PNNL

Abstract

A new description of tropospheric aerosols is developed on monthly timescales and with global coverage. By providing all required sub-spectral aerosol radiative properties for radiative transfer applications, this data-sets lends itself to simplified and computationally efficient representations of tropospheric aerosol in climate studies. Properties are provided for both total and anthropogenic aerosol from pre-industrial times well into the future. Central to the aerosol description are merged aerosol optical properties for year 2000 conditions, which are derived with the help of global modeling and high quality statistics by ground-based sun-photometer networks. For year 2000 conditions the global annual mid-visible AOD is 0.13 for total aerosol and 0.037 for anthropogenic aerosol. In a demonstration application associated aerosol radiative effects are determined. From an estimated reduction of -1.6W/m2 to the radiative budget at the top of the atmosphere for total aerosol during the year 2000, reductions of about -0.5 W/m2 (with an uncertainty of +/- 0.2 W/m2) are associated with anthropogenic activities. This average value hides its strong variability, as direct aerosol forcing on a regional and seasonal basis can be to an order of magnitude stronger and of both signs. To better convey this diversity, regional and seasonal distributions of aerosol properties and their radiative effects are explored.