Characterization of the annual cycle of atmospheric aerosol over Mindelo, Cabo Verde, by means of continuous multiwavelength lidar observations

Abstract. This paper presents an analysis of the annual cycle of aerosol optical and geometrical properties based on multiwavelength-Raman-polarization lidar measurements for Mindelo, Cabo Verde, from July 2021 to August 2023. A quality-assured data set of more than 70 automatically-calibrated lidar profiles was manually evaluated. For the first time, a two-year time series of, e.g. layer-resolved aerosol optical depth (AOD), lidar ratio profiles, and particle depolarization profiles are presented for Cabo Verde to characterize the complete annual cycle of aerosol in the planetary boundary layer (PBL) and in the lofted aerosol layers. The aerosol conditions over Mindelo are complex with different mixing states of dust and non-dust components. A strong annual cycle was found in the overall aerosol layer top height and the geometrical extent, the AOD, and the dust fraction of the lofted layers. Furthermore, the data was used to explicitly define aerosol-related seasons. The dust season (June–September) is characterized by geometrically and optically thick lofted layers dominated by Saharan dust (up to 7 km height) above a slightly polluted marine PBL. Seasonal mean lidar ratios at 355(532) nm are 34±18 (32±19) sr (PBL) and 48±19 (39±18) sr (lofted layers). The particle depolarization ratio is <0.05 (PBL) and 0.16±0.07, 0.22±0.06, and 0.20±0.05 (lofted layers) at 355, 532, and 1064 nm. The mixing season (often mixtures of Saharan dust with biomass burning aerosol, November–March) is characterized by a large variability of aerosol with mean lidar ratios of 60±32 (48±32) sr at 355 (532) nm and depolarization ratios of 0.09±0.06, 0.11±0.07, and 0.16±0.08 at 355, 532, and 1064 nm in the lofted layers.