Aircraft measurements have been made of the downward and upward solar irradiance under cloud-free conditions over a range of aerosol loadings in the summer haze plume off the East Coast of the United States during the Tropospheric Aerosol Radiative Forcing Observational Experiment (TARFOX). Optical properties calculated from measured aerosol microphysical and chemical properties have been used as input to a shortwave radiative transfer model. This model was used to calculate the diurnally averaged direct aerosol forcing and to compare with values deduced from the aircraft radiative measurements. The modeled and observed forcings agree well when the aerosol has a significant absorbing component. ¿ 1999 American Geophysical Union