Environmental Science and Engineering Seminar

Satellite-based observations of Earth's top-of-atmosphere radiative fluxes report that the two hemispheres have the same all-sky albedo. The symmetry is surprising given the large hemispheric asymmetry in clear-sky albedo and motivates research into mechanisms that compensate hemispheric albedo asymmetries. The talk presents simulations with a comprehensive atmosphere model to explore possible compensation mechanisms. In the simulations clouds adapt such as to compensate the imposed hemispheric asymmetries in clear-sky albedo. The compensation results from a shift of the ITCZ and tropical clouds into the hemisphere with low clear-sky albedo. The efficiency of the tropical compensation mechanism is directly linked to the magnitude of the ITCZ shift, which is found to be sensitive to the representation of convection and the strength of the seasonal cycle. Overall, the results lend support to the idea that the climate system prefers hemispheric albedo asymmetries to be small.