| The earth maintains an energy balance between incoming solar radiation and outgoing longwave radiation by adjusting its temperature and radiating energy according to Stefan-Boltzmann's law. Particulate matter in the atmosphere called aerosols are an important constituent of the energy transfer process. Fluctuations in their concentrations constitute a perturbation of the energy balance of the atmospheric system and this is termed aerosol forcing. Aerosols interact directly with incoming solar radiation, absorbing but largely scattering it back to space and thereby reducing the amount of radiation striking the earth's surface. Aerosols with high black carbon content, however, absorb more solar radiation than they scatter, resulting in local heating of the atmosphere. Aerosols also interact with solar radiation indirectly by serving as cloud condensation nuclei and thereby modifying cloud optical and microphysical properties in what is termed aerosol indirect effect.; Estimates of the magnitude of climate forcing due to aerosol direct and indirect effects are highly uncertain partly because of the relatively short lifetime of aerosols but also because of their strong spatial and temporal variations. Obtaining good duality data from different climate regimes is exceedingly difficulty with this degree of variability.; In this dissertation, a method for characterizing aerosol indirect effect over the Mid-Atlantic region is developed and applied. Using surface-based remote sensing and back trajectory analysis, aerosols and clouds are classified according to their sources and investigated for evidence of aerosol indirect effect. Furthermore, established measurement protocol from the Atmospheric Research Measurement (ARM) sites are adopted to ensure good quality data.; Cloud effective radius is derived for the same period of time from diffuse measurements of the MFRSR, and cloud liquid path from a 2 channel microwave radiometer. When segregated by air mass history, cloud effective radius in air masses with high aerosol loadings is on average 0.9 mum smaller than that observed under more pristine conditions. This result is the average difference for observed cloud liquid water paths between 80 gm-2 and 200 gm-2. |
