Separation of aerosol fine- and coarse-mode radiative properties: Effect on the mineral dust longwave, direct radiative forcing

An improvement of the estimation of mineral dust longwave, direct radiative forcing is presented. It is based on recent developments that combine Sun photometer and multiwavelength lidar data to retrieve range-resolved coarseand fine-mode extinction coefficients. The forcings are calculated separately for each mode, and their sum is compared to the classical approach in which only the total extinction is considered. The results of four cases of mineral dust intrusion in Barcelona, Spain, show that when the coarse mode predominates, the longwave forcings calculated with the classical approach are underestimated up to 20% near the surface. In all cases the strong coarse-mode predominance near the surface has also an effect on the forcing in the upper layers.