Comparisons of climate model simulations of aerosol indirect forcing with in-situ and remote sensing observations

Aircraft and ground observations of aerosol and cloud microphysics are blended with satellite observations of shortwave cloud radiative forcing to quantify the top-of-atmosphere radiative forcing resulting from aerosol variations and their effect on cloud microphysics. Intensive aircraft measurements were collected over the Northeast Pacific Ocean as part of the Cloud Indirect Forcing Experiment (CIFEX) in April 2004; coinciding with springtime dust and pollution transport from Asia. These data demonstrate that clouds of equivalent liquid water content are brighter during periods of elevated aerosol particle concentrations below cloud. However, the increase in shortwave cloud radiative forcing is partially mitigated by decreases in liquid water path and cloud fraction. Observations from the ARM SGP site, in addition to the CIFEX data, are used to test the implementation of an aerosol nucleation parameterization in the NASA GEOS atmospheric model where cloud microphysical and radiative properties respond to variations in the aerosol load. A set of single column simulations over the Northeast Pacific Ocean and the ARM Southern Great Plains site are compared with observations to test the simulated cloud microphysics and radiative forcing against the observed sensitivity to aerosols. Complete simulations of the global aerosol indirect forcing are evaluated based on conclusions from the detailed tests of the parameterization.