Effect of spectral‐dependent surface albedo on Saharan dust direct radiative forcing

Abstract

Direct radiative forcing (DRF) due to mineral dust has quite large uncertainty. Surface albedo is one of the most important factors affecting dust radiative forcing and climate. Here we investigate the effect of spectral‐dependent surface albedo on dust DRF over the Saharan desert region using MODIS surface albedo data and a size‐resolved global aerosol model. In one simulation, surface albedo in 7 wavebands from MODIS‐retrieved data is interpolated to the corresponding 4 solar wavebands of the radiation transfer model (case 1). In another simulation, surface albedo for visible wavebands is applied to all 4 solar spectral‐bands (case 2), which was previously used by many global model simulations. Our results show that the annual averaged DRF for all sky over the Saharan dust is −2.4 W m−2 and −5.6 W m−2 at TOA, and −9.9 W m−2 and −12.9 W m−2at surface for cases 1 and 2, respectively. Such a large difference highlights the importance of using accurate spectral‐dependent surface albedo, and implies that previous studies employing only visible‐band surface albedo might have significantly overestimated the dust cooling effect over the Saharan dust.