Variability in aerosol optical properties and radiative forcing over Gorongosa (18.97oS, 34.35oE) in Mozambique

Abstract

This paper reports the observational results of aerosol optical, microphysical and radiative characteristics for the time measured over Gorongosa (18.97oS, 34.35oE, 30 m asl) in Mozambique using a ground-based AERONET sun-sky radiometer. In the present study, the data recorded during the period July–December, 2012 have been used and particular attention was paid to show how aerosol loading evolves during the biomass burning season (spring) including pre- and post-months. The results reveal that the monthly mean aerosol optical depth (AOD) at 500 nm was high (low) with 0.64 ± 0.34 (0.20 ± 0.06) in September (November), while the Angstrom Exponent (AE) (α 440–870) decreased, except September (1.56 ± 0.26) due to increase in the fine-mode aerosol concentration produced from biomass burning. The volume size distribution (VSD) has bimodal lognormal structure and has fine-mode (coarse) maximum at a radius of 0.15 µm (3.0 µm) in September (December). The single scattering albedo (SSA) decreases with wavelength from July to October and almost stable in November and December. The imaginary (Im) refractive index (RI) showed a strong evidence of black carbon aerosol origin during the biomass burning months. Aerosol radiative forcing (ARF) computed from SBDART model shows large negative values at the surface (−89.22 W m−2) and at the top (−22.36 W m−2), with a higher value of atmospheric forcing (+66.87 W m−2) resulting in average tropospheric heating rate of 1.88 K day−1 for the study period. Further, the comparison shows good agreement between the ARFs at the top and bottom of the atmosphere derived from AERONET to SBDART.