Item

Abstract

A simple plume implementation of the second version (v2) of the Max Planck Institute Aerosol Climatology, MACv2-SP, is described. MACv2-SP provides a prescription of anthropogenic aerosol optical properties and an associated Twomey effect for the harmonized use in climate modelling studies. It has been designed to be easy to implement, change and use, and thereby enable studies exploring the climatic effects of different plausible aerosol distributions and their impact on clouds.MACv2-SP is formulated in terms of nine spatial plumes associated with different major anthropogenic source regions. The shape of the plumes is fit to the Max Planck Institute Aerosol Climatology, version 2, which is based on present day (2005) observations. Decadal variations in the amplitude of the plumes over the historical (post 1850) period is derived by scaling the plumes with associated national emission sources of SO2 and NH3. Two types of plumes are considered: one predominantly associated with biomass burning the other with industrial emissions. The two types of plumes differ in the prescription of their annual cycle and in their optical properties, thereby implicitly accounting for different contributions of absorbing aerosol to the different plumes. A Twomey effect for each plume is prescribed as a change in the host model’s background cloud droplet population density using relationships derived from satellite data. Experiments using the simple plume model are performed with the Max Planck Institute Earth System Model. The instantaneous and effective aerosol radiative forcings is estimated to be