Exploring stratospheric aerosol radiative forcing using the SASKTRAN radiative transfer framework

The radiative forcing associated with stratospheric aerosol is often diagnosed using coupled general circulation models. The radiation codes within such models are state-of-the-art, but contain simplifications in order to optimize computational efficiency and make it feasible to perform simulations on climate-relevant time scales. Calculating radiative forcing using different radiative transfer techniques is useful to validate results from GCMs, and explore sensitivities to parameters that are not easily modified in such models. Here, we report on progress toward quantifying global stratospheric aerosol radiative forcing using the SASKTRAN radiative transfer framework, which has a rich heritage in the context of the retrieval of aerosol and gas species from limb scattered radiation. SASKTRAN is coupled to the Easy Volcanic Aerosol (EVA) forcing generator, allowing for realistic but adjustable stratospheric aerosol properties in global or single column radiative transfer calculations. Simulations are used to assess the impact of multiple scattering on the global radiative forcing, and its dependence on location and aerosol perturbation magnitude. We also assess the impact of using the simplified scattering parameters used as input to most GCMs (extinction, single scattering albedo and asymmetry factor) compared to using the full Mie scattering phase function computed from a given aerosol size distribution.