PNNL

Abstract

Two of the primary objectives of the Department of Energy Atmospheric Radiation (ARM) are: 1) relate observations of radiative fluxes and radiances to the atmospheric composition and, 2) use these relations to develop and test parameterizations to accurately predict the atmospheric radiative properties [Ackerman and Stokes, 2003]. Consequently, ARM has pursued measurement and modeling activities that attempt to determine how aerosols impact atmospheric radiative transfer, both directly and indirectly. This special issue presents papers dealing with one such activity, the May 2003 Aerosol Intensive Operations Period (IOP). The Aerosol IOP was conducted between May 5-31, 2003 over the ARM Southern Great Plains (SGP) Climate Research Facility (CRF) site (36.606 N, 97.50 W, 315 m). The scientific hypotheses that were investigated during this IOP were posed as “closure experiments” - that is that an observable quantity may be observed in two different ways, or may be observed as well as calculated (modeled) using other observable quantities. The comparison of these two (or multiple) measures of the same quantity is often called a "closure experiment"; that is, closure is achieved if the measures agree within the propagated uncertainties. The investigations attempted to address the following four questions: (a) Can closure between measurements and models of diffuse radiation be achieved under low AOT conditions with accurate measurements of the aerosol single scattering albedo? (b) How well do the routine ARM SGP Raman lidar and In Situ Aerosol Profiling measure aerosol scattering and extinction profiles and aerosol optical thickness? (c) How well can the cloud nucleating properties of particles just below cloud base be represented using surface measurements of cloud nucleating properties of particles along with profiles of relative humidity and aerosol extinction? (d) To what extent are remotely sensed parameters adequate for detecting indirect effect?