Sensitivity of Land–Ocean Circulations, Precipitation, and Soil Moisture to Perturbed Land Surface Albedo

Abstract

Using general circulation model experiments, it was found that thermally induced overturning circulations that flow between oceans and land at low latitudes can be affected by perturbations to the land surface albedo. When surface albedo is reduced over land at low latitudes, radiative heating of the surface is increased and additional heat is transferred from the surface to the atmosphere, which is largely offset by adiabatic cooling associated with upward motion. This enhanced upward motion is associated with greater low-level convergence of air over the continents, compensated by divergence over the oceans. The enhanced flux of water vapor onto the continents due to this pattern further enhances the thermal forcing through the release of latent heat. In these low-latitude regions with reduced surface albedo, precipitation and soil moisture are increased. Qualitatively opposite effects are obtained by increasing surface albedo. In midlatitude regions, circulation and precipitation are not significantly affected by land surface albedo. However, decreased surface albedo does increase the amount of heat available at the surface for evaporation. This greater heat availability depletes soil moisture earlier in the season. Again, qualitatively opposite effects are obtained by increasing surface albedo. Similar perturbations in land surface albedo are used as an analog to the effects of low-level atmospheric aerosols, which have been proposed as a mechanism that may presently be offsetting CO2-greenhouse warming. The resulting temperature changes are compared with those occurring in an increased CO2 simulation.