Comparison of observed and modeled direct aerosol forcing during TARFOX

Aircraft measurements have been made of the downward and upward solar irrad iance under cloud-free conditions over a range of aerosol loadings in the s ummer haze plume off the East Coast of the United States during the Troposp heric Aerosol Radiative Forcing Observational Experiment (TARFOX). Optical properties calculated from measured aerosol microphysical and chemical prop erties have been used as input to a shortwave radiative transfer model. Thi s model was used to calculate the diurnally averaged direct aerosol forcing and to compare with values deduced from the aircraft radiative measurement s. The modeled and observed forcings agree well when the aerosol has a sign ificant absorbing component.