is the largest global source of mineral dust, with significant impacts on climate, air quality, and biogeochemical cycles. While temporal variations in dust loading from daily to interannual scales are well studied, the long‐term evolution of the diurnal cycle itself is often overlooked. Here, we investigate 20‐year trends in dust optical depth (DOD) over West Africa, applying a recently developed parameterization to Moderate Resolution Imaging Spectroradiometer observations. We find a striking summertime shift in the diurnal contrast of dust loading: the afternoon‐minus‐morning DOD difference (DOD) increases significantly over the record, flipping from negative near 2003 to positive by 2022. ERA5 reanalysis indicates that this divergence is associated with coordinated changes in regional meteorology, including less frequent nocturnal low‐level jets and a relative shift in near‐surface wind forcing toward the afternoon. This diurnal shift in dust activity has implications for regional air quality, radiative forcing, and aerosol–cloud interactions.